Shy guys

OCCASIONALLY, BEACH WALKERS find small smooth brown or striped pouches cast up on the sand. They’re rectangular and have tightly curled tendrils at their edges. They’re usually empty and may have a small hole in them or, in some cases, be entirely open at one end. These are mermaid’s purses and they’re the capsules in which baby shysharks begin their lives.

Shysharks, or catsharks, are so named because of their habit, when threatened, of curling up into a defensive circle with their tails over their faces. The idea is possibly to make it more difficult for a predator to swallow them. Certainly, to human observers, it makes them seem rather more cute than anything else.

The catshark family is a large one, including more than 150 species, and members are found in almost every ocean habitat, though many are found only in deep water. At least 17 species live in Southern African waters and luckily for local divers, most of those are inshore shallow water species. The average size is about 80cm, though they can be as small as 30cm or grow up to 160cm in total length depending on species. They have the standard shark body format of two dorsal fins, one anal fin and a lower eyelid that closes up against the upper eyelid. Their eyes, though, are like cats’ eyes with vertical slit pupils, and are apparently unique to each animal in pattern.

Though they’re somewhat lacking in the big teeth area, shysharks are predators that eat small bony fishes, crustaceans, worms, octopus and squid, echinoderms, snails and occasionally kelp or algae. They are all relatively long-lived, and can survive to at least 22 years of age.

They’re mostly nocturnal, and are usually seen under overhangs or in caves having a snooze during the day though they can also be out and about, investigating the reefs for food or mates. In our waters, mating seems to take place year round, again, unlike the catsharks in other parts of the world, which have definite breeding seasons.

Mating can be rather an arduous process for the males, though at first glance it seems that the females have the worst of it. The male begins by biting the female and changing his grip until he has her firmly by the pectoral fin. This ensures leverage for inserting his clasper(s) for fertilisation. The biting, however, doesn’t appear to affect the females, and it is the males that land up with bleeding or grazed claspers, which then calcify with age.

The female meanwhile develops the fertilised eggs in cases in her oviducts and in due course lays two (or occasionally more) mermaid’s purses. The tendrils emerge first and, watching laying behaviour, it looks as though they irritate the female as she then swims to a gorgonian or a kelp holdfast and slowly swims in circles around it. This may help with pulling the egg case out of her body. A couple more twirls of tendril follow on after the egg case proper has emerged, and these then secure the purse against a support for the incubation of the baby catshark. In the case of the shysharks, the attachments often seem rather casual, with egg cases seen dangling from sea fans or rolling around with reef debris.

Initially, the yolk is clearly visible through the walls of the mermaid’s purse. As time goes on, the larger egg cases become encrusted with many different forms of life, from barnacles to limpets to moss animals, making it difficult to see what is going on inside the case. Sometimes though, shining a torch onto one side of the mermaid’s purse and looking into it from the otherside will reveal the little shark swimmingaround inside the egg case as it grows,connected to the yolk. Other times, the eggcases are empty, either because the babyshark has grown and left, or else becausethe contents may have been eaten bysnails, starfish or other sharks – the yolkand shark embryo make a desirable meal.

If the mermaid’s purse remains intactthough, when the baby is big enough, typically after several months, it chewsits way out of the case and swims off, asa mostly functioning shark. At this stagefatal accidents can easily befall them: onebaby hatched in an aquarium was speedilyeaten by a waiting anemone.

In fact, the just-emerged babies areadorably terrible swimmers, bumping intoanything in their paths. Whether this isbecause they need to practise their swimmingor whether they simply haven’t quitegot the hang of how their eyes work isanyone’s guess. They’re also covered withwhat looks like a short fuzz, and watchingthem bumble around is enough to convertanyone to thinking of the shysharks asentirely delightful.

PHOTOGRAPHS: GEORGINA JONES