Food habits of the commercially important groundfishes in the Gulf of Alaska in 1990, 1993, and 1996

Abstract

A total of 13,928 stomachs from 13 species, walleye pollock (Theragra chalcogramma), Pacific cod (Gadus macrocephalus), arrowtooth flounder (Atheresthes stomias), Pacific halibut (Hippoglossus stenolepis), sablefish (Anoplopoma fimbria), Pacific ocean perch (Sebastes alutus), northern rockfish (Sebastes polyspinis), dusky rockfish (Sebastes ciliatus), rougheye rockfish (Sebastes aleutianus), shortraker rockfish (Sebastes borealis), shortspine thornyhead (Sebastolobus alascanus), flathead sole (Hippoglossoides elassodon), and Atka mackerel (Pleurogrammus monopterygius), were-analyzed to describe the food habits of the major groundfish species in the Gulf of Alaska in 1990, 1993, and 1996.

Arrowtooth flounder, Pacific halibut, sablefish, Pacific cod, and pollock were the main piscivores. Pollock were the dominant prey fish. The main predators that feed on Tanner crabs are Pacific halibut and Pacific cod. Pollock, shortspine thornyhead, shortraker rockfish, flathead sole, and rougheye rockfish are the main consumers of pandalid shrimp. Pacific ocean perch, northern rockfish, dusky rockfish, and Atka mackerel fed mainly on zooplanktons (mainly euphausiids and calanoid copepods).

A significant finding in this document is the predation on pandalid shrimp, capelin, and pollock. In 1990 and 1993, the percentages of the pandalid shrimp consumed by pollock, Pacific cod, arrowtooth flounder, and sablefish were high (more than 10% by weight). However, in 1996, only Pacific cod still maintained 11% of pandalid shrimp in their diet. And the percentages of the pandalid shrimp in other predators declined dramatically to less than 10%. A similar trend was found in the consumption of capelin. A relatively large amount of capelin were consumed in 1990, and then declined in 1993 and 1996 by most species. However, during this period, the consumption of pollock increased dramatically in 1996 for most of the species. The percent similarity index (PSI) was calculated by using the proportions of the prey items in the stomachs to show the diet overlap between groundfish species in the Gulf of Alaska in 1990, 1993, and 1996.


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