Latest CBB News | Archives | About Us | Free Newsletter




Latest CBB News
Heat-Stressed Large Sturgeon Dying;States Close Sturgeon Fishing From Bonneville Dam To Mid-Columbia
Posted on Friday, July 17, 2015 (PST)

As many as 80 large, broodstock-sized sturgeon were found dead this week in the Columbia River upstream of Bonneville Dam, triggering a complete closure of fishing for what some are calling “valuable, almost irreplaceable fish.”


Preliminary investigations point to warmer than average water temperatures as the cause of the die-off, prompting the two-state Columbia River Compact to close the river to recreational sturgeon fishing until further notice, effective Saturday, July 18 -- an action that  was unanimously supported by biologists and river guides alike.


At its Thursday call-in meeting, the Compact closed fishing from Bonneville Dam upstream to the Oregon and Washington border. The Washington Department of Fish and Wildlife immediately followed with a closure up through Hanford Reach, including adjacent tributaries.


“What we see in the river is extremely disturbing,” said WDFW’s Guy Norman. “Especially since it is happening to large, broodstock-sized sturgeon at a time when they are actively spawning. While there is no evidence that this is directly related to fishing, it is prudent to minimize the stress on these fish.”


River conditions are lower, warmer and clearer than recent five- and ten-year averages, according to Compact staff. Outflow at Bonneville Dam is 137,000 cubic feet per second, while the five-year average at this time of year (July 1-14) is 287 kcfs. Water temperature at the dam is 73 degrees Fahrenheit, while the five-year average is 65 degrees.


The high water temperatures, biologists believe, is the cause of the sturgeon die-off in the Columbia River, as well as salmon and steelhead deaths in other Northwest rivers, including confirmed mortalities due to warm water in the Willamette, Deschutes and John Day rivers.


“What we’re seeing right now is higher levels of summer mortality and indications that sturgeon are under a lot of stress this summer. This is something we can do immediately to give them some relief,” said Chris Kern, deputy administrator of the Oregon Department of Fish and Wildlife fish division, of the closure.


Robin Ehlke, a member of the Compact staff from WDFW, said that 67 of the sturgeon were found in the John Day Dam pool, 5 in the Bonneville pool, 13 in The Dalles pool and 5 in the McNary pool. WDFW had some information that is not confirmed of dead sturgeon in the Hanford Reach, she added. “There are at least five and it could be as many as sixteen,” she said.


Biologists have been seeing dead sturgeon for the past one to two weeks upstream of Bonneville Dam, but the number of dead fish found significantly increased this week as stream temperatures continue to rise.


“The frequency and magnitude of the reported mortalities in areas upstream of Bonneville Dam have increased sharply in recent days,” the Compact staff report says of the sturgeon deaths, as it recommended the sturgeon angling closure.


Staff is investigating the cause of the sturgeon mortalities, but say that elevated temperatures and low dissolved oxygen levels in the water may be significant factors.


Of the 67 dead sturgeon observed in the John Day pool in the last two weeks, biologists were able to retrieve 29 that were in good enough condition to study.


“Externally, there were no marks or visible trauma, so they were in good physical condition,” Ehlke said. “They had full bellies and there were no hooks in the belly.” Two of the 29 fish had hook marks on the body.


All the sturgeon stomachs were full of sockeye salmon, but it appears that at least most of the salmon had died prior to ingestion. This, according to biologists, is common feeding behavior for sturgeon. 


Biologists are finding a few dead sockeye in the pool as well. There is no confirmation that the sockeye had died of columnares, a bacteria commonly found in fish, but exacerbated by water temperatures that exceed 60 degrees and that has been found in dead salmon in the Willamette and Deschutes rivers.


However, even if that were the cause of the sockeye deaths, WDFW pathologists say that it would be highly unlikely the disease could be transferred to the sturgeon through ingestion.


Although it is rare, this year is not the first time biologists have seen sturgeon die due to warm water. Ehlke pointed to a smaller die-off in the John Day pool a couple of years ago and most recently there was a die-off in the Fraser River in British Columbia.


A more likely cause of the sturgeon die-off is the decreasing amount of dissolved oxygen as the water warms, according to information garnered from the Fraser River sturgeon die-off, Ehlke said. The issue is specific to large sturgeon that typically have a lower metabolic rate than smaller sturgeon and so are less efficient in getting oxygen from the water.


It’s uncertain how this die-off will impact the total abundance of sturgeon in the mid-Columbia River. In the size range of greater than 55 inches long, according to Ehlke, the abundance in the Bonneville pool is estimated to be about 3,000 fish. There are 1,300 fish in The Dalles Pool and approximately 2,800 fish in the John Day pool.


In other action this week, the Compact extended by one day treaty Indian fishing to 6 pm Thursday, July 16. The treaty fishing this week began 6 am, Monday, July 13. The change extends fishing to three and one half days this week. The Compact will meet again Monday to consider more treaty fishing.


At the same time, the Compact rescinded planned commercial gillnetting in the Columbia River downstream of Bonneville Dam. That 12-hour opening was to have been 7 pm Tuesday, July 14 to 7 am Wednesday, July 15. Non-treaty commercial gillnetters have taken 99 percent of their allotted fish, according to Compact staff.


This is despite a higher estimate of the summer chinook run size to 108,000 fish, up from 100,000 fish estimated by the U.S. v Oregon Technical Advisory Committee last week. This is the largest run of summer chinook since 1960. Summer chinook are not listed under the federal Endangered Species Act and is considered a healthy run of fish. All are destined for Priest Rapids Dam.


TAC also increased its estimate of the sockeye salmon run to 500,000 fish, up from 480,000 last week.


Bookmark and Share


The Columbia Basin Bulletin, Bend, Oregon. For information or comments call 541-312-8860.
Bend Oregon Website Design by Bend Oregon Website Design by Smart SolutionsProduced by Intermountain Communications  |  Site Map