In a paper published in the open access journal PLoS Biology, researchers used new tagging and tracking technologies to show the surprising result that the survival of juvenile salmon in two major west coast rivers was similar, despite the presence of an extensive network of dams in one river system.
Researchers have used tags to follow larger ocean dwellers such as sharks, sturgeon, tuna and sea turtles, and to follow migrations of mature salmon along marine coasts. Now for the first time they have tagged and directly tracked small juvenile Pacific salmon, from their release in freshwater far upriver to distant ocean destinations, a major step towards understanding the full life experience and decline of this species.
The authors stress that dams are not good for salmon. What is unclear is whether the Fraser River has a problem that cuts salmon survival to that of a heavily dammed river, or whether factors other than dams play a larger, unsuspected role in salmon survival.
Says lead author David Welch: "Wherever future research leads on those questions, the electronic and acoustic technology has demonstrated itself as a useful tool for obtaining unique scientific data of importance in a number of public policy arenas."
In 2006, the researchers implanted the new tags in roughly 1,000 juvenile steelhead (www.eol.org/taxa/17050441) and Chinook salmon (www.eol.org/taxa/17154704) roughly the same length and half the weight of a hot dog, 14-17 centimeters long, 20-30 grams weight - for a study in the Columbia and Fraser Rivers, and followed their journeys. The 1,000 tagged juvenile salmon were followed via an extensive network of detectors in the Columbia and Fraser Rivers and along the Pacific continental shelf.
The underwater array of detectors in the rivers and ocean capture signals when a tagged fish passes by, akin to an electronic toll booth that records a passing vehicle equipped with a transponder.
The team found that the two species of juvenile salmon migrating through the Columbia River's eight dams survived the freshwater and early marine portions of their journey to the ocean as well as those in the un-dammed Fraser River, challenging widely-held notions about factors affecting salmon abundance. In fact, more survived in the dammed river journey once distance or travel time was taken into account - and survival was greater during migration within the hydropower system than below the dammed section.
An animation illustrating the migrations is online at: www.postcoml.org/page.php?section=community&page=PLoSembargo
The cornerstone of this study lies in its new method of tagging the salmon, which although larger than previously existing hardware is much more versatile. These new tags no not require the tagged fish to be funnelled towards a short range detector, but instead can be monitored using a series of listening arrays maintained as part of the Pacific Ocean Shelf Tracking Project, which is based at the Vancouver Aquarium. These listening arrays allow measurements to be taken not only in controlled, dammed rivers but also in free-Flowing flowing rivers and even in the coastal ocean, a great step forward.
This study, as well as the technology it introduces, has imminent applications to the study of other species, such as herring, halibut and cod, to explore their behaviour and survival. It also opens up a wider debate about the factors that influence salmon survival, especially regarding human intervention and adaptation of rivers.
Citation: Welch DW, Rechisky EL, Melnychuk MC, Porter AD, Walters CJ, et al. (2008) Survival of migrating salmon smolts in large rivers with and without dams. PLoS Biol 6(10):e265. doi:10.1371/journal.pbio.0060265
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