AquaNet - Network in Aquaculture
Atlantic salmon swim back to Great Lakes
Once abundant in Ontario, Atlantic salmon disappeared from our lakes at
the end of the 19th century due to over fishing and habitat loss. Since
then, Pacific salmon species like chinook and coho have been used to stock
Ontario lakes for sports fishing.
But despite efforts to re-introduce Atlantic salmon to its natural Ontario
habitat, its Pacific cousin may actually be preventing the stock from
recovering. University of Western Ontario zoology professor and AquaNet
researcher, Dr. Robert Scott, is trying to determine the effect that these
Pacific salmon have had on attempts to restore the native Atlantic salmon
to Lake Ontario.
What have the researchers with the Network of Centres of Excellence
learned so far? Preliminary results indicate that the Pacific chinook
set up social hierarchies, showing little regard for the Atlantic salmon.
In fact, the Pacific salmon physically and aggressively displace the Atlantic
salmon whenever they're in the way. As a result, the Atlantic fish have
to find a new area, setting off a chain reaction of aggression.
"There have been many attempts to restore Atlantic salmon, and
all have been met with little to no success," says Dr. Scott. But
there's no indication that the researchers have given up on finding a
solution. They are already looking at behavioural interactions between
the two fish types, and have recently begun examining spawning habitat
characteristics and juvenile foraging behaviour.
Dr. Scott and his team first began the project in the fall of 2000 by
examining the interactions between the Atlantic and Pacific salmon on
spawning grounds in a creek that flows into Lake Ontario near Oshawa.
The creek was divided into sections, with Atlantic salmon in all of the
sections and Pacific chinook salmon in only half. Their goal was to observe
how the Atlantic salmon behaved both alone and with Pacific salmon around.
When the Atlantic salmon were alone, says Dr. Scott, they were much
more relaxed. That's because the Atlantics normally set up their own hierarchy.
In the presence of Pacific juveniles, however, this hierarchy is disrupted
and juvenile Atlantics spend more time being aggressive toward one another
rather than feeding. The fish tended to follow a cycle of fighting and
settling down.
In the spring of 2001, the researchers began examining juvenile foraging
behaviour. Since Pacific salmonids are all stocked as juveniles, they
compete for the same food as the Atlantic juveniles. If the Pacific juveniles
show the same aggressiveness as the adults and manage to deprive the Atlantic
juveniles of food, Dr. Scott says the Atlantic fish would have no chance
of survival and this could explain why the restoration efforts are failing.
Ultimately, the researchers hope to create a sophisticated model that
can be used to make predictions about whether a river can support Atlantic
salmon. "We need to know two things about the fish interactions:
first, what are the potential outcomes when an Atlantic salmon meets a
Pacific salmonid? And second, how common is each outcome?" states
Dr. Scott. "When we have all the answers, we'll be able to develop
the model."
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