Science Advisory Report  2011/052

Pre-season run size forecasts for Fraser River Sockeye & Pink Salmon in 2011

Summary

• Salmon forecasts remain highly uncertain due to both stochastic (random) variability in annual survival rates and uncertainty about changes to average survival (productivity) experienced by stocks from the egg stage to adult returns.

Fraser River Sockeye

• Fraser Sockeye survival has been particularly uncertain in recent years due to systematic declines in productivity exhibited by most stocks and the extremely variable productivity in the past two brood years (2005 and 2006 brood years corresponding, respectively, to 2009 and 2010 returns for most Sockeye).
• Alternative assumptions of Sockeye productivity are presented as separate forecasts: ‘Long-Term Average Productivity’ (Table 2) and ‘Recent Productivity (brood years: 1997-2004)’(Table 4). The ‘Recent Productivity’ scenario is considered most plausible. The ‘Long-Term Average Productivity’ scenario is considered plausible, but less likely.
• Under the assumption of ‘Recent Productivity’, there is a one in ten chance (10% probability) the Fraser River Sockeye Salmon return will be at or below 1.0 million, and a nine in ten chance (90% probability) it will be at or below 12.1 million. The mid-point of this distribution (50% probability) is 3.2 million (there exists a one in two chance the return will be above or below this value assuming recent stock productivity). Under the assumption of ‘Long-Term Average Productivity’, there is a one in ten chance (10% probability) the return will be at or below 1.7 million, and a nine in ten chance (90% probability) it will be at or below 15.1 million. The mid-point of this distribution (50% probability level) is 4.6 million.
• The 2011 forecast has a higher age-5 proportion (35-50% of age-4 + age-5 returns) than average (~20%), given the generally higher brood year escapements for age-5 Sockeye and the use of average (in the case of ‘Recent Productivity’ forecasts) to above average (for ‘Long-Term Average Productivity’ forecasts) 2010 age-4 productivity, to forecast age-5 returns for some stocks.

Fraser River Pink:

• Based on the assumption of ‘Long-Term Average Productivity’, there is a one in ten chance (10% probability) the Pink return will be at or below 9.2 million and a nine in ten chance (90% probability) it will be at or below 37.5 million. The mid-point of this distribution (50% probability level) is 17.5 million. Recent productivity scenarios were not compared for Pink Salmon as they have not exhibited similar declines in productivity as Fraser Sockeye.
• The Fraser Pink forecast is highly uncertain because predictions are made outside the observed data range given the record high fry abundance in 2010.

This Science Advisory Report has resulted from a Fisheries and Oceans Canada, Canadian Science Advisory Secretariat, Regional Advisory Meeting of February 4, 2011 on 2011 Fraser River Sockeye and Pink Salmon forecasts.  Additional publications from this process will be posted as they become available on the DFO Science Advisory Schedule.

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