Ecology Edited by Michael Arvedlund, PhD ILLUSTRATIONS BY PETER SYMES The biology of Text by Michael Arvedlund, Tyge Dahl Hermansen and Peter Symes Stingrays Can they be handled? PETER SYMES There are more Stingray kills television host During the filming for a documen- What kind of fish are stingrays? over 100 less species than rays and Their habitat The headlines soon spread all tary, Steve Irwin was swimming Stingrays are rays, i.e. cartilaginous skates—sharks have received con- Most species live on the sea than 500 species over the world when the famous along with the ray and apparently fishes related to skates and sharks. siderably more attention than rays floor, in a variety of geographical of rays and skates Australian philanthropist and televi- spooked it, causing it to raise its tail Rays and skates comprise a scien- and skates, both from the general regions—many in coastal waters sion host, “crocodile hunter” Steve in defence. In a terrible instant, the tific so-called super-order of carti- public and from the scientific com- and a few species live in deep Irwin, was recently killed by a sharp and serrated barb on the laginous fishes named Batoidea. munity... at least until now. waters. Most batoids have a rather stingray, also known as tail went into Irwin’s chest inflict- Cartilaginous fishes do not have cosmopolitan distribution in tropical a whiptail stingray. ing a lethal injury by perforated his a skeleton of bone. Instead, it con- The Dasyatids and subtropical marine environ- heart. Steve Irwin just managed to sists of cartilage, a type of dense The scientific name for the family ments or temperate waters. Only pull the denticle out before he lost connective tissue. It is composed of stingrays, or whiptail stingrays, a few species, like manta rays, are conciousness, and soon after, he of collagenous fibers and/or elastic is Dasyatids. They are common in oceanic, i.e. they live in the open died. fibers, and cells called chondro- tropical coastal waters through- sea. A couple of species are con- Steve Irwin often took chances, cytes, all of which are embedded out the world. Freshwater species fined to freshwater. Some batoids yet, somewhat paradoxically, risk in a firm gel-like ground substance are also known from e.g. Asia and can live in brackish bays and taking didn’t lead to his demise. called the matrix. Africa. The species of the genera estuaries. Bottom-dwelling batoids This time, he didn’t do anything Potamotrygon, Paratrygon, and breathe by taking water in through other than swim. Based on these Over 500 species Plesiotrygon are thus endemic to so-called spiracles, rather than and other similar conditions, it may There are more than 500 species of the freshwaters of South America. through the mouth as most fishes be worth revising the belief that rays and skates in twelve families, Rays range in size from just a do, and passing it outward through stingrays are harmless. including stingrays, skates, electric few cm to several meters wide. the gills. Their mouths and gills (like The ‘sting’, which gives these fish- rays, guitarfishes and sawfishes (Box The smallest ray is probably the almost all rays) are located on es their common name, is a modi- 1). The Batoids are closely related short-nose electric ray, which is the the underside of their flat bodies fied dermal denticle mounted near to sharks. In fact, in the early part size of a pancake; it is only 10 cm making breathing an issue if you the base of the tail, about one- of the Batoid life cycle, they look across and weighs about half a lie on or are more or less buried in third along its total length. The sting much alike young sharks. It is inter- kilo. The biggest ray is the manta, sand. To overcome this hurdle they consists of a blade-like barb with esting to notice that there while which can reach a width of over have developed extremely large serrations along both there are only approximately 370 three meters as an adult. FAO edges and a venom extant species of sharks—which is gland at the base. (see figure next page) NOAA PETER SYMES 59 X-RAY MAG : 14 : 2006 EDITORIAL FEATURES TRAVEL NEWS EQUIPMENT BOOKS SCIENCE & ECOLOGY EDUCATION PROFILES PORTFOLIO CLASSIFIED NATIONAL INSTITUTE OF WATER AND ATMOSPHERIC RESEARCH The biology of has reached the point where they will eagerly accept scraps straight from the hands of tourists. Although these interac- tions have altered the stingrays natural Stingrays behavior, there is no evidence that they have lost the ability to hunt on their own. ters is a welcome change that may be a critical factor in their future survival. Reproduction The batoids are extraordinarily varied in their mode of reproduction. Most rays and skates are benthic, lying on the PETER SYMES substrate for extended periods, often to A whiptail stingray lies buried in the sand, keeping a watchful eye on matters some extent buried. Some forms, how- ever (particularly the eagle, cownose, manta and devil rays) are secondarily spiracles (spiracles are the openings substrate it is a free swimming ray that pelagic, swimming strongly in mid-water positioned just behind the eyes through preys on oceanic squid and mid water and rarely resting on the bottom. Mating which a shark or ray can suck in oxygen fishes, which it manipulates by holding season occurs in the winter. When a rich water to flush over the gills). Through them between its pectoral fins. Because male is courting a female, he will follow this mechanism rays are able to remain of its unique behavior the Pelagic her closely, biting at her pectoral disc. motionless for hours at a time. Stingray is sometimes categorized in its During mating, the male will go on top Many whiptail stingrays are restricted to own genera—Pteroplatytrygon. Whiptail of the female (his belly on her back) and “Clearly, there are limits marine habitats but some are known to stingrays usually inhabit shallow coastlines put one of his claspers into her vent. Most migrate into brackish estuarine environ- down to 100 or 200 meters, but some spe- rays are viviparous bearing live young in to acclimatory processes ments. A few species can live year round cies can be found at 600 meters or even PETER SYMES “litters” of five to ten. Therefore, batoid that can counter coral in both fresh and salt water. Whiptail deeper. Stingrays are crawling all over visitors in Stingray City on Grand Cayman. This location is prob- eggs, unlike those of most other fishes, stingrays are benthic. They spend much ably the island’s biggest tourist attraction are fertilized inside the female’s body. bleaching” time buried with only their eyes sticking Diet The female holds the embryos in the Softcoral Red sea out. This is a defensive strategy rather Most batoids have developed rounded three sardines, three anchovies, two flat- Stingray City tours are now a multimillion womb without a placenta. Instead, the Nephtheidae family than a stealthy way to surprise prey. teeth for crushing the shells of snails, fish, one mojarra, four flatheads, three dollar industry that attracts hundreds of embryos absorb nutrients from a yolk sac, Because they tire easily when swimming, clams and crustaceans and some fish, pufferfish, five squids, two crabs, and two tourists daily. Although the large Southern and after the sac is depleted the mother remaining buried is the ideal way to depending on the species of ray or mollusk shells! Stingrays get quite aggressive while they provides uterine milk. Skate egg cases avoid becoming lunch. Whiptail stingrays skate. Manta rays are plankton feeders Whiptail stingrays are known to gather are competing for handouts of squid, are often rectangular with extended are heavily preyed upon by a number Whiptail stingrays known to eat mollusks, at fishermen’s fish cleaning stations they rarely harm the tourists, preferring to tendrils at each corner, which serve to of shark species (especially by hammer- crustaceans, jellyfish, and bony fishes. to take advantage of the scraps that back off when trodden on rather than anchor them to bottom growth (washed heads). An exception to The recorded stomach contents of one end up on the seabed. In some loca- use their defensive tail stings. Traditionally, ashore, the empty cases are known as the benthic lifestyle is honeycomb stingray included: eight tions, such as Stingray City in Grand stingrays were feared by fishermen and “mermaid’s purses”). Fetal electrical rays the pelagic stingray threadfin bream, three mackerel, eight Cayman and Hamelyn Bay in Western beach goers alike, so the positive press (Torpediniformes) are nourished by pro- Dasyatis violacea. ponyfish, eight cardinalfish, Australia, their tolerance towards humans that the rays receive from these encoun- tein-rich secretions from the uterine wall, Although this ray can while fetal stingrays (Myliobatiformes) get also be found on the The tail spines of a whiptail stingray are actually highly modified dermal denticles. Each their nourishment delivered to them via spine features a soft center of venom-producing tissue and an enameloid casing with ser- secretions from pseudo-placentae that THYGE DAHL HERMANSEN rations pointing toward the base. This is a feature that makes removal hard and painful for enter their bodies through the spiracles. the unlucky victim. Like other dermal denticles, such as shark teeth, these stinging spines are replaced continually. Most Are stingrays dangerous? stingray species have two such spines, each stemming from Stingrays are not, as their close relatives, its own site on the tail and with its own cycle of develop- ment, growth and replacement. Substitute spines usually the sharks, known for being dangerous.