Scientists have discovered that management efforts intended to assist migrations of salmon and steelhead trout can have unintended consequences for fish populations. Juveniles that are transported downstream on boats can lose the ability to migrate back to their breeding grounds, reducing their survivorship and altering adaptations in the wild.
Transportation programs have been in place for over three decades to improve the survival of fish that hatch in rivers but migrate downstream to the ocean, where they live most of their adult lives. Adults then swim back up the river to mate, lay eggs and finally die in the same area where they were born. These fish can travel hundreds of miles and make dramatic ascensions up waterfalls and past dams.
When dams block rivers, however, the migrating fish especially juveniles can have a tough time traveling between their spawning grounds and the open ocean.
"Juveniles trying to get back to sea usually go over the spillways or past the dam's turbines," says Matthew Keefer, a biologist at the University of Idaho and the lead author on the study, which appears in the November issue of Ecological Applications.
Going past a dam's turbines, however, can kill many young fish. In response, management efforts help salmon and steelhead trout avoid dams altogether by transporting juveniles past dams toward the ocean on river-faring barges.
But Keefer has found that this free ferry ride can create problems when the juveniles grow up. He and his colleagues Christopher Caudill, Christopher Peery and Steven Lee at the University of Idaho tracked the movement patterns of adult salmon and steelhead trout along the Columbia and Snake rivers in Washington and Oregon. They found that, when compared to fish that migrated naturally, transported juveniles had lower survivorship as adults and were less likely to find their way home.
"Adult fish usually move steadily upstream tow
|Contact: Christine Buckley|
Ecological Society of America