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MARINFORSKHAV-Marine ressurser og miljø - havmiljø

Effects of multiple stressors on Norwegian killer whales: MULTIWHALE

Alternative title: Samlede effekter av ulike stressfaktorer på norske spekkhoggere: MULTIWHALE

Awarded: NOK 12.5 mill.

The aim of MULTIWHALE is to study the cumulative effects of three stressors in Norwegian killer whales: pollutants, human disturbance (e.g. boat activity), and fluctuating food sources. We investigate the effects of these stressors at both individual and population levels, taking into account that some killer whales are more vulnerable to pollutants by eating marine mammals, which are higher in the food chain. Man-made pollutants build up in the blubber of whales, which can be released into the bloodstream when the fat is utilized during stressful situations, such as persistent disturbance by boats or starvation. The pollutants can lead to harmful effects such as impaired reproductive and immune systems, potentially affecting the population. As such, top predators such as killer whales function as “indicator species” for the impact of human activities. To achieve the aims of the MULTIWHALE project, we collected skin and blubber samples from over 100 killer whales using a minimally-invasive biopsy system. We carefully split each sample so that it could be used for over eight different analyses, to provide information on pollution levels, diet, stress levels, health responses, genetics and more. Norwegian Orca Survey's multi-decadal database on individual killer whales in the population provided information on when and where every sampled killer whale has previously been seen, with whom, if it has had offspring, its diet, and an estimation of age. Combined, this makes it possible to forecast the long-term effects of multiple stressors and population development. The COVID-19 pandemic led to restrictions on tourism in Norway and provided us with a unique opportunity to collect samples from a season of low boat activity in Winter 2020. By collecting samples from other, busier, winter seasons, as well as the summer months, we can now compare the stress and health of whales to assess the impact of human activity. Approximatively 10 individuals were sampled in seasons of both high and low boat activity, allowing us to compare health parameters in the same individual. Preliminary results indicate that re-sampled whales have higher cortisol (stress hormone) levels in seasons of high boat activity than low, and work is ongoing to look at further health parameters. MULTIWHALE is a broad national and international collaboration, and includes members from all stages of the scientific career. This has led to the development of groundbreaking techniques. A new genetic marker specifically developed for MULTIWHALE has given insights into social and ecological structuring, and a state-of-the-art hormone analyses at NMBU was developed just for this project. PhD Candidate Clare Andvik spent 3 months at OceanWise, Vancouver, Canada learning how to quantify the health of the whales from tiny pieces of blubber and skin. Postdoc Eve Jourdain and a master student spent several months at McGill University in Montreal, Canada, to use stable isotopic ratios of amino acids and fatty acid analysis as an advanced marker of diet and energy source. These analyses have shown much individuality in feeding habits. While some killer whales appear to specialize on one fish prey resource throughout the year, others feed on a variety of fish and mammal prey. Such capacity to prey switch indicates a certain level of resilience to changing food sources, however, it may lead to a higher pollutant exposure for mammal-feeding whales. Individuals’ plasticity and overlap in feeding behavior explained the lack of social and genetic structuring found. Now, data types will be combined to address potential cumulative effects, and underlying mechanisms, of stressors on Norwegian killer whales. Teeth were obtained from killer whales harvested in Norway in the 1980s, and from killer whales found dead in 2015-2022. Teeth growth layers have been analyzed for dietary markers (stable isotopic nitrogen and carbon ratios) and pollution (mercury), acting as repositories of ecological change between the two periods. Results are underway and will help placing findings from the biopsies into the context of ecological change that may have occurred at larger time scales. The project has contributed to the education and training of two graduated master students, with two further master projects and a PhD underway. By visiting our collaborators, protocols could be harmonized for easier comparison of our findings with other populations, and brought expertise on novel and advanced lab techniques to Norway. Many results have already been communicated to the scientific community in international journals and at conferences, and to the public through social media, radio appearances and in-person presentations at fieldwork sites. As the project progresses, we expect the results from MULTIWHALE to be increasingly relevant for other animal populations facing anthropogenic and ecological pressures.

The research project MULTIWHALE addresses the urgent and complex challenge of how multiple stressors affect individual killer whales and populations, and how these responses can vary across time and between ecological groups of whales. The stressors we focus on are anthropogenic contaminants (including both legacy and emerging contaminants of concern), disturbance from tourism (boat traffic/whale-watching) and nutritional status (fluctuating prey resources). We investigate the response to these stressors in the context of intra-species variability in risk: some killer whales eat marine mammals in addition to fish and are thus exposed to higher levels of contaminants. We analyse how the difference in contaminant exposure affects the response to other stressors in these whales and, using modelling, how it affects population development and viability. Using long time trends from analysing archived teeth, we compare contaminant (mercury) and diet variation between whales in two periods of contrasting ecosystem states: 1960-1980 (collapse of the Norwegian Spring Spawning herring) vs. 1995-2015 (“recovered” ecosystem) to understand killer whale response and exposure to long term human impacts. The project team is composed of national and international leading experts on killer whale population and behaviour, gene expression, chemical analyses of legacy and emerging contaminants, dietary descriptors and health responses, population genetics and modelling - ensuring broad expertise and feasibility when assessing the effect of human interactions on whales status and health. We will work closely with our killer whale partners in Canada to exchange knowledge and protocols, and harmonise our methods to ensure future comparison across regions and populations. The MULTIWHALE results are relevant for understanding human impacts on killer whales, their harvestable prey resources (seal and fish) and for development of sustainable tourism.

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MARINFORSKHAV-Marine ressurser og miljø - havmiljø