Standardized Catch Rates by Sex and Age for Swordfish (Xiphias gladius) from the U.S. Longline Fleet 1981-2001

摘要

Swordfish (Xiphias gladius) catch and effort data collected from the US Pelagic longline fleet operating in the western north Atlantic were used to develop indices of abundance for the north Atlantic swordfish stock. Standardized catch rates were estimated using a Generalized Linear Mixed Modeling approach assuming a delta-lognormal error distribution. Indices of abundance in units of biomass (dressed weight) were estimated for fish greater than 33 lbs due to U.S. size restrictions implemented in 1991. For comparison, indices of abundance in numbers of fish for ages 3-10+ combined sexes. The age-sex slicing algorithms used were the size at age by sex relationship employed during the 1999 swordfish stock assessment. The explanatory variables considered for standardization included geographical area, seasonal trimesters, fishing target species, and a fixed factor operational procedure (OP) that classifies the US longline fishing fleet according to boat and fishing gear characteristics, and fishing styles. Analyses were also conducted to account for potential effects of recent domestic time-area closures on US swordfish catch rates.