Distinct habitat use strategies of sympatric rorqual whales within a fjord system

• Published in: Marine environmental research Vol. 140; pp. 180 - 189
• Main Authors: Keen, E.M., Wray, J., Pilkington, J.F., Thompson, K.L., Picard, C.R.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.09.2018; Elsevier BV
• Subjects: Animal behavior; Animals; Anthropogenic factors; Aquatic mammals; Balaenoptera physalus; Cetacea; Cetacea - physiology; Comparative analysis; Comparative studies; Critical habitat; Ecosystem; Ecosystems; Environmental changes; Estuaries; Feeding; Fin Whale; Fins; Fjord system; Fjords; Habitat changes; Habitat partitioning; Habitat selection; Habitat use; Habitat utilization; Habitats; Human influences; Humpback Whale; Inland waters; Kitimat fjord system; Marine ecology; Marine mammals; Megaptera novaeangliae; Nursery grounds; Ocean floor; Oceanography; Prey; Properties (attributes); Random forest; Salinity gradients; Site loyalty; Species; Surface properties; Surveys; Sympatric populations; Sympatry; Whales; Whales & whaling; Balaenoptera physalus; Habitat use; Fjord system; Fin whale; Kitimat fjord system; Habitat partitioning; Critical habitat; Humpback whale; Megaptera novaeangliae; Site loyalty; Random forest
• ISSN: 0141-1136; 1879-0291
• DOI: 10.1016/j.marenvres.2018.06.014

We used ecosystem sampling during systematic surveys and opportunistic focal follows, comparison tests, and random forest models to evaluate fin whale (Balaenoptera physalus) and humpback whale (Megaptera novaeangliae) habitat associations within an inland feeding ground (Kitimat Fjord System, British Columbia, Canada). Though these species are sympatric and share a common prey source, they were attuned to different aspects of the local habitat. The fin whales were associated with habitat properties reminiscent of the open ocean. Humpback whales, in contrast, were associated with features more commonly associated with the inland waters of fjords. Fixed habitat features, such as seafloor depth and distance from the fjord mouth, were the most important predictors of fin whale presence, but fixed and dynamic variables, such as surface properties, predicted humpback whale presence with equal (moderate) success. With the exception of strong salinity gradients for humpback whales, habitat conditions were poor predictors of feeding state. Fin whales practiced a spatially confined, seasonally stable, and thus more predictable use of certain channels within the fjord system. These findings are compatible with site loyal behavior, which is interesting in light of the species' historical, unique use of this fjord system. The relatively lackluster performance of humpback-habitat models, coupled with the importance of oceanographic properties, makes the humpback's habitat use strategy more uncertain. The fact that two sympatric species sharing a common prey source exhibited different habitat use strategies suggests that at least one species was informed by something in addition to prey. Given that the two species are attuned to different aspects of the fjord habitat, their responses to habitat changes, including anthropogenic impacts, would likely be different in both nature and degree. Our findings highlight the value of comparative studies and the complexity of rorqual habitat use, which must be understood in order for critical habitat to be identified and protected. •Of Pacific Canada fjords, fin and humpback whales regularly co-occur in only one.•Though sharing a common prey resource (krill) here, habitat associations differ.•Fin whales associate strongly with oceanic conditions in system's outer channels.•Humpback whales associate with fjordic features in both inner and outer channels.•Factors in addition to prey inform whale habitat use in feeding grounds.