FISHERY BULLETIN: VOL. 72. NO. 1 



(i.e., have the same distribution by time and 

 area) . 



Field Operations 

 Marking and Release Procedures 



Artificial propagation procedures were simi- 

 lar at all coho salmon hatcheries during the 

 study period. Adults normally returned to the 

 hatcheries during September-November and 

 were spawned during October-November. Fry 

 generally reach the free-swimming stage in 

 March. The fish were released as smolts 13 mo 

 later at an average length of 12-15 cm (4.5-6 

 inches) and were available during the following 

 year to the fisheries from central British Colum- 

 bia to central California. 



The marking phase of this study began in 

 May 1966 and ended in June 1967. About 10% 

 of the 1965- and 1966-brood coho salmon were 

 marked. A modified sampling tool (Worlund, 

 Wahle, and Zimmer, 1969) was used to obtain 

 a random sample for marking. The "10-part 

 sampler" consisted of a cylindrical liner con- 

 taining a circular metal frame divided into 10 

 equal pie-shaped sections with a zipper-bot- 

 tomed net pocket hung from each section. When 

 a 10% sample was to be taken, the zippers on all 

 but one of the pockets were opened, the frame 

 and liner were placed in a water-filled tub. and 

 about 18 kg (40 pounds) of fish were placed 

 into the liner. The closed net pocket retained 

 the desired sample when the line and frame 

 were lifted. The fish that passed through the 

 open net pockets remained in the tub and were 

 placed into another pond. This procedure was 

 followed until all the coho in each pond were 

 processed. 



Fish to be marked were anesthetized with 

 MS-222' (tricaine methanesulfonate). The fins 

 and maxillary bones were clipped with bent- 

 nosed scissors. Marked fish were held in hatch- 

 ery troughs until they recovered from the anes- 

 thetic, then returned to the group from which 

 they came. To insure that fins and maxillary 

 bones were actually removed, quality control of 

 marking was maintained by periodic random 

 sampling of the marked fish throughout the 

 marking operation. 



■* Reference to trade names in this publication does not 

 imply endorsement of commercial products by the National 

 Marine Fisheries Service. 



The entire coho salmon production of each 

 hatchery was sampled to estimate the propor- 

 tion and numbers of marked fish released. The 

 "10%" samples removed initially by the cali- 

 brated pocket were set aside then resampled to 

 obtain a "1%" sample which was sorted into 

 marked and unmarked groups, counted, and 

 weighed. The counts together with an estimate 

 of the proportion removed by the particular 

 pocket of the sampler were used to estimate the 

 numbers of marked and unmarked fish released. 



In Table 2, the estimated numbers of marked 

 and unmarked fish released and the percentages 

 marked are summarized for each mark type and 

 brood year. Detailed data for each hatchery 

 are given in Appendix Tables la and lb. Over 

 40 million coho salmon of both broods were 

 released from the study hatcheries. The number 

 of marked fish released by section for the 1965- 

 and 1966-brood years combined were Lower 

 River, 0.9 million; Middle River, 1.7 million; 

 Upper River, 1.3 million; and Uppermost River, 

 0.2 million. A total of 39.1 million coho from 

 both broods was released from the study hatch- 

 eries in the Lower, Middle, and Upper River 

 sections. Of these, 9.8% were marked. About 

 0.9 million coho were released from the Upper- 

 most River section, of which 21.1% were 

 marked. 



Recovery of Marks in Fisheries 



The mark-sampling phase of this study was 

 designed in 1963 for fall chinook salmon and 

 was expanded to include coho in 1967, 1 year 

 before the 1965-brood coho were expected to 

 appear in great numbers in the fishery. This 

 advanced sampling was done for two reasons: 

 (1) to locate the sampling problem areas and 

 correct any deficiencies before the major 

 appearance of the 1965-brood coho in the fish- 

 eries and (2) to assist the Washington Depart- 

 ment of Fisheries in recovering their marked 

 1964-brood Puget Sound coho. This phase of 

 the investigation ended in 1969. Catch sampling 

 covered major ocean fisheries from Pelican, 

 Alaska, southward to Avila Beach, Calif., and 

 Columbia River fisheries. Sampling for marks 

 in each area consisted of recording numbers of 

 fish examined for marks and the recoveries of 

 each type of mark detected. Lengths and 

 weights of marked coho salmon from both 

 broods were recorded also. The sampling sea- 



144 



