Differential Effects of Three Crab Trap Escape Ring Sizes on Retention of Male and Female Blue Crabs

The blue crab Callinectes sapidus supports a valuable commercial fishery in Texas waters. Several regulatory tools are used to manage the catch of blue crabs, including the use of escape rings, which are designed to allow for the escapement of undersized individuals. In this study, we first examined the relationship between carapace width (CW) and carapace length (CL) for male and female blue crabs (with an eye toward the effectiveness of the escape rings). Second, we examined the retention rates for male and female blue crabs across a range of CWs for three different escape ring sizes: 60.3 (current Texas minimum escape ring size), 63.5, and 66.7 mm. Male crabs were found to have a greater CL at a given CW than did female crabs, and this discrepancy between the sexes increased at larger CWs. Assuming that CL is the primary determinant in crab trap retention, this would suggest that males are typically retained at a smaller CW than females and this discrepancy at size of retention increases for larger escape rings. This interpretation was validated in the retention analyses for the three escape ring sizes examined in this study. Overall, the carapace width at 50% retention (CW50) increased with increasing escape ring size for each sex and the discrepancy between CW50 for male and female crabs increased from 4.4 mm (60.3-mm ring) to 5.0 mm (63.5-mm ring) to 7.2 mm (66.7-mm ring). The probability of retention is given for a range of potential minimum CWs (127, 140, and 152 mm) for each escape ring size. Fishery managers should select appropriate escape ring sizes given the target legal minimum CW for the blue crab fishery and also consider the differential performance of these escape ring sizes between sexes when using crab trap escape rings as a management tool.

Automated summary

This study examined the relationship between carapace width (CW) and carapace length (CL) for male and female blue crabs and the retention rates across a range of CWs for different escape ring sizes. The results showed that males have a greater CL at a given CW than females, and this difference increases with larger CWs. The study also found that increasing escape ring sizes resulted in increased carapace width at 50% retention, with a larger discrepancy between males and females.