Fluctuations and forecasts in the ﬁshery for queen scallops (Aequipecten opercularis) around the Isle of Man B. J. Vause, B. D. Beukers-Stewart, and A. R. Brand Vause, B. J., Beukers-Stewart, B. D., and Brand, A. R. 2007. Fluctuations and forecasts in the ﬁshery for queen scallops (Aequipecten opercularis) around the Isle of Man. – ICES Journal of Marine Science, 64: 1124–1135. The annual success of the queen scallop ﬁshery around the Isle of Man in the northern Irish Sea is dependent on the strength of recruitment. We examined data from surveys and commercial logbooks on the annual density of spat, juvenile, and adult queen scal- lops in the ﬁshery between 1982 and 2002. These were used to examine past population and ﬁshery trends and the potential for formulating a predictive model for the ﬁshery. The results were highly variable on both temporal and spatial scales, but there were some general trends. Density appeared to have been relatively stable during the 1980s, declined sharply from the early to mid-1990s, then recovered to produce relatively good catch rates thereafter. There was no relationship between spat settlement and the subsequent density of juveniles or adults in stock surveys or with commercial catch rates. However, within the stock surveys, there were three different signiﬁcant relationships between cohort densities over time. Additionally, there was a signiﬁcant relationship between the density of 1-year-olds caught on the surveys and commercial catch rates the following year. Monitoring juvenile queen scallop density would therefore allow prediction of recruitment and ﬁsheries variations at least 1 year in advance, allow- ing perhaps for more effective management, including reducing the ﬂuctuations in the ﬁshery and helping to ensure long-term sustainability. Keywords: Aequipecten opercularis, catch predictions, ﬁsheries management, recruitment variation, stock assessment. Received 25 July 2005; accepted 6 May 2007; advance access publication 3 July 2007. B. J. Vause, B. D. Beukers-Stewart, and A. R. Brand: Port Erin Marine Laboratory, University of Liverpool, Port Erin, Isle of Man IM9 6JA, British Isles. B. D. Beukers-Stewart: Marine Conservation Society, Unit 3, Wolf Business Park, Alton Road, Ross-on-Wye HR9 5NB, UK. Correspondence to B. D. Beukers-Stewart: tel: þ44 1989 561584; fax: þ44 1989 566815; e-mail: bryce@mcsuk.org Introduction Fluctuations in the abundance of ﬁsh and shellﬁsh populations are often attributed to variations in recruitment (Sissenwine, 1984). This is generally caused by several interacting factors (Rothschild, 2000), most commonly the size of the spawning stock (Ricker, 1954; Beverton and Holt, 1957; Shepherd, 1982) and environmental conditions (Caputi, 1993; Neill et al., 1994; Hofmann and Powell, 1998; Le Pennec et al., 2003). It is important that such variation in recruitment be accounted for in managing exploited stocks, even when the cause of the variation cannot be identiﬁed. An ability to predict the level of recruitment, deﬁned here as the abundance of individuals entering the ﬁshery, contri- butes to more effective ﬁsheries management (Smith, 1993). Such prediction would be particularly valuable for ﬁsheries that are heavily dependent on the strength of the recruiting year class, such as many shellﬁsh stocks. The queen scallop (Aequipecten opercularis) is a commonly exploited species in the Northeast Atlantic (Brand, 1991), and is common around the British Isles (Mason, 1983; Ansell et al., 1991). It is rare to ﬁnd scallops older than 6 years (Brand et al., 1991a), possibly because of the combined effect of cumulative ﬁshing mortality and the onset of senescence (Allison and Brand, 1995), but in this time, they can grow to 90 mm shell height (Brand et al., 1991a). The most valuable ﬁshery for the species is in the Irish Sea; 9286 t (45% of the total landings in the Northeast Atlantic) were taken from the region in 2001 (FAO, 2003). A signiﬁ- cant part of the ﬁshery operates out of the Isle of Man, with an average of .2300 t of queen scallops landed there each year between 1982 and 2002 (Isle of Man Department of Agriculture, Fisheries and Forestry statistics). The Manx queen scallop ﬁshery operates mainly during summer (June–October inclusive), and is prosecuted with two different types of ﬁshing gear, dredges or trawls. Both are size-selective to target animals .55 mm shell height, because of the economics of processing (Brand et al., 1991a). During the ﬁshing season, there is a change in the size structure of the popu- lation, caused by rapid growth of scallops in summer. This can produce a change in the age structure of the catch as the recruiting cohort, generally 2-year-olds, often attain 55 mm in the later part of the season and so become vulnerable to ﬁshing (Allison, 1993). The ﬁshery is dominated by scallops 2–4 years old (Brand et al., 1991a; Allison and Brand, 1995) and the few age classes in the exploited population dictates that the success of the ﬁshery each year is very dependent on the strength of the incoming year class. For ﬁsheries such as this, recruitment variation is a major contributor to temporal variations in the commercial catch. Scallop stocks have a well established reputation for being tem- porally and spatially variable, and the main causes have been sum- marized into three groups; recruitment variability, catastrophic mortality, and the longevity of the species (short-lived species have no buffer zone if there is a period of poor recruitment, # 2007 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org 1124 by guest on March 22, 2013 http://icesjms.oxfordjournals.org/ Downloaded from