Mermaid’s Purses


Mermaid’s purses are the egg cases of dogfish and skates.  The parent fish attaches these egg cases to objects such as seaweeds growing on the sea bed.  Empty egg cases from which the baby fish have hatched out, are often found washed up along the strand line of sandy beaches.  Occasionally a storm may rip the seaweed and egg cases from the sea bed and throw them up with the eggs or a baby fish still inside.  Mermaid’s purses are made of  collagen which is a common protein found in vertebrate animal tissues that is slow to break down and so may persist in the sea for months or years.  Identification of egg cases found on a beach can indicate which species live in the vicinity and point to areas where there may be nursery grounds.  Many of these fish are listed as threatened or endangered species throughout the world.

Amongst the close relatives of the fish described below are the spurdog and sharks of which Porbeagle, Basking Shark, Thresher, Tope and Blue Shark have been recorded as adult fish from this region.  None of these larger sharks produce ‘mermaid’s purses’ but give birth to live young.  In any case they are not known to breed Irish waters.  A short section at the bottom of this page includes notes and references to publications concerning these sharks in Sligo’s waters.  There is also a note below discussing the Common Names used for these fish.


There are two species of dogfish that produce egg cases in Irish waters.  Their ‘mermaid’s purses’ are very distinctive with curly tendrils coming from each corner (see photograph shown below).  Some related species such as the Spurdog, give birth to live young and so don’t lay egg cases. 


The egg cases of skates are larger; generally black or dark brown; more rectangular; and instead of tendrils they have pointed extensions (‘horns’) arising from their four corners (see photograph shown below). 

A collection of mermaid’s purses from the shores of Sligo and Leitrim was made between 1981 and 2015.  These were identified with the help of Sarah Varian of ‘Marine Dimensions’ and Cat Gordon of ‘The Shark Trust’ the following list is a summary of what was found :

In the above table the ‘Conservation Status’ as determined by the IUCN (International Union for the Conservation of Nature) is listed.  Skates and sharks are in serious trouble in European waters and here in the Sligo-Leitrim area we appear to have breeding populations of some rare and endangered fish.

The records of three Starry Skate egg cases would appear to be the first records for Ireland and the egg cases of Common Skate and White Skate have very rarely been found in Ireland.

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Blonde Skate (Raja brachyra)

Called the Blonde Ray in many publications but it is a skate and not a ray.  Rehydrated length is typically about 105 mm long (range 90-125 mm) this is quite a large egg case.  It can be black or brown in colour.  There are irregular fringes along the sides and between the ‘horns’ giving it a rather untidy appearance.  The horns are distinctly unequal in length, the longer ones being stout for all of their length unlike the wirey horns of Small-eyed Skate.  Only 7 of these egg cases have been found on Sligo’s beaches so this would appear to be quite an uncommon skate in this region.  The fish are occasionally caught on rod and line off the Sligo coast.

Spotted Skate (Raja montagui)

The egg case of this species is quite small, black or sometimes brown in colour, is smooth and slightly shiny with four very similar ‘horns’ that are stout and about equal in length.  A very distinctive feature is the way in which the anterior horns curve away upwards at right angles away from the case (see lower photograph).  The edge of the case is neat and without any irregular ‘frills’.  There are 37 records of this egg case from 7 different beaches in Sligo so it is widespread and quite frequent in occurrence.  Adult fish are occasionally caught on rod and line off the Sligo coast including 3 ‘specimen’ sized fish.

Lesser Spotted Dogfish (Scyliorhinus canicula)

The smallest egg cases are also the most common on Sligo’s beaches and these belong to a small shark called the Lesser Spotted Dogfish.  These egg cases are about 50 mm in length and have long curly tendrils extending from each of their four corners.  They vary in colour from a pale yellow through to black.  On one occasion I found 200 of these on Trawgar beach and another time recorded 141 on Tra Bui (Trawwee) strand.  Adult fish are commonly caught on rod and line but are said to be less common since the 1990‘s when trawlers began to fish closer in to shore.  Some fish shops sell this and related species under the name ‘rock salmon’.

The criteria used in the identification of their egg cases include size (length excluding the ‘horns’ after soaking in water for an hour); the presence or absence of a keel of ‘frills’ along the edges; the relative lengths of the horns at either end and how the horns curve (straight, towards each other, up/down to the plane of the photograph).  Having said this, identification can be quite tricky and help may be sought from information in :

Marine Dimensions (Ireland) website

or at

The Shark Trust (UK) website

The following brief descriptions and photographs include all 7 species of mermaid’s purses so far recorded from Sligo; and also mention of another 3 species that are known as adult fish but their egg cases have so far not been found.

*Locations of beaches can be seen on map here

Small-eyed Skate (Raja microocellata)

This egg case is quite similar to the Blonde Skate but it is significantly smaller (65-80 mm as opposed to 90-125 mm for Blonde Skate).   It is also wider in proportion to its length making it more square in shape.  In fact it will be noticed that the shape is actually trapezoidal because one end (anterior) is narrower than the other.  For example a specimen measuring 65 mm had an anterior width of 45 mm whilst the posterior width was 55 mm.  The horns at the posterior end are distinctive in being long bristles and as these are often still intact this is a good identification feature (Blonde Skate has more stout curved horns).  The horns at the anterior end are stout and curve strongly to point at right angles to the plane of the main body.   The fringing keels make the outline somewhat irregular so this is a rather untidy-looking species.  There are records from 8 beaches in Sligo.  Of the 20 specimens observed, 10 were found at Tra Bui on 30 September 2007.  Only one adult fish has been recorded from the Sligo coast.

Thornback Skate (Raja clavata)

Most commonly known as Thornback Ray but as previously mentioned if it has an egg case then it must be a skate.  Also called a Roker and a Maiden Ray.  This egg case is a little smaller than Small-eyed Skate and of a similar size to Spotted Skate.  Like Spotted Skate the egg case is smooth and neat.  It is of also broader in width resulting in a more square shape.  The shorter horns add to the somewhat squat appearance.  The only records I have are one from Streedagh on 16 November 2007 and one from Lissadell Strand on 12 December 2015.  The adult fish is quite well known to sea anglers in this area with several ‘specimen’ fish having been taken.

White Skate (Raja clavata)

This species of egg case is unmistakable because of its large size (125 mm) and distinctive shape as shown in the photograph.  Only recorded from Tullaghan Bay, County Leitrim on 10 January 1987.  An adult fish was caught on rod and line in the same general area on 02 June 1996 (Cotton 2002).  The White Skate is classified as ‘Endangered’ on the IUCN Red List and the possibility of a breeding population off the Sligo coast is highly significant.

Common Skate (Dipturus batis)

The huge size (160 mm) and shape of this egg case that lacks horns makes it unmistakable.  The only record for Sligo came from Tra Bui on 30 September 2007.  The adult fish has been caught on several occasions along the Sligo coast but this is a species under serious threat and is ‘Critically Endangered’.  Fish caught on rod and line should be returned to the water uninjured.

Starry Skate (Amblyraja radiata)

This fish is also known as the Thorny Ray and as the Thorny Skate!  Its egg case looks black when wet but dries out with a greenish tinge as shown below.  It is similar in shape to the Thornback Skate and of a similar size but the texture of the outside of the case is like velvet.  The upperside is very convex in shape and the underside is slightly concave.  All of these characters make this egg case very distinctive and unmistakable.  There are only two Irish records for egg cases of this species and both are from County Sligo.  The first was from Streedagh on 10 January 1987 and the second (shown in photograph) was found at Yellow Strand on 25 November 2015.  This species is on the IUCN list as ‘Vulnerable’.


Many of the specimens described herein were collected with the assistance of, or by Jean Dunleavy.  Identifications I made were verified by Sarah Varian (Marine Dimensions and by Cat Gordon (The Shark Trust  I would like to thank Martin Howe for allowing me to use his image of the egg case of Greater Spotted Dogfish until I find one of my own!

Some observations of sharks have been given to me by the late Rodney Lomax (recreational fishing boat owner) and Peter Green of the Central Fisheries Board.

Greater Spotted Dogfish (Scyliorhinus canicula)

This species is also called the Nursehound and Bull Huss.  It is included under the name of ‘rock salmon’ in some fish shops.  The egg case is very similar in general appearance to that of the Lesser Spotted Dogfish having long tendrils at each corner but it is larger being at least 90 mm long and about 30 mm wide.  When first laid the egg cases are milky white in colour and become darker as they mature.  The adult fish is occasionally caught on rod and line along the Sligo coast.  So far there is no record of the egg case having been found on a Sligo beach.

The two egg cases shown above are the same specimen, the upper one being dehydrated and the lower one hydrated.  Egg cases do not normally change their appearance so radically but this is a lesson in not always trusting photographs!

Sharks  (under construction - more to follow)

The sharks mentioned below have all been recorded from the Sligo coast.  They do not produce egg cases because they are ovoviviparous which means they ‘lay’ their eggs within the mother’s body and after a gestation of between months and years they give birth to live young.

Lamna nasus (Porbeagle)

Typically 2.5 m long. Long distance seasonal migration.  Feeds on other fish.  Ovoviviparous i.e. eggs hatch within mothers body, young eat other eggs before being born alive.  The International Union for Conservation of Nature (IUCN) has assessed the Porbeagle as Vulnerable worldwide, and as either Endangered or Critically Endangered in different parts of its northern range.

Cetorhinus maximus (Basking Shark)

Second largest fish on the planet at 6-8 m long.  It is is a filter feeder that migrates in to coastal waters in summer where there are concentrations of plankton.  In the winter it moves to offshore waters where it feeds on deep water plankton.  Social animals often being seen feeding together in small groups.  Ovoviviparous the female hatching the eggs inside her body and giving birth to live young after more than a year.  This species is considered as vulnerable on the Red List of the IUCN.

Photograph taken by Martin Howe.  Downloaded from The Shark Trust website ( and modified to follow the conventions of this website.

Note on Common Names

The only reliable names for species are the Scientific Names (also often referred to as ‘Latin Names’.  The Common Names (also called English Names or Vernacular Names) are especially confusing for these fish because they have been inconsistently applied by fishermen, anglers and naturalists in different regions around the coasts of Britain and Ireland.

First of all it is important to know that Rays give birth to live young and that Skates lay eggs in egg cases (mermaid’s purses).  So every fish named in this part of the web site must be a Skate and none can be called Rays!  Yet most of them have been called Rays up until now.  To add to the confusion, most species have two or more Common Names depending upon which part of the coast you are on.  Finally, in some instances the same Common Name has been applied to two and even three different species!

Galeorhinus galeus (Tope)

Squalus acanthias (Spurdog (Spiny Dogfish))

Alopias vulpinus (Thresher Shark)

Normally reaches up to 5 m in length of which the long upper part of the tail may make up almost half of this.  Feeds on shoaling fish such as mackerel and herring.  Is a warm water species but migrates north in the summer following warm currents such as the Gulf Stream.  IreIand is about as far north as it goes.  Is ovoviviparous and gives birth to live young after hey have fed inside the mothers body on unfertilized eggs for about 9 months.  The IUCN have assessed this species as Vulnerable.

The only local record is of one that was found freshly dead on Bartragh Island, Killala Bay (technically in Mayo but the mouth of the bay is shared with Sligo!) in late October 1899 by Captain Kirkwood.  It was originally recorded as a Blue Shark (Warren 1900b) but was later corrected to be a Fox Shark (= Thresher) (Warren 1900c).  It measured 3.2 m long.  The lateness of the record and exceptional size that exceeds most of Sligo’s Blue Sharks is in-keeping with this identification and it was included in a review of Irish records by Quigley et al. (2008).  The IUCN have listed this species as Vulnerable.

Prionace glauca (Blue Shark)

Growing to between 2 and 3 m in length and weighing 30 to 50 kg in males but 90 to 150 kg in females.  This species is a long distance migrant that appears to follow a circular route coming across the north Atlantic Ocean with the Gulf Stream in summer from late-July to the end of September, then migrates south down the European and African coast past the Canaries and Azores to tropical waters where it crosses the ocean to reach the America’s.  Females give birth to live young (viviparous) with many baby sharks being born in a brood.  Does not breed in Irish waters.

Robert Warren described how a Blue Shark was shot by wildfowlers in the Moy Estuary in mid-November 1899 (Warren 1900a).

A tagging programme has revealed more about this migrant and there are several returns from Donegal Bay off the Sligo coast :

A shark tagged by Rodney Lomax was re-captured off Newfoundland coast of Canada

A female shark tagged off Mullaghmore Head on 04 September 1999 was recaptured twelve years later on 15 November 2011 at 1125 km south of the Canary Islands by Spanish long-liners

Often there are photographs of Blue Sharks caught locally in the Sligo Champion e.g. (Anon 1994).

References (to all elasmobranchs in Sligo and Leitrim)

Anon (1892)  Notes.  Zoology.  Fishes.  Pipe fishes at Cork and Killala.  Irish Naturalist 1:43.

Anon (1892)  Notes.  Zoology.  Fishes.  Leptocephalus larvae of conger at Killala Bay.  Irish Naturalist 1:43.

Anon (1909)  Notes.  Zoology.  Herrings at Killala Bay.  Irish Naturalist 18:99.

Anon (1956)  Eel investigations, L.Arrow: preliminary report.  Annual Report of the Inland Fisheries Trust for 1955:8-13,16-18.

Anon (1984)  Big shark caught.  Sligo Champion of 09 September 1984.

Anon (1988)  Shark hunted in Killala Bay. [newspaper not known]

Anon (1989a)  [Photograph of blue shark with Arron Power and Joe McGowan].  Sligo Champion of 15 September 1989.

Anon (1989b)  [Photograph of blue shark with Charles Elliot].  Sligo Champion of 06 October 1989.

Anon (1991)  [Photograph of blue shark with Ethna and Joe McGowan].  Sligo Champion of 30 August 1991.

Anon (1992a)  [Photograph of Tope with Aiden Foley].  Sligo Champion of 03 July 1992. Anon (1992b)  First shark caught.  Sligo Champion of 17 July 1992.

Anon (1994)  [Photograph of blue shark with Ethna].  Sligo Champion of 19 August 1994. Anon (2001)  Water safety course. Sligo Champion of 19 September 2001.

Central Fisheries Board & North Western Regional Fisheries Board (2009)  Sampling Fish for the Water Framework Directive - Transitional Waters 2008.  Garavoge Estuary.  Central Fisheries Board, Dublin.

Cotton, D.C.F. (1992)  Marine Nature Notes for Sligo in 1991.  Privately circulated. (4 pages).

Cotton, D.C.F. (2002)  Fish Notes.  White skate Raja alba Lacépède, 1803 in Sligo Bay.  Irish Naturalists' Journal 27(1):45-46.

Green, Peter (2005)  How far do they go?  Boat Fishing Monthly 41:48-49.

Dunlop, N. (2009)  A Guide to Sea Angling in the North Western Fisheries Region.  North Western Regional Fisheries Board, Ballina.

Fahy, E. & R. O’Reilly (1990)  Distribution patterns of rays (Rajidae: Batoidei) in Irish waters.  Irish Naturalists Journal 23(8):316-320.

Fisheries Branch, Department of Agriculture (1937)  The Angler’s Guide to the Irish Free State. Stationery Office, Dublin.

Fitzmaurice, P. (1974)  Size distribution and size of thornback rays (Raja clavata L.) caught on rod and line on the Mayo coast.  Irish Fisheries Investigations Series B (Marine) 1:1-18.

Henry, The Rev. William (1739)  Hints towards a Natural and Typographical History of the Counties Sligoe, Donegal, Fermanagh and Lough Erne.  Unpublished manuscript in the National Archives, Ireland.  (A description of the County of Sligoe 33 pages).

Holt, E.W.L. (1892)  Survey of fishing grounds, west coast of Ireland, 1890-1891.  Report on the results of the fishery operations.  Scientific Proceedings of the Royal Dublin Society 7(28):225-387.

Irish Specimen Fish Committee (1981)  Irish Specimen Fish 1980  Irish Specimen Fish Committee, Central Fisheries Board, Dublin.

Irish Specimen Fish Committee (1983)  Irish Specimen Fish 1982  Irish Specimen Fish Committee, Central Fisheries Board, Dublin.

Irish Specimen Fish Committee (1985)  Irish Specimen Fish 1984  Irish Specimen Fish Committee, Central Fisheries Board, Dublin.

Irish Specimen Fish Committee (1990)  Irish Specimen Fish 1989.  Central Fisheries Board, Dublin.

Irish Whale & Dolphin Group website, stranding records (accessed 04/01/2011).

Marine Institute (2012)  Atlas of Irish Groundfish Trawl Surveys.  Supporting fish stock assessment and new ecosystem advice.  Marine Institute, Galway.  61 pages.

Quigley, D.T.G. (1984)  White skate, Raja alba Lacépède. 1803 (R. marginata, Lacép.) in Irish waters: a further record and a review of Irish records.  Irish Naturalists' Journal 24(2):72-74.

Quigley, D.T.G.; G. Hannon & K. Flannery (2008)  Thresher shark Alopias vulpinus (Bonnaterre, 1788) in Irish waters: further records and a review of Irish records.  Irish naturalists' Journal 29(1):7-12.

Sea Fish records for NW area.

Warner, D.; K. Linnane & P.R. Brown (1980)  Fishing in Ireland.  The Complete Guide.  Appletree Press, Belfast.

Warren, R. (1893)  Notes.  Zoology.  Fishes.  Basking-shark (Selache maxima) on the Sligo coast.  Irish Naturalist 2(7):200.

Warren, R. (1893)  Notes and queries.  Fishes.  Basking shark on coast of Sligo.  Zoologist 3rd Series Volume 17:270.

Warren, R. (1900a)  Blue sharks in Killala Bay, Co. Mayo.  Zoologist 4th Series Volume 4:40-41.

Warren, R. (1900b)  Blue sharks in Killala Bay.  Irish Naturalist 9(2):48.

Warren, R. (1900c)  Sharks in Killala Bay - a correction.  Irish Naturalist 9(4):108-109.

Warren, R. (1900)  Notes.  Zoology.  Fishes.  Porbeagle Shark and Tope in Killala Bay.  Irish Naturalist 9(12):292-293.

Warren, R. (1904)  Notes.  Zoology.  Porbeagle shark in Killala Bay.  Irish Naturalist 13:44.

Warren, R. (1904)  Notes and queries.  Pisces.  Porbeagle shark in Killala Bay.  Zoologist 4th Series Volume 8:36.

Went, A.E.J. (1972)  Interesting fishes taken in Irish waters in 1971.  Irish Naturalists' Journal 17(7):210-215.

Went, A.E.J. (1975)  Interesting fishes taken in Irish waters in 1974.  Irish Naturalists' Journal 18(7):205-208.

Went, A.E.J. (1977)  Specimen skates and rays taken in Irish Waters (1956-1975).  Irish Specimen Fish Committee.  Report for the year 1976.  Inland Fisheries Trust, Dublin.

Wheeler, A.C.; N.R. Merrett & D.T.G. Quigley (2004)  Additional records and notes for Wheeler’s (1992) List of the Common and Scientific Names of Fishes of the British Isles.  Journal of Fish Biology 65 (Supplement B):1-40.

Wood-Martin, W.G. (1882-1892)  History of Sligo, county and town.  Volumes 1-3.  Hodges, Figgis & Co., Dublin.

Review of Species

An interesting collection of egg cases found at Dunmoran Strand by John-Mark Dick on 09 February 2016 includes 4 joined together in a chain (see photograph shown below).  This may be an original observation that indicates how that adult fish must lay several egg cases at one time.

Three Basking Sharks at Trawgar, Streedagh on 12 May 2003.

Basking Shark killed by being entangled in 30 m long drift net.

Sligo Harbour at Dorrins Strand, County Sligo 24 May 2011.

One of the greatest threats to Basking Sharks along the Sligo coast is entanglement in fishing nets and ropes (see photograph shown below).  This is not a new problem because Robert Warren described the following instance that happened on 05 June 1893;

“On the 5th inst. a splendid specimen of the Basking-Shark became entangled in the salmon-net of Mr. Kilgallan, at Aughriss, Co. Sligo, a short distance off the pier, and after a desperate struggle, in which it caused great damage to the net and ropes, was, by the united efforts of four boats, turned into shallow water on the sandy beach, where it was killed.  The great fish was evidently full-grown, for it measured thirty feet in length.” (Warren 1893).

In the 1990’s before salmon drift nets were banned I received reports from several fishermen of their experiences, for example;

“1989 or 1990.  Large one drowned in fishing net.  About 1 km off Cloonagh in 12 fathoms of water.”

1991.  Killala Bay.  “Accidentally caught off Inishcrone Pier”

“11 June 1993.  Off Long Rock, Dunmoran Strand.   Released from net.  8 m (25 feet) long.”

“1992. Sligo Bay.  1st week in July.  Basking Shark 25 feet long was accidentally caught in a fishing net.”

“One caught accidentally in drift nets on each of three occasions between late June and early July 1994.  At least two fish were involved.  All were safely released”.

22 June 1993.  Mid-way out to sea between Sligo and Mayo.  Caught in salmon net but unhurt.”

“Caught accidentally in drift net in late June/early July 1994”

Hopefully this issue no longer exists with the banning of drift nets but specimens of Basking Sharks washing ashore would suggest that it still is an issue just that the accidental entanglements have become more secretive.

Blue Shark, 2 m long and stranded at

Lissadell Strand, Drumcliff Bay on 29 August 2007

Spurdog found dead on Dunmoran Strand, County Sligo on 13 September 2014.