Summer heat hits striped bass hard


No one argues that summer heat in the South climbs well above the comfort level – for humans and animals.

The beaming August sun makes the cooling waters of the Savannah District’s three reservoirs inviting for a cool dip or swift boat ride. But while the surface water feels cool to humans, some fish find it most uncomfortable – particularly striped bass and blueback herring.

During the summers of 2013 and 2018 Hartwell Lake officials discovered a large number of striped bass died during the hottest part of the season. Members of the public noticed the large sport fish floating on the surface.

Since these were the first instances of fish kills in the history of the reservoir, their deaths caught the attention of Corps officials, representatives of the two states’ Department of Natural Resources and the public.

“Two things really impact striped bass in Hartwell,” James Sykes, fisheries biologist for the Savannah District’s reservoirs, said. “One is temperature and the other is dissolved oxygen.”

While humans find most open water below body temperature “cool” fish don’t. Their body temperature matches the water temperature – and they must have it cooler.

As summer heat drags on, the surface of the reservoirs warms up during the day but doesn’t cool enough at night. By August the surface level is much warmer than the lower levels, Sykes explained.

In addition, the upper warm layer, exposed to the atmosphere, has plenty of dissolved oxygen, but the cool deep layer experiences an ever shrinking amount of oxygen as the summer progresses.

So fish, particularly striped bass and blueback herring progressively dive deeper. There they reach another obstacle – little oxygen at deep depth. It just doesn’t exist at greater depths naturally.

The fish get caught between low-oxygen below and declining oxygen and high heat above, according to Anthony Rabern, also a fisheries biologist who works for the Georgia Department of Natural Resources. Rabern has spent years studying reservoirs and lakes in northeast Georgia, including Savannah’s Hartwell reservoir.

Georgia Department of Natural Resources fisheries biologist Anthony Rabern explains how a shrinking “bubble” of oxygen-laden water in Lake Hartwell contributed to never-before-seen deaths of striped bass in late summer of 2013 and 2018. The Georgia DNR tracks fish movements within the reservoir using transmitters surgically embedded inside 39 striped bass released into Lake Hartwell earlier in 2019. Rabern compares the fish movements with water quality information gathered by the Savannah District’s fisheries biologist, James Sykes and Natural Resource Specialist Jess Fleming.

As the water warms and the deeper layer continues to lose oxygen, the zone of cool, oxygenated water in the reservoir gets smaller and smaller. In 2018, it finally disappeared altogether, Rabern discovered. Georgia DNR has an ongoing study of water quality in the fisheries of Hartwell Lake. Rabern heads the data-gathering effort.

Rabern and colleague Tony Anderson spend much of their time on Lake Hartwell tracking fish movements. They use tracking devices surgically implanted into 39 striped bass that send a signal that sensors attached to buoys in the reservoir to detect and record the fish as they move about the 55,900 acres of Hartwell Lake.

The shrinking oxygen habitat for fish commonly occurs in Southeastern U.S. reservoirs, according to Rabern.

“We call it ‘the bubble’ or ‘the summer squeeze,’” Sykes said. In most years the bubble is of sufficient size to support striped bass and blueback herring through the summer, but in 2018, according to Rabern’s data, ‘the bubble’ finally disappeared altogether.

Then the dead and dying fish floated to the surface near the dam grabbing the attention of anglers and the passing public.

Biologists like Rabern and Sykes can detect when the bubble begins to shrink and know the fish will soon suffer distress.

“It’s like a train,” Sykes said. “You can see it coming, but there’s not a lot you can do about it.”

Not all the bass died. Most managed to find safe haven somewhere else in Hartwell Lake. In order to find cool water with oxygen, some fish travel many miles.

That includes one tracked striper nicknamed “The Wanderer,” a 12-pound specimen, which has passed receivers more than 4,000 times since its capture, tagging and release early this year.

Some “pings” have happened more than 28 miles from The Wanderer’s release location. The study aims to find where the other locations in the reservoir that support fish in the summer may be.

Natural Resource Specialist Jess Fleming takes water quality measurements in Lake Hartwell on the Georgia-South Carolina state line. The Corps of Engineers shares water temperature and dissolved oxygen data with the Georgia Department of Natural Resources in an effort to learn more about fish habitat and survivability in the reservoir.

Besides fish movement, Sykes and Park Ranger Jess Fleming provide water quality data in the joint effort. The South Carolina Department of Natural Resources also contributes to the three-way partnership. They all want to determine the reasons behind the possible decline in heavy-weight bass populations.

“Until about five years ago, folks would pull in 40 to 50-pound stripers from time-to-time,” Sykes said. “Those are very rare now.” Stripers grow about two pounds per year, Rabern explained.

Unusual rainfall or high water release rates in 2013 and 2018 may have factored into the loss of the bubble those years, Sykes speculated. In both years Lake Hartwell received well above average rainfall which led to higher discharge rates, according to project records.

The root cause that led to the fish mortality in those years may remain a mystery for a while. However, Georgia and South Carolina continually stock Hartwell Lake and other reservoirs and lakes in the region with striped bass and other sport fish to replenish the population.

Many of the stocked fish carry tags easily visible to anglers. Those tags include a message for reporting the catch, which also carries a small reward. The DNRs use the information about the catches to aid in their management of the fish population.

As the summer heats up, fishing will likely remain a popular pastime for those seeking relaxation and who want the challenge of finding and catching those elusive fish. It may take extra skill to find them, but an old American proverb says, “The worst day fishing beats the best day working.”

~ Billy Birdwell, Corporate Communications Office

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Striped bass tracking project to begin on Lake Hartwell

HARTWELL — Striped bass fishing is a favorite pastime for many Lake Hartwell anglers. For more than 40 years, the striped bass population in Lake Hartwell has been maintained by stocking small fish into the lake each spring. Given enough time and “groceries,” these striped bass can reach weights of 40 pounds or more.

However, over the last few years, Lake Hartwell anglers have expressed concern about the declining numbers of striped bass in the lake.

“We attribute the decline in the striped bass population to low levels of dissolved oxygen found down deep where striped bass live during the summertime,” Georgia DNR fisheries biologist Anthony Rabern said. “Droughts and floods can have a strong influence on water quality in the lake, especially during the summer months.”

To determine how striped bass in Lake Hartwell respond to harsh summertime conditions when these low oxygen levels occur, DNR biologists are surgically-implanting small radio transmitters into 40 striped bass this winter and will track their movements for the next 12 to 36 months.

“One of the goals for this project is to determine the seasonal migration patterns of striped bass in Lake Hartwell, and identify potential areas in the lake where summertime water quality may be better suited for their survival,” Project Leader Anthony Rabern said. “Another goal is to determine how many striped bass may actually die during the course of the year from either natural causes or from being harvested by anglers.”

It might be possible that some anglers will catch one of these striped bass that has an internal transmitter. If you catch a striped bass with a 3-inch long filament protruding from its belly, the DNR encourages you to report the tag number by calling (888) 824-7472 and to release the fish alive, if possible, so officials can continue to track the fish. If the fish is harvested, instructions will be provided on how to return the transmitter.

This project would not be possible without the combined efforts of both state DNRs, and the support of the U.S. Army Corps of Engineers.

“In the long run,” Rabern said, “we will use the results from this study to make Lake Hartwell the best fishing destination it can be.”

For more information about the Lake Hartwell Striped Bass Telemetry Project, contact Rabern, at (706) 947-1507.


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Clemson Marina

Join us during Clemson Marina’s biggest boat sales event of the year!  The BIG Splash is coming to Clemson Marina Thursday, March 7th through Saturday, March 9th!  On Saturday (3/9), bring the whole family for a day full of fun!  We’ve got kids entertainment, catfish fry and discount beer provided by The Grill, hourly giveaways, demo rides, and more!  We will have a ton of new and used boats to see, tours of the marina, and local vendors from our area!  You don’t want to miss this fun-filled event!  Doors will be open from 9 AM to 5 PM.

It’s the best deals of the year – dealer discounts up to $3000 OFF select models!  Also, enter for a chance to win an additional $1000 OFF your new boat purchase.  Come see the newest 2019 models of Xpress’s original all-welded aluminum fishing boats, Monterey sport boats, and Veranda Luxury Pontoons with Yamaha Outboard motors that will give you the quality, performance, and features you demand!  We are determined to get you in the boat that you have always wanted!

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