The success or failure of seabirds depends heavily on the availability of forage fish during their breeding season. Two aspects of "availability" are important:  abundance in waters around the colony, and depth in the water column. Hydroacoustic surveys conducted near 3 major colonies in lower Cook Inlet reveal some significant differences among these colonies with respect to forage fish availability. Firstly, in all years of study we have found that forage fish densities are always highest around the Barren Islands and lowest in the vicinity of Chisik Island. Secondly, we found that forage fish biomass is concentrated in relatively shallow waters (10-40 meters depth) around the Barrens and Kachemak Bay, but are found in deeper waters around Chisik. These patterns of forage fish abundance and distribution probably explain why seabirds at Chisik have a hard time raising chicks, while those at the Barrens and Kachemak usually have higher breeding success.

Relative Fish Biomass at Three Seabird Colonies in lower Cook Inlet