Bycatch of sharks (Elasmobranchii) in the Patagonian red shrimp Pleoticus muelleri (Bate, 1888) fishery

Abstract

The double–beam trawl fishery for the Patagonian red shrimp (Pleoticus muelleri) is the main crustacean fishery of the Southwestern Atlantic Ocean. The shark bycatch in 723 tows of this fishery was surveyed from April 2003 to October 2003. Six species of sharks were recorded: Squalus acanthias (n=321); Squalus mitsukurii (n=1); Squatina sp. (n=1); Schroederichthys bivius (n=327); Galeorhinus galeus (n=4) and Mustelus schmitti (n=13). Length-frequency structure, sex composition, spatial distribution and estimation of density and bycatch per unit of effort are given for the main species. The bycatch of sharks in this fishery was estimated in ~61 mt/ year, equivalent to 0.15% of the shrimp total capture in 2003. S. acanthias contributed with 30.5 mt (50.15%) whilst S. bivius contributed with 22.6 mt (37.2%). Whereas the abundance for S. acanthias in Patagonian waters increased by three fold between 1997 and 2001, the abundance of S. bivius in the same period have decreased in the same amount. In addition, losses of important reproductive sites in southern Patagonia for S. bivius were detected. These issues together with the results presented herein add the Patagonian red shrimp fishery to the potential threats S. bivius is exposed to.