USING LONG-TERM SURVEY DATA TO PREDICT BLUE CRAB (<i>Callinectes sapidus</i>) ABUNDANCE AND COMMERCIAL LANDINGS IN CHARLESTON HARBOR, SOUTH CAROLINA
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Czwartacki, Stephen Richard
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Abstract
Fluctuations in blue crab (<i>Callinectes sapidus</i>) abundances are typical throughout the species native range in the U.S., with some populations showing declines in recent years. Despite several long-term fishery-independent surveys encountering blue crab in South Carolina, predictive models have not been developed to explain variation in annual abundance. The goal of this study is to assess the status of blue crab in SC and develop a predictive understanding of population abundances. This goal is met through several objectives: 1) assess long-term trends in, and correlation between, commercial landings and survey adult indices of abundance (CPUE), 2) test for a predictive relationship where juvenile CPUE in one year predict adult CPUE in subsequent years, 3) test for a predictive relationship where size class, sex and maturity categories CPUEs predict total or adult CPUE in subsequent years, and 4) explore predictive relationships where fisheries-independent size class, sex and maturity CPUEs and commercial landings. Trend analysis showed no evidence for a decline in population. Linear correlation statistics show long-term trends in abundance are generally non-synchronous, although correlation exists between surveys similar in sampling. Commercial landings were found to be strongly correlated to fishing effort. Juvenile CPUEs were shown to not have explanatory power on variation in adult CPUEs. In the Ashley River Potting survey, adult and total CPUEs were significantly correlated with adult CPUE in successive years. In the Creek Trawl survey, several small-sized and sexually immature CPUEs were related to total crab CPUE from subsequent years. Multiple life stage CPUEs from the Estuarine and Creek Trawl surveys were related to commercial landings. These results suggest integrated indices of several year-classes from surveys could be used to predict commercial landings. The high annual variation in blue crab abundance could further be explained by combining habitat and environmental conditions with integrated indices of abundance.