Differential Selectivity of Three Gear Arrays Used in Commercial Trolling for Coho and Chinook Salmon

Identification Information

Citation

Originator: Lawson, Peter W.

Publish Date: 23 October 1990

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: Management of the commercial ocean troll salmon fishery in Oregon often requires regulations prohibiting the landing of coho salmon ( Oncorhynchus kisutch) during time periods when chinook (0. tshawytscha) fishing is open. Hooking mortality in these "all-except- coho" fisheries has been estimated to be up to 16 percent of the total allowable troll fishery-related mortalities south of Cape Falcon, Oregon in recent years. A reduction in the overall number of coho hooked and released (coho encounters) during periods closed for coho would reduce mortalities and increase the number of coho available for harvest. This experiment was designed as a field test of the idea that trolling for chinook with fewer spreads (hooks) per line would reduce coho encounter rates without seriously affecting the chinook catch rate. Coho are generally found higher in the water column than chinook. With more spreads per line, more gear would be near the surface, with higher coho encounter rates on the upper spreads. Three chartered vessels trolled for chinook with four, seven, or ten spreads per line for 24 days (72 vessel days total) during May and June, 1990. Observers recorded coho and chinook encounters for each spread and gear type. Fewer coho per day were caught on four spreads per line (x = 9.3) than on seven (x = 19.9) or ten (x = 19.9) spreads over the course of the study. Chinook catch rates were similar on all gear arrays (x = 7.6). Coho were distributed higher on the gear than chinook. This vertical separation was more pronounced later in the study when upwelling lowered sea surface temperatures. Through interviews with fishermen it was determined that commercial trollers typically were using from four to eight spreads during the study period. Data from this experiment could be used by fishery managers to estimate the savings in coho mortality which would result from a four spread regulation. Local fishermen observe that coho are frequently found higher in the water column than chinook. Similar differences in depth are also referred to by Miller (1982), Milne (1955), and Van Hyning (1951). The present study was designed to test the idea that, due to the distribution of fish in the water column, shallower spreads contribute to a higher coho encounter rate. By limiting boats to fewer spreads, shallower spreads would be eliminated. Coho encounter rates should be lowered and coho hooking mortality reduced without seriously affecting chinook catch. Should such a gear restriction be adopted as a management tool, this study would provide quantitative data for use in adjusting coho mortality rates.

Purpose:

Time Period of Content:

Geographic Extent: Oregon Coast

Status: Final

Use Constraints:

Format: PDF file

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Bibliography Information

Field Name	Value
Biblio ID	8264
Year	1990
Publisher
Request Type	Report
Location	Salem HQ
Date Created	Oct. 1990
Date Cataloged	7/27/05
Date Published	1990
Type	clipped
Pages	1/4" thick
Volume
Status	2
Descriptor	3 gear arrays; commercial trolling; coho; Chinook;
Date Entered	2005-07-27 14:09:32
Location In Clackamas Library	E wall, troll fishing
Author	Peter W Lawson
Duplicates	0
Number Remaining After Requests
Presumed All Distributed
Back Room Duplicates
Author
Risk
Species
Disposition Of Requests	Tim Dalton: Requested, but no copies available
Disposition Of Requests	StreamNet Library: Requested, but no copies available
Disposition Of Requests	Chris Kern: Requested, but no copies available

Is a physical copy maintained for reference at Headquarters? No