Swellshark, California Swellshark.
Stout body. Snout short and bluntly rounded. Mouth width approximately 3x snout length. First dorsal origin posterior to level of pelvic fin origin. Second dorsal fin level with anal fin origin. Anal fin much larger than second dorsal. Anal fin apex acutely rounded. Lower caudal lobe broad but poorly defined. Dorsal surface covered in irregular brown saddles on a lighter brown base, and scattered black spots. Saddles outlined by broken rows of small cream coloured spots.
Maximum length approx. 100cm. Size at birth 13-15cm.
Temperate/sub-tropical rocky reefs, kelp forests, and somtimes on continental shelves. 5m to 457m but usually found on shallow reefs down to about 40m.
The swellshark is found in the eastern Pacific from northern California to Mexico, and in central Chile. Records from in-between these areas are sparse or non-existent.
The swell shark is not targeted commercially (Moreno-Báez et al. 2012). While this species is taken as a minor bycatch in gillnets and trawls, its habitat (rocky reefs and kelp) is generally unsuitable for trawling, providing the species protection from fishing. Swell Shark is captured in both the small scale lobster trap fishery and the set gill net fishery as a small percentage of the bycatch in Baja California, Mexico (Shester and Micheli 2011). Approximately 1% of gill net landings along the pacific coast of Baja California are comprised of this species, and it is absent from long line catches (Ramirez-Amaro et al. 2013). Ramirez-Amaro et al. (2013) also noted that this species was usually caught as juveniles, suggesting that fishing effort might be opportunistically targeting nursery areas. A survey of the artisanal gillnet fishery in Baja California found that this species comprised only 1% of total elasmobranch catches, and was not valued either for its flesh or fins. This study also found carcasses of this species at discard sites surrounding fishing camps, representing only 0.6% of all carcasses (Cartamil et al. 2011). Along the Sonoran coast of the Gulf of California in Mexico, (Bizzarro et al. 2009) observed that this species is landed by artisanal fishers, however, it represented less that 1% of the total catch. There was no size difference among landed males and females, however, there was 2-fold more males landed than females.
This species is listed by the United States National Marine Fisheries Service as a landed species, however, there are no listings for this species in any recent years (PacFin). For the years in which this species was recorded, there were minimal landings, with only 1978 having the west coast shark fishery land more than 1,000 pounds (Holts, 1988).
However fisheries data often lists shark as “other”, which could possibly obfuscate true landings. This is especially true in Mexico, where small sharks are simply listed as cazonés. However, species-specific surveys in Baja California do suggest that this species may indeed be relatively uncommon in catches. This species is occasionally taken by recreational anglers and spearfishers (Compagno in prep), but this catch is likely not significant.
Citations and References
Villavicencio-Garayzar, C.J., White, C.F. & Lowe, C.G. 2015. Cephaloscyllium ventriosum. The IUCN Red List of Threatened Species 2015: e.T60227A80671800. https://dx.doi.org/10.2305/IUCN.UK.2015-4.RLTS.T60227A80671800.en. Downloaded on 14 November 2020.
Oviparous. The swell shark produces large flattened egg cases that are 9-12.5cm long and 2.8-5.5cm wide. When stretched out, the egg’s adhesive tendrils may be more than 150cm long!
The swell shark feeds on small crustaceans and annelid worms.
Swell sharks remain in deep crevices during the day. They are able to suck in water to inflate their bodies. This may make them more intimidating to predators, and it may help them stay in position against the pull of surge within the reef.
Reaction to divers
Easy to approach when resting on the reef. Not known to respond to chum.
Easily encountered at numerous dive sites in Central and Southern California. Kelp forests that have large shelves of rock for swell sharks to hide under, are prime habitat.
Refugio Beach is one area where I have seen numerous swell sharks on a single dive. Refugio is a popular shore diving site north of Santa Barbara.
In this area, long ridges of rock run parallel to shore; probably sculpted by the surf. To find swell sharks, simply drop into one of the shallow gullies between the rock ridges and look in the shadows with a dive light.
Like many California shore dives, Refugio is choked with kelp and heavily affected by surge, so pay attention to the surf conditions, and bring a dive knife to cut your way out of trouble if you become entangled.
Redspotted Catshark Distinguished by more slender, firmer body, and larger second dorsal fin which is larger than anal fin. Sympatric in Chile.
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