ISAB Says Fish Plans Need To Deal With Climate Change  

Northwest Fishletter

May 24, 2007

Warming temperatures could cause changes in both freshwater and ocean habitat, short-circuiting salmon recovery efforts over the long term while having a huge effect on the hydro system, according to the Independent Scientific Advisory Board review of the potential impacts of global warming on regional salmon populations.

With more rain and less snowpack expected in the future, the board cited a 2004 study that estimated the FCRPS may have to forgo up to 20 percent of its firm power production commitments just to meet flow targets developed in the recent hydro BiOps. The shortage is expected because of the reduced prospects for filling reservoirs after so much water is used to help migrating fish.

The ISAB findings presented last week to the Northwest Power and Conservation Council noted that the subbasin fish and wildlife plans developed in a lengthy council process have "poorly addressed" impacts of future climate change.

However, the board also said the technical nature of climate change information has made it hard for planners to interpret and use it, and that the situation is improving, as future climate projections at the subbasin scale are becoming more available.

The board cited a recent U.W./NMFS study that estimated warming effects on one Puget Sound watershed. The report said a moderate restoration strategy would not overcome negative warming effects by 2050, and would reduce salmon numbers between about 5 percent and 25 percent. Even with a full-restoration strategy, overall salmon numbers were likely to decrease by five percent.

"The changes caused by climate change will be similar to those changes already caused by the hydro system," the board said, also noting that the warmer climate won't change river conditions as drastically as construction of the power system did.

With reservoirs warming water earlier and keeping it warm longer than before the dams were built, Columbia Basin water could heat up by one degree C by 2040--that's still less effect than the dams had on historical conditions, according to the report.

But water temperatures could rise beyond that in future years, with potential losses of at least 40 percent of salmon habitat in Oregon and Idaho by 2090. Washington would be less affected, with about a 20-percent habitat loss expected.

The board expects detrimental effects on eggs, as well, from higher flood flows and earlier hatch. Bull trout habitat would likely be most severely affected--from 22 percent to 92 percent of their cold water habitat may disappear.

Warmer freshwater habitat could also mean that juvenile fish, by hatching earlier, would be smaller and more vulnerable to predators.

The Columbia estuary could be negatively affected as well, if fresh water species move in and compete with juvenile salmon for food--or use them for food.

With earlier snowmelt, juvenile salmon may migrate earlier in the spring, when ocean conditions are likely to be poor, because higher temperatures could delay the onset of that spring upwelling that brings nutrient blooms and food for migrating fish.

Warm ocean temperatures could also affect the diet of some salmon species--small-shelled animals may suffer from reduced numbers because increasing CO₂ levels lower the pH of seawater, which lowers the amount of carbonate available for shell building.

If fish range farther north to find adequate food supplies, they may take longer to mature and return later than they do now.

But the board's scientists said some actions could mitigate adverse affects from earlier snowmelt and increasing temperatures--controversial strategies like adding more cool water for fish flows. Such drastic action might mean that more dams would have to be built to store water for augmentation.

They also supported removable spillway weirs to keep fish from hanging out too long in the warm water of dam forebays, and they called for drawing water from lower strata in the reservoirs to cool fish ladder passage.

They also advised that transport activities for fall chinook be more in tune with temperature criteria, and even suggested looking into transporting returning adults through the lower Snake to bypass lethal late-summer water temperatures.

Other ways to cope could be to expand predator control programs of species now left alone, such as bass, walleye and channel catfish.

The ISAB also suggested opening more back-channel habitat along mainstem reservoirs to encourage increased flow to reduce water temperatures and provide cool-water refugia.

To reduce ocean mortality, they said, fish transport could be timed to coincide with more favorable conditions by the time they reach the ocean. Also, during periods of poor ocean productivity, it might be prudent to release fewer hatchery fish in order to improve survival of wild stocks, but they said this issue needed more research.

They also said managers should adapt their harvest levels to ocean conditions to ensure fish populations could be recovered when conditions are bad, and that enough would reach spawning areas to recolonize freshwater habitats when conditions are good.

The ISAB's recommendation to augment summer and early autumn flows to reduce future temperature increases has put them in something of a bind--one they acknowledge, because they readily admit such a strategy will probably mean increasing water storage in the basin--and that means more dams.

They said "careful consideration of the benefits and negative impacts ... will be required. Such consideration should occur in the near future if storage capacity is to be increased in time to address climate change impacts."

The following links were mentioned in this story:

Climate Change Impacts on Columbia River Basin Fish and Wildlife, ISAB, May 11, 2007

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