June 2003

Midnight Maneuvers on Mad Island

By M. Todd Merendino

Why do grown men and women run around the marsh chasing alligators and mottled ducks? It's called research.

Under a dark moon and a star-filled, mid-summer sky, the marsh at Mad Island Wildlife Management Area is eerily still and ghostly serene. Frogs and crickets sing their night choruses. The Milky Way appears as a hazy sheen across the sky. It's a good night for going into the 3,000-acre freshwater marsh, one of the richest in Texas.

I'm at the helm of one of the airboats, and another Texas Parks and Wildlife Department biologist, Matt Nelson, drives the other. Tonight, two crews, consisting of Marc Ealy, Monte Hensley, Robert Korenek, Kevin Kriegel and Pam Carroll, are heading out to search the marsh for alligators and mottled ducks.

With a flick of a wrist, the beams of four 400,000-candlepower spotlights rip the night. Hundreds of red dots - reflections of the eyes of alligators - glow across the marsh. Mottled ducks caught in the glare of the lights scurry for the cover of marsh grasses.

Our night maneuvers are part of the Central Coast Wetland Ecosystem Project, a Texas Parks and Wildlife Department study designed to help us better understand the ecology and function of marshes. One of the ways we do this is by studying two of the marsh's year-round residents, the American alligator and the mottled duck.

The alligator is the top predator in the marsh and helps keep populations of many other species in balance with the habitat. (In some areas, however, they can also become overabundant.) Mottled ducks, which resemble female mallards, are year-round residents of the Texas Coast. Unlike other ducks that migrate north in the spring, mottled ducks rely on our coastal marshes and wetlands for all their survival needs. Like the canary in the coal mine, these two species serve as barometers for the health of our coastal wetlands ecosystem.

Catching alligators can be a rush. Catching ducks can be comic. The mission starts at 9:30 at night and often ends at 4 in the morning, when the tired crews clean out the boats and head for home. We get paid to do this, but driving airboats at night, wrestling alligators and chasing ducks in the mud is too much fun to be called work.

Grabbing 'Gators

TPWD began a marsh ecology study at Mad Island WMA in 1993. One purpose has been to examine changes in the distribution, abundance and growth rates of alligators in the marsh ecosystem. Considerable research had been done in Louisiana, but little had been conducted on Texas alligators. Back in 1993 we were putting in water-control structures at Mad Island and changing water flows back to a more natural pattern, and we needed to see how those changes were affecting the alligator population.

TPWD staff developed a research project that involved capturing alligators at night from airboats. Exciting in theory, it is even more exciting in application. From May through August, during the dark phases of the moon, TPWD crews head to Mad Island WMA to conduct their research. Two three-person crews use airboats and spotlights to search the coastal marsh for alligators. When eyes in the water glow red, our adrenaline begins pumping. It's 'gator-grabbing time.

Alligators shorter than four feet in length are generally captured by hand. The catchers lie on the bow of the airboat as the driver maneuvers toward the swimming alligator. If all goes well, the catchers grab the alligator behind the head and wrestle it onto the bow of the boat. Alligators longer than four feet are captured with a snare at the end of a six-foot pole. When snared, large alligators will spin and thrash. We've developed a simple device for dealing with large alligators. When the alligator tires from fighting the snare, we drag it into a five-foot-long piece of 10-inch diameter PVC pipe with a slit cut along its length through which the snare can be pulled. Once inside the pipe, the alligator is immobilized and can be handled safely.

Captured alligators are examined with a hand-held scanner to see if they have been captured previously. The scanner works like those at the grocery store checkout. It detects small metal/glass PIT (Passive Integrated Transponder) tags, each about the size of a small automobile fuse, that can be implanted under the alligator's skin with a large hypodermic needle. If the alligator has been tagged on a previous mission, the scanner reads the tag's number and the alligator is measured and released. New captures receive a tag inserted under the skin near the right rear leg. A numbered plastic cattle tag also is attached to the tail to aid in identifying recaptured alligators. The 'gator is then measured and its gender determined. After all data are recorded, the animal is released. On a good night, the two crews may catch 40 or more alligators between them.

Since 1993, more than 500 alligators have been captured. Of those, 125 have been recaptured in subsequent nighttime missions. The data indicate that alligators at Mad Island grow an average of six inches a year. Conventional wisdom held that alligators grew a foot a year. Since alligators breed when they reach about six feet in length, we see that it takes 10 to 12 years for these alligators to reach breeding size. That gives us answers as to how our harvest is impacting alligator populations, if at all. Information such as this is critical in developing management strategies. Variations in growth rate may be due to an overabundance of alligators, lack of prey, environmental conditions or, most likely, a combination of many factors.

Alligators appear to be homebodies, as most "recaps" are found within a few hundred yards of where they were captured originally. At Mad Island WMA, this limited movement may be more of a function of water salinity than the alligators' desire to stay put. Although larger alligators may be seen in saltier bay waters, they cannot tolerate high salinities, those greater than 15 parts per thousand. Young alligators will die if water salinity exceeds 10 parts per thousand for extended periods of time.

At Mad Island WMA, the majority of alligators seem to prefer the fresher portions of the marsh, where salinity is less than five parts per thousand. They move into the lower areas of the marsh only when rains flush saltier water from the system. To maintain alligator habitat, the marsh must be managed to allow freshwater inflows and prevent saltwater intrusion. Proper harvest management also is necessary to keep alligator populations in balance with their prey.

Banding Ducks

Unlike other, more familiar waterfowl species, mottled ducks do not migrate north in the spring. They may move along the Gulf Coast, back and forth between Texas and Louisiana, but they generally spend their lives within 60 miles of the Gulf of Mexico. Given that mottled ducks are endemic to the coastal environment, they make a good barometer for determining the health of our coastal wetlands.

During the past 30 years, the coastal wetland homes of mottled ducks have changed dramatically because of natural and human-caused factors. However, the last banding study on mottled ducks had been done in the 1970s by TPWD biologist Charles Stutzenbaker (see sidebar). Since that time, we had had bag limit, season and habitat changes, and we had no idea how those three things were affecting mottled duck populations.

In 1997, TPWD began a five-year banding study to examine survival rates and movements of mottled ducks along the Gulf Coast. This cooperative study involves personnel from TPWD, U.S. Fish and Wildlife Service and the Louisiana Department of Wildlife and Fisheries. We can compare our data to Stutzenbaker's from the 1970s and determine whether we need to adjust harvest limits.

As with alligators, nightlighting from airboats is the most efficient (and exciting) way to capture the ducks. This is done during the molt, when young birds are not yet able to fly and mature birds have lost their old feathers and are growing new ones. Both young and old are unable to fly for four to six weeks, during which time they hide in heavy cover to avoid predators. This makes capturing them all the more exciting.

The crews slowly maneuver the airboats through the marsh, scanning from side to side with spotlights. When flightless ducks - either ducklings or molting adults - are sighted, the crew gives chase. Some ducks can be captured by leaning over the bow or side of the boat, but often the catcher has to get out of the boat and run the ducks down. This part of the work can be somewhat dangerous, but it is usually comical as the ducks zig and zag in the grass and shallow water with the catcher in pursuit. On these nighttime sorties, each crew usually captures about 40 mottled ducks, but more than 200 have been captured on a single excursion.

Biologists also use rocket netting in some locations. Once a suitable site is located, the crew sets a 40-foot by 60-foot small-mesh net affixed to four short lengths of pipe into which small explosive charges are loaded. These are the rockets. The crew uses rice to bait a small area directly in front of the net. Once the ducks begin using the baited site, the crew waits a mile away while the shooter watches from a nearby blind. Once sufficient numbers of birds are feeding within the capture area, the shooter fires the net with a charge from a six-volt battery. Pandemonium generally ensues as birds try to escape the net and the crew rushes in to remove them. Average net shots generally capture about 40 ducks, but more than 125 have been captured in a single net shot.

Captured mottled ducks are classified as either adults or immatures that hatched that summer. After their gender is determined, they are outfitted with a numbered aluminum leg band. When banding crews recapture one of these ducks, they can determine its age and how far it has traveled from the banding site. Waterfowl hunters are an important part of the project. When they shoot a banded mottled duck, the information they provide on its location and date of harvest can be used to determine survival probabilities and movement along the coast.

Since 1997, TPWD has banded more than 6,000 mottled ducks. The U.S. Fish and Wildlife Service and the Louisiana Department of Wildlife and Fisheries have banded additional mottled ducks during that time. Recovery data indicate that the ducks move about considerably up and down the Gulf Coast. Most of this movement appears to depend on the seasonal availability of wetland habitat. For example, if it is dry on the Texas mid-coast, mottled ducks appear to move northward across Galveston Bay and into Louisiana in search of better habitat. When conditions improve, the ducks will return to more familiar surroundings. Smaller numbers of mottled ducks move from the rice prairies west of Houston to coastal marshes during late summer and early fall and then return to the rice prairies later in the winter.

Although they inhabit most of the Gulf Coast, mottled ducks are true Texas natives and, as such, should be a species of special management status. Protection and management of key coastal marshes are critical because mottled ducks use coastal marshes extensively. However, newly hatched ducklings will die if water salinity exceeds 10 parts per thousand for any length of time. Because the Texas Coast is dry and salty during most summers, managers of habitat for mottled ducks should strive to reduce saltwater intrusion, maintain freshwater inflows and provide for shallow freshwater breeding areas.

Perhaps Charles Stutzenbaker best sums up why we should care about alligators and mottled ducks and the freshwater marshes where they live. "Think of the animals you like to see and the fish you like to catch and the crabs you like to eat as the interest earned on the marsh," he says. "The marsh itself is the principal. As the habitat declines and the principal gets smaller, the interest - the things you enjoy - also gets smaller. That's why it is necessary to preserve the whole array of marsh habitat."

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