Although Marine Mammals are not fish, they have a heavy impact on fish ecology through consumption of fish species. People living in remote regions of Alaska rely on all forms of subsistence hunting including many kinds of fish, seals, and walruses. As a Biologist, it is important to learn about all of the different trophic levels in the food web so that you can better understand how all of these organisms interact with one another, and therefore base your management techniques accordingly.

On October 21st I watched Jill-Marie Seymour’s dissertation defense on Pacific Walrus ecology in Alaska. Her thesis was based around four points; are Pacific Walruses eating more higher trophic level prey (HTLP) such as seals and sea birds because of climate change and early sea ice reduction, is consumption of these HTLP are potentially increasing risks of contracting disease such as Trichinella , is overcrowding on mainland shores are spreading disease, and are these factors reducing over-all body health? Pacific Walruses are known to feed on a variety of benthic invertebrates on the oceanic shelf and their diets are thought to be dictated on the presence or absence of sea ice. Seymour’s research suggests that Walruses are beginning to rely more on HTLP based on stable isotope analyses that were conducted. Seymour was also able to use a less invasive method of contracting blubber samples from live Walruses, and in doing so was able to discover that the stress hormone Cortisol can be extracted from blubber. In conclusion to her work, Seymour states that Walrus feeding on HLTP most likely do not have damaging effects on their populations.

Overall I found the dissertation to be quite fascinating and I was able to learn allot about Walrus ecology that I hadn’t known before. I would like to see if more research comes from the whether or not Trichinella in Pacific Walruses are being contracted form Spotted Seals, who are known to carry this parasite as well as long lasting effects of sea ice reduction. This dissertation is important to fisheries because the Pacific Walrus has the potential to become and endangered species, especially with climate changes occurring. If the Pacific Walrus populations heavily decline, that will have effects on seal populations, benthic invertebrate populations, and fishes that rely on benthic invertebrates or are consumed by seals.

-Katherine Opp

Unfortunatly i was unable to find her dissertation powerpoint or her article in the Journal of Parasitology

4 thoughts on “”

  1. Nice summary of some very current research! As fisheries scientists we need to be aware of other trophic levels and how their abundances can influence the populations of fishery species, or the food source that these fishery species rely on.

  2. The link that you provided stated that the walruses were tested and they found that switching to HTLP will not likely have an effect on pacific walrus populations. I was thinking if they didn’t find Trichinellosis do you think that maybe it may take a while for it to show up considering they may be just starting to move up the tropic level? I was just wondering because I wonder if this sort of thing while tested can appear rather fast and they can get accurate results.
    -Jazmin Peterson

    1. Honestly i am not sure how long the life cycle of Trichinosis is so i cannot answer your question efficiently. However, in her defense she did go over the life history and where it lives in the animal but i cannot remeber it off hand. i thing she did take that into account in her research though. Another reason may be that Trichinosis is not commonly found in walruses. A small percentage have been found to have t when sampled. Unlike polar bears how have been found to have it roughly 60% of the time. She may have just not sampled enough walruses to get enough information on it.

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