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A Better Fishery for Lake Norman?

Feb 1

Written by:
2/1/2013 9:24 AM  RssIcon

Talking Hybrids with Piedmont Region Fisheries Supervisor Brian McRae

The N.C. Wildlife Resources Commission currently stocks 162,500 striped bass annually into Lake Norman, which is located in Iredell, Catawba, Lincoln and Mecklenburg counties. Brian McRae, Piedmont Region fisheries supervisor, answers a few commonly asked questions about Lake Norman’s striped bass and hybrid striped bass fisheries.

Is the Commission stocking 162,500 hybrid striped bass into Lake Norman this year?

Yes, we are replacing the striped bass fishery at Lake Norman with a hybrid striped bass fishery.  We will stock 162,500 hybrids into Lake Norman this summer instead of 162,500 striped bass.

The hybrids will be the traditional cross between white bass males and striped bass females. 

Why is the Commission stocking hybrid striped bass instead of striped bass at Lake Norman?

This change is an effort to address the increased frequency and magnitude of the striped bass kills that occur during the summer. 

From 1969 when the lake was first stocked until 2003, there was only one striped bass mortality event, which occurred in 1983.  However, since 2004 five mortality events have occurred, including each of the past four years:

Year

Dead Striped Bass Collected

2012

833

2011

395

2010

6,993

2009

362

2004

2,479

Will the Commission survey and monitor the hybrid striped bass fishery?     

Yes, as the hybrid striped bass population becomes established, biologists will survey and monitor it annually.  These surveys will help determine if this management change to a hybrid striped bass fishery is a success. 

We will consider the hybrid striped bass fishery successful if three criteria are met:

    1. Hybrid striped bass have significantly better body condition than what we have historically observed for striped bass;
    2. Summer mortality of the hybrids is minimal; and
    3. Hybrid striped bass escapement downstream is negligible.

If one or more of these criteria is not met, the Commission will re-evaluate managing for a hybrid striped bass fisherya t Lake Norman.

Why did striped bass die during the past summers?

Summertime fish kills have,unfortunately, become a recurring theme mainly because of the habitat preferences and feeding habits of striped bass and ecological changes withinthe reservoir. A YouTube video we created last year shows howthese kills occur. 

During summer, striped bass follow river herring, their preferred food, to the cold, deep layer (hypolimnion) of the reservoir to feed.  However, as the summer progresses this deep layer eventually turns into a type of “oxygen bubble” that is created when the middle layer (metalimnion) of the water column loses oxygen faster than the deep layer. This process occurs naturally during the summer in deep reservoirs (greater than 100 feet).  The deep layer, or oxygen bubble, eventually runs out of oxygen, and sometimes striped bass become trapped and die.  We term this a “deep-water” or “hypolimnetic”kill because this kill is a result of striped bass being trapped in the deep layer called the hypolimnion. 

Sometimes striped bass can escape from the oxygen bubble into the upper layer (epilimnion) of the water column.  Successful escapement from the oxygen bubble depends on the thickness of the middle layer and how quickly the oxygen levels decline.

This deep-water kill is different than the striped bass kills in most other reservoirs that result from a “temperature/dissolved oxygen squeeze.” In these kills, striped bass are “squeezed” between hot, oxygenated water in the upper layer and cool water without oxygen in the bottom layer.  Temporary refuge in the form of a deep-water “oxygen bubble” does not play a role in the kills associated with the “temperature/dissolved oxygen squeeze.”     

Will hybrid striped bass survive the summers better than striped bass?

Yes, we expect that hybrid striped bass will generally remain in the upper layer of the lake during the summer and avoid the deep-water oxygen bubble, unlike striped bass.  However, we have not completed a specific research project in Lake Norman to evaluate this question.  A research project was conducted at Claytor Lake, in Virginia, which did evaluate summer habitat preferences of adult hybrid striped bass compared to adult striped bass. 

This research, conducted by John Kilpatrick at Virginia Polytechnic Institute and State University, will soon be published by the American Fisheries Society in a book titled Biology and Management of Inland Striped Bass and Hybrid Striped Bass.  Mr.Kilpatrick’s results indicate that hybrid striped bass will remain in the top layer of the water column during severe summer stratification, even though the water temperature is warmer, instead of following river herring into the deep layer, like striped bass do.

Further, we recently obtained information from the U.S. Army Corps of Engineers at J. Strom Thurmond Reservoir in South Carolina that supports the idea that hybrid striped bass will not be as susceptible to these deep-water kills as striped bass. In 2009,about 1,550 striped bass died at J. Strom Thurmond during a deep-water kill.  However, only about 250 hybrid striped bass died during the same time period. This is a pretty substantial difference considering that the stocking rate for hybrid striped bass was almost twice what it was for striped bass in the years just prior to the 2009 kill.

While it is possible that some hybrid striped bass will still die during years of severe reservoir stratification, the observations at J. Strom Thurmond Reservoir, in conjunction with Mr.Kilpatrick’s work at Claytor Lake, suggest that substantially fewer hybrid striped bass will die as compared to striped bass.       

Will the current size and creel limit stay in place for hybrid striped bass?

The current hybrid striped bass and striped bass regulation at Lake Norman allows anglers to harvest four fish in aggregate that are 16 inches or larger from Oct. 1 to May 31 and to harvest four fish in aggregate with no minimum size limit from June 1 to  Sept. 30. These regulations will remain in place while we initially evaluate the fishery, but changes may be needed in the future.

The “summer season” was implemented because striped bass are known to suffer significant catch-and-release mortality during the summer months. Catch-and-release mortality rates are high for striped bass in the summer because they are usually caught in the deep, cold water but released into the warm water near the surface. This change in depth and water temperature increases their stress levels and can result in death.  The hope was that anglers would catch their four striped bass and then start fishing for some other species, reducing the chances of catch-and-release mortality.  We think that hybrid striped bass will not suffer the same catch-and-release mortality rates because they will generally be located in the upper layer during the summer and will not die when released back into the warm water near the surface. 

The 16-inch minimum size limit might be appropriate for hybrid striped bass because we want to provide anglers with the opportunity to harvest some fish. Further, we do not want to set an inappropriately high minimum size limit and risk the possibility of hindering growth and condition.  For example, if a high minimum size limit is set and few hybrids are harvested, the result would be that too many fish remain in the reservoir and without enough food to sustain good growth and condition for the abundant population. Condition is a measure of how fat the fish are and considering that condition is one of our criteria for success, we would not want to negatively affect condition by implementing a minimum size limit that is too high.     

10 comment(s) so far...


Re: A Better Fishery for Lake Norman?

I see a few problems with the hybrid bass stocking you have proposed.
1. the number of fish planned in your program breaks down to roughly 6 fish per acre. Even if fully grown hybrids were stocked an established foothold seems unlikely.
2. If stocked hybrids are less than 12 inches all we are doing is feeding the thriving species that already inhabit our lake I.E. spotted bass, large mouth, and catfish.
3. I admit I'm not a biologist but I do know that fish follow their food. The supposition that hybrids won't follow the herring I believe is flawed.
4. some years ago a proposition to put an bubbler in the (kill zone) was proposed can you explain why that never came to fruition. Thanks for your time. Capt. Kirk

By capt. Kirk Drowne on   2/5/2013 10:10 AM

Re: A Better Fishery for Lake Norman?

1) You are correct, we will be stocking hybrid striped bass at about 5 fish per acre. Like striped bass, hybrid striped bass cannot reproduce in Lake Norman. Therefore, we will be stocking 5 fish per acre each year. This is the same rate at which we have been stocking striped bass since 1990 in Lake Norman (we were actually at a lower rate for most years from 1975 to 1989). We are confident that a hybrid striped bass fishery will develop as this rate was successful in producing a striped bass fishery.
2) We have had similar concerns about the size of fish that we stock, which are typically between 2-4 inches. As a result, we funded North Carolina State University to evaluate predation rates after a stocking event at Lake Norman. The results from this research indicated that less than 0.1% of the stocked fish were consumed by predators within 72 hours post stocking. Further, the striped bass fishery was established and maintained by stocking 2-4 inch fish; therefore, we are confident that this size of fish will also establish a hybrid striped bass fishery.
3) Other sources of food, specifically threadfin shad and sunfish, are plentiful in the upper layer of the water column. Therefore, we presume that the research and example described in the blog will hold true and that hybrid striped bass will stay in the upper layer to target threadfin shad and sunfish instead of following river herring into the undesirable water temperatures of the bottom layer.
4) You are correct, a dissolved oxygen injection system has been discussed as an option to reduce the frequency and magnitude of the summer striped bass kills at Lake Norman. However, at this time, the scope and costs associated with a dissolved oxygen injection system limit the feasibility of this option. Therefore, after a thorough investigation, we decided that hybrid striped bass are the best option currently available to limit future summer kills at Lake Norman.

By NCWRC blogger on   2/12/2013 10:29 AM

Re: A Better Fishery for Lake Norman?

What about the ever hungry white perch, will they be a threat to the hybrid fingerling? I attended a fishing seminar a few years ago and the guide said there were no more white bass in Lake Norman due to the white perch, is that true? Did NCWRC stock the white perch?

By Mike Hughes on   2/13/2013 10:50 PM

Re: A Better Fishery for Lake Norman?

1) We do not expect white perch to be a threat to the establishment of a hybrid striped bass fishery. We acknowledge that white perch will consume some of the hybrid striped bass fingerlings that are stocked. However, we expect to establish a hybrid striped bass fishery in the presence of white perch just as we maintained a striped bass fishery while white perch were present. Further, research by North Carolina State University, referenced in the above post, indicates that some recently stocked fingerlings are consumed; however, not an a level that would hinder the establishment of a viable fishery.
2) Very few white bass have been observed in Lake Norman over the past few years. Anecdotal evidence has suggested that the introduction of white perch and alewife in the late 1990s led to the decline in the white bass population. This decline is likely a result of white perch and alewife feeding on white bass eggs and/or larvae. Further, the decline in the white bass population could be attributed to white perch displacing white bass from their preferred spawning habitats.
3) No. The North Carolina Wildlife Resources Commission did not stock white perch or alewife into Lake Norman.

By NCWRC blogger on   2/14/2013 4:53 PM

Re: A Better Fishery for Lake Norman?

If this is successful at Lake Norman, would it be possible to do the same thing at Badin Lake? We're having problems with stripers there as well. Thanks

By Mark Browning on   3/10/2013 11:33 PM

Re: A Better Fishery for Lake Norman?

Thanks for adding this information to your website. As a frustrated LKN striper fisherman I look forward to keeping up with your efforts to restore the fishery.

By CastAway on   3/11/2013 8:19 PM

Re: A Better Fishery for Lake Norman?

Even though I do not agree with all of the facts relative to the fish kills over the last 5 years. I do commend the commission for finally agreeing to stock the Hybrids. The problem with Lake Norman is that it is actually thermally polluted at certain times of the year and the levels of dissolved oxygen get too low during these periods. Also the nutrient content of the lake is lower then desired for proper fish growth. We should continue to look at solving the oxygen content, there are solutions to this problem, although expensive. Lets see how the hybrids take here, but lets not take our eye off the other problems related to making this a great fishery.

By Jake Bussolini on   3/12/2013 11:43 AM

Re: A Better Fishery for Lake Norman?

Since we have now started at ground zero with the hybrids, it might be worth considering setting up an easy e mail reporting system for anglers to report hybrid catches. We know there have already been some but they are not related to the recent stocking. In a year or two the stocked fish should start biting and we could get a good data sampling as a baseline for measuring the success of this stocking program.

By Jake Bussolini on   3/14/2013 10:59 AM

Re: A Better Fishery for Lake Norman?

I'm looking forward to the day that we can hunt striped fish on LKN and once again have a reasonable chance to be successful. Thanks for taking this initiative.

Frequently, larger striped bass caught in LKN have a parasite that we call "gill maggots". These fish are often thin and of poor body condition in general. Can you tell us a little about the parasite, and do hybrid striped/white bass show any greater resistance to the parasite?

By Phil Smith on   3/15/2013 7:20 AM

Re: A Better Fishery for Lake Norman?

Jake - a terrific idea, and one that should be implemented.

Also, good to see you weighing in Capt. Kirk! Let's fish!

By Phil Smith on   3/15/2013 11:30 AM

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