How many carp does it take to tango?

Asian Carp
These two Asian carp could have produced over three-quarters-of-a-million fertile eggs. (University of Michigan photo)

I wrote a column in Michigan Outdoor News recently about a single Asian carp being found in an eastern Michigan stream. This one happened to be a grass carp which, if a body of water has to be infested with Asian carp, the grass carp is likely to be the least disruptive. It’s sort of like a guy having prostate cancer instead of pancreas cancer – neither is good, one is only less bad.

That was (hopefully) just one lone fish and with grass carp and the other Asian carp threatening Michigan – the bighead, black and silver carp – one single carp won’t reproduce. As with most (not all) species, it takes two to tango – two of the opposite sex.

Let’s say, however, two Asian grass carp had been captured and the biologists who nabbed them determined they could have danced the tango. Had that dance occurred, would that spell the end?

The best answer is “possibly.”

There’s a reason a female  Asian carp spews out about three-quarters of a million eggs each time she spawns. It’s because each individual egg has less than a one-in-a-million chance of hatching and surviving long enough to tango with another survivor and thus proliferate the species. There’s actually a better than even chance, if one boy Asian carp and a girl Asian carp were to swim past the existing barriers keeping them out of the Great Lakes, they either wouldn’t tango or none of the three-quarter million future spawners they would produce if they did would hatch and survive to maturity.

Obviously, it could happen with just two fish and the odds would increase if there were three of them, or four, or a dozen. How many Asian carp would it take to ensure a successful invasion?

That’s a question researchers at CIGLR (Cooperative Institute for Great Lakes Research) are asking. Obviously, the scientists can’t devise many “in the field”  tests. Instead, they produce models, which crunch all the numbers, details, facts, possibilities and other information to come up with an answer.

The answer they’ve come up with is: “it depends.”

It depends on where, when, and other factors that a slug of tango-capable Asian carp were to somehow gather.

The model they worked up indicated if 100,000 bighead carp were to be stocked randomly in Lake Huron, the odds for them to survive, tango and make a mess of the lake’s ecosystem is remote. However, using the same model but moving the stocking site to Saginaw Bay, the odds are that just 10 stocked bigheads would likely allow tango-dancing to occur and start an unstoppable road to ecological devastation.

Ten is not many, compared to the millions of Asian carp now swimming in much of middle America’s big rivers and many lakes. The presence of Asian carp has irrevocably changed the fish communities everywhere they have become established.

This research does nothing to curb the invasion, but it does highlight the need to sideline political and economic concerns and keep Asian carp out of the Great Lakes.

Categories: Asian Carp, Michigan – Mike Schoonveld

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