View source for Ovalipes catharus

{{Short description|Species of crab}}
{{Speciesbox
| image = Ovalipes catharus White, 1843 (AM MA78855).jpg
| image2 = Ovalipes catharus ventral view puddle.jpg
| genus = Ovalipes
| species = catharus
| authority = ([[Adam White (zoologist)|White]] ''in'' White and Doubleday, 1843)
| synonyms = * ''Portunus catharus'' {{small|White ''in'' White and Doubleday, 1843}}
| synonyms_ref = <ref name="WoRMS"/>
}}

'''''Ovalipes catharus''''', commonly known as the '''paddle crab''', '''swimming crab''', or {{langx|mi|'''pāpaka'''}},<ref name="Māori Dictionary">{{cite web |last1=Moorfield |first1=John C. |title=pāpaka |url=https://maoridictionary.co.nz/search?idiom=&phrase=&proverb=&loan=&histLoanWords=&keywords=p%C4%81paka |access-date=5 March 2022 |website=Te Aka Māori Dictionary |language=en}}</ref> is a [[species]] of [[crab]] in the [[family (biology)|family]] [[Ovalipidae]].<ref name="WoRMS">{{cite WoRMS |last=De Grave |first=Sammy |title=''Ovalipes catharus'' (White in White & Doubleday, 1843) |date=10 April 2022 |id=442757 |access-date=28 October 2024}}</ref><ref name="Poore & Ahyong 2023">{{cite book|last1=Poore|first1=Gary C.B.|last2=Ahyong|first2=Shane T.|author-link2=Shane T. Ahyong|title=Marine Decapod Crustacea: A Guide to Families and Genera of the World|publisher=CRC Press|year=2023|isbn=978-1-4863-1178-1|pages=695–696}}</ref> They are found in shallow, sandy-bottomed waters around the coasts of [[New Zealand]], the [[Chatham Islands]], and uncommonly in southern [[Australia]].<ref name="Wilkens and Ahyong 2015" /><ref name="O'Hara & Barmby 2000" /><ref name="Richards 1992" /> They are opportunistic and versatile feeders active mostly at night, preying predominantly on [[Mollusca|molluscs]] and [[Crustacean|crustaceans]].<ref name="Wear and Haddon 1987">{{cite journal |last=Wear |first=Robert G. |last2=Haddon |first2=M. |date=1987-01-27 |title=Natural diet of the crab ''Ovalipes catharus'' (Crustacea, Portunidae) around central and northern New Zealand |journal=[[Marine Ecology Progress Series]] |volume=35 |pages=39–49 |doi=10.3354/meps035039 |issn=0171-8630 |jstor=24825007 |doi-access=free}}</ref><ref name="Fisheries Assessment Plenary" /> They are also highly prone to [[cannibalism]] both as part of their regular diet and as part of their mating behaviour.<ref name="Wear and Haddon 1987" /><ref name="Haddon 1995" /> Their paddle-shaped rear legs and streamlined [[carapace]] allow them to swim rapidly to capture prey and to burrow in the sand in order to escape predation.<ref name="McLay & Osborne 1985" /> Their [[Seasonal breeder|mating season]] is in winter; the male carries the female until she [[Moulting|moults]], after which the two mate and the female moves into deeper waters to [[Marine larval ecology|disperse her larvae]].<ref name="Haddon 1994" />

The paddle crab has been targeted by [[Commercial fishing|commercial fisheries]] since the 1970s, although the amount caught has dramatically decreased since a peak in the late 1990s.<ref name="Fisheries Assessment Plenary" /> Their population is expected to be increasing,<ref name="Fisheries Assessment Plenary" /> although [[Ecology|ecologists]] have raised concerns that the paddle crab could become outcompeted by ''[[Charybdis japonica]]'', an [[invasive species]] with a similar size, diet, and habitat.<ref name="Fowler et al. 2013" /> ''O. catharus'' is present in [[Māori culture]], both as an artistic motif and as a traditional source of food.<ref name="Secrets" />

==Description==
[[File:Ovalipes catharus swimming in water.jpg|alt=Rear view of ''Ovalipes catharus'' swimming with its rear, paddle-shaped legs raised and its walking legs spread out laterally. Set against a teal, watery background.|thumb|right|''O. catharus'' use their paddle-shaped rear legs to swim.<ref name="Osborne 1987" />]]
''O. catharus'' has an oval-shaped, streamlined, and slightly grainy [[carapace]] with five teeth to either side of the eyes and four teeth at the front.<ref name="Wilkens and Ahyong 2015">{{Cite book |last=Wilkens |first=Serena L. |last2=Ahyong |first2=Shane T. |author-link2=Shane T. Ahyong |url=https://webstatic.niwa.co.nz/static/web/coastal_crabs_2015.pdf |title=Coastal Crabs: A Guide to the Crabs of New Zealand |publisher=[[National Institute of Water and Atmospheric Research|NIWA]] |year=2015 |edition=First |pages=3–5, 43}}</ref><ref name="McLay & Osborne 1985" /><ref name="White 1843">{{cite book|last=White|first=Adam|author-link=Adam White (zoologist)|last2=Doubleday|first2=Edward|author-link2=Edward Doubleday|year=1843|chapter=List of Annulose Animals hitherto recorded as found in New Zealand, with the Descriptions of some New Species|title=Travels in New Zealand; with Contributions to the Geography, Geology, Botany, and Natural History of that Country|editor-last=Dieffenbach|editor-first=Ernest|editor-link=Ernst Dieffenbach|publisher=John Murray|volume=II|url=https://archive.org/details/travelsinnewzea01diefgoog|via=the [[Internet Archive]]|page=265}}</ref> It is overall sandy grey with orange-red highlights and dotted with small, brown spots.<ref name="Wilkens and Ahyong 2015" /><ref name="White 1843" /> Its carapace has two large, maroon eye-spots at the rear and two smaller ones near the front.<ref name="Wilkens and Ahyong 2015" /><ref name="Naylor et al. 2005">{{Cite report |url=https://webcat.niwa.co.nz/documents/NZAEBR2.pdf |title=A guide to common offshore crabs in New Zealand waters |last=Naylor |first=J.R. |last2=Webber |first2=W.R. |date=2005 |publisher=[[Ministry of Fisheries (New Zealand)|New Zealand Ministry of Fisheries]] |issue= |page=24 |issn=1176-9440 |id=New Zealand Aquatic Environment and Biodiversity Report No. 2 |last3=Booth |first3=J.D.}}</ref> Its underside is white, and its rear legs – which are flattened and function as swimming paddles<ref name="Osborne 1987" /> – have a purplish tinge.<ref name="Wilkens and Ahyong 2015"/>

Mature paddle crabs can reach carapace widths ranging from >{{Convert|100|mm|in|abbr=on}} up to a reported {{Convert|150|mm|in|abbr=on}}.<ref name="Fisheries Assessment Plenary">{{cite report |url=https://fs.fish.govt.nz/Doc/25465/55%20PAD%202023.pdf.ashx |title=Fisheries Assessment Plenary May 2023 Volume 2 – Paddle Crabs (PAD) |date=21 June 2023 |publisher=[[Fisheries New Zealand]]}}</ref> Individuals from shallow waters, {{convert|0.1|-|0.5|m|in|0}} deep, have a carapace width of only {{convert|10|-|15|mm|1}}, while those from {{convert|5|-|15|m|abbr=on}} are {{convert|100|-|140|mm|abbr=on}} wide.<ref name="Bay of Plenty Polytechnic worksheet">{{Cite web |title=Biology and Ecology of ''Ovalipes catharus'' |url=http://marine.boppoly.ac.nz/download.cfm?DownloadFile=096C5B00-910A-70A0-7CCF25CC962C59BA |url-status=dead |type=worksheet |archive-url=https://web.archive.org/web/20110820161450/https://marine.boppoly.ac.nz/download.cfm?DownloadFile=096C5B00-910A-70A0-7CCF25CC962C59BA |archive-date=20 August 2011 |publisher=[[Bay of Plenty Polytechnic]] |postscript=. Adapted from “Form 7 Biology Animal Study” by Paul Furneaux of Otumoetai College.}}</ref> Its left [[Chelae|chela]] is smaller than its right.<ref name="Davidson 1986">{{Cite journal |last=Davidson |first=Robert J. |date=November 1986 |title=Mussel selection by the paddle crab ''Ovalipes catharus'' (White): Evidence of flexible foraging behaviour |journal=[[Journal of Experimental Marine Biology and Ecology]] |volume=102 |issue=2–3 |pages=281–299 |doi=10.1016/0022-0981(86)90182-6}}</ref>

It has a long period of larval development with eight [[Crustacean larva|zoeal stages]]. The zoea is transparent or blackish, later develops red [[chromatophore]]s, and then turns black when it moults into a megalopa.<ref name="Wear & Fielder 1985" /> The zoea features a prominent [[Dorsum (anatomy)|dorsal]] spine and similarly prominent [[Rostrum (anatomy)|rostral]] spine; neither are present in its megalopal form, whose carapace is entirely smooth.<ref name="Wear & Fielder 1985" />

== Taxonomy ==
''O. catharus'' was described in 1843 by zoologist [[Adam White (zoologist)|Adam White]], originally placed into the genus ''[[Portunus]]''.<ref name="White 1843" /> They are colloquially known as the paddle crab, the swimming crab, or {{Langx|mi|pāpaka}}.<ref name="Māori Dictionary" /> The following cladogram shows the relationship between ''O. catharus'' and the other extant species of ''[[Ovalipes]]'':<ref name="Parker, Mckenzie & Ahyong 1998">{{cite journal|last1=Parker|first1=Andrew R.|last2=Mckenzie|first2=David R.|last3=Ahyong|first3=Shane T.|author-link3=Shane T. Ahyong|title=A unique form of light reflector and the evolution of signalling in ''Ovalipes'' (Crustacea: Decapoda: Portunidae)|journal=[[Proceedings of the Royal Society B: Biological Sciences]]|date=22 May 1998|doi=10.1098/rspb.1998.0371|pmc=1689053}}</ref>{{Efn|''[[Ovalipes]]'' itself sits within the [[Monotypic taxon|monogeneric]] family [[Ovalipidae]].<ref name="Poore & Ahyong 2023"/>}}
{{Ovalipes cladogram}}

==Distribution and habitat==
''O. catharus'' is native to New Zealand, where it can be found from [[Stewart Island]] to [[Northland Region|Northland]] and in the [[Chatham Islands]].<ref name="Gust and Inglis 2006">{{Cite journal |last=Gust |first=Nick |last2=Inglis |first2=Graeme J. |date=March 2006 |title=Adaptive multi-scale sampling to determine an invasive crab's habitat usage and range in New Zealand |url=https://www.researchgate.net/publication/225792276_Adaptive_Multi-scale_Sampling_to_Determine_an_Invasive_Crab's_Habitat_Usage_and_Range_in_New_Zealand |journal=[[Biological Invasions (journal)|Biological Invasions]] |volume=8 |issue=2 |pages=339–353 |doi=10.1007/s10530-004-8243-y |via=[[ResearchGate]]}}</ref><ref name="Osborne 1987">{{Cite thesis |last=Osborne |first=T. A. |title=Life history and population biology of the paddle crab, ''Ovalipes catharus'' |date=1987 |degree=PhD |publisher=University of Canterbury |url= |doi=10.26021/6494 |doi-access=free |language=en}}</ref> They are also uncommon on the southern coast of Australia, where they're known as far west as the state of [[South Australia]] and as far east as [[Port Phillip|Port Phillip Bay]] in [[Victoria (state)|Victoria]].<ref name="Wilkens and Ahyong 2015" /><ref name="O'Hara & Barmby 2000">{{Cite report |url=https://www.researchgate.net/publication/237384212_Victorian_marine_species_of_conservation_concern_Molluscs_Echinoderms_and_Decapod_crustaceans |title=Victorian Marine Species of Conservation Concern: Molluscs, Echinoderms and Decapod Crustaceans |last=O'Hara |first=Tim |last2=Barmby |first2=Victoria |date=May 2000 |publisher=Victoria Department of Natural Resources and Environment |page=45 |isbn=0-7311-4561-5 |via=[[ResearchGate]]}}</ref><ref name="Wear & Fielder 1985">{{Cite book |last=Wear |first=Robert G. |url=https://archive.org/details/nzoimemoir00921985/page/n49/mode/2up |title=The marine fauna of New Zealand: Larvae of Brachyura (Crustacea, Decapoda) |last2=Fielder |first2=D. R. |date=1985 |isbn=0-477-06722-0 |series=New Zealand Oceanographic Institute Memoir 92 |pages=50–52 |issn=0083-7903 |via=the [[Internet Archive]]}}</ref> They live along sandy-bottomed coastal waters, generally at depths of <{{Convert|10|m|ft|abbr=on}} in [[Estuary|estuaries]] and the [[subtidal zone]],<ref name="Gust and Inglis 2006"/><ref name="Richards 1992">{{Cite thesis |last=Richards |first=R.N. |title=The structure and function of the gills of the New Zealand paddle crab: ''Ovalipes catharus'' |date=1992 |degree=Master of Sciences |publisher=University of Canterbury |url= |doi=10.26021/13400 |doi-access=free}}</ref><ref name="Miller et al. 2006">{{Cite journal |last=Miller |first=Aroha |last2=Inglis |first2=Graeme J. |last3=Poulin |first3=Robert |date=2006 |title=Comparison of the ectosymbionts and parasites of an introduced crab, ''Charybdis japonica'', with sympatric and allopatric populations of a native New Zealand crab, ''Ovalipes catharus'' (Brachyura: Portunidae) |journal=New Zealand Journal of Marine and Freshwater Research |volume=40 |issue=2 |pages=369–378 |doi=10.1080/00288330.2006.9517428 |issn=0028-8330 |doi-access=free}}</ref> and they move into the [[intertidal zone]] during the evening or the night in order to feed.<ref name="Fisheries Assessment Plenary" /> Although they generally stick to shallow waters, they can be found at depths of up to {{Convert|100|m|ft|abbr=on}},<ref name="Gust and Inglis 2006" /> and their larvae can be found in deeper waters, up to at least {{Convert|700|m|ft|abbr=on}}.<ref name="Fisheries Assessment Plenary" /> They have been observed to be highly migratory.<ref name="Fisheries Assessment Plenary" /> Anecdotal information suggests a dramatic population increase since the 1970s.<ref name="Fisheries Assessment Plenary" />

==Diet==
[[File:Paphies australis on rocks.jpg|alt=The off-white shell of a lone specimen of ''Paphies australis'' sitting on a background of grey pebbles|thumb|right|Bivalves such as ''[[Paphies australis]]'' are a significant portion of the paddle crab's diet.<ref name="Wear and Haddon 1987" />]]
The diet of paddle crabs consists predominantly of [[Mollusca|molluscs]] (especially of genus ''[[Paphies]]'') and [[crustacean]]s, but they also feed on fish, [[Polychaete|bristle worms]], and occasionally [[algae]].<ref name="Wear and Haddon 1987" /><ref name="Fisheries Assessment Plenary" /><ref name="Osborne 1987" /> Large ''O. catharus'' tend to feed less frequently but on larger animals such as [[Decapoda|decapod]]s and [[teleost]]s, while smaller ones prey frequently on smaller, softer crustaceans such as [[Amphipoda|amphipods]], [[Isopoda|isopods]], [[Mysida|opossum shrimp]], and [[Cumacea|hooded shrimp]].<ref name="Osborne 1987" /> A major portion of their diet is cannibalizing other members of ''O. catharus'' which are either smaller than them or have lost their shell during the winter moulting season.<ref name="Wear and Haddon 1987" /><ref name="Osborne 1987" />

The flattened hind legs and streamlined body shape of the crab allow them to swim rapidly and catch faster prey,<ref name="Osborne 1987" /><ref name="McLay & Osborne 1985" /> and they have relatively small [[chelae]] which are well-suited to handling small molluscs.<ref name="Davidson 1987">{{Cite thesis |last=Davidson |first=Robert J. |title=Natural food and predatory activity of the paddle crab, ''Ovalipes catharus'': A flexible forager |date=1987 |degree=Master of Science |publisher=University of Canterbury |url= |doi=10.26021/6041 |doi-access=free |pages=2–15}}</ref> Its chelae are dimorphic; the left is used for cutting while the right is used for crushing.<ref name="Davidson 1986" />

== Predators and other interactions ==
[[File:Ovalipes catharus burrowing.gif|alt=A video of ''Ovalipes catharus'' retreating backward into loose, pebbly sand on the seabed, fully covering itself from back to front over a period of 6.5 seconds. The video is shot from the front at an angle of about 45 degrees to the right relative to where the crab is facing. Brownish seaweed is visible in the foreground of the shot.|thumb|right|''O. catharus'' burrow in the seabed to escape predation.<ref name="McLay & Osborne 1985"/>]]
Predators of the paddle crab include [[spiny dogfish]],<ref name="Hanchet 1991">{{Cite journal |last=Hanchet |first=Stuart |date=September 1991 |title=Diet of spiny dogfish, ''Squalus acanthias'' Linnaeus, on the east coast, South Island, New Zealand |journal=[[Journal of Fish Biology]] |volume=39 |issue=3 |pages=313–323 |doi=10.1111/j.1095-8649.1991.tb04365.x}}</ref> [[Australasian snapper|snapper]] (''Pagrus auratus''), [[Spotted estuary smooth-hound|rig]] (''Mustelus lenticulatus''),<ref name="King & Clark 1984">{{Cite journal |last=King |first=Ken J. |last2=Clark |first2=Malcolm R. |year=1984 |title=The food of rig (''Mustelus lenticulatus'') and the relationship of feeding to reproduction and condition in Golden Bay |journal=New Zealand Journal of Marine and Freshwater Research |volume=18 |issue=1 |pages=29–42 |doi=10.1080/00288330.1984.9516026 |issn=0028-8330 |doi-access=free}}</ref>, [[Hāpuku|groper]] (''Polyprion oxygeneiosis''), [[Hector's dolphin]],<ref name="Miller et al. 2012">{{Cite journal |last=Miller |first=Elanor J. |last2=Lalas |first2=Chris |last3=Dawson |first3=Stephen M. |last4=Ratz |first4=Hultrun |last5=Slooten |first5=Elisabeth |date=August 2012 |title=Hector's dolphin diet: The species, sizes and relative importance of prey eaten by ''Cephalorhynchus hectori'', investigated using stomach content analysis |url=https://www.researchgate.net/publication/230788987_Hector's_dolphin_diet_The_species_sizes_and_relative_importance_of_prey_eaten_by_Cephalorhynchus_hectori_investigated_using_stomach_content_analysis |journal=[[Marine Mammal Science]] |volume=29 |issue=4 |pages=606–628 |doi=10.1111/j.1748-7692.2012.00594.x |via=[[ResearchGate]]}}</ref> and the [[Invasive species|invasive]] crab species ''[[Charybdis japonica]]''.<ref name="Fowler et al. 2013">{{Cite journal |last=Fowler |first=Amy E. |last2=Muirhead |first2=Jim R. |last3=Taylor |first3=Richard B. |date=September 2013 |title=Early Stages of A New Zealand Invasion By ''Charybdis Japonica'' (A. Milne-Edwards, 1861) (Brachyura: Portunidae) from Asia: Behavioral Interactions with A Native Crab Species |journal=[[Journal of Crustacean Biology]] |volume=33 |issue=5 |pages=672–680 |doi=10.1163/1937240X-00002177 |jstor=43835684 |doi-access=free}}</ref> Younger individuals are prone to being cannibalized,<ref name="Wear and Haddon 1987" /><ref name="Osborne 1987" /> and all paddle crabs are vulnerable to cannibalism during moulting.<ref name="Osborne 1987" /> Commercial fisheries additionally target the paddle crab.<ref name="Fisheries Assessment Plenary" /> In order to escape predation, ''O. catharus'' creates temporary burrows in soft sand using their paddles, taking only several seconds to completely submerge itself.<ref name="McLay & Osborne 1985">{{Cite journal |last=McLay |first=C.L. |last2=Osborne |first2=T.A. |year=1985 |title=Burrowing behaviour of the paddle crab ''Ovalipes catharus'' (White, 1843) (Brachyura: Portunidae) |journal=New Zealand Journal of Marine and Freshwater Research |volume=19 |issue=2 |pages=125–130 |doi=10.1080/00288330.1985.9516078 |issn=0028-8330 |doi-access=free}}</ref>

''O. catharus'' do not appear to be typically parasitized by [[nematode]]s or [[barnacle]]s.<ref name="Miller et al. 2006" /> Instead, the overwhelming majority of them{{Efn|97.4% of ''O. catharus'' surveyed from six sites were hosts to ''Triticella capsularis''.<ref name="Miller et al. 2006" />}} are hosts to the [[Ctenostomatida|ctenosome bryozoan]] ''Triticella capsularis'', which forms a fur of up to almost {{Convert|10|mm|in|abbr=on|sigfig=1}} thick on their underside after their final moult.<ref name="Gordon & Wear 1999">{{Cite journal |last=Gordon |first=Dennis P. |last2=Wear |first2=Robert G. |year=1999 |title=A new ctenostome brozoan ectosymbiotic with terminal-moult paddle crabs (Portunidae) in New Zealand |journal=[[New Zealand Journal of Zoology]] |volume=26 |issue=4 |pages=373–380 |doi=10.1080/03014223.1999.9518200 |doi-access=free}}</ref><ref name="Miller et al. 2006" /> It is only found on ''O. catharus'',<ref name="Gordon & Wear 1999" /> and it is speculated to be an obligate [[Symbiosis|symbiont]] of the crab.<ref name="Miller et al. 2006" /> ''O. catharus'' does not appear to be affected by parasites present in the invasive ''C. japonica'', which tends to be [[Sympatry|sympatric]] with the paddle crab and is heavily parasitized by [[Serpulidae|serpulids]].<ref name="Miller et al. 2006" />

== Mating and reproduction ==
''O. catharus'' reach sexual maturity within the first year of [[Benthic zone|benthic]] life, and females produce clutches of eggs from early spring to late summer.<ref name="Armstrong 1988">{{Cite journal |last=Armstrong |first=James H. |date=1988 |title=Reproduction in the paddle crab ''Ovalipes catharus'' (Decapoda: Portunidae) from Blueskin Bay, Otago, New Zealand |journal=New Zealand Journal of Marine and Freshwater Research |volume=22 |issue=4 |pages=529–536 |doi=10.1080/00288330.1988.9516323 |issn=0028-8330}}</ref><ref name="Osborne 1987" /> It is not known how many clutches can be fertilised from one insemination, but females have been observed to produce up to four or five without re-mating.<ref name="Osborne 1987" /><ref name="Haddon 1994">{{Cite journal |last=Haddon |first=Malcolm |date=1994 |title=Size ‐ fecundity relationships, mating behaviour, and larval release in the New Zealand paddle crab, ''Ovalipes catharus'' (White 1843) (Brachyura: Portunidae) |journal=New Zealand Journal of Marine and Freshwater Research |volume=28 |issue=4 |pages=329–334 |doi=10.1080/00288330.1994.9516622 |doi-access=free |issn=0028-8330}}</ref> In one clutch the female crabs produce between 82,000 and 683,000 eggs, but like in other crabs, a very large proportion of these are lost to disease or predation.<ref name="Haddon 1994" /> [[Fecundity]] is also heavily influenced by [[carapace]] width and body mass, with larger and heavier crabs having higher fecundity.<ref name="Haddon 1994" /> Larvae develop synchronously and are released in large numbers by vigorous waving of the female's body, which disturbs their egg cases and causes them to break out.<ref name="Haddon 1994" /> Females mostly release their larvae at night and when releasing they stand on their [[Dactylus|dactyli]] before extending themselves as far as possible. They then angle themselves up and begin flexing their abdomen to release large clouds of larvae.<ref name="Haddon 1994" /> Females have also been observed to preen the egg mass during development. Higher temperatures have been observed to prolong the breeding season, increase growth rates, and cause them to obtain sexual maturity sooner.<ref name="Osborne 1987" /> This causes slight differences in mating times between populations of ''O. catharus'' living at different locations in the wild.<ref name="Osborne 1987" />

=== Mating behaviours ===
Males and females meet in shallow sheltered bays during winter, which is July to August in New Zealand. The time is also variable between populations with some mating as early as May and some as late as November. Males often attract mates by creating a rasping sound, by rubbing their legs together vigorously.<ref name="Secrets">{{citeq|Q114871191|pp=78–83}}</ref><ref name="Haddon 1994" />

In these shallow bays, they mate when the females [[Moulting|moult]]. Male crabs can only mate with soft post-moult females, so they begin to carry female crabs under their bodies up to 8 days prior to the females moulting.<ref name="Haddon 1994" /> Once the female has moulted, she depends entirely on the male for protection, and he will even assist with the moulting process by using his legs to remove parts of the female's old carapace. Once moulting is complete they will mate for between 12 and 36 hours and even up to four days.<ref name="Haddon 1994" /> After mating the female is released and the females move onto spawning grounds deeper in the water, of which the location is not known, and the males move to foraging grounds.<ref name="Osborne 1987" />

=== Sexual cannibalism ===
[[Sexual cannibalism]] has been frequently observed in ''O. catharus'', and it is directed by males towards females. This sexual cannibalism occurs when the female is soft-shelled after moulting during the mating process.<ref name="Haddon 1995">{{Cite journal |last=Haddon |first=Malcolm |date=1995 |title=Avoidance of Post-Coital Cannibalism in the Brachyurid Paddle Crab Ovalipes catharus |journal=[[Oecologia]] |volume=104 |issue=2 |pages=256–258 |doi=10.1007/BF00328590 |jstor=4221102 |pmid=28307362}}</ref> Male crabs protect the females they mate with from being cannibalised, but unreceptive females or those that have mated with other crabs are in danger of being cannibalised.<ref name="Haddon 1995" /> This is most likely done to maximize the number of eggs fertilised by his sperm.<ref name="Buskirk et al. 1984">{{Cite journal |last=Buskirk |first=Ruth E. |last2=Frohlich |first2=Cliff |last3=Ross |first3=Kenneth G. |date=May 1984 |title=The Natural Selection of Sexual Cannibalism |journal=[[The American Naturalist]] |language=en |volume=123 |issue=5 |pages=612–625 |doi=10.1086/284227 |jstor=2461241}}</ref> Some examples of males cannibalising females they have mated with have also been observed.<ref name="Haddon 1995" /> This sexual cannibalism is not about mate choice or adaptation and is instead more opportunistic.<ref name="Prenter et al. 2006">{{Cite journal |last=Prenter |first=John |last2=MacNeil |first2=Calum |last3=Elwood |first3=Robert W. |date=March 2006 |title=Sexual cannibalism and mate choice |journal=[[Animal Behaviour (journal)|Animal Behaviour]] |language=en |volume=71 |issue=3 |pages=481–490 |doi=10.1016/j.anbehav.2005.05.011}}</ref><ref name="Schneider 2014">{{Cite journal |last=Schneider |first=Jutta M. |date=2014 |title=Sexual Cannibalism as a Manifestation of Sexual Conflict |journal=[[Cold Spring Harbor Perspectives in Biology]] |language=en |volume=6 |issue=11 |pages=a017731 |doi=10.1101/cshperspect.a017731 |pmc=4413240 |pmid=25213095 |doi-access=free}}</ref><ref name="Zuk 2016">{{Cite journal |last=Zuk |first=Marlene |date=5 December 2016 |title=Mates with Benefits: When and How Sexual Cannibalism Is Adaptive |journal=[[Current Biology]] |volume=26 |issue=23 |pages=R1230–R1232 |doi=10.1016/j.cub.2016.10.017 |doi-access=free |pmid=27923131}}</ref> In one example, male crabs that had not cannibalised female crabs all accepted frozen squid afterwards, while very few males that had cannibalised female crabs accepted frozen squid afterwards. This indicates that hunger could be a part of the cause behind the cannibalism, and male crabs just take the opportunity to feed while the females are vulnerable in their soft-shelled state. Unlike in other examples of sexual cannibalism, size was not shown to have an effect on whether cannibalism occurred.<ref name="Haddon 1995" /><ref name="Prenter et al. 2006" /> Sexual cannibalism in ''O. catharus'' is very prevalent, with a study on the diet of the crab detecting it in almost every location tested.<ref name="Wear and Haddon 1987"/> Part of the prevalence of ''O. catharus'' in its own diet could be due to males consuming each other during the breeding season, as the smaller males guarding females do not have protection themselves from cannibalism and can sometimes be mistaken for females.<ref name="Haddon 1995"/>

==Relation to humans==

''O. catharus'' is a common motif in [[Māori art]], with designs being incorporated into weaving patterns, [[tā moko]], and the designs of [[wharenui]] and whare wānanga (houses of learning). The crabs are known to be a traditional food source, but researchers in the early [[Colony of New Zealand|Colonial]] period did not record much about harvesting traditions.<ref name="Secrets"/>

[[Commercial fishing|Commercial fisheries]] have targeted targeted paddle crabs since the late 1970s, mostly to the east of the [[North Island]] and the north of the [[South Island]].<ref name="Osborne 1987"/><ref name="Fisheries Assessment Plenary"/> Catch is sold both locally in New Zealand and overseas to Japan.<ref name="Jester et al. 2009">{{Cite journal |last=Jester |first=Rozalind J. |last2=Rhodes |first2=Lesley L. |last3=Beuzenberg |first3=Veronica |date=January 2009 |title=Uptake of paralytic shellfish poisoning and spirolide toxins by paddle crabs (''Ovalipes catharus'') via a bivalve vector |journal=Harmful Algae |volume=8 |issue=2 |pages=369–376 |doi=10.1016/j.hal.2008.08.002 |issn=1568-9883}}</ref> The paddle crab is known for having meat with both good flavor and texture.<ref name="Osborne 1987"/> The amount of paddle crabs landed generally increased until the late 1990s, reaching a peak at {{Convert|519|t|lb|abbr=on}} in 1998–99, at which point it began generally decreasing for the next two decades, reaching an average of {{Convert|16.6|t|lb|abbr=on}} annually from the five-year period of 2017–2022.<ref name="Fisheries Assessment Plenary" />

They are known for their aggression on beaches, often pinching swimmers in New Zealand.<ref name="Secrets"/><ref name="Wilkens and Ahyong 2015"/> 

==Notes==
{{notelist}}

==References==
{{Reflist|30em}}

==External links==
*{{Commons category-inline|2=''Ovalipes catharus''}}
*{{Wikispecies-inline|2=''Ovalipes catharus''}}

{{Taxonbar|from=Q7113226}}

[[Category:Portunoidea]]
[[Category:Crabs of the Pacific Ocean]]
[[Category:Crustaceans described in 1843]]
[[Category:Taxa named by Adam White (zoologist)]]
[[Category:Marine crustaceans of New Zealand]]
[[Category:Edible crustaceans]]