Steller Sea Lion Parasitology
Recently, the Team has directed effort at attempting to understand the role that disease and parasitism
may have had on the decline of the Steller sea lion (SSL) (Eumatopius jubatus). Of equal, but of more
proximal importance, the Team is conducting research on how disease and parasitism may delay recovery
of this endangered species. In general, the Team is contrasting parasite ecology in prey around selected
SSL rookeries and comparing parasitic fauna and densities of the SSL between rookeries. Preliminary
evidence suggests that parasite ecology around rookeries are similar, but that parasite prevalence and
densities in SSL may vary between rookeries. In addition, new evidence indicates that the hookworm,
Uncinaria sp. may affect pup health and survival. This revelation is critical as it appears that increased
pup and juvenile mortalities are a major cause for recruitment failure in recent years.
Bitter Crab Syndrome
Bitter Crab Syndrome (BCS) is a 100% fatal disease of North Pacific Chionoecetes crabs that is caused by
an undescribed parasitic dinoflagellate of the genus Hematodinium. First identified because of a very
bitter taste imparted to large heavily infected cooked crabs, current data indicates that the
disease is not a public health concern. Although, the method of infection and the complete life history of
the parasite is is not known, various stages of the dinoflagellate are evident. Two such stages are shown in the
photograph above (cellular-level of a snow crab, Chionoecetes opilio, eyestalk), pre-spore stages and
vegetative stages. Note the darker nucleus of the pre-spore stages as
opposed to the larger nucleus and foamy cytoplasm of the vegetative stage. Our data indicate that small
crabs are more susceptible to infection than large crabs which could affect recruitment. The Team continues
to monitor the prevalence and distribution of BCS in North Pacific crabs and is developing tools to more
accurately detect BCS in affected populations. Molecular tools will be employed to identify the parasite
and compare it with known similar parasites in other crustaceans worldwide.
Juvenile Walleye Pollock
Walleye pollock (Theragra chalcogramma) are a major North Pacific fishery which experiences population
fluctuations. In nature, the causes of many of these episodes are unknown and probably complicated. For
15 years, the Team has investigated the diseases of juvenile walleye pollock as a means of attempting to
understand how disease affects recruitment. Several parasites and diseases have been identified, but only a
microsporidan infection appears important. The undescribed microsporidan (Pleistophora sp.), indicated by the
asterisk in the photograph at right, infects the skeletal muscle of both juveniles and adults with likely
different effects. In juvenile walleye pollock, mortalities are possible but it is more likely that affected
fish will have increased difficulty in capturing prey or evading predators. In adults, Pleistophora is likley
to affect fecundity. Future research is being planned to more accurately monitor the parasite in walleye
pollock populations and to characterize the parasite at the molecular level.