Stingray Reproduction | ROLLING HARBOUR ABACO

SOUTHERN STINGRAYS: KEEPING AN EYE ON YOU

The SOUTHERN STINGRAY Dasyatis americana is a ‘whiptail stingray’ found in the Western Atlantic Ocean. Their habitat and personal habits – feeding and mating – are similar to those of the YELLOW STINGRAY. They live on the seabed, where they feed on small crustaceans, molluscs and fish. They expose their prey by flapping their ‘wings’ (= pectoral fins) to disturb the sand

You want to avoid treading on one of these if possible. Their tails have a serrated barb covered in venomous mucous, used for self-defence. These spines are not fatal to humans, but if you step on one it may be an experience in extreme pain to tell your grandchildren about.

Luckily they are likely to see you long before you notice them, and to swim away from your approach

IUCN LISTING: ‘DATA DEFICIENT’

Surprisingly, the ‘at risk’ status of the Southern Stingray is not known. However, as with other marine species that humans like to befriend in the wild for the perceived benefit of both parties, there are parts of the Caribbean where stingray swims involve rather more than merely swimming with and enjoying the rays in their own environment. There is organised hand-feeding with cut-up fish, even general fondling and cuddling, that can make these wild creatures seem ‘tame’. There is growing concern that such close dependent interactions with humans is not a good thing, at least for the stingrays.

A diver admiring a ray while keeping a respectful distance

If you watch out for them… they’ll keep an eye out for you

Credits: Melinda Riger of Grand Bahama Scuba; Wiki for thumbs / material; selected online trawlings

My incompetent first ever underwater video at Fowl Cay Marine Preserve, Abaco. I hadn’t snorkelled for X decades, and frankly had some breathing-and-swimming-simultaneously issues, let alone trying to hold a tiny camera steady. Still, here it is (with a proper diver’s video below)

Music credit on my vid to the fairly litigious Joe Satriani – see JS v Coldplay ‘If I could Fly’ / ‘Viva La Vida’ plagiarism case (settled, to no one’s great advantage). Hey, Joe, what you doin’ with that writ in your hand? For anyone the slightest bit interested in the alleged similarities, here is a mash-up reward for reading about stingrays. Or penalty.

BAHAMAS REEF FISH (4) – YELLOW STINGRAY Uboritas jamaicensis

The YELLOW STINGRAY (Uboratis jamaicensis) is one of several ray species found in the tropical western Atlantic ocean. They live in shallow water on sandy or seagrass bottoms, and are commonly found near coral reefs. Their light and dark splotchy colouring can rapidly change according to the surroundings and the need for camouflage. Look at the photos below with half-closed eyes and (apart from knowing perfectly well that there’s a ray there), the blending in is remarkable.

The yellow stingray feeds on small invertebrates and fishes. It can use its ‘wings’ to uncover buried / hiding prey by disturbing the sand. It also has a subtle ‘passive’ method of hunting by using its mantle to form a lethal ‘cave’ that attracts shelter- or shade-seeking prey.

Yellow stingrays breed in seagrass. They are quite prolific, breeding year round and usually having two litters a year of up to 7 young. This species is ‘aplacental viviparous’: the developing embryos are sustained initially by yolk and later by uterine milk. To find out more about viviparity, you’ll find a section at the bottom of this post where the inquiring may opt in… Not everyone’s sac of yolk, I quite understand.

The yellow stingray is innocuous towards humans, but can inflict a painful injury with its venomous tail spine. The threats to the species are (1) taking as bycatch by commercial fisheries; (2) collection for the aquarium trade; (3) negative impact from habitat degradation, both of reef areas and seagrass breeding grounds. For now, it remains common and widespread and retains its IUCN LISTING of ‘Least Concern’.

REPRODUCTIVE STRATEGIES (Marine Biodiversity, Canada)

As with all elasmobranchs, skate and rays are internal fertilizers. Internal fertilization is beneficial because it increases the likelihood and efficiency of fertilization by reducing sperm wastage. In addition, it ensures that the energy-rich eggs produced by the female are not consumed by predators, and that all the energy allocated to reproduction is passed to the embryos and not lost to the environment. This is especially the case for species that retain their embryos until the embryos have completely developed, a reproductive mode termed viviparity. Elasmobranches that practice viviparity are called viviparous (or live-bearing). There are many types of viviparity, which can be divided into two broad categories: aplacental and placental viviparity. Placental viviparity is the most advanced mode of reproduction, during which the embryos are initially dependent on stored yolk but are later nourished directly by the mother through a placental connection. This type of reproduction is not exhibited by any type of batoid. Ovoviviparity (or aplacental viviparity), on the other hand, is the only mode of reproduction employed by rays. In rays, the embryos rely on the substantial yolk within the ovulated egg only during the initial stages of development. After the nutrients stored in the egg have been consumed, the embryo ingests or absorbs an organically rich histotroph (or “uterine milk”) produced by the mother and secreted into uterus. The most highly developed of these strategies occurs in some rays in which the lining of the uterus forms tiny, finger-like projections (termed trophonemata) that increase the surface area for histotroph secretion. This form of nutrient supply (or maternal investment) results in very large offspring, which is characteristic of most species of ray.

For those now fluent in viviparity, the treat of one of Melinda Riger’s fabulous aquatic close-up photos – keeping a close eye on you…Credits: Melinda Riger of Grand Bahama Scuba, with thanks; Wiki for other images / source material; selected online pickings