Bycatch of skates (Elasmobranchii: Arhynchobatidae, Rajidae) in the Patagonian red shrimp fishery

Landings of batoids (rays and skates) have been rising in Argentina, reaching 14 856 mt in 1998. These species are poorly known, and their low fecundity, late maturity and slow growth rates make them vulnerable to stock collapse even when subjected to low levels of fishing pressure. Skates are commonly present as bycatch of commercial fisheries. Bycatch is of great concern both ecologically and in terms of fishery management, particularly in shrimp fisheries. The Patagonian red shrimp (Pleoticus muelleri) is the main crustacean fishery of the Southwestern Atlantic Ocean. The skate bycatch in 313 tows of the double-beam trawl fishery was surveyed from September 2001 to September 2002. Seven species were recorded: Bathyraja albomaculata (n = 1), Dipturus flavirostris (n = 1008), Dipturus trachydermus (n = 138), Psammobatis normani (n = 1137), Psammobatis bergi (n = 9), Psammobatis rudis (n = 25), and Sympterygia bonapartei (n = 1081). Length-weight relationships, length-frequency by sex, and estimation of density and bycatch per unit of effort are given for each species. While shrimp catches for the double-beam trawl fleet were up to 55 000 mt, overall estimation of skate bycatch for the period under consideration was nearly 1000 mt. Although rajids are released alive at sea, post-catch mortality is unknown.