Abstract
The Au'au Channel between the islands of Maui and Lanai, Hawaii comprises critical breeding habitat for humpback whales (Megaptera novaeangliae) of the Central North Pacific stock. However, like many regions where marine mega-fauna gather, these waters are also the focus of a flourishing local eco-tourism and whale watching industry. Our aim was to establish current trends in habitat preference in female-calf humpback whale pairs within this region, focusing specifically on the busy, eastern portions of the channel. We used an equally-spaced zigzag transect survey design, compiled our results in a GIS model to identify spatial trends and calculated Neu's Indices to quantify levels of habitat use. Our study revealed that while mysticete female-calf pairs on breeding grounds typically favor shallow, inshore waters, female-calf pairs in the Au'au Channel avoided shallow waters (<20 m) and regions within 2 km of the shoreline. Preferred regions for female-calf pairs comprised water depths between 40–60 m, regions of rugged bottom topography and regions that lay between 4 and 6 km from a small boat harbor (Lahaina Harbor) that fell within the study area. In contrast to other humpback whale breeding grounds, there was only minimal evidence of typical patterns of stratification or segregation according to group composition. A review of habitat use by maternal females across Hawaiian waters indicates that maternal habitat choice varies between localities within the Hawaiian Islands, suggesting that maternal females alter their use of habitat according to locally varying pressures. This ability to respond to varying environments may be the key that allows wildlife species to persist in regions where human activity and critical habitat overlap.
Highlights
Emerging research indicates that marine mammals fulfill a range of crucial functions within marine systems, from serving as bio-indicators of the health of marine eco-systems [1,2] to the maintenance of key nutrient levels in surface waters in temperate marine regions [3,4]
We demonstrate that maternal females avoid these waters and we evaluate the roles that different environmental factors may play in shaping maternal habitat use in this area
Accurate and up-to-date information on local patterns of habitat use is a pre-requisite for effective conservation of marine fauna, especially in heavily used regions such as coastlines
Summary
Emerging research indicates that marine mammals fulfill a range of crucial functions within marine systems, from serving as bio-indicators of the health of marine eco-systems [1,2] to the maintenance of key nutrient levels in surface waters in temperate marine regions [3,4]. As many marine mammal populations typically aggregate to feed and to breed, protected area management can be highly effective [5]. Where these aggregations coincide with areas of high anthropogenic activity and/or the aggregations themselves attract high levels of human activity in the form of ecoand wildlife tourism, effective management can be challenging. A range of different mechanisms results in reduced individual fitness: in big horn sheep (Ovis canadensis), foraging in urban areas leads to increased parasite loads [7], in pronghorn antelope (Antilocapra americana), increased vigilance close by roadways reduces foraging time [8] and in forest elephants (Loxodonta cyclotis), individuals forego access to high quality food and habitat resources in response to human presence within favored areas [9]. The collective concern in all these studies is that in the absence of ameliorative management, changes in individual fitness may lead to population level impact
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