DOCSLIB.ORG

Ireland's Understudied Flatfish: Reproduction, Age and Growth Of

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Ireland's Understudied Flatfish: Reproduction, Age and Growth Of 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..................................................................................
Load more

Recommended publications
  • Supplementary Tales
    Metabarcoding reveals different zooplankton communities in northern and southern areas of the North Sea Jan Niklas Macher, Berry B. van der Hoorn, Katja T. C. A. Peijnenburg, Lodewijk van Walraven, Willem Renema Supplementary tables 1-5 Table S1: Sampling stations and recorded abiotic variables recorded during the NICO 10 expedition from the Dutch Coast to the Shetland Islands Sampling site name Coordinates (°N, °E) Mean remperature (°C) Mean salinity (PSU) Depth (m) S74 59.416510, 0.499900 8.2 35.1 134 S37 58.1855556, 0.5016667 8.7 35.1 89 S93 57.36046, 0.57784 7.8 34.8 84 S22 56.5866667, 0.6905556 8.3 34.9 220 S109 56.06489, 1.59652 8.7 35 79 S130 55.62157, 2.38651 7.8 34.8 73 S156 54.88581, 3.69192 8.3 34.6 41 S176 54.41489, 4.04154 9.6 34.6 43 S203 53.76851, 4.76715 11.8 34.5 34 Table S2: Species list and read number per sampling site Class Order Family Genus Species S22 S37 S74 S93 S109 S130 S156 S176 S203 Copepoda Calanoida Acartiidae Acartia Acartia clausi 0 0 0 72 0 170 15 630 3995 Copepoda Calanoida Acartiidae Acartia Acartia tonsa 0 0 0 0 0 0 0 0 23 Hydrozoa Trachymedusae Rhopalonematidae Aglantha Aglantha digitale 0 0 0 0 1870 117 420 629 0 Actinopterygii Trachiniformes Ammodytidae Ammodytes Ammodytes marinus 0 0 0 0 0 263 0 35 0 Copepoda Harpacticoida Miraciidae Amphiascopsis Amphiascopsis cinctus 344 0 0 992 2477 2500 9574 8947 0 Ophiuroidea Amphilepidida Amphiuridae Amphiura Amphiura filiformis 0 0 0 0 219 0 0 1470 63233 Copepoda Calanoida Pontellidae Anomalocera Anomalocera patersoni 0 0 586 0 0 0 0 0 0 Bivalvia Venerida
    [Show full text]
  • Published Estimates of Life History Traits for 84 Populations of Teleost
    Summary of data on fishing pressure group (G), age at maturity (Tm, years), length at maturity (Lm, cm), length-at-5%-survival (L.05, cm), time-to-5%-survival 3 (T.05, years), slope of the log-log fecundity-length relationship (Fb), fecundity the year of maturity (Fm), and egg volume (Egg, mm ) for the populations listed in the first three columns. Period is the period of field data collection. Species Zone Period G Tm Lm L.05 T.05 Fb Fm Egg Data sources (1) (1) (2) (3) (4) (4) (5) (1) (2) (3) (4) (5) Clupeiformes Engraulis capensis S. Africa 71-74 2 1 9.5 11.8 1.8 3.411 4.856E+04 0.988 118 119 137 118 138 Engraulis encrasicholus B. Biscay 87-92 2 1 11.5 14 1.4 3.997 9.100E+04 1.462 125 30, 188 170, 169 133, 23 145 Medit. S. 84-90 1 1 12.5 13.4 2.3 4.558 9.738E+04 0.668 161 161 160 161, 120 120 Sprattus sprattus Baltic S. 85-91 1 2 12 13.8 6.2 2.84 2.428E+05 1.122 15 19 26 184, 5 146 North S. 73-77 1 2 11.5 14.3 3 4.673 8.848E+03 0.393 8 107 106 33 169 Clupea harengus Baltic S. 75-82 1 3 16 24 4.9 3.206 4.168E+04 0.679 116 191 191 116 169 North S. 60-69 3 3 22 26.9 2.7 4.61 2.040E+04 0.679 52 53, 7 52 39 169 Baltic S.
    [Show full text]
  • Collapse and Recovery of Marine Fishes
    letters to nature sulphide complexes, indicating that Cu sulphide clusters are more 7. Al-Farawati, R. & van den Berg, C. M. G. Metal-sulfide complexation in seawater. Mar. Chem. 63, 331–352 (1999). stable than Cu organic complexes. This explains why laboratory 8. Luther III, G. W., Rickard, D. T., Theberge, S. M. & Olroyd, A. Determination of metal (bi)sulfide cultures of oceanic phytoplankton have been observed to increase stability constants of Mn2+,Fe2+,Co2+,Ni2+,Cu2+, and Zn2+ by voltammetric methods. Environ. Sci. the production of total dissolved sulphides when the concentrations Technol. 30, 671–679 (1996). of free Cu and Zn in the culture media were increased22. Although 9. Helz, G. R, Charnock, J. M., Vaughan, D. J. & Garner, C. D. Multinuclearity of aqueous copper and zinc bisulfide complexes—an EXAFS investigation. Geochim. Cosmochim. Acta 57, the data that we report here suggest that metal sulphide formation is 15–25 (1993). a means of detoxifying trace metals for organisms, further toxico- 10. Luther III, G. W., Theberge, S. M. & Rickard, D. T. Evidence for aqueous clusters as intermediates logical studies are needed to quantify the roles both sulphides and during zinc sulfide formation. Geochim. Cosmochim. Acta 19/20, 3159–3169 (1999). ‘natural’ organic ligands play in controlling Cu toxicity in natural 11. Peters, J. W., Lanzilotta, W. N., Lemon, B. J. & Seefeldt, L. C. X-ray crystal structure of the Fe-only hydrogenase (Cpl) from Clostridium pasteurianum to 1.8 angstrom resolution. Science 282, 1853– waters. 1858 (1998). Sulphur complexation may have a dramatic effect on the acute 12.
    [Show full text]
  • Identification of Larvae of Three Arctic Species of Limanda (Family Pleuronectidae)
    Identification of larvae of three arctic species of Limanda (Family Pleuronectidae) Morgan S. Busby, Deborah M. Blood & Ann C. Matarese Polar Biology ISSN 0722-4060 Polar Biol DOI 10.1007/s00300-017-2153-9 1 23 Your article is protected by copyright and all rights are held exclusively by 2017. This e- offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com”. 1 23 Author's personal copy Polar Biol DOI 10.1007/s00300-017-2153-9 ORIGINAL PAPER Identification of larvae of three arctic species of Limanda (Family Pleuronectidae) 1 1 1 Morgan S. Busby • Deborah M. Blood • Ann C. Matarese Received: 28 September 2016 / Revised: 26 June 2017 / Accepted: 27 June 2017 Ó Springer-Verlag GmbH Germany 2017 Abstract Identification of fish larvae in Arctic marine for L. proboscidea in comparison to the other two species waters is problematic as descriptions of early-life-history provide additional evidence suggesting the genus Limanda stages exist for few species. Our goal in this study is to may be paraphyletic, as has been proposed in other studies.
    [Show full text]
  • Scenario Calculations of Mercury Exposure
    VKM Report 2019:3 Scenario calculations of mercury exposure from fish and overview of species with high mercury concentrations Opinion of the Panel on Contaminants of the Norwegian Scientific Committee for Food and Environment Report from the Norwegian Scientific Committee for Food and Environment (VKM) 2019:3 Scenario calculations of mercury exposure from fish and overview of species with high mercury concentrations Opinion of the Panel on Contaminants of the Norwegian Scientific Committee for Food and Environment 05.04.2019 ISBN: 978-82-8259-319-9 ISSN: 2535-4019 Norwegian Scientific Committee for Food and Environment (VKM) Po 4404 Nydalen N – 0403 Oslo Norway Phone: +47 21 62 28 00 Email: [email protected] vkm.no vkm.no/english Cover photo: Colourbox Suggested citation: VKM, Heidi Amlund, Kirsten Eline Rakkestad, Anders Ruus, Jostein Starrfelt, Jonny Beyer, Anne Lise Brantsæter, Sara Bremer, Gunnar Sundstøl Eriksen, Espen Mariussen, Ingunn Anita Samdal, Cathrine Thomsen and Helle Katrine Knutsen (2019). Scenario calculations of mercury exposure from fish and overview of species with high mercury concentrations. Opinion of the Panel on Contaminants of the Norwegian Scientific Committee for Food and Environment. VKM report 2019:3, ISBN: 978-82-8259-319-9, ISSN: 2535-4019. Norwegian Scientific Committee for Food and Environment (VKM), Oslo, Norway. Scenario calculations of mercury exposure from fish and overview of species with high mercury concentrations Preparation of the opinion The Norwegian Scientific Committee for Food and Environment (Vitenskapskomiteen for mat og miljø, VKM) appointed a project group to answer the request from the Norwegian Food Safety Authority. The project group consisted of three VKM-members, and three employees, including a project leader, from the VKM secretariat.
    [Show full text]
  • Pleuronectidae
    FAMILY Pleuronectidae Rafinesque, 1815 - righteye flounders [=Heterosomes, Pleronetti, Pleuronectia, Diplochiria, Poissons plats, Leptosomata, Diprosopa, Asymmetrici, Platessoideae, Hippoglossoidinae, Psettichthyini, Isopsettini] Notes: Hétérosomes Duméril, 1805:132 [ref. 1151] (family) ? Pleuronectes [latinized to Heterosomi by Jarocki 1822:133, 284 [ref. 4984]; no stem of the type genus, not available, Article 11.7.1.1] Pleronetti Rafinesque, 1810b:14 [ref. 3595] (ordine) ? Pleuronectes [published not in latinized form before 1900; not available, Article 11.7.2] Pleuronectia Rafinesque, 1815:83 [ref. 3584] (family) Pleuronectes [senior objective synonym of Platessoideae Richardson, 1836; family name sometimes seen as Pleuronectiidae] Diplochiria Rafinesque, 1815:83 [ref. 3584] (subfamily) ? Pleuronectes [no stem of the type genus, not available, Article 11.7.1.1] Poissons plats Cuvier, 1816:218 [ref. 993] (family) Pleuronectes [no stem of the type genus, not available, Article 11.7.1.1] Leptosomata Goldfuss, 1820:VIII, 72 [ref. 1829] (family) ? Pleuronectes [no stem of the type genus, not available, Article 11.7.1.1] Diprosopa Latreille, 1825:126 [ref. 31889] (family) Platessa [no stem of the type genus, not available, Article 11.7.1.1] Asymmetrici Minding, 1832:VI, 89 [ref. 3022] (family) ? Pleuronectes [no stem of the type genus, not available, Article 11.7.1.1] Platessoideae Richardson, 1836:255 [ref. 3731] (family) Platessa [junior objective synonym of Pleuronectia Rafinesque, 1815, invalid, Article 61.3.2 Hippoglossoidinae Cooper & Chapleau, 1998:696, 706 [ref. 26711] (subfamily) Hippoglossoides Psettichthyini Cooper & Chapleau, 1998:708 [ref. 26711] (tribe) Psettichthys Isopsettini Cooper & Chapleau, 1998:709 [ref. 26711] (tribe) Isopsetta SUBFAMILY Atheresthinae Vinnikov et al., 2018 - righteye flounders GENUS Atheresthes Jordan & Gilbert, 1880 - righteye flounders [=Atheresthes Jordan [D.
    [Show full text]
  • Appendix 13.2 Marine Ecology and Biodiversity Baseline Conditions
    THE LONDON RESORT PRELIMINARY ENVIRONMENTAL INFORMATION REPORT Appendix 13.2 Marine Ecology and Biodiversity Baseline Conditions WATER QUALITY 13.2.1. The principal water quality data sources that have been used to inform this study are: • Environment Agency (EA) WFD classification status and reporting (e.g. EA 2015); and • EA long-term water quality monitoring data for the tidal Thames. Environment Agency WFD Classification Status 13.2.2. The tidal River Thames is divided into three transitional water bodies as part of the Thames River Basin Management Plan (EA 2015) (Thames Upper [ID GB530603911403], Thames Middle [ID GB53060391140] and Thames Lower [ID GB530603911401]. Each of these waterbodies are classified as heavily modified waterbodies (HMWBs). The most recent EA assessment carried out in 2016, confirms that all three of these water bodies are classified as being at Moderate ecological potential (EA 2018). 13.2.3. The Thames Estuary at the London Resort Project Site is located within the Thames Middle Transitional water body, which is a heavily modified water body on account of the following designated uses (Cycle 2 2015-2021): • Coastal protection; • Flood protection; and • Navigation. 13.2.4. The downstream extent of the Thames Middle transitional water body is located approximately 12 km downstream of the Kent Project Site and 8 km downstream of the Essex Project Site near Lower Hope Point. Downstream of this location is the Thames Lower water body which extends to the outer Thames Estuary. 13.2.5. A summary of the current Thames Middle water body WFD status is presented in Table A13.2.1, together with those supporting elements that do not currently meet at least Good status and their associated objectives.
    [Show full text]
  • Hyperpigmentation in North Sea Dab Limanda Limanda. I. Spatial and Temporal Patterns and Host Effects
    Vol. 103: 9–24, 2013 DISEASES OF AQUATIC ORGANISMS Published March 13 doi: 10.3354/dao02554 Dis Aquat Org OPENPEN ACCESSCCESS Hyperpigmentation in North Sea dab Limanda limanda. I. Spatial and temporal patterns and host effects F. Grütjen1, T. Lang2,*, S. Feist3, D. Bruno4, P. Noguera4, W. Wosniok5 1Department of Biological Sciences, Zoology, University of Rostock, 18055 Rostock, Germany 2Thünen Institute of Fisheries Ecology, 27472 Cuxhaven, Germany 3Centre for the Environment, Fisheries and Aquaculture Science, Weymouth, Dorset DT4 8UB, UK 4Marine Scotland Science, Aberdeen AB11 9DB, UK 5Institute of Statistics, University of Bremen, 28334 Bremen, Germany ABSTRACT: Hyperpigmentation is a term describing a specific pigment anomaly affecting com- mon dab Limanda limanda in the North Sea and, less frequently, in adjacent areas, e.g. the Eng- lish Channel, Irish and Celtic Seas, western Baltic Sea and Icelandic waters. Other North Sea flat- fish species are also affected, but at a markedly lower prevalence. The condition is characterised by the occurrence of varying degrees of green to black patchy pigment spots in the skin of the upper (ocular) body side and pearly-white pigment spots in the skin of the lower (abocular) body side. In the course of fish disease monitoring programmes carried out by Germany and the UK (England and Scotland), a pronounced spatial pattern of hyperpigmentation has been detected in the North Sea. An increase in prevalence has been recorded in almost all North Sea areas studied in the past 2 decades. The prevalence recorded in hot spot areas of the condition increased from 5 to >40% between 1988 and 2009.
    [Show full text]
  • Mellergaard3
    Downloaded from orbit.dtu.dk on: Oct 01, 2021 Epidemiology of X-cell gill disease in common dab Limanda limanda Mellergaard, Stig; Nielsen, Else Published in: Diseases of Aquatic Organisms Link to article, DOI: 10.3354/dao025107 Publication date: 1996 Document Version Publisher's PDF, also known as Version of record Link back to DTU Orbit Citation (APA): Mellergaard, S., & Nielsen, E. (1996). Epidemiology of X-cell gill disease in common dab Limanda limanda. Diseases of Aquatic Organisms, 25(1-2), 107-116. https://doi.org/10.3354/dao025107 General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. DISEASES OF AQUATIC ORGANISMS Vol. 25: 107-116, 1996 Published May 9 Dis Aquat Org Epidemiology of X-cell gill disease in common dab Limanda limanda Stig ~ellergaard'~*,Else ~ielsen~ 'Danish Institute for Fisheries Research, Department for Marine and Coastal Zone Ecology, Fish Disease Laboratory, Biilowsvej 13, DK-1870 Frederiksberg C, Denmark 'Danish Institute for Fisheries Research, Department for Marine and Coastal Zone Ecology, Charlottenlund Castle, DK-2920 Charlottenlund.
    [Show full text]
  • Liver Histopathology in Baltic Flounder
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Electronic Publication Information Center Marine Pollution Bulletin 53 (2006) 488–496 www.elsevier.com/locate/marpolbul Liver histopathology in Baltic flounder (Platichthys flesus)as indicator of biological effects of contaminants Thomas Lang a,*, Werner Wosniok b, Janina Barsˇiene_ c, Katja Broeg d, Justyna Kopecka e, Jari Parkkonen f a Federal Research Centre for Fisheries, Institute of Fishery Ecology, Deichstrasse 12, 27472 Cuxhaven, Germany b University of Bremen, Institute of Statistics, Bibliothekstrasse 1, 28334 Bremen, Germany c Institute of Ecology of Vilnius University, Akademijos 2, 08412 Vilnius, Lithuania d Alfred Wegener Institute for Polar and Marine Research, Am Handelsshafen 12, 27570 Bremerhaven, Germany e Institute of Oceanology, Powstancow Warszawy 55, P.O. Box 197, 81-712 Sopot, Poland f Gothenburg University, Box 463, 40530 Gothenburg, Sweden Abstract Results are presented of a study on liver histopathology in Baltic flounder (Platichthys flesus) carried out in 2001 and 2002 in four coastal sampling areas of the Baltic Sea: Kva¨do¨fja¨rden (Swedish east coast, reference area), Klaipeda-Butinge (Lithuanian coast), Gulf of Gdansk (Polish coast), and Wismar Bay (German coast) within the framework of the EU-funded BEEP project. Liver lesions were diagnosed and categorised using standardised methodologies and, for a spatial and temporal assessment of the prevalence and types of lesions detected, a scoring system was applied, involving the calculation of mean histopathology lesion scores. 83.0% of the 436 female flounder examined (size range: 20–43 cm total length, age range: 2–8 years) were affected by liver lesions, out of which 74.3% were assigned to the category of non-specific, 3.4% to the category of early toxicopathic non-neoplastic, 4.6% to the category of pre-neoplastic and 0.7% to the category of neoplastic lesions.
    [Show full text]
  • 9.2 Greater North Sea Ecoregion – Fisheries Overview
    ICES Fisheries Overviews Greater North Sea Ecoregion Published 4 July 2017 DOI: 10.17895/ices.pub.3116 9.2 Greater North Sea Ecoregion – Fisheries overview Executive summary Around 6600 fishing vessels are active in the Greater North Sea. Total landings peaked in the 1970s at 4 million tonnes and have since declined to about 2 million tonnes. Total fishing effort has declined substantially since 2003. Pelagic fish landings are greater than demersal fish landings. Herring and mackerel, caught using pelagic trawls and seines, account for the largest portion of the pelagic landings, while sandeel and haddock, caught using otter trawls/seines, account for the largest fraction of the demersal landings. Catches are taken from more than 100 stocks. Discards are highest in the demersal and benthic fisheries. The spatial distribution of fishing gear varies across the Greater North Sea. Static gear is used most frequently in the English Channel, the eastern part of the Southern Bight, the Danish banks, and in the waters east of Shetland. Bottom trawls are used throughout the North Sea, with lower use in the shallower southern North Sea where beam trawls are most commonly used. Pelagic gears are used throughout the North Sea. In terms of tonnage of catch, most of the fish stocks harvested from the North Sea are being fished at levels consistent with achieving good environmental status (GES) under the EU’s Marine Strategy Framework Directive; however, the reproductive capacity of the stocks has not generally reached this level. Almost all the fisheries in the North Sea catch more than one species; controlling fishing on one species therefore affects other species as well.
    [Show full text]
  • 6 North Sea 6.1 Ecosystem Overview 6.1.1 Ecosystem Components
    6 North Sea 6.1 Ecosystem overview 6.1.1 Ecosystem components Seabed topography and substrates The topography of the North Sea can be broadly described as having a shallow (<50 m) southeastern part, which is sharply separated by the Dogger Bank from a much deeper (50–100 m) central part that runs north along the British coast. The central northern part of the shelf gradually slopes down to 200 m before reaching the shelf edge. Another main feature is the Norwegian Trench running east along the Norwegian coast into the Skagerrak with depths up to 500 m. Further to the east, the Norwegian Trench ends abruptly, and the Kattegat is of depths similar to the main part of the North Sea (Figure 6.1.1). The substrates are dominated by sands in the southern and coastal regions and fine muds in deeper and more central parts (Figure 6.1.2). Sands become generally coarser to the east and west, with patches of gravel and stones existing as well. In the shallow southern part, concentrations of boulders may be found locally, originating from transport by glaciers during the ice ages. This specific hard-bottom habitat has become scarcer, because boulders caught in beam trawls are often brought ashore. The area around, and to the west of the Orkney/Shetland archipelago is dominated by coarse sand and gravel. The deep areas of the Norwegian Trench are covered with extensive layers of fine muds, while some of the slopes have rocky bottoms. Several underwater canyons extend further towards the coasts of Norway and Sweden.
    [Show full text]