Calibrating 6.1-m Shrimp Trawls with Seamap Trawls Off Texas

Effective fisheries management depends on monitoring population abundance.  Fishery-independent data are being developed to detect long-term abundance changes.  The Gulf States Marine Fisheries Commission (GSMFC) implemented the Southeast Area Monitoring and Assessment Program (SEAMAP), a large-scale, state-federal-university partnership using 12.2-m wide semi-balloon trawl in the Gulf of Mexico in 1981 to monitor primarily penaeid shrimp populations.  But, the Texas Parks and Wildlife Department (TPWD) continued using a 6.1-m wide trawl.  Data collected off Texas in 1985 were used to calibrate catches between the trawls.  TPWD trawls caught fewer species (85) than SEAMAP (113) and fewer individuals than SEAMAP trawls (4,206 versus 32,844 animals).  A polynomial regression forced through the origin explained 74.7% (adjusted R²) of the variation in the total-catch relationship between the trawl types.  Conversion of individual species catches in TPWD trawls into expected SEAMAP-trawl catch comprised three categories: 1) infrequently caught species in both trawl types--no conversion warranted; 2) infrequently caught species in TPWD, but not SEAMAP trawls, and species with statistically similar catches—conversion uses combined mean catch in all trawls; and 3) species with significant correlation coefficients—conversion used regression coefficients.  Results can be used to convert TPWD trawl catches into SEAMAP catch estimates and improve population monitoring.