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Seasonal to Interannual Forecasts

Forecasting Oregon Coho Marine Survival

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April 2007 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 2006 (before ocean entry) 11.65°C Well above average (highest since 1999)

Unfavorable
Spring Transition Date, 2006 Day 112 (April 22) About average Neutral
Neah Bay Coastal Sea Level (proxy for upwelling and alongshore transport), April-May-June 2006 -30.64 mm On the high side Somewhat unfavorable
Oregon Coastal Sea Surface Temperature, January-February-March 2007 (after ocean entry)

9.21°C

 

 Cold Favorable

Current Forecast

Issue date: April 30, 2007

FORECAST RETURN RATE FOR ADULTS RETURNING FALL 2007:

Forecasted Jan-March 2007 Sea Surface Temperature
Forecasted Return Rate for Fall 2007 (mean rate)
9.21°C
4.5% (+/- 0.9%)

Ocean conditions, as measured by our simple model, were moderately good for OPI coho smolts in 2006. 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).
Although Jan-Mar SST in 2005 was above average and unfavorable, January through March SST in 2007 was quite cold and favorable.

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%
  

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.