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Hurricane Could Have Caused Huge Increase in Fish Populations

Red drum VIMSFishermen reported catching record-breaking numbers of red drum in Virginia and Maryland last year -- 2.7 million, more than thirty times the number the year before, according to state fisheries managers.

The increase in the southern species of fish –- more common in the Carolinas, Florida and the Gulf of Mexico -– could have been played a contributing role in the decline in the number of young blue crabs in the Chesapeake Bay last year, according to the Virginia Institute of Marine Science. Drum love to eat baby crabs.

But why such a sudden jump in drum populations last year?

Lee Paramore, a biologist with the North Carolina Division of Marine Fisheries who studies red drum, has a theory.  He believes that unusual weather conditions in 2011 spurred a population boom that spread from North Carolina into Virginia and Maryland.

“One thing that happened of interest in 2011 was Hurricane Irene,” Paramore said. “The time that Hurricane Irene passed through was exactly during the peak spawn of red drum, which occurred in late August.”

While you might not think that hurricanes would affect creatures beneath the waves, as it turns out, red drum are highly dependent on favorable winds and currents for their survival, Paramore said. Winds from the East off the Carolinas blow drum eggs and larvae from open waters –- where the fish spawn -- into more protected bays and inlets, where they find shelter. Hurricane Irene these winds in abundance. So the drum survived and grew in abundance, Paramore said.

Red drum from the North Carolina DMF“That is entirely possible,” said Dr. Susan Lowerre-Barbieri, a biologist with the Florida Fish and Wildlife Conservation Commission who has been studying red drum for a quarter century. “If you happen to get a hurricane year and more Easterly winds, the eggs are buoyant, and that should help the currents take more of them into the nursery area where they would be more protected. So I think that makes a lot of sense.”

As part of an effort to track drum movements and reproduction, Lowerre-Barbieri tape records the drum-like sounds that male red drum make with their swim bladders during spawning.  It is this drumming sound that gives the fish their name.

In Florida, a pattern has emerged:  When drum populations go up, crabs go down, because more are eaten by the fish, said Dr. Lowerre-Barbieri.

“There is a very clear connection between red drum populations and the blue crabs,” said Dr. Lowerre-Barbieri. “If we have really good year classes of juvenile red drum, we have lower indices of our blue crabs.”

An unusually warm winter in 2011-2012 may also have contributed to the large number of drum in the Chesapeake Bay last year, said Susanna Musick, Marine Recreation Specialist with the Virginia Institute of Marine Science.

“Something that we noticed at the beginning of last year was the unusually high number of red drum that we had sticking around in the Bay,” said Musick.  “Usually what happens is the red drum migrate out of the Bay in winter, and then come back in in the springtime.  And there was nearly a year-round presence of them (last year).”

The dramatic increase in drum was seen by anglers across the region. In Maryland, more than 240,000 red drum were reported caught and released last year (released, either because they were too small, or because the fishermen had already met the catch limit of one per day), according to the Maryland Department of Natural Resources.

“A lot of years we don’t see hardly any,” said Harry Rickabaugh, a biologist with the Maryland Department of Natural Resources.   “We never see numbers like this. Last year’s drum harvest was 10 times higher than anything else that was estimated from 1981 through 2012.”

Red drum are a popular sport fish in the Carolinas, Florida and Gulf of Mexico. They are a golden-rose colored migratory species that travel in huge schools that look like  cascading rivers of gold beneath the waves.  They sport fake-eye spots on their tails that some scientists believe the fish evolved to fool predators into attacking the wrong end, allowing the drum to escape. Drum live up to 60 years, growing up to three feet long and sixty pounds.

Red drum were nearly wiped out during the 1980s when Cajun style “blackened red fish” became trendy in restaurants. A ban on commercial harvesting allowed a rebound in red drum during the 1990s.

Lowerre-Barbieri photo“It’s quite a success story,” Dr. Lowerre-Barbieri (pictured at right) said of the resurgence of red drum. “It’s amazing that there was the will to take such measures in the 1980s and close down the fisheries and protect this stock.”

But everything in an ecosystem is linked together.  The overall number of blue crabs in the Chesapeake Bay dropped by more than half this year, compared to last, falling from 765 million to 300 million, according to estimates from an annual winter dredge survey. The number of juvenile blue crabs dropped from 581 million to 111 million.

Scientists say that several factors likely played roles in this year’s crab decline, including a low number of spawning-age females the previous year, and a die-off of some of the  Bay's underwater grasses caused by storms and heat. With less aquatic vegetation to hide in, young crabs are eaten by a variety of fish –- and also by other crabs.

“Predation and cannibalism probably had a large part in that (decline),” of young crabs, said Dr. Rom Lipcius, Professor of Marine Science at the Virginia Institute of Marine Science. “The red drum in particular are voracious, generalist predators, and they can consume large numbers of juvenile blue crabs. ….It could have had a severe effect on juvenile (crab) abundance.”

Dr. Anson “Tuck” Hines, Director of the Smithsonian Environmental Research Center, cautioned that crab populations often fluctuate widely from year to year, and it’s often difficult to say exactly why.

“What exactly caused the demise of all those little crabs is not really known.  And we shouldn’t fool ourselves that we have the single answer,” Dr. Hines said.

The big picture, Dr. Hines said, is that six years now have passed since crab populations in the Bay crashed to such low levels that the federal government declared a disaster.  In an effort to turn around the fishery, Virginia and Maryland five years ago imposed restrictions on catching female blue crabs, including banning winter-time dredging for hibernating females.

In four of the five years the crabbing regulations have been in place, crabs have experienced healthy increases –- with this year being the exception, Dr. Hines said.

A silver lining to the generally discouraging crab numbers this year is that populations of adult female crabs in this winter’s survey rose by more than 50 percent.

With this healthy number of mothers, an increase in baby crabs could well follow, next year.

“Overall, I think it’s a very good news story of a recovery of a population, and adaptive management that seems to be working,” Dr. Hines said.

The same could be said of the resurgence of red drum, a beautiful and musical fish.

By Tom Pelton

Chesapeake Bay Foundation

(Photo at top by Ken Neill of his wife Tricia Neill holding a red drum, from Virginia Institute of Marine Science website.  Drawing of red drum from South Carolina Department of Natural Resources.  At bottom, photo provided by Dr. Susan Lowerre-Barbieri.)

Comments

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- I wish that someone had mentioned the fact that South Carolina stocked millions of red drum from texas fish hatcheries right before this increase in "red drum population". Someone should genetically identify these fish as wild or stocked. I bet you'll find it's not the hurricane that caused this dramatic increase. - Undergraduate biology student

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