Christoffersen, Mads

Online Research Database In Technology

                       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.     Downloaded from orbit.dtu.dk on: Dec 20, 2017Relative abundance of Round Goby in a brackish Danish FjordChristoffersen, MadsPublication date:2015Document VersionPeer reviewed versionLink back to DTU OrbitCitation (APA):Christoffersen, M. (2015). Relative abundance of Round Goby in a brackish Danish Fjord [Sound/Visualproduction (digital)]. Round goby – need for collaborative science and management in Nordic and Balticcountries, Charlottenlund, Denmark, 04/09/2014Relative abundance of Round Goby in a brackish Danish Fjord  Mads Christoffersen DTU Aqua       For the workshop: Round goby – need for collaborative science and management in Nordic and Baltic countries September 4-5, 2014 Charlottenlund Castle  2 DTU Aqua How to monitor the round goby?  From Ubl & Dorow 2014 • New monitoring approach used in Germany to quantify stock size of coastal European eel • This monitoring was used in Denmark for the first time • Consists of two parts – A) External part - boundary net (100x100 m=1ha). Fyke net    chambers in each corner  – B) Inside area - 6 chains of 5 double chamber fykes    3 DTU Aqua Location  • Karrebæk and Dybsø Fjord – South western part of Zealand  • Fishermen observed the round goby in the fjord for the first time in 2009-2010 Photo: Henrik Carl 4 DTU Aqua Location • Observations made in June 2014 • Two enclosures in Karrebæk Fjord • Fishing time was 48 hours   5 DTU Aqua Results – overall  • Ten species with a total catch of 869 fish   (5-81 cm) • No pelagic species • Flounder the most dominant fish species • 185 round goby caught in total  •  21 % of total catch Photo: Henrik Carl 6 DTU Aqua Results - round goby • From 6–18 cm (avg. 10.3 cm) • Most individuals between 7–12 cm    Photo: Henrik Carl 7 DTU Aqua Results - round goby  • Enclosure experiment covered 1 ha each – in total 2 ha   • A total of 185 round gobies found • From length/weight relationship the total weight of the round gobies in the enclosures was 4200 g • The total biomass of round gobies in Karrebæk fjord is estimated to be   8400 kg Photo: Mads Christoffersen 8 DTU Aqua Predators – Great Cormorant • Ormø colony is a large cormorant colony • 1000 nests ~ 4000 birds • 15 km from Karrebæk Fjord    Comorant  colony Photo: Michael I Pedersen 9 DTU Aqua Predators - Great Cormorant • Visited the colony a few times – small island – totally invaded by cormorants Photo: Mads Christoffersen Photo: Michael I. Pedersen 10 DTU Aqua Predators - Great Cormorant • Revealed several half-eaten fish under the nests • PIT tagged smaller eels were released in the fjord in June 2014 to     document if cormorant fourage in Karrebæk Fjord Photo: Michael I. Pedersen 11 DTU Aqua     Photo: Gordon P. Henriksen Predators - fish  • Recreational fishermen soon discovered that predatory fish liked the round goby  Photo: Gordon P. Henriksen Photo: Gordon P. Henriksen Photo: Gordon P. Henriksen 12 DTU Aqua Predators - fish • Small eel stocked in Karrebæk fjord in 2011-12        Photo: Mads Christoffersen 13 DTU Aqua Predators - fish • In 2014 turbot were stocked  • Hopefully some of these fish will use the round goby as their prey Photo: Mads Christoffersen 14 DTU Aqua Perspectives • The impact of the round goby on the trophic dynamics in the system needs to be investigated • More effective field experiments with specific focus on the round goby is needed • Stomach content in predators (eel, turbot etc.) should be investigated • Do mesocosm experiments with/without the round goby to study behaviour and interactions with other fauna  • The potential for round goby as a food source for commercial and recreational important fishes should be explored 15 DTU Aqua Thank you Thanks to  Niels Jepsen Michael I. Pedersen Malthe Dorow Peter Möller Bodo Dolk Jeff Rømer Marie Brousse  Photo: Henrik Carl 16 DTU Aqua  Photo: Michael I. Pedersen 

Relative abundance of Round Goby in a brackish Danish Fjord

http://orbit.dtu.dk/ws/files/105558765/Mads_Christoffersen_Relative_abundance_of_Round_Goby_in_a_brackish_Fjord.pdf

Relative abundance of Round Goby in a brackish Danish Fjord

Abstract

Similar works

Full text

Available Versions

Online Research Database In Technology