Abundance and size structure of flatfish species on the west side of the Gulf of California, Mexico

Some flatfish’s species are caught incidentally in bottom-trawls and some of them are the target of an artisanal fishery in the Gulf of California, Mexico. To know the number of individuals removed from a population and the effects of their removal, the aim in this study was to estimate the abundance of flatfishes caught as bycatch in bottom-trawls and by artisanal or small-scale fishery in the Gulf of California and determinate the possible competition between fleets (bottom-trawl and artisanal with gillnets) for the same resource. During 2002 and 2003, samples were collected from 3 sources: (1) surveys of 2 vessels from the shrimp trawl fleet; (2) surveys in 2 research cruisers; and (3) from an artisanal fleet operating in the coast of the state of Sonora, Mexico. Abundance of flatfishes caught in bottom-trawls was estimated using the swept area method, and through the catch-at-size analysis for the flatfishes caught by the artisanal fishery. Fourteen flatfish species were identified as bycatch in the bottom-trawl, of which those that stand out in abundance were: Paralichthys woolmani, Etropus crossotus, Citharichthys fragilis, Citharichthys gilberti, Achirus mazatlanus and Syacium ovale. Six of the 14 flatfishes incidentally captured by the shrimp fleet were caught by artisanal fishery, of which 70% consist of P. woolmani. Each fleet operated on different population fractions; sizes from 25 to 90 cm in total length were obtained by the artisanal fleet with fishing mortality values and exploitation rates-at-size < 0.01 while bycatch in the shrimp fleet consisted of individuals from 4 to 20 cm, which shows fishing pressure on younger individuals. However, removals of these young individuals could have negative effects because they could be recruits for artisanal fishery.