Chinook Salmon at-sea Maturity Studies 1976-1978, Including a Summary of Oregon Commission Ocean Salmon Maturity Sampling 1948 - 1975 Information Report 84-5

Identification Information

Citation

Originator: Malcom Zirges, ODFW

Publish Date: 1984

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: Chinook salmon are exploited in the ocean beginning with their second year of life. Although male chinook. mature as early as age-2 and females as early as age-3. Many individuals, particularly females, mature as late as age-6. The ocean troll fishery historically has exerted the greatest pressure on three year old chinook. a significant portion of which are still immature. Troll and sport Chinook salmon fisheries have historically been regulated primarily through minimum size and season length regulations. These regulations are designed to protect immature chinook salmon which still have significant potential growth remaining. This objective is balanced however, by a desire to fully harvest maturing fish not needed for spawning escapement before they leave the ocean. Maturity information is needed to assist in the management of ocean salmon fisheries. For example, chinook jacks (early-maturing age-2 male fish), are less likely to be harvested after they leave the ocean and are rarely needed on the spawning grounds. A high percentage of jacks in a given ocean fishery might warrant adjusting minimum size limits to increase harvest of these smaller fish. A stock needing greater protection might be conserved effectively by closing an area or time period when a large percentage of maturing females are available thus providing increased spawning escapement. A recent controversial example is the Chinook fishery off the southern Oregon-northern California area which includes both depressed and early-maturing runs with a high percentage of jacks. Maturation rates of chinook salmon available to ocean fisheries in this area are poorly understood, particularly for those fish caught early in the season near the legal minimum commercial size limit of 26 inches. Various management problems in recent years have caused the Pacific Fisheries Management Council, which is responsible for salmon management in the 3 to 200 mile zone offshore, to alter chinook harvest regulations including size limits. For example, the minimum size limit for commercially caught chinook has changed from 26 to 28 inches north of Cape Falcon, Oregon. The sport-caught chinook limit has changed from 20 to 24 inches north of Cape Falcon, and ranged from zero to 22 inches south of that point. These changes have generated considerable pressure to either retract these new limits or enact them uniformly coastwide. The need for maturity information reaches almost every aspect of chinook management. The "ideal" size limit is a function of balancing gains from additional growth by undersized (and immature} fish released and re-caught later against losses from shaker and natural mortality plus emigration of maturing fish. Protecting potential spawners or optimizing yield by taking advantage of growth potential also requires valuating percentage of maturing fish. ln 1976, ODFW Ocean Salmon Program personnel began analysis of file data and implemented at-sea sampling of Chinook salmon length-frequencies and other maturity parameters. Although this work initially addressed chinook along the entire Oregon coast, the size limit issue resulted in a change of focus in 1977 to small fish off the south coast. An effort was made to: (1) determine the most suitable method of detecting maturity in ocean-caught chinook salmon, particularly in the 20-28 inch size range, and (2) to utilize this method to assess the relative abundance of mature and immature chinook in the mixed stock ocean fisheries off southern Oregon. The study was expanded in 1978 to a joint program with the California Department of Fish and Game under the Anadromous Fisheries Act, PL 89-304, Grant-in-Aid project-AFC-92 (administered through the Pacific Marine Fisheries Commission) . This included development of an improved method for determining maturity in small male fish with the assistance of personnel of the Oregon Cooperative Fishery Unit at Oregon State University. This report contains a summarization of Chinook salmon maturity sampling data collected during the past by ODFW (earlier the Fish Commission of Oregon or FCO). and data collected by ODFW during the 1976-78 project. It presents maturity information derived from that data, and includes methodologies for a promising histological technique developed with the particular help of the Coop Fish Unit for determining state of maturity in male Chinook salmon.

Purpose:

Time Period of Content:

Geographic Extent: Oregon

Status: Final

Use Constraints:

Format: PDF File

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Data Information

No data information was supplied.

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Attributes Description: Not yet described

Bibliography Information

Field Name	Value
Biblio ID	288
Year	1984
Publisher
Request Type	Information Report
Location	Salem HQ
Date Created
Date Cataloged	3/26/2001 20:44:40
Date Published	1984
Type	info repo
Pages	58 pp
Volume	84-5
Status	2
Descriptor	Chinook; Ocean Salmon; Harvest; Coast, Oregon; maturity sampling
Date Entered	2005-06-22 00:00:00
Location In Clackamas Library	S wall, yellow info reports top row
Author	Malcolm H Zirges
Duplicates	0
Number Remaining After Requests	3
Presumed All Distributed
Back Room Duplicates
Author	Zirges, M.H.
Risk	Harvest
Species
Disposition Of Requests	StreamNet Library: Request filled
Disposition Of Requests	State Archive: Request filled

Is a physical copy maintained for reference at Headquarters? Yes