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Alaska Department of Fish and Game


Harbor Seal Research
Vessel Interactions

Background Information

Two harbor seals on the ice with a cruise ship in the background

Glacial fjords in Alaska are popular tourism destinations. Harbor seals are plentiful in some of these fjords, and many may have traveled from elsewhere to pup and breed amid the icebergs. Numerous studies have noted that approaching vessels disturb seals, causing them to leave their resting platforms. There is concern that the cumulative effects of the additional energetic costs of such disturbance could decrease a seal’s ability to reproduce and, ultimately, to survive.

We monitored behavior and heart rates of radio-tagged seals before, during, and after vessel disturbance (see harbor seal heart-rate study) and are analyzing the data to quantify the energetic costs of a single vessel disturbance to harbor seals. Currently, no data are available to determine how often individual harbor seals are disturbed by vessels. A few disturbances may be inconsequential; however, if an individual is repeatedly disturbed the impact may be more serious. Pups may be especially at risk, because they are small and thin at birth and have approximately 3 weeks to fatten up before they are abruptly weaned and abandoned, and then must learn to forage on their own. Repeated disturbance by vessels could decrease a pup’s nursing and resting time and increase their energetic costs of staying warm as a result of spending more time in the icy water. Continued disturbances could deplete a pup’s energy reserves during their early, inefficient foraging, which could reduce their probability of survival. Repeated disturbance of reproductive females may result in energetic costs that will deplete their body stores resulting in termination of pregnancy or inadequate lactation performance, potentially compromising their fitness and the survival of their offspring. Any one of these factors or a combination of them could result in population declines.

Study Objectives

To better understand whether vessel disturbance is stressful to seals to the extent that individuals or the population are negatively impacted, we need to study seals in areas that experience substantial vessel traffic (i.e., “disturbed” areas) and compare them to seals in an area with minimal vessel influence (an “undisturbed area”). If vessel disturbance has negative effects, seals in the “disturbed” areas should have one or more of the following indicators: higher stress levels, poorer health, lower reproduction, and less time spent resting and foraging. Because we cannot continuously observe an individual seal (hauled out on an iceberg among hundreds of other seals on adjacent bergs) we need to radio tag a sufficient number of seals to understand what happens to the ‘average seal’ in the disturbed areas.

Application to Management and Conservation

Currently, the National Marine Fisheries Service (NMFS) is considering whether vessel-viewing regulations in glacial areas with harbor seals need revision, due in part to concerns about the impacts of disturbance on seals. Pending successful completion of our studies, we anticipate being able to evaluate the frequency of disturbance (possibly by specific vessel types) that would result in negative consequences to individual seals and the population. Thus, our results should contribute information that will allow NMFS to make a more informed decision on whether vessel regulations need revision.

For additional information about this project contact Gail Blundell at 907-465-4345 or email her at gail.blundell@alaska.gov.

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