A mark-recapture experiment to estimate the escapement of chinook salmon in the Unuk River, 1997
By: by Edgar L. Jones III, Scott A. McPherson and David L. Magnus.
Contributors: McPherson, Scott A.; Magnus, David L.; Alaska. Division of Sport Fish.
Series: Fishery data series -- no. 98-23.
Publisher: Alaska Dept. of Fish and Game, Division of Sport Fish
Published: 1998
Place of publication: Anchorage, Alaska
Language: eng
Number of pages: 35
Subjects: Fish tagging -- Study and teaching.; Fish populations -- Alaska -- Unuk River -- Measurement.; Chinook salmon -- Alaska -- Unuk River -- Statistics.
Description: The abundance of medium and large chinook salmon Oncorhynchus tshawytscha that returned to spawn in the Unuk River in 1997 was estimated using a mark-recapture experiment. Fish were captured in the lower Unuk River using set gillnets from June through July, and each healthy fish was individually marked with a solid-core spaghetti tag sewn through its back and was given two secondary marks in the form of an upper-left operculum punch and removal of the left axillary appendage. Spawning grounds sampling took place from July through August to estimate the fraction of the escapement that had been marked. During this study, 404 chinook salmon were captured in the lower Unuk River, and 382 of these were marked and released alive. Three hundred seven (307) fish were considered large (660 mm mid-eye to fork [MEF]) and 75 were considered medium (401659 mm MEF) in size. At the spawning grounds, 965 fish were sampled; 761 were considered large fish, and of these, 78 were recaptures which had been previously marked in the lower river with spaghetti tags. One hundred fifty-six (156) medium fish were sampled, and 16 of these were recaptures. A modified Petersen model was used to estimate that 2,970 (SE = 277, M = 307, C = 761, R = 78) large, 701 (SE = 158, M = 75, C = 156, R = 16) medium, and 3,671 (SE = 320) fish >400 mm MEF in length immigrated into the Unuk River in 1997. An estimated 32% of this immigration was sampled during the project. Peak survey counts in August totaled 636 large chinook salmon, about 21% of the mark-recapture estimate of large fish, a trend seen in similar studies. Of the spawning population >400 mm MEF, 38% were estimated to be age-1.4 fish from the 1991 brood year, 34% were estimated to be age-1.3 fish, and 25% were estimated to be age-1.2 fish.
Notes: "September 1998"

Includes bibliographical references: p. 18-19.

Also issued online.