2008 Ocean Indicators Summary
A summary of ocean indicators of the northern California Current for 2008.
During 2008, the trend towards cold ocean conditions, which started to become established in 2007, has continued. The fact that cold ocean conditions have now become well-established bodes well for marine fish (especially salmon) and bird species since many of them will almost certainly have a good recruitment year.
Below we discuss each of our indicators in the context of how our measurements in 2008 compare to those made by our research team since the late 1990s.
Pacific Decadal Oscillation
The PDO continued to be strongly negative throughout 2008. When we compare PDO behavior over the past 13 years, we find the most negative value for winter occurred in winter 1999–2000, and the second most negative value in winter 2007–2008. This is an important leading indicator: 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 for summer also indicate that 2008 can be characterized as a year of greatly improved ocean conditions. Averaged over the May-September upwelling season, the PDO value was the most negative in our 13–year time series, and the most negative since 1955 -- the summer-averaged PDO in 2008 was -7.63; the next lowest values were -10.2 (in 1955), a similar value, -6.36 was seen in 1956.
Multivariate ENSO Index
The MEI has been negative since June 2007 and has continued negative through 2008. This indicates La Niña, and cold ocean conditions in equatorial waters of the eastern Pacific. La Niña conditions affect the Northeast Pacific through an atmospheric teleconnection, and generally result in colder–than–normal temperatures. Averaged from January to November 2008, the MEI value is similar to that seen during the last La Niña event of 1999 (-0.65 in 2008 compared to -0.85 in 1999). Thus, a strongly negative MEI index is somewhat unusual. This is another positive indicator that the ocean has transitioned into a state highly favorable for salmon survival.
Sea Surface Temperature
In line with the strongly negative PDO and MEI, wintertime sea surface temperatures (SSTs) measured at the NOAA Buoy 46050 off Newport (Dec 2007-March 2008) were the coldest in 11 years. SSTs measured at the NOAA Buoy during the summer of 2008 were also among the coolest measured during our 13-year time series, except August 2008 when a month-long warming event was observed (discussed in the “Coastal Upwelling” section), and Oct-Nov when some warming was observed. Summertime SST values at station NH 05 were also cooler than normal by -0.7°C, second only to the year 2000 when the anomaly was – 0.85°C.
Upwelling was initiated early in the year (day 88; 28 March) but did not become strong until one month later, on 28 April. Winds remained steady through much of the summer except for a lull (and southwesterly storms) in August, from days 204 through 240. This period of weak winds was reflected in the SST data, where warming of 1.6°, was observed for August. Winds resumed in late August, and although winds were steady the upwelling season (May-September) was slightly below average.
Deep Water Temperature and Salinity
Temperature and salinity profiles are recorded every two weeks during our biweekly monitoring cruises off Newport. Values were similar to those measured during the earlier years with negative PDO values – 1999 and 2001, but slightly colder. Sea surface temperatures at NH 05 were relatively low (except for August), indicating that winds were sufficiently strong to bring upwelled water to the surface, promoting high phytoplankton production rates. Thus, 2008 may be among the most productive years of the past decade. This situation contrasts with summer 2007, when very cold, deep water was observed on the shelf but seldom reached the sea surface, as shown by the relatively high SST values during 2007. Thus productivity was probably lower in 2007 than in 2008.
During winter months off the Pacific Northwest, winds are often from the south or southwest, driven by the Aleutian Low-Pressure system, which sits 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 offshore. In the spring, the North Pacific High-Pressure system begins to build, and the winds reverse direction and begin blowing from the north towards the equator. Coastal currents reverse direction, sea level drops, and waters from the north (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.” In some years, the transition is abrupt, but in other years, it can be somewhat ill–defined in that the winds and currents do not reverse suddenly. Rather they can start and stop, then start again. Logerwell et al. (2003) used various techniques for smoothing the time series of sea level and daily upwelling indices to define the date of spring transition rigorously. The year 2008 had a relatively early start to the upwelling season, and when compared to a year with a very late transition (2005), the difference was nearly two months. An early transition result implies an early start to the upwelling season, which is good for salmon (Logerwell et al. 2003).
Copepod Species Biodiversity (Richness)
Monthly measures of copepod species composition track those of the PDO and SSTs 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 2008. These values are similar to those observed in the 1999–2002 cool phase of the PDO, but not as consistently low as seen during the year 2000.
Northern Copepod Anomalies
Copepods are transported to the Oregon coast either from the north or from the east & south. Copepods that arrive from the north are cold-water species that originate from the coastal Gulf of Alaska and are referred to as "northern copepods." Their presence indicates that coastal Gulf of Alaska waters 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. We recently re-calculated this index using the three species’ log biomass’s monthly anomalies, with the averaging period based on the samples collected from 1996-2008. In the past, we used quarterly anomalies as the basis for making this calculation. Therefore, the values we now use (based on monthly anomalies) are somewhat different from the old values (based on quarterly anomalies).
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 was during the 1998 El Niño event (-1.96) and during the summer of 2005 (-1.78). 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 1.78 + 0.75 = 2.53, or 339 times greater in 2008 compared to 2005 (339 = 10^2.53).
Of particular interest in 2008 (and 2007) has been the presence in large numbers of the very large and lipid-rich Neocalanus species. They frequently occur off the Oregon coast during winter and spring months, and their presence indicates the presence of subarctic waters off Oregon that originated from the deep waters of the Gulf of Alaska. However, during both 2007 and 2008, the species Neocalanus plumchrus has been 4-5 times more abundant than during the previous "cold phase" of the PDO. Moreover, high numbers were seen far offshore—to at least 125 miles from shore—suggesting that the more oceanic species of fishes, such as sablefish, will also benefit from their increased biomass during the past two years.
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. The data lags the physical transition due to the time lag between the date when the coastal currents begin to reverse and the date when animals from distant sources arrive at the Oregon coast (i.e., from the coastal Gulf of Alaska in spring and from the coastal central California in autumn). During 2008, the transition came very early, in early March (day 64). This is a positive sign for fisheries because it means that the food chain was populated by northern species very early in the year.
Catches of Spring Chinook in June
Pelagic trawl surveys have been carried out for 11 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 Columbia River Chinook’s strong returns beginning in 2010.
Catches of Coho Salmon in September
Catches of juvenile coho salmon in our September surveys appears to be another good indicator of rates of return of coho the following year. Catches in September 2008 were average (rank of 6 out of 11), suggesting average returns in fall 2009. We were surprised to have caught relatively few juvenile coho salmon in our September survey. If it is true that returns are only average in autumn/winter 2009 (whereas ocean conditions during their first summer at sea (2008) were the best in our 11-year time series, suggesting high returns), the reason for average returns might be the 35 days of warm ocean conditions observed from 22 July until 22 August led to their demise. We suggest this because coho salmon reside within the upper few meters of the water column. Thus, warm SSTs could possibly be a contributing factor both through increased metabolism of the fish plus relatively low availability of prey.