Preliminary recovery of coastal sharks in the south‐east United States |
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| Authors: | Cassidy D Peterson Carolyn N Belcher Dana M Bethea William B Driggers III Bryan S Frazier Robert J Latour |
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| Institution: | 1. Virginia Institute of Marine Science, College of William & Mary, Gloucester Point, VA, USA;2. Georgia Department of Natural Resources, Coastal Resources Division, Brunswick, GA, USA;3. NOAA Southeast Fisheries Science Centre Panama City Laboratory, Panama City, FL, USA;4. National Marine Fisheries Service, Southeast Fisheries Science Centre, Mississippi Laboratories, Pascagoula, MS, USA;5. South Carolina Department of Natural Resources, Marine Resources Research Institute, Charleston, SC, USA |
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| Abstract: | Relative abundance of many shark species in the Atlantic is assessed by compiling data from several independently conducted, but somewhat spatially limited surveys. Although these localized surveys annually sample the same populations, resulting trends in yearly indices often conflict with one another, thereby hindering interpretation of abundance patterns at broad spatial scales. We used delta‐lognormal generalized linear models (GLMs) to generate indices of abundance for seven Atlantic coastal shark species from six fishery‐independent surveys along the US east coast and Gulf of Mexico from 1975 to 2014. These indices were further analysed using dynamic factor analysis (DFA) to produce simplified, broad‐scale common trends in relative abundance over the entire sampled distribution. Effects of drivers including the North Atlantic Oscillation index, the Atlantic Multidecadal Oscillation index, annually averaged sea surface temperature and species landings were evaluated within the DFA model. The two decadal oscillations and species landings were shown to affect shark distribution along south‐east US coast. Estimated common trends of relative abundance for all large coastal shark species showed similar decreasing patterns into the early 1990s, periods of sustained low index values thereafter and recent indications of recovery. Small coastal shark species exhibited more regional variability in their estimated common trends, such that two common trends were required to adequately describe patterns in relative abundance throughout the Gulf of Mexico and Atlantic. Overall, all species’ (except the Gulf of Mexico blacknose shark) time series concluded with an increasing trend, suggestive of initial recovery from past exploitation. |
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| Keywords: | coastal sharks data conflict dynamic factor analysis generalized linear models index of abundance |
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