Beware The Gizzard Shad, My Son

Roosevelt Lake bass, crappie, bluegill continue to decline



Gizzard shad are believed by some to be the reason for the sharp decline of bass, crappie and bluegill in Roosevelt Lake.

The sharp decline in Roosevelt Lake’s once stellar reputation as a bass fishery continues to bedevil local businesses and the Arizona Game and Fish Department.

Some 63 local fishermen, business people and local officials gathered on Dec. 4 to appeal to Game and Fish to save the nationally renowned bass fishery. Most present blamed the decline of the bass on a population explosion among invading gizzard shad, which may have kicked the legs out from under the stool of the lake’s underwater ecosystem.

The algae and plankton-eating gizzard shad showed up in the lake more than six years ago, apparently outcompeting the much smaller species of shad that previously formed the basis of the reservoir’s food chain.

The gizzard shad feed on the same zooplankton that sustains the shad, the bluegill, the crappie and the tiny, newborn bass. Unfortunately, the gizzard shad can quickly grow up to a foot long, too big for the largemouth bass to swallow.

At least, that’s the theory. No one knows for sure whether to pin the blame for the decline of the bass, crappie and bluegill on the invading gizzard shad. Lake levels have fluctuated dramatically in the past five years. At one point, they hit record levels — inundating brush along the shoreline and resulting in a bass population boom. But the lake has now dwindled to less than half its capacity, which has a big impact on all the fish populations there.

However, the gizzard shad remain the leading suspects. Moreover, they’ve also spread to Apache Lake, which means gizzard shad will likely colonize all of the Salt River reservoirs, with their economically important bass fisheries.

Certainly, something has affected the bass fishery in a lake that has drawn nationally televised bass tournaments and rave reviews in fishing magazines.

Fishing expert James Goughnour reported that in the 2011 Roosevelt Lake FLW EverStart Tournament 92 percent of the competing fishermen weighed their limit — with a total weight of fish among just the top 10 finishers tipping the scales at over 350 pounds. By contrast, in the EverStart tournament held just over two months ago, only 13 percent of the pros brought in their limit, with a total weight for all fish brought to the scales of just 200 pounds.

Several years ago, Bassmaster Magazine listed Roosevelt as one of the top-100 bass fisheries in the country. But now backers fear the lake will have trouble attracting national tournaments, which give the region huge exposure.

Fishermen spend an estimated $831 million annually in Arizona, according to a study by economists from Arizona State University. Fishing and water recreation remain the mainstay of the Tonto Basin economy and get a big boost from those nationally televised tournaments. An estimated half a million people view the national bass tournament weigh-ins televised live and about a million people a week visit the FLW’s Web site.

Recent surveys by the Arizona Game and Fish Department bear out the apparent crash in the numbers of bass, crappie and bluegill as the gizzard shad population has exploded, according to a presentation by Game and Fish Branch Fisheries Chief Chris Cantrell at the meeting.

Game and Fish used electro-shocking to sample fish populations in the lake in October of 2013 and October of 2011. Cantrell advised his listeners to view the figures cautiously due to the different conditions on the sample days. He said fish managers couldn’t come to any firm conclusions about population trends without a much more extensive — and expensive — sampling system. Nonetheless, the trend was alarming.

For starters, even the gizzard shad have seemingly dwindled. In 2011, the samplers shocked to the surface 75 gizzard shad per hour. This year, they netted just 15 per hour. On the other hand, in 2011 the gizzard shad were mostly 13 to 17 inches long. This year, they seemed to come in all sizes.

On the other hand, the number of bluegill sampled per hour fell from 30 to just seven and they proved much smaller than in 2011.

The number of largemouth bass sampled per hour dropped from 50 to 10, with much smaller fish than in 2011.

Crappie generally stay in deeper water, so the electro-shock sampling method doesn’t work on them.

Overall, gizzard shad accounted for 27 percent of the fish counted. Most fish recover from the shock after a few minutes of floating at the surface.

Many of the fishermen expressed frustration that Game and Fish continues to ponder the problem without taking any direct action to save the bass fishery.

Cantrell cautioned that no one knows how to get rid of gizzard shad once they’ve become established, except to drain the lake, get rid all of the fish and start all over. Roosevelt Lake remains the main drinking water reservoir for the Valley in a period marked by intermittent drought, so the prospect of draining it remains remote — unless a return of the drought does the job.

However, other suggestions included stocking more bass into the lake — reinforcements against the wave of invaders. That suggestion bears more than a hint of irony, since the non-native bass, catfish, bluegill, crappie and carp have played a leading role in almost exterminating most of the native Arizona fish that teemed in the state’s streams and rivers before the era of dams, reservoirs and non-native sport fish.

Other suggestions included finding some game fish that could prey on the gizzard shad, even when they grow to more than foot in length.

Still others suggested building a series of underwater structures that would give the ambush predator largemouth bass a place to hide and hunt, improving their success rate. Such structures also concentrate the bass and increase fishing success.

On the other hand, some bass experts in lakes and streams in the South maintain that gizzard shad don’t pose a long-term problem once populations come into balance.

For a discussion of bass and gizzard shad see:


Heather Dotson 3 years ago

The lake looks like hell now that they've let the water level drop down so low. We don't even go there anymore. Last year was the last straw- we went to camp and the shoreline was littered with dead & rotting fish. We won't be back until the water levels rise.


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