Mystic Aquarium & Institute for Exploration

Within the United States there are two stocks of wild Steller sea lions. The eastern stock is currently listed as a threatened species, though is fairly stable, whereas the western stock continues to decline and is listed as an endangered species. There are many theories as to why the western stock has declined so drastically.

Scientists at Mystic Aquarium have investigated one specific hypothesis related to nutrition stress i.e. that there has been a change in the primary diet available to the Steller sea lions. Their previous diet consisted mainly of a fatty fish called herring, while their current diet contains more Pollock- a leaner fish. The hypothesis was that the change from a high fat diet to a lower fat diet might also have resulted in decreased consumption of fat soluble vitamins, specifically vitamins A and E. Both of these vitamins are important in reproductive success. If the decrease in dietary vitamin A and E intake was enough to actually cause an overall deficiency, then this diet change may have contributed to the decline. The results of the study showed that this is not the case. There were no significant differences in serum vitamin concentrations between the two stocks. At first glance one might think that an insignificant result means that the study failed. However as there are so many possible reasons for the decline, the only way to get to the root of the problem is to eliminate possibilities along the way. This study eliminated diet and vitamin deficiency as a possible cause of the decline. Much research still continues on the Steller sea lion and its conservation in the wild.