Monster stingrays: Field notes from a global wrangler
By Janet Raloff
Web edition : Monday, July 6th, 2009
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MONSTER FISHHeigh-ho, Hogan! Imagine hooking one of these freshwater behemoths — which you could if you were angling in parts of Thailand.Z. Hogan, National Geographic/University of Nevada-Reno

Tonight, couch potatoes with access to the National Geographic channel can watch a biologist pursue some of the biggest fish on Earth: giant stingrays. Since 2006, National Geo has been funding Zeb Hogan’s research on “megafish” — global treks to study freshwater behemoths that strain our vocabularies for appropriate superlatives. When the University of Nevada-Reno scientist was in Washington, recently, I sat down with him at the National Geo office (just down the street from ours) to learn what drives this scientist and what he hopes to learn.

We focused on those stingrays.

I thought these fish were marine denizens. After all, that’s where one infamously — and lethally — spiked Steve Irwin three years ago.

“Nine times out of 10, that’s where people are going to see these fish,” Hogan admits “— in the ocean.” But there are the occasional species of freshwater stingrays in Asia, Africa and North America. “And there are a couple dozen species of obligate freshwater stingrays in the Amazon,” he points out.

The ones Hogan has been following in Thailand for the past year or so — Himantura chaophraya — can be found in many places throughout Southeast Asia, including Indonesia, Malaysia and possibly northern Australia (although the Aussie variety, which may be another species, tends to be half the size of the Thai fish that Hogan’s been tagging).

At least in Thailand, these stingrays are huge — with bodies up to 2 meters in diameter and tip-to-tail lengths that can span more than twice that (like the length of a car). In tonight’s telecast, anglers find a possibly record-size female (the girls are always the largest). This big mama was carrying at least three young, babies that would be born live and immediately able to live on their own. This mom was the largest ray Hogan’s team had measured and was suspected of far exceeding the 200 kilograms (~440 pounds) at which these fish often tip the scales. (By the way, Hogan warns that the purported record 771 pound giant stingray that anglers reported hauling in earlier this year was never officially weighed. Its mass was merely guesstimated at some 350 kg. And this fish tale was later bandied about the Internet as fact.)

The Thai giant stingrays are sandy brown with white bellies. Anglers tend to hunt them with several-pound baits consisting of fish that are dragged along river bottoms. Although well known to Asian fishers, H. chaophraya was unknown to science until 20 years ago — and remains little studied.

Hogan hopes to change that. He’s tagged more than 15 with devices that ping. Unfortunately, their signal has a range of only about the width of the rivers these rays inhabit, so the fish have proven hard to follow. By seeding broad expanses of the river with receivers, Hogan has been trying to chart how far they wander. To date, he says, “I’ve only ever been able to follow two fish. It’s not much, but we’ll take what we can get.” It's not that the tags don't work, he explains. It's just that some tagged fish don't hang out where they were caught — or, apparently, in the vicinity of the receivers.

The good news, he says, is that unlike many big fish, some of these rays don’t seem to wander far. So the chances of his acquiring enough tagging information to begin to fill in the many gaps in knowledge about their life histories is good. Right now, they don't appear widespread. Pollution appears to curtail their presence to a few stretches of relatively clean river.

Hogan doesn’t catch the rays (or most of the fish he studies). He leaves that to experienced anglers — subsistence fishermen, when necessary, but usually the catch-and-release recreational rod-and-reel anglers. It takes perseverence to land one of these fish since the species usually flaps gracefully well below the radar screen. To find them, Hogan often hitches along for a couple days as anglers ply promising patches of river so that he will be present if and when a heavyweight is finally hauled in.

To understand this and other megafish species, and hopefully get them the respect that will compel governments and conservation groups to protect them, Hogan has been traipsing around the globe an average of eight months a year, and sharing some of his findings before a television camera.

About the stingrays, he reports that “almost all of the females we catch are pregnant, which to me indicates that they probably have long gestation periods — and get pregnant again shortly after giving birth.” Fecundity is low. Typically, a litter contains just three to eight baby rays.

He has witnessed two unplanned deliveries by captured females — one full-term in April, and another, aborted litter, earlier in the year. That would suggest the fish bear babies in spring. But Hogan observes he'll need way more data to know if this is a rule for Thai rays or whether they might drop babies year round.

It also appears that this species doesn’t enter the ocean, but more research will be necessary to confirm that as well. And Hogan is collecting tissue biopsies that will be DNA fingerprinted to probe how related this beast is to other giant stingrays in Asia and Australasia.

If these rays are like most members of their extended family — which includes sharks and skates — they probably mature slowly, reproducing only occasionally. That would suggest that hunting these fish as dinner or as entertainment could put undue stress on the species’ ability to survive. Indeed, Hogan warns, freshwater fish are currently “experiencing a global biodiversity crisis.” And big fish — which tend to exist in smaller numbers than their tinier brethren — can’t survive fishing pressure or harassment well.

Hogan, the exuberant fish wrangler, slyly imparts education through his televised adventures. His passion helps us appreciate those cold-blooded denizens of the watery world. But if we value biodiversity in all its forms, especially Hogan’s charismatic megafish, then we better figure out how to keep from appreciating them to a speedy extinction.

World-famous "Crocodile Hunter" Steve Irwin, known for seeking out and handling some of the most dangerous animals in existence, died on September 4, 2006, in a shocking accident with a stingray. Six weeks later, a stingray jumped into a fishing boat in Florida and stabbed 81-year-old James Bertakis in the chest.

Stingrays are considered by most experts to be docile creatures, only attacking in self-defense. Most stingray-related injuries to humans occur to the ankles and lower legs, when someone accidentally steps on a ray buried in the sand and the frightened fish flips up its dangerous tail. Officials are calling the Florida incident a totally freak occurrence. In the early stages of examining the Steve Irwin accident, some experts have hypothesized that the combined positions of Irwin (above the fish) and his cameraman (in front of the fish) could have made the stingray feel trapped and triggered a defensive attack; others point out that completely unprovoked stingray attacks are not unheard of.
The Blue-Spotted Stingray
Casey and Astrid Witte Mahaney/Getty Images
The Blue-Spotted Stingray (Taeniura lymma), Red Sea., Egypt, Africa. See more saltwater fish pictures.

Stingray-related fatalities (in humans) are extremely rare, partly because a stingray's venom, while extraordinarily painful, isn't usually deadly -- unless the initial strike is to the chest or abdominal area. In Irwin's case, the barb actually pierced his heart. James Bertakis was also stabbed in the chest, and possibly in the heart, but he did not attempt to remove it, which could prove to be part of the reason he survived the attack.

News agencies have reported that Irwin's encounter was with an Australian bull ray, estimated to weigh about 220 pounds (100 kg). Irwin was snorkeling in about 6 feet (2 meters) of water, filming a new documentary titled "Ocean's Deadliest" off the coast of Australia. Irwin was swimming with one of the larger species of rays out there -- Australian bull rays can be up to 4 feet (1.2 meters) wide and 8 feet (2.4 meters) long -- but all stingrays use the same attack mechanism regardless of size. The mechanism is called a sting, up to 8 inches (20 cm) long in a bull ray, located near the base of the tail. The sting contains a sharp spine with serrated edges, or barbs, that face the body of the fish. There is a venom gland at the base of the spine and a membrane-like sheath that covers the entire sting mechanism.


Photo courtesy NOAA's National Marine Fisheries Service
Australian bull ray, a.k.a. southern eagle ray, Myliobatis australis

When a stingray attacks, it needs to be facing its victim, because all it does is flip its long tail upward over its body so it strikes whatever is in front of it. The ray doesn't have direct control over the sting mechanism, only over the tail. In most cases, when the sting enters a person's body, the pressure causes the protective sheath to tear. When the sheath tears, the sharp, serrated edges of the spine sink in and venom flows into the wound.

Stingrays are dangerous creatures which are related to the shark and have a skeleton which
is made of a cartilaginous material, lighter than bone, allowing them to maintain buoyancy.
Their unique coloring, evident in the above graphic, makes it easier to identify and to avoid
this stingray species. There is another species, the Urolophus cruciatus, (banded stingaree)
found in waters off the continent of Australia....which does not have blue dots but more closely
resembles the manta ray in coloring. These rays are also dangerous.

Stingrays prefer warmer coastal waters with depths of 350 feet or less and spend a lot of time
searching for food in shallow waters along sandy beaches. Some ray species do well in fresh
water, some in saline and others can survive in both.

The graphic below shows a Urolophus cruciatus cruising along the oceans bottom....searching
for food.

Picture of a stingray cruising along the bottom of the ocean.

The reason stingrays are dangerous is because of the rather large poisonous spine located on
their tail. This spine is hard and very sharp and is used to pierce the hard outer covering of
shellfish which makes up a large portion of the stingray's diet. This sharp spine can grow to
over 12 inches long in some species and because of these dangerous spines and the poison
it injects, stingrays are often avoided by all but the hungriest fishermen. Several swimmers
have been killed after being struck by the poisonous spines and neglecting to get immediate
medical attention.

If wounded by a stingray, get out of the water immediately. Remove any part of the spine that
may remain in the wound and apply hot water to the affected area as soon as possible. The
temperature should be around 95-105 degrees Fahrenheit, which will be hot enough to detoxify
the poison but not to cause burns. The wound should be treated with hot water for 1 to 1 1/2
hours. The wound should then be irrigated with an anesthetic such as lidocaine (lignocaine) or
longer lasting bupivacaine. This will help deal with the pain until the wound starts to heal. It is a
good idea to check the wound for fragments of spine which may still remain..remove all fragments,
apply an antibiotic cream, and bandage the wound.

Another picture of a bottom swimming stingray.

Stingrays often weigh 650-750 lbs and are 14-16 ft. in length, including the tail. They mate
from March to late September or early October and lay 2-8 eggs with the normal amount
being 2-5. The gestation period is from April to late August. The lifespan of the stingray
is not known but they have lived in captivity for over 20 years. Stingrays eat crustaceans (crabs,
small mollusks), small fish and floating algae.

Color picture of a stingray.

Stingrays have a keen sense of smell and good eyesight and are able to locate food items
very readily. Notice the long tail of the ray in the above graphic. As stated earlier, this
tail with its sharp spine is used for killing hard shelled crustaceans, but it also is often used
for protection and to steer the stingray...aiding the large fins in propelling the ray through
the water.

One interesting trait of the stingray is to settle to the bottom of the ocean, flapping its large fins
around in the soft seabed. This causes sand to swirl around and cover the ray with a layer of
dirt camouflage. The ray then lays motionless until fish or other prey swims close by. The ray
then swiftly lunges forward, grabbing his meal and crushing its prey with flattened teeth and
powerful jaws. Shell fragments and other non digestible items are spat out.

Picture of a non-spotted stingray species.

Although stingrays are not on the endangered list and more than likely won't appear there
anytime soon... like any ocean creature who prefers shallow coastal waters, their numbers
are adversely affected by pollution.

In the graphic below, shaded in blue, is the range of the various species of stingray.

Area of the world where stingrays are found.

Be sure to check back next month for July's "Creature of the Month"

stingrays danger on the reef

Stingrays
Species - Over 35 speciesSting Ray - The Great Barrier Reef

Description

Stingrays are a triangular flat shape. With a tapering tail that is armed with one or more spines. Most of them don’t have pelvic or dorsal fins. Stingrays are not usually aggressive.

Habitat

Stingrays live in warm and tropical areas. As the climate gets cooler they move to a deeper place.Stingrays are not usually aggressive. They rummage on the sea bottom and only attack if they have been stepped on or threatened. They feed on molluscs, small fish, worms and other little creatures.

Venom

Although stingrays are venomous, the major clinical problem is often related to mechanical trauma from the sting.

Fisrt Aid for Stingray wounds First Aid. It may produce severe penetrating injuries or and subsequent infection, including tetanus. Envenomation may result in increasing local pain which may spread to involve the entire limb, with swelling and a characteristic bluish white appearance of the wound. Systemic symptoms are rare, but may include nausea and vomiting, muscle cramps, diarrhea, salivation, sweating, syncope, cardiac arrhythmias and convulsions

my stingrays

Stingray Dasyatidae A stingray gliding across the ocean floor Photograph by Wolcott Henry Stingray Profile Stingrays are commonly found in the shallow coastal waters of temperate seas. They spend the majority of their time inactive, partially buried in sand, often moving only with the sway of the tide. The stingray's coloration commonly reflects the seafloor's shading, camouflaging it from predatory sharks and larger rays. Their flattened bodies are composed of pectoral fins joined to their head and trunk with an infamous tail trailing behind. While the stingray's eyes peer out from its dorsal side, its mouth, nostrils, and gill slits are situated on its underbelly. Its eyes are therefore not thought by scientists to play a considerable role in hunting. Like its shark relatives, the stingray is outfitted with electrical sensors called ampullae of Lorenzini. Located around the stingray's mouth, these organs sense the natural electrical charges of potential prey. Many rays have jaw teeth to enable them to crush mollusks such as clams, oysters, and mussels. When they are inclined to move, most stingrays swim by undulating their bodies like a wave; others flap their sides like wings. The tail may also be used to maneuver in the water, but its primary purpose is protection. The stingray's spine, or barb, can be ominously fashioned with serrated edges and a sharp point. The underside may produce venom, which can be fatal to humans, and which can remain deadly even after the stingray's death. In Greek mythology, Odysseus, the great king of Ithaca, was killed when his son, Telegonus, struck him using a spear tipped with the spine of a stingray.