Out (of range) for the count

Posted on June 26, 2010


Although mobile acoustic surveys are widely used to estimate fish stocks in both marine and freshwater environments,  little is known about the reactions of fish to survey vessels operating in the relatively shallow waters of rivers and lakes.  Canadian researchers used a side-scanning sonar system on the bank of theFraserRiverto investigate the responses of migrating adult salmon to a 6.7 m motor boat.  They found that fish within 4 m of the vessel’s propeller swam off to one side, away from the downward-pointing sonar system towed by the boat.  These observations help to explain why, in recent studies in the same river,  mobile sonar recorded only 36% of nearshore fish passages that were simultaneously monitored by shore-based sonar, and show that avoidance responses can lead to serious underestimates of fish abundance in shallow water.

Reference: Xie, Y., Michielsens, C.G.J., Gray, A.P., Martens, F.J. & Boffey, J.L.  2008. Observations of avoidance reactions of migrating salmon to a mobile survey vessel in a riverine environment. Canadian  Journal of Fisheries and Aquatic Sciences. 65, 2178-2190.

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Posted in: behaviour, fish