Echo integration-trawl survey of Pacific whiting, Merluccius productus, off the west coasts of the United States and Canada during July-September 1995

Abstract

Results are presented from the seventh triennial echo integration-trawl survey of Pacific whiting, Merluccius productus, along the west coasts of the United States and Canada. Areal coverage during the survey was more extensive than for earlier surveys both in increased effort offshore and to the north. The survey was conducted from 1 July to 1 September 1995, and extended along the Pacific coast from Point Conception, California, to Dixon Entrance, Alaska. Aggregations of Pacific whiting were detected throughout the study area, with the heaviest Pacific whiting echo sign observed off California near Point Arena and Cape Mendocino, off central Oregon, over Juan de Fuca Canyon near Cape Flattery, and off northern Vancouver Island. Trends in size composition for Pacific whiting exhibited a latitudinal cline over the study area, with larger fish generally more abundant in the northern areas. Over 75% of the population numbers and biomass was composed of the 1984, 1987, 1990, and 1993 year classes. The coastwide biomass for Pacific whiting was estimated at 1.39 million t, which was similar to earlier triennial acoustic survey biomass estimates. Acoustic backscattering was converted into abundance estimates using a target strength (TS) to length (L) model of TS = 20 Log L -68 rather than the historically used model of TS = -35 dB/kg of fish. Justification for the use of the 20 Log L -68 model is discussed, and estimates based on both models are compared.


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