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A telemetry study for reintroducing wild Atlantic salmon (Salmo salar L.) in the Daugava and Ogre Rivers, Latvia.
Karlstad University, Faculty of Health, Science and Technology (starting 2013).
2015 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesisAlternative title
En telemetristudie för återinförandet av vild Atlantlax (Salmo salar L.) till Daugava och biflödet Ogre i Lettland. (Swedish)
Abstract [en]

Hydropower facilities are obstacles in the rivers, which mostly are impassable for fish. The loss of longitudinally connectivity in many rivers prevents salmon fulfilling their reproductive cycle, leading to worldwide reduction of the Atlantic salmon population. Three hydropower stations today exploit the river Daugava, Latvia. This has resulted in extirpation of the native Atlantic salmon population. To investigate the possibilities of reintroducing salmon, a telemetry study with trap- and transport-approach was carried out. Eighteen Atlantic salmon were caught near the river mouth of River Daugava and tagged. Two groups were transported past the most downstream obstacle in River Ogre to two different release sites, R1 and R2 (n = 8 and 6), and a third group, R3 (n = 4) group and was released in Riga reservoir, above Riga HES, in River Daugava. All salmon released in River Ogre migrated downstream, eventually ending up in River Daugava. In total seven salmon passed downstream through the turbines of Riga HES, whereof the recapture success downstream Riga HES was 71%, and the survival rate of turbine passage was at least 60%. This indicates there is a high fishing pressure on salmon in Daugava. The majority in the first group (R1), passed through the turbines of Riga HES, likely due to the high discharge event. However, none in the second group (R2) did. Half of the fish in the third group (R3) released in River Daugava either went downstream passing the turbines of Riga HES or moved upstream standing below the next hydropower station Kegums HES. Six individuals remain missing, presumably because of poaching and/or lack of feedback reporting. After passing downstream from the River Ogre to the Daugava River, about 13% and 17% of groups R1 and R2, respectively, migrated upstream to reach Kegums HES, the furthest possible migration point in River Daugava. The results from this study give valuable information of the possibilities of reintroducing the wild Atlantic salmon to Daugava. Fishing pressure might be a decisive problem for the reintroduction of Atlantic salmon in the Daugava system. Since all the fish released in Ogre went downstream to Daugava, probable due to flooding, the main objectives of this study were impaired and remain to be investigated to determine if the salmon could find the suitable habitats upstream in River Ogre. 

Abstract [sv]

Vattenkraft utgör vandringshinder för fisk i vattendragen. Förlusten av konnektiviteten i vattnet har lett till minskning bland laxpopulationer. Vattenkraften i floden Daugava, Lettland, hindrar helt vandrande fiskarter från att nå reproduktionsområden, som har resulterat i att den vilda populationen av Atlantlax (Salmo salar L.) försvunnit. I biflödet Ogre finns lekhabitat för lax. I denna telemetristudie undersöks huruvida en fångst- och transport-lösning skulle kunna återetablera en vild laxpopulation i Daugava. Studien utfördes på lax som fångats i Daugavas mynning och därefter transporterats förbi och delvis släppts ut uppströms Riga kraftstation samt delvis uppströms Ogre kraftstation i biflödet Ogre. Totalt fångades 18 laxar av odlat ursprung i Daugavas mynning. Individerna radiomärktes och sattes sedan ut vid Ogre (n = 8 + 6) och i dammen uppströms Riga kraftstation (n = 4) i huvudfåran Daugava. Samtliga fiskar som släpptes ut i Ogre vandrade nedströms till Daugava. Totalt sju laxar passerade turbinerna vid Riga HES. Återfångsten av de fiskar som passerat Riga HES genom turbinerna var 71 % och överlevnaden var 60 %. Den höga återfångsten tyder på ett extremt högt fisketryck på lax i Daugava. Majoriteten av de fiskar som sattes ut vid första tillfället (gruppen R1) i Ogre passerade nedströms genom turbinerna i Riga HES, vilket sammanföll i tiden med att det inträffade ett hundraårsflöde i Ogre. Ingen av individerna från den andra utsättningen (R2) passerade turbinerna i Riga HES. Hälften av kontrollgruppen som sattes ut i Daugava passerade via turbinerna vid Riga HES, medan den andra hälften vandrande uppströms mot nästa kraftverk (Kegums HES). Dessutom försvann sex individer spårlöst, vilket sannolikt beror på tjuvfiske och/eller utebliven återrapportering. Av fiskarna som sattes ut i Ogre vandrade 13 % respektive 17 % av fisken från den första respektive andra utsättningen uppströms i Daugava mot Kegums HES.

Resultaten i denna studie ger viktig information om möjligheterna till att återetablera en vild laxpopulation i Daugava. Det höga fisketrycket är sannolikt ett avgörande problem för en fullskalig återintroduktion av lax i Daugava. Eftersom resultaten troligen var påverkade av översvämningen återstår det undersöka om laxen kan hitta habitaten i biflödet Ogre.

Place, publisher, year, edition, pages
2015. , 19 p.
Keyword [en]
salmon, Atlantic salmon, Daugava, Ogre, telemetry
Keyword [sv]
lax, atlantlax, Daugava, Ogre, telemetri
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:kau:diva-36435OAI: oai:DiVA.org:kau-36435DiVA: diva2:822264
Subject / course
Biology
Educational program
Master Programme in Biology with specialisation in Stream Ecology, 120 hp
Supervisors
Examiners
Available from: 2015-06-22 Created: 2015-06-16 Last updated: 2015-06-22Bibliographically approved

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