Fish Bycatch of Shrimp Trawling Fishery and Length-Weight Relationships of 138 Fishes from the Tropical Eastern Pacific, El Salvador

Abstract

Marine biodiversity is significantly impacted by bottom-trawling fisheries, which generate substantial bycatch. Bycatch species are often discarded, unreported, and undocumented, hindering conservation and management efforts. Quantifying bycatch volumes and characterizing the biological traits of bycatch species remain challenging yet critical for sustainable fisheries management. This study aimed to (1) describe spatiotemporal patterns of bycatch in El Salvador’s shrimp bottom-trawl fisheries and (2) estimate length-weight relationships (LWRs) for fish bycatch species. A total of 428 trawls were conducted at depths of 20 to 100 m across four marine zones between April and November. Bycatch was categorized as either traditional (all non-target species) or flexible (species with no commercial value). Species vulnerability was assessed using CITES, IUCN, and Fishing Vulnerability Index classifications. Bycatch accounted for 22–100% of total catch per trawl, averaging ~ 93%. Bathymetric differences were significant, with the highest bycatch volumes in shallow waters (230 ± 24 kg/h at 20 m) declining to 32 ± 8 kg/h at 80 m. Temporally, bycatch peaked in April (140 ± 27 kg/h) and reached its lowest levels in October (82 ± 22 kg/h). There were no significant spatial differences observed among the four fishing zones, and trends were consistent across both bycatch classifications. Bottom trawling in shrimp fisheries affected at least 14 bycatch species listed under IUCN threat categories and 58 species with moderate to very high fishing vulnerability. Length-weight measurements were taken from 16,384 specimens representing 138 fish bycatch species. Strong length-weight correlations (r > 0.8) were found for 107 species, and LWRs were newly documented for 62 species in the Tropical Eastern Pacific.