Stock status of northern boundary coho: Canadian Report



This document presents an assessment of the status of coho salmon (Oncorhynchus kisutch) in the Canadian northern boundary areas with emphasis on the Skeena River. The content of this assessment has largely been drawn from published assessments (Holtby et al, 1999a; Holtby et al, 1999b; Holtby and Kadowaki, 1998; Holtby and Finnegan, 1997).

Biological assessment of coho across such a vast area is highly problematic. First, quantitative data are sparse and, in most of the area, assessment relies on escapement indices derived from visual escapement counts of uncertain quality from a highly variable stream set. Second, measures of exploitation and marine survival are of short duration and have been made in only a few streams. Third, there are only two measures of FW production (smolt output) in the area and they are of short duration and come from populations that may be of higher productivity than the norm for the area. Fourth, there has been significant sockeye enhancement in Babine Lake, one of the major systems of concern, but the impacts of that assessment on the limnology of the lake and on other species are largely unknown. Fifth, the biology of coho in interior systems has been little studied compared to the extent of study in southern coastal systems, which makes interpretation of what observations are available uncertain.

This section of the report has three sections. The first deals with information derived from exploitation rate-survival indicator populations. The second summarizes data from a variety of abundance indicators and presents an area wide synopsis of status. The third presents some comparative analyses of stock productivity and discusses a hypothesis to explain the pattern of status across the area.