Fish food: Hungry and abundant salmon could be too much for Lake Ontario alewives

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Fish food: Hungry and abundant salmon could be too much for Lake Ontario alewives

 

 

Feb. 5, 2010

Jeff Gillies / ://greatlakesecho.org

 

 

Too many Lake Ontario Chinook salmon threaten the

survival of the alewives they eat. Photo: GLERL

 

 

A biological balancing act between the premier Great Lakes sportfish and its prey could be at a tipping point in Lake Ontario.

 

Chinook salmon are the foundation of the Lake Ontario recreational fishery, which is worth $76 million to New York alone. But new research shows that the popular predators could be so abundant in the lake that there may not be enough alewives – the Chinook’s main prey fish – to go around.

 

If there aren’t enough alewives to both reproduce and feed the salmon, each species will collapse. That’s what happened over the past five years in Lake Huron, where alewives and the Chinook salmon fishery have all but disappeared.

 

“The alewife population could be at severe risk of collapse like what happened at Lake Huron,” said Brent Murry, a biology research assistant professor at Central Michigan University who did doctoral research on Lake Ontario. “We need to reevaluate the stocking plan.”

 

Same story, different lake

 

In 2006, Lake Michigan managers fearing the same fate as Lake Huron cut back Chinook salmon stocking by 25 percent, hoping to make life easier for alewives. So far, that strategy has worked, said Randy Claramunt, research biologist with the Michigan Department of Natural Resources and Environment.

 

“Reducing stocking has contributed to a reduced number of Chinook salmon in Lake Michigan,” he said. “Likewise, we’ve seen a response in the increased survival of alewife.”

 

And the salmon that remain are bigger and healthier than they were a few years ago, he said.

 

A similar salmon stocking cut could ease the pressure on Lake Ontario alewives, Murray said. But such a move is unpopular with the lake’s recreational anglers.

 

Charter boat captains on Lake Ontario have already seen salmon catch-rates decline after stocking cuts in the mid-90s, said George Watkins, secretary of the Ontario Sportfishing Guides’ Association.

 

“Part of our livelihood is the number of fish that are available to us,” he said. “Are you going to do a charter if all you’re going to do is go around on a boat ride?”

 

But there may be reason to believe that a stocking cut might not be so bad for anglers looking to hook a Chinook.

 

Wild fish surprise

 

The link between salmon stocking and catch rates is based on an old assumption that the only salmon in Lake Ontario are the fish that were planted in there, said Michael Connerton, a senior research biologist with the New York State Department of Environmental Conservation.

 

A 2009 study shows that’s probably not the case.

 

The study, co-authored by Connerton and Murray, found that the 2.3 million Chinook salmon planted by New York and Ontario annually produce less than half of the Chinook in Lake Ontario. Most have never seen a hatchery; they were born wild in tributary streams like the Salmon River in north central New York.

 

“So the widely held belief that there was limited to no natural reproduction is just completely and absolutely wrong,” said Murray.

 

Around half of the Chinook in Lake Michigan are born wild, Claramunt said. That makes a cut in salmon stocking for the sake of alewives easier to swallow for the lake’s anglers.

 

In a new study, Connerton and Murry estimated Chinook salmon abundance in Lake Ontario in a way that accounted for natural production. By coupling that estimate with the rate at which the salmon eat alewives, they determined that “predation pressure on the Lake Ontario alewife population may be high enough to raise concerns about long-term stability of this predator–prey system,” according to an article in the January 2010 issue of Transactions of the American Fisheries Society.

 

Managers hold stocking levels steady

 

Lake Ontario managers still aren’t convinced that a new stocking plan is needed, Connerton said.

 

The best indicator of the balance between Chinook and alewives is the average size of full-grown salmon, he said. That average was recently near an all-time low, but has since rebounded and stabilized.

 

“I think what they’ve decided over the past ten years is there doesn’t seem to be enough to indicate a stocking change,” he said.

 

But it’s something that biologists and managers alike will have to keep an eye on.

 

“Could we push the alewife population to a point where there’s too few alewife to sustain the population and our Chinook size would drastically decline because there isn’t enough to eat? Yes, of course. I think it could happen,” he said. “Hopefully it won’t happen so quickly that we can’t make adjustments.”