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Effects of the swimbladder parasite Anguillicola crassus on the migration of European silver eels Anguilla anguilla in the Baltic Sea
Stockholm University, Faculty of Science, Department of Systems Ecology. Swedish Board of Fisheries, Institute of Freshwater Research, Sweden.ORCID iD: 0000-0002-9803-7260
Stockholm University, Faculty of Science, Department of Systems Ecology.
2009 (English)In: Journal of Fish Biology, ISSN 0022-1112, E-ISSN 1095-8649, Vol. 74, no 9, 2158-2170 p.Article in journal (Refereed) Published
Abstract [en]

In a mark–recapture study in 2006, migrating European Anguilla anguilla silver eels were caught,tagged and released in the Baltic Sea and recaptures in commercial pound nets examined for possibleeffects on migration of infection with the swimbladder parasite Anguillicola crassus. The overallrecapture rate was 36%. The prevalence of infection was lowest at the northernmost sampling site.There were no significant differences between infected and uninfected A. anguilla in conditionindices, body fat content and estimated migration speeds. Parasite infection intensity levels weresignificantly negatively correlated with times and distances covered between release and recapture,but did not correlate with migration speed. It appears that more heavily infected A. anguilla wererelatively more vulnerable to recapture in pound nets. It is hypothesized that parasite-induced damageto the swimbladder inhibited vertical migrations and infected A. anguilla tended to migrate inshallower coastal waters, relatively close to the shore.

Place, publisher, year, edition, pages
2009. Vol. 74, no 9, 2158-2170 p.
Keyword [en]
parasite incidence, parasite infestation, parasite prevalence, swimming speed, tagging experiment, vertical migration
National Category
Ecology
Research subject
Marine Ecology
Identifiers
URN: urn:nbn:se:su:diva-113826DOI: 10.1111/j.1095-8649.2009.02296.xISI: 000268271100021OAI: oai:DiVA.org:su-113826DiVA: diva2:787847
Available from: 2015-02-11 Created: 2015-02-11 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Eel migration - results from tagging studies with relevance to management
Open this publication in new window or tab >>Eel migration - results from tagging studies with relevance to management
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In response to the drastic decline of the European eel (Anguilla anguilla (L.)) fisheries have been reduced and elvers are stocked in areas where natural abundances are low. Are these measures adequate? To answer different aspects of this question, we have analysed more than a century of eel tagging, using both traditional and more novel capture – recapture analyses. Based on these long-term data, we have evaluated the impact of the Swedish eel coastal fisheries using Survival analysis. Our analysis indicates that the fishing mortality just prior the 2009 fishing restrictions were in the order of 10%.

More recent tagging programs have focused on issues related to the fate of stocked fish. If and how they migrate out of the Baltic Sea and further on towards the Atlantic Ocean. Both earlier and our new studies reveal that all eels recaptured on the Swedish East Coast, no matter of their origin, migrate at a reasonable speed and direction towards the outlets of the Baltic Sea. Even though it is sometimes difficult to determine their origin, our analyses indicate that stocked fish were scarce among the recaptures. In an experiment on the Swedish West Coast, we knew the individuals’ origin (stocked or wild) and they had similar migration patterns.

In contrast, silver eel in Lake Mälaren – assumed to have been stocked as elvers or bootlace eels – seemed to have difficulties in finding the outlets. Instead they overwintered and lost weight. However, weight losses are also significant among non-stocked individuals in the Baltic Sea, both if they overwinter and if they appear to be on their way out from the area. It remains an open question whether eels from the Baltic region in general, and whether the overwintered fish in particular, manage to reach the spawning area in the Atlantic Ocean.

Based on current knowledge, I advocate invoking the precautionary approach and to concentrate Swedish eel stockings to the West Coast and allow the young fish to spread out on their own.

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University, 2015
Keyword
Anguilla anguilla, Migration, Stocking, Marking, Anguillicola crassus, Data storage tags, Carlin tagging, Strontium, Survival analysis, Dormancy, Lake Mälaren, Baltic Sea, Atlantic Ocean, Sargasso Sea
National Category
Ecology
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-113829 (URN)978-91-7649-097-6 (ISBN)
Public defence
2015-04-17, the lecture hall, Department of Ecology, Environment and Plant Sciences, Lilla Frescativägen 5, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 2: Manuscript.

 

Available from: 2015-03-26 Created: 2015-02-11 Last updated: 2016-10-18Bibliographically approved

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