Large–scale Ocean and Atmospheric Indicators

Local and Regional Physical Indicators

Local Biological Indicators

Indicators Under Development

Introduction to Pacific Northwest Oceanography

Ocean Sampling Methods

Forage Fish and Pacific Hake Abundance

We plan to develop an index that describes food web interactions between juvenile salmon and their fish predators, chiefly Pacific whiting, also known as Pacific hake.  The index will be based on interactions between forage fish (e.g., anchovies, smelt and herrings), juvenile salmon, and hake. 

This interaction is somewhat complex and probably non–linear:  the hypothesis is that during most warm years, hake moves into continental shelf waters, where salmon may be more susceptible to predation.  During cold years, hake feeds in deeper waters offshore, near the shelf break; thus they may not be actively feeding in water inhabited by juvenile salmon.

During cold conditions, where zooplankton production is high, small forage fish biomass increases.  The advantage to salmon of high forage fish abundance is that predators are more likely to "see" forage fish than salmon because there are far more of them present in the water column.  Since forage fish populations do well during cold conditions but tend to crash during warm conditions, there will likely be time lags of one or more years between boom and bust periods.  Thus, the interaction among zooplankton production, forage fish abundance, juvenile salmon survival, and hake predation is likely to be non–linear. 

We have not yet initiated any sophisticated analysis or modeling of these interactions.  Figures 23a and 23b show pronounced interannual differences in abundance, which are in part related to the ocean condition cycles discussed in this report. 

	Figure 23a.	Catches of potential pisciine predators on juvenile salmon from surveys conducted by R. Emmett during May to July, 1998–2006.  Whiting numbers are usually very high during "warm years" such as the 1998 El Niño event and during the first 2 years of a warm PDO (2003-2004); however numbers were surprisingly low in both 2005 and 2006.

For Pacific hake, (Figure 23a) note that low abundances were observed during the 4–year cool period of 1999–2002, and high abundances occurred during three of the warm years (1998, 2003, and 2004).  These correspond respectively to "good" and "poor" periods for coho survival.  We expected high abundance levels for hake in 2005 and 2006, but this expectation was not met, due possibly to the timing of its northward migration.  That is, hake may have moved further north (off Canada) during the warm years of 2004 and 2005, and thus may have been a key predator on salmon only early in the season (May rather than June/July).

Forage fish on the other hand, clearly show a 1–year lag between change in ocean phases and population response:  anomalously low abundances were observed during the first year of a "cool phase" (1999), and anomalously high abundances were observed during the first year of "warm phase" (2003).  Given the failure of hake to maintain high abundances in 2005 and 2006, and the 1–year lag in response of forage fish to changes in ocean conditions, there were no simple linear relationships between either salmon catches or survival and forage fish or hake. 

Forage fish numbers remained low in 2006 (Figure 23b), probably as a result of poor recruitment in 2005.  These low numbers comprise a negative indicator, since juvenile forage fish (ages 0 and 1) are among the favored prey of both coho and Chinook salmon.  Thus salmon may have been food-limited in 2006.  Low numbers of forage fish in 2006 may also be a negative indicator for 2007; however, we will not know the recruitment level of age-1 fish until summer 2007. 

	Figure 23b.	Catches of forage fish during May-July surveys from 1998-2006, carried out by R. Emmett.  Note low numbers of forage fish in 2006; note also low numbers in 1999, demonstrating that there can be time lags of at least one year following a poor year before forage fish numbers begin to increase.  Thus, since numbers were low in 2006, we may not see increased number of forage fish rather in 2008.