Evidence of a dietary shift in Tamanend’s bottlenose dolphins in South Carolina waters during a cold‐water anomaly

Resumen

Diet analysis can reveal how predators respond when prey distributions are altered. Cold‐water temperatures in the winter of December 2010 to March 2011 were concurrent with a Tamanend’s bottlenose dolphin (Tursiops erebennus) Unusual Mortality Event (UME) in 2011 in South Carolina. During this time, prey die‐offs occurred that were documented in fishery surveys, and bottlenose dolphins consumed unusual prey items based on gross observation. We analysed the stomach contents of bottlenose dolphins that stranded from 2009 to 2014 and summarised frequency of occurrence (%F) and numerical abundance (%N) of prey species overall, annually and seasonally. Prey species with numerical abundance ≥ 5% overall were tested for significant differences annually and seasonally. From the stomach contents of 114 dolphins, the most frequently occurring (%F) and numerically abundant (%N) species were Atlantic croaker (Micropogonias undulatus; %F = 54%; %N = 16%) and star drum (Stellifer lanceolatus; %F = 45%; %N = 16%). Star drum, hake (Urophycis sp.) and squid (family Loliginidae) numerical abundances differed annually, while spot (Leiostomus xanthurus), silver perch (Bairdiella chrysoura), bay anchovy (Anchoa mitchilli), hake and squid numerical abundances differed seasonally. Bottlenose dolphins consumed significantly more hake during the 2011 UME compared with 2009, 2010, 2012 and 2013. This dietary shift to hake likely occurred due to increased hake availability relative to other prey items typically available during this period. Numerical abundances peaked in the following seasons: summer for spot, winter for silver perch and bay anchovy, spring for hake, and the fall for squid. Our findings demonstrate that bottlenose dolphins can shift their diet when prey distributions are altered to maintain their caloric needs.