Using life-history information to assess potential effects of shrimp trawling on small fishes

The current study presents information on size distributions, size at recruitment to the fishery, size at maturity and patterns of reproduction for several small benthic fishes caught as by-catch in the southern Gulf of California (Mexico) shrimp trawl fishery: sand perch Diplectrum spp., lumptail searobin Prionotus stephanophrys, bigscale goatfish Pseudupeneus grandisquamis and silver stardrum Stellifer illecebrosus. Pseudupeneus grandisquamis, P. stephanophrys and S. illecebrosus populations were all sexually dimorphic in size. Total-length (L(T))-based analyses did not provide reliable information on survival and growth. The majority of sampled P. grandisquamis and S. illecebrosus were caught before reproductive maturity, whereas the majority of Diplectrum spp. and almost all P. stephanophrys were mature when caught. L(T) at 50% gear retention (L(Tc), mm) v. 50% maturity (L(Tm), mm): Diplectrum spp. 124.53 v. 131.43; P. grandisquamis 90.98 v. 135.20; S. illecebrosus 82.55 v. 137.30. L(Tc) for P. stephanophrys was 104.73, but L(Tm) could not be modelled for this species as almost all captured individuals were mature. Diplectrum spp., P. grandisquamis and S. illecebrosus were indeterminate spawners, whereas P. stephanophrys appeared to be a determinate spawner. Sex ratios were equal for each of the gonochoristic species. In general, the gonado-somatic index (I(G)) increased with increasing L(T) for all except P. stephanophrys, where I(G) decreased with increasing L(T) for both males and females. Mature individuals of all taxa were found throughout the sampling period (September to March), and I(G) increased with sample day for all except females of P. grandisquamis. The current data suggest the potential for fishery effects on sampled populations of P. grandisquamis and S. illecebrosus.