Stephen Petersen

Geographic and temporal dynamics of a global radiation and diversification in the killer whale

Global climate change during the Late Pleistocene periodically encroached and then released habitat during the glacial cycles, causing range expansions and contractions in some species. These dynamics have played a major role in geographic radiations, diversification and speciation. We investigate these dynamics in the most widely distributed of marine mammals, the killer whale (Orcinus orca), using a global data set of over 450 samples. This marine top predator inhabits coastal and pelagic ecosystems ranging from the ice edge to the tropics, often exhibiting ecological, behavioural and morphological variation suggestive of local adaptation accompanied by reproductive isolation. Results suggest a rapid global radiation occurred over the last 350 000 years. Based on habitat models, we estimated there was only a 15% global contraction of core suitable habitat during the last glacial maximum, and the resources appeared to sustain a constant global effective female population size throughout the Late Pleistocene. Reconstruction of the ancestral phylogeography highlighted the high mobility of this species, identifying 22 strongly supported long‐range dispersal events including interoceanic and interhemispheric movement. Despite this propensity for geographic dispersal, the increased sampling of this study uncovered very few potential examples of ancestral dispersal among ecotypes. Concordance of nuclear and mitochondrial data further confirms genetic cohesiveness, with little or no current gene flow among sympatric ecotypes. Taken as a whole, our data suggest that the glacial cycles influenced local populations in different ways, with no clear global pattern, but with secondary contact among lineages following long‐range dispersal as a potential mechanism driving ecological diversification.

Sustained disruption of narwhal habitat use and behavior in the presence of Arctic killer whales

Significance Predators are widely understood to impact the structure and stability of ecosystems. In the Arctic, summer sea ice is rapidly declining, degrading habitat for Arctic species, such as polar bears and ringed seals, but also providing more access to important predators, such as killer whales. Using data from concurrently tracked predator (killer whales) and prey (narwhal), we show that the presence of killer whales significantly changes the behavior and distribution of narwhal. Because killer whales are effective predators of many marine mammals, similar predator-induced changes would be expected in the behavior of tracked animals in marine ecosystems worldwide. However, these effects are rarely considered and may frequently go unrecognized. Although predators influence behavior of prey, analyses of electronic tracking data in marine environments rarely consider how predators affect the behavior of tracked animals. We collected an unprecedented dataset by synchronously tracking predator (killer whales, N = 1; representing a family group) and prey (narwhal, N = 7) via satellite telemetry in Admiralty Inlet, a large fjord in the Eastern Canadian Arctic. Analyzing the movement data with a switching-state space model and a series of mixed effects models, we show that the presence of killer whales strongly alters the behavior and distribution of narwhal. When killer whales were present (within about 100 km), narwhal moved closer to shore, where they were presumably less vulnerable. Under predation threat, narwhal movement patterns were more likely to be transiting, whereas in the absence of threat, more likely resident. Effects extended beyond discrete predatory events and persisted steadily for 10 d, the duration that killer whales remained in Admiralty Inlet. Our findings have two key consequences. First, given current reductions in sea ice and increases in Arctic killer whale sightings, killer whales have the potential to reshape Arctic marine mammal distributions and behavior. Second and of more general importance, predators have the potential to strongly affect movement behavior of tracked marine animals. Understanding predator effects may be as or more important than relating movement behavior to resource distribution or bottom-up drivers traditionally included in analyses of marine animal tracking data.

Decreasing sea ice conditions in western Hudson Bay and an increase in abundance of harbour seals (Phoca vitulina) in the Churchill River

Harbour seals (Phoca vitulina) occur in the Arctic but little is known of their population abundance and natural history. In western Hudson Bay, they occur at lower numbers relative to ringed seals (Pusa hispida) and their distribution is largely unknown. However, a reduction in the duration of periods of ice cover in Hudson Bay may be shifting the habitat suitability of the region towards one that favours harbour seals. Harbour seal counts from a known haul-out site at the upstream extent of the Churchill River estuary, located in northern Manitoba, were examined in relation to sea ice conditions in western Hudson Bay. The Churchill River estuary haul-out site was observed directly or remotely (via GigaPan™ photos) during the open-water seasons in 1996, 1999, 2000, and 2005, and from 2014 to 2016. We documented an increase in abundance over the study period; the maximum number of harbour seals observed hauled out at one time was 142 in 2016, compared to a maximum of 32 observed during monitoring activities conducted between 1996 and 2005. In addition, newly born harbour seal pups were observed at the haul-out site during the latter study years, an occurrence not observed from 1996 to 2005. We suggest that an increase in the abundance of harbour seals in Hudson Bay and potentially the entire Arctic may be observed if climate change related reductions in the duration of ice cover continue.