Climate Change May Stymie Salmon Recovery Plans

Northwest Fishletter

April 16, 2007

Northwest scientists who juggled five different computer models to complete their analysis say that increasing temperatures could have devastating effects on local salmon populations by 2050, according to an article published earlier this month in Proceedings of the National Academy of Sciences.

The seven scientists from NOAA Fisheries and the University of Washington used two climate models, a salmon population model and a model for land use and hydrology, to estimate that an increase of about 1 degree C could reduce chinook spawning populations in the Snohomish Basin from 20 percent to 40 percent. The range of reduced numbers depended on which climate model was used, while land use was held constant.

The models pegged current wild chinook numbers around 6,000 spawners, higher than the past 20-year average, "but lower than some recently recorded returns. "

Returns over the past few years have been all over the map. According to data from WDFW harvest reports, the 2003 return to the basin was about 5,400 chinook, the 2004 return was a whopping 10,400 and in 2005, about 4,500 chinook returned.

The authors estimated a full restoration strategy in the Snohomish Basin could actually boost spawners by 20 percent in 2050 using the less draconian climate model -- the more pessimistic one showed overall losses to around 5 percent, even with full restoration.

Both climate models showed that a moderate restoration strategy would not overcome the negative effects of warming by 2050, reducing numbers between about 5 percent and 25 percent.

NOAA Fisheries scientist James Battin told Northwest Fishletter that time constraints didn't allow them to estimate what fish numbers would be like from restoration scenarios under current conditions, but he said a moderate restoration strategy was likely to boost numbers in the 15-percent range by 2025 and 23 percent by 2050, while numbers would improve by 46 percent in 2025 and 61 percent if the full restoration strategy was implemented.

The article also pointed out that salmon may be resilient enough to respond better to warming water and higher peak flows, but no adverse impacts were modeled from rising sea levels and warming ocean waters.

The scientists also said recovery efforts may be more beneficial at lower elevations than higher areas that may see more rain and less snow in the future.

They said in the highest-elevation parts of the watershed, where warming effects are estimated to be greatest, there is little potential for future restoration because most areas are already protected. But by restoring juvenile rearing capacity, threatened populations may benefit -- especially groups in the lower watershed, whose numbers may grow to make up for losses at higher elevations. The following links were mentioned in this story:

Projected Impacts of Climate Change on Salmon Habitat Restoration, PNAS, April 5, 2007

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