Master‘s thesis Expansion of the brown shrimp Crangon crangon L. onto juvenile plaice Pleuronectes platessa L. nursery habitat in the Westfjords of Iceland Marla J. Koberstein Advisor: Jόnas Páll Jόnasson University of Akureyri Faculty of Business and Science University Centre of the Westfjords Master of Resource Management: Coastal and Marine Management Ísafjörður, February 2013 Supervisory Committee Advisor: Name, title Reader: Name, title Program Director: Dagný Arnarsdóttir, MSc. Marla Koberstein Expansion of the brown shrimp Crangon crangon L. onto juvenile plaice Pleuronectes platessa L. nursery habitat in the Westfjords of Iceland 45 ECTS thesis submitted in partial fulfillment of a Master of Resource Management degree in Coastal and Marine Management at the University Centre of the Westfjords, Suðurgata 12, 400 Ísafjörður, Iceland Degree accredited by the University of Akureyri, Faculty of Business and Science, Borgir, 600 Akureyri, Iceland Copyright © 2013 Marla Koberstein All rights reserved Printing: Háskólaprent, Reykjavik, February 2013 Declaration I hereby confirm that I am the sole author of this thesis and it is a product of my own academic research. __________________________________________ Student‘s name Abstract Sandy-bottom coastal ecosystems provide integral nursery habitat for juvenile fishes, and threats to these regions compromise populations at this critical life stage. The threat of aquatic invasive species in particular can be difficult to detect, and climate change may facilitate the spread and establishment of new species. In 2003, the European brown shrimp Crangon crangon L. was discovered off the southwest coast of Iceland. This species is a concern for Iceland due to the combination of its dominance in coastal communities and level of predation on juvenile flatfish, namely plaice Pleuronectes platessa L., observed in its native range. The purpose of this study was to 1) determine the expansion of the brown shrimp in the Westfjords and map its relative density and 2) determine the role the Westfjords plays in providing essential nursery habitat to juvenile Icelandic plaice, a commercial fishery in Iceland that has experienced a decline in landings in recent years. Research goals were achieved by collecting juvenile plaice and brown shrimp using a beam trawl at eleven sampling stations between July 24 and July 31, 2012. Results indicate a northward expansion of the brown shrimp as far as Bolungarvík. The highest density (26.67 ind. per 100m2), was found at Brjánslækur. Multiple generations of the brown shrimp were also observed, indicating reproducing populations. High densities (greater than 200 ind. per 100m2) of 0-group plaice were also found at three sites. These two findings offer a preliminary assessment of the potential risk the brown shrimp may pose to 0-group plaice, and establish the need for continued monitoring of the brown shrimp at these stations. Further, this study has identified essential juvenile plaice habitat in the Westfjords for the success of the Icelandic plaice fishery. Útdráttur Sandfjörur gegna mikilvægu hlutverki sem uppeldisslóðir fyrir ungviði fiska. Öll röskun á slíkum svæðum er líkleg til að skaða stofnana á viðkvæmum lífsstigum. Erfitt er að greina áhrif af ágengum tegundum í sjó en hlýnandi loftslag getur auðveldað flutning og viðgang nýrra tegunda. Árið 2003 varð fyrst vart við sandrækju Crangon crangon L.við Íslandsstrendur. Rétt er að gefa henni gaum því í upprunalegum heimkynnum er sandrækjan einkennistegund sandfjara og mikilvægur afræningi á ungviði flatfiska, sér í lagi skarkola Pleuronectes platessa L. Markmið þessarar ritgerðar er að 1) kanna útbreiðslu og hugsanlega stækkun á útbreiðslu svæði sandrækju á Vestfjörðum. 2 ) skoða og meta hlutverk sandstranda á Vestfjörðum sem kjöruppeldisstöðvar fyrir skarkolann sem er mikilvæg nytjategund, en aflinn hefur dregist nokkuð saman undanfarin ár. Til að svara settum markmiðum var sýnum safnað dagana 24 – 31 júlí með bjálkatrolli á 11 sandströndum. Niðurstöðurnar benda til að útbreiðsla sandrækju nái nú að minnsta kosti norður í Bolungarvík. Hæsti þéttleiki sandrækju var á Brjánslæk (26.67 einstaklingar á 100m2), en nokkrar kynslóðir voru greinanlegar sem bendir til þess að stofninn er að fjölga sér. Hár þéttleiki af skarkola (hærri en 200 einstaklingar á 100m2) var ennfremur á þremur stöðvum. Niðurstöðurnar veita grunnupplýsingar um mögulega hættu sem skarkolaseiðum gætu stafað af sandrækju á þessum slóðum. Rannsóknin skilgreindi ennfremur áður óþekkt mikilvæg uppeldissvæði fyrir skarkola á Vestfjörðum sem hjálpar til við að vernda og nýta þennan mikilvæga nytjafisk. Table of Contents List of Figures ..................................................................................................................... viii List of Tables ........................................................................................................................ ix Acknowledgements .............................................................................................................. xi 1. Introduction ................................................................................................................... 1 1.1 Project aims ............................................................................................................. 3 1.2 Materials and Methods ............................................................................................ 4 1.3 Limitations of the study .......................................................................................... 4 1.4 Paper outline ........................................................................................................... 4 2. Theoretical overview ..................................................................................................... 7 2.1 Global invasive species trends ................................................................................ 7 2.2 Invasive species management ................................................................................. 8 2.3 Invasive species management plans ....................................................................... 9 2.4 Introduced species in Iceland ................................................................................ 10 2.5 Brown shrimp ....................................................................................................... 11 2.5.1 Ecogeography ................................................................................................ 11 2.3.1 Reproduction ................................................................................................. 12 2.3.2 Food web interactions .................................................................................... 13 2.3.3 Fisheries significance .................................................................................... 13 2.4 Icelandic Plaice ..................................................................................................... 13 2.4.1 Ecogeography ................................................................................................ 13 3.4.1 Reproduction and spawning .......................................................................... 14 3.5 Influence of brown shrimp predation on flatfish .................................................. 16 4 Research methods ........................................................................................................ 17 3.1 Site description ..................................................................................................... 17 3.2 Oceanographic conditions ..................................................................................... 17 3.3 MRI survey for P. platessa and C. crangon ......................................................... 18 3.4 Sampling stations .................................................................................................. 18 3.5 Sampling Techniques ............................................................................................ 20 3.6 Lab Analysis ......................................................................................................... 20 3.7 Data Analysis ........................................................................................................ 21 4 Results ......................................................................................................................... 23 vi 4.1 Range expansion of brown shrimp ....................................................................... 23 4.2 Shrimp length distribution .................................................................................... 25 4.3 Plaice density and length distribution ................................................................... 27 4.4 Shrimp density as a function of plaice density ..................................................... 32 5 Discussion .................................................................................................................... 33 5.1 Range expansion of the brown shrimp.................................................................. 33 5.2 Plaice densities in the Westfjords ......................................................................... 36 5.3 Potential impacts of the C. crangon expansion in the Westfjords ........................ 41 5.4 Management Recommendations ........................................................................... 42 5.4.1 Essential habitat designation ........................................................................