Forecasts and Planning Tools

Seasonal to Interannual Forecasts

Forecasting Oregon Coho Marine Survival

People Involved

• Elizabeth Logerwell (contact person), NOAA Fisheries/Alaska Fishery Science Center
• Nathan Mantua, University of Washington, Climate Impacts Group
• Peter Lawson, NOAA Fisheries/Newport Lab
• Robert Francis, University of Washington, Climate Impacts Group and School of Aquatic and Fishery Sciences
• Vera Agostini, University of Washington, Climate Impacts Group and School of Aquatic and Fishery Sciences

Background

Marine survival rates for Oregon coho salmon are influenced by several sequential environmental processes that affect coastal ocean food webs:

1. Winter climate prior to smolt migration from rivers to the ocean;
2. Date of occurrence of the “spring transition”, the period when alongshore winds (off the Pacific Northwest (PNW) coast) shift from being mostly northward to mostly southward;
3. Total coastal upwelling during the spring;
4. Ocean conditions during the maturing cohos’ only winter at sea.

By monitoring conditions during each cohort’s lifecycle, we can provide an experimental forecast of Oregon coho marine survival rates.

Recent and Forecasted Conditions

Current Forecast

Issue date: May 20, 2009

FORECAST RETURN RATE FOR ADULTS RETURNING FALL 2009:

Ocean conditions, as measured by our simple model, were favorable for OPI coho smolts that entered the ocean in 2008. The spring transition was near average and spring sea level was very low (low sea level is indicative of good upwelling and strong north-south transport). January 2009 sea surface temperature (SST) was 8.64°C, which was among the coldest on record and strongly favorable. February SST was fairly typical (9.02°C) but March (9.67°C) and April (9.69°C) were among the coldest years in the time series.

Based on these favorable conditions this model projects return rate of 13.4% (+/- 1.7%) for fall 2009. This preliminary forecast predicts higher marine survival rates than any we've previously predicted (dating back to 2000). This prediction is also higher than any in the historical database for OPI coho survival that begins in 1969. However, there is some doubt as to whether this high survival rate will materialize. Because 13% has never been observed, the 13.4% prediction falls outside the range of historical survival rate variations that are part of the data used to parameterize the model. On the other hand, our forecast for last year was closer to the actual marine survival than the prediction based on jack returns.

Past Forecast Performance

Forecast Methodology

To better understand and predict Oregon coho marine survival, we developed a conceptual model (Figure 2) of key environmental processes that influence coastal ocean food webs and ultimately marine survival rates for Oregon coho salmon. The key processes are sequential:

1. winter climate prior to smolt migration from rivers to the ocean;
2. date of occurrence of the spring transition, when alongshore winds (off the PNW coast) shift from being mostly northward to mostly southward;
3. total coastal upwelling during the spring;
4. ocean conditions during the maturing cohos’ only winter at sea.

We then parameterized a general additive model (GAM) with Oregon Production Index (OPI) coho smolt-to-adult survival estimates from 1970-2001 and the environmental processes listed above. For the model training period (smolt year data from 1969-2000), the GAM explained 75% of the variance in observed OPI smolt-to-adult survival rates.

Selected References

Logerwell, E. A., N. J. Mantua, P. Lawson, R. C. Francis, and V. Agostini. 2003. Tracking environmental processes in the coastal zone for understanding and predicting Oregon coho (Oncorhynchus kisutch) marine survival. Fisheries Oceanography 12(3):1-15.