The Effects of Fishing on Deep-water Fish Species to the West of Britain Final Report for Joint Nature Conservation Committee (F90-01-216) by Marinelle Basson1, John D.M. Gordon2, Philip Large3, Pascal Lorance4, John Pope5 & Brian Rackham3. October 2001 1. Commonwealth Scientific & Industrial Research Organisation, Hobart, Tasmania 2. Scottish Association for Marine Science, Oban, UK. 3. Centre for Environment, Fisheries & Aquaculture Science, Lowestoft, UK 4. Institut Francais de Recherche pour l'Exploration de la Mer, Boulogne-sur-Mer, France. 5. NRC Ltd, Burgh St Peter, UK. 1 Acknowledgements of Project Funding This project was commissioned and funded by the Joint Nature Conservation Committee (JNCC). Additional funding was provided by the Ministry of Agriculture, Fisheries and Food (MAFF) and the Institut Francais de Recherche pour l’Exploration de la Mer (IFREMER). Contributions in kind were made by the Centre for Environment, Fisheries & Science (CEFAS), IFREMER and the Scottish Association for Marine Science (SAMS). This study uses data from the Commission of the European Communities Agriculture and Fisheries (FAIR) specific RTD programme, (contract) CT95-0655, Developing deep-water fisheries : data for their assessment and for understanding their interaction with and impact on a fragile environment. It does not necessarily reflect its views and in no way anticipates the Commission's future policy in this area. Acknowledgements of Sources of Survey Data Survey data for this project were provided by the Scottish Association for Marine Science (SAMS), the Institut Francais de Recherche pour l’Exploration de la Mer (IFREMER), the Centre for Environment, Fisheries & Science (CEFAS), Fisheries Research Services (FRS), Aberdeen and the Institut fur Seefischeri (ISH), Hamburg, Germany. Survey data provided by SAMS and IFREMER from cruises conducted in 1999 were particularly valuable for this study and special thanks are extended to these institutes. 2 Contents 1. Summary 2. Introduction 2.1 Definition and general features of the deep-water areas and fisheries to the west of Britain 2.1.1 Topography and geology 2.1.2 Hydrography 2.1.3 Fish populations 2.1.4. Invertebrate fauna 2.1.5 Description of fisheries 2.1.5.1 Bottom trawl fisheries in ICES Sub-areas VI, VII and Division Vb 2.1.5.2 Other fisheries 2.2 Previous studies of the effects of fishing on deep-water species to the west of Britain 2.3 Project Aims 2.4 Project overview 3 Compilation of data for deep-water areas to the west of Britain 3.1 Deep-water survey database 3.2 Commercial catch, effort and discard data. 4. Ecological studies 4.1 Factors relevant when using trawl survey data to investigate the effect of fishing on fish assemblages. 4.1.1 Gear effects 4.1.2 Area effects 4.1.3 Depth effects 4.1.4 Seasonal effects 4.1.4.1 On biology 4.1.4.2 On fish distribution 4.1.5 Episodic events 4.1.6 Effects of local topography 4.2 A way forward 4.3 Investigation and comparison of size-spectra 4.3.1 General background 4.3.2 Previous studies of deep-water fish assemblages to the west of Britain 4.3.3 General protocol for the calculation of size-spectra 4.3.4 Size spectra results 4.3.4.1 Graphical comparisons pre- and post-exploitation 4.3.4.2 Analysis of covariance of size spectra 4.3.4.2.1 Choice of factors in the analysis of covariance 4.3.4.2.2 The analysis of covariance model chosen 4.3.4.2.3 Results of the analysis of covariance : gear grouping A 4.3.4.2.4 Results of the analysis of covariance : gear grouping B 4.3.5 Discussion 3 4.4 Effect of fishing on the species composition of fish assemblages 4.4.1 Introduction and general background 4.4.2 Graphical comparisons pre- and post-exploitation 4.4.3 Detrended correspondence analysis 4.4.4 Discussion 4.5 Investigation and comparison of diversity indices pre- and post-exploitation 4.5.1 Introduction and general background 4.5.2 Data 4.5.3 Methods 4.5.4 Comparison of diversity indices and discussion 4.6 Long term trends inferred from survey indices of relative biomass and abundance 4.6.1 Introduction and general background 4.6.2 Data 4.6.3 Standardised time series of survey CPUE 4.6.3.1 Data 4.6.3.2 Methods 4.6.3.3 Results 4.6.3.3.1 Exploited species 4.6.3.3.2 Unexploited species 4.6.3.3.3 Comparison of results 4.6.3.3.4 Results based on SAMS data only 4.6.3.3.5 Results : roundnose grenadier (Coryphaenoides rupestris) 4.6.4 Presence/absence analyses of survey data 4.6.4.1 Data 4.6.4.2 Methods 4.6.4.3 Results 4.6.5 Discussion and results from CPUE and presence/absence analyses 5. Assessment studies 5.1 Background and general history of previous assessments 5.2 Precautionary Approach 5.3 Assessment methodology and software 5.3.1 Methods 5.3.1.1 Depletion models 5.3.1.2 Production models 5.3.1.3 Virgin biomass estimation from fish densities calculated using the swept area method and subsequent calculations of estimates of maximum sustainable yield (MSY) 5.3.1.4 Estimation of natural mortality (M) 5.3.2 Software 5.4 Landings and discard data 5.4.1 Landings data 5.4.2 Discard data 5.4.2.1 Irish discard studies 5.4.2.2 French discard studies 5.4.2.3 Scottish discard studies 5.4.2.4 Mortality of escapees 4 5.5 General description of the methodology used to construct French effort and CPUE indices 5.6 Stock assessments 5.6.1 Orange roughy (Hoplostethus atlanticus) 5.6.1.1 Distribution and general biology 5.6.1.2 Stock structure 5.6.1.3 Description of fisheries 5.6.1.4 Landings and discard data 5.6.1.5 Commercial catch-effort data 5.6.1.6 Length and age compositions 5.6.1.7 Natural mortality 5.6.1.8 Assessment results 5.6.1.8.1 Orange roughy in Sub-area VI 5.6.1.8.2 Orange roughy in Sub-area VII 5.6.1.8.3 Orange roughy in Sub-area VI and Divisions VIIb,c 5.6.1.9 Comments on the assessments 5.6.1.10 State of stocks 5.6.2 Black scabbardfish (Aphanopus carbo) 5.6.2.1 Distribution and general biology 5.6.2.2 Stock structure 5.6.2.3 Description of fisheries 5.6.2.4 Landings and discard data 5.6.2.5 Commercial catch-effort data 5.6.2.6 Length and age compositions 5.6.2.7 Natural mortality 5.6.2.8 Assessment results for black scabbardfish in Sub-areas VI, VII, XII and Division Vb 5.6.2.9 Comments on the assessments 5.6.2.10 State of stock 5.6.3 Deep-water sharks 5.6.3.1 Distribution and general biology 5.6.3.2 Stock structure 5.6.3.3 Description of fisheries 5.6.3.4 Landings and discard data 5.6.3.5 Commercial catch-effort data 5.6.3.6 Length and age compositions 5.6.3.7 Natural mortality 5.6.3.8 Assessment results for deep-water sharks in Sub-areas VI, VII and Division Vb 5.6.3.9 Comments on the assessments 5.6.3.10 State of stock 5.6.4 Roundnose grenadier (Coryphaenoides rupestris) 5.6.4.1 Distribution and general biology 5.6.4.2 Stock structure 5.6.4.3 Description of fisheries 5.6.4.4 Landings and discard data 5.6.4.5 Commercial catch-effort data 5.6.4.6 Length and age compositions 5.6.4.7 Natural mortality 5.6.4.8 Assessment results 5 5.6.4.8.1 Roundnose grenadier in Sub-areas VI, VII and Division Vb 5.6.4.8.2 Roundnose grenadier in Sub-area VI and Divisions VIIb,c 5.6.4.9 Comments on the assessments 5.6.4.10 State of stock 5.6.5 Blue ling (Molva dypterygia) 5.6.5.1 Distribution and general biology 5.6.5.2 Stock structure 5.6.5.3 Description of fisheries 5.6.5.4 Landings and discard data 5.6.5.5 Commercial catch-effort data 5.6.5.6 Length and age compositions 5.6.5.7 Natural mortality 5.6.5.8 Assessment results 5.6.5.8.1 Blue ling in Sub-areas VI, VII and Division Vb 5.6.5.8.2 Blue ling in Sub-area VI and Divisions VIIb,c 5.6.5.9 State of stock 5.6.6 Greater forkbeard (Phycis blennoides) 5.6.6.1 Distribution and general biology 5.6.6.2 Stock structure 5.6.6.3 Description of fisheries 5.6.6.4 Landings and discard data 5.6.6.5 Commercial catch-effort data 5.6.6.6 Length and age compositions 5.6.6.7 Natural mortality 5.6.6.8 Assessment results 5.6.6.9 State of stock 5.7 Discussion 6. Recommendations for further work 7. References 8. Bibliography 9. Appendices 9.1 List of participants 9.2 Descriptions of the fishing gears used on deep-water trawl surveys to the west of the Britain. 9.3 Species codes used in the detrended correspondence analyses (Section 4.4.3). 9.4 Technical appendix for investigations of long term trends inferred from survey indices of relative biomass and abundance (Section 4.6).