Center of Expertise in Marine Mammalogy

Scientific Research Report
2015-2017

Table of Contents

• Complete Text
• Introduction
• Using aerial infrared images to count ringed seals on ice
• The use of unmanned aerial vehicles (UAV)
• 2017: A Marine Mammal Odyssey, Eh!
• Mark-recapture analysis from long-term study on Sable Island identifies changes in demographic rates in northwest Atlantic Grey Seals
• OTN – Using grey seals (Halichoerus grypus) as bioprobes to estimate phytoplankton biomass
• Northwest Atlantic International Sightings Survey (NAISS) of Marine Megafauna on the Continental Shelf From Northern Labrador to the Bay of Fundy
• Monitoring Movements of Whelping Seals on Drifting Pack Ice
• Marine Mammal Genomics Research in the Central and Arctic Region
• OTN and predator-prey interactions
• Listening in on the Deep: Passive Acoustic Monitoring of Whales off Nova Scotia
• Sharing Meals Keeps Killer Whale Families Together: Provisioning relatives maintains long-term social bonds and helps pass on shared genes
• New developments in the use of fatty acids to determine marine mammal diets
• More than a mouthful – unlocking bowhead whale foraging and reproductive histories from baleen
• Observing walrus behaviour at haulout sites in quasi real-time
• Moving towards automated counting
• References

Sharing Meals Keeps Killer Whale Families Together: Provisioning relatives maintains long-term social bonds and helps pass on shared genes

Brianna Wright, Eva Stredulinsky, Graeme Ellis, John Ford

A study conducted by researchers at the Pacific Biological Station (Fisheries and Oceans Canada, Pacific Region) has received the award for the Assistant Deputy Minister’s 2016 Science Paper of the Year. The award recognizes an innovative and thought-provoking scientific paper in a peer-reviewed journal that advances a field of study of relevance to DFO’s mandate. The paper, entitled “Kin-directed food sharing promotes lifetime natal philopatry of both sexes in a population of fish-eating killer whales, Orcinas orca”, was published in the journal Animal Behaviour. The study found that northern resident killer whales frequently share fish with members of their family groups (known as matrilines). Over a twelve-year period (2002-2014), researchers observed killer whales from this population catch 685 salmon, over 70% of which they shared with other individuals. Animals of all ages (except very young calves) and both sexes participated in this behaviour. When prey was shared, one whale usually made a long foraging dive while other individuals milled at the surface. Once the hunting whale surfaced with prey, it carried the fish towards the milling individuals or it was approached and joined by one or more of these animals. Killer whales frequently swam from as far as 400 m away to join in, although more often, they were within 100-200 m when the salmon was brought to the surface. Fish scales and pieces of tissue were typically found at the surface of the water where whales came together, indicating that fish had been broken apart for sharing. Researchers identified the species and age of the shared fish by collecting these scraps or ‘left-overs’. This prey sharing behavior was also captured on video, using an underwater camera on a pole that was lowered off the side of the research boat.

Resident killer whales prey almost exclusively on salmon and depend particularly on Chinook (the least common species of salmon in the Pacific Northwest), which makes up the majority of their known diet. Despite the importance of Chinook to the survival of individual killer whales, they frequently choose to share this critical resource with family members. This behaviour is quite remarkable, since any of these fish could easily be eaten whole by a single whale, but instead they choose to break them apart and share them. The vast majority of salmon that were shared by whales were given to close maternal relatives (84%) − fish were rarely shared with animals outside the matriline. This type of self-sacrificing behaviour can actually end up benefitting whales that give up a portion of their meal. First, it limits the level of competition among family members for access to salmon, and second, by helping close relatives and ensuring their health and survival, it helps to pass on shared genes to future generations. In other words, performing a helping behaviour that favours the successful reproduction of close relatives results in the proliferation of genes common to both the helping individual and the recipient; this is an evolutionary strategy known as kin selection. Kin selective behaviours provide the greatest benefit to helpers when they assist individuals that are the most closely related to themselves, as well as those with the highest potential future reproductive output.

Food sharing is a kin selective behaviour that helps to reveal how the exceptionally stable social structure of resident killer whales may have evolved. Typically, male mammals leave their social groups when they reach reproductive age, to prevent inbreeding and to reduce competition between relatives. However, neither male nor female resident killer whales ever leave their mother’s social group, a pattern that has been documented in only a handful of species worldwide. Resident killer whales remain with their mothers for their entire lives because food sharing with close maternal relatives provides significant benefits, such as proliferation of shared DNA. These benefits are only available to whales that stay with the group they are born into. Resident killer whales are able to avoid inbreeding without permanently leaving their mother’s group because they have sophisticated acoustic dialects that help them to recognize and avoid mating with kin.

Although both sexes of resident killer whale remain with their mother’s group throughout life, the study found a significant difference in the way that males and females shared fish with their family members (Figure 13). Adult females shared almost all of the fish that they caught (91%), and shared most frequently with their offspring. Unlike females, adult males shared fish much less frequently (25% of salmon caught), which might be explained by several factors. The first is that a male’s offspring are born to females outside of his matriline, and therefore males are less related, on average, to the members of their family group and as a result are less likely to share fish with them. Adult males also have greater nutritional requirements because of their large body size, and therefore probably need to retain more food in order to meet these needs.

When adult males did share fish, it was often with their mothers. Since these females were usually older, post-reproductive matriarchs (Figure 14), this behavior is surprising, because assisting an individual that can no longer reproduce does not help perpetuate shared genes. There is no apparent advantage in doing this from a kin selection perspective. However, post-reproductive matriarchs favoured sons when they shared salmon (Figure 14), and other research has shown that adult sons whose mothers have died are less likely to survive themselves. Adult males probably share fish with their mothers to ensure that their mothers survive and continue to provision them into adulthood.

Conversely, the study found that mothers stop sharing prey with their daughters around the time that daughters reached adulthood and produced their first calves. This is probably because daughters became more focused on provisioning their calves than on sharing food with their mothers. Mothers may also choose to favour adult sons instead of daughters because sons have a greater expected lifetime reproductive output (female killer whales produce around 5-7 calves in their lifetime, whereas a successful male could potentially sire many more). Mothers who share fish with sons to enhance their survival therefore receive a greater return on their investment (in terms of shared genes passed to the next generation). The decline in sharing with daughters may help to explain why resident killer whale groups sometimes split across maternal lines – daughters that no longer receive the benefit of salmon from mom may strike out on their own with their offspring.

The research paper is available online, free of charge, at the following link, along with video of northern resident killer whales sharing a salmon: http://www.sciencedirect.com/science/article/pii/S0003347216000737