Population dynamics and stock assessment for Octopus maya (Cephalopoda : Octopodidae) fishery in the Campeche Bank, Gulf of Mexico

The octopus (Ociopus maya) is one of the most important fish resources in-t he Mexican Gulf of Mexico with a mean annual yield of 9000 ton, and a reaso nable number of jobs created; O. maya represents 80% of the total octopus c atch, followed by Octopus vulgaris. There are two artisanal fleets based on Octopus maya and a middle-size fleet that covers both species. Catch-at-le ngth structured data from the artisanal fleets, for the 1994 season (August 1(st) to December 15(th)) were used to analyze the O. maya population dyna mics and stock and to estimate the current level of exploitation. Von Berta lanffy growth parameters were: L infinity = 252 mm, mantle length; K=1.4 ye ar(-1); oscillation parameters C=1.0. WP=0.6; and tz=0.842 years. A rough e stimate of natural mortality was M=2.2, total mortality from catch curve Z= 8.77, and exploitation rate F/Z=0.75. This last value suggests an intensive exploitation, even when yield per recruit analysis indicates both fleets m ay increase the minimum legal size on about 10% to increase yields. The len gth-based VPA also shows that the stock is being exploited under its maximu m acceptable biological limit. These apparently contradictory results are e xplained by biological and behavioral characteristics of this species. Beca use most females die after reproduction, a new gross estimation of natural mortality was computed as M=3.3. The new estimate of exploitation rate was F/Z=0.57. This new value coincides with results From the length-VPA and the Thompson and Bell methods, the former suggesting that a reduction of 20% i n fishing mortality may provide larger yields. This fishery resource is ful ly exploited and current management measures must be revised to sustain and probably optimize yields.