Famously, this fall, Sockeye Salmon have returned to spawn in unexpectedly large numbers in the Fraser River system in southern British Columbia. This is after several years of such unexpectedly low returning numbers that commercial fishing ceased. We clearly don’t understand what’s happening, except that we know the predictive models have failed.
Actually, after two and a half years growing to adults in the North Pacific, Sockeye have returned in colossal numbers, 35 million of them – the most in a century – to breed in the inland tributaries of the Fraser River, many swimming for 17 days 480 km up to the 12 km of the Adams River where they spawn in the shallows, and then die.
For a long time, every fourth year the number of returning salmon has been particularly great, celebrated by the quadrennial mid-October festival ‘Salute to the Sockeye’. When a large number spawn, four years later their offspring should return in large numbers. If a small number spawn, four years later the run ought to be small as well.
In fact, in 2006, only 1.5 million fish returned to the mouth of the Fraser. In 2007 only 1.4 million returned, and fishing for them was radically curtailed. In 2008, 1.6 million returned, and the species was ‘red listed’ by the IUCN, identified as threatened. In 2009, when 11 million were expected, only 1.5 million showed up, and everyone agreed a fishery collapse had occurred.
Why so few? Was this the end of the fishery? A Canadian federal inquiry is trying to understand the causes of the collapse, assessing the roles of ocean warming, overfishing, diseases, pollution, sea lice infections, government fisheries policies, and food shortages in the Pacific. A challenge, to say the least.
Some evidence suggests the fish die not long after swimming the gauntlet of 70 possible contaminating fish farms as they head north from the Fraser River as juvenile. And yet the 35 million fish that returned in 2010 also had to swim the same gauntlet of 70 fish farms when they were juveniles. How do we account for that success?
Years of terminally low runs, now the largest run in a century. What on earth is going on?
A recent suggestion is that, when the Alaskan Kasotochi volcano erupted in 2008, it fertilized the Gulf of Alaska with iron rich ash which then supported an explosion of plankton over an area 1000 km wide. This year’s returning Sockeye population would have been there at the peak of the bloom, feeding heavily and growing rapidly. In other words, a one-off event.
Whatever the causes, we now have the image of a spectacular run despite all the other horrible things going on in the ocean’s ecosystems, indicating that recovery of wild Sockeye salmon populations is at least possible – possible perhaps by protecting, nourishing, and increasing the productivity of the Gulf of Alaska. Another huge challenge.
There is alway potentially immense and unpredictable variation in the size of any fish population, even under what we think are relatively stable environmental conditions. Adding then the changes that are occurring in the oceans as a result of ocean warming, overfishing, and contamination, predictability becomes increasingly unlikely. How do you make predictions when the rules are changing in unpredictable ways?
Can we say with certainty what lies ahead for us?
Of course we can: increasing unpredictability.