Ocean Ecosystem Indicators 2008
During 2008, the trend of 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. Actual values for each indicator for all years since 1998, are listed in Table 1.
Pacific Decadal Oscillation—The PDO continued to be strongly negative throughout 2008 (Figure 5). 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.
Summer PDO values in 2008 also indicated that 2008 can be characterized as a year of greatly improved ocean conditions: the average PDO value over the May–September upwelling season was the most negative of our 13–year time series (Figure 2). With a value of –7.63, this summer average PDO was the third most negative on record, exceeded only by values of –10.2 in 1955 and −9.77 in 1950.
Multivariate ENSO Index—The MEI has been negative since June 2007, and has continued negative through 2008 (Figure 4). 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 was 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 (SST)—In line with the strongly negative PDO and MEI, sea surface temperatures at NOAA Buoy 46050 off Newport, Oregon, during winter 2008 (Dec 2007–Mar 2008) were the coldest measured in 11 years. Summer SSTs at Buoy 46050 were also among the coolest measured during our 13–year time series (Figure 5). The only exception to this trend occurred during August 2008, when a month–long warming event was observed (discussed in the Coastal Upwelling section below). Summertime SST values at station NH 05 were also cooler than normal by −0.7°C during 2008 (Figure 5a), with the size of the anomaly second only to that in 2000, when the anomaly was −0.85°C.
Coastal Upwelling—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 (days 204–240). This period of weak winds was reflected in the SST data (Figure 5a) where a warming of 1.6°C was observed for the month of August. Winds resumed in late
August, and although they were steady thereafter, the upwelling season (May–September) was slightly below average (Figure 7).
Deep Water Temperature and Salinity—Temperature and salinity profiles are recorded every 2 weeks during our biweekly monitoring cruises off Newport. During summer 2008, we observed the coldest deep water temperatures since our time series for these data began in 1997 (Figure 12 and Figure 12a). Values in 2008 were similar to but slightly colder than those measured during earlier years with negative PDO values (1999 and 2001). Because sea surface temperatures at NH 05 were also relatively low (except in August), winds during 2008 must have been sufficiently strong to bring upwelled water to the surface. Upwelling promotes high rates of phytoplankton production; thus, in terms of trophic productivity, 2008 was one of the best years in the past decade. This situation contrasts with that of summer 2007, when very cold, deep water was observed on the shelf but seldom reached the sea surface, as reflected by relatively high SST values during 2007 (see Figure 5a and Table 1). Thus productivity was probably lower in 2007 than in 2008.
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 recedes, and the North Pacific High Pressure system begins to build. Winds in the region 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."
In some years, this transition is abrupt; however, in other years, it can be somewhat ill–defined. Instead of reversing suddenly, the winds and currents 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 rigorously the date of spring transition (Figure 9). The upwelling season had a relatively early start in 2008, and when compared to 2005, a year when upwelling started very late, the difference was nearly 2 months. An early transition implies an early start to the spring 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 (Figure 15). When the PDO is negative, surface waters are cold (see Figure 5), 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 lower values were similar to those observed in the 1999–2002 cool phase of the PDO, but were not as consistently low as those seen during the year 2000.
Northern Copepod Anomalies—Copepods are transported to the Oregon coast, either from the north or from the east and 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. We recently recalculated this index, using monthly anomalies of the log biomass of these three species, with the averaging period based on samples collected from 1996 to 2008. In the past, we used quarterly anomalies as the basis for making this calculation; therefore, the values now (based on monthly anomalies) are somewhat different from the old values (based on quarterly anomalies).
Figure 16a shows time series of the PDO and of northern copepod biomass 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 observations were during the 1998 El Niño event (−1.96) and 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 than in 2005 (339 = 102.53).
Of particular interest in 2008 (and 2007) has been the presence in large numbers of the very large and lipid–rich species of the genus Neocalanus. They frequently occur off the Oregon coast during winter and spring, and their presence indicates the presence of subarctic waters off Oregon. However, during both 2007 and 2008, the species Neocalanus plumchrus was roughly 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 the presence of these copepods.
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. 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 being the coastal Gulf of Alaska in spring and coastal central California in autumn). During 2008, the biological transition came very early, in early March (day 64), as shown in Table 1b and Table 2 . This is a positive sign for fisheries because it means that the food chain was populated by northern species very early in the year. Several methods are used to calculate dates of the spring and fall transition, and a compilation of the different methods is available from Columbia River DART (Data Access in Real Time), a project of the University of University of Washington School of Aquatic and Fishery Sciences.
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 (Figure 22); this is a harbinger for strong returns of Columbia River Chinook beginning in 2010.
Catches of Coho in September—Catches of juvenile coho salmon in our September trawl surveys have been another good indicator of rates of return of coho the following year. We were surprised that catches in our September 2008 survey were only average (ranked 6th of 11), even though ocean conditions were the best (1st of of 11) during summer 2008, their first summer at sea.
If adult returns in autumn/winter 2009 are only average, as the catch suggested, 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 upper few meters of the water column. Thus warm SSTs could have been a factor contributing to low survival through both increases in metabolism of the fish and relatively low availability of prey.
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