Not to be cited without prior reference to the authors ICES CM 2005/N:01 Comparison of trends in long term survey data for Squalus acanthias with a preliminary stock assessment for this species Helen Dobby 1 , Doug Beare 1, 2 , Emma Jones 1 , and Kirsteen MacKenzie 3 Spurdog (Squalus acanthias) is a relatively small viviparous squaliform shark that has become one of the most commercially important elasmobranch species caught in the northeast Atlantic. Although the landings of this species have been declining for a number of years, the status of the stock in this area is not well understood. The assessment is hampered by the lack of age-structured catch data and by uncertainties in historic total landings due to the common practice of recording landings as generic ‘dogfish’ rather than in species specific categories. Fishery independent data should therefore be considered an important source of information on the stock status. This paper explores the spatial and temporal trends in abundance, size distribution and sex ratio obtained from Scottish trawl survey data and discusses how such data may be useful from a stock assessment perspective. Results are compared to preliminary stock assessments (based largely on commercial data), conducted by the ICES WGEF. Contact author: Helen Dobby: e-mail: dobbyh@marlab.ac.uk. 1 FRS Marine Laboratory, PO Box 101, Victoria Road, Aberdeen, AB11 9DB, UK [tel: +44 1224 876544, fax: +44 1224 295511] 2 Present address: Institute for the Protection of the Citizen (IPSC), European Commission, Joint Research Centre, I-21020 Ispra(VA), Italy. 3 Joint Nature Conservation Committee Monkstone House, City Road, Peterborough, PE1 1JY (Headquarters) Introduction The Piked Dogfish, or Spurdog has a worldwide distribution in temperate and boreal waters occurring mainly in depths of 10-200m, but up to 900m. In the northeast Atlantic this species is found from Iceland and the Barents Sea southwards to the coast of Northwest Africa (Compagno et al., 2005). Early tagging programmes in the 1950s focused on individuals captured in the northern North Sea. These were regularly recaptured off the coast of Norway, indicating a winter migration from Scotland, returning in the summer (Aasen 1960, 1962). Other tagging studies in the English Channel indicated summer movement into the southern North Sea (Holden, 1965). Since few individuals were recaptured outside of these areas distinct Scottish-Norwegian and Channel stocks were believed to exist. A tagging study initiated in the Irish and Celtic Seas in 1966 has yielded recaptures over 20 years from all round the British Isles and suggests that a single Northeast Atlantic stock is more likely (Vince, 1991). Transatlantic migration is known to have occurred (Holden, 1967 and Templeman, 1976), but only occasionally, and therefore the two north Atlantic stocks are assumed to be separate. Based on these studies ICES considers that a single ‘northeast Atlantic’ stock (Barents Sea, Sub-area I to the Bay of Biscay, Division VIIIa) is the most appropriate unit for assessment and management (ICES 2005). Historically spurdog were not commercially important and were regarded as a nuisance to fishermen, both as a competitive predator and through damage to fishing nets (Day, 1884). However, during the early part of the 20 th century, this small shark became highly valued, both for liver oil and for human consumption, and landings of northeast Atlantic spurdog increased to a peak of over 60,000 tonnes in the early 1960s. Following this heavy level of exploitation reported landings have declined steadily to 5000 tonnes in 2004 1