Bridge blocks migrating trout

Talk about a bridge to nowhere. A floating bridge in Washington is hindering the passage of migrating steelhead trout, making the fish more likely to be eaten by seals.

The 1.5-mile-long Hood Canal Bridge allows drivers to easily hop between two peninsulas across part of Puget Sound. But the bridge’s concrete pontoons, which reach 3.6 meters underwater, may be less convenient for fish trying to migrate to the Pacific Ocean.

A research team tagged 582 steelhead smolts with transmitters and set up four receiver arrays in the region to detect the transmitter signals. From 2006 to 2010, 27 of the fish appeared to have died near the Hood Canal Bridge. In contrast, the authors detected only one likely death in the other monitored areas.

The transmitter signals received near the bridge suggest that “smolts in the Hood Canal migrate on a relatively tortuous path,” the team writes in PLOS ONE. The fish might have trouble finding their way around the concrete pontoons. And harbor seals might take advantage of the confusion to nab more tasty trout. Roberta Kwok | 9 September 2013

Source: Moore, M., B.A. Berejikian, and E.P. Tezak. 2013. A floating bridge disrupts seaward migration and increases mortality of steelhead smolts in Hood Canal, Washington State. PLOS ONE doi: 10.1371/journal.pone.0073427.

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