Tidal influences on humpback whale habitat selection near headlands

Abstract

In order to design marine protected areas that are ecologically meaningful, it would be useful to improve our understanding of headland wake foraging systems, which are commonly exploited by baleen whales and other mobile marine predators. We used humpback whale Mega- ptera novaeangliae sighting data from 1997 to 2008 in combination with tidal prediction software to investigate the effects of current direction (ebb vs. flood) and tidal amplitude on the distribution and abundance of humpback whales around 3 headlands and 5 non-headlands in Glacier Bay and Icy Strait in southeastern Alaska, USA. Headlands were defined as points of land that disrupt tidal flow creating distinct tideward and leeward conditions. We used an advanced tidal circulation model (ADCIRC) to identify these conditions. Current direction and tidal amplitude each significantly affected whale distribution at only one non-headland (χ 2 = 6.1, p < 0.01; χ 2 = 13, p = 0.002, respec- tively). At all 3 headlands, current direction significantly affected whale distribution (p < 0.0001). Whale abundance was greater in the leeward areas. Tidal amplitude significantly affected distribu- tion at the 3 headlands (χ 2 = 97, p < 0.0001; χ 2 = 75, p < 0.0001; χ 2 = 6.1, p = 0.05) such that whales selected habitat that moderated, rather than maximized, the effect of tidal amplitude, suggesting that headlands also have the potential to be important features in areas with less extreme tidal exchange.