Ireland’s understudied flatfish: Reproduction, age and growth of the dab Limanda limanda(L.) in Irish coastal waters ^ g oiNSTirjg; GMIT I GALWAY-MAYO INSTITUTE OF TECHNOLOGY IlHSTiriUID TEICNEOLAtOCHTA NA GAILUHHEMAIGH EO Laura M. Langan Department of Life Science Galway -Mayo Institute of Technology Submitted in partial fulfilment of the requirements for the degree of Masters of Research in Fisheries Science Supervisors: Dr. Pauline A King and Dr. Hans Gerritsen Submitted to the Higher Education and Training Awards Council, October 2012 Contents List of Figures......................................................................................... v List of Tables .................. vi Abstract.................................................................................................. vii Acknowledgements................................................................................ x 1 Literary Review 1 1.1 Fisheries: stock assessment and management........................... 2 1.1.1 Europe............................................................................... 2 1.2 Management of Limanda lirnanda.......................................... 3 1.3 Taxonomy and description......................................................... 5 1.4 Habitat and distribution............................................................ 7 1.5 Age and Growth ......................................................................... 8 1.6 Reproductive B iology.................................................................. 9 1.7 The role of dab in the marine ecosystem ................................. 11 1.8 Aim and Objectives...................................................................... 13 2 Reproductive Biology 14 2.1 Introduction.................................................................................. 15 2.2 Materials and m ethods............................................................... 17 2.2.1 Histology ......................................................................... 19 2.2.2 Condition indices............................................................. 20 2.2.3 Data Analysis................................................................... 22 2.3 Results........................................................................................... 23 2.3.1 Gonadal Development ................................................... 23 2.3.2 Histological verification of macroscopic phase description 24 2.3.3 Maturity ogives................................................................ 29 2.3.4 Condition Indices............................................................. 30 2.4 Discussion..................................................................................... 32 2.4.1 Macroscopic and microscopic criterion ........................ 32 2.4.2 Maturity ogives................................................................ 34 2.4.3 Gonadal Developm ent.................................................... 34 2.4.4 Condition in d ices............................................................. 35 2.4.5 Conclusion......................................................................... 36 Ireland’s understudied flatfish Contents 3 Age 38 3.1 Introduction....... .......................................................................... 39 3.2 Materials and Methods................................................................. 41 3.2.1 Marginal increment analysis.......................................... 42 3.2.2 Age determination.......................................................... 42 3.2.3 Data Analysis................................................ 43 3.3 Results........................................................................................... 45 3.3.1 Marginal Increment Analysis.......................................... 45 3.3.2 Comparison of readers against modal ag e ...................... 47 3.3.3 Comparison of Readers..................................................... 48 3.3.4 Comparison of Institutes.................................................. 52 3.4 Discussion..................................................................................... 52 3.4.1 Marginal Increment Analysis........................................... 52 3.4.2 B i a s .................................................................................. 53 3.4.3 Precision............................................................................ 54 3.5 Future direction............................................................................. 56 4 Growth 58 4.1 Introduction.................................................................................. 60 4.2 Materials and methods................................................................. 61 4.2.1 Corroboration of correct ageing structure....................... 62 4.2.1.1 Precision and bias in ageing methodology . 63 4.2.2 Growth ............................................................................ 64 4.2.3 Comparison of growth between different regions .... 67 4.3 Results........................................................................................... 67 4.3.1 Meristic Parameters ........................................................ 67 4.3.1.1 Length-weight Relationship.............................. 67 4.3.1.2 Age-at-length...................................................... 68 4.3.1.3 Sex-ratio ............................................................ 71 4.3.2 Comparison of ageing m ethodology.............................. 71 4.3.2.1 Within reader bias and p recision .................... 72 4.3.2.2 Between reader bias and precision.................... 73 4.3.3 Growth of Limanda limanda........................................... 74 4.4 Discussion..................................................................................... 78 4.4.1 Meristic Parameters ........................................................ 78 4.4.2 Age and Growth ............................................................... 79 4.4.3 Conclusion......................................................................... 83 Ireland’s understudied flatfish Contents 5 Conclusions 85 5.1 Implications of the study on similar populations elsewhere . 87 5.2 Recommended Future W o r k ...................................................... 88 5.2.1 Estimates of Fecundity.................................................... 89 5.2.2 Validation of age determinations.................................... 89 5.2.3 Improved knowledge about how dab stocks react to external factors, both abiotic and biotic........................ 89 5.2.4 Improved monitoring of biological param eters............ 90 6 Appendix 91 6.1 Protocols:.................................................................................... 92 6.2 ICES Sub divisions..................................................................... 94 6.3 Sampling Locations..................................................................... 95 6.4 Converting model parameters for growth model comparisons . 96 6.4.1 Schnute Paramaterization.............................................. 96 6.4.2 Gallucci and Quinn Parameterization........................... 96 iv List of Figures Figure 1.1 The common dab Limanda limanda ............................. 6 Figure 1.2 The appearance of the epithelium of Limanda limanda can change based on the presence of specific skins diseases such as hyperplasia............................................................. 6 Figure 1.3 Computer generated map of distribution of Limanda limanda................................................................................ 7 Figure 2.1 Gonadosomatic index for both male and female dab . 23 Figure 2.2 Bias plots of reproductive methodologies....................... 25 Figure 2.3 Photomicrographs of ovarian and testicular histology . 26 Figure 2.4 Maturity ogives for male and female d a b ....................... 29 Figure 2.5 Relative condition (kn) and Hepatosomatic indice (HS1) 31 Figure 3.1 Image of whole otolith immersed in water....................... 43 Figure 3.2 Monthly changes in mean marginal increment for section otoliths of dab, with 95% confidence intervals. Number of observations per point can be seen in table below figure. 46 Figure 3.3 Age bias plots for age estimation of dab using whole otoliths 51 Figure 4.1 Sectioned sagittal otolith of Limanda limanda.............. 64 Figure 4.2 Length frequency p l o t ...................................................... 70 Figure 4.3 Age frequency plot for female and male d a b ................. 71 Figure 4.4 Female growth model, with all four growth curves plotted 75 Figure 6.1 ICES Sub-division Boundaries ....................................... 94 Figure 6.2 Ireland and surrounding fishing grounds. The squares are the locations where samples were caught during scientific sampling surveys carries out by the Marine Institute during the year of 2009. The circles represent dab samples collected using commercial fishing vessels from February 2009 to June 2010................................................................ 95 v List of Tables Table 1.1 Total allowable catch of of dab and flounder................. 5 Table 1.2 Various recorded growth rates of L.lim anda................. 9 Table 1.3 Cyclical changes in gonads of Limanda limanda........... 10 Table 2.1 Summary of catch during sampling p eriod ..................... 18 Table 2.2 Sample sizes of macroscopic maturity phases during study period..................................................................................