DNA testing helping gauge impact of stocking

[Lee Borgersen]

 5/21/11
DNA testing helping gauge impact of stocking
By Marshall Helmberger...Timberjay news
 
 DNR fisheries staff clip a fin from a walleye last month for genetic testing. The work is giving officials a better idea of effects of fish stocking.  
 
The Department of Natural Resources is testing DNA from fish populations across Minnesota in hopes of learning more about the genetic diversity of fish populations in the state as well as the impact of stocking operations.

DNR fisheries staff collected DNA samples from 100 walleye last month, during their operations at the Pike River hatchery. The samples are being tested to establish a genetic baseline that DNR officials can use to gauge how well stocked fry from Vermilion are surviving and reproducing in area lakes. They can also determine whether the Vermilion strain is replacing native strains in area lakes, a development that would tend to reduce genetic diversity over time and make walleye populations more subject to disease or other problems.

One of the first lakes that DNR officials are examining is northern Red Lake, where the DNR implemented a major stocking effort using Lake Vermilion walleye several years ago. The walleye population in Red Lake had crashed following years of over-harvest, but the restocking effort combined with strict harvest limits did allow the lake’s walleye to recover.

DNR officials are interested to see whether the influx of so many Lake Vermilion fry had changed the genetics of fish at Red Lake. So far, it appears that the native Red Lake strain is holding its own. “It’s not entirely swamped with the Pike River strain, that’s for sure,” said Loren Miller, a DNR geneticist working on the project. “There was enough of the Red Lake strain still there to maintain viability,” said Miller. “It’s hard to get an exact estimate, it’s clear that both are successfully spawning,” said Miller.

In most cases, the native fish strain should outperform the transplanted fish and the DNR is using the genetic data it is gathering to determine whether that’s happening. “Over time, we can continue to track to see if there is a shift back towards the Red Lake strain,” said Miller.

The information, applied to fish populations in lakes across the state, will be useful in assessing how effective stocking efforts have been, as well as which strains of fish are the most successful in which lakes. “We can look back at areas where fish from multiple sources were stocked and see if the genetics are mixed or if one out-performed others,” said Miller. The data should also help the DNR determine in which lakes stocking is ineffective and should be discontinued.

In general, aiding natural reproduction is the best approach to improving fish populations, and that’s one reason that the DNR does not stock lakes with adequate natural reproduction. “We don’t want to reduce genetic diversity, so we try to maintain natural reproduction first,” said Miller.

Even so, in those lakes where conditions don’t allow for sufficient reproduction, stocking can be important, said Miller. “We have walleyes in a lot of lakes that wouldn’t be there if we didn’t stock them,” he said.




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