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Notes on food attraction and the demographics of blue crab (Callinectes sapidus) trapping in Tres Palacios Bay, Texas.

Article Excerpt
Abstract.-The null hypothesis that blue crabs which enter typical commercial-style baited traps are random draws from populations with equal sex ratios and physical characteristics was evaluated. Trap demographic data (sex, size and number of crabs) were collected during ten single-day trials comprising six traps each (n = 60) over a 3-week period in April 2006. These data indicate that blue crabs tend to be caught in same-sex assemblages more frequently than expected by chance, and that males caught in crab traps have different width-weight ratio trajectories than do females. Interestingly, blue crabs in Tres Palacios Bay are more readily attracted to remains of fish that are endemic and common in the Gulf of Mexico, rather than those that are exotic and/or relatively rare. These data relate directly to previously unexplored aspects of the blue crab fishery in Texas and therefore will be useful to fishery managers.

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Blue crabs (Callinectes sapidus Rathbun) are subject to a significant commercial fishery on the coast of Texas, harvested at a rate surpassed only by shrimp and oysters (in total organisms landed) (Sutton & Wagner 2007). Landings have declined considerably since 1987, due to a combination of many factors including overharvest (Sutton & Wagner 2007). Currently, Texas Parks and Wildlife (TPW) regulates the harvest of blue crabs by a minimum-size limitation of five inches (127 mm), a ban on harvest of egg-bearing females, commercial trap limitations (200 traps) and design specifications, and a 10-day to 30-day closure of the fishery each year (February or March). To evaluate trends in blue crab abundance and biomass, TPW typically relies on fishery-independent data collected during annual routine monitoring. However, sparse data is available that pertains to the demographics of crabs specifically targeted by current trapping methodologies. Although abundant data is available detailing the effects of trap design on retention of various crab size ranges (Guillory & Prejean 1997; Guillory 1998; Guillory & Hein 1998a; 1998b) there is a lack of available data on the size and sex ratios of crabs typically retained in traps in the western Gulf of Mexico. Behavioral and ecological characteristics such as mutual antagonism during foraging (Mansour & Lipcius 1991; Clark et al. 1999) and intra-population habitat partitioning (Hines et al. 1987) may result in different demographic characteristics between wild crab populations, and what is typically found in commercial traps. Here, the demographics of crabs captured in commercial-style traps in Tres Palacios Bay, Texas are described in an effort to improve the data upon which future management decisions are based.

METHODS

Six identical commercial-style crab traps which consisted of a coated wire frame throughout, a bait compartment and four entrance funnels were used in this study. The dimensions of the traps were 60 cm width, by 60 cm length, by 44 cm height. Entrance funnels were approximately oval in shape,...

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