Stock assessment and forecasting challenges

It’s always a challenge in the gloom of mid-winter storms to be thinking ahead to the summer fishing season ahead and what opportunities there will be, but nonetheless planning for the seasonal management regime is well underway for 2017. In fact the deadline for input into what is termed the salmon integrated fishing management plan (IFMP) is the beginning of February.

For salmon stocks not listed as “of concern” – yes, it’s true, there are many and don’t let the media or anyone else convince you otherwise! – planning is fairly straightforward. And for those salmon stocks that are persistently at low abundance – and yes, it’s equally true that there are more of these than anyone would like – planning is similarly fairly straightforward, albeit with a different objective, to constrain mortality rather than allow it. Complications arise in developing harvest opportunities for those salmon stocks and species which can bear fishing pressure but which are co-migrating at the same time with those that can’t.

And then there are those salmon stocks and species that move between the two, varying considerably in abundance between years making fisheries management planning for or around them a particular challenge. In the absence of certainty DFO utilizes the precautionary principal, meaning that in some years at least some management flexibility and subsequent harvest opportunities are foregone but which avoids fishing pressure that could compromise the survival of the stock of concern.

A prime example of this are a stock of coho salmon known as the Interior Fraser River (IFR) management unit, which includes all the coho spawning in the Fraser River watershed, including the Thompson drainage, upstream of the Hell’s Gate Canyon. Management of the IFR coho MU and potential impacts to them from fisheries for all species of salmon by all fishing gear types has been the framework around which planning for salmon fisheries across southern BC has been based for almost twenty years.

For reasons still not entirely understood coho in the southern part of their range have since the early 1990’s been especially susceptible to periods of poor survival, mostly but not entirely linked to changes in the productivity in the near shore marine environment, although with climate change more severe impacts to freshwater survival are being recorded as well. With one exception, in 2014, since 1998 Canada has managed all SBC salmon fisheries fisheries in a highly risk averse regime, with the general objective to keep the exploitation rate (ER, which is to say the sum of all the harvest rates in individual fisheries) on IFR coho at 3% or less. Considering that prior to the early 1990’s the ER on this salmon stock was frequently 70% or more you can appreciate what a change this has meant to the broad fishing community, essentially ending retention of all wild coho unless there is considerable certainty that IFR coho are not present. And in this IFR coho have served as a proxy for the management of all wild coho around southern BC except in those places where local stocks are doing better, for example on the west coast of Vancouver Island.

In the absence of directed harvest in most years IFR coho have managed to exceed the short-term recovery goal of 20,000 fish and increasingly meet or exceed the long-term recovery goal of 40,000 fish. However, and most unfortunately, there appears to be no consistency to the rebuilding trend, with several years of solid returns well above the long-term goal (e.g. 2012 & 2013) followed by the stock plunging back down again (e.g. 2014 & 2015). The escapement in 2015 was about 14,000 fish, a quarter the return in the 2012 broodyear and this despite the highly restrictive fishing management regime.

Some people quite rightly have asked if forecasting could predict these swings in abundance to better allow for a more flexible fishing management regime if sufficient abundance allowed. Perhaps so but the record over the past two years isn’t encouraging although it has to be said once again that the resources that government directs to fisheries science are consistently inadequate so possibly the forecasting could be improved. That said, the 2015 forecast for the Interior Fraser coho MU was about 50,000 fish, within a range of 32 to 77,000; as noted it didn’t even make half the lowest end estimate.

Conversely, for 2016 some good news. Although the assessment is not yet complete, as these fish sometimes don’t move onto the spawning grounds until the new year, the preliminary estimate is that the return is likely similar to the 2013 broodyear, in the 50,000+ fish range, confounding the forecast of 14,000 coho within a range of 9 to 23,000. Sometimes there’s no rhyme nor reason and the best science in the world might not detect the environmental changes that would signal these big swings in abundance.

As mentioned earlier, with a warming climate the freshwater survival of coho has become more challenging for them, especially those that originate from small creeks. The long, hot and dry summers beloved by so many human inhabitants of this land are increasingly becoming a death sentence for juvenile coho that have to make it through to the second spring following their birth before they migrate to sea.

One highly important tool in the assessment of wild coho survival and abundance around the Strait of Georgia is the fence/trap operation on the Black Creek. Situated just above tidewater with the objective of measuring the numbers of both out-migrating smolts in the spring and returning adults in the fall this fence, which has been in continuous seasonal operation since 1984, is now the last one remaining of three, the other two having fallen victim to the steady erosion of DFO’s budget over time.

The fall of 2013 saw one of the largest adult returns in the 30+ year time series at the fence, 10,000+ coho, yet the smolt count in 2015 was the lowest since 1996. The fact that the subsequent adult return in fall 2016 was about 4,000 coho indicates that the 2015 smolt cohort actually did pretty well at sea, consistent with the Interior Fraser coho stock, but if you didn’t know how the fry survival in freshwater had been and simply compared the 2013 broodyear with the 2016 return it could easily have given the impression that poor at-sea conditions had hammered coho once again.

All this is to describe just how complicated assessing and then managing salmon and their dependent fisheries is and how critical it is to enable the best possible science to underpin the decision making, something that Canadian federal governments regardless of political persuasion seem loath to do. Things might be marginally better under the present Trudeau administration but there’s a long way to go before the stock assessment resourcing can be considered anywhere close to adequate. Fish here in the Pacific region and the fishing community that depends on them deserve better.