2010 Ocean Indicators Summary
A summary of ocean indicators of the northern California Current for 2010.
The trend of cold ocean conditions, which started to become established in 2007, ended in mid-2009 due to the emergence of an El Niño event at the equator. This event continued into spring 2010 before dissipating. Because of the 2009-10 El Niño event, the ocean began to warm and remained warm through April 2010. A cooling trend resumed in May 2010. Thus, 2010 began as a “warm year,” began to cool in May, but by July, the ocean was the coldest observed in recent years. Thus we had very mixed signals in 2010, making it difficult to offer any reliable outlooks in returns of coho salmon in 2010 and Chinook salmon in 2010. We blame this on the pronounced El Niño/La Niña cycle which gave us “the best of times” and “the worst of times.” Here we discuss each of our indicators in the context of how our measurements in 2010 compare to those made by our research team since 1998.
Pacific Decadal Oscillation
The PDO turned positive in August 2009 and remained positive through the winter of 2009-2010. Winter PDO values are thought to be important leading indicators of ocean conditions. Logerwell et al. (2003) showed that one prerequisite for good coho salmon survival is a cold winter preceding the spring when they enter the sea. We assume that the same is true for yearling Chinook salmon. The PDO values during the winter of 2009-10 were positive (i.e., warm), an indicator of “poor ocean conditions” during the winter immediately before the 2010 salmon broods entered the sea. PDO values in 2010 changed sign to negative in May 2010, signaling the end of the El Niño and the beginning of productive ocean conditions. The PDO value averaged over the May–September 2010 period was the 3rd most negative of our time series. The fact that the PDO was negative throughout the summer of 2010 is an indicator of “good ocean conditions.”
Multivariate ENSO Index
The MEI turned positive in May 2009 (signaling the start of a small but perhaps significant El Niño event) and remained positive through May 2010, indicating poor ocean conditions during late summer 2009 and through the winter of 2009-10. Perhaps more significantly, the MEI went negative in June 2010, but from August through November 2010, extremely negative values were seen, which were similar to values not seen since the mid-1950s and the mid-1970s. The persistence of the El Niño through winter and spring 2010 suggests “poor ocean conditions” during that period; however the strongly negative values (a.k.a. La Niña) in late summer-fall indicates “good ocean conditions” and points to the likelihood of especially good ocean conditions in 2011.
Sea Surface Temperature (SST)
During 2010, the ocean was warm (anomalies of ~ 1 deg C) but certainly not as warm as in past El Niño events –anomalies of + 2 to +3 deg C were seen during the 1997-98 event and + 2 deg C during the 2002-03 event (SST data from the NOAA Buoy 46050, located 22 miles off the coast of Newport). SST anomalies were consistently + 1 deg C from January through most of April before the first major cooling event began in mid-May 2010. With the onset of the La Niña pattern, near-record cooling was observed in July and August 2010, with anomalies of -3 to -4 deg C observed. However, significant warming was again observed in September-November.
Summertime SST values at station NH 05, five miles offshore of Newport, measured biweekly during our hydrographic cruises, were near the long-term average of 11.55 deg C.
Upwelling was initiated in early April (day 95; 06 April), one week earlier than the average start date, and continued until mid-September (day 256), nearly a month earlier than the average ending date (day 283; Oct. 10) for the upwelling season. The upwelling season was initially interrupted by a strong down-welling event towards the end of May. The strong downwelling event dampened the trend of increasingly cool water temperatures on the shelf and contributed to a negative anomaly for April-May upwelling and the 3rd worst start to the upwelling season observed in the past 13 years.
Physical Spring Transition
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 date in 2010 came on day 95 (6 April) however, northerly winds were weak and inconsistent until day 160 (9 June). Thus, even though the strong winter storms ended in early April, consistent upwelling winds did not commence until early June, after which they were quite strong. The upwelling season ended early, on 13 September.
Deep Water Temperature and Salinity
Temperature and salinity profiles are recorded every two weeks during our biweekly monitoring cruises off Newport. Data from 2010 clearly show the differences in ocean conditions observed in spring (at the end of the El Niño) compared to summer (during the La Niña). During spring 2010, deep water temperature and salinity were slightly warmer and fresher than “normal.” In contrast, the data from summer 2010 indicated that the deep waters were the coldest of our 14-year record (data from 1997-present) but not quite as salty as other cold years. The presence of warm low salinity water in spring indicates relatively “poor ocean conditions”, however the sudden change to cold and salty water in July 2010 indicates that the latter half of the upwelling season could be characterized as having “good ocean conditions.”
Length of the Upwelling Season
Even though the strong winter storms ended in early April and the first puff of upwelling winds began on 6 April (day 95), significant amounts of upwelling did not begin until 9 June. The season ended early, on 13 September, resulting in an upwelling season that was 161 days in length, or 20% shorter than the climatological average. Despite the shortness of the season, some of the coldest waters of the decade were observed during the summer of 2010.
Copepod Biodiversity (Species Richness)
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 very high values of species–richness values throughout 2010 that rivaled values from the 1998 El Niño event, thus given that the 2009-10 El Niño was judged as a relatively weak event (i.e., SST anomalies were not particularly warm), we are uncertain how to interpret these very high values of copepod biodiversity. Species richness is weakly 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. An average value of 13.2 species in 2010 suggests low coho returns in 2011.
Northern Copepod Anomalies
Copepods are transported to the Oregon coast, either from the north/northwest or from the east/south. Copepods that arrive from the north are cold-water species. They originate in the coastal Gulf of Alaska and are referred to as "northern copepods." The presence of northern copepods indicates that waters from the coastal Gulf of Alaska are being fed into the coastal California Current. The "northern copepod index" is the log biomass anomaly of three species of cold-water copepods: Calanus marshallae, Pseudocalanus mimus, and Acartia longiremis. The index is calculated monthly with the averaging period based on samples collected from 1996 to 2009.
Note that the data from 1996 to the present closely track the PDO. This is especially significant for the summer of 2010 when the PDO had negative values for all months from May-September (the 3rd highest values since 1998), and the log of the northern copepod biomass anomaly was also quite high, the 4th highest since 1998). These are both indications of “good ocean conditions” and stand in stark contrast to the “copepod biodiversity index,” which points to “poor ocean conditions” in 2010. The “northern copepod biomass index” suggests coho returns of 3.7% in 2011 as well as above-average returns of both fall and Chinook salmon in 2010.
Biological Spring Transition
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 2010, the biological transition came late, on day 135 (15 May). This is a somewhat negative indicator for salmonids fisheries in 2011 and 2012 because it means that ocean productivity was probably low early in 2010 when juvenile salmon first entered the sea (in April/May).
Catches of Spring Chinook in June
Pelagic trawl surveys have been carried out for 13 years (since 1998). Catches of spring Chinook salmon have been high for the past three years, with the highest catches in 2008 and the 4th and 5th highest catches in the June 2009 and June 2010 survey, respectively; results from the June 2010 surveys suggest above-average returns of spring-run Chinook salmon to the Columbia River in 2012.
Catches of Coho in September
Catches of juvenile coho salmon in our September trawl surveys have been a fairly good indicator of rates of return of coho the following year. Catches over the past two years have been among our lowest since 1998. The September 2010 survey caught the 11th lowest number of coho since 1998 (September 09 saw the lowest, 13th of 13 surveys). This suggests very low coho returns both in 2010 as well as 2011.
When all of the indicators are taken as a whole (see overall ranks of all indicators presented in the bottom line of data in Table 3), the year 2010 has a rank of 8 out of 13, suggesting below-average returns of coho in 2011 and Chinook in 2012. However, certain indicators suggest the potential for above-average returns: the strong La Niña conditions that became established in late spring 2010, the negative PDO and positive northern copepod biomass anomalies averaged over the May-September period, very cold deep waters on the continental shelf from July-September, the winter-time biomass of fish larvae, and the high catches of spring Chinook in June. These all point to higher than average spring Chinook returns in 2012. Oddly, despite what appears to be good ocean conditions in 2010, surface waters (where coho live) were quite warm, upwelling was delayed, and the season was among the shortest in recent years, copepod biodiversity was very high, and coho catches in September were among the lowest of our records. All of these point to “poor ocean conditions”. Therefore, because of these mixed signals we are not able to provide a definitive outlook or forecast. We are actually excited about this outcome since once the results of the run-sizes are known, we may, in the end, find that we need to separate our indicators into sets, with one that works well for coho salmon but with another set that works best for spring Chinook. Moreover, we may find that fall Chinook need a third set of indicators, and so on. In 2011 we will explore sets of indicators that might be useful in providing outlooks for the returns of sockeye and chum salmon, as well as for steelhead.