Texas Parks & Wildlife Magazine   


Killer Storms

When the Texas coast gets slammed by tropical storms, fish often pay the ultimate price.

By Chester Moore

On a low tide, the banks of Sabine Lake's East Pass are usually dark brown, revealing the influence of the convergence of two murky, silt-laden rivers. Specks of white shell highlight the shore, appearing as sparsely spaced snowflakes.

On a sweltering day in September 1998, however, the shoreline appeared unusually white.

Acting on a tip from a reader of my column in the Port Arthur News, Sabine Lake fishing guide Skip James and I went out to investigate reports of a fish kill along Sabine's eastern shoreline.

On our way out of East Pass into the main body, we noticed that something was amiss as we gazed to our east. Noticing the white, we first thought it was trash that Tropical Storm Frances had carried in from the flooded streets of nearby Port Arthur, but the pungent smell of rotting fish indicated something more sinister.

Approaching closer, our hearts sank as we realized the white along the shoreline was the undersides of dead flounder. Scattered 15 yards into the marsh and along more than 100 yards of shore were flounder of all sizes. This was the time of year flounder in the area school up in the surrounding marsh before the ensuing fall run. "However," James said, as we stood aghast at the haunting site, "there will be no run for us. Frances just gave our flounder fillets to the crabs."

Frances poured on Southeast Texas for a week, and when the water that had been standing still during that time moved into the bays, it choked out the dissolved oxygen level and began killing fish and other marine organisms, by the millions.

Texas Parks and Wildlife Department officials said there was no way of getting an accurate tally of the damage, but it was significant. The same scene we saw at Sabine Lake also appeared in East Matagorda Bay, throughout the Galveston ecosystem and in parts of Louisiana.

According to TPWD field reports, species killed in Galveston and East Matagorda Bay included flounder, blue crabs, shrimp, redfish, croaker and speckled trout. There were also massive kills of white shrimp and juvenile game fish in key estuaries such as those near Bastrop Bayou in the Lake Jackson area; ditto for the fertile marshes that make up the Anahuac National Wildlife Refuge.

Near Freeport, TPWD coastal fisheries biologists reported finding an estimated 5,000 dead flounder along 4.5 miles of the Intracoastal Waterway.

In Taylor and Hillebrandt Bayous near Port Arthur, TPWD reported thousands of dead blue and channel catfish, crappie, largemouth bass, mullet, crabs and crawfish.

That was seven years ago, but as a lifelong coastal angler it was something I will never forget. For me, it was a great learning experience about the nature of fish kills.

"When fish kills occur, there is a natural public tendency to look for some human cause, such as a toxic spill," said Dave Buzan, TPWD coastal conservation branch chief, in a statement to the press at the time of the disaster.

"But the main cause can be natural. This shows how coastal ecosystems have to deal periodically with severe natural stresses that we can't control, which makes it even more important for us to conserve natural resources with those factors we can control."

Underlying Causes

Tropical storms bring lots of wind, rising sea tides and intense rain down on coastal areas in a short amount of time. These natural forces combined are all part of the process of a fish kill, but each can do its own damage.

The key reason for post-storm fish kills is a low or virtually nonexistent level of dissolved oxygen in the water. This part is quite simple to understand because when the oxygen is low, fish can not acquire enough to metabolize and they get weak and may eventually die.

Many coastal anglers are familiar with small-scale fish kills during summer months when oxygen levels dip in certain areas. Storm kills operate on the same principle, but on a much larger scale, and are caused by different forces.

Wind is the culprit that most people would not suspect of decreasing the dissolved oxygen content, but it is a major factor. What happens in lakes and ponds within coastal marshes is that the wind pushes the surface water to one side. At this point, water from the bottom comes to the surface and fills the area the surface water occupied previously. And this is where the problem lies.

The bottom water brings with it various organic matter that, when stirred up, can take away the oxygen in the water. Many bottom materials are high in hydrogen sulfide, which can be lethal to fish and is what is responsible for the raw sewage odors often reported with fish kills. While inspecting Frances' wrath, I experienced this firsthand as some of the area smelled like a leaking septic tank.

The odor was bad enough that some anglers thought sewage from local industry might have leaked out in the rain and caused the kill. What happened, however, was the result of a completely natural phenomenon.

TPWD Coastal Fisheries Biologist Lance Robinson says this phenomenon is akin to what residents around Mobile Bay, Alabama, call a "jubilee."

"At some level these kills are a bit mysterious and can occur even without tropical systems," Robinson says.

"Take, for example, Mobile Bay's 'jubilees,' which are so named because fish, shrimp and crabs beach themselves on the shores. For years this was celebrated because people would go in and get fish by the ice chest full, but it's really part of a process that kills the fish and other marine organisms," he adds.

During these events in Mobile Bay, heavy winds blow toward the eastern shoreline, which is of quite a bit higher relief than the western. As this occurs, Robinson explains, "the bay turns over and the water that was on the bottom is pushed toward the top."

The bottom water brings with it more sediment, and this creates a wall of oxygen-depleted water that is toxic to marine life.

"This will literally push fish onto the beaches as they retreat from the water that is dangerous to them," Robinson says.

Similar situations can occur in Texas and as part of tropical storm systems, when oxygen-depleted water from storm systems purge from the marsh. These occurrences can literally trap fish in areas as they form and are responsible for the deaths of many of the fish killed during storms.

Species that dwell on the bottom, such as southern flounder and blue crabs, are especially susceptible to this. In fact, the kill I observed at Sabine Lake's East Pass was most likely due to that phenomenon. During that time of year, the flounder are in the marshes and oftentimes in lakes and ponds that are hard to access by anglers. Toxic water trapped the mass of flounder that came out of the marsh and when the tides started to recede, the bodies made their way out to the shorelines.

I remember watching as the tides fell and black, odorous water from the marsh entered the bay. In one area, we saw millions of shrimp at the surface seemingly trying to get some oxygen. I was literally able to scoop live but dying shrimp up with my hand and observe tiny flounder and croaker at the surface, gulping for air.

"Those were likely fish that got trapped and had to deal with the toxic conditions they found themselves in," Robinson says.

There is yet another source of fish kills that spawns from tropical storms or happens separately, and that involves a lack of sunlight penetrating the water.

Officials with the Florida Fish and Wildlife Institute who have had to deal with numerous kills caused by the relentless storms that have hit the state over the last few years explain this component of fish kills as quite complex.

"In aquatic ecosystems, the oxygen manufacturing system consists of microscopic organisms and aquatic plants that carry out photosynthesis: using energy from sunlight to create carbon-based nutrition for themselves with oxygen as a by-product," according to a paper they published entitled "How Do Hurricanes Kill Fish?"

It goes on to say that when there are long periods of cloudy days, these organisms produce less oxygen.

"At night, photosynthesis doesn't occur at all, and these same oxygen-producers are actually using up oxygen during respiration, just like fish and other animals. Under these conditions, it does not take long before there is little oxygen left for fish. Low-dissolved-oxygen fish kills often occur early in the morning, when oxygen levels are at their lowest."

Long-term Effects

Robinson says despite the carnage that ensues after one of these kills, they are probably important for the long-term health of the ecosystem.

"They are probably more of a benefit overall because those kinds of events occur throughout history," he says, " A good analogy would be the old range fires that occur throughout the grasslands. Fire is a natural component of maintaining healthy grasslands, and these kills are likely equally as important to an estuary although they certainly do not appear to be that way when you witness one for yourself."

These events tend to knock back a lot of the vegetation, including the undesirable plants, and in time, there is a major growth of new, healthy plant material and vegetation.

James says for him, the kill on Sabine Lake hurt the flounder fishing from which he derives a good portion of his income.

"When the big kill hit, it really did a number on my fishing in those certain areas because flounder were hit really hard," he says.

"I wondered if it might have serious, long-lasting effects on the area, but a few years later those bayous and shorelines were back to normal in terms of flounder activity. I will say that witnessing something like that firsthand is disheartening, but in the end it's all part of the big picture."

James says what worries him is the intrusion of seawater into coastal marshes, which could cause more long-term damage.

"Manmade waterways like the Intracoastal have allowed much more saltwater to get into the marshes and when you have a storm, they certainly make storm surges more devastating to our ecosystems, at least from what I have seen being a fishing guide for 20 years. They are certainly necessary for commerce, but seem to come with an environmental price," he says.

Robinson says the Intracoastal Waterway and other channelization projects have thrown a wild card into the mix with these storms and with saltwater intrusion in general, but that TPWD officials are closely studying ways to protect the marshes and learn more about naturally caused fish kills.

"We got hit hard in '98 and have had small, localized kills since then. We are learning more about these factors all the time and are working to find ways to counteract any negatives that might possibly ensue," he says.

Nevertheless, in the end, Mother Nature does what she wants despite our opinions on the matter.

Take it from someone who had the opportunity to witness one of these kills firsthand, when the carnage stretches as far as the eye can see, it is hard to comprehend how this could actually be good for the environment in the long run.

Flounder Stocking Is On the Way

The sport fish that tropical storms typically hit hardest is the southern flounder. Dwelling on the bottom where oxygen levels are lowest and not as easily mobile as speckled trout or redfish, they are more susceptible to oxygen depletion.

Already hit hard by shrimping-related bycatch, flounder numbers get sucker-punched by these storms, but TPWD coastal fisheries biologists are hoping to rejuvenate flounder populations.

"We are working on developing a full-scale flounder stocking program that would greatly supplement natural spawning in the wild," says TPWD biologist Robert Vega.

Working with Joan Holt of the University of Texas Marine Science Institute, TPWD officials are still working through a number of obstacles, but remain positive.

Holt has spawned some flounder at a facility in Port Aransas, but there have been some problems rearing them in outside ponds.

"We have a number of hurdles to overcome, but the goal is worthwhile. A stocking program could make a significant contribution to recovery," Vega says.

Currently, there is flounder brood stock at three TPWD coastal hatcheries, including Sea Center Texas in Lake Jackson, showing that the coastal fisheries crew is optimistic that this project will move forward.

"Flounder have a big following along the coast, and we hope to aid their long-term conservation by stocking them like we have red drum and spotted seatrout. Those programs have been successful, and we hope the same for southern flounder in the near future."

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