587 American Fisheries Society Symposium 49, 2007 © 2007 by the American Fisheries Society * Corresponding author: farregui@ipn.mx Interacting Industrial and Artisanal Fisheries and Their Impact on the Ecosystem of the Continental Shelf on the Central Pacific Coasts of Mexico VÍCTOR HUGO GALVÁN-PIÑA Centro Interdisciplinario de Ciencias Marinas del IPN Apartado Postal 592, La Paz, 23000, Baja California Sur, México Departamento de Estudios para el Desarrollo Sustentable de Zonas Costeras Universidad de Guadalajara. San Patricio Melaque, Jalisco, México FRANCISCO ARREGUÍN-SÁNCHEZ* Centro Interdisciplinario de Ciencias Marinas del IPN Apartado Postal 592, La Paz, 23000, Baja California Sur, México Abstract.—A trophic model based on Ecopath was constructed to describe the structure and flow of biomass of an ecosystem of the continental shelf on the central coasts of Mexico, particularly in front of Jalisco and Colima states. The model consisted of 38 functional groups; including 22 fish, 9 invertebrates, zooplankton, phytoplankton, dead fish (bycatch), detritus, and one group each for marine mammals, birds, and turtles, Detritus, phytoplankton, and zooplankton positively impacted most groups via the food web, including those exploited by fishing. Most important negative impacts were on groups of higher trophic levels with sharks as the top predator. Responses observed suggested an important role for top-down processes controlling ecosystem structure. Regarding ecosystem flow, 24.8% is associated with detritus, 18.9% represents energetic cost via respiration, 17.6% goes to exportation (mainly fishing), and 38.6% to consumption. The net production of the system was calculated to be 1,394.7 tons/km 2 /year. Six discrete trophic levels were identified, with a relative high average transfer efficiency of 18.5%. Regional fisheries are based on artisanal fleets (mainly gill nets and diving) with the incorporation of a seasonal shrimp trawling fleet. Artisanal fishers argue that shrimp trawling has a negative impact on the ecosystem and consequently on their target fish stocks. The artisanal fleet generally targets top predators, while shrimp fleet targets low trophic levels. However, trawling also impacts other groups in the ecosystem via bycatch. The impact of trawling fleet on the artisanal fishery and on the ecosystem structure is evaluated and management strategies discussed.