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Algunas especies de lenguados son capturadas incidentalmente con redes de arrastre y algunas de estas son especies objetivo de una pesqueria artesanal en el Golfo de California, Mexico. Con el proposito de conocer cuantos individuos de la poblacion estan siendo capturados y cuales son los efectos de estas capturas, el objetivo de este estudio fue estimar la abundancia de los lenguados capturados incidentalmente con redes de arrastre y en una pesqueria artesanal o de pequena escala en el Golfo de California, y determinar la posible competencia entre flotas (con redes de arrastre y la flota artesanal con redes agalleras) por el mismo recurso. Las muestras fueron recolectadas durante 2002 y 2003 de 3 diferentes fuentes: prospecciones de 2 barcos de la flota camaronera comercial, prospecciones en 2 cruceros de investigacion y de una flota artesanal la cual opera a lo largo de la costa del estado de Sonora, Mexico. La abundancia de los lenguados capturados en las redes de arrastre fue estimada usando el metodo de area barrida y a traves de analisis de cohortes por talla fue estimada la abundancia para los lenguados capturados por la flota artesanal. Catorce especies de lenguados fueron identificados en las capturas incidentales con redes de arrastre, destacando Paralichthys woolmani, Etropus crossotus, Citharichthys fragilis, Citharichthys gilberti, Achirus mazatlanus y Syacium ovale. Seis de las 14 especies de lenguados capturados incidentalmente fueron tambien capturados por la flota artesanal, de la cual el 70% corresponde a P. woolmani. Se demostro que cada flota opera sobre diferentes fracciones de la poblacion, individuos de 25 a 90 cm en longitud total fueron capturados por la flota artesanal y los valores de mortalidad por pesca y tasa de explotacion fueron < 0,01, mientras que en las capturas incidentales (flota camaronera) los individuos presentaron tallas entre 4 y 20 cm, demostrando presion de pesca en los individuos juveniles cuya captura podria tener efectos negativos, debido a estos pueden ser reclutas para la pesca artesanal.

Population dynamics of 3 Callinectes species: C. arcuatus, C. bellicosus, and C. toxotes are reported for the first time as incidental shrimp bycatch samplings captured in the eastern Gulf of California in a range from 10 to 77 m in depth from September 2004 to March 2005. Growth, longevity, recruitment pattern, mortality (natural, total, and by fishing), and exploitation rate were analyzed. Also, size comparison among the organisms captured by the shrimp and artisanal fishing fleets was calculated. Callinectes arcuatus (n = 737) was more abundant than the other two (C. bellicosus, n = 291 and C. toxotes, n = 344). Significant differences were shown between size distribution of C. arcuatus and C. bellicosus captured by the 2 fleets; the shrimp fleet extracted mainly organisms in sizes ranging from 50 to 120 mm in carapace width (CW), while the artisanal fleet extracted sizes from 75 to 155 mm in CW from both species. Growth parameters were moderate (L∞= 160, 173, and 168 mm; K= 1.1., 1.3 and 0.9 year-1 for C. arcuatus, C. bellicosus, and C. toxotes, respectively), estimating a 4-year longevity for the 3 species. The reproductive recruitment pattern showed a continuous period with a peak from May to August. The exploitation rate did not show a significant degree of overexploitation for any of the species. There are some differences in the parameters of population dynamics (sizes, growth) of this species based on data from commercial captures and those obtained with data of incidental captures. It is important to perform an analysis including both types of information for an adequate fishery management of these resources.

Palabras clave: Contenido estomacal, superposicion de dieta, especialista, Punta Lobos, Baja California Sur, Mexico Abstract.- The Brown smooth-hound Mustelus henlei is part of an important commercial fishery on the western coast of Baja California Sur (BCS), Mexico. However, very few studies have been performed on the feeding and reproduction biology of these sharks in Mexico. Our study is the first work focusing on this species on the western shelf (14 m to 250 m in depth) of B.C.S. We identified a total of 24 types of prey contents in the stomachs of M. henlei: 15 crustaceans, 6 fish, and 3 cephalopods. According to the index of relative importance (IRI) the main prey items for M. henlei was the pelagic red crab Pleuroncodes planipes (81.4%), followed by unidentified organic material (UOM) (15.7%), the mackerel Scomber japonicus (0.94%), and fish remains (0.84%). Conducting a prey analysis considering sex of M. henlei, P. planipes was the most important prey in both females and males, followed by UOM, and S. japonicus. Sharks found in deeper areas (120-150 m) and those caught on board the exploration ship BIP XII had a similar dietary composition to those found in the shallow waters of Punta Lobos (14-40 m) where for both regions, the dominant prey items were the pelagic red crab and UOM. According to Levin's index, M. henlei may be a specialist feeder in this area. A diet overlap according to sex, area, and size was observed. The SIMPER analysis showed a low similarity in diet in relation to sex, size, and area. According to the ANOSIM test there were no significant differences. Knowing that M. henlei shows a specialist behavior could help research studies not only for species conservation but also for its habitat and the organisms that inhabit it, which are both of vital importance for this shark.