generosa were investigated with animals collected from Bahia de San Quintin and Islas Coronado on the west shore of the Baja Peninsula, Baja California, Mexico (30[degrees]23'N, 115[degrees]55'W and 32[degrees]25' N, 117[degrees] 15'W, respectively).
Monthly samples were collected from the subtidal between 15 m and 25 m depth from April 2008 through January 2009, with sample sizes as follows: April (30 m), May (30 m), June (17 In), July (30 m), August (30 m), September (30 m), October (30 m), November (0 m), December (22 m), January (45 m).
Individual total wet weight was obtained after draining water from the body cavity, and tissue wet weight and shell weight were measured by separating the shell from the tissue and blotting both dry to remove excess water.
Ages were obtained by counting growth bands in cross-sections of the shell hinge plate and utilizing cross-dating methods to increase accuracy. The asymptotic length was found to be 134 mm, the mean total weight was 764 [ or -] 255 g, the Brody growth coefficient (k) was 0.191, and the natural mortality rate was estimated to range from 0.0274-0.046, depending on the method used.
These parameter values are similar to those of more northern populations of the same species.
generosa at the southernmost extent of its distribution that is required to establish a biological basis for fishery management decisions.
This article was further motivated to assess the appropriateness of the current minimum legal size of 130 mm established by the Mexican fishing authorities.
In Washington, the fishing mortality rate is based on the output of an age-structured equilibrium yield model (Bradbury & Tagart 2000), which relies on the 3-parameter von Bertalanffy growth model. (2000) conducted a study in 4 regions of Washington state and found that growth parameters were different among regions and among sites within regions. (2002) and Campbell and Ming (2003) in locations throughout British Columbia, with similar results: Parameters of the von Bertalanffy growth model were different among locations. (2004) and Zhang and Hand (2006) have found that key parameters required to estimate biomass and productivity differ among regions. The Mexican fisheries authority, Comision Nacional de Acuacultura y Pesca, attempts to pursue a conservative approach in regulating the fishery by limiting license entry, imposing a minimum legal size of 130 mm, restricting fishing to within identified beds, and imposing a maximum allowable catch of 0.5% of total estimated biomass for prospective fisheries (for which there are no catch data) or 1% for commercial fisheries (postprospective beds that have catch data).
The estimation of growth parameters requires accurate estimates of age. The 130-mm shell length for minimum legal size is an arbitrary reference point, following the precautionary approach for responsible fisheries established by the Food and Agriculture Organization.
An acetate peel impression was made by pressing acetate film, softened with 1 drop of acetone, onto the etched cross-section of the hinge plate. 1) were counted using a Carl Zeiss microscope (Primostar, Carl Zeiss Imaging, Gottingem, Germany).
Each peel was counted by 2 readers to confirm the estimated age.
Morphometric relationships, age, and growth, and natural mortality of P.