Differences in the exploited oyster (Crassostrea virginica (Gmelin, 1791)) populations from different coastal lagoons of the Gulf of Mexico.

Abstract

1 - Oyster fishery is one of the most important coastal fisheries of Mexico. Production from the Gulf of Mexico coast makes up 93.4% of national production; during 2000-2002 it reached over 49,000 mT, with value of 9.2 to 15.5 million USD. Production is based on enhanced beds management. It is an activity of social importance, as many coastal communities find their income and work opportunities in it. In the state of Tabasco there are 1,371 oyster fishers in 14 cooperative societies, and 3,000 shuckers. There is an extensive bed management activity with seeding of collected spat and shell laying. Although a minimum legal size of 80 mm is required, it is not observed. 2 - We identified the growth equation parameters for size structure data for five beds from three lagoons. Maximum height varied between 118 and 140 mm with means between 58 and 63 mm. The von Bertalanffy growth equation parameters were L$∈fty$ between 124 and 154 mm, with K between 0.71 and 1.21. In most cases a significant influence of seasonality was detected, mostly during winter, but at some localities it was during summer. Total mortality Z varies from 1.64 to 2.39. As no data on natural mortality M were available we applied 25, 50 and 75% of Z to M, which allowed us to model the behaviour of the populations under different rates of fishing mortality F and the impact of different M in yields. 3 - We conclude that the populations are over exploited in size and this is affecting yields. Besides, the populations are at risk of collapse if natural mortality increases awing to any environmental impact. It is recommended to increase mean size to 90 mm which means a minimum catch size of over 70 mm, as required by the official norm, this would increase yields in weight 100% and there would be a significant number of organisms to buffer any increase on natural mortality.