Salmon Shark:
By Aaron Carlisle     Awards: Myers
What is a salmon shark?
The salmon shark (Lamna ditropis) is the smaller (though still large at 8-9 ft, ~500 lbs), less well known cousin of the great white and mako shark.  It is a wide-ranging, highly active shark that is found throughout the North Pacific, ranging from the cold productive waters of Alaska and the Bering Sea to regions as far south as Baja California and Hawaii. Salmon sharks are apex predators in the North Pacific, which means that they reside at the top of the food webs in these ecosystems alongside other large predators such as orcas, seals, and sea lions. They are opportunistic predators, feeding on a wide variety of prey species, including Pacific salmon, walleye pollock, herring, squid, mackerel, and rockfish. One of their most unusual characteristics is that they are endothermic (warm-bodied), with internal temperatures as high as 21°C above ambient water temperature.
Salmon SharkA salmon shark (Photo Scot Anderson)
Why study salmon sharks?
As apex predators, salmon sharks play a very important role in the ecology of these highly productive ecosystems.  It is important to understand details of their biology, such has their life history, migratory patterns, habitat use, trophic ecology and physiology, in order to understand and effectively manage this species and the ecosystems of which it is an important part. This is especially important given that salmon sharks have the life history characteristics typical of elasmobranchs (sharks, skates, and rays) of being long lived (30 yrs), slow growing, and having a low reproductive rate (4-5 pups/litter); traits that make this group of animals particularly susceptible to overexploitation.
Salmon shark attacking salmonA salmon shark breaching with a salmon in its mouth in Prince William Sound, AK (Photo: Scot Anderson) The fact that salmon sharks are voracious predators of a number of commercially important species makes them of particular interest as well.  Whenever a predator like a shark has a taste for something that humans also like to eat, this species effectively becomes a competitor for the resource, and in order to effectively manage this resource we have to understand the trophic ecology of the predator, meaning we have to understand what it eats, where it eats it, when it eats it, and how much it eats of it. For example, as their name suggests, Pacific salmon are commonly consumed by salmon sharks, and one study estimated that salmon sharks may consume as much as 12 – 25% of Pacific salmon, a fact that is very important if you also like to eat salmon, or especially if you are trying to manage salmon fisheries.
Salmon sharks also consume species that although they may not be as well known to the general public as salmon, are equally if not more important for human consumption. One such species is the walleye pollock, which is the largest single species fishery in the world.  If you’ve ever had seafood salad or California roles (which generally include "imitation crab meat") or ordered breaded or battered fish items at a fast food restaurant (ever had McDonald’s Filet-O-Fish sandwich?) then you’ve very likely had pollock, and wasn’t it delicious?
How are we studying salmon sharks?
As part of the Tagging of Pacific Predators program (TOPP), I am studying the ecology of this interesting species of shark using a combination of electronic tagging technologies (satellite, archival, and acoustic tags) and stable isotope analysis. The electronic tags provide us with information about where sharks go, when they go there, and details about their behavior and environmental preferences. Stable isotope analysis is a technique that uses the stable isotope composition of elements present in tissues to provide information on the feeding and migration of an organism.
Shark in front of research shipA salmon shark swims in front of the ADFG research vessel used for tagging in Prince William Sound, AK (Photo: TOPP).
The combination of these techniques has the potential to be quite powerful and informative, with tagging data telling you about the movements and behavior of the sharks and stable isotope analysis telling you about where sharks are foraging and what they are eating.  We hope that by learning more about the role of salmon shark in the North Pacific we will be better able to manage and conserve this ecologically important species and improve overall management of north Pacific ecosystems.