Migration and Predation of Atlantic Salmon Smolts from Vosso Final Report FHF Project #900778
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NA Migration and predation of Atlantic salmon smolts from Vosso Final report FHF project #900778 Laboratorium for ferskvannsøkologi og innlandsfiske LFI Uni Miljø Thormøhlensgt. 48B 5006 Bergen Telefon: 55 58 22 28 ISSN nr: Ikke tilgjengelig LFI-rapport nr: Ikke tilgjengelig Tittel: Migration and predation of Atlantic salmon smolts from Vosso / Smoltvandring og predasjon ut av Vosso Dato: 26.02.2014 Forfattere: Knut Wiik Vollset, Bjørn Torgeir Barlaup, Shad Mahlum, Bjørnar Skår, Helge Skoglund, Eirik Straume Normann, Jens Christian Holst, Vidar Wennevik, Georg Skaet, Jan Grimsrud Davidsen Geografisk område: Hordaland, Norge Oppdragsgiver: Fiskeri og Havbruksnæringens Forskningsfond (FHF) Antall sider: 100 Emneord: Laks, smolt, predasjon, Vosso, vandringsatferd, dødelighet Subject items: Salmon, smolt, predation, Vosso, migration, behavior, mortality Migration and predation of Atlantic salmon smolts from Vosso / Smoltvandring og predasjon ut av Vosso Final report FHF project #900778 Project leader Bjørn Torgeir Barlaup Authors Laboratory of freshwaterecology and Inlandfisheries, UNI Research Knut Wiik Vollset, Bjørn Torgeir Barlaup, Shad Mahlum, Bjørnar Skår, Helge Skoglund, Eirik Straume Normann Ecosystembased advisors and developers AS Jens Christian Holst Institute of Marine Research Vidar Wennevik, Georg Skaet FHF coordinator: Kjell Maroni 3 Contents Abstract ..................................................................................................................................................................4 Extended summary ..............................................................................................................................................7 Chapter 1 ............................................................................................................................................................ 18 Composition of piscivorous fish communities in three estuaries in the Osterfjordsystem during the salmon smolt run. .............................................................................................................................................. 18 Chapter 2 ............................................................................................................................................................ 33 Estuarine migration speed and mortality estimates of Atlantic salmon smolt from the Vosso river based on acoustic transmitters and multiple recaptures in large trap nets. ......................................... 33 Chapter 3 ............................................................................................................................................................ 53 Estuarine habitat use of brown trout (Salmo trutta) and its potential overlap with and predation on Atlantic salmon smolt. ...................................................................................................................................... 53 Chapter 4 ............................................................................................................................................................ 66 Acoustic investigations on smolt migration dynamics in the Bolstadfjord ............................................ 66 Chapter 5 ............................................................................................................................................................ 89 Characteristics of the sprat and sea trout stocks in Osterfjorden from 1960 to present .................... 89 4 Abstract In English: The goal of the current project was to examine the migration, survival and predation of wild and cultivated smolt from the Vosso system and to evaluate whether predation from sea trout in the Vosso estuary is a bottleneck that hinders the restoration of the Vosso salmon. Our study suggests that survival of cultivated smolt through the estuary of Vosso is low (< 20 %) and may potentially be dependent on smolt migration speed through the complex fjord system. The current trout population in the Vosso system seems to be at historically low levels and it is most likely the reason for the relatively low catches of trout observed within Bolstadfjorden. The results indicate that trout aggregate in areas where acoustically tagged smolt disappear which suggests that predation from trout can partly explain the mortality of smolt through the estuary. However, tag losses related to these aggregations are not particularly high compared to estimates from other studies. In conclusion, it is not apparent from the results in this study that predation from trout in Bolstadfjorden alone can explain the low recruitment of salmon to the Vosso system. The release of cultivated smolt in the river yields very low returns due to fact that few fish are able to navigate through the estuary. Moreover, we cannot conclusively answer to what degree this applies to the wild smolt, however there are indications that navigation and survival of wild fish are higher than cultivated fish. Our results also suggest that the output of wild salmon smolt from the Vosso river is low compared to the estimated potential for smolt production and is an important subject that requires further evaluation in order to increase our understanding of what is needed to re-establish and sustain a viable salmon stock in the Vosso system. 5 In Norwegian: Hovedmålet med prosjektet var å studere vandringen, overlevelsen og predasjon på vill og kultivert laksesmolt fra Vossovassdraget og evaluere om predasjon fra sjøørret i Bolstadfjorden er en flaskehals som hindrer reetableringen av vill laks til vassdraget. Overlevelsen av kultivert og merket smolt gjennom Bolstadfjorden og forbi Stamnes var lav (< 20 %), og er sannsynligvis koblet til at laksesmolten har en lang oppholdstid i estuariet. Sjøørret bestanden i Vossovassdraget virker til å være i dårlig forfatning sett i forhold til historiske fangster. Dette kan være en av årsakene til at fangstene av sjøørret i Bolstadfjorden var lave. Samtidig viser merkeforsøk på sjøørret og laksesmolt at en del av de merkede laksesmoltene forsvinner i de områdene sjøørreten samler seg i Bolstadfjorden. Det er derimot ikke noen oppsiktsvekkende høy estimert dødelighet knyttet til disse aggregeringene i Bolstadfjorden sammenlignet med dødelighets estimater fra andre estuarier. Vi konkluderer med at det ikke virker til at den nåværende predasjonen fra sjøørret i Bolstadfjorden hindrer en reetablering av vossolaksen. Det er derimot åpenbart en lav overlevelse gjennom estuariet av grupper av kultivert smolt som blir sluppet i vassdraget. Vi har ikke resultater som med sikkerhet kan si hvor overførbart dette er for villfisk. Resultatene våre indikerer derimot at overlevelsen til villfisk gjennom estuariet er høyere enn kultivert fisk. Estimater for hvor mye vill smolt som vandrer ut av vassdraget var betydelig lavere enn det forventede potensiale for smoltproduksjons i Vossovassdraget, og dette misforholdet bør undersøkes nærmere. 6 biological, cultural and economic value Extended summary of the Vosso salmon, the Norwegian Directorate for Nature Management The population collapse of the Vosso initiated an interdisciplinary project in salmon and threats to the stock 2000 called the ‘Vosso project’ to identify threats and implement a long-term plan The Vosso salmon is one of Norway’s for the restoration of a sustainable run of most best-known runs of salmon because Vosso salmon. of the huge size the fish attain. Its lifecycle is distinguished by the long Over the next decade, several man- ocean residence of a high percentage of induced impacts and threats were the run, resulting in the large average identified; water regulation for size of returning spawners (10-11 kg). hydropower purposes (including flow The salmon stock in the Vosso River adjustments and temperature changes), system collapsed at the end of the 1980s. habitat degradation, acidification The cause of the population decline was causing aluminum to accumulate on fish not identified, but all fisheries for Vosso gills both in fresh- and brackish water, salmon were terminated starting in 1992. effects of sea-lice transmitted by salmon In order to secure the stock and to farms on migrating smolts and the reduce the risk of genetic impact from genetic threat posed by escaped farmed escaped farmed salmon, a brood stock salmon entering a decimated spawning population was established in the stock (see Table 1 for details and Figure 1 National Live Gene Bank for wild Atlantic for a map of the region). salmon. Motivated by the large Figure 1 The Vosso river and fjords were known for its large sized salmon. Unknown photographer. 7 Efforts to restore the Vosso salmon accumulated in the ongoing project was used to initiate an up scaling of the In parallel to the work of identifying the already proven successful enhancement man-induced impacts, a work plan was method based on towing cultivated designed to implement the restoration of smolts to the coast before release. This the Vosso salmon. The plan relied on two up scaling was financed by the fish pillars; firstly, all human-induced threats farmers and the Aquaculture and had to be minimized or mitigated by Fisheries research fund (FHF) after long efforts by all stakeholders based on the and heated debates of the effect of fish principle of “best practice”. Secondly a farming on the wild population of Vosso large cultivation effort to reintroduce salmon. The fish farmers formed a salmon from the living gene bank was conglomerate of companies called