Alaskan waters growing hospitable to sharks while seals and sea lions decline

um, which receives money from those in the fishing industry interested in the relationship of fishing and marine mammals and from NMFS.

There have been changes in the populations of fish these animals eat. Climate conditions in recent decades have favored salmon in Alaskan waters for a number of years and heavy hatchery production has added millions more fish, to the benefit of both pinnipeds and sharks. On the other hand, commercial fishing of pollock in competition with sea lions may have indirectly benefited sharks, Gallucci says.

"Sharks, being the more efficient eaters, just may be able to take greater advantage of changes in the food that's available," he says.

Then there are other factors such as the 1992 moratorium on drift-net squid fisheries that eliminated a source of incidental shark mortality. And, while there is no direct evidence of sharks preying on sea lions or seals in Alaskan waters, sharks do feed on pinnipeds in other parts of the world. Gallucci says more investigation is needed to know for sure.

The interactions that have been occurring, and those possible in the future, are impossible to determine without knowing the life history of the sharks, Gallucci says. Fieldwork last summer, for instance, revealed that most of the salmon sharks caught were females but researchers don't know why. Among other things, Gallucci's group is trying to find ways to analyze hormones from blood samples that might allow them to determine the age, sexual maturity and other information. Such life-history data can then be used to model shark dynamics.

Unraveling the basic biology of the animals also may give scientists insight on how these large predators might shape the ecosystem in the future.


Contact: Sandra Hines
University of Washington

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