Stock assessment of whitefish in the Chatanika River during 1996 and 1997

Description

In 1996, 623 humpback whitefish Coregonus pidschian 360mm FL and 529 least cisco C. sardinella 290mm FL were sampled from a 30 km section of the Chatanika River during August and September. The August sampling period corresponded to the timing of 1992-1994 assessments, while the September sampling corresponded to the time when the sport spear fishery was open to exploitation (prior to 1994). Ages 4, 5 and 6 predominated in humpback whitefish indicating strong pre-recruit classes; ages 4, 5 and 6 also dominated in least cisco, however the younger age classes (ages 2 and 3), normally vulnerable to sampling gear, were low in abundance. Significantly fewer age 4 humpback whitefish were sampled in September than in August (2 = 25.38, df = 11, P=0.008). There was no significant difference among the August and September age samples for least cisco. In 1997, we conducted a mark-recapture experiment in a 53 km (33 mi) section of the Chatanika River from August 20-28 to estimate abundance and stock composition 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 timing of a recreational spear fishery. An estimated 16,107 (SE = 1,260) humpback whitefish ( 360 mm FL) were present in the study area. The assessed stock was characterized by a high proportion of humpback whitefish between 390 and 430 mm FL with ages 5, 6, and 7 predominating. An estimated 22,811 (SE = 4,496) least cisco ( 290 mm FL) were present in the study area. The assessed least cisco stock was predominated by age 5 and 6 fish, and primarily comprised of fish greater than 340 mm FL. Poor recruitment within the least cisco stock was indicated by the age composition, and estimated recruitment levels of age 3 fish were the lowest in 11 years of stock assessment.

Subjects

Series Statement

• Fishery data series -- no. 97-36.

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