One suspected cause of their precipitous decline was the overfishing of Alaska pollock, herring, and other fish stocks in the Gulf of Alaska. This stems largely from the "junk-food hypothesis" representing a shift in their diet from fatty herring and capelin to leaner fare such as pollock and flounder, thereby limiting their ability to consume and store fat. Other hypotheses include increased predation by orcas and sharks, indirect effects of prey species composition shifts due to changes in climate, effects of disease or contaminants, shooting by fishermen, and others. The decline is certainly due to a complex of interrelated factors which have yet to be defined by the research effort.