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MESA: Pacific Ocean Perch Ecology

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Rockfish eggs.
Euphausiids are common prey for Pacific ocean perch.

Pacific ocean perch (POP) are mostly planktivorous. In a sample of 600 juvenile POP stomachs, juveniles fed on an equal mix of calanoid copepods and euphausiids. Larger juveniles and adults fed primarily on euphausiids, and to a lesser degree copepods, amphipods, and mysids. In the Aleutian Islands, myctophids have increasingly comprised a substantial portion of the Pacific ocean perch diet, which also compete for euphausiid prey. It has been suggested that Pacific ocean perch and walleye pollock compete for the same euphausiid prey. Consequently, large removals of Pacific ocean perch by foreign fishermen in the Gulf of Alaska in the 1960s may have allowed walleye pollock stocks to greatly expand in abundance.

Predators of adult Pacific ocean perch are likely sablefish, Pacific halibut, and sperm whales. Juveniles are consumed by seabirds, other rockfish, salmon, lingcod, and other large demersal fish.

Pacific ocean perch is a very slow growing species, with a low rate of natural mortality (estimated at 0.06), a relatively old age at 50% maturity (10.5 years for females in the Gulf of Alaska), and a very old maximum age of 98 years in Alaska (84 years maximum age in the Gulf of Alaska). Despite their viviparous nature, the fish is relatively fecund with the number of eggs/female in Alaska ranging from 10,000-300,000, depending upon the size of the fish.

Recent work on black rockfish (Sebastes melanops) has shown that larval survival may be dramatically higher from older female spawners. The black rockfish population has shown a distinct downward trend in age-structure in recent fishery samples off the west coast of North America, raising concerns about whether these are general results for most rockfish species. Pacific ocean perch were examined for senescence in reproductive activity of older fish and found that oogenesis continued at advanced ages. It appears that older individuals have slightly higher egg dry weight than their middle-aged counterparts. Further research is being conducted on the relationship between age and larval production for Pacific ocean perch or other rockfish species in Alaska.

Dana Hanselman
Auke Bay Laboratories
Alaska Fisheries Science Center, NOAA Fisheries

Ted Stevens Marine Research Institute
17109 Pt Lena Loop Rd
Juneau AK 99801

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