Forecasts and Planning Tools

Seasonal to Interannual Forecasts

Forecasting Oregon Coho Marine Survival

Archive copy - Feb 2006

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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 2005 (before ocean entry) 10.74° C Above average

UNFAVORABLE

Spring Transition Date, 2005 Day 145 (May 25) Extremely late UNFAVORABLE
Neah Bay Coastal Sea Level (proxy for upwelling and alongshore transport), April-May-June 2005 -16.09 mm Among the highest on record UNFAVORABLE
Forecasted Oregon Coastal Sea Surface Temperature, January-February-March 2006 (after ocean entry) 11.65°C
(mean value for January only)
Well above average UNFAVORABLE

Current Forecast

Issue date: February 1, 2006

FORECAST RETURN RATE FOR ADULTS RETURNING FALL 2006:

Forecasted Jan-March 2006 Sea Surface Temperature
Forecasted Return Rate for Fall 2006 (mean rate)
11.65°C
(mean value for January only)
~0 to 0.8% (+/- 0.8%)

Ocean conditions, as measured by our simple model, were extremely poor for OPI coho smolts in 2005. The spring transition was one of the latest on record and spring sea level was one of the highest (low sea level is indicative of good upwelling and strong north-south transport). Additionally, Jan-Mar SST in 2005 was above average and unfavorable, and January SST in 2006 is well above average and unfavorable.

Note that during past years with such unfavorable conditions (like 1983 and 1997 outmigration years), the model has predicted near-zero survival rates while actual observations were ~2% for 1983 and ~1% for 1997 outmigrants, respectively.

Next Forecast Update:
Spring 2006 (approx. April 2006)

Past Forecast Performance

Coho Returns (Year)
2002
2003
2004
2005
2006
Forecast
4-8%
5-7%
0-2%
0-1%
0-0.8%
Observed
2.6%
3.9%
2.5%
   

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.