Recently I attended a workshop on wildlife tagging projects. Researchers from across the Gulf of Mexico who had projects going on in the northern Gulf were invited to present their updates. I was there to help present what we have learned about diamondback terrapins but there were numerous other talks, and the results were fascinating. Fascinating enough that I thought the public would be interested in them as well. Most of the presentations were on fish or reptiles, but the fish included interesting species such as whale sharks, tiger sharks, cobia, and tarpon. So, I am going to run a series of posts on the different species along with another series on barrier island wildlife.
I thought I would start with an introduction on the methods of wildlife tagging and why scientists tag animals. Some of the reasons may seem obvious, but with today’s modern tags, there is a lot of information scientists can gain from doing this.
Why do they tag?
With the types of tags they used when I was in school there were a few things that you could learn. (1) How far do the animals range, (2) how fast they reached those locations, (3) some idea of live longevity – you at least knew how long they were “at freedom”. With these data you could get a better idea of what their habitat range was and how they used the habitat. Some, like blue sharks, may move great distances all year long. Others, like nurse sharks, may not move more than a few miles from the point where they were tagged. Others may move seasonally, spending summer in one region and winter in another. All of these data are useful to resource managers responsible for maintaining the species population.
With the more modern electronic tags, they can learn such things as how deep they dive, how long they stay at depth, what water temperatures they may frequent, what salinity they prefer, and let you know where the animal is at any given moment in time. Today’s tags are pretty amazing.
This tag is similar to the ones we used in the 1980s on sharks. They provide a number for individual identification. Ours also had a capsule with a note on water resistant paper.
Photo: Hallprint.
How do they tag?
Well… step one to answering this question is HOW DO YOU CATCH THE ANIMAL? – not as easy as you think. Whale sharks and leatherback sea turtles are quite a handful. If your target species is something like a white shark, tiger shark, diamondback rattlesnake, there is an extra danger added. As you plan a method for your safety, you must also plan a method for their safety. The objective is not harm or kill the creature – you will learn nothing from this. When I began my career, I saw a program on how they tagged polar bears in the 1980s. They would fly over the ice in a helicopter looking for the bears. When the bears saw the helicopter, they would run for the safety of water. The scientist would try to shoot a dart into the animal to put it asleep long enough to get a tag on it. BUT if you overdosed the bear, and it made it to the water, it could drown. So, from the air, they had to gauge the weight of the bear, guess what amount of the drug to shoot, and hope they were right. If the bear did fall asleep, how “asleep was it? Did you give ENOUGH drug? Polar bears can be very dangerous. In the episode I watched the bear was asleep, but the researchers did mention that they will “play sleep” and you need to be ready. Such was the world of wildlife tagging 40 years ago.
One of the things that was also discussed when I was in school was what type of tag you were going to place on the animal. They did not have the neat tools they have now. Most tags had a capsule with a piece of paper, sometimes written in multiple languages, to call said person and report where and when they found the animal. There was usually a monetary award for doing so, or sometimes a hat or T-shirt. I remember the hat you got for reporting a tagged redfish was really neat, but I never caught a tagged one.
You did not want to place a tag that would alter the natural behavior of the animal. In the case of the polar bear, they would place an ear tag and paint a large number on its side in black paint. This made sense from the biologist’s side – flying over the ice you could see the large black “3” on a bear and know the individual. But that large black number could also be seen by their prey. Not good. I saw researchers painting the shells of gopher tortoises with all sorts of neon colors to make detection by them easier, but easier for their predators as well.
Radio tagging was used 40 years ago. This involves capturing the animal (as we have already seen – fun in itself), putting it asleep and attaching/inserting a radio tag. This tag provides a radio signal that can be detected by a receiver carried by the research holding an antenna walking/driving around following the animal. You had to be within range to hear the signal and – honestly – good at detecting the signal. Some researchers were better at this than others. As you can imagine this was only as good as your ability to keep up with the animal. At some point your car/boat would need fuel, or the animal crossed a river you could not. It provided some good data, but there were limits.
Today modern tags have solved a lot of these issues. Some new tags do not have typed notes but sensors that can detect the elevation/depth, temperature/salinity, all sorts of information that was unknown in my college days. These tags can be retrieved and downloaded on a computer to give a much better idea of how the animal spends its time and what it seeks.
This modern shark tag could provide additional information such as diving depth, water temperature, and more.
Satellite tags work well for creatures who surface frequently – sea turtles, whales, whale sharks. Satellites can detect them, and you can follow their movements/habitat preferences as they are actually using them.
For species at depth, like some sharks, cobia, tarpon, etc. there are now acoustic tags. The tag emits a signal that is detected by an array of receivers the researchers place in the environment. As the animal passes within range of the receiver it is detected, and the downloaded data gives a similar picture of how the animal uses the environment. A couple of neat things about acoustic tags are that (a) you can track satellite tagged animals while they are diving, and (b) your receivers can detect other species tagged by other researchers and let them know where their creature was. This was one reason for the workshop – so, everyone could meet everyone else and know who has tagged what and how to share information.
No tag is permanent. All are designed to fall off. Battery power will eventually fail. But no animal is stuck with this all of their lives as they could have been when I was in school. In future articles we will look at the results of some of these studies.
This tag with an antenna can be detected by a satellite and tracked real time.
Photo: USGS
A deer darting across a path, a bobwhite calling at sunrise, or the tracks of a coyote in the mud are all fascinating examples of how we enjoy our natural areas. Have you ever wished you could watch wildlife all day to understand the intricate relationships they have with one another? What if you could learn more about their behavior? And their habitat and daily activities?
Deer captured on a digital game camera.
Image: Dr. Carolina Barzzui.
Dr. Carolina Baruzzi at the UF/IFAS North Florida Research and Education Center and Dr. Corey Callaghan at the UF/IFAS Fort Lauderdale Research and Education Center are launching “ConservationCam”, a new extension program to help you monitor wildlife on your property using camera traps.
Camera traps are a valuable tool for wildlife monitoring. When an animal moves in front of a camera, they trigger a motion sensor to take a picture or video. Camera traps can be set up in multiple ways to target a species or habitat of interest, such as a forest opening or a wildlife burrow. Thanks to their versatility and relative low cost, camera traps are being used in a variety of contexts, for example, understanding the effects of wildlife or habitat management on target species.
Images of turkeys captured on a digital game cam.
Image: Dr. Carolina Barzzui.
The primary goal of ConservationCam is to provide private landowners with access to camera traps, and expert guidance about monitoring wildlife and managing natural resources for biodiversity based on camera trap observations. Armed with this knowledge, landowners can make informed decisions about land management practices that positively impact biodiversity on their property. If you live in the Florida Panhandle, and are interested in using camera traps to monitor wildlife on your property, while learning how to answer different ecological questions, we are gathering expressions of interest through this online form.
Rabbit near a burrow on a digital game came.
Image: Dr. Carolina Barzzui.
Back in the spring, I wrote an article about the natural history of this ancient animal. However, Florida Fish and Wildlife Conservation Commission (FWC) is interested in the status of horseshoe crabs and they need to know locations where they are breeding – and Florida Sea Grant is trying to help.
Horseshoe crabs breeding on the beach. Photo: Florida Sea Grant
If you are not familiar with the horseshoe crab, it is a bizarre looking creature. At first glance, you might mistake it for a stingray. It has the same basic shape and a long spine for a tail. But further observation you would realize it is not a stingray at all.
So then… What is it?
When you find one, most are not comfortable with the idea of picking it up to look closer. The spine is probably dangerous and there are numerous smaller spines on the body. Actually, the long spine in the tail region is not dangerous. It is called a telson and is most often used by the animal to push through the environment when needed, as well as righting itself when upside down. It is on a ball-and-socket joint and if you pick them up, they will swing it around – albeit slowly – but it is of no danger. Note though, do not pick them up by the telson – this can damage them.
If you do try to pick them up with your hands on their sides, you will find they are well armored and have numerous clawed legs on the bottom side. At first, you are thinking it is a crab, and the claws are going to pinch, but again we would be mistaken. The claws are quite harmless – they even tickle when handled. I have held them to allow kids to place their hands in there to feel this. However, when held they will bend their abdomen between 90° and 120°, as if attempting to roll into a ball – which they cannot. At this point, they become difficult to hold. Your hands feel they are in the way and the small spines on the side of the abdomen begin to pierce your skin. So, you flip it on its back. It begins to try a 90° bend in the other direction and begins to swing the telson around. This is probably the most comfortable position for you to hold – but I am not sure what the crab thinks about it.
So, what do you have?
Well, you can see why they call it a crab. It has clawed legs and a hard shell. The body is very segmented. You can also see why it is called a “horseshoe”. But actually, it is not a crab.
Crabs are crustaceans. Crustaceans have two body segments – a head and abdomen, no middle thorax as found on insects. This is the case with the horse crab as well.
Crustaceans have 10-segmented legs, though the claw (cheliped) and swimming paddles (swimmerets) of the blue crab count as “segmented legs”. Horseshoe crabs have 10 as well – seems this IS a crab – but wait…
Crustaceans have two sets of antenna – two short ones and two long – horseshoe crabs do not have any antenna. Traditionally biologists have divided arthropods into two subphyla – those with antenna and those without – so the horseshoe crab is not a crab. It is actually more closely related to spiders, ticks, and scorpions.
Blue crabs are one of the few crabs with swimming appendages. Photo: Molly O’Connor
It is an ancient animal, fossil horseshoe crabs in this form date back over 440 million years – out dating the dinosaurs. There are four different species of today and there probably were more species in the past. Their range extends from the tropics and temperate coastlines of the planet. Today three of the remaining four species live in Southeast Asia. The fourth, Limulus polyphemus, lives along the eastern and Gulf coast of the United States.
Unfortunately, this neat and ancient creature is becoming rare in some parts of its range. There is a commercial harvest for them. Their blood is actually blue and contains properties beneficially in medicine. Smaller ones are used as bait in the eel fishery, and there is always the classic loss of habitat. These are estuarine creatures and are often found in seagrass and muddy bottom habitats where they forage on bottom dwelling (benthic) animals.
FWC is interested in where horseshoe crabs still breed in our state. Some Sea Grant Agents in the panhandle are assisting by working with locals to report sightings. Sea Grant also has a citizen scientist tagging program to help assess their status. Horseshoe crabs typically breed in the spring and fall during the new and full moons. On those days, they are most likely to lay their eggs along the shoreline during the high tide. This month the full moon is October 5 and the new moon is October 19. We ask locals who live along the coast to search for breeding pairs on October 4-6 and October 18-20 during high tides. If you find breeding pairs, or better yet, animals along the beach laying eggs – please contact your local Sea Grant Agent. We will conduct these surveys in the spring and fall of 2018 and post best search dates at that time.
Talk about weird and cool at the same time! The horseshoe crab is one of the oldest living species we have in the Gulf of Mexico. Fossils of this animal date back to almost 500 million years… this is before there was such a thing as fish! The separating of Pangea, the rise and fall of the dinosaurs, oh what stories these guys could tell! And they are here today, trudging along in the soft sands of estuaries along the Atlantic and Gulf coasts… but they seem to be on the decline. After all they have been through… they may be slipping away.
Horseshoe crabs breeding on the beach. Photo: Florida Sea Grant
Actually, horseshoe crabs are not crabs at all. They belong to the same large group of animals the crabs belong to, Arthropods, but differ from true crabs in that they have fewer jointed legs and no antennae. They are actually more closely related to spiders and scorpions. There are 4 species remaining on Earth. Limulus polyphemus is the local variety with the other three living in Asia. They are tolerant of a wide range of environmental conditions. Huge swings in water temperature and salinity do not bother them. This is not surprising considering all of the environmental changes that have occurred since the species first appeared on the planet. They are scavengers, plowing through the soft bottom of estuaries, they feed on worms, mollusk, and whatever else their crop-gizzard system can breakdown. Their protective shell deters many predators; most horseshoe crabs meet their fate on the beach – where they must go to breed.
Breeding occurs all year in Florida. It typically takes place three days before and after the new or full moon. The smaller males come near shore and patrol for the oncoming females. As the females are intercepted the males will use their “hook” to hold on and the pair ride onto the beach. This usually happens at night (though not always) during the peak of a spring high tide. The female digs a small depression and deposits between 200 and 300 eggs, the male fertilizes them, and the female buries them. They leave the young on their own for a month, at which time the next spring tide arrives and the larva, which resemble trilobites, emerge. Many fall prey to shorebirds and many adults actually become stranded on the beach during nesting and die.
So why the population decline?
Well, they do tolerate large swings in environmental change, so increase temperatures, rainfall, salinities, do not bother them. Studies have shown that they are actually quite tolerant of many of the pollutants, including oil, we discharge into our bays – though mercury is a problem for the developing trilobite larva. Along the Atlantic coast the animals are collected for bait and the biomedical industry. Horseshoe crabs are used in eel traps and there are several medical uses for their blood. Some biomedical industries collect the crabs, remove some of the blood, and return them – but not all survive this. A big problem they are facing, and this would be closer to home, is the loss of nesting habitat. Seawalls, jetties, groins, and coastal development in general have disturbed nesting beaches.
That said, they seem to be making a comeback on Pensacola Beach. There have been sightings at both Big and Little Sabine. We would like to record where they are nesting in the panhandle. If you would like to help – the full moon for the next few months will occur on March 22, April 22, May 21, and June 20. The new moon will occur March 8, April 7, May 6, and June 4. If you do see a horseshoe crab please contact me at (850) 475-5230, or email at roc1@ufl.edu.
