February 7, 2010 Featured Article Read More →

400 million years old and critically endangered

Is one of the longest running shows on earth about to come to an end?

Meet the stars of the show; the Spurdog, the Thornback Ray and the (not so) Common Skate the products of over 400 million years of evolution whose population numbers are now under serious threat primarily from over-fishing.

The Species:

The Spurdog also known as the spiny or piked dogfish (Squalus acanthias) exhibits schooling behaviour and lives in close aggregations of similar sized individuals of the same sex. Juveniles school offshore and pregnant females close to shore.

Spurdogs have one of the lowest population growth rates of any shark. Maturity occurs between the ages of 6-14 yrs for males and 12-35 yrs for females. The gestation period is between 18-24 months, which is the longest gestation period of any vertebrate.

The biggest threat to spurdog populations is over-fishing and it is currently deemed one of the world’s most commercially important species. Spurdog meat is sold and consumed in European countries and spurdog fins enter international trade for use in shark fin soup and constitute a large percentage of shark fins exported from Europe. The targeting of pregnant females due to their larger size, damages the population structure and sex ratio, hampering population resilience and recovery.

The IUCN (International Union for the Conservation of Nature) lists the spurdog as “vulnerable” globally and in the case of the N.E. Atlantic population off Europe “critically endangered”. With a loss of 95% of the population since targeted fisheries began over 100 years ago. Data from the Food and Agriculture Organisation shows that 89% of the world’s spurdog landings reported to the FAO between 1950 and 2001 were taken from the N.E. Atlantic.

There is an urgent need for stringent fishing restrictions, as current limits are routinely higher than scientific recommendations and have been insufficient to rebuild populations, which ultimately could result in a total collapse. Germany proposed that spurdogs should be included in Appendix II of the Convention on International Trade in Endangered Species (CITES), however at the last CITES conference in June 2007 the proposal fell short of the two thirds majority required for adoption.

The Thornback Ray (Raja clavata) is found all around the British coastline, from 10m-300m with juveniles aggregating in the shallower coastal waters which are used as nursery grounds for the developing rays. Females mature around 8 ½ years old and males at around 7 years old.

The Thornback is one of the most commonly found rays in European fish markets and constitutes an extremely important part of commercial fisheries. It is targeted by gillnet and longline fisheries and taken as by-catch in otter and beam trawls. Little species-specific landing data is available, although market sampling suggests the Thornback is one of the most frequently landed of all rays and skates across Europe, constituting 30% of all skates and rays landed in France from 1982-1994.

Evidence suggests declining catch rates in recent years in N.W. Europe and there is concern that current intensity of fishing pressure is unsustainable. Due to the rays large size (maximum length of males is 105cm and females 130cm) and thorns they rarely escape from trawl nets.

The Total Allowable Catch (TAC) system in EU waters for Skates and Rays between 1999 and 2005 of 6,060 tonne TAC was reduced by 47% and by a further ~50% from 2005-2008 (ICES 2008). These management strategies, although undoubtedly a step in the right direction, are unlikely to be significant for the conservation of specific populations. At the moment there is no effective management plan for the Thornback Ray.

The Common Skates (Dipturus batis) distribution around the UK occasionally includes reports of individuals from the Irish Sea, Bristol Channel and Central North Sea but it would appear that its range is now effectively limited to N.W. Scotland and the Celtic Sea where it can be found from coastal waters to 600m.

Males and females mature around 11 years old. It is the largest Skate found in EU waters, with females reaching a maximum length of 285cm. The large size of the common skate allows it to be caught by most fishing gear from birth (when they measure 21 ½ cm long), giving individuals little chance to reach maturity in heavily fished areas.

There has been a drastic decline in populations during 20th century around UK and data is subjective for some areas for example French landings appear stable but fishing fleets have re-directed their fishing efforts from the continental shelf into deeper water.

In 1999 common skates were included on the UK Biodiversity Action plan (BAP) list. This doesn’t provide legal protection but includes provisions to work towards European Conservation legislation. Its main targets included plans to stabilise populations in refuge areas by 2004 and to facilitate the migration of animals from refuge populations to areas where they are scarce or extinct. In 2009 common skates received protection from the European council in certain ICES areas, meaning they cannot be retained by commercial fisheries and must be released. “Catch and Release” of elasmobranch species is successful as they have no swim-bladder that can over inflate or rupture meaning they are more likely to survive capture and release than teleost fish.

Problems and Solutions

With all 3 species there is a common theme, the typically slow growth rates, relatively late age of maturity and low fecundity are life history traits shared by the sharks, skates and rays which make them particularly vulnerable to over-fishing. The presence of these species within coastal waters makes them prime targets for inshore commercial fisheries and in the case of the spurdog and the thornback ray where pregnant females inhabit coastal waters and the shallower waters are used as nursery areas respectively, it is all to easy for an entire generation of the populations to be fished out.

Thankfully the UK has recently (November 2009) made a significant step forward in protecting both the coastal environment and its inhabitants by introducing the Marine and Coastal Access Act in England and Wales (a Marine Scotland bill has just been passed), this means the government will have a duty to designate Marine Conservation Zones (MCZs) which will include “no take” marine reserves which are closed to commercial fishing and dredging, these zones will be implemented by 2012. The Marine Conservation Society (MCS) and The Co-operative are calling for 30% of UK seas to be designated as marine reserves by 2020, this is a figure that scientific advisors say is required if fish stocks and the marine environment as a whole is to recover from the decades of over-fishing and habitat destruction.

Marine Bill’s such as this one get passed thanks to the phenomenal efforts of specific individuals and organisations who have the foresight to consider the future, gather data on certain areas and lobby governmental organisations until the cogs start turning, such an example was provided by Scottish Anglers working with the SSACN and the SSTP (Scottish Sea Angling Conservation Network and the Scottish Shark Tagging Program) on the weekend of the 14th and 15th of November 2009. 100+ anglers including students and scientists from SAMS (the Scottish Association for Marine Science) and SNH angling club (Scottish Natural Heritage) gathered on the shores of Loch Sunart and Etive to take part in “Tagathon 2009” a fun event with a serious purpose; to capture tag and release prime targets of Common Skate, Spurdog and Thornback rays whilst recording numbers of all other shark species caught during the event. With fishing efforts from 25 boats as well as kayaks and shore fishermen a total of 65+ Spurdog, Thornback Rays and Common Skate were tagged. Spurdog tagging also involved the attachment of data storage tags recording depth and temperature deployed by myself in order to gain some more comprehensive data about the Spurdogs preferred habitat.

Why Loch’s Sunart and Etive? Anecdotal evidence suggests the presence of a resident population of Spurdog, with animals remaining in the lochs year round, the fact that young of the year Spurdog pups have been caught iclip_image002n the Loch’s proves that the areas are breeding grounds for this species and thus are in immediate need of government protection and as such a prime candidate for a designated MCZ to be outlined following the enactment of the Scottish Marine Bill hopefully within the next few months.

The identification of those UK species and habitats which are of immediate concern is paramount and once outlined effective management can hopefully cross country specific boundaries and effective collaborative management policies can be implemented.


Dr Lauren Smith with tagged Spurdog

Posted in: Shark Bites
Rss Feed Facebook button Webonews button Digg button Flickr button Newsvine button