Forecast of Adult Returns for Coho in 2008 and
Chinook Salmon in 2009
From the colorized table below, one can see that the recent 3–year period of poor ocean conditions (2003–2005) has come to a close, with improving conditions in 2006 and greatly improved conditions in 2007. Indicators and their values were evaluated by year, with color assigned based on rank among the past 10 years (see charts below). For example, in 2007 average sea–surface temperatures in summer at NOAA Weather Buoy 46050 were the 9th highest of the past 10 years (indicating poor upwelling of cooler, nutrient–rich waters). Thus the SST at NOAA Buoy 46050 was ranked 9th in 2007. Low ranks indicate better conditions and higher ranks worse conditions for salmon. The ranking system is shown in greater detail below, but in brief, ranks of 1–4 were coded green, 5–6 yellow, and 7–10 red.
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Table 1. |
Ocean ecosystem indicators of the Northern California Current. Colored squares indicate positive (green), neutral (yellow), or negative (red) conditions for salmon entering the ocean each year. In the two columns to the far right, colored dots indicate the forecast of adult returns based on ocean conditions in 2007. |
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Most indicators in 2007 pointed toward greatly improved ocean conditions compared to the previous few years. Indicators that point to good salmon survival included a cold ocean in winter/spring 2007, an early spring transition date, high biomass of cold–water lipid–rich copepods, and a long upwelling season. Negative indicators included weak upwelling in late spring and summer, very warm sea surface temperatures, and low catches of juvenile coho in September surveys.
The chart below provides more information about the color coding used in Table 1. Again, lower numbers indicate better conditions, or "green lights" for salmon growth and survival, with ranks 1–4 green, 5–6 yellow, and 7–10 red. To arrive at these rank scores, the past 10 years of sampling data were compared among one another. Thus for each indicator, a given year will receive a rank score between 1 and 10.
Naturally, these scores are assigned based on the type of data collected. For example, higher sea–surface temperatures in summer translate to higher (worse) rank scores, while higher catches of coho in September will receive lower (better) rank scores.
In future years, as more data are collected, the range of possible scores will increase. Note also that some indicators have 2 years with the same score. For example, among all years for which we have data, the best in terms of deep–water temperature was a tie between 2001 and 2002. Thus there are two ranks of 1 and no rank of 2 for this indicator.
To generalize conditions for each year, the sum of all the rank scores for that year is divided by the number of indicators observed in that year. Mean ranks are then compared among years to give a generalized concept of "good" vs. "bad" ocean conditions for salmon in a given year.
Note from the adult return data above that the 4–year period of cold ocean conditions (1999–2002) resulted in good returns of Chinook salmon. In contrast, the warm ocean conditions from 2003 to 2006 correspond with declining returns. We expect at least one more year of poor returns from this period, after which returns should begin to increase, so long as the cold ocean conditions observed in 2007 continue into 2008 and beyond.
Coho Salmon—Although the indicators were sending very mixed messages overall, we expect improved survival for coho that went to sea in 2007 (and which will return in fall 2008) as compared to the past few years. As an example of the range in estimated return rates for OPIH fish among different indicators, a regression of return rates of coho salmon vs. catches of coho in September surveys suggests only 2% of the coho will return in 2008. However, the relatively early transition of the zooplankton community in spring, and the high biomass of cold–water zooplankton species suggest an adult return rate closer to 4.1%, a much larger proportion.
Chinook Salmon—Ocean conditions at the time of ocean entry and through the month of May 2007 were very good. Since spring Chinook juveniles reside in waters off Oregon and Washington for only a few weeks before migrating north to unknown waters, their survival might have been relatively well supported by these conditions. These fish could begin to return as early as spring 2009.
Data used in the rank scores above are shown in the chart below. Note that counts of spring and fall Chinook salmon at Bonneville Dam are shown lagged by 3 years. For example, the number listed for 1998 indicates fish that returned in 2001. This lag in timing is used because Chinook lives in the ocean for 1–5 years before returning to freshwater. For coho, the ocean life is 1–3 years; thus a lag of only 1 year is used.
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