Trends in wild adult steelhead (Oncorhynchus mykiss) abundance in British Columbia as indexed by angler success

Abstract

Intraregional similarities and interregional differences in wild steelhead (Oncorhynchus mykiss) abundance trends over time throughout British Columbia were identified using catch-per-angler-day (CpAD) as an index of abundance. This index was calculated using sport angler catch and effort data obtained by an ongoing mail-out questionnaire begun in the fiscal year 1967-1968. Despite high interannual variability in CpAD for individual rivers, its validity as an index of trends over time in wild steelhead abundance for geographic regions or watersheds is reinforced by similar trends yielded by both fishery-dependent and fishery-independent data. Time series methods generally could not build statistical support for the hypotheses that sudden regulation changes, or the gradual introduction over time of a catch and release philosophy, are generally important factors affecting trends over time in CpAD. This bolsters our confidence that the general patterns in mean CpAD over time within regions and watersheds reasonably index actual wild adult in-river steelhead abundance. We propose that the trends that we observe in wild steelhead CpAD are primarily driven by environmental influences. Some candidate environmental time series currently being considered and investigated are coastal upwelling, various ocean and atmospheric climate indices, freshwater discharge histories, and ultraviolet radiation.