Response of Guiana dolphins to the construction of a bridge in Ilhéus, Northeastern Brazil.
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Abstract
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Response of Guiana dolphins to the construction of a bridge in Ilhéus, Northeastern Brazil
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,* Alice Lima, Formal analysis, Validation, Visualization, Writing – original draft, Writing – review & editing,
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Erica Gomes, Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Writing – original draft,
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Winnie Silva, Conceptualization, Data curation, Formal analysis, Investigation, Writing – original draft,
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Khamila Tondinelli Souza Cruz, Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Writing – original draft,
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and Gastón Andrés Fernandez Giné, Formal analysis, Investigation, Methodology, Software, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing
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Abstract
This study aimed to investigate whether the use of space and movements of Guiana dolphins were altered during the construction of a cable-stayed bridge at the mouth of the Cachoeira River estuary in Ilhéus, Brazil. We described and compared the visitation rate, use of space, and movements of the Guiana dolphins across two periods: before the construction began (2015–2016) and during the construction of the bridge (2017–2020). A theodolite and a total station were used to observe and record the trajectories of the dolphins. From these trajectories, we estimated the Utilization Distribution (UD) using the biased random bridge kernel (BRBK) method, the area of use, and the core area, based on the 95% and 50% BRBK density, respectively. The dolphins did not change their visitation frequency to the estuary. No significant change in area fidelity was identified by comparing the overlap of areas used during two-month periods. No change occurred in the velocity and linearity of the trajectories of the dolphins swimming close to the bridge. However, contrary to expectations, the results indicated an increase in the use of areas close to the bridge during its construction. This may have been caused by the change in the distribution of their prey in the estuary due to the emergence of a sandbank near the bridge. Bridge construction work seems not to have directly affected the Guiana dolphins’ use of the area, but the impact of the construction on the local topography has changed their areas of use and core areas of activity.
Introduction
Monitoring dolphin behavior in relation to anthropogenic activities that could potentially impact them is a useful tool for developing a better understanding of the potential adverse effects of such activities on dolphins and for planning mitigation strategies [1,2]. The construction and demolition of structures are known to negatively impact aquatic organisms [1]. Regarding dolphins, most studies focus on the impacts of vessel traffic and underwater noise (for example [3–5]), but few examine the effects of construction and demolition activities (for example [1,6]). Noise pollution can negatively affect marine mammals, many of which rely on sound as their primary means of exploration and communication [7,8]. Pile driving and dredging are common reasons why cetaceans temporarily avoid or stay away for long periods from areas near coastal constructions [6,9,10], but changes in water and sediment flow can also have an impact [11]. Dredging, a critical component of most major marine infrastructure developments that involves excavating and relocating sediment from lakes, rivers, estuaries, or sea beds, also affects the fish [12] that dolphins rely on to use an area [13].
Several negative impacts have been observed as a result of construction and demolition of structures, such as a decrease in the presence of resident female bottlenose dolphins (Tursiops truncatus) near the construction site of the John’s Pass Bridge in Tampa Bay, United States [6], and an increase in the swimming speed of Indo-Pacific humpback dolphins (Sousa chinensis) in areas close to pile-driving activities during the construction of an aviation fuel reception tank in a bay in Hong Kong [14]. Some studies indicate that dam construction can have serious consequences for river dolphins such as the boto (Inia geoffrensis) [15] and Ganges river dolphins (Platanista gangetica gangetica) [16,17], potentially leading to unsustainable population fragmentation and even local extinction [16]. However, bottlenose dolphins in the Gulf of Mexico adapted to the impact of a bridge replacement through behavioral and temporal adjustments [9]. Similarly, Ganga River dolphins altered their preferred areas, increasing their occurrence in certain portions of the river after the construction of a barrage [18]. Bottlenose dolphins and harbour porpoises (Phocoena phocoena) seemed only slightly impacted by vibration piling in a Scottish estuary [19], indicating that the effects of anthropogenic activities vary according to the type of disturbance and the species concerned. However, the consequences of cumulative short-term effects of human activities are largely unknown.
Guiana dolphins (Sotalia guianensis) have a potentially continuous distribution in shallow coastal and estuarine waters from Nicaragua [20] to southern Brazil [21] and are the most common marine mammal in many areas exposed to anthropic development and consequent perturbations in Brazil (for example [22–25]), such as by-catch, habitat degradation, heavy vessel traffic, and exposure to pollutants. These threats have even caused a drastic decline in one of their populations in Brazil [23]. The species is classified globally as Near Threatened by the IUCN [26] and as vulnerable to extinction in Brazil [27], where it is exposed to 11 types of anthropogenic activities [28]. However, despite the species inhabiting areas affected and modified by human activities, studies on habitat use and preference have seldom considered anthropogenic factors [29,30]. To date, little is known about the impact of constructions on Guiana dolphins [28].
In Ilhéus (Northeast Brazil), a resident population of Guiana dolphins regularly visits the lower part of the Cachoeira River estuary (hereafter called Pontal Bay), mainly for foraging purposes [31]. It is the only dolphin species that frequent the estuary. As a top predator restricted to coastal waters less than 50 m deep, it plays an important role in regulating populations of fish and other marine animals of this ecosystem [32]. A cable-stayed bridge was constructed near the mouth of the estuary from September 2016 to July 2020. The construction has narrowed the mouth of the Cachoeira River, a crossing point for boats and organisms, also causing siltation in parts of the estuary. The silting process was already known before the construction of the Jorge Amado Bridge, with records of changes in bathymetry dating back to the 1970s [33]. The silting process might have intensified with the construction of the Bridge, changing the coastal physiography of Ilhéus due to the obstruction of the south-north coastal sediment drift caused by these constructions [34]. During the construction of the bridge, a small outboard boat frequently crossed the mouth of the estuary to transport materials and workers, and the installation of pillars and other construction activities caused noise pollution. It is likely that the construction of the bridge and the human activities associated with it have impacted the Guiana dolphins in Pontal Bay, leading to behavioral changes. These changes may result from modifications in prey distribution and behavior, as well as the removal or creation of foraging opportunities due to siltation.
In this context, we aimed to assess the impact of the bridge construction on the behavior of Guiana dolphins, particularly regarding their site fidelity, space use, habitat selection, and movements. Our hypothesis is that dolphin behavior changed during the bridge construction compared to the previous period: we expected a decrease in their visitation rate to Pontal Bay, a reduction in the repeated use of sites within the bay (lower overlap of areas used), a preference for sites further away from the construction and the banks, and more linear and faster movements near the construction site.
Methods
Study area
We conducted this study in the lower part of the Cachoeira River estuary, popularly known as Pontal Bay, located in the municipality of Ilhéus, Bahia, Brazil (39°00′ to 3903W; 14°47′ to 14°50S; Fig 1). This estuary is formed by the confluence of the Fundão, Cachoeira, and Santana rivers, and it flows into the Atlantic Ocean. The depth of Pontal Bay varies from 0.6 to 19.5 m and its width from 200 to 540 m [34]. It is primarily surrounded by urban areas with deteriorated banks where the dumping of rubble (pers. obs.) and domestic sewage is common [35,36], with mangrove vegetation present only in its western portion. The Jorge-Amado Bridge was constructed at the estuary’s mouth, where the width of the bay is narrow (around 200 m). The construction of the suspension bridge began in 2016 and it was opened to traffic in July 2020. During the construction of the bridge, earthworks were carried out to facilitate the construction of the main pillar. The width of the estuary mouth was reduced, and the sandbank expanded (Fig 1). The reinforced concrete base (44 x 14 m) of the main pillar is the only submerged support remaining after the earthworks were removed at the end of the bridge construction.
Illustrative maps based on satellite images from December 2015 (A) and September 2020 (B) depicting Pontal Bay before (A) and 3 months after (B) the completion of the Jorge Amado Bridge, respectively. The Jorge Amado Bridge is shown in the eastern part of Fig 1B.
Data collection
Groups of S. guianensis are regularly observed off the coast of Ilhéus and in Pontal Bay [31]. Guiana dolphins can be seen all year round in groups generally of 2 to 5 individuals [31,37]. We monitored the Guiana dolphins in Pontal Bay during the period before the construction of the Jorge Amado Bridge (from April 2015 to January 2016) and during its construction (from October 2017 to September 2018 and from July 2019 to February 2020), three days a week, totaling 563.22 and 734.03 hours of sampling effort, respectively (Table 11). During each sampling day, we conducted two monitoring sessions, each lasting 3 hours, during two of the following daytime periods: 07:00 to 10:00, 10:30 to 13:30, and 14:00 to 17:00. The observation sessions took place only when there was no precipitation. We collected data from two fixed points on the shore of Pontal Bay (Point A and Point B, Fig 1), which offered a panoramic view of the estuary. These observation points allowed us to monitor the behavior and location of Guiana dolphins across an area of 111.6 ha (sampled area), from the river mouth up to 2300 m upstream. The observation site and the two periods of the day to be monitored were pseudo-randomly selected, ensuring a similar sampling effort was maintained between the observation site and the periods.
Table 1
| Sampling effort | Before the construction | During the construction | Total |
|---|---|---|---|
| Number of monitoring days | 105 | 151 | 256 |
| Number of monitoring sessions | 207 | 278 | 485 |
| Number of sessions in the site Point A | 101 | 140 | 241 |
| Number of sessions in the site Point B | 106 | 138 | 244 |
| Number of monitoring hours | 563.2 | 734.0 | 1297.3 |
| Number of registered locations | 1126 | 1332 | 2458 |
| Number of recorded trajectories | 75 | 72 | 147 |
During each observation session, we continuously scanned the sampled area with the naked eye and binoculars (Ocean Xtreme 7x50WP, Lugan brand) to detect the presence of dolphins. Once an animal or group was sighted, we used a digital theodolite (Leica Model T110) or a total station (TOPCON, ES105) with 30× magnification to triangulate the dolphins’ location using two reference positions of known geographical coordinates (and elevation) to record the geographical coordinates of the dolphins [38]. A group was defined as a set of individuals swimming in an apparent association, close to each other, no more than three body lengths apart [39], moving in the same direction, and often engaged in the same activity [40]. The locations of a group were successively obtained at the shortest possible time intervals for the central position of the group. We recorded the time associated with each location, once the straight line connecting successive locations subsequently composed the group trajectories. After six minutes passed without sighting the monitored group, the successive observations of the trajectory were completed. Only trajectories comprising more than three successive locations were considered, totaling 75 trajectories recorded before the construction of the bridge and 72 trajectories recorded during the construction (Table 1). The sampling was completed prior to the COVID-19 lockdown in Ilhéus. Data collection and analysis procedures are summarized in Fig 2. No permits were required for this study, which was carried out in an unprotected area and involved the remote observation of animals in the wild.
Data analysis
We assessed the impact of bridge construction works on the behavior of Guiana dolphins in Pontal Bay by comparing their site fidelity, space use, habitat selection, and movements before and during the construction of the bridge.
Impact of bridge construction on temporal and spatial site fidelity
To assess the dolphins’ temporal fidelity to the estuary, we calculated the monthly visitation rate, defined as the percentage of sessions in which dolphins entered the study area during a month. We compared the monthly visitation rates before and during the bridge construction using an independent two-sample t-test.
To assess spatial site fidelity, we used the degree of bimonthly overlap between areas of use and between core areas as indicators of spatial fidelity. We used the dataset of trajectories to estimate the Utilization Distribution (UD) of dolphins within the study area for each two-month period using the Biased Random Bridge Kernel (BRBK) method [41], implemented with the adehabitatHR package [42]. For the BRBK estimates, we used a raster resolution of 1 m, and we defined the parameter tmax (maximum time threshold for connecting two successive relocations) as 6 min, tau (interpolation time) as 3 seconds, lmin (minimum distance between successive relocations, defining intensive use or resting) as 1 m, and hmini (minimum kernel bandwidth associated with relocations) as 5 m. The D (diffusion coefficient) was estimated using maximum likelihood with the BRB.likD function from the adehabitatHR package [43]. Details on these parameters are provided in the adehabitatHR package and method description [41,42]. Considering the 95% and 50% UD probability densities, we delimited the bimonthly area of use (bimonthly BRBK-95%) and the core area (bimonthly BRBK-50%) of the dolphins in each two-month period. We estimated the overlap of the bimonthly areas of use (and core areas) using the Home Range Overlap Index (HR) and the Utilization Distribution Overlap Index (UDOI), considering all possible combinations of two-month periods with the kerneloverlaphr function from the adehabitatHR package [43]. Details on the overlap indices are described by [44]. We performed Kruskal-Wallis tests to evaluate differences in the overlap values estimated for each period (two treatments: before and during the bridge construction) and inter-period overlap values (comparing an additional treatment: before versus during the bridge construction) to evaluate: 1. if the site fidelity (overlap) during the bridge construction was lower than in the previous period (i.e., if there was a greater change in the space used during the bridge construction than in the previous period); and 2. if site fidelity (overlap) was lower between the two periods than within each period (i.e., if the change in used space due to the transition provoked by bridge construction was greater than expected within each period).
Influence of bridge construction on dolphin space use and habitat selection
We estimated the UD, area of use (BRBK-95%), and core areas (BRBK-50%) of the dolphins for the two periods separately (before and during the bridge construction) using the same BRBK method and UD probability density described above, without dividing the data bimonthly. Then, we fitted Resource Selection Functions (RSFs, sensu [45]) for each period to assess whether dolphins preferred to establish their areas of use and core areas further away from construction sites and riverbanks during the construction of the bridge, or if they remained as before the construction. The units selected by the animals (resource) was considered the raster cells of the bay (resolution of 1 m), and the predictor variables associated with these resource units were the distance to the river bank (D.Bank) and the distance to the bridge (D.Bridge). We systematically sampled points every 60 m in the bay to obtain values from the raster data. For each point, we extracted: the usage value, assigning 1 for points within the area of use and 0 for points outside (representing sites used and available, respectively), the distance to bridge, and the distance to the riverbank. Based on these data, we fitted GLM models with a binomial distribution and log link functions for each period separately, considering “usage” as the response variable and all combinations of the two predictor variables (D.Bank and D.Bridge). Then, we ranked all the candidate models, including the null model, based on their Akaike’s Information Criterion corrected for small sample size (AICc) scores. This was done using the “dredge” function from the “MuMIn” package [46]. We selected only those models with AICc differences less than 2 (ΔAICc < 2), which were considered equally plausible in explaining the observed pattern [47]. We calculated the cumulative model weights (∑ωi) for each predictor variable in our set of selected models, i.e., the sum of weights of all models containing the covariate [47], to evaluate the importance of the predictor variables on the dolphins’ preference for establishing their area of use within the Bay before and during bridge construction. We used the sign of the estimated coefficient for each variable in the models to indicate the direction of the relationship between the predictor variables and the response (positive or negative effect). We included D.Bank and D.Bridge as predictor variables in the models because a low correlation (Spearman correlation: r < 0.5) was observed between these two variables. Additionally, we depicted the changes in the utilization distribution (UD) in Pontal Bay by calculating and plotting on a map the difference in the UD estimated during and before the bridge construction (ΔUD = UDduring—UDbefore), as well as estimating the Spearman correlation between the ΔUD and the predictor variables.
Impact of bridge construction on dolphin movement (speed and linearity). To assess whether the animals showed more linear and faster movements near the construction site during the construction period compared to before, we first selected the trajectories that occurred close to the bridge construction (mean distance < 200 m) for each period (before and during) and calculated the mean velocity and linearity of each selected trajectory. We first estimated the following basic movement parameters: step length ‘dist’, the distance travelled between successive locations; net squared distance ‘R2n’, the squared distance between the first and last relocation of each trajectory; and the time elapsed between successive locations Δt, using the adehabitatLT package [48]. Then, we calculated the mean velocity of each trajectory, which was the average velocity of each step (dist/Δt). The linearity of each trajectory was estimated by the straightness index [49], which is calculated as the ratio of the distance between the first and last points of the trajectory to the total track length (i.e., the square root of R2n divided by the sum of the step lengths of the trajectory [50]). Finally, we used the Wilcoxon signed-rank test to compare the mean velocity and linearity of the dolphins’ trajectories before and during bridge construction.
All statistics and spatial analyses were performed in R software version 4.3.2 [51]. We tested the data for normality and homoscedasticity using Shapiro-Wilk’s and Levene’s tests, respectively, before performing the statistical tests. Means are given ± standard deviation (SD) throughout the text.
Results
Temporal and spatial site fidelity
Dolphins were sighted in Pontal Bay during 18.8% (n = 91) of the 485 monitoring sessions, with a mean monthly visitation rate of 0.19± 0.09 (± SD). The monthly visitation rate did not significantly differ between the period before (0.22 ± 0.11) and during (0.16 ± 0.08) the construction of the bridge (two-sample t-test, t = 1.274; df = 21; p = 0.2168): the dolphins’ fidelity of use of the estuary (here referred to as temporal site fidelity) was similar during both periods. Additionally, the dolphins’ use of space within the estuary varied significantly from one bimester to another, both during and across the two study periods, with a relatively low overlap (median HR < 40%, Fig 3). There was no significant change in the degree of overlap both within and between periods for the bimonthly areas of use (BRBK-95%, Fig 3A and 3C) and core areas (BRBK-50%, Fig 3B and 3D), considering both indices: HR overlap (Kruskal–Wallis, χ2 = 1.6484, df = 2, p = 0.4386; and χ2 = 1.7727, d.f. = 2, p = 0.412, respectively) and the UDOI (Kruskal–Wallis, χ2 = 0.9423, df = 2, p = 0.6243; and Kruskal–Wallis, χ2 = 0.7648, df = 2, p = 0.6822). These results indicate that dolphins showed no significant change in spatial site fidelity within the estuary during the bridge construction.
Top boxplots show comparisons of overlap using the Home Range overlap index (HR), while the bottom ones use the Utilization Distribution overlap index (UDOI). Within each boxplot, horizontal black bold lines correspond to median values; boxes extend from the 25th to the 75th percentile of each group’s distribution of values; the whiskers (vertical lines) extend to adjacent values (i.e., the most extreme values within 1.5 interquartile range of the 25th and 75th percentile of each group); black dots beyond the whiskers denote outliers’ observations (i.e., observations outside the range of adjacent values).
Influence of bridge construction on dolphin space use and habitat selection
The estimated area used by dolphins (BRBK-95%) in the sample area was 69.0 ha before the construction of the bridge and 65.3 ha during construction, with a reduction in the area used during construction primarily in the western part, which is the part of the bay furthest from the bridge (Fig 4). The estimated core area used by dolphins (BRBK-50%) was 17.4 ha before construction and 17.5 ha during construction.
A and B illustrate the area of use (BRBK-95%, in yellow) and core area (BRBK-50%, in red) of the dolphins in the sampled area before and during the construction of the bridge, respectively. C shows the Jorge Amado Bridge located at the mouth of Pontal Bay (Photo: Y. Le Pendu). D and E show the spatial variation in the Utilization Distribution (UD) of the dolphins before and during the construction of the bridge, respectively (gradient from blue to red indicates the least to most used areas). F shows the difference in the estimated Utilization Distribution (ΔUD) between both periods (ΔUD = UDduring—UDbefore), where red color indicates an increase in the intensity of local use (positive values), and blue color indicates a reduction in the intensity of local use (negative values). The black and inclined rectangle in the eastern portion of the Pontal Bay maps (A, B, D, E, and F) represents the bridge, while the star in B indicates the approximate central location of the sandbank that emerged and expanded during the construction of the bridge.
The estimated area used by dolphins (BRBK-95%) encompassed only 61.8% of the sampled area (111.6 ha) before the construction and 58.5% of the monitored area during the construction of the bridge (Fig 4). Before the bridge was built, the GLM analyses showed that the distance to the river banks (D.Bank) was the key factor influencing where dolphins chose to establish their area of use in the sampled area during the period. This variable appears in both equally plausible models (with ΔAICc < 2, Table 2), including the simpler model, and the cumulative weight of the models including this variable was 1. The effect of D.Bank was positive (Table 2), indicating that the animals preferred to use sites further away from the river banks. The effect of the distance to the bridge (D.Bridge) was positive but weaker than that of the distance to the bank (D.Bank), with a cumulative weight of 0.573 (Table 2). In contrast, during the construction of the bridge, the model combining D.Bank and D.Bridge was by far the most effective in explaining dolphins’ preferences: it was the only model with ΔAICc < 2 and had a high Akaike weight (ωi = 0.992; Table 2). During the construction, the effect of the D.Bank was positive, while the effect of the D.Bridge was negative (Table 2), indicating that the animals continued to prefer areas distant from the riverbanks, but began to prefer areas near the bridge during its construction. Complementarily, the difference between the UD estimated before and during the construction of the bridge (ΔUD, Fig 4F) indicates an increase in the intensity of use of a site close to the bridge construction site (red color) and a reduction in the intensity of use of western sites (blue color), which are farther from the bridge.
Table 2
Generalized linear models used the predictor variables: distance to the bank of the river (D.Bank) and distance to the bridge (D.Bridge). We also present the number of degrees of freedom (df), differences in corrected Akaike Information Criterion (ΔAICc), Akaike weights (ωi), and the direction (positive or negative, indicated in superscript) of the effect of the predictor variables.
| Model rank | Candidate modelsa | Df | AICc | ΔAICc | ωi |
|---|---|---|---|---|---|
| a) Use before the construction of the bridge | |||||
| 1 | D.Bank+ + D.Bridge+ | 3 | 308.68 | 0.00 | 0.573 |
| 2 | D.Bank+ | 2 | 309.27 | 0.59 | 0.427 |
| 3 | Null model | 1 | 416.42 | 107.74 | 0.000 |
| 4 | D.Bridge- | 2 | 418.44 | 109.76 | 0.000 |
| b) Use during the construction of the bridge | |||||
| 1 | D.Bank+ + D.Bridge- | 3 | 352.48 | 0.00 | 0.992 |
| 2 | D.Bank+ | 2 | 362.06 | 9.58 | 0.008 |
| 3 | D.Bridge- | 2 | 404.74 | 52.26 | 0.000 |
| 4 | Null model | 1 | 422.10 | 69.62 | 0.000 |
Impact of bridge construction on dolphin movement (speed and linearity)
There was no significant difference in the linearity (mean before = 0.3185± 0.1482, mean during = 0.2895± 0.1717) and speed (mean before = 1.4097 m/s ± 0.5578, mean during = 1.5785 m/s ± 0.7117) of dolphin movements near the bridge before and during construction (Wilcoxon signed-rank tests: linearity, t = 59, p = 0.9742; speed, t = 72, p = 0.4562).
Discussion
In this study, we found that the use of space by Guiana dolphins in Pontal Bay changed in certain ways during the construction of the Jorge Amado Bridge, albeit not as expected. Although the site fidelity (assessed through visitation rate and bimonthly overlap area) and movement parameters (velocity and linearity near the bridge site) remained consistent before and during the construction, the dolphins concentrated their activities closer to the bridge during its construction. They reduced the use of the western portion of Pontal Bay and increased their use of an area closer to the bridge, located a few meters from it (< 200 m, Fig 4). This result is contrary to what we expected. Given that the bridge construction process entailed dredging and depositing materials (silt, sand, stones, concrete) to construct the access ramp, driving piles, a higher frequency of boats, an increased human presence, and noisy equipment along the banks, we expected that dolphins would avoid areas close to this infrastructure project during its construction, primarily due to noise pollution and other disturbances. The lack of avoidance suggests that the Guiana dolphins have a high degree of tolerance towards such anthropogenic disturbances. If the construction of the Jorge Amado Bridge did not negatively affect the use of the area as expected, what prompted the dolphins to use an area close to the bridge during its construction? We discuss this below, considering biological aspects and physical changes close to the bridge that may have led to a change in the Guiana dolphins’ preferred feeding areas in the estuary.
Guiana dolphins are considered top predators in estuarine systems [52] and primarily use the estuary for feeding [31]. Habitat selection is closely linked to foraging opportunities and habitat characteristics that improve foraging success. They prefer steeper slopes and shallow areas [30,53].
The reduction in river flow and the entry of ocean sediments have caused a sandbank to form over the last decade in the area where dolphin activity increased near the bridge and the mouth of the bay. This sandbank had already been described before bridge construction work began [34], but it has become increasingly larger and shallower since then. Ocean sediments that accumulate during high astronomical tides and northeast winds are removed from the estuary by the force of river waters [34], but the narrowing of the mouth during the construction of the bridge may have limited their removal [54]. The formation of this sandbank influenced the dolphins’ area of use over time (see the location indicated by a star in Fig 4B), as it appears they avoided shallow water locations on the sandbanks, preferring areas around them instead (Fig 4B). The main reason for the increased use of this area close to the bridge during its construction is probably the new feeding opportunities that the elevation of the sandbank provided for the dolphins. It is common for Guiana dolphins to prefer areas close to breakwaters and seawalls, where they engage in "barrier-feeding", a foraging strategy in which the animals herd fish against these structures [29,55,56]. The sand bank formed in Pontal Bay may act as one of these barriers, turning the area close to it into a new and interesting foraging site. As the geomorphological and sedimentological dynamics of Pontal Bay are unpredictable, only monitoring the growth of the sandbank and the presence of dolphins will reveal whether the new opportunistic feeding area identified in this study will continue to attract dolphins or whether they will have to forage in other areas.
However, a single variable hardly explains habitat selection by dolphins [e.g. 4,32,49]. The dolphins consistently avoided locations close to the river banks before and during the construction of the bridge, suggesting that they did not use the strategy of corralling the fish on the banks of the river. The urbanized shores of Pontal Bay may pose a risk to dolphins due to the presence of construction debris and stranded boats. Under these conditions, dolphins likely choose deeper areas and only take advantage of newly formed natural barriers for foraging, as they are free from debris.
Our findings suggest that bottom depth plays a crucial role in habitat selection by dolphins, as the change in space use within this estuary by Guiana dolphins seems to be linked to changes in bathymetry. A study conducted in 2006 in Pontal bay [31] concluded that dolphins were more frequent in areas deeper than 3 m and at the end of the flood, adapting the direction of their feeding movements to the tide. Another study in the Caravelas river estuary (located approximately 400 km south of the study area) suggests that depth is the main limiting factor for habitat use by Guiana dolphins [57].
This study offers insights into the movement patterns of Guiana dolphins during significant human-induced habitat changes. The construction of bridges, involving pile driving and dredging, significantly alters the acoustic environment of dolphins. This can lead to long-term behavioral changes, potentially affecting their habitat use or causing injuries [1,28,58]. The construction of the Jorge Amado Bridge seemingly did not have a direct impact on the behavior of the Guiana dolphins, but it did have an indirect effect on their use of space, likely due to changes in local bathymetry and the consequent redistribution of suitable feeding sites. We did not observe any short-term negative behavioral responses to the construction of the bridge, indicating a high tolerance for such disturbances. This does not mean the environment was optimal or that there were no consequences for the survival and reproduction of individuals, but rather that the dolphins can tolerate sub-optimal conditions to obtain certain resources in areas with such disturbances. We highlight that Pontal Bay has suffered continuous silting due to the deposition of continental and oceanic sediments. This is caused by the low vegetation cover on the riverbanks and the construction of port projects along the ocean coast, issues that have been neglected to date. The Jorge Amado Bridge poses yet another threat that could reduce the depth and width of Pontal Bay over time, two environmental characteristics that could decrease habitat suitability for dolphins. A continuous monitoring of Guiana dolphins in this area is highly recommended to understand the long-term impacts and to proactively conserve this population.
Conclusions
Guiana dolphins adjusted their use of space during bridge construction.
Dolphins concentrated their activities close to the bridge under construction, contrary to expectations of avoidance due to worksite disturbances.
Despite the presence of dredging, pile driving, increased boat traffic, human presence, and noise, dolphins did not avoid the bridge area, suggesting a high tolerance to some anthropogenic disturbances.
The formation of a sandbank near the bridge influenced dolphin activity, which made greater use of the areas around the sandbank.
The construction of the bridge indirectly affected the use of space by Guiana dolphins due to changes in local bathymetry and a probable spatial redistribution of feeding sites.
Acknowledgments
We thank Bahia Pesca and Pontal Praia Hotel for allowing us to use their locations to observe the Guiana dolphins and the company OAS for providing the construction schedule for the Jorge Amado Bridge. We also thank Professor Niel Nascimento Teixeira and the Zoology Graduate Programme (UESC) for providing the theodolite and total station on loan and for the training in their use.
Funding Statement
AL received a post-doctoral scholarship from Universidade Estadual de Santa Cruz (PROBOL-UESC), <http://www.uesc.br/arint_english/). E G, received a scholarship grant from the Fundação de Amparo à Pesquisa do Estado da Bahia (FAPESB), <https://www.fapesb.ba.gov.br/). KC received a scholarship grant from the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) <https://www.gov.br/capes/en), and small grants from the Animal Behavior Society (ABS), <https://www.animalbehaviorsociety.org/web/index.php> and the Programa de Pós-Graduação em Sistemas Aquáticos Tropicais da Universidade Estadual de Santa Cruz (PPGSAT-UESC), <https://ppgsat.uesc.br/>. KC research was suported by Fundação de Amparo à Pesquisa do Estado da Bahia (FAPESB, PET0032/2012 project). W S received a scholarship grant from the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES). Funders did not play any role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Data Availability
Raw data are available in Biostudies repository DOI:10.6019/S-BSST1636 URL: https://www.ebi.ac.uk/biostudies/studies/S-BSST1636.
References
Decision Letter 0
30 Jul 2024
PONE-D-24-14912Do bridge constructions affect dolphin use of space? Responses of Guiana dolphins from Ilhéus, Northeastern BrazilPLOS ONE
Dear Dr. Le Pendu,
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have received of the comments of two independent reviewers. I have also critically gone through the manuscript. This is very pertinent question how the construction work affect river cetacean. As in present case "Do bridge constructions affect dolphin use of space? I find it very interesting.
Changes in the site bathymetry due to bridge construction and the resulted sandbank formation, are the major reasons for the dolphin space use pattern. Can the Ms be correlated with habitat chief of dolphins during Covid-19 lock down i.e. in contrary to bridge construction work (disturbance) undisturbed regime also affect home range of these river cetaceans . Some such explanation about bankcard shifting of Gangetic dolphins have been provided. in following paper: COVID-19 lockdown affects zooplankton community structure in dolphin appearing site of the River Ganga at Patna_26_1
August 2023Aquatic Ecosystem Health and Management 26(1):20-31
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Additional Editor Comments:
I have received of the comments of two independent reviewers. I have also critically gone through the manuscript. This is very pertinent question how the construction work affect river cetacean. As in present case "Do bridge constructions affect dolphin use of space?
Changes in the site bathymetry due to bridge construction and the resulted sandbank formation, are the major reasons for the dolphin space use pattern. Can the Ms be correlated with habitat chief of dolphins during Covid-19 lock down i.e. in contrary to bridge construction work (disturbance) undisturbed regime also affect home range of these river cetaceans . Some such explanation about bankcard shifting of Gangetic dolphins have been provided. in following paper: COVID-19 lockdown affects zooplankton community structure in dolphin appearing site of the River Ganga at Patna_26_1
August 2023Aquatic Ecosystem Health and Management 26(1):20-31
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Reviewers' comments:
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Reviewer #1: Yes
Reviewer #2: Yes
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Reviewer #1: Yes
Reviewer #2: Yes
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Reviewer #1: Yes
Reviewer #2: Yes
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Reviewer #2: Yes
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Reviewer #1: This manuscript by Pendu et al addresses an important aspect of the impact of structural interventions on riverine species. Overall, the manuscript read smooth, figures ad tables are well organized. I recommend this manuscript may be accepted for publication. Authors may consider to incorporate the following suggestions; I hope these may help to improve the quality of the manuscript.
In introduction, please review the similar studies conducted globally. For example, author can find a similar studies on the Indus and the ganga river river dolphins. You may find Sonkar et al 2020, where they have studied the impact of large barrages on the ganga river dolphins, a similar study has been conducted by Sinha et al as well.
Methods:
Please don’t keep study area and subjects under the methodology section. You can create a separate section for study area. If possible, use some satellite imager to show the condition of river before and after the construction of bridge. It will help readers to understand the change in the river patter or morphology due to the construction activities.
In method section, if possible, include a flow chart to illustrate the overall procedure followed in this study. I believe this will help reader to quickly understand the setps followed.
Discussion:
Here you discuss your findings in chronological order and try to explain the result with finer details.
Conclusion:
Please add a separate section for conclusion. And highlight the major findings in bullet.
Reviewer #2: Manuscript entitled “Do bridge constructions affect dolphin use of space? Responses of Guiana dolphins from Ilhéus, Northeastern Brazil”. I have gone through the entire manuscript thoroughly.
This manuscript investigates the impact of the construction of the Jorge Amado Bridge on the space use and movement patterns of Guiana dolphins (Sotalia guianensis) in the Cachoeira River estuary (Pontal Bay) in Ilhéus, Brazil. The authors used theodolite and total station observations to track the dolphins' trajectories and estimate their utilization distribution, area of use, and core areas before and during the bridge construction.
The key findings of the manuscript are:
1. Contrary to the authors' expectations, the dolphins increased their use of the areas close to the bridge during its construction. This was likely due to the formation of a sandbank near the bridge, which may have provided new foraging opportunities for the dolphins.
2. The dolphins consistently avoided areas close to the river banks, both before and during the bridge construction, possibly due to the presence of debris and stranded boats.
3. The authors suggest that changes in the local bathymetry, caused by the bridge construction and the resulting sandbank formation, were the main drivers of the observed changes in the dolphins' space use.
Scientific Observations:
1. The introduction provides a comprehensive background on the potential impacts of coastal constructions on cetaceans, particularly Guiana dolphins, which are the focus of this study. The introduction is well-structured and effectively sets up the rationale for the study.
2. The methods section is detailed and the data analysis approaches are appropriate for the research questions. The use of theodolite and total station observations to track the dolphins' movements and estimate their utilization distributions is a robust approach.
3. The results are clearly presented, and the authors make good use of figures to illustrate the changes in the dolphins' space use before and during the bridge construction.
4. The discussion section provides a thoughtful interpretation of the results, considering both the direct and indirect impacts of the bridge construction on the dolphins' behavior and habitat use. The authors' hypothesis about the role of bathymetric changes in driving the observed patterns is well-supported by the data.
A few of my specific comments and suggestions are as follows:
Comment. 1
"What specific environmental changes associated with the construction of the Jorge Amado Bridge may have facilitated new foraging opportunities for Guiana dolphins, and how might these changes influence their long-term habitat selection and behavior in Pontal Bay?
Additionally, what other factors—such as prey availability, habitat complexity, and social dynamics—might influence dolphin behavior and habitat selection in response to anthropogenic disturbances?
Comment. 2
Line 42: Describe more about Guiana dolphins (Sotalia guianensis) like what functions paly in that ecosystem, How is it different from other dolphin species?, its ecological roles/ importance in Cachoeira River estuary.
Comment. 3
Line 84: Few description of under Construction Bridge should be included like, how much area was covered by the pillars of the bridge, what was the distance between the two pillars during construction? etc.
Comment. 4
Line 85: During the construction of the bridge, the width of the estuary mouth was reduced, and the sandbank expanded. This study was conducted in the estuary; have the any tidal affect observed in the behaviors of dolphin population during the study period? Or what were the visiting / sighting frequencies during the variation in the depth of the estuary.
Comment. 5
Mention the table number in the entire manuscript
Comment. 6
Justify lines and correct some minor grammatical mistakes in the manuscript
Overall, this is a well-designed and executed study that provides valuable insights into the behavioral responses of Guiana dolphins to the construction of a major coastal infrastructure project. The authors' findings contribute to the limited knowledge on the impacts of anthropogenic activities on this vulnerable species and can inform conservation and management efforts.
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Reviewer #1: No
Reviewer #2: No
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Author response to Decision Letter 0
12 Sep 2024
PONE-D-24-14912
Do bridge constructions affect dolphin use of space? Responses of Guiana dolphins from Ilhéus, Northeastern Brazil
PLOS ONE
Dear Academic editor:
First of all, we are grateful for the interest of the journal PLOS ONE' in publishing our manuscript. This revision note is a detailed response to your helpful comments and those of the two independent reviewers and complements the revised version of the manuscript, for your consideration. We have taken all comments into account, and responses to each comment are organized by reviewer.
Journal requirements:
When submitting your revision, we need you to address these additional requirements.
1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming.
Done
2. In your Methods section, please provide additional information regarding the permits you obtained for the work. Please ensure you have included the full name of the authority that approved the field site access and, if no permits were required, a brief statement explaining why.
We added the following sentence in the Data collection section: “No permits were required for this study, which was carried out in an unprotected area and involved the remote observation of animals in the wild.”
3. We note that your Data Availability Statement is currently as follows: [All relevant data are within the manuscript and its Supporting Information files. Please confirm at this time whether or not your submission contains all raw data required to replicate the results of your study. Authors must share the “minimal data set” for their submission (…).
We uploaded in Biostudies repository (Licence CCO, DOI: 10.6019/S-BSST1636) the following set of 4 excel tables corresponding to the data analyzed in the article to be published in PLOS ONE:
1.visitation rate: Visitation rate of Guiana dolphins in Pontal Bay.
2.bimonthly_overlap: Raw data used to analyze the degree of bimonthly overlap between areas of use and between core areas (HR95, HR50, UDOI95, UDOI50).
3.RSF_and_UD_diff_analysis: Resource Selection Functions and Utilization Distribution differences analysis.
4.velocity_and_linearity_analysis. Raw data used to analyze the impact of bridge construction on dolphin movement (speed and linearity)
4. We note that Figures 1 and 3 in your submission contain [map/satellite] images which may be copyrighted. (…).
We modified Fig 1: the map does not contain anymore original satellite image, only illustrative maps created by the authors. Fig 4 (formerly Fig 3) contains maps created by the authors, and we have mentioned the name of the author of the bridge photograph (Fig 4C) in the figure legend (Photo: Y. Le Pendu).
5. Please review your reference list to ensure that it is complete and correct. (…).
Done.
Response to academic editor comments:
Changes in the site bathymetry due to bridge construction and the resulted sandbank formation, are the major reasons for the dolphin space use pattern. Can the Ms be correlated with habitat chief of dolphins during Covid-19 lock down i.e. in contrary to bridge construction work (disturbance) undisturbed regime also affect home range of these river cetaceans. Some such explanation about bankcard shifting of Gangetic dolphins have been provided. in following paper: COVID-19 lockdown affects zooplankton community structure in dolphin appearing site of the River Ganga at Patna_26_1
August 2023Aquatic Ecosystem Health and Management 26(1):20-31
R: Although analyzing the influence of COVID-19 is certainly a promising direction for future research, our data collection was completed in February 2020, prior to the onset of the COVID-19 lockdown in our study area. The first confirmed case of the virus in Brazil was on February 25, 2020, and protective measures in Ilhéus began on March 6, which halted our sampling. Consequently, our results are not influenced by the COVID-19 lockdown, and addressing this is beyond the scope of our study. To clarify this, we have added the sentence, 'The sampling was completed prior to the COVID-19 lockdown in Ilhéus', to the Data Collection section, ensuring that readers do not misinterpret our findings.
Response to reviewer #1 comments:
This manuscript by Pendu et al addresses an important aspect of the impact of structural interventions on riverine species. Overall, the manuscript read smooth, figures ad tables are well organized. I recommend this manuscript may be accepted for publication. Authors may consider to incorporate the following suggestions; I hope these may help to improve the quality of the manuscript.
In introduction, please review the similar studies conducted globally. For example, author can find a similar studies on the Indus and the ganga river river dolphins. You may find Sonkar et al 2020, where they have studied the impact of large barrages on the ganga river dolphins, a similar study has been conducted by Sinha et al as well.
R: We added a sentence citing the review by Campbell et al. (2022) and the studies by Pavanato et al. (2016), Aggarwal et al. (2020): “Some studies indicate that dam construction can have serious consequences for river dolphins such as the boto (Inia geoffrensis)[16] and Ganges river dolphins (Platanista gangetica gangetica)[15,17], potentially leading to unsustainable population fragmentation and even local extinction [15]”. We also cite the study of Sonkar et al. (2020) in the sentence: “Similarly, Ganga River dolphins (Platanista gangetica) altered their preferred areas, increasing their occurrence in certain portions of the river after the construction of a barrage [18].”.
Methods:
Please don’t keep study area and subjects under the methodology section. You can create a separate section for study area.
R: We have renamed the "Study area and subjects" section to "Study area”. We moved the two sentences referring to dolphins [Groups of S. guianensis (…) consist of 2 to 5 individuals] to the beginning of the "Data collection" section. We hope to have contemplated your request.
If possible, use some satellite imager to show the condition of river before and after the construction of bridge. It will help readers to understand the change in the river patter or morphology due to the construction activities.
R: Figure 1 shows two illustrative maps based on satellite images depicting Pontal Bay before (A) and after (B) the completion of the Jorge Amado Bridge, in particular the evolution of the sandbank.
In method section, if possible, include a flow chart to illustrate the overall procedure followed in this study. I believe this will help reader to quickly understand the setps followed.
R: We added a new figure 2, a flowchart summarizing the stages of data collection, selection, organization and analysis carried out.
Discussion: Here you discuss your findings in chronological order and try to explain the result with finer details.
Correct
Conclusion: Please add a separate section for conclusion. And highlight the major findings in bullet.
R: A separate section for conclusion was added, with the major findings highlighted in bullets, although such conclusion in bullets does not seem to be a common practice in articles published in PLOS ONE. According to guidelines, “Results, Discussion and Conclusions may all be separate, or may be combined to create a mixed Results/Discussion section (commonly labeled “Results and Discussion”) or a mixed Discussion/Conclusions section (commonly labeled “Discussion”)”.
Response to reviewer #2 comments:
Comment. 1. "What specific environmental changes associated with the construction of the Jorge Amado Bridge may have facilitated new foraging opportunities for Guiana dolphins, and how might these changes influence their long-term habitat selection and behavior in Pontal Bay?
R: Thank you for this suggestion. We pointed out in the third paragraph of the discussion [The reduction in river flow...] that the formation of a sandbank near the bridge was the environmental change that facilitated new foraging opportunities, as it probably functions as a barrier that allows fish to be trapped. At the end of the third paragraph of the discussion, we have added the following sentence to address the long-term impact of environmental changes: “As the geomorphological and sedimentological dynamics of Pontal Bay are unpredictable, only monitoring the growth of the sandbank and the presence of dolphins will reveal whether the new opportunistic feeding area identified in this study will continue to attract dolphins or whether they will have to forage in other areas.”. Potential long-term effects are outlined at the end of the discussion: “We highlight that Pontal Bay has suffered continuous silting due to the deposition of continental and oceanic sediments.” (…) “The Jorge Amado Bridge poses yet another threat that could reduce the depth and width of Pontal Bay over time, two environmental characteristics that could decrease habitat suitability for dolphins. A continuous monitoring of Guiana dolphins in this area is highly recommended to understand the long-term impacts and to proactively conserve this population.”
Additionally, what other factors—such as prey availability, habitat complexity, and social dynamics—might influence dolphin behavior and habitat selection in response to anthropogenic disturbances?
R: The multiplication of anthropogenic disturbances along the coastal zone can have an impact on dolphin behavior. However, the manuscript focuses on the impacts of bridge construction on the space use of dolphins in Pontal Bay, which is only part of the home range of these dolphins, that also feeds and socializes in the coastal waters of the ocean.
Comment. 2. Line 42: Describe more about Guiana dolphins (Sotalia guianensis) like what functions paly in that ecosystem, How is it different from other dolphin species?, its ecological roles/ importance in Cachoeira River estuary.
R: We added the following information to the text: (…) Guiana dolphins regularly visits (… Pontal Bay), mainly for foraging purposes [31]. It is the only dolphin species that frequents the estuary. As a top predator restricted to coastal waters less than 50 m deep, it plays an important role in regulating populations of fish and other marine animals of this ecosystem [32].
Comment. 3. Line 84: Few description of under Construction Bridge should be included like, how much area was covered by the pillars of the bridge, what was the distance between the two pillars during construction? etc.
R: We added the following sentences: “During the construction of the bridge, earthworks were carried out to facilitate the construction of the main pillar. The width of the estuary mouth was reduced, and the sandbank expanded (Fig 1). The reinforced concrete base (44 x 14 m) of the main pillar is the only submerged support remaining after the earthworks were removed at the end of the bridge construction.”
Comment. 4. Line 85: During the construction of the bridge, the width of the estuary mouth was reduced, and the sandbank expanded. This study was conducted in the estuary; have the any tidal affect observed in the behaviors of dolphin population during the study period? Or what were the visiting / sighting frequencies during the variation in the depth of the estuary.
R: We did not analyze the effect of tides in this study but added information on this topic in the discussion: “A study conducted in 2006 in Pontal bay [31] concluded that dolphins were more frequent in areas deeper than 3 m and at the end of the flood, adapting the direction of their feeding movements to the tide. Another study in the Caravelas river estuary (located approximately 400 km south of the study area) suggests that depth is the main limiting factor for habitat use by Guiana dolphins [57]”.
Comment. 5 Mention the table number in the entire manuscript
R: “Table 2” is now quoted in the text along with the numerical results.
Comment. 6. Justify lines and correct some minor grammatical mistakes in the manuscript
We have made a second in-depth revision to avoid formatting and grammatical errors.
Response to reviewer #3 comments:
Few comments:
It appears that Guiana dolphins forage in shallow water and estuaries and therefore, sand banks created due to bridge construction and other barriers facilitated herding of fishes by dolphin towards the barrier. It is an opportunistic foraging behavoiur. However, it imperative to look at the long-term impact of such barriers and adopted behaviour on the dolphin.
Authors would like to add such prospectives in their introduction as well as discussion. This will help in formulating long term planning for systematic monitoring of such projects which affects the critical aquatic lives.
R: Thank you for your comments and suggestions. We have added several sentences to address the long-term impact of environmental change in the introduction “These changes may result from modifications in prey distribution and behavior, as well as the removal or creation of foraging opportunities due to siltation.” and in the discussion: “As the geomorphological and sedimentological dynamics of Pontal Bay are unpredictable, only monitoring the growth of the sandbank and the presence of dolphins will reveal whether the new opportunistic feeding area identified in this study will continue to attract dolphins or whether they will have to forage in other areas.”. Potential long-term effects are outlined at the end of the discussion: “We highlight that Pontal Bay has suffered continuous silting due to the deposition of continental and oceanic sediments.” (…) “The Jorge Amado Bridge poses yet another threat that could reduce the depth and width of Pontal Bay over time, two environmental characteristics that could decrease habitat suitability for dolphins. A continuous monitoring of Guiana dolphins in this area is highly recommended to understand the long-term impacts and to proactively conserve this population.”
Decision Letter 1
27 Sep 2024
PONE-D-24-14912R1Do bridge constructions affect dolphin use of space? Responses of Guiana dolphins from Ilhéus, Northeastern BrazilPLOS ONE
Dear Dr. Le Pendu,
Thank you for considering all the comments and suggestions made by the reviewers. I have critically perused the manuscript and I find that the Ms still need some minor revision to strengthen the results obtained in the Ms. After careful consideration, Therefore, we invite you to submit a revised version of the manuscript that addresses the following points: .
Do bridge constructions affect dolphin use of space? Responses of Guiana dolphins from Ilhéus, Northeastern Brazil
I have critically perused the manuscript .Title: Actually I am not in favour of a title in Interrogation; Interrogation is more often used for direct manipulation/experimental study
However for space use by dolphins there are several determinants including river water, morphometric flow patterns etc. Authors themselves explains in the text as “However, a single variable hardly explains habitat selection by dolphins [e.g. 4, 32,49].” Thus I would suggest a better title that could reflect this kind of study as follow:
“Effect of bridge constructions on dolphin use of space: A case study of Guiana dolphins from Ilhéus, Northeastern Brazil'
Or
"Responses of Guiana dolphins from Ilhéus Northeastern Brazil to bridge constructions"
Regarding the comments belowComments for text:
I think earlier statement has been misconstrued i.e. Can the Ms be correlated with habitat shift of dolphins during Covid-19 lock down i.e. in contrary to bridge construction work (disturbance) undisturbed regime also affect home range of these river cetaceans.
I did not intend to mention the effect of Covid-19; as other studies have reported reduced human disturbance due to covid -19 lock down
Some such explanation about bankward shifting of Gangetic dolphins have been provided in following paper: COVID-19 lockdown affects zooplankton community structure in dolphin appearing site of the River Ganga at Patna_26_1 August 2023Aquatic Ecosystem Health and Management 26(1):20-31
The comment does not suggest mentioning Covid -19 effects. Covid-19 did not directly affect any nonhuman animal, however the lockdown offered opportunity to study behavioural changes in wild lives in the absence of human activities. So the comment suggests Habitat shifting, space use/ food base etc. in relation to anthropogenic disturbances. I am still of the view that this will further strengthen the quality of the paper. Covid-19 lock down was considered as reduced anthropogenic pressure /activity /disturbance from river bank side and no motor boat activity, undoubtedly these are determinants of shifting of dolphin habitat.
The suggested paper has (i) presented data on food base of dolphin and habitat shifting as this manuscript directly explains the new opportunistic feeding area attracting dolphins. (ii) a probable spatial redistribution of feeding sites in lack of human activities during the lock down .
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Additional Editor Comments:
Do bridge constructions affect dolphin use of space? Responses of Guiana dolphins from Ilhéus, Northeastern Brazil
I have critically perused the manuscript . Actually I am not in favour of a title in Interrogation; Interrogation is more often used for direct manipulation/experimental study
Howeevr for space use by dolphins there are several determinants including river water, morphometric flow patterns etc. Authors themselves explains in the text as “However, a single variable hardly explains habitat selection by dolphins [e.g. 4, 32,49].” Thus I would suggest a better title that could reflect this kind of study as follow:
“Effect of bridge constructions on dolphin use of space: A case study of Guiana dolphins from Ilhéus, Northeastern Brazil'
Or
"Responses of Guiana dolphins from Ilhéus Northeastern Brazil to bridge constructions"
Regarding the comments below
Authors misconstrued my comments i.e. Can the Ms be correlated with habitat shift of dolphins during Covid-19 lock down i.e. in contrary to bridge construction work (disturbance) undisturbed regime also affect home range of these river cetaceans.
I did not intend to mention the effect of Covid-19; as other studies have reported reduced human disturbance due to covid -19 lock down
Some such explanation about bankward shifting of Gangetic dolphins have been provided in following paper: COVID-19 lockdown affects zooplankton community structure in dolphin appearing site of the River Ganga at Patna_26_1 August 2023Aquatic Ecosystem Health and Management 26(1):20-31
The comment does not suggest mentioning Covid -19 effects. Covid-19 did not directly affect any nonhuman animal, however the lockdown offered opportunity to study behavioural changes in wild lives in the absence of human activities. So the comment suggests Habitat shifting, space use/ food base etc. in relation to anthropogenic disturbances. I am still of the view that this will further strengthen the quality of the paper. Covid-19 lock down was considered as reduced anthropogenic pressure /activity /disturbance from river bank side and no motor boat activity, undoubtedly these are determinants of shifting of dolphin habitat.
The suggested paper has (i) presented data on food base of dolphin and habitat shifting as this manuscript directly explains the new opportunistic feeding area attracting dolphins. (ii) a probable spatial redistribution of feeding sites in lack of human activities during the lock down .
It may be kept in mind that the Covid -19 lockdown is just a means that facilitated negligible or lower human disturbance. Justifiably anthropogenic disturbance are the direct determinant not the Covid-19.
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Author response to Decision Letter 1
2 Oct 2024
Response to reviewers
PONE-D-24-14912
Dear Ram Kumar:
We are grateful for the interest of the journal PLOS ONE' in publishing our manuscript. This revision note is a response to your two comments on the revised version of our manuscript, for your consideration.
Title: Actually I am not in favour of a title in Interrogation; Interrogation is more often used for direct manipulation/experimental study
However for space use by dolphins there are several determinants including river water, morphometric flow patterns etc. Authors themselves explains in the text as “However, a single variable hardly explains habitat selection by dolphins [e.g. 4, 32,49].” Thus I would suggest a better title that could reflect this kind of study as follow:
“Effect of bridge constructions on dolphin use of space: A case study of Guiana dolphins from Ilhéus, Northeastern Brazil' Or "Responses of Guiana dolphins from Ilhéus Northeastern Brazil to bridge constructions"
As suggested, we have adopted an affirmative form for the title: Response of Guiana dolphins to the construction of a bridge in Ilhéus, Northeastern Brazil.
I think earlier statement has been misconstrued i.e. Can the Ms be correlated with habitat shift of dolphins during Covid-19 lock down i.e. in contrary to bridge construction work (disturbance) undisturbed regime also affect home range of these river cetaceans. I did not intend to mention the effect of Covid-19; as other studies have reported reduced human disturbance due to covid -19 lock down Some such explanation about bankward shifting of Gangetic dolphins have been provided in following paper: COVID-19 lockdown affects zooplankton community structure in dolphin appearing site of the River Ganga at Patna_26_1 August 2023Aquatic Ecosystem Health and Management 26(1):20-31 The comment does not suggest mentioning Covid -19 effects. Covid-19 did not directly affect any nonhuman animal, however the lockdown offered opportunity to study behavioural changes in wild lives in the absence of human activities. So the comment suggests Habitat shifting, space use/ food base etc. in relation to anthropogenic disturbances. I am still of the view that this will further strengthen the quality of the paper. Covid-19 lock down was considered as reduced anthropogenic pressure /activity /disturbance from river bank side and no motor boat activity, undoubtedly these are determinants of shifting of dolphin habitat. The suggested paper has (i) presented data on food base of dolphin and habitat shifting as this manuscript directly explains the new opportunistic feeding area attracting dolphins. (ii) a probable spatial redistribution of feeding sites in lack of human activities during the lock down . It may be kept in mind that the Covid -19 lockdown is just a means that facilitated negligible or lower human disturbance. Justifiably anthropogenic disturbance are the direct determinant not the Covid-19.
We understood that your previous comment referred to the decrease in anthropogenic pressure resulting from the lockdown and not to any direct effects of COVID. Although analysing the influence of COVID-19 lockdown is certainly a promising direction for future research, our results are not influenced by the COVID-19 lockdown, because 'The sampling was completed prior to the COVID-19 lockdown in Ilhéus'. We added this sentence to the Data Collection section in the R1 revised version of the manuscript and detail the chronology of the events in our previous response to reviewers.
Consequently, we cannot comment about “a probable spatial redistribution of feeding sites in lack of human activities during the lock down” or any other change in the dolphins’ behaviour during the lockdown because we did not conduct visual monitoring of the dolphins in the area during the lockdown. It was forbidden precisely because of the confinement requirement.
Decision Letter 2
8 Oct 2024
Response of Guiana dolphins to the construction of a bridge in Ilhéus, Northeastern Brazil
PONE-D-24-14912R2
Dear Yvonnick Le Pendu,,
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Academic Editor
PLOS ONE
Acceptance letter
6 Nov 2024
PONE-D-24-14912R2
PLOS ONE
Dear Dr. Le Pendu,
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Funding
Funders who supported this work.
Animal Behavior Society
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Fundação de Amparo à Pesquisa do Estado da Bahia (1)
Grant ID: PET0032/2012
