Crossback Stingaree, Urolophus cruciatus
The crossback stingaree or banded stingaree (Urolophus cruciatus) is an abundant species of ray that is unique to southeastern Australia. Its range is from New South Wales to South Australia, mainly inhabiting the Victoria and Tasmania regions.
It is bottom-dwelling typically found around reefs and sandy floors deeper than 330 feet and found up to 690 feet along the continental slope. In the shallow bays and estuaries it is seen where there is muddy bottoms and occasionally in brackish water.
The disc of the crossback stingaree is slightly wider than it is long and in an oval shape. It has a blunt snout that seldom extends beyond the disc. The eyes are small and have teardrop-shaped air holes behind. The nostrils have a knob on the outer rim toward the back and a skirt-shaped layer of skin between them. The small mouth contains three to six nipple-like structures on the inside bottom and a group of them on the outside of the lower jaw. The teeth are small and oval on both the upper and lower jaws and arranged in a quincunx (like a dice’s five) pattern. The crossback has five pairs of short gill slits.
The tail is 63 to 84 percent as long as the disc, which is short for a typical tail length in the stingray family. It is a flattened oval at the base and halfway of its length is a serrated stinging spine and ends with a deep, leaf-shaped tail fin. The body color of the crossback is a grayish to a yellowish brown with dark markings. One runs lengthwise and crossed by three other marks, one near the eyes, one over the gills and one on the center of the disc. The underside is an off-white that occasionally becomes darker at the disc’s margin. The tail fin tends to be a little darker than the body and sometimes contains blotches. The maximum known length is 20 inches with the female slightly larger than the male.
During gestation the embryos feed on the yolk until depleted, then will gets its nutrition from the mother’s uterine milk by glands in the uterus. Every other year, the female will give birth to one to four pups ranging in length from 3.9 to 5.9 inches. Both sexes mature around six years of age and can live to be 11 or more. The species may also crossbreed with the yellow back stingaree producing a intermediate color pattern of the two.
Known to be nocturnal, the crossback will spend the majority of the day motionless on the bottom buried in the sediment. Some will arrange in groups, even with other ray species. It mainly feeds on crustaceans and small organisms buried in the sea floor. The young will mainly feed on smaller organisms including shrimp. As they age they will incorporate larger prey into their diet.
If the crossback stingaree becomes threatened it will raise its tail in a scorpion-like position. The stinger contains venom that can produce an agonizing injury. If the stinger breaks of inside the wound, surgery may be needed to remove it.
The crossback has such a great population and is seldom caught by fishermen in the shallow water, it has maintained its numbers and is as listed as least concern by the International Union for Conservation of Nature. However, in deeper water more are caught in trawls and gillnets causing a decline in population where captured rays usually have a high mortality rate or abort their young.
Image Caption: Crossback stingaree (Urolophus cruciatus). Credit: Mark Norman / Museum Victoria/Wikipedia (CC BY-SA 3.0)