A Bridge Is Troubled Waters For Hood Canal Steelhead Smolts

It’s a bridge that for over five decades we Puget Sound anglers, drift boats in tow, have zipped across on our way to the West End’s fabled steelhead rivers, but oddly, our favorite fish appear to have trouble crossing underneath it.

Federal scientists earlier this fall reported that an unusual number of smolts die when they reach the Hood Canal Bridge, or they otherwise spend more time around it than they would if their path to the Pacific was clear of the obstruction.

“Assuming telemetry-tagged smolts provided an unbiased representation of the larger Hood Canal steelhead smolt population, the HCB may directly or indirectly cause mortality of a minimum of 4.9% (2006) to 36.4% (2010) of the steelhead smolts migrating from Hood Canal,” write Megan Moore, Barry A. Berejikian and Eugene P. Tezak in an article published in the journal PLoS One.

WHILE BOTH ENDS OF THE HOOD CANAL BRIDGE ARE RAISED, RESEARCHERS SAY THAT IT COVERS 95 PERCENT OF THE WIDTH OF THE FJORD AT LOW TIDE. (WASHINGTON DEPARTMENT OF ECOLOGY)

WHILE BOTH ENDS OF THE HOOD CANAL BRIDGE ARE RAISED, RESEARCHERS SAY THAT IT COVERS 95 PERCENT OF THE WIDTH OF THE FJORD AT LOW TIDE. (WASHINGTON DEPARTMENT OF ECOLOGY)

The authors, who work for the National Oceanic and Atmospheric Administration’s Northwest Fisheries Science Center in Manchester, Wash., are among a group of federal, tribal, state and public utility researchers looking into why Puget Sound steelhead are doing so poorly these days.

More and more research is pointing to death zones in the inland sea itself.

Their paper, titled “A Floating Bridge Disrupts Seaward Migration and Increases Mortality of Steelhead Smolts in Hood Canal, Washington State,” says that over five years, 27 mortalities were recorded by sonar arrays at the bridge (another eight probably also perished there) during the spring migration to sea, but only one young fish died elsewhere on the route to the ocean.

The authors suspect that smolt confusion about how to pass under the bridge’s pontoons leads to an increased risk of being snacked upon.

True, these days blaming predators is all the rage amongst us anglers and hunters as we look for reasons why our game and fish populations are troubled, but it’s another possible example of a manmade bottleneck — think the Ballard Locks and Bonneville Dam — being exploited by smart pinnipeds.

There’s a harbor seal haulout just a few miles from the bridge, the federal scientists point out, and they add that the marine mammal’s population increased “exponentially” in Puget Sound since the 1970s, and is now thought to be near carrying capacity.

A PAIR OF HARBOR SEALS AT PROTECTION ISLAND, NEAR THE HEAD OF ADMIRALTY INLET, THE ENTRY TO CENTRAL AND SOUTHERN PUGET SOUND. (DOW LAMBERT, USFWS)

A PAIR OF HARBOR SEALS AT PROTECTION ISLAND, NEAR THE HEAD OF ADMIRALTY INLET, THE ENTRY TO CENTRAL AND SOUTHERN PUGET SOUND. (DOW LAMBERT, USFWS)

Predation was not listed as a major factor when in May 2007 the region’s steelhead stocks were given Endangered Species Act protections. NOAA pointed to “degraded habitat, blockages by dams and other man-made barriers, unfavorable ocean conditions and harmful hatchery practices.”

One need only look sideways while driving through the Puyallup, Green/Duwamish, Snohomish and Skagit Valleys to see the hash we’ve made of estuaries and mountainsides over the past 150 years.

But the question is, why haven’t Puget Sound steelhead, which along with other salmonid stocks collapsed in the 1990s because of rotten ocean conditions, recovered when the rest of the fish have to some degree? Research at the bridge and elsewhere is beginning to show that the Whulge itself is another major danger zone for the smolts.

As an alternative theory about why smolts are dissapearing around the Hood Canal Bridge, Moore, Berejikian and Tezak say it is possible that for some reason they somehow shed the tags from their bodies there, leading to the presumption of mortality. They also point out that sea lions in the Columbia have been found to prey more on fish with acoustic tags than those without.

And I wonder if perhaps water quality issues in the streams the smolts rear and the canal itself somehow make them less able to intuitively swim past the bridge.

More research is needed.

There are a couple other interesting notes in the article.

First, most of the tagged steelhead that died at the bridge — 22 of 27 — were wild-origin fish from the Kitsap Peninsula’s Big Beef Creek, where the species has been known to interbreed with coastal cutthroat, but the authors don’t believe that hybridization had an impact. Big Beef smolts represented 51 percent of the 300-plus fish tagged in the Hood Canal study.

Also, in 2009, when the bridge underwent extensive repairs, including to its pontoons, no mortalities occurred there amongst radio-tagged fish, the authors report. Steelhead smolts are believed to use the top 12 meters, or 40 feet, of the water column, and the bridge’s pontoon’s extend 3.6 meters, or 12 feet, down.

The reason you should care is simple: the healthier the wild steelhead population, the more hatchery production can be done, but until that day, fisheries overseers are managing to protect the nates.

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