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

More than a mouthful – unlocking bowhead whale foraging and reproductive histories from baleen

Cory Matthews, Fisheries and Oceans Canada
Nadine Lysiak, University of Massachusetts, Boston
Kathleen Hunt, Northern Arizona University
Conny Willing, Fisheries and Oceans Canada
Claire Hornby, Fisheries and Oceans Canada
Mads Peter Heide Jørgensen, Greenland Institute of Natural Resources
Steve Ferguson, Fisheries and Oceans Canada

Effective management of marine mammal populations requires knowledge of habitat use (for example, where do they feed, and where do they raise their calves?). Understanding reproductive rates, which allows for projecting population growth from current levels, is also important. Bowhead whales, which exist as two populations in the eastern and western Canadian Arctic, are currently recovering from severe depletion from commercial whaling over the past several centuries. While their populations are now doing well, a good understanding of when and where bowhead whales feed throughout the year, as well as the calving rates of mature females, can help us understand how bowhead whale populations may respond to climate change-related stressors such as changes in prey availability, increased shipping activity, and oil exploration.

Studying the ecology and reproduction of large whales is difficult, especially for bowhead whales that migrate long distances in a region that is inaccessible to conduct research during much of the year. Recent scientific studies have shown that measurement of the composition of baleen, a keratinous material (like fingernails) that grows in long, thin plates from the upper jaw of bowhead whales, can be used to reconstruct diet, movements, and reproductive histories. Baleen plates, which are closely packed together and coated in long hairs, allow the whales to filter tiny organisms called zooplankton – which form their diet – from the water. Baleen grows continuously at about 20 centimeters a year, and can reach lengths of 3 to 4 meters in bowhead whales – in other words, one baleen plate can represent up to 20 years of growth!

One of the most interesting developments in marine mammal research over the past decade is the measurement of the chemical composition of continuously growing structures like baleen to learn about past diet and migration patterns, and reproductive history. Because baleen forms directly from dietary metabolites in the blood, its composition reflects that of the whale’s diet at the time of growth. The nitrogen and carbon composition of animal tissues like baleen in particular can be used to assess what and where an animal eats because ratios of stable isotopes of these two elements vary with an animal’s trophic position (where it is located within the food web), and its habitat. Similarly, hormone concentrations that peak in an animal’s blood, for example, progesterone during pregnancy, are also incorporated into baleen as it forms. Baleen is therefore an archive of an animal’s dietary and reproductive history that can be accessed by measuring the isotope and hormone composition along its length.

Fisheries and Oceans Canada and the Greenland Institute of Natural Resources have collected baleen plates from more than 20 whales harvested in subsistence hunts in both countries over the past 10-15 years. Researchers have drilled small samples of baleen in 2-cm increments along the length of each plate, which corresponds to a sampling interval of about 1 to 2 months, and measured them for stable isotope and hormone concentrations. All individuals exhibited stable isotope cycles every 20 cm, or equivalent to the annual baleen growth rate. By matching zooplankton isotope values with the baleen isotope peaks (Figure 15), which occurred in summer, and troughs, which occurred in winter, researchers showed that bowhead whales forage throughout their annual range. While it has long been known that bowhead whales forage intensively during the summer months on zooplankton known as copepods, it has been assumed that winter, when the cover of sea ice limits ocean productivity, was a time that bowhead whales fasted and relied on their blubber stores for energy. However, results of the baleen isotope research indicate that bowhead whales feed to some extent during winter, perhaps on copepods that hibernate at the sea floor. This research therefore indicates bowhead whales may select winter habitat in regions that allow them to dive to the bottom and forage, and that winter feeding forms a more important part of their annual energy budget than previously thought.

More recent analyses of baleen hormones are ongoing, but initial results have shown this to be a promising technique to learn more about both female and male reproductive behaviour. For example, progesterone peaks indicating pregnancy were detected along the baleen plates of 10 females. The next step – analysis of the placement of these peaks relative to annual isotope cycles – will allow for researchers to determine calving interval, or how often each female was pregnant and gave birth (versus pregnancies that were terminated prematurely). Simultaneous measurement of the stress hormone corticosterone showed that all progesterone peaks were associated with elevated stress, likely reflecting the extra investment required by females in terms of allocating resources to the developing fetus. Researchers were also able to detect annual peaks in testosterone in male bowheads, which indicates they breed annually. Further, testosterone peaks were offset from the peaks in nitrogen and carbon isotopes that occurred in summer, which is consistent with observations of bowhead whales breeding in the spring.

The long baleen plates of bowhead whales make them an ideal species for applying this novel method of reconstructing dietary and reproductive histories. Research has already shown foraging patterns that were previously unknown, and further analysis of reproductive hormone data will allow for researchers to develop better models of bowhead whale population growth. Ultimately, isotope and hormone patterns in individual plates, including remnants from commercial whaling hundreds of years ago that are currently housed in museums, can be combined to examine changes in diet and reproduction over much longer periods of time. For example, a clear decline in stable isotope values was observed across the three decades represented by the sample of 20 whales that have been measured so far, which may be related to diet shifts. As the Arctic climate continues to change, future analysis of diet variations and concomitant variation in reproductive parameters and stress levels may be used to indicate negative health impacts and population trends.