Alaska Department of Fish and Game
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Harbor Seal Research Projects
Situated near the top of the food chain, harbor seals serve as indicators of the health of the marine ecosystem. Our research focuses on gaining a better understanding of harbor seal ecology and population dynamics. We compare various health and condition parameters, along with diet and diving data among areas to understand what factors may be contributing to the different regional population trends, including precipitous declines in harbor seal numbers in some areas. Harbor seals use a variety of reefs, islands, and coastal habitat to haul out on; however, tidewater glacial fjords are used seasonally by large numbers of harbor seals that apparently travel from elsewhere to pup, breed, and molt on icebergs. Glacial fjords are also popular tourist destinations; large numbers of vessels visit these areas resulting in disturbance of seals during critical life-history phases. Other aspects of our research seek to determine where seals that pup and breed in glacial ice originate from, and whether disturbances associated with increasing vessel traffic and the rapid retreat of Alaskan glaciers associated with climate change could negatively affect harbor seals beyond the confines of specific glacial inlets.
Just as a visit to the doctor’s office often involves blood tests, we obtain a variety of samples from seals that we capture in different areas to assess their general health, diet, disease exposure, and contaminant levels.
We measure the body condition of seals to determine whether their % body fat indicates that they are healthy or are undernourished. Seals store fat in a blubber layer under their skin that helps with thermal regulation and buoyancy, and provides energy stores. We determine body condition using laboratory analysis of blood samples or using ultrasound to measure blubber thickness.
Comparison of diet “signatures” of seals and the signatures of their potential prey items lets us reconstruct what seals eat -- you are what you eat. We investigate diets of seals using fatty acid or stable isotope signatures to determine whether there is evidence of a lower-quality diet in areas that are experiencing population declines.
We discovered that harbor seals using glacial habitat have markedly different life-history strategies than seals using terrestrial sites. Because some seals appear to travel great distances to pup, breed, and molt on icebergs, we continue to explore costs and benefits for seals using glacial ice to better understand the importance of glacial habitat to harbor seals.
We use heart rate as a proxy for metabolic rate to calculate energetic expenditures in free-ranging harbor seals disturbed by approaching vessels. Our study measures behavioral responses to approaching vessels and the physiological and energetic cost of those responses.
Radio signals from VHF telemetry transmitters can only be heard from short distances (typically less than 10 miles) and require that researchers or monitoring equipment be present in the area where seals were tagged. However, some harbor seals make long-distance moves and cannot be relocated with VHF telemetry. Equipping seals with radio tags that transmit their locations to satellites allows us to track their movements from our office, no matter how far they travel.
Historically, as one of the largest harbor seal haulouts in the world, Tugidak Island (south of Kodiak) hosted over 20,000 seals until declines of over 80% occurred in the 1970s and 80s. Seal numbers began increasing in the early 90s but still remain depressed. We use sophisticated photo identification to determine seal survival as an indicator of the health of the marine ecosystem in the Gulf of Alaska.
Harbor seals may leave their resting platforms and enter the water when vessels approach too close. If this type of disturbance is repeated, seals may experience increased energetic costs and stress levels, potentially compromising their health and survival. The objective of this research project is to determine the frequency at which seals are disturbed by vessels, and whether seals in areas that experience high vessel traffic are more stressed, have lower reproductive success, and spend less time resting and foraging compared to seals in an area with little or no vessel traffic.