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Scientists Share Signals for Clues to Ocean Abundance by Bill Rudolph NW Fishletter, October 22, 1996

Researchers around the Pacific Rim are looking at everything from satellites to sea lion whiskers for clues to one of the greatest global puzzles--what makes the ocean tick?

They count tree rings, study baleen from bowhead whales, pick through mud from the bottom of Alaska lakes and study sediments off Santa Barbara where one scientist has discovered a 1,500 year record of past fish populations. Others have scanned historical wind records and found that since the turn of the century, summer is now two months longer off the West Coast.

These are just a few of the fascinating facts presented before a group of scientists at a week-long conference in Nanaimo, B.C., the fifth annual meeting of PICES, the North Pacific Marine Science Organization.

Soft-spoken Seattle oceanographer Curtis Ebbesmeyer told the group the transition from winter to spring off the mouth of the Columbia River occurs a month sooner than it did around 1900. The transition comes about when winds switch from prevailing southerlies to northerlies and the coast-hugging fresh water plume from the river discharge fans out and moves towards the southwest in summer. The record shows that fall now comes a month later, when winds switch back to southerlies and the river plume again hugs the coast.

Ebbesmeyer and co-authors Rich Hinrichsen, and James Ingraham Jr., looked at the implications of this phenomenon for the Columbia region. Since juvenile fish feed in the area around the river plume (it's where nutrient-rich, deeper saline waters are transported into the photic zone), they think it is important to document the timing of these transitions since the intensified food chain is so important to the health of young salmon.

If fish emerge from the river before the spring transition has occurred, the authors expect juvenile mortality to be increased. This could have major implications for hatchery releases and fish barging schedules. Fish barged downstream in the spring reach the estuary three weeks ahead of their river riding counterparts.

But a longer summer could mean good news for salmon. The upwelling season would last longer, affecting circulation of estuarine water bodies like Georgia Strait and Puget Sound.

Prof. James Anderson from the University of Washington addressed that issue in a separate paper, noting that hatchery fish could exhibit more variability in year-class strength than a wild stock because they arrive downstream in such a narrow window of time compared to a wild stock's traditionally protracted migration.

Anderson said tag studies have found that late migrating juveniles (barged), had a two-fold increase in survival over early migrating fish. He cited a 1996 study (Deriso, Marmorek, and Parnell) that attempted to separate hydrosystem effects from year-to-year effects, and showed that the mortality rate of spring chinook exhibited a pattern tied to the Pacific Northwest Index (PNI), a group of temperature and precipitation measurements that reveals a pattern of alternating warm/dry and cold/wet climate regimes approximately 20 years long. In 1976 the region moved out of a cold/wet regime that correlates with lower salmon mortality rates into a warm/dry period that has not been kind to West Coast salmon. The region may soon be cycling back again.

In that vein, J.J Polovina of the NOAA Honolulu Laboratory told the group of his work studying the biological effects of the strong/weak atmospheric oscillations over the ocean. He reported that the strong current gyres in both the subarctic and subtropics started to weaken after 1988-89. By using historical data on sea level height that goes back nearly 100 years, he has figured that the North Pacific gyres have spun-up and spun-down four times between 1910 and 1995.

Satellite altimetry suggests that circulation of the gyres has been stronger the past couple of years, which, according to Polovina, "could signal the beginning of a shift to a decadal period of strong ocean circulation." The subtropical gyre is a downwelling gyre that could provide the West Coast with the nutrient base responsible for improved fish abundance.

Japanese researchers have evidence of cycles from their vantage point, too. Shoshiro Minobe of Hokkaido University reported on a 50- to 60-year oscillation he has detected over the North Pacific, and others reported on important changes in fish stocks off Japan after 1976.

The group was awed by Bruce Finney's results from core sediments from Alaska lakes. He used them to trace variations in sockeye salmon abundance back 500 years, by sampling the cores for Nitrogen-15, an isotope that comes only from the ocean, that is brought back to the lakes in salmon when they return to spawn. Finney's work has mapped periods of abundance and decline from systems on Kodiak Island--peaks in the late 1800s, and declines in the early 1800s and mid-1900s that correspond to periods of colder temperatures.

Perhaps the most unusual work was presented by D.M. Schell of the University of Alaska who has examined whale baleen and sea lion whiskers for trace isotopes of carbon that he hypothesizes may show a 40-percent reduction in basic plankton production in the Bering Sea during the past 20 years.

The most all-encompassing study is Tim Baumgarnter's work with sediments from the Santa Barbara Basin which contain enough fish scales to estimate alternating sardine and anchovy abundance back nearly 2,000 years. Baumgarnter's sediment analysis shows evidence of an approximate 60-year cycle--sardines like warm phases, anchovies like cold--that may reflect interdecadal fluctuations in climate on a scale never before seen by fisheries-oriented researchers. He speculated that overall, there has been a large decrease in upwelling over the past 2,000 years.

Just what mechanisms may run these cycles is the subject of much speculation. Super-computer modellers have tried to corral the basic energy interactions between the ocean and the atmosphere. One such model has come up with a predicted 20-year time frame for a southern ocean heating event to circulate around the Pacific Basin.

What these findings and speculations tell salmon biologists is a lesson in humility. As University of Washington researcher Nate Mantua, along with co-authors Steven Hare, Juan Zhang, John M. Wallace, and Robert Francis, put it in a paper presented at the Nanaimo proceedings, "Management goals, such as the current legislative mandate to double Washington State salmon production may simply not be attainable when environmental conditions are unfavorable. Conversely, in a period of climatically-favored high productivity, managers might be well-advised to exercise caution in claiming credit for a situation that may be beyond their control".