Texas Parks & Wildlife Magazine   


Photo by Earl Nottingham / TPWD

Texas Tag

Tracking animals offers insight into their habits and habitats.

By Melissa Gaskill

Whale sharks conserve energy by gliding.
A mako shark swam from Texas waters to those off the coast of Virginia — twice.
One bighorn sheep traveled from Black Gap Wildlife Management Area 40 miles into Mexico, then returned a few weeks later.
Once male whooping cranes establish a territory, they stay in it for life.
Female Kemp’s ridley sea turtles stay near the coastline when traveling across the Gulf of Mexico, while green sea turtles head straight across, hopping the Gulf Stream into the Atlantic Ocean.
How do we know?

Texas scientists and conservationists learned these valuable nuggets of information thanks to tags, collars and other methods of tracking animals. Such insights into where animals go and how they behave can help protect them and their habitats.

Photo by Sonja Sommerfeld / TPWD

Hummingbirds are being tracked by scientists to learn about their movements.

Photo by Earl Nottingham / TPWD

Tags on purple martins reveal their migration patterns.

Whale sharks follow their prey, plankton, in ocean depths during the day and nearer the surface at night.

“These are large marine animals that eat small food,” says Lee Fuiman at the University of Texas Marine Science Institute. “There’s not a lot of energy in individual plankton, and large animals require a lot of energy, so how do they survive? Part of the answer is that they regulate the energy they use while swimming — by gliding, for instance. We learned that from accelerometers.”

Accelerometer tags report the speed and direction of an animal to which they are attached, as well as its movements, including how frequently and how fast a shark moves its tail. That, in turn, reveals how much energy it uses when swimming.

Scientists at the Center for Sportfish Science and Conservation (CSSC) at the Harte Research Institute for Gulf of Mexico Studies have placed numbered tags on more than 6,000 sharks off the Texas coast, satellite tags on about 50 and acoustic tags on another 100 or so.

When scientists tag an animal and that tag is recovered, usually by anglers, it provides two locations and a rough approximation of the animal’s travels. Acoustic tags emit a sound detected by listening stations scattered along the coast, creating connect-the-dots routes. Satellite tags transmit their position to a satellite in real time, providing the most accurate picture of an animal’s movements. Acoustic tags last longer, however, because they are surgically implanted inside the animal’s body.

Photo © Jesse Cancelmo


CSSC director Greg Stunz says all tags help fill information gaps about shark distribution, feeding habits and movement patterns. With many shark populations in serious decline, filling those gaps is critical to properly managing them.

“Sharks are key apex predators important to the ecosystem,” Stunz says. “One of the first questions when managing them is, where do they go? We also want to know where they come from and whether they move through or, for example, come here to pup.”

Texas sharks don’t stay in Texas, he adds, as proved by that mako, named Pico.

Knowing that sharks travel through a lot of territorial seas and jurisdictions, where regulations vary wildly, highlights the importance of international cooperation on protection efforts.

In 2019, Nature Conservancy of Texas scientist Jorge Brenner tagged along, pun intended, with Texas Parks and Wildlife Department fisheries managers collecting catch data. He fitted two bull sharks with satellite tags and two black-tipped reef sharks with acoustic tags. In the past several years, Brenner has tagged a number of other sharks off the Texas and Florida coasts.

One of his main findings is that, even though considered offshore animals, bull sharks spend a lot of time near the coast. Management must therefore take into account both areas. He also observes that individuals of a species have unique behaviors.

“You need to tag a lot of animals to be able to infer aspects of their biology,” he says. “You can’t just tag one animal and expect to learn all you need to know.”

The value of tagging for a conservation organization is to find the most specific, relevant sites to protect.

Another CSSC project, the Great Red Snapper Count, aims to provide an estimate of the size of that population in U.S. waters of the Gulf of Mexico.

“Without knowing how many are out there, we can’t allocate the resource properly,” Stunz says. “Our role is to provide science to improve conservation and management of the species.”

The project tagged 4,000 fish from Brownsville to Florida and offered $250 for returned tags. Data collection for the two-year project went through the end of 2019, with a final report on fish numbers due this spring.

Follow tagged sharks at www.sportfishcenter.org/outreach/meet-our-sharks.

Sea turtles

At Padre Island National Seashore, Donna Shaver, chief of the Division of Sea Turtle Science and Recovery, has tagged some 700 nesting Kemp’s ridleys and more than 3,000 stranded sea turtles. Her data came in handy when TPWD revised the shrimp fishery management plan in the late 1990s.

Shaver also developed a computer model to distinguish foraging and migratory movements and define what areas the sea turtles use for each. She uses passive integrated transponders, or PITs, microchips with unique barcodes detected by a reader (also used by people to mark their pets). The tags provide the same point-to-point data as numbered tags, but last much longer because they are injected under the skin.

Black bears

Across the state on dry land, Louis Harveson at Sul Ross State University’s Borderlands Research Institute (BRI) spent five years monitoring 13 radio-collared black bears in Big Bend National Park to find out what kind of areas they used for dens. The bears chose dens in high, remote areas easy to defend. The Big Bend region is likely home to 50 to 100 bears currently, Harveson says, although during a recent drought, tracking data showed that many retreated into Mexico.

Photo by Earl Nottingham / TPWD

Bighorn sheep

BRI also used satellite collars to determine habitat use by bighorn sheep at Elephant Mountain Wildlife Management Area. Current research tracks the animals at Black Gap WMA.

“One thing we’re interested in is what may be keeping populations from reaching their potential. We investigate mortality, just like CSI,” Harveson says.

Things that kill the sheep include pathogens, mountain lions, poisonous plants and even falling off cliffs.

“It’s amazing what we can learn from collars — travel corridors, how often they go to water, group size, mortality,” he says. “We look through a certain lens and think we know good habitat, but track an animal, and they’ll tell you. This is a chance to learn why they choose, say, this water source versus another.”

A major takeaway for Harveson is the amount of space required by large animals such as bears and mountain lions, another species BRI has collared.

“The sheer vastness of what they require to survive is an important message from a landowner’s perspective,” he says. “We need to do better working with our neighbors.”

Photo © Johann Schumacher

Whooping cranes

Scientists know that the journey endangered whooping cranes make from Canada to the Aransas National Wildlife Refuge in Texas for the winter accounts for 40 percent to 60 percent of deaths in the population. To find out exactly what kills them, they began tracking chicks from Canada to Texas. The project also identifies stopover areas along the route that may need protection. Wade Harrell, whooping crane recovery coordinator at the U.S. Fish and Wildlife Service, says the newest tracking devices use cellular towers to provide locations every few minutes. Previously, satellite tags provided only three or four locations a day.

“Now we can basically see flight paths, and whether the birds choose a path to avoid something,” he says. “It gives us more info, literally day and night.”

Photo © Johann Schumacher


Compared to a large whooping crane, diminutive butterflies might seem impossible to tag. But hundreds of thousands have been, through Monarch Watch, a citizen science project initiated in 1992 to define the iconic butterfly’s fall migration. Thanks to tiny numbered stickers, scientists discovered that monarchs overwinter in Mexico, flying there from across the U.S. Each fall, the program distributes some 250,000 stickers to volunteers across North America who use them to tag monarchs and then submit data to Monarch Watch.

Craig Wilson at Texas A&M University provides tags each year to elementary students who capture monarchs passing through a garden he developed outside the USDA Building in College Station. The goal is to work out the butterflies’ paths and the time it takes them to fly south.

Do no harm

Scientists who tag or collar animals put a lot of effort into not harming their subjects, following established protocols and obtaining required permits.

“We want to answer scientific questions without taking a toll on the overall population,” Brenner says. “We know how fragile animals are. We work quickly and don’t handle the animal any more than we have to.”

Technological improvements have made a difference.

“There has been a lot of thought given to the design of the tags themselves,” Brenner says. “Tags are smaller. They also collect data for longer, so new ones don’t have to be applied. And multiple researchers share tracking data.”

Tagged sharks return to normal behavior within minutes of their release, says Stunz. Harveson notes that if a collar seems to bother an animal, it can be programmed to drop off.

Experts have developed guidelines for the percent of body weight for a tag so it won’t handicap an animal; for birds, Harrell says, it is 3 percent. Better battery technology makes a difference as well.

Tracking has taught scientists things they otherwise wouldn’t know, Harveson says. “For forever, we only got a glimpse. It’s still a glimpse, but now a much bigger one. As the Texas human population grows, we have to be better at managing our natural resources, and this technology allows us to do that. What we do and how we do it needs to be driven by data, by science-based decision making.”

Melissa Gaskill is an Austin-based writer, blogger and wildlife enthusiast.

What to do if you find/see a tagged animal

FISH The "Report a Tag” section of sportfishresearch.org has instructions for entering tag information. The tags themselves include brief instructions and contact info. On every shark tagged, the Nature Conservancy includes a plastic “spaghetti tag” with a phone number and an email for reporting it.

SEA TURTLES Report nesting sea turtles, tracks or hatchlings, or stranded sea turtles, tagged or untagged, immediately to (866) TURTLE-5.

WHOOPING CRANE Go to the Texas Whooper Watch website (tpwd.texas.gov/whoopingcranes) and click on "Is It a Whooping Crane?" to double-check identification, then submit details listed on the page via iNaturalist.org.

MONARCH BUTTERFLY Submit tag information via monarchwatch.org/tagging and scroll down to "Recoveries of Tagged Monarchs."

All illustrations © Punnawich Limparungpatanakij | Dreamstime.com

back to top ^

Related stories

Bayou Beasts 

Solving the Ridley Riddle

» Like this story? If you enjoy reading articles like this, subscribe to Texas Parks & Wildlife magazine.


Texas Parks & Wildlife Magazine 
Sign up for email updates
Sign up for email updates