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Monsters and Mermaids

Image credit; Louise Duignan

Image credit: Louise Duignan

Placed high and dry upon the clean blue pebbles by a spring tide, the mermaid’s purse I found last week was not hard to spot. Another purse some months ago was easier to miss, dark and unlovely as they are and cast as it was amongst the deposited kelp of similar leathery brown shades. That relationship of camouflage was once so necessary underwater, when the four pronged purse held a tiny shark, skate or ray and the kelp held to the rock and provided cover for the purse until its inhabitant was ready to leave. How curious that now, far from those dynamic undersea worlds, they defiantly continue this relationship as they desiccate together on the still shore, the kelp now concealing the purse from the eyes of hurried beach walkers.

The purses, egg cases which once protected a fertilised embryo, are the unremarkable reproductive clue to species such as the dogfish, our smallest and most common shark. But not all sharks reproduce like this. Mayo’s legendary basking sharks, which once entertained enough mystery in their labelling as a sea monster as Gaeilge (An Liabhán Mór) are still almost a mystery to scientists in this regard. It is believed the sharks give birth to live young, but a pregnant female has only ever been seen once and nobody knows when or where or how many young are born. Porbeagle sharks which have been landed in Clew Bay definitely do give birth to live young, usually four at a time. And although they won’t be found in Clew Bay anytime soon, its worth noting the female hammerhead shark which gave birth in a zoo in The U.S. in 2001 – despite no male contact in three years. Sharks are apparently capable of such immaculate feats, but only in extreme circumstances and it’s bad for genetic diversity.

The un-immaculate mermaids’ purses are not so dramatic. And the almost blind dogfish, which spends 23 hours a day dozing on the seafloor, is no hammerhead, but there is still useful information to be gleaned from them. Compiling records of their distribution can provide valuable information on the location of nursery areas of sharks, skates and rays. Many of these are severely threatened such as the common skate, which was once found throughout European waters, now ironically titled as it is only found in a few select locations. Purse Search Ireland are one group who have undertaken the task of compiling this info, and provide a user-friendly online form at http://www.marinedimensions.ie for you to log your report.

Sharks, skates and rays are related and together make up the Elasmobranch class of fish, a very ancient class dating back 400 million years. They are different to other fish having cartilage skeletons instead of bone. The Dogfish (Sycliorhinus canicula) is found all around our coastline in sandy bays and off-shore. It feeds mostly on prawns, crabs and occasionally fish. They breed annually, and nine months after mating, the female lays approximately 25 eggs which develop inside mermaid’s purses for nine months. The Basking Shark (Cetorhinus maximus) is a filter feeder, passively filtering small fish, invertebrates and zooplankton near the surface with its gaping mouth open. Recent satellite tagging studies have confirmed that the some sharks undertake huge migrations in winter. They were almost fished to extinction in the west of Ireland until the 1970s but are now believed to be making a recovery.

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Discussion

One thought on “Monsters and Mermaids

  1. Beautiful.

    Posted by lenny | February 15, 2010, 8:24 pm

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