Report: Sea lions may take 20% of springers

After snatching and eating almost 9,000 spring chinook salmon and steelhead through May 31, the number of pinnipeds lurking at Bonneville Dam has dropped to just one, a California sea lion. Steller sea lions were completely absent by the end of May.

Sea lions at Bonneville this year ate more than twice what they’ve averaged over the past ten years. Of the estimated 8,986 fish, California sea lions (CSL) ate 71 percent of the adult salmonids – both spring chinook salmon and steelhead – while Steller sea lions (SSL), those found most commonly along the Oregon and Washington coastlines, consumed 29 percent.

Estimated consumption of chinook salmon by CSL was 6,267 fish and by SSL was 2,459.

However, biologists estimate that as many as 3,300 sea lions had resided in the Columbia River from Astoria to Bonneville Dam this spring and could be taking as much as 20 percent of the entire spring chinook salmon run in the river.

Together, the two species residing at Bonneville consumed an estimated 5.5 percent of adult salmonids migrating through the dam’s fish ladder, according to the sixth and last pinniped status report by the U.S. Army Corps of Engineers for the 2016 monitoring season. The report covers the period January 1 to May 31 and includes observed sea lions, observed catch and an expanded estimate of sea lion catch that includes nights and weekends when direct observations were not possible.

The report, “Status Report – Pinniped Predation and Deterrent Activities at Bonneville Dam,” by Patricia L. Madson and Bjorn van der Leeuw, both of the Corps, can be found at http://www.nwd-wc.usace.army.mil/tmt/documents/fish/2016/160415_Bonneville_pinniped_update.pdf

The decline in the number of sea lions at the dam has been dramatic, but is normal this time of year. In the last two weeks of May, the number of CSLs declined from 37 in mid-May to just 1 at the end of the month. SSLs were gone by the end of the month.

The first CSL was observed on February 26. The daily average for CSLs was 4 in March, 22 in April, and 31 in May, according to the sixth report. The maximum number of CSLs observed on a single day at the dam was 66 on May 4. The Corps documented 131 uniquely branded individual CSLs through May 31. Of these, 89 have been seen in multiple years and 42 were newly identified.

SSLs were present when observations began January 4. The daily average for SSLs was 13 in January, 5 in February, 14 in March, 40 in April, and 21 in May. The maximum number of

SSLs observed on a single day at the dam were 54 on May 4. The Corps documented 39 unique individual SSLs this season. Of these, 36 were observed in previous years and three were newly identified.

The maximum number of pinnipeds (CSLs and SSLs combined) on a single day was 120 on May 4, higher than the previous record of 116 on April 22, 2015.

Observed catches by the marine mammals was less than half of what the Corps estimates the actual (expanded) catches (nights and weekends added) to be. Of course, catches declined significantly as the sea lions departed the dam in late May. Observed catches of adult salmonids through May 31 was 4,196 fish, including 4,094 spring chinook and 102 steelhead.

Some 1,150 chinook were taken by SSLs and 2,944 by CSLs. SSLs took 43 steelhead and CSLs took 59.

SSLs took more white sturgeon than CSLs with 26, while CSLs were observed to take just 3. The expanded number of sturgeon taken was a total of 86. However, predation on sturgeon was far below the 10-year average. No sturgeon catches were observed the last two weeks of May.

Bonneville Dam is not the only dam with sea lions. Up to three were observed at The Dalles Dam tailrace feeding on salmonids. One was a branded sea lion and was last seen at The Dalles Dam May 4, but sighted afterwards in the Bonneville Dam tailrace. One branded CSL was observed in the Bonneville pool and has been seen there in multiple years.

To discourage sea lion presence and predation, the Columbia River Inter-Tribal Fish Commission used boat-based hazing, beginning March 7. CRITFC hazed Mondays, Thursdays, and Fridays, but that ceased May 16.

am-based hazing by the U.S. Department of Agriculture began March 8. USDA hazed seven days a week in 8-hour shifts, but that ceased May 31.

Sea lion exclusion devices (SLEDs) were deployed at powerhouse 2 on October 26, 2015 and the remaining SLEDS were installed by March 5, 2016. Specifically, the SLEDS at powerhouse 1 were installed on March 1, 2016, the report said.

After several SSLs were seen climbing over the floating orifice gates (FOGs) at powerhouse 2 and entering the fishway, according to the report. wood panels were placed on top of the FOGs to prevent this behavior from recurring. To date there have been no additional reports of sea lions accessing the fishway channel via the FOGs.

Pinniped management activities by the states of Oregon and Washington were ended May 24 at Bonneville Dam for 2016. Some 59 CSLs were removed in 2016 under the section 120 permit. Fifty CSLs were branded at Bonneville Dam in 2016. In May, 16 CSLs were trapped and euthanized.

Sea lions are protected under the Marine Mammal Protection Act. However, the states are able to trap and euthanize California sea lions under a section 120 permit under the MMPA. The latest permit expires June 30 and NOAA Fisheries is currently mulling over renewing that permit for five more years. The states applied January 27, 2015, to NOAA for an extension of their previous Section 120 permit.