Atlantic salmon migration

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First off, let me introduce myself.  I'm Pam, I've been a GMRI intern for the last 5 months or so and have been lucky enough to be part of the salmon team here.  It's been a great experience and I've definitely learned a lot! 


There's a couple of salmon-related projects going on at GMRI, I've been involved with work studying Atlantic salmon migration in the Gulf of Maine.  In the Gulf of Maine, salmon begin their migration when they enter the marine environment.  This initial migration phase occurs as they move through the Gulf of Maine to the coast of Nova Scotia by Halifax (they then continue all the way up to Greenland).  However, we don't know where in the Gulf of Maine the salmon are moving through, how they're finding their way through or how the variability in the Gulf of Maine physical environment (currents and temperatures) affects them.  I've spent the last several months trying to address these questions using what's known as "individual-based modeling" (IBM).


IBMs let us simulate individual fish.  We can give the fish different sets of rules to define their behavior.  This is neat because it lets us experiment with different orientation methods to see what methods might be plausible and lets us simulate the path an individual fish follows through the Gulf of Maine.  Then by using physical conditions from different years, we can see how these paths change due to differences in temperatures and currents. 

Salmon tracks.jpg

This figure shows simulated tracks for fish- each red line is a different fish.  For this figure, the fish were instructed to swim in the direction the current was flowing.

As it turns out, the salmon are affected by interannual variability in their environment.  In general, stronger currents result in fewer salmon successfully navigating their way through the Gulf of Maine.  However, the degree to which changes in currents affect salmon depends on how salmon orient for migration.  If salmon use directed swimming (know the direction they want to go and try to swim in that direction), then changes in currents do not have that large of an impact.  However, if salmon use other behaviors (such as using temperatures and/or currents to navigate), then changes in currents do have a larger impact.  Also, while we have no way right now of concluding what behavior salmon do use to orient, we can rule out a couple of possibilities.  Based on the lack of success (i.e. no fish make it to Halifax), we know that the salmon aren't passively drifting and aren't simply swimming in the opposite direction of the currents.  

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This page contains a single entry by Pam Moriarty published on November 18, 2011 5:34 PM.

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