Ocean changes are affecting salmon biodiversity and survival

Posted Aug 4, 2015 by Karen Graham
El nino-associated changes at the Equator may be putting the biodiversity and survival of two species of North Pacific salmon at risk, according to a study conducted by researchers at U.C. Davis.
A school of Chinook salmon.
A school of Chinook salmon.
Zureks (CC BY-SA 3.0)
Researchers studied two species of North Pacific salmon, the Chinook, and the Coho salmon, tracking them from hatcheries in North America between 1980 and 2006.
The scientists found that before the 1990s, the survival rates of the Chinook and coho salmon varied separately from each other. But as the study went on, researchers were surprised to see that the survival rates of the two species were becoming more similar.
Lead author of the study, Patrick Kilduff, a postdoctoral scholar under Louis Botsford in the UC Davis Department of Wildlife, Fish and Conservation Biology says, “Two species that historically have had different responses and seem to be very different in their coastal-wide patterns now appear to be more synchronized." He added that this can be very good, or very bad for everyone, sort of like the stock market.
Actually, this could have some bad economic consequences because if the catch of one species is low, this means the catch of the other species is low, too. The study points out that this synchronous response to ocean changes represents a loss of biological diversity and is something that cannot be addressed by freshwater management.
Researchers were left with an interesting question. They wanted to know what was causing the increasingly similarity between the two species. Was it a change in coastal ocean food-web linkages, or was it a change in the species themselves?
Looking at El nino and salmon survival
Let's define some terms. First, there is something called the Pacific Decadal Oscillation (PDO). The PDO is a recurring, El nino-associated Eastern Pacific warming pattern. It recurs every 20 to 30 years. Historically, Pacific salmon were thought to be influenced by the PDO.
The PDO is the leading EOF of monthly sea surface temperature anomalies over the North Pacific after...
The PDO is the leading EOF of monthly sea surface temperature anomalies over the North Pacific after the global mean sea surface temperature anomaly is removed. The global pattern is computed as the regression of monthly sea surface anomalies on the principal component time-series. Data derived from HadISST (1880-2010).
Another term, called the North Pacific Gyre Oscillation (NPGO), has become increasingly important, and its impact on salmon is not yet well understood. The NPGO is something relatively new. It was first described in 1932 by researchers with the Royal Meteorological Society and is described as a north-south "seesawing" in sea level pressure over the North Pacific. This movement of the NPGO impacts weather conditions from Siberia to North America.
The North Pacific Gyre Oscillation (NPGO) is an oceanic expression of the NPO. Source: Journal of Cl...
The North Pacific Gyre Oscillation (NPGO) is an oceanic expression of the NPO. Source: Journal of Climate, May 2008.
What is interesting about this study is that researchers found that coho and Chinook salmon survival rates were more affected by the NPGO than by the PDO. “Changes in equatorial conditions lead to more of the large-scale Pacific Ocean variability being explained by North Pacific Gyre Oscillation, and it’s influencing the survival of salmon from Vancouver Island south to California,” Kilduff said.
The study was published in the journal Proceedings of the National Academy of Sciences Aug. 3, 2015, and entitled: "Changing central Pacific El Niños reduce stability of North American salmon survival rates."