Does climate-driven variability in the oceanographic structure of the Gulf of Alaska shelf affect fish community composition by modulating the degree of interspecific competition between juvenile pollock and capelin?
E. Logerwell, A. Hollowed, C. Wilson and P. Stabeno
Abstract
The results of AFSC and PMEL research during 2000-2002 off Kodiak Island in the Gulf of Alaska indicate that ocean conditions affect the cross-shelf distribution of juvenile walleye pollock and capelin. Pollock were found in warmer waters inshore of a mid-shelf hydrographic front, whereas capelin were found offshore in cool waters advected from the slope. Although this pattern was consistent among years, there was intra-annual variability in the location of the front. A weakening of the front over the course of approximately 10 days in 2002 resulted in an expansion of warm nearshore water towards the outer shelf. Juvenile pollock distribution similarly extended towards the outer shelf. Coincident with the change in pollock distribution, the abundance of capelin declined in the outer shelf region. These changes in fish distribution are consistent with competitive exclusion of capelin by juvenile pollock. We hypothesize that the intra-annual dynamics in water mass properties and fish distributions are a model of the larger-scale processes that resulted in the apparent community re-organization on the Gulf of Alaska shelf following the late 1970?s regime shift. Patterns in the oceanography and fish distributions during the 2004 survey off Kodiak Island will be examined in light of this hypothesis. There are several mechanisms by which climate variability could influence physical structure off Kodiak Island. We will discuss the linkages between large-scale climate and local physical structure on the Gulf of Alaska shelf as well as the need for further understanding of the potential for competition between pollock and capelin.
