Parasitic sea louse infestations on wild sea trout: separating the roles of fish farms and temperature

Overview
TitleParasitic sea louse infestations on wild sea trout: separating the roles of fish farms and temperature
AuthorsVollset KW, Qviller L, Skår B, Barlaup BT, Dohoo I
TypeJournal Article
Journal NameParasites & vectors
Volume11
Issue1
Year2018
Page(s)609
CitationVollset KW, Qviller L, Skår B, Barlaup BT, Dohoo I. Parasitic sea louse infestations on wild sea trout: separating the roles of fish farms and temperature. Parasites & vectors. 2018 Nov 29; 11(1):609.

Abstract

BACKGROUND
The causal relation between parasitic sea lice on fish farms and sea lice on wild fish is a controversial subject. A specific scientific debate has been whether the statistical association between infestation pressure (IP) from fish farms and the number of parasites observed on wild sea trout emerges purely because of a confounding and direct effect of temperature (T).

METHODS
We studied the associations between louse infestation on wild sea trout, fish farm activity and temperature in an area that practices coordinated fallowing in Nordhordland, Norway. The data were sampled between 2009 and 2016. We used negative binomial models and mediation analysis to determine to what degree the effect of T is mediated through the IP from fish farms.

RESULTS
The number of attached lice on sea trout increased with the T when the IP from fish farms was high but not when the IP was low. In addition, nearly all of the effect of rising T was indirect and mediated through the IP. Attached lice remained low when neighbouring farms were in the first year of the production cycle but rose substantially during the second year. In contrast to attached lice, mobile lice were generally seen in higher numbers at lower water temperatures. Temperature had an indirect positive effect on mobile louse counts by increasing the IP which, in turn, raised the sea trout louse counts. Mobile louse counts rose steadily during the year when neighbouring farms were in the first year of the production cycle and stayed high throughout the second year.

CONCLUSIONS
The estimates of the IP effect on louse counts along with the clear biennial pattern emerging due to the production cycle of fish farms clearly indicate that fish farms play an important role in the epidemiology of sea lice on wild sea trout. Furthermore, the mediation analysis demonstrates that a large proportion of the effect of T on louse counts is mediated through IP.

Author Details
Additional information about authors:
Details
1Knut W Vollset
2Lars Qviller
3Bjørnar Skår
4Bjørn T Barlaup
5Ian Dohoo
Properties
Additional details for this publication include:
Property NameValue
Journal CountryEngland
Publication TypeJournal Article
Language Abbreng
LanguageEnglish
ISSN1756-3305
Publication ModelElectronic
Elocation10.1186/s13071-018-3189-6
DOI10.1186/s13071-018-3189-6
Journal AbbreviationParasit Vectors
Publication Date2018 Nov 29
eISSN1756-3305
Cross References
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PMID: PMID:30497499