OREGON STATE UNIVERSITY

El Nino forecasts could help save coho salmon

10/23/1996

CORVALLIS - The ability to forecast the onset of an El Nino would help efforts to stem the decline of coho salmon on the West Coast, suggests a research report issued by scientists at Oregon State University.

The economic value of improved El Nino forecasting to the coho fishery varies from $250,000 to $900,000 a year, depending on the accuracy of the forecast, the interdisciplinary team of scientists found.

The researchers combined biological, statistical and economic models to measure the long-term benefits of incorporating information about El Nino in management decisions for the coho salmon fishery. The research was funded by a grant from the National Oceanic and Atmospheric Administration.

The report supports doubling the number of wild coho allowed to enter coastal streams to spawn and reducing by as much as 75 percent the yearly coho hatchery production. The findings corroborate recommendations of Oregon's Coastal Salmon Restoration Initiative, established by Gov. John Kitzhaber.

"Improved El Nino forecasts would allow fishery managers to make more effective decisions and perhaps reduce the need for drastic short-term measures, such as closing the commercial and recreational coho fishing seasons," said Richard Adams, a professor of agricultural and resource economics who works with the OSU Agricultural Experiment Station.

Coho salmon along Oregon, Washington and California have been in steep decline since the late 1970s. In an attempt to halt the loss of coho, the National Marine Fisheries Service is considering listing coho as an endangered species. The listing would result in lengthy and constant review by federal agencies of many activities that occur in the coastal zone, including public and private land use, release of hatchery fish and regulation of fisheries. El Nino is part of a global climate system called the "southern oscillation" that affects weather throughout the world. In El Nino years, West Coast water temperatures become abnormally warm, which disrupts the upwelling of colder, nutrient-rich water containing the species coho depend on for food.

With their usual food supply unavailable, a larger number of salmon die prematurely. Those that do survive have lower average weights and the females produce fewer eggs.

Although the capability to predict an El Nino already exists, its accuracy is only slightly better than guessing, according to the report. However, forecasting accuracy is likely to improve due to ongoing NOAA data collection and monitoring efforts.

In 1982-83, the West Coast experienced an El Nino now thought to be one of the worst this century. This unanticipated El Nino had a devastating effect on coho salmon and played havoc with the assumptions upon which fishery management policies were based.

For example, fishery experts had predicted that nearly 1.6 million wild coho would return to spawn in Pacific Northwest streams that year. Only an estimated 667,000 showed up, or 42 percent of what had been expected.

"If accurate forecasts of the 1982-83 El Nino had been available and incorporated into fishery management decisions prior to the 1983 event, the effect of El Nino might have been less severe," Adams said. "Incorporating forecasts in subsequent years would also have helped to avoid extreme measures, such as closing the fishing season."

El Ninos may last from a few months to a few years. A recent, lingering El Nino is thought to have contributed to the current low population level of coho that led to the closure of the commercial and recreational ocean coho salmon fishing seasons from 1994-96. Other factors contributing to the decline of coho include dams, destruction of spawning and rearing habitat, high harvest rates, and the introduction of hatchery coho.

El Ninos vary in their intensity. Seven notable El Ninos have occurred in the past 100 years. Very strong ones occurred in 1925-26 and 1982-83, and strong ones took place in 1899-1900, 1932, 1940-41, 1957-58 and 1972-73.

"Historical catch statistics of Oregon salmon indicated that the abundance and average size of coho were below normal during these events," said David Sampson, a fisheries scientist in the OSU Department of Fisheries and Wildlife and member of the El Nino research team.

The impact of an El Nino is not uniform along the Pacific coast, according to the report. Even during strong events, the coho off Washington and British Columbia may not be as susceptible to ocean changes. And research on the abundance of Alaska salmon shows no appreciable connection between coho abundance and El Nino.

The primary indicator of an El Nino is the southern oscillation index, a measurement of the difference in the atmospheric pressure between Easter Island and Darwin, Australia. These differences usually occur 12-18 months before an El Nino occurs on the West Coast of the United States.

NOAA makes El Nino forecasts on an annual basis. Because these forecasts are available 12-18 months ahead of time, the researchers recommend that harvest rates and hatchery releases be adjusted in anticipation of the El Nino. Their research showed that, over time, a strategy of incorporating this information would yield higher benefits to society.

They also recommend changes in the number of wild coho allowed to migrate to their native streams to spawn.

"Current coho management policies call for 200,000 wild coho to return and spawn each year," Sampson said. "We concluded that the optimal level should be around 400,000 fish each year, depending on the predicted strength of the El Nino."

Other scientists on the interdisciplinary team were Andrew Solow, statistician, Woods Hole Oceanographic Institution; Stephen Polasky, OSU agricultural economist; and Christopher Costello, graduate student in the OSU Department of Agricultural and Resource Economics.