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Common Bottlenose Dolphin (Tursiops truncatus) Gillnet Bycatch Estimates along the US mid-Atlantic Coast, 2007-2015
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2018
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Description:Mortality and serious injury from bycatch of common bottlenose dolphins (Tursiops truncatus) in gillnet fisheries along the US Mid-Atlantic coast has been documented by US federal fishery observer programs operating from Maine to North Carolina. This bycatch, while biologically important, consists of statistically rare events that are further complicated by the spatial and temporal overlap of 4 coastal bottlenose dolphin stocks in North Carolina (NC) where stock affiliation is uncertain. To assess the impact on dolphin stocks from observed gillnet bycatch, mean annual minimum and maximum bycatch were calculated by stock and compared to the stock’s Potential Biological Removal (PBR) level. A matrix of spatial and temporal stock boundaries was applied to both sampled and total gillnet effort to assign documented bycatch to dolphin stock(s), and a model-averaging approach was used to estimate bycatch for the 4 dolphin stocks. From 2007-2015, 4 bycatch events resulting in mortality were documented by fishery observers, and 1 event resulted in an animal being released alive and not seriously injured. Estimated minimum mean annual bycatch between 2011-2015 was 6.11 (CV = 0.32) for the Northern migratory stocks and 0 or unknown for the remaining 3 stocks. Estimated maximum mean annual bycatch increased between 2011-2015 compared to 2007-2011 for both coastal migratory stocks and the Northern NC estuarine stock. Mean annual maximum bycatch between 2011-2015 was 16.42 (CV = 0.22) for the Northern NC estuarine stock, 12.47 (CV = 0.32) for the Southern migratory stock, and 12.23 (CV = 0.22) for the Northern migratory stock. The recent bycatch estimate for the Northern NC stock is 210% of its PBR. In contrast, recent bycatch estimates for both migratory stocks are below their PBR levels. Stranding data may be a useful indicator to detect bycatch events for the Southern NC Estuarine stock where observer coverage is too low to detect a bycatch event. Fisheries observer monitoring of bottlenose dolphin bycatch should continue to be directed to nearshore coastal waters, particularly in regions adjacent to the coast of North Carolina.
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Rights Information:Public Domain
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