Salmon Shark (Lamna ditropis)

Salmon sharks move into areas of high food abundance, or “hot spots.” They consume the schools of fish until the amount of prey is reduced or dispersed. Then the sharks move on to the next patch of food. Salmon sharks have learned where and when these hot spots occur. This behavior may result in salmon sharks intercepting salmon runs but they take far less than the number of fish harvested by fishermen.

An interesting thing about salmon shark predation in Alaskan waters is that it may afford some stability to the ecosystem. Mathematical models show that if a predator-control program removed these sharks from the ecosystem some marine species populations would decline. Scientists think it would work like this: If the sharks were removed, several fish species numbers would increase, especially arrowtooth flounder. The increased flounder population would remove smaller forage fish such as capelin and herring, which reduces the food supply for other fish, seabirds and marine mammals. Some marine mammal populations in the Gulf of Alaska are already at critically low numbers, so further declines would have a devastating effect on the ecosystem and likely would force more fishing restrictions to protect the food of the marine mammals. The complexities of the predator–prey relationship and their effects on the marine ecosystem are difficult and next-to-impossible to predict and manage. A precautionary approach to fisheries and predator management is the wisest choice.