Summer distribution patterns of southern resident killer whales Orcinus orca: core areas and spatial segregation of social groups

Abstract

A diverse range of marine wildlife species respond to dynamic environments and patchy resources with variations in their distribution pattern. For many cetacean species, highly structured social systems add to the complexity of modeling distribution patterns and understanding the effects on population viability. Southern resident killer whales Orcinus orca are comprised of 3 distinct, yet cohesive, matrilineally related social groups called pods, and recent population declines have prompted conservation actions in the US and Canada, including listings as an endangered species. Habitat protection is a major component of each listing, yet little is known about pod-specific core areas or patterns of space use for this population. Using 6 yr of sighting information within the inshore waters of Washington and British Columbia, we modeled pod-specific summer distribution and measured relative variation in the density of sightings on a uniform spatial grid. Our results indicate that the pods exhibit complex, non-uniform summer space-use patterns. Although some regions are used in common by all pods, some areas are used almost exclusively by individual pods or certain combinations of pods, indicating specialization to particular areas. Our results indicate that pod groups display variable patterns of space use; therefore, each pod may experience unique habitat conditions or exposure to potential risk factors. This result is highly relevant when considering podspecific mortality rates and the relative contribution of each pod to overall population trends. Our analyses highlight important areas of conservation, and provide the necessary description for podfocused conservation initiatives.

Delineation of a coastal gray whale feeding area using opportunistic and systematic survey effort

“…Identifying and delineating critical habitat for species of conservation concern is important when developing management plans and assessing and mitigating potential impacts of anthro pogenic activities (Hauser et al 2007, Williams et al 2013). Critical habitat for baleen whales includes breeding areas, calving grounds, migration routes, and feeding areas (Gregr & Trites 2001, Wheeler et al 2012).…”

Local abundance, apparent survival and site fidelity of Bryde’s whales in the Hauraki Gulf (New Zealand) inferred from long-term photo-identification

“…This indicates that the area is an important habitat for some whales. However, site fidelity patterns are not static and change over time, possibly due to responses to environmental conditions, prey availability, age-class and/or reproductive status (Switzer 1993, Hauser et al 2007, Foote et al 2010, Barnett et al 2011. During the course of this study, 13 whales were sexed as females and 3 whales were sexed as males based on molecular identification (Wiseman 2008) and/or on photographs of the whales in close association with young calves.…”

Predicted polybrominated diphenyl ether (PBDE) and polychlorinated biphenyl (PCB) accumulation in southern resident killer whales

“…The summer geographic range of SRKWs is comprised primarily of the semi-enclosed ('inland') marine waters of Washington, USA, and British Columbia, Canada (Bigg 1982, Osborne 1999, Hauser et al 2007. Although there are pod-specific variations in distribution in the summer months, all 3 pods spend a large proportion of time in the Haro Strait, west of San Juan Island, Washington (Hauser et al 2007). The winter ranges are less clear but appear to differ among pods and extend along the outer coast of British Columbia, as far north as the Queen Charlotte Islands and as far south as Monterey Bay, California (Osborne 1999, Krahn et al 2004.…”

“…In the 'uniform' scenario, J pod exclusively consumed the more contaminated Chinook salmon from the inland marine 267 Mar Ecol Prog Ser 453: 263-277, 2012 waters of British Columbia and Washington State, whereas K and L pods exclusively consumed the less contaminated Chinook salmon from along the outer coast from Vancouver Island to California. The 'mixed' scenario assumed J pod consumed Chinook salmon from the inland waters two thirds of the time and consumed outer coast Chinook salmon one third of the time to correspond with their seasonal distribution (Bigg 1982, Osborne 1999, Krahn et al 2004, Hauser et al 2007). Conversely, K and L pods consumed Chinook salmon from the inland waters one third of the time and consumed Chinook salmon from the outer coast two thirds of the time, also reflecting their seasonal distribution (Bigg 1982, Osborne 1999, Krahn et al 2004, Hauser et al 2007).…”

“…Individual pods are likely to consume different proportions of the different salmon stocks (Krahn et al 2007). The summer geographic range of SRKWs is comprised primarily of the semi-enclosed ('inland') marine waters of Washington, USA, and British Columbia, Canada (Bigg 1982, Osborne 1999, Hauser et al 2007. Although there are pod-specific variations in distribution in the summer months, all 3 pods spend a large proportion of time in the Haro Strait, west of San Juan Island, Washington (Hauser et al 2007).…”