Research Document - 2004/007
Stock Status of Wild Chum Salmon (Oncorhynchus keta Walbaum) Returning to British Columbia's Central Coast and Johnstone and Georgia Straits (excluding the Fraser River)
By Godbout, L., Irvine, J.R., Bailey, D., Van Will, P., and McConnell, C.
Abstract
We describe the status of six main chum salmon stock groupings from the Central Coast and the southern non-Fraser Inner Study Area (ISA). The first four correspond to the chum returning to Statistical Areas 7, 8, 9, and 10 and are referred as “northern stocks”. The fifth stock is those fish returning to Area 11 (Seymour Inlet). The sixth stock comprises fish spawning in the ISA (Johnstone and Georgia straits) but excludes fish from the Fraser River. Our overall goal was to assess the status of these stocks and describe how status varied temporally between 1953- 2002.
Status was based primarily on trends in escapement as well as a comparison of escapement to reference points. We calculated two reference points based on the long-term median escapement (LTME) that defined three zones (red:≤ 60% LTME, amber:>60 % LTME < escapement < 80%LTME, and green: ≥ 80%LTME). We performed a similar analysis using total run sizes. Status variability within stock groupings was assessed by calculating and comparing relative rates of change in escapement per year for individual streams. Temporal variations in stock status were analysed by evaluating the stock status based on the complete time series and based on data from the last three generations only.
Chum salmon in Areas 7 and 8 were generally in the green zone. While there are no apparent management concerns with these fish, we recommend that Area 7 chum should be monitored closely since total run size appears to have been reduced by ~22% during the last three generations.
We have some concerns for chum returning to Areas 9-11, and north-eastern Johnstone Strait (EJST). Although long and short-term trends in escapements to Area 9 were not negative, the median escapement and total run size during the last three generations were in the amber zone. Escapements in Area 10 showed a negative trend during the last three generations, although the median escapement was in the green zone. Inefficient escapement surveys during the last 3 generations might be responsible for this apparent decline in escapement. Escapements in Area 11 declined over time, and the median of the last three generations was in the amber zone while total run size was in the green zone.
There was significant variability in patterns for the southern stocks. Stocks on both sides of Johnstone Strait have declined recently. The decline of the Eastern stock was the most drastic of all; recent escapements and total run sizes were in the red zones, both being reduced to less than half their long-term median.
Interestingly, chum in North West Georgia Strait (NWGS) increased during the last three generations; escapements and total run size generally were in the green zone. This increase may be related to changing fishery practices on enhanced chum returning to this area. Chum returning to NEGS, SWGS, and SEGS had similar patterns to each other. All Georgia Strait stocks increased during the complete time series and during the last generations and were in the green zone.
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