Aquatic Environment and Biodiversity Annual Review 2012

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AEBAR 2012: Non-protected bycatch 6.3.2. Ling longline fishery The first analysis of bycatch and discards in this fishery covered the period from 1990–91 to 1997–98, and the second (and latest) analysis covered the following years up to 2005–06. To enable a comparison of estimates between studies, which used slightly different methodologies, the 1994–95 fishing year was re-assessed in the recent analysis. In addition to estimating the bycatch of all quota species combined, and all non-quota species combined, in the recent analysis annual bycatch was estimated separately for three commonly caught individual species, spiny dogfish, red cod, and ribaldo. Comparative estimates of only total annual bycatch are available from the first analysis for 1990–91 to 1997–98. The ratio estimator used in these analyses to calculate bycatch and discard rates was based on the number of hooks set. The ratios were applied to hook number totals calculated from commercial catch-effort data to make annual estimates for the target fishery as a whole. Regression tree methods were used to minimise the number of levels of season and area variables used to stratify data for the calculation of annual discard bycatch totals in all categories with minimal loss of explanatory power. This reduced the number of areas in each category from eight down to between two and four, and split the year into three or four periods. The area variables created in this way tended to have more explanatory power. . Between 1998–99 and 2005–06 only 9% of the vessels operating in this fishery were observed (14 vessels in all) but these tended to be the main operators (including most of the larger autoliners) and accounted for between 7.7% and 52.5% of the annual target ling catch and 7.8% to 61% of the annual number of longlines set during these years. The annual number of observed sets ranged from 324 to 1605 compared with the total target fishery effort of about 2500 to 4150 sets. Observer coverage before 1998–99 was very low, exceeding 5% of the annual target ling catch only in 1994–95 and 1996–97. Ling accounted for 68% of the total estimated catch from all observed sets targeting ling between 1998–99 and 2005–06, and spiny dogfish accounted for about a further 14%. About half of the remaining 18% of the catch comprised other commercial species; especially red cod (Pseudophycis bachus), (2.3%), ribaldo (Mora moro) (2.2%), rough skates (Zearaja nasuta, 1.9%), smooth skates (Dipturus innominatus) (1.8%), and sea perch (Helicolenus spp.) (1.2%). Altogether, 93% of the observed catch was comprised of QMS species, representing 40 of the 96 species in the QMS prior to 1 October 2007. Over 130 species or species groups were identified by observers, the majority being non-commercial species caught in low numbers, especially black cod (Paranotothenia magellanicus) and Chondrichthyans, often unspecified but including shovelnose spiny dogfish (Deania calcea), Etmopterus species, and seal sharks (Dalatias licha). A surprising number of echinoderms, especially starfish (of which almost 200 000 were observed caught during the period), anemones, crustaceans, and other invertebrates were also recorded by observers. Total annual bycatch estimates for 1998–99 to 2005–06 ranged from about 2200 t to 3700 t, compared with approximate target species catches in the same period of between about 3500 and 8700 t. A large part of this bycatch (40–50%) comprised a single species, spiny dogfish, and 80% of the bycatch were quota species (Figures 6.4 & 6.5). Bycatch levels decreased during the period, in line with decreasing effort in the fishery. Total bycatch estimates for the years before 1998–99 ranged from about 880 t to 3900 t. Differences in methodology between the two studies, coupled with generally low observer coverage, resulted in significantly different estimates of total bycatch for 1994–95. 129
AEBAR 2012: Non-protected bycatch Figure 6.4: Annual estimates of fish bycatch in the target ling longline fishery, calculated for commercial (QMS) species (COM), non-commercial (non-QMS) species (OTH), and overall (TOT) for the years 1994–95 and 1998–99 to 2005–06 (in black). Also shown (in grey) are estimates of total bycatch calculated for the period 1990–91 to 1997–98 by Anderson et al. (2000). Error bars show the 95% confidence intervals. 130
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Aquatic Environment and Biodiversit
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AEBAR 2012 Acknowledgements In addi
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AEBAR 2012 Contents PREFACE .......
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1. INTRODUCTION 1.1. Context and pu
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AE&B Review: Protected species: Sea
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5.1. Context AEBAR 2012: Protected
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11.1.2. Defining biodiversity AEBAR
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12. Appendices AEBAR 2012: Appendic
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PROTECTED SPECIES AEBAR 2012: Appen
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ISBN: 978-0-478-40503-3 (print) ISB
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Aquatic Environment and Biodiversity Annual Review 2012

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