ABUNDANCE, INTERACTION AND MOVEMENT IN A EUROPEAN LOBSTER STOCK Daniel J. Skerritt Thesis submitted to Newcastle University for the degree of Doctor of Philosophy School of Marine Science and Technology July 2014 Abstract Abundance, interaction and movement in a European lobster stock Daniel J. Skerritt Supervisors: Dr Clare Fitzsimmons and Prof. Nicholas V.C. Polunin Examiners: Dr Colin Bannister and Dr Ben Wigham Abstract European lobsters form one of the most economically valuable portions of UK landings, yet they are little regulated, despite stocks being considered fully exploited. Biological and behavioural knowledge is lacking, managerial effort is low and understanding is often inferred from other species. To ensure continued productivity of this important fishery, improved data on fishing activity, population dynamics, catchability, recruitment, movement and distribution are urgently required. Through analysis of capture-mark-recapture data, fishery-independent catches, behavioural- interaction studies and acoustic telemetry tracking, this thesis aims to provide a basis for future research and management. Capture-mark-recapture (CMR) and fishery-independent catch data established estimates of density, proportionate distribution, movements and site-fidelity and catchability parameters. These revealed high site fidelity and catchability differences between sexes leading to female-skewed density estimates. If these findings are corroborated, the effect and causes of disproportionate sex ratios must be addressed. The mixed-species nature of UK shellfisheries led to studies recording the impact of inter-specific and intra-specific interactions on catchability and catch rates. Lobster presence significantly lowered catchability of crab species and occurrences of same- sex lobster pairings were lower than expected. Findings highlight both the inconsistency of using catch per unit effort (CPUE) as a direct index of abundance and the danger of analysing crab and lobster catch data in isolation from each other. The final study employed an acoustic telemetry array to quantify in situ lobster movement, providing unique information on short-term home-ranges and habitat- utilisation. There were both transient and resident portions of the population, not predictable by sex or size. Males had significantly larger home-ranges than females, i Abstract which could explain their increased catchability estimated in the CMR study. In contrast to trap catch data, most lobsters were recorded using soft substrate outwith their home-range. Movement behaviour changed accordingly, from ‘searching’ behaviour on mixed and hard substrates to ‘exploratory’ behaviour on soft. This highlighted a potential connectivity between isolated rocky habitats. The present study reveals the importance of undertaking local lobster studies in order to elucidate behavioural traits and highlight sampling uncertainties that can have important impacts on methods of stock assessment. Findings provide an initial baseline for further data collection, allowing changes in the population to be monitored. ii Acknowledgements Acknowledgements I took on the challenge of this PhD under no illusions of the task at hand; I never underestimated the amount of hard work that would be involved. However, the three years have also been a great deal of fun and was an experience I am unlikely to forget. Since moving to Newcastle in 2005, I have regarded it as my home, therefore this study has had a particular resonance with me. Working alongside fishermen and managers within Northumberland, with focus on this relatively understudied population of lobster within such close vicinity to my doorstep, has been a rare privilege. I would like to think that the findings, outcomes and working relationships built during this study will prove useful for years to come. Numerous people have provided help, advice and support during the three years of planning and implementing of fieldwork and writing this thesis. Unfortunately I do not have space to thank them all, but I am grateful for the experience that each one has shared with me. I would first like to thank my supervisors Dr Clare Fitzsimmons and Prof. Nicholas Polunin for all their help throughout the PhD. They have offered support, guidance and plenty of patience. I have learnt a great deal and enjoyed every aspect of working together over the past five years. I would also like to thank Dr Mike Bell and Dr Aileen Mill for all your statistical advice and help, particularly Mike for provision of the R-code used in Chapter 2. Thank you for always answering my emails and questions, even without the incentive of cake on occasion. I would also like to thank; everyone within our research group at Newcastle University; distractions from study during coffee on Thursday (CoT) were a great motivation to get ample work done by 1100; all members, past and present, of 2.60, it has been a pleasure, although I’m not sure who was the biggest distraction to my work, but thanks for putting up with me and Ted; and Dr Catherine Scott, for creating my first opportunity to conduct research. The first year was a steep learning curve for many of us and hopefully the success of the following years will promote further collaboration between Newcastle University, Natural England and the NIFCA. Special thanks must go to the NIFCA officers, without their help I could never have begun to gain samples to study these animals. Particularly, I would like to thank those iii Acknowledgements who helped with fieldwork and the painting of hundreds of lobsters and thousands of crabs during 2010, the coldest winter since records began. I know some mornings you despaired, but it was all good fun in the end. Without the NIFCA officers most of this PhD would not have been possible. I would also like to thank Robert Oliver for first showing me how to rig traps and tie an eye-splice; Peter Berney and all other volunteers during this study, for tirelessly helping during field work. Finally I must thank all those involved with the RV Princess Royal. Especially, Dr Ben Wigham for helping to make time in the schedule for my work and Neil Armstrong and Barry Pearson for helping with the planning and conducting of the final two years of field work. I learnt a vast amount from these two, although to their annoyance I often forgot some of it too. This PhD was made possible by initial funding and belief from Natural England and the NIFCA. Further investment from Newcastle University and the MMO helped it expand into a PhD. Hopefully this financial investment and personal involvement will help to begin to increase our knowledge and understanding of lobster in the North East, and help to prepare for the continued sustainability of this regionally important species. I am proud to have had the opportunity to conduct research within Northumberland, alongside the great people I have worked with. I am also incredibly grateful to all my family and friends for the support and love they have offered me throughout, particularly, Dr Paul Woods for affording me the opportunity to remain within academia. Finally, and most importantly, I would like to thank Chloe. Thank you for your patience while I have completed this thesis. Thank you for your support, encouragement and love, I could not have completed this without your inspiration. iv Table of contents Table of contents Chapter 1: Introduction 1 1.1 Clawed lobsters 2 1.2 Biology, reproduction and larval ecology 3 1.3 Behaviour and distribution 6 1.3.1 Movement 7 1.3.2 Habitat 9 1.4 Fishing 10 1.4.1 Seasonality 11 1.4.2 Soak time 12 1.4.3 Effective area fished 13 1.4.4 Species interactions 14 1.5 Management 15 1.5.1 Stock assessment 17 1.5.2 Capture-mark-recapture 20 1.5.3 Tracking technology 20 1.5.4 Marine protected areas 22 1.5.5 Aquaculture and enhancement 23 1.6 Future research and discussion 24 1.7 Thesis outline and objectives 26 Chapter 2: Estimating Homarus gammarus densities from continuous, short-term capture-mark-recapture catch data 28 2.1 Introduction 29 2.2 Methodology 31 2.2.1 Study site 31 2.2.2 Data collection 31 2.2.3 Model framework 34 2.2.4 Model fitting and goodness-of-fit 41 2.2.5 Effort modelling 42 2.3 Results 44 2.3.1 Catch data 44 v Table of contents 2.3.2 Capture-mark-recapture data and model selection 45 2.3.3 Goodness-of-fit 49 2.3.4 Effective effort estimation 50 2.3.5 Population size and density estimates 51 2.4 Discussion 53 2.4.1 Population size estimates 53 2.4.2 Assumptions and uncertainties 58 2.4.3 Sampling design 60 2.4.4 Model framework 61 2.5 Conclusion 61 Chapter 3: Inter- and intra-specific interactions affecting the Homarus gammarus catch in a mixed coastal fishery 63 3.1 Introduction 64 3.2 Methodology 67 3.2.1 Study sites 67 3.2.2 Data collection 69 3.2.3 Statistical analysis 71 3.3 Results 72 3.3.1 Fishery-independent trap survey data 72 3.3.2 Pre-loaded trap-catch data (2011 – 2012) 75 3.3.3 Pre-loaded trap-catch data (2013) 78 3.4 Discussion 83 3.4.1 Intra-specific interactions 84 3.4.2 Inter-specific interactions 86 3.4.3 Methodological improvements 87 3.4.4 Future implications of the study 88 3.5 Conclusion 89 Chapter 4: Investigating spatial distribution and movements of Homarus gammarus via fishery-independent trap surveys and mark-recapture 91 4.1 Introduction 92 4.2 Methodology 94 vi Table of contents 4.2.1 Study sites 94 4.2.2 Data collection 96 4.2.2.1 Fishery-independent trap data 97 4.2.2.2 Capture-mark-recapture 100 4.2.3 Statistical analysis 101 4.3 Results 103 4.3.1 Fishery-independent trap