Sunday, November 10, 2013

Following salmon from the rivers into the ocean

The JSAT acoustic tags. Source: Lotek Wireless
The first encounter between juvenile salmon and the sea is a very risky time. They have to run a gantlet of predators- larger fish and birds-- before becoming safely dispersed. However, little is known about what juvenile salmon in the first few days of this critical transition. There's a nice little story about telemetry methods tracking different species of salmon using acoustic fin tags to find out what they do as they exit the Columbia river.  These tags last about 30 days and emit an acoustic signal, which can be picked up by semi-permanent listening devices set up at the fish letters and in an array around the mouth of the Columbia river. By tagging several thousand fish, they could track the aggregate movements and also get some idea of where predation was at its most intense.
A lot of the research paper involves data crunching from all of the acoustic pings recorded. The authors were able to see differences between salmon species in terms of how quickly they headed into deep water.  One trend was that the salmon of all species scattered along the north-south extent of the Columbia to a much greater extent than had been appreciated. This means that the counts of juveniles, which are important measurements of fisheries health, may be underestimated.

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