Wondrous Wildlife – November 2010

Wondrous Wildlife

By Vern and Lori Gieger

Sea of Gold


golden-cownose-rayIt’s that time of year when many feel that familiar chill in the air, a change of season; for some this also means a change of scenery and not just for people. Many species migrate to a more agreeable environment, for a variety of reasons, whether they are following a food source, or simply could not survive the cold weather.

Most here know of the famous monarch migration; however lesser known but just as spectacular is the mass migration of the Golden cownose ray. Thousands of Golden cownose rays can be seen gathering off the coast of Mexico, as they migrate to the Yucatan area. Gliding silently beneath the waves they turn the vast blue green sea into shades of gold resembling a flurry of autumn leaves gently drifting with current; truly an awe inspiring sight to see.

The cownose ray is a smaller species of ray. The average size varies from one area to another. The females tend to be slightly larger than males. The largest male reported had a 37.8 in width; the largest female a 41in width. Cownose rays are somewhat diamond shaped and have the long, pointed pectoral fins typical of the rays. Their fin width is approximately 1.5 to 2 times the ray’s length and the long, slender tail is about 1.5 times the length of the body. The head extends beyond the fins. Unlike any other rays, the rostrum (nose) is moderately notched; hence the name cownose.

Cownose rays like other rays are primarily bottom feeders. They prefer a diet of mollusks and crustaceans. When feeding, they cruise the bottom with a fluttering motion using senses of smell, touch, to find food on or in the substrate. Their pectoral fins are used to create suction to remove substrate over prey. Sediment is also removed by sucking it through the mouth and expelling it through the gill slits. Teeth in both jaws of these animals are arranged to form hard flat plates. Hard-shelled prey is crushed between the plates.

Cownose rays mature very slowly and both males and females generally exceed half of their adult size before breeding. In mid-summer after a gestation period of 10-12 months, only one pup is born. The larger the female, the larger the pup. The pup emerges tail first with its pectoral fins wrapped around its body. Its spines are pliable and encased in sheaths, preventing injury to the female during birthing. The natal sheath is discarded and the spines harden soon after birth. The pups resemble miniature adults and are independent at birth. Mating occurs again shortly after the birthing process.

At this time their populations are threatened. A major concern factor in the conservation of this species is the low reproduction rate due to slow sexual maturity and the fact that only one pup per year is produced. If the population is ever over-fished or otherwise further depleted, recovery would be a very slow process.

For those who enjoy unique adventures, observing the biannual migrations of these dazzling marine animals, would certainly be a memorable experience.

For more information about Lake Chapala visit: chapala.com

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