The Weight of Evidence

Over many years in the fisheries business I’ve witnessed more predictions regarding salmon returns than I care to remember. One thing I’ve not forgotten, however, is my overriding impression – if you want to be wrong, just make a prediction. British Columbia is replete with examples of that this year. I don’t think I’m overstating it to say the batting average was so low there wouldn’t be a glimmer of hope for a new contract for any of the predictors if they were ball players. I don’t see that as a lack of available information as much as I do failure to look for it and/or apply it.

The business of predicting steelhead returns involves much greater uncertainty than for salmon. Steelhead have so many combinations of freshwater and ocean ages and repeat spawning frequencies that confidence in anything other than broad scale forecasts is probably not something most managers want to think about. That aside, here’s some information that should be top of mind.

The warm water intrusion (“the blob”) that befell virtually the entire ocean migration and rearing area for steelhead, especially those originating from British Columbia, during 2015 and well into 2016 clearly had major impacts on the returns to our streams in 2017. That was 100% predictable but I see no evidence of anything but surprise on the part of fisheries managers when it happened. Lots of head scratching after the fact but no acknowledgement of the science that predicted it. Now there is even more science that is sounding alarms for 2018 and even beyond.

The National Oceanic and Atmospheric Administration (NOAA) is my go to source for research results on happenings in the ocean environments occupied by North American origin salmon and steelhead. NOAA has been at it for a very long time and their people have published more highly instructive findings and reports on steelhead at sea than everyone else combined. Dr Nathan Mantua, a prominent member of NOAA as well as a steelhead angler, is the presenter of the prestigious Peter Larkin Lecture at the University of British Columbia for 2017. They don’t extend that invitation to just anyone! (Dr. Peter Larkin was the very first chief fisheries biologist appointed to serve the provincial government in 1948. He passed away in 1996 after a long and distinguished career in the science community, mostly at UBC.) Dr. Kate Myers, another remarkable high seas researcher (recently retired) out of the University of Washington’s School of Aquatic and Fisheries Sciences was a frequent research colleague of Mantua. Together they have provided a tremendous amount of quality information on steelhead. Here’s a bit of a synopsis of what some of the research they have been directly involved in over recent years has been telling us.

Steelhead migrate and feed in the surface and near surface layers of the ocean (usually 6m or less). The high end of their preferred temperature range is 13-15C. The ocean rearing area most frequented by North American origin steelhead is bounded on the south by what is known as the Sub-Arctic boundary, the area south of which water temperature becomes a barrier to steelhead. To the north, the ocean feeding area includes the Gulf of Alaska and all the areas westward through the central north Pacific to well past the mid-point between North America and Asia. The northern boundary, the Aleutain Islands chain, is physical rather than temperature determined. The area within these physical and temperature controlled limits is the one that will lose the most thermally suitable steelhead rearing habitat under increased ocean temperatures whenever that Sub-Artic temperature dependent boundary shifts north. Whereas the blob has largely dissipated now, don’t bet the farm on a return to broad scale cooler ocean temperatures any time soon.

The temperature issues are, by no means, straightforward but the pathways through which they manifest themselves are becoming reasonably understood. One of the important points related specifically to steelhead at sea and elevated temperatures is the influence on their metabolic requirements. As temperature warms metabolic requirements increase while the energy supply from preferred food items is reduced through a combination of less of them and their lower size and quality. The companion feature out there in the central north Pacific is ocean acidification or, as Kate Myers once parroted, ocean warming’s evil twin. Squid, that preferred steelhead food item, are particularly sensitive to acidification. The predictions around trends in ocean acidification are consistent. It isn’t going away.

I spoke to some of the research findings with respect to steelhead and chinook way back in February (“Science Messages”, February 1). A couple of points made then deserve repeat. The numbers of enhanced pink and chum salmon being pumped into the North Pacific ecosystem are outstripping its capacity to grow sufficient food supplies to sustain everything feeding on them. Massive numbers of enhanced pink salmon, from both Alaska and Asia, prey heavily on the same squid that are the food item of choice for maturing steelhead and chinook. Those enhancement programs are about as likely to go away as ocean acidification. All things considered we’re looking at more fish competing for less food of lower quality than needed to sustain the once known survival and growth of steelhead in their main ocean feeding grounds. Fishers and managers need to lower their expectations on the supply side of the picture. The fact that the abundance of steelhead from Alaska to California this year was nowhere near what everyone wanted and expected ought to have been a wake up call but I still don’t see any evidence of concern for next year and beyond.

Another aspect of ocean conditions I wonder about is the distance between the river of origin of steelhead smolts and the high seas rearing areas they are known to occupy. It seems logical that smolts from rivers closest to those areas would not be subjected to the inhospitable conditions for as long as those that had to migrate greater distances to arrive at the same destination. This is obviously pure conjecture but it might explain at least part of the increasingly negative steelhead abundance trend as one moves from north to south down the B C coast.

Some recent results of NOAA’s near shore sampling of coho and chinook illustrate more of the problems now confronting us. What their people are telling us is the research and standard sampling they have been conducting off the Pacific Northwest coast for more than 20 years turned up the fewest juvenile coho and chinook salmon ever in 2017. Here is their graphic:



Couple that with the markedly increased incidence of species known to prey on salmon and it is delusional to believe there won’t be consequences.



One might argue the NOAA surveys don’t necessarily apply to BC steelhead because these recent sample results don’t come from Canadian coastal waters. There may be some validity to that position if one looks far enough north but I struggle to believe predators know where the 49th parallel is. Remember, too, threatened interior Fraser River stocks (the Thompson being the best known of the group) are undoubtedly faced with these conditions, especially if they travel the Juan de Fuca route to reach their ocean rearing areas. I’ll add that I’ve seen a remarkable abundance of mackerel in waters off the northern tip of Vancouver Island in recent years. Observing them preying on juvenile salmon all around Winter Harbour was an eye opener. Then, of course, there have been uncountable numbers of reports of sub-tropical species of fish (sunfish, sharks, tuna, etc.) throughout the BC coast and all the way to Alaska over the past many years. Such encounters were once rare.

Reference to the freshwater side of the steelhead production equation darkens the picture even further. How soon everyone forgets that the summer of 2015 produced the earliest and most prolonged drought conditions on record for many streams in at least south western BC. Desperately low water and much higher than normal water temperatures undoubtedly had major negative consequences for every year class of steelhead present. In most cases that would have been three. The worst off was the 2015 age class, in which case we can expect a very poor smolt crop in 2018. The summers of 2016 and 2017 were also uncharacteristically drought like and warm, although not for as long. That says reduced steelhead smolt production won’t end in 2018. Poor adult returns that produce less than full seeding of habitat that is then subjected to serious drought conditions that further limit production is a bad combination. Steelhead are worse off than salmon which don’t have as long a river dependence and therefore have the potential to rebound more quickly.

When all the pieces of available information are knitted together the inescapable conclusion is the sorts of steelhead returns of we’ve seen to to BC’s streams this year are very likely to be repeated in the foreseeable future. Given a chance, wild steelhead are resilient. That much we know. However, we would seem to be at a point in history where both their fresh water and ocean rearing environments are at the worst we’ve ever measured. What are the management responses going to be if/when the enhanced Babine sockeye return at average levels and Skeena steelhead limp along at an abundance similar to 2017? Alternately, what if that enhanced sockeye stock and most or all of the chinook stocks continue to be depressed such that DFO constrains commercial fisheries and historically timed FN fisheries for both and (again) encourages FNs to target coho and steelhead as compensation? What about the Dean when enhanced Bella Coola chums arrive on top of its steelhead? How about those interior Fraser steelhead? Will the Fraser sockeye and chinook stocks show up in harvestable numbers or will they too continue to be the focus of DFO invoked fishing closures that push commercial and First Nations fisheries onto enhanced chum returning right on top of the peak timing of the last few steelhead?

There is obviously no control over what has already happened in our rivers and at sea. Winter steelhead return outside commercial and FN fishing seasons and should be on the provincial radar but they are not the primary concern right now. Its those revered summer fish that command immediate attention. The commercial and FN fisheries have the greatest identifiable influence on those stocks. Those are forces we can do something about. Dear Ottawa and Victoria, what is your plan for 2018?

Comments 2

  • All bets are off if any harvestable surplus of Adams sockeye show up next year Bob. And if the socks don’t show up…

  • For a thoughtful article and certainly a piece of wonderful writing, if a bit too much of a primer for some, search: Smithsonian magazine “What Can Humans Do to Save the Pacific Northwests Iconic Salmon.” author Priscilla Long.” If nothing much else, savor the language, the imagery of the river and yes, the note of optimism.

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