Forecasts and Planning Tools

Seasonal to Interannual Forecasts

Forecasting Oregon Coho Marine Survival

May 2008 archive copy

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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

Environmental Index Observed/
Forecasted
Conditions
Relative Condition Implication for coho marine survival
Oregon Coastal Sea Surface Temperature, January-February-March 2007 (before ocean entry) 9.94°C Cold

Favorable

Spring Transition Date, 2007 Day 74 (March 15) Near average Favorable
Neah Bay Coastal Sea Level (proxy for upwelling and alongshore transport), April-May-June 2007 -93.65 mm Low Favorable
Oregon Coastal Sea Surface Temperature, January 2008
(after ocean entry)

8.92°C

 

Cold (among the coldest on record) Strongly favorable

Current Forecast

Issue date: May 8, 2008

FORECAST RETURN RATE FOR ADULTS RETURNING FALL 2008:

Observed Jan-March 2008 Sea Surface Temperature
Forecasted Return Rate for Fall 2008 (mean rate)
8.64°C
5.4% (+/-0.8%)

Ocean conditions, as measured by our simple model, were better than average for OPI coho smolts that entered the ocean in 2007. The spring transition was near average and spring sea level was low (low sea level is indicative of good upwelling and strong north-south transport). January through March SST in 2008 was among the coldest on record and strongly favorable.

Based on these favorable conditions this model projects return rate of 5% (+/- 1%) for fall 2008. However, jack (2-year-old male) returns in the fall of 2007 to the Columbia River were at low levels typical of the 1990s, resulting in a projected return rate of 0.9%. It was also notable that upwelling in June, July and August 2007 were weak, and coastal ocean temperatures failed to cool as they typically do. These summer conditions are not considered in our simple model, but may help to explain the discrepancies between our model forecast and the jack-based forecast that calls for much lower return rates.

Past Forecast Performance

 

Forecast Year
(Y1)
Year prior (Y0)
(before ocean entry)
Oregon SST, Y0
(Jan-Mar)
Spring Transition, Y0 Neah Bay Sea Level , Y0 (April-June) Oregon SST, Y1
(Jan-Mar, after ocean entry)
Predicted OPI survival for Y1 Observed OPI survival for Y1
2000 1999 9.53°C Day 91 -142.73 mm 10.5°C 6%
2001 2000 10.5°C Day 72 -70.03 mm 10°C 5%
2002 2001 10°C Day 61 -122.43 mm 9.7°C
8%
2.6%
2003 2002 9.7°C Day 80 -141.29 mm 10.8°C 7% 3.8%
2004 2003 10.8°C Day 112 -60.82 mm 10.5°C 1% 2.6%
2005 2004 10.5°C Day 110 -75.02 mm 10.74°C 0.5% 1.9%
2006 2005 10.74°C Day 145 -16.09 mm 11.65°C 0.3% 2.0%
2007 2006 11.65°C Day 112 (April 22) -30.64 mm 9.21°C
4.5%
2.2%
2008 2007 9.21°C Day 74 (March 15) -93.65 mm 8.64°C 5.4% TBA

See Figure 1 for the model’s performance at hindcasting for the period 1969-1998.

click image to enlarge

model’s performance at hindcasting for the period 1969-1998

Figure 1

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.

click image to enlarge

conceptual model of key environmental processes that influence coastal ocean food webs

Figure 2

For More Information

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.