Estimating tailbeat frequency of herring (Clupea harengus) caught by pelagic trawl and purse seine – an assessment of capture induced stress

Atlantic Herring (Clupea harengus) supports large fisheries, it is the top 6 species at world scale (FAO). In Norway, it is the most predominant pelagic species caught with annual catches of about 500 000 tonnes which represented 34 per cent of the total catches of pelagic species in 2018 (Directorate of fisheries “register of landings” https://www.fiskeridir.no/English). The fish are mainly caught by purse seine and trawl, which fishing gear is used depends on the distribution and availability of the fish as well as tradition (Gezelius 2006). Purse seine is mainly used in Norway and requires that fish swim in relatively dense aggregations while trawl can be used on less dense aggregations and on fish distributed deeper down in the water. The fishing method used is likely to have an impact on the welfare of the fish (Huntingford et al. 2006). It is well established that the behaviour of fish, both, individually or in group is an important indicator of their welfare status (Huntingford et al. 2006). It is also known that a fish under stress behave differently than a fish in “normal condition” (Rfc), we can easily deduce that by assessing the stress response of fish during the catch operation we can have an idea of its welfare status. Fish welfare in wild capture fisheries has received relatively little focus but is of ethical interest and may also affect catch quality and survival of released or escaping catches (A. Marçalo et al. 2013). Indeed, it is a topic that is receiving increasing focus mainly because of the importance of the product quality in the market but also because the consumers are becoming more concerned about animal welfare in general and demand that what they eat has been treated in a humane way (reference). Using data collected aboard fishing vessels during different research cruises, the overall objective of this study was to assess capture induced stress suffered by herring (Clupea harengus) during two different capture process: pelagic trawling and purse-seining. In that perspective, two metrics known to be relevant in the stress response of fish were chosen: the tailbeat frequency (TBF) and the scale loss (SL). Unfortunately, the original approach used to analyze scale loss has to be review and the results of the first analysis were judged to weak to appear in this thesis. Most of the work consisted of video and image analysis using the softwares: Avidemux 2.7.1 (http://www.avidemux.org), Adobe Premiere Pro CC version 13.0.3 Build 9 (https://www.adobe.com/fr/products/premiere.html), Corel VideoStudio 22.3.0.439 (http://www.corel.com), Free Video to JPG Converter v. 5.0.101 build 201 () and ImageJ 1.52h (http://imagej.nih.gov/ij). The statistical analysis was realized with the software R version 1.1383© 2009-2017 Rstudio,Inc. The results show that the TBF is in average higher in trawling conditions than in purse-seining ones. A significant decrease was observed in the purse seine case between fishing stage 1 and 3. Concerning the TBF in trawl conditions no significant difference where found between stages. This study could be a starting point for further studies which aim to understand the relation between capture induced stress and fish welfare in pelagic fisheries.