Spurdog

Biology

Spurdogs are a highly migratory species that is capable of moving great distances in very little time. They grow slowly and have a low rate of reproduction meaning that this species is very vulnerable to fishing. Biological vulnerability rating is high 69%, Cheung et al 2005. Spurdog (spiny dogfish, dogfish, rock salmon or flake) are sharks. In the North Atlantic female dogfish grow to a maximum total length of 110-124cm, males 83-100cm. In the Northwest Atlantic spurdog mature at around 60cms total length and at an age of 6 years for males and at around 75cms, at an age of 12 years for females. In the Northeast Atlantic females are reported to mature slightly larger and older at 83cm total length and 15 years. Gestation or pregnancy lasts between 18 and 22 months, one of the longest recorded for any vertebrate, and they give birth to live young. The fecundity of spurdog increases with length, and females of 100-120cm produce a higher number of pups (10-21) than those females below this length. Spurdog tend to aggregate in groups of one sex and size.

Stock Info

As the most commercially valuable shark species caught in European waters spurdogs have been fished at high levels for the last 40 years and stocks are thought  to have decreased by over 90% since the 1970’s in European waters (ICUN). The species is assessed as Critically Endangered in the North East Atlantic by IUCN and has been recently added to the OSPAR list of threatened and/or declining species and habitats.

ICES say that Spurdog stocks suffered a high fishing mortality for more than four decades, and was not managed during this time. Management measures have been restrictive only since 2007. The spawning biomass and recruitment have declined substantially since the 1960's and are now stable at a low level. Exploitation is now below MSY level which is good but stocks are not yet above safe levels.

Spurdogs  have tough skin which means that they have a higher survivability when accidentally caught and released back into the sea by fishermen, providing they haven’t drowned from lack of oxygen. 

ICES latest advice is unchanged - although fishing pressure is below sustinable levles stocks overall (despite patchyness) are depleted below MSY, and they advice zero catch in 2021. 

Management

It is currently illegal to land spurdogs commercially, a Zero Total Allowable Catch has been set in European Waters since 2010. As spurdogs are patchy in their distribution when fishermen accidentally catch spurdogs they will usually catch large numbers. The Spurdog by-catch avoidance project  (CEFAS, Sharktrust  and Cornish Fish Producers Organisation) has given permission to 6 participating vessels to land spurdogs (2 tonnes per boat per month), which have died in fishing gear, as long as accurate catch and discard records are kept. Real time infomation is then collated and used to inform other fishers of areas where there is more of a chance of accidentally catching spurdogs. 

Capture Info

Spurdogs have been targeted in the past using nets and longlines but are now not targeted but are occasionally caught accidentally in gill nets, trawls and with longlines. Any caught currently have to be discarded as they are not allowed to be landed, except for thos e vessesl working in the spurdog by catch avoidance project with CEFAS.  In 2018 37 tonnnes of spurdog were landed to Cornish ports (MMO) data. Fishermen say that it is very frustrating when they accidentally catch spurdogs as they damage gear and very large quantities are caught. It is reportedly very hard to avoid catching them despite sharing infomation with other skippers as the movement of schools is random. 

References