Growth and mortality rates of Pseudupeneus grandisquamis and Urobatis halleri bycatch species in the shrimp fishery

Population dynamics of the goatfish Pseudupeneus grandisquamis and the round ray Urobatis halleri were assessed as dominant shrimp trawl bycatch species in the Gulf of California. Samplings were collected during the 2004-2005 shrimp season onboard 13 shrimp vessels. A total of 3,586 organisms were analyzed (n = 2,463 of P. grandisquamis and n = 1,123 of U. halleri); size frequencies were obtained by the von Bertalanffy model; growth, natural mortality (M), mortality by fishing (F), total mortality (Z), and exploitation rate (E) were determined by Pauly, Jensen, Ricker, and Taylor equations and the catch curve method. Size of P. grandisquamis ranged from 20-210 mm in total length (TL); growth parameters (L∞ 213 mm; K/year 0.9; t0/year -0.19) indicated moderate growth, longevity (3.3 years), and high mortality rates (Mp = 1.73/ year; Mj = 1.35/year). Size of U. halleri ranged from 90-450 mm in TL; growth parameters (L∞ 472 mm; K/year 0.27; t0/year -0.54) indicated slow growth, moderate to high longevity (11.1 years), and moderate mortality rates (Mp = 0.6; Mj = 0.4 year-1). Exploitation rate was <0.5 for P. grandisquamis and 0.8 for U. halleri, which was greater than the value suggested for a healthy stock (E ≤ 0.5). According to the high mortality and exploitation rates estimated, it is concluded that shrimp trawl fishery represents a risk for U. halleri but not for P. grandisquamis