UNIVERSITY OF GHENT- FACULTY OF SCIENCES RESEARCH GROUP MARINE BIOLOGY ACADEMIC YEAR 2015-2016 FISHING FOR A FEEDING FRENZY Effect of Shrimp Beam Trawling on the diet of Dab and Plaice in Lanice conchilega habitats Submitted by MARIA INÊS COELHO MEIRELES RIBEIRO PROMOTER: Prof. Dr. Ann Vanreusel SUPERVISORS: Jochen Depestele and Jozefien Derweduwen Master thesis submitted for the partial fulfilment of the title of MASTER OF SCIENCE IN MARINE BIODIVERSITY AND CONSERVATION Within the International Master of Science in Marine Biodiversity and Conservation EMBC+ No data can be taken out of this work without prior approval of the thesis promoter Prof. Dr. Ann Vanreusel ([email protected]) and supervisors Jochen Depestele ([email protected]) and Jozefien Derweduwen ([email protected]) TABLE OF CONTENS LIST OF FIGURES............................................................................................................................. 3 LIST OF TABLES .............................................................................................................................. 4 EXECUTIVE SUMMARY ...................................................................................................................5 ABSTRACT....................................................................................................................................... 6 1. INTRODUCTION …........................................................................................................................... 7 2. MATERIALS AND METHODS........................................................................................................... 9 2.1 EXPERIMENTAL DESIGN…........................................................................................................ 11 2.2 STUDY AREA AND FISHING GEARS........................................................................................... 12 2.3 FISH CONTENT ANALYSIS ...……..……........................................................................................ 13 2.4 DATA ANALYSIS: EFFECT OF TRAWLING ON THE DIET OF DAB AND PLAICE...........................16 3. RESULTS ……………………………........................................................................................................... 17 3.1 DAB…………………………….…......................................................................................................... 17 UNIVARIATE DIETARY INDICES........................................................................................... 17 MULTIVARIATE ANALYSIS ...……..……...................................................................................20 Biomass…………………..................................................................................................... 20 Abudance………………….................................................................................................. 21 3.2 PLAICE…………………………….….................................................................................................... 23 UNIVARIATE DIETARY INDICES........................................................................................... 23 UNIVARIATE ANALYSIS ...……..…….......................................................................................24 Biomass…………………..................................................................................................... 24 Abudance………………….................................................................................................. 25 3.3 COMPARISON OF DAB AND PLAICE’s DIET ACROSS TIME……………………................................ 29 UNIVARIATE DIETARY INDICES........................................................................................... 29 UNIIVARIATE ANALYSIS ...……..……..................................................................................….31 Biomass…………………..................................................................................................... 31 1 Abudance………………….................................................................................................. 32 4. DISCUSSION ……………………………..................................................................................................... 33 UNACCOUNTED VARIABILITY OF FEEDING ACTIVITY......................................................... 33 DAB DIET AFTER FISHING ...……..…….................................................................................. 34 PLAICE DIET AFTER FISHING............................................................................................... 35 COMPARISON BETWEEN DAB AND PLAICE’s DIET AFTER FISHING .................................. 36 5. CONCLUSION ……………………………................................................................................................... 37 ACKOWLEDGMENTS ……………………………............................................................................................ 38 REFERENCES ……………………………........................................................................................................ 39 6. APPENDIX ……………………………........................................................................................................ 45 2 LIST OF FIGURES Fig 1. A schematic overview of all the hauls performed over time, the vessel type, the vessel name and the type of gear. ……………………………………………………………………………………………………………………………….…..9 Fig 2. Location of the study area (blue), Box 9. …………………………………………………………………………………..…11 Fig 3. Map of the study area bathymetry (black polygon). Green as shallow mud; Brown as shallow coarse and mixed sediment; Yellow as shallow sands……………………………………………………………………………11 Fig 4. Total number of complete stomachs sampled by time step, time of sampling and name of the vessel……………………………….……………………………………………………………………………………………………………….….12 Fig 5.Stomach Fullness Index (SFI) (±SE) and Stomach Vacuity Index (%V) for Dab before (T0) and after fishing (T1, T2 and T3) …………………………………………………………………………………………………………………………...17 Fig 6. Mean number of prey species per stomach (S) and Shannon-Wiener Index (H’) for Dab before (T0) and after fishing (T1,T2 and T3). ……………………………………………………………………………………………………………18 Fig 7. Frequency of occurrence (%F) of higher taxon on the diet of Dab in each time step. …………………..19 Fig 8. Percentage Index of Relative Importance (%IRI) of higher taxon on the diet of Dab in each time step. ………………………………………………………………………………………………………………………………………………………………19 Fig 9. Mean prey biomass by higher taxon and by time (T0- before fishing; T1, T2 and T3 – after fishing) for Dab. …………………………………………………………………………………………………………………………………………………21 Fig 10. Mean prey abundance by higher taxon and by time (T0- before fishing; T1, T2 and T3 – after fishing) for Dab. …………………………………………………………………………………………………………………………………………………22 Fig 11. Stomach fullness (SFI) (±SE) and Stomach Vacuity (%V) indices for Plaice before (T0) and after fishing (T1, T2 and T3). ………………………………………………………………………………………………………………………….23 Fig 12. Mean number of prey species per stomach (S) (±SE) and Shannon-Wiener Index (H’) (±SE) for Dab before (T0) and after fishing (T1, T2 and T3). …………………………………………………………………………………………24 Fig 13. Frequency of occurrence of higher taxon on the diet of Plaice to all time steps………………………….25 Fig 14. Percentage Index of Relative Importance (%IRI) by higher taxon on the diet of Plaice to all time steps. …………………………………………………………………………………………………………………………………………………….25 Fig 15. Mean prey biomass by higher taxon and by time (T0 – before fishing; T1,T2,T3 – after fishing) for Plaice. ……………………………………………………………………………………………………………………………………………………27 Fig 16. Mean prey abundance by higher taxon and by time (T0 – before fishing; T1,T2,T3 – after fishing) for Plaice. ………………………………………………………………………………………………………………………………………………28 Fig 17. Stomach fullness (SFI) (±SE) for Dab (Green) and Plaice (Blue) before (T0) and after fishing (T1, T2 and T3). …………………………………………………………………………………………………………………………………………………29 Fig 18. Frequency of occurrence (%F) of higher taxon before (T0) and after fishing (T1, T2 and T3) for Dab and Plaice. …………………………………………………………………………………………………………………………………………….30 Fig 19. Percentage Index of Relative Importance (%IRI) of higher taxon before (T0) and after fishing (T1, T2 and T3) for Dab and Plaice………………………………………………………………………………………………………………..30 Fig 20. MDS-plot for prey biomass by time (T0,T1, T2 and T3 – Different symbols) and by species (Dab – Green and Plaice – Blue). ………………………………………………………………………………………………………………………32 3 Fig 21. MDS-plot for prey abundance by time (T0,T1, T2 and T3 – Different symbols) and by species (Dab – Green and Plaice – Blue). …………………………………………………………………………………………………………………33 LIST OF TABLES Table 1. Study area coordinates (Box9) ……………………………………………………………………………………………..11 Table 2. ANOSIM-test with the p-values for the differences between Time steps for prey biomass for Dab. (Global R = 0.037). ……………………………………………………………………………………………………………………..20 Table 3. ANOSIM-test with the p-values for the differences between Time steps for prey abundance for Dab. (Global R = 0.0006) …………………………………………………………………………………………………………………….21 Table 4. ANOSIM-test with the p-values for the differences between Time steps for prey biomass for Plaice. (Global R = 0.135) ……………………………………………………………………………………………………………………26 Table 5. ANOSIM-test with the p-values for the differences between Time steps for prey abundance for Plaice. (Global R = 0.087) ……………………………………………………………………………………………………………………28 Table 6. Average similarities, from SIMPER, between Dab and Plaice’s diet by time and for the prey species biomass and abundance. ……………………………………………………………………………………………………….31