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Barrett-Lennard L.G.,Cetacean Research Program | Barrett-Lennard L.G.,University of British Columbia | Matkin C.O.,Gulf | Durban J.W.,National Oceanic and Atmospheric Administration | And 3 more authors.
Marine Ecology Progress Series | Year: 2011

As apex predators, killer whales Orcinus orca are expected to strongly influence the structure of marine communities by impacting the abundance, distribution, behavior, and evolution of their prey. Empirical assessments of these impacts are difficult, however, because killer whales are sparsely distributed, highly mobile, and difficult to observe. We present a 4 yr time series of observations of foraging and feeding behavior of >150 transient killer whales that aggregate annually during the northbound migration of gray whales past Unimak Island, Alaska. Most predatory attacks were on gray whale Eschrichtius robustus calves or yearlings and were quickly abandoned if calves were aggressively defended by their mothers. Attacks were conducted by groups of 3 to 4 killer whales, which attempted to drown their prey. Gray whales generally tried to move into shallow water along the shoreline when attacked; if they succeeded in reaching depths of 3 m or less, attacks were abandoned. Kills occurred in waters from 15 to 75 m deep or were moved into such areas after death. After some hours of feeding, the carcasses were usually left, but were re-visited and fed on by killer whales over several days. Carcasses or pieces of prey that floated onshore were actively consumed by brown bears Ursus arctos, and carcasses on the bottom were fed on by sleeper sharks Somniosus pacificus, apparently increasing the local density of both species. © Inter-Research 2011. Source


Riera A.,University of Victoria | Ford J.K.,Cetacean Research Program | Ross Chapman N.,University of Victoria
Journal of the Acoustical Society of America | Year: 2013

Killer whales in British Columbia are at risk, and little is known about their winter distribution. Passive acoustic monitoring of their year-round habitat is a valuable supplemental method to traditional visual and photographic surveys. However, long-term acoustic studies of odontocetes have some limitations, including the generation of large amounts of data that require highly time-consuming processing. There is a need to develop tools and protocols to maximize the efficiency of such studies. Here, two types of analysis, real-time and long term spectral averages, were compared to assess their performance at detecting killer whale calls in long-term acoustic recordings. In addition, two different duty cycles, 1/3 and 2/3, were tested. Both the use of long term spectral averages and a lower duty cycle resulted in a decrease in call detection and positive pod identification, leading to underestimations of the amount of time the whales were present. The impact of these limitations should be considered in future killer whale acoustic surveys. A compromise between a lower resolution data processing method and a higher duty cycle is suggested for maximum methodological efficiency. © 2013 Acoustical Society of America. Source


Rudd A.B.,Hawaii Institute of Marine Biology | Titmus A.J.,Pacific Rim Conservation | Gisborne B.,Cetacean Research Program | Heath J.P.,Simon Fraser University
Marine Ornithology | Year: 2011

Foraging in association with other species can be an important strategy that facilitates locating or capturing prey. We studied the association of Marbled Murrelets with foraging Gray Whales along a 105 km transect on the west coast of Vancouver Island, British Columbia, in June 2005. Gray Whales forage on benthic invertebrates by scooping up bottom sediments. Spatial association was analyzed across the extent of the transect and within a 50 m radius of surfacing whales. At both spatial scales, murrelets were more closely associated with Gray Whales than would be expected by chance. Murrelets were observed feeding in direct association with foraging whales, and qualitative observations from plankton tows indicated much more abundant zooplankton near surfacing whales. More research is needed to elucidate this relationship. Identifying facilitative relationships among marine organisms is important in understanding structure of food webs and adaptability to environmental change. Source


Grebner D.M.,Pennsylvania State University | Parks S.E.,Pennsylvania State University | Bradley D.L.,Pennsylvania State University | Miksis-Olds J.L.,Pennsylvania State University | And 2 more authors.
Journal of the Acoustical Society of America | Year: 2011

Northern resident killer whale pods (Orcinus orca) have distinctive stereotyped pulsed call repertoires that can be used to distinguish groups acoustically. Repertoires are generally stable, with the same call types comprising the repertoire of a given pod over a period of years to decades. Previous studies have shown that some discrete pulsed calls can be subdivided into variants or subtypes. This study suggests that new stereotyped calls may result from the gradual modification of existing call types through subtypes. Vocalizations of individuals and small groups of killer whales were collected using a bottom-mounted hydrophone array in Johnstone Strait, British Columbia in 2006 and 2007. Discriminant analysis of slope variations of a predominant call type, N4, revealed the presence of four distinct call subtypes. Similar to previous studies, there was a divergence of the N4 call between members of different matrilines of the same pod. However, this study reveals that individual killer whales produced multiple subtypes of the N4 call, indicating that divergence in the N4 call is not the result of individual differences, but rather may indicate the gradual evolution of a new stereotyped call. © 2011 Acoustical Society of America. Source


Deecke V.B.,University of St. Andrews | Deecke V.B.,Cetacean Research Laboratory | Deecke V.B.,University of British Columbia | Barrett-Lennard L.G.,Cetacean Research Laboratory | And 4 more authors.
Naturwissenschaften | Year: 2010

A few species of mammals produce groupspecific vocalisations that are passed on by learning, but the function of learned vocal variation remains poorly understood. Resident killer whales live in stable matrilineal groups with repertoires of seven to 17 stereotyped call types. Some types are shared among matrilines, but their structure typically shows matriline-specific differences. Our objective was to analyse calls of nine killer whale matrilines in British Columbia to test whether call similarity primarily reflects social or genetic relationships. Recordings were made in 1985-1995 in the presence of focal matrilines that were either alone or with groups with non-overlapping repertoires. We used neural network discrimination performance to measure the similarity of call types produced by different matrilines and determined matriline association rates from 757 encounters with one or more focal matrilines. Relatedness was measured by comparing variation at 11 microsatellite loci for the oldest female in each group. Call similarity was positively correlated with association rates for two of the three call types analysed. Similarity of the N4 call type was also correlated with matriarch relatedness. No relationship between relatedness and association frequency was detected. These results show that call structure reflects relatedness and social affiliation, but not because related groups spend more time together. Instead, call structure appears to play a role in kin recognition and shapes the association behaviour of killer whale groups. Our results therefore support the hypothesis that increasing social complexity plays a role in the evolution of learned vocalisations in some mammalian species. © Springer-Verlag 2010. Source

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