A rare nursery of the blackmouthed dogfish (Galeus melastomus), one of our smallest shark species, has been discovered by scientists some 200 miles off the west coast of Ireland.
Footage of the area was captured during a seabed-mapping Marine Institute ‘SeaRover’ survey in July using the remotely operated vehicle (ROV) Holland 1, deployed from Irish Lights ship Granuaile and has just been released following careful study by experts. Incredibly, the nursery lies at a depth of up to 750m and is also located within one of Ireland’s six designated offshore Special Area’s of Conservation (SAC); areas which are strictly protected under European law for various species and where no trawling is allowed.
David O’Sullivan, the chief scientist on the SeaRover survey, said “It was incredible, real David Attenborough stuff. This is a major biological find and a story of this magnitude would have been on Blue Planet if they’d known about it. Very, very little is known on a global scale about deep-sea shark nurseries.”
The footage and images show an abundance of shark egg cases, commonly known as ‘mermaids purses’, lying on the remains of dead coral in what has become the largest shark nursery found in Irish waters to date. Blackmouthed dogfish (also known as catsharks) are unusual in their particular genus as they (like about a third of all sharks) routinely exhibit multiple oviparity, in which more than one egg can mature simultaneously. Females may contain up to 13 developing eggs, though 1-4 is more typical. The number of eggs laid annually can vary from an estimated 60-100, increasing with female size.
Blackmouthed dogfish are very common in the NE Atlantic but typically live at depths of 200-500m, although they have been recorded at over 2000m. For this reason, they are rarely encountered by anglers although in recent years (since 2008) more have been targeted and caught recreationally off northern coasts. The Irish record, as set by the Irish Specimen Fish Committee (ISFC) currently stands at 1.33kg (just under 3lbs) and was caught from the deep waters of Red Bay, off the Antrim coast.
The species is often taken as bycatch in demersal trawl and longline fisheries and is generally discarded despite being placed on the International Union for the Conservation of Nature (IUCN) ‘Red list’ of threatened species.