Stock assessment and relative age validation of humpback whitefish and least cisco in the Chatanika River during 1993

Description

Stock assessment of humpback whitefish Coregonus pidschian and least cisco Coregonus sardinella occurred in a 78.2 km (48.9 miles) section of the Chatanika River, near Fairbanks, Alaska during August 1993. Mark-recapture experiments were utilized to estimate abundance of both species. The investigation was timed to correspond to the upstream spawning migration of both species, and to provide in-season estimates of abundance prior to the onset of a recreational spear fishery. An estimated 13,112 (SE = 1,096) humpback whitefish (>360 mm FL) were present in the study area. The assessed stock was characterized by a high proportion of large humpback whitefish (>430 mm FL) with ages 7, 8, and 9 predominating. An estimated 46,562 (SE = 5,971) least cisco (>290 mm FL) were present in the study area. The majority of the assessed stock was between 310 and 350 mm FL, with ages 3, 4, and 5 most abundant. Survival of fully represented age classes between August 1992 and August 1993 ranged from approximately 47 to 53 percent for least cisco and humpback whitefish, respectively. Patterns of annual catches, migratory movements, and abundances were examined in the context of a non-consecutive spawning life history pattern found in other corregonids in Alaska and Canada. The ability to detect annular growth on scales of both species was evaluated using data from release-recapture studies. Annular growth, formed during a hiatus of one or more years, was correctly detected approximately 31% of the time with humpback whitefish, and 35% with least cisco.

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