BIRD PREDATORS MAY LIMIT SALMON RECOVERY





        Cormorant,  Caspian tern, and gull colonies on the Columbia River


are large and may limit salmon recovery.  Research by Dr. Carl Schreck,


Oregon State University, and Dr. Dan Roby, Columbia River InterTribal Fish


Commission has accumulated information that show heavy predation by birds on


juvenile salmon.  This research is co-funded by the U.S. Army Corps of


Engineers and the Bonneville Power Adminsitration.


        The results from the first year of study have shown there are nine


major colonies of fish eating birds in the lower Columbia River, and most of


these colonies have grown in recent years.  


        The Rice Island Caspian tern colony has increased over 600% during


the last eleven years and the East Sand Island double-crested cormorant


colony has increased over 160% during the last five years.  Both of these


colonies are in the Columbia River estuary.  The Richland, Washington area


supports a mixed California and ring-billed gull colony of over 35,000


nesting pairs.  


        The Caspian tern feed mostly on juvenile salmon (86% of the fish


consumed), with steelhead, coho and chinook smolts making up the majority of


the salmonids taken.  This was discovered when a high density of PIT tags


were found on the colony's nesting area on Rice Island.  Based on PIT tag


recoveries, these birds ate six to twenty million juvenile salmonids during


1997.  This Caspian tern colonly is the largest in North America with 8,000


nesting pairs.  


        Double-crested cormorants also feed heavily on juvenile salmonids.


This colony of 6,000 nesting pair is believed to be consuming millions of


salmon smolts each year.  


        The study indicates that hatchery juvenile salmon are more


vulnerable to avian predation than are wild salmon.


        Dr. Schreck and his team say that various sources of stress to


juvenile salmonids in the Columbia may contribute to reduced health of


smolts, increasing their vulnerability to avian predation.  Premature


development may be causing juvenile salmonids to avoid sea water therefore


residing in the surface waters which are fresh, making them more vulnerable


to tern predation.  The stress factors may include passage conditions at the


upstream dams, barging and disease.  


        In an article that appeared in the Oregon State University Fisheries


and Wildlfie Department News and Views (Winter 1997), the author Dan Roby


cautioned fish managers to not jump to conclusions because variations in


weather and ocean conditions and smolt behavior likely result in considerable


annual variation in predation rates.  


        But if brid predation is a problem, what can be done about it?  The


article suggests a few:  1) modify habitat features to reduce foraging


efficiency of bird predators, 2) modification of nesting habitat, and 3)


biological control of brid predators through encouraging natural predation


or competition.


        "Measures...to reduce avian predation will, however, need to be


justified, particularly if those measures include direct control of bird


populations", said Roby.  The OSU article speculated that "bird management


activities" might be controversial among the public.


        Future research must tackle numerous uncertainties.  What is the


magnitude of this predation on juvenile salmon;  is this predation the


result of natural conditions or is it related to unnatural problems such as


poor fish health or an excessive number of birds?   If the fish are


unhealthy, they may perish anyway.  The OSU article speculates that


"management alternatives focusing on birds may be effective and efficient


components of a comprehensive plan to restore runs of Columbia Basin


salmonids."