Research Document - 2001/157

Review of year 2000 return of Barkley Sound sockeye salmon and forecasts for 2001

By K. Hyatt, W. Luedke, P. Rankin, J. Till, D. Lewis

Abstract

Returns of Barkley Sound sockeye have been variable but well below the long term average return of 820,000 adults for the past 7 years (Figure 2). Although variable, recent year returns reflect a continuation of a pattern of predictable variations in ocean climate and survival conditions for juvenile sockeye salmon that have lead to repeated "crashes" (1978, 1985-86, 1989-90, 1994-95) usually followed within 1-3 years by recoveries (1979-81, 1987-88, 1991-93, 1996-98) of WCVI sockeye returns. The prolonged interval of sub-average returns between 1994 and 2000 is anticipated to end in 2001 as ocean climate signals suggest increased marine survival rates for Barkley Sound sockeye smolts migrating seaward during the 1998-2000 interval.

Over the past 13 years, four independent techniques have been tested for their utility in generating reliable pre-season forecasts of Barkley Sound sockeye returns for harvest managers. The four techniques are known as the Salinity Survival Method (SSM), the Survival Stanza Method (SStM), the Sibling Age Class Method (SACM), and the Salmonid Enhancement Program Biostandard Method (SEPB). Updates on the performance of three of these techniques in the year 2000 are as follows:

1. The SStM forecast exhibits the best overall performance with a Mean Absolute Percent Error (MAPE) value of approximately 31% over the most recent 13 years of forecasting (Table 5.). Further, SStM forecasts account for the majority of variations in returns if the extreme observation associated with the 1991 return year is omitted from the analysis (returns = 1.17 SStM forecasts - 66.35, r2 = 0.77, P<0.01).
2. If the year 2000 forecast is excluded, the SSM forecast exhibits the next best performance with a MAPE value of 35% over the most recent 12 years of forecasting. SSM forecasts also exhibited a statistically significant association with returns between 1988 and 1999. However, the SSM forecast was biased high by more than 400% relative to year 2000 returns such that its MAPE value increased to 68.7%. Consequently, the full set of SSM forecasts was reduced to a statistically insignificant relation with observed returns (Table 5.).
3. SEPB forecasts have performed well over some return intervals but not others. During the 1988-1998 testing interval SEPB forecasts exhibited a substantially higher MAPE value (54%) than that displayed by both SSM and SStM forecasts (28-34%). The SEPB forecast, like the SSM forecast was biased high by a large margin (194%) relative to year 2000 returns, although the predictive power of the SEPB forecasts still achieved statistical significance. Large magnitude deviations between SEPB forecasts and actual returns tend to occur in consecutive years which seriously erodes the confidence of harvest managers as well as fishers in their utility.

Forecasts provided by different models exhibit less divergence in predicted returns of Barkley Sound sockeye in 2001 than was the case in the year 2000. Midpoint forecast estimates range from a low of 907,000 (SStM model) to a high of 1,865,000 (SSM model) Barkley Sound sockeye of all ages. Comparative performance of the various forecast options, along with DFO's recent pursuit of a more risk averse approach to management recommends initial adoption of the SStM forecast range of 738,000 (75% probability) to 1,091,000 (25% probability) sockeye as the preferred, pre-season forecast for the year 2001 (Table 13.). However, supplementary information (from coho leading indicator observations) suggests that returns are likely to be closer to the upper than the lower end of this range.

Complete document (PDF, 260 KB)

Accessibility Notice

This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.