US EPA

7230895 

Journal Article 

AGE, GROWTH, AND MORTALITY OF THE NORTHERN SHRIMP PANDALUS-BOREALIS KROYER IN PAVLOF BAY, ALASKA 

Anderson, PJ; , 

1991 

1 

Fishery Bulletin
ISSN: 0090-0656 

NATL MARINE FISHERIES SERVICE SCIENTIFIC PUBL OFFICE 

SEATTLE 

541-553 

WOS:A1991GU46000001 

Northern shrimp Pandalus borealis carapace length-frequency data collected from shrimp surveys and commercial catches between 1972 and 1986 were studied to estimate age, growth, and mortality in Pavlof Bay, Alaska. Dominant size modes representing 1971 and 1975 year-classes were separated from carapace length-frequency distributions by the use of a maximum-likelihood separation technique. The growth rate for the 1975 year-class was significantly greater than that of the 1971 year-class. Because the abundance of the 1975 year-class was lower than that of the 1971 year-class, an inverse relationship of growth to year-class strength was suggested. Age-at-sex transition appears to be related to year-class abundance or overall density as 1975 year-class shrimp completed transition at a younger age than that of 1971. Increases in natural mortality occurred after the 1971 year-class completed transformation to the female sex at age 6.4, and may indicate a combination of spawning stress and senescence or increasing abundance of the predator, Pacific cod Gadus macrocephalus. Dynamic pool yield-per-recruit analysis indicated maximum biomass of year-classes was achieved at or prior to full recruitment to the survey and commercial fishing gear. Because mortality rates are high, yield-per-recruit is optimized by harvesting more of the smaller male shrimp.