A summary of ocean indicators of the northern California Current for 2009.
During 2009, the trend of cold ocean conditions, which started to become established in 2007, continued only through July. After that, the ocean began to warm significantly, leading to detrimental changes in the pelagic food web and likely high mortality of juvenile salmonids.
Here we discuss each of our indicators in the context of how our measurements in 2009 compare to those made by our research team since 1998.
The PDO continued to be strongly negative through April 2009, but then became less negative and then turned positive in August 2009. However, by November 2009, the PDO once again turned slightly negative. When we compare PDO behavior over the past 13 years, we find the most negative value for winter occurred in winter 2008–2009 (Nov-Feb), the second most negative value in winter 1999-00 and the third most negative values during 2008-09. Winter PDO values are important leading indicators of ocean conditions because Logerwell et al. (2003) showed that one prerequisite for good coho salmon survival is a cold winter preceding the spring when fish enter the sea. We assume that the same is true for yearling Chinook salmon.
PDO values in 2009 changed sign to positive in August 2009, signaling a change from the very productive ocean conditions observed for nearly two years to poor ocean conditions: in 2008, the total of the PDO values over the May–September upwelling season was the most negative of our time series, with a value of – 6.1, however in 2009, the summer-averaged PDO was only the 5th highest, with a value of -1.11.
The MEI was negative from June 2007, continued to be negative through 2008 (a positive sign), but changed to positive in May 2009, a negative sign. This indicates the La Niña and cold ocean conditions in the eastern Pacific’s equatorial waters have come to an end. It is clear that an El Niño is developing in equatorial waters; NOAA climate scientists are predicting that the effects of this El Niño will be felt in the Pacific Northwest during winter 2009 and spring 2010. However, at the time of this writing (January 2010), there are as yet no clear signs of an El Niño event in coastal waters off Oregon or Washington.
During 2009, the trend of cold ocean conditions, which became established in 2007, persisted through 2008 but began to fade beginning in mid-May of 2009. The cold period did continue intermittently through mid-August due to strong upwelling winds but was interrupted by several major relaxations of the upwelling (and significant warming), in June, mid-July, then from mid-August to mid-September (SST data from the NOAA Buoy 46050, located 22 miles off the coast of Newport). The latter relaxation of the winds resulted in water that was nearly four °C warmer than average. The warmest temperature was observed on 19 September (17.3°C).
Summertime SST values at station NH 05, five miles offshore of Newport, measured biweekly during our hydrographic cruises, were only slightly warmer than normal, +0.44 °C during 2009, expected with a weakly negative PDO and strongly positive MEI indices.
Upwelling was initiated early in the year (day 82; 23 March) and continued into September and October). However, upwelling was never established for any lengthy periods. Rather the process was interrupted by five major events when upwelling relaxed, causing downwelling at the coast. The first downwelling event (early April) did not result in anomalously warm water. However, the other four events resulted in onshore transport of very warm water, clearly seen in the SST time series. These warm water “downwelling” events occurred in mid-June, mid-July, and throughout much of August, then September.
During winters off the Pacific Northwest, winds often originate from the south or southwest, driven by the Aleutian Low-pressure system, which persists over the Gulf of Alaska. These winds cause coastal currents to flow northward and onshore, raising sea level at the coast and transporting plankton from the south (central California Current) and from offshore. In spring, the Aleutian Low weakens, and the North Pacific High-Pressure system begins to build. Winds off the coast of Oregon and Washington reverse direction and begin blowing from the north towards the equator. Coastal currents also reverse direction, sea level drops, and north Pacific waters (from the coastal Gulf of Alaska) begin to appear off the Pacific Northwest. This signals the start of the upwelling season. The "date" when this transition takes place is known as the "spring transition."
The spring transition came early in 2009, day 82 (23 March) however, winds were weak and inconsistent, especially after May. An early start to the upwelling season is a necessary condition for good survival; however, in 2009, despite the early start of the upwelling season, upwelling was weak and ended early (early September).
Temperature and salinity profiles are recorded every two weeks during our biweekly monitoring cruises off Newport. During summer 2009, deep waters were warmer and fresher than in other years. The presence of warm water of lower salinity is consistent with the lack of consistent and strong upwelling in that it indicates that surface waters from offshore dominated the continental shelf in 2009.
The upwelling season began on 23 March (day 82); however, the end data is more ambiguous; one could select 1 September; however the warm period that persisted through much of September was interrupted by a strong upwelling event that lasted for three weeks (from 19 Sep to 10 Oct). After this date, upwelling ceased. Thus we select 10 Oct as the end of the upwelling season.
Species richness is simply the number of copepod species in plankton samples. Monthly averaged values of copepod species composition continue to track the PDO and SST quite closely. When the PDO is negative, surface waters are cold, and the copepod community is dominated by only a few cold–water, subarctic species; however, when the PDO is positive, SSTs are warm, and the community is dominated by a greater number of warm–water, subtropical copepod species. We found moderately low species–richness values during 2009 but not as low as during 2008. Species richness is correlated with coho survival one year in advance of their return to their natal streams to spawn, making this index a potentially useful forecasting tool.
The year 2008 had the second-highest biomass of northern copepods since 1996 (a value of 0.75), with the highest value observed in 2002 (0.83). In contrast, the smallest biomass observations were during the 1998 El Niño event (−2.08) and the summer of 2005 (−1.89). Biomass of northern copepods has been steadily increasing since the dismal summer of 2005. For example, the difference in log10 biomass between 2005 and 2008 was 1.89 + 0.75 = 2.64, or 436 times greater in 2008 than in 2005 (antilog 2.64 = 436). Values for 2009 were still strongly positive (0.54), similar to values seen in 2007 (0.499)
The biological spring transition is defined as the date when the zooplankton community has transitioned from a warm–water "winter" community to a cold–water "summer" community. In most years, there is a time lag between the date when coastal currents begin to reverse (the physical spring transition) and the date when animals from distant sources arrive in waters off the Oregon coast (distant sources such as the coastal Gulf of Alaska in spring and coastal central California in autumn). During 2009, the biological transition came very early, in early March (day 64). This is a positive sign for salmonids fisheries because it means high ocean productivity and indicates that the food chain was populated by northern copepod lipid-rich species early in the year.
Pelagic trawl surveys have been carried out for 12 years (since 1998). In the June 2008 survey, we collected the highest number of juvenile spring Chinook salmon of the 11–year time series; this is a harbinger for strong returns of Columbia River Chinook beginning in 2010. However, catches in June 2009 were lower, but still fairly high, earning a rank of 4.
Catches of juvenile coho salmon in our September trawl surveys have been another good indicator of rates of return of coho the following year. Catches in the September 2009 survey were the lowest on record (12th of 12), a negative sign.
If adult returns in autumn/winter 2009/10 are only average, as the catch data suggest, then the reason for the average returns might be the 35 days of warm ocean conditions observed from 22 July until 22 August 2008. This period of warm conditions may have led to their demise because coho salmon reside within the water column’s upper few meters. Thus warm SSTs could have been a factor contributing to low survival through both increases in the metabolism of the fish and relatively low availability of prey. We suggest a similar scenario for coho during the summer of 2009 due to two extended periods of warm ocean conditions throughout most of August and much of September 2009.
Cape Shirreff Field Camp, Livingston Island, Antarctica. Credit NOAA Fisheries/Sergio Morales
NOAA Ship Bell M. Shimada during 2010 Pacific Hake Inter-Vessel Calibration off Eureka, California. Credit: NOAA
