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Overwintering dormancy behaviour of the European eel (Anguilla anguilla L.) in a large lake
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Institute of Freshwater Research, Swedish University of Agricultural Sciences, Sweden.ORCID iD: 0000-0002-9803-7260
2015 (English)In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 24, no 4, 532-543 p.Article in journal (Refereed) Published
Abstract [en]

Overwintering dormancy behaviour was studied in female silver eels in Lake Mälaren in Sweden between 2008 and 2010. Depth choices and movements in relation to temperature were analysed from pressure andtemperature records for 13 eels with implanted data storage tags, covering 17 overwintering periods and threeintervening summer periods. Dormancy commenced in October–November as temperatures fell below 4–12 °C.Eels tended to remain motionless throughout the winter, with some short periods of activity signalled by smallchanges in depth distributions. During dormancy, the eel shows a clear avoidance of shallow areas <5 m in favourof the 10–25-m-depth interval. Activity tended to resume 4–6 months later in April–May as temperatures roseabove 3–7 °C and ice cover broke, and eels spent more time at shallower depths of <5–10 m. The majority of theeels were assessed as being in the silver eel stage at the time of tagging. During the autumn months, the divingbehaviour, with frequent and large vertical excursions and periods at the surface, was similar to that seen inmigrating eels in the Baltic and Atlantic Ocean. In spring and summer, the behaviour differed, being dominated bymore gradual depth variations, implying that the eels reverted from silver eel migration behaviour to yellow eelforaging behaviour. Body weight declined during dormancy, but other studies of starvation over comparable timeperiods showed significantly higher average specific weight losses, implying that the Mälaren silver eels must havefed between the end of dormancy and recapture.

Place, publisher, year, edition, pages
2015. Vol. 24, no 4, 532-543 p.
Keyword [en]
Anguilla anguilla, hibernation, dormancy, data storage tag, annual activity cycle, starvation, growth rate
National Category
URN: urn:nbn:se:su:diva-113822DOI: 10.1111/eff.12165ISI: 000361010500004OAI: diva2:787841
Available from: 2015-02-11 Created: 2015-02-11 Last updated: 2015-10-12Bibliographically 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
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
Research subject
Marine Ecology
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)

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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