Effective Fishing Effort in the Oregon Groundfish Trawl Fishery

Identification Information

Citation

Originator: Sampson, David B.

Publish Date: 1997

Online Link: None

BPA Project #:

Contact Information

Agency: Oregon Department of Fish and Wildlife

Name: Cedric Cooney

Job Position: Natural Resources Data and Systems Manager

Telephone: 503-947-6094

E-Mail Address: cedric.x.cooney@odfw.oregon.gov

Description

Abstract: In this study logbook data from the Oregon bottom trawl fishery were used to estimate effective, standardized catch-per-unit-effort (CPUE) for fifteen groundfish species or species groups. The data, which included skippers' tow-by-tow estimates of retained catch, were compared with landing receipts to remove inaccurate information; trips influenced by regulatory trip limits and tows longer than four hours duration were also excluded. From the remaining data a subset was chosen for detailed analysis to identify influential factors, to develop simplified statistical models of catch rates for each species, and to identify boats that could be used for estimating standardized CPUE. Excluded from the detailed analyses were boats that did not operate throughout the study period, and areas in which there was limited fishing. The selected data were analyzed in a stepwise manner using generalized linear models of catch rates to measure the importance of the factors Year (1987-93), Season (bimonthly intervals), Boat (29 boats), Net type (generic bottom trawl, trawl with roller gear, sole trawl), Latitude (20 minute intervals), and Depth (40 fathom intervals). Because for each species there were large numbers of tows with catches that were zero, catch rates were modeled using a delta-lognormal distribution; the numbers of tows with non-zero catch were treated as binomial random variables and the catch rates for the non-zero tows were treated as lognormal random variables. The process of data verification and screening resulted in the exclusion of data from about half the fishing trips. The data subsets that were subjected to the detailed analyses of influential factors consisted of tow-by-tow catch rates (lb/hr) from 26,256 tows. In the logistic regression analyses of the zero-catch tows, essentially all factors were found to be highly significant (P<1%) for all species from both states. Boat was the first or second most influential factor for 12 of the 15 species, and Depth was the first or second most influential factor in 12 combinations. In the analyses with pairwise interactions, the Year·Boat interaction was the first or second most influential interaction for all 15 species. In the analyses with lognormal models of the non-zero tows, essentially all factors were found to be highly significant (P<l%) and Boat was the most influential factor for 14 of 15 species and was the second most influential factor for one other species, Latitude was the second most influential factor for 7 species, and the Year·Boat interaction was the first or second most influential interaction for 13 of 15 species. Estimates of annual fishing power coefficients were examined to identify boats with stable fishing power. To estimate standardized CPUE for each species for individual areas (defined by the factors Latitude and Depth), the simplified statistical models, developed from the detailed analyses, were applied to data from the top 40 boats for each species from each state. The data were further restricted to those areas that had been fished in during the entire study period. The area-specific CPUE estimates, defined as the estimated average catch (lb) per hour of towing for those boats selected as the standards, were then averaged to estimate the effective, standardized CPUE for each species. There were substantial declines indicated for lingcod, miscellaneous rockfish, and sablefish, and moderate declines for petrale sole, Dover sole, and arrowtooth flounder; and there were increases indicated for English sole, rex sole, widow rockfish, yellowtail rockfish, and thornyheads.

Purpose:

Time Period of Content:

Geographic Extent: Oregon

Status: Final

Use Constraints:

Format: PDF

Data Quality Information

Lineage-Source: Final Report to the Oregon Trawl Commission

Data Information

No data information was supplied.

Entity and Attribute Information

Attributes Description: Field attribute information is available in the attached file(s).

Is a physical copy maintained for reference at Headquarters? Unknown