Avian Predation in the Columbia River Estuary

April 14, 1998

Mr. Bob Willis
Corps of Engineers, Portland District
Attn: CENWP-PE-E
P.O. Box 2946
Portland, Oregon 97208-2946

Re: Avian Predation in the Columbia River Estuary

Dear Mr. Willis:

Thank you for participating at the April 8, 1998, meeting with the National Marine Fisheries Service (NMFS), U.S. Fish and Wildlife Service (USFWS), Oregon Department of Fish and Wildlife (ODFW), Washington Department of Fish and Wildlife (WDFW), and the Columbia River Inter-Tribal Fish Commission (CRITFC) regarding tern and cormorant nesting colonies on dredge spoil islands in the Columbia River estuary and subsequent predation on juvenile salmonoids.

The USFWS, CRITFC and Corps indicated at the meeting that additional studies should continue to acquire more information on which to base management decisions. The original objectives of the study were to:

1. Estimate the size of the piscivorous waterbird colonies in the Columbia River, and determine population trends. This has been accomplished. The colonies are huge and have increased at a rapid rate since the construction of nesting islands.
2. Estimate the number of juvenile salmonids consumed by these colonies. This has been accomplished. 1997 estimates are a minimum of 10 million smolts and perhaps 4 times that number. This represents from 25 to over 50 percent of all anadromous salmonid smolts that attempted to pass through the estuary in the spring of 1997.
3. Identify factors that influence avian predation rates on smolts. The creation of artificial nesting, resting and feeding sites, which has allowed the development of the large colonies at the saltwater interface, is the major factor.
4. Recommend ways to reduce predation on smolts, if warranted by the study results. Recommendations in the draft annual report include modification of the habitat, removal of the birds, encouragement of predators.

The CRITFC proposed plan is to conduct one more year of research to:

1. Attempt to refine the consumption estimates with emphasis on cormorants.
2. Attempt to better define factors contributing to predation.
3. Conduct some small experiments with vegetation and decoys to determine the feasibility of relocating the tern colony.

This position was strongly supported by USFWS personnel and some Corps personnel. The position was not supported by WDFW nor ODFW.

Personnel from CRITFC and the Corps state that the 1997 data may be an anomaly, there is not enough data to take action, and we can’t prove that saving 25 million smolts would increase adult returns or aid recovery of listed fish. The issues of laws protecting the birds, such as migratory bird treaties and the need for NEPA compliance prior to major actions were brought up. Largely because of these issues, most of the group felt that it was too late to attempt to reduce predation in 1998. They felt that additional results from this year will be available by late summer and plans for action in 1999 can be made.

The NMFS does not agree that further delay is acceptable. The 1997 smolt losses will reduce the number of adult salmon and steelhead returning in 1998, 1999 and 2000 by tens of thousands of adult fish. We have every reason to believe that 1998 impacts will be similar. Every wild or natural spring yearling smolt consumed by the enhanced bird colonies belongs to a stock that is currently listed or proposed. While we agree that refined estimates of total predation and identification of which stocks of fish are most susceptible would be desirable, listed species cannot support the sacrifice of a high percentage of the population in order to continue studies, and the river managing agencies cannot afford to spend millions of dollars on recovery of listed species to feed artificially enhanced predator populations

The fact that there are thousands of PIT tags on Rice Island and that estimated mortality on outmigrating juvenile salmonids may reach as high as 20 million smolts is evidence enough that action must be taken. The potential for the loss of 20 million smolts is unacceptable, and may, in fact, preclude the ability of some up-river listed stocks to recover.

The Corps should take immediate action to implement a short-term remedy to minimize predation on this year’s out-migrants. To that end, the Corps should immediately begin attempts to dissuade nesting activities on the up-river islands (Rice Island and Miller Sands) through human presence and intervention. In addition, the Corps should also take immediate steps to preclude bird nesting on Corps maintained navigation structures and pilings. Besides having human presence on the islands, placement of fresh dredge spoils on the nesting colony may also be an option.

The NMFS is willing to work on development of a long term strategy that will prevent extensive predation in future years. We recommend that the Corps begin that process as soon as possible.

This page was last modified on Monday, 11-Oct-2004 19:02:00 PDT.

---

Related Information