Seasonal distribution and environmental predictors of the movement of male blacktip sharks Carcharhinus limbatus off the US East Coast

Migrations of many marine species have shifted poleward in response to global climate change. It is imperative to gather baseline distribution data on migratory species so that these shifts can be measured and overexploitation can be avoided. Migratory species can be tracked over great distances using acoustic telemetry within cooperative networks. We reconstructed tracks from acoustic telemetry data using movement modeling and determined the seasonal distribution of male blacktip sharks Carcharhinus limbatus along the US East Coast using hot spot analyses. In addition, we modeled the environmental drivers of blacktip shark movement. We show that male blacktip sharks exhibit partial migration, and that individual migration patterns vary. The migrating population frequently migrates farther than what has been described in the scientific literature; several individuals migrated from Palm Beach County, FL, in the winter to as far north as Long Island, NY, in the summer. A smaller proportion of the population remains off southeastern Florida year-round. Male blacktip shark movements correlated with chlorophyll a and sea surface temperature in spring, photoperiod in autumn, and chlorophyll a and photoperiod in winter. Variable migration patterns likely concealed reliable predictors of movement during the summer. Like many other migratory species, the blacktip shark may have adapted photoperiod as a forecaster of environmental changes. Global climate change will affect many environmental processes but photoperiod will remain unchanged. If sharks use photoperiod as a migratory cue, they may encounter unfavorable conditions more often under climate change scenarios, which could impose stress on individuals and the population.