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Fishing for Answers at Harris Lake

Why are largemouth bass harder to catch recently and why the threadfin shad die-off?

Author: NCWRC blogger/Friday, March 19, 2021/Categories: Blog, Conservation, Fishing

Fishing for Answers at Harris Lake

Harris Lake has long been known for its excellent largemouth bass and crappie fishing. Recently anglers have voiced concern about the health of the fish in the lake after noticing a die-off of threadfin shad and a reduced number of largemouth bass caught. 

The N.C. Wildlife Resources Commission has been collecting data on Harris Lake since 1992 and is currently managing a five-year habitat enhancement project on the reservoir. We sat down with a couple of our fisheries biologists to find out more about what makes this fishing hole so special and why recent fishing conditions are causing concern.

NCWRC Blogger: Urban legend or truth: Harris Lake has some of the best largemouth bass fishing in the state.

Fisheries biologist: Truth! Harris Lake condition factors, which is the weight of a fish relative to its length, are consistently above average for a N.C. Piedmont reservoir. Electrofishing catch rates, which is the number of largemouth bass caught per hour of electrofishing, are above average too.

NCWRC Blogger:  What qualifies as “above average”?

Fisheries biologist:  Catch rates average 30 to 60 fish per hour in Piedmont reservoirs. Catch rates at Harris Lake are normally above 70 fish per hour. That is just over one fish per minute of sampling time!

A good benchmark for the growth rates of most largemouth bass populations in the southeastern U.S. is the average length of 3-year-old largemouth bass, which is normally 12-14 inches. In most years at Harris Lake, most 3-year-old largemouth bass are approximately 15 inches.  Annual mortality is relatively low with fish at least 12-years-old collected in most years. Lakes that often produce good numbers of trophy largemouth bass are normally those with low annual mortality and fast growth. The percentage of largemouth bass greater than 20 inches (approximately five pounds) sampled is normally close to 10 percent, which is excellent.

NCWRC Blogger:  Recently, there have been complaints about anglers not catching as many fish at the lake as in years past. How would you explain this decline and why doesn’t your data show any declines?

Fisheries biologist:  Harris Lake is still producing healthy largemouth bass and in good numbers. It’s a small reservoir that receives a lot of fishing pressure being so close to Raleigh. High fishing pressure can make angling hard when fish have seen a large diversity of baits. Our data indicate that the Largemouth Bass population has been excellent for at least the past two decades.

NCWRC Blogger:  Has a decline in Hydrilla changed the largemouth bass population?

Fisheries biologist:  No. The largemouth bass population has remained consistent in terms of weight, abundance and growth rates throughout our surveys, which consist of years where Hydrilla was present and in years where it was not present.

NCWRC Blogger: If there hasn’t been a change in the largemouth bass population, why has fishing changed?

Fisheries biologist:  It’s likely that the behavior of largemouth bass has changed. The Hydrilla provided a dense habitat in the shallow water areas of the lake. Now that it’s been reduced, fish tend to hold farther off the bank. They hold on points and depth changes to ambush prey rather than orienting on vegetation.

NCWRC Blogger:  Were any herbicides sprayed to treat the Hydrilla?

Fisheries biologist:  No herbicides were used. The North Carolina Division of Water Resources Aquatic Weed Management Program stocked the lake with sterile grass carp. There has also been a decrease in water clarity likely due to increased urbanization in the watershed. This combination of effects has reduced Hydrilla to almost non-existent levels according to our 2020 vegetation surveys.

NCWRC Blogger:  Recently there was a threadfin shad die-off. Why?

Fisheries biologist:  Threadfin shad are sensitive to cold water events. When water temperatures drop below 45 degrees, fish kills can occur. In addition, a sudden drop in water temperature can trigger a fish kill event.

NCWRC Blogger:  Can a threadfin shad die-off cause a decrease in catching largemouth bass?

Fisheries biologist:  It can. When prey, like the threadfin shad, are readily available for predators, like the largemouth bass, predators are less likely to attack an artificial bait, resulting in less angler catches.

NCWRC Blogger: Does the threadfin shad die-off harm other fish populations? Will the threadfin shad return to Harris Lake? Did they all die?

Fisheries biologist:  No, other fish populations will not and have not been harmed, and not all threadfin shad died. Once they spawn this spring, their numbers will return. Harris Lake has a high abundance of threadfin shad, which contribute to the impressive growth rates of largemouth bass.

NCWRC Blogger:  How can anglers learn more about the largemouth bass fishery at Harris Lake?

Fisheries biologist: The N.C. Wildlife Resources Commission website is an excellent resource for anglers. Anglers can access Harris Lake sport fish current reports and fact sheets, as well as information about other sport fishing areas across the state.

NCWRC Blogger:  When will staff perform another largemouth bass and crappie population sample?

Fisheries biologist: The largemouth bass population is sampled every other spring and the crappie population is sampled every other fall. Largemouth bass sampling will occur this spring from April-May and October-November for crappie.

NCWRC Blogger:  How can anglers become more involved with what goes on at Harris Lake?

Fisheries biologist:  Anglers can contact their district’s fisheries biologists if they ever have questions about Harris Lake. In addition, anglers can submit a formal written proposal if they feel a management change is needed. District biologists are here to help and can assist with that process.

NCWRC Blogger: I had no idea that there were so many ways to get involved in the management of Harris Lake. Thanks for this valuable information, and thanks for all y’all are doing to keep the largemouth bass population healthy and strong.

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Gregory Griffin

3/19/2021 3:22 PM

Thank you for .New crappie fishermen could use some pointers also

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