Factors Affecting Catchability in Longline Fishing of Red Grouper in the Southeastern Gulf of Mexico

Catchability (q) is a key parameter in stock assessment that can vary in response to biological (e.g., abundance), spatial (e.g., fishing zones), and fishing technique and tactic (e.g., fishing gear design) factors. Few studies have been done on the influence of these sources of variation on q estimates. Catchability was calculated for Red Grouper Epinephelus morio caught with bottom longlines in two coastal zones fished by the small‐scale fleet in Yucatan, Mexico. Experimental data collected from these catches were used to assess the effect on q‐values of fishing zone and depth stratum, hook and bait size, and fish length. Three longlines were each equipped with one of three sizes (13/0, 14/0, or 15/0) of Mustad circle hooks. Bait was Atlantic Thread Herring Opisthonema oglinum in one of two sizes: 4 or 8 cm long. Sampling occurred in two zones (west and east coast) and in three depth strata (10–15 m, 15–20 m, and >20 m). Generalized linear models were used to identify any effect of the analyzed variables on q. Fishing depth and bait size alone had no apparent effect on q, but a combined effect of hook (14/0) size and bait (8 cm) size on q was observed. Fishing zone, hook size, and fish total length were significant sources of variation. The observed catchability patterns suggest possible high fishing mortality in juvenile Red Grouper related to fishing zone, hook and bait size, and fish length, highlighting the need to consider these variables to improve stock assessments of the Campeche Bank Red Grouper fishery.