Here’s an interesting sidebar to the ongoing interior Fraser steelhead issues. This comes from a request I put in to the provincial fisheries staff in Surrey a couple of weeks ago. I’ve just got around to looking at it today. Mike Wilcox gets the nod for the assist here.
Most of the hard corps steelhead anglers out there know there are two distinct groups of summer steelhead in this province – coastal and interior. In the Fraser system we have examples of both. The coastal variety is present in the Coquihalla while the Thompson, Chilcotin and those other forgotten stocks in the Nahatlatch, Stein and Bridge represent the interior variety. Coastal summer fish come earlier in the summer than their interior counterparts. Those Coquihalla fish are moving through the lower Fraser well ahead of the timing for most of the salmon stocks that we’re told are still healthy enough to sustain some commercial and First Nations fisheries. In other words, Coquihalla fish enjoy a relatively unimpeded trip home. On the other hand, the run timing for those Thompson fish is several weeks later and overlaps numerous salmon stocks and species that are subjected to harvest by commercial and First Nations nets.
If we look at the data compiled through annual snorkel surveys conducted on the Coquihalla over the past many years it points to the fishery interception problem that is a big part of the status of the Thompson fish. Here are the data:
Contrast that with the estimated escapement of Thompson steelhead over a reasonably comparable time period. (This is the combined total for both the Thompson and Chilcotin and it represents the pre-fishing mortality, not the spawning population. The latter is about 20% lower than the figures shown.) The estimated 2018 spawing population of the combined Thompson and Chilcotin stocks as of this date is 195 steelhead, a figure almost off the bottom of the graph.
The most important feature of these two figures is the slope of the line in the latter. The Coquihalla stock obviously fluctuates over time but its abundance does not display the steady downward trend shown by the Thompson/Chilcotin stock. The past two or three years of Coquihalla data may well be minimized by a geological event that resulted in delay and blockage of some of the fish that might otherwise have been present and counted. Even still, there is no evidence of the same downward trend displayed by the later returning, upriver bound Thompson and Chilcotin steelhead.
Some would contend the Thompson scenario is not necessarily a direct result of commercial and First Nations harvest. What about those seals and sea lions or the fish farms or the warm water blob or high seas interception by foreign fleets or……….? Well, whichever of those issues is at play for the interior stocks can’t reasonably be held to differ for the coastal stock originating right next door. The only plausible explanation for the contrasting trends in abundance is the differential mortality rates exerted on them by nets during the late stages of their migration to their river of origin.