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Size selection of fish in the trap fisheries of the Baltic and Bothnian Seas

Lundin, Mikael (2014). Size selection of fish in the trap fisheries of the Baltic and Bothnian Seas. Diss. (sammanfattning/summary) Umeå : Sveriges lantbruksuniv., Acta Universitatis agriculturae Sueciae, 1652-6880 ; 2014:15
ISBN 978-91-576-7978-9
eISBN 978-91-576-7979-6
[Doctoral thesis]

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Abstract

A sustainable fishery in the Baltic Sea requires fishing gear that fishes selectively and at the same time excludes raiding seals. A successful type of trap recently developed in response to the seal problem is the pontoon fish chamber, which significantly decreases damage to gear and catch losses caused by grey seals. However, a common problem with traps is the bycatch of juvenile and non-marketable fish which constitutes a threat to the sustainability of the fishery and a time-consuming problem for the fishers.

This thesis deal with bycatch reduction of young herring, whitefish and perch in pontoon traps. Rigid grids and square mesh panels were installed in traps during commercial fishing operations and continuously monitored with underwater cameras. The selection efficiencies were calculated for different species and selection panel designs. The importance of abiotic and biotic factors for the selection efficiency, the diurnal activity levels of species, and the positions of escape through a selection panel were analysed. This thesis also addresses the survival changes of herring after being released from a trap and the potential size-structuring effects on the herring stock after a size-selective fishery.

The results showed that several tonnes of young fish were able to escape through selection panels from the traps during a season. 70-80% of young herring and whitefish escaped through an encircling selection panel while 90-100% of young perch and roach escaped through a rigid grid. Both biotic and abiotic factors were influencing the selection efficiency of herring. The factors which had most effect were the quantity of fish in the trap, the season of the year, the time of day, and the presence of seals. The diurnal activities were significantly different between species. Herring and roach preferred to escape during night while perch escaped mostly during dusk and dawn. The passing through a rigid grid did not affect the short term mortality of young herring and the risk that extensive use of traps will induce selection for phenotypic changes in mature herring, leading to an evolutionary change on the Bothnian Sea herring population is low.

The overall conclusion of this thesis is that bycatch can be reduced by equipping traps with selection panels. The appropriate design of the selection panel depends mainly on the behaviour and physiology of the fish. The survival changes of released fish seem high and the risk that extensive use of size-selective traps will induce evolutionary changes on the herring stock is low.

Authors/Creators:Lundin, Mikael
Title:Size selection of fish in the trap fisheries of the Baltic and Bothnian Seas
Series/Journal:Acta Universitatis agriculturae Sueciae (1652-6880)
Year of publishing :24 February 2014
Volume:2014:15
Number of Pages:55
Papers/manuscripts:
NumberReferences
I.Lundin, M., Calamnius, L., Hillström, L., Lunneryd, S.G. 2011. Size selection of herring (Clupea harengus membras) in a pontoon trap equipped with a rigid grid. Fisheries Research, 108: 81-87.
II.Lundin, M., Ovegård, M., Calamnius, L., Hillström, L., Lunneryd, S.G. 2011. Selection efficiency of encircling grids in a herring pontoon trap. Fisheries Research, 111: 127-130.
III.Lundin, M., Calamnius, L., Lunneryd, S.G. 2012. Survival of juvenile herring (Clupea harengus membras) after passing through a selection grid in a pontoon trap. Fisheries Research, 127-128: 83-87.
IV.Lundin, M., Calamnius, L., Fjälling, A. Size-selection of whitefish (Coregonus maraena) in a pontoon trap equipped with a square mesh selection panel (manuscript).
V.Lundin, M., Calamnius, L., Lunneryd, S.G., Magnhagen, C. The efficiency of selection grids in perch pontoon traps (manuscript).
VI.Lundin, M., Östman, Ö., Hillström, L., Magnhagen, C., Larson, N. Effects of a size-selective trap fishery on the Bothnian Sea herring stock (manuscript).
Place of Publication:Umeå
Publisher:Dept. of Wildlife, Fish, and Environmental Studies, Swedish University of Agricultural Sciences
ISBN for printed version:978-91-576-7978-9
ISBN for electronic version:978-91-576-7979-6
ISSN:1652-6880
Language:English
Publication Type:Doctoral thesis
Full Text Status:Public
Agris subject categories.:M Aquatic sciences and fisheries > M01 Fisheries and aquaculture - General aspects
M Aquatic sciences and fisheries > M40 Aquatic ecology
Subjects:(A) Swedish standard research categories 2011 > 1 Natural sciences > 106 Biological Sciences (Medical to be 3 and Agricultural to be 4) > Zoology
(A) Swedish standard research categories 2011 > 1 Natural sciences > 106 Biological Sciences (Medical to be 3 and Agricultural to be 4) > Ecology
(A) Swedish standard research categories 2011 > 1 Natural sciences > 106 Biological Sciences (Medical to be 3 and Agricultural to be 4) > Behavioural Sciences Biology
Agrovoc terms:fishes, clupea harengus, coregonus, perca fluviatilis, body size, fishing gear, catch composition, bycatch, survival, baltic sea, gulf of bothnia, sweden, finland, fisheries
Keywords:Baltic Sea, Pontoon trap, Bycatch, Size-selection, Selection panel, Grid
URN:NBN:urn:nbn:se:slu:epsilon-e-1791
Permanent URL:
http://urn.kb.se/resolve?urn=urn:nbn:se:slu:epsilon-e-1791
ID Code:11029
Faculty:S - Faculty of Forest Sciences
Department:(S) > Dept. of Wildlife, Fish and Environmental Studies
External funders:European Fisheries Fund and Fiskeriverket - Swedish Board of Fisheries and Jordbruksverket / Swedish Board of Agriculture and Swedish Environmental Protection Agency
Deposited By: Mikael Lundin
Deposited On:25 Feb 2014 11:12
Metadata Last Modified:14 Dec 2014 00:39

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