Recommendations on size and position of surgically and gastrically implanted electronic tags in European silver eel

Økland, Finn; Thorstad, Eva B.

doi:10.1186/2050-3385-1-6

Cited by 11 publications

(6 citation statements)

References 25 publications

(37 reference statements)

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“…Only eels that matched silvering stages III, IV or V were tagged. We performed surgical implantation into the abdominal cavity (Baras and Jeandrain, 1998;Winter, et al, 2006;Simon, et al, 2011), a procedure proven to be a suitable tagging method for the European eel (Økland and Thorstad, 2013). During surgery, the heads and gills of the anaesthetized eels were placed in fresh river water.…”

Section: Study Site Eel Capture and Taggingmentioning

confidence: 99%

Downstream Migration of the European Eel (Anguilla Anguilla) in the Elbe River, Germany: Movement Patterns and the Potential Impact of Environmental Factors

et al. 2015

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Recruitment of European eels (Anguilla anguilla) has declined to the extent that they have been added to the IUCN Red List of Threatened Species. Therefore, it is critical to ensure that eels complete their outward river migration in order to contribute to the available spawning stock. We conducted a 4-year (2007)(2008)(2009)(2010)(2011) telemetry study to understand the migratory behaviour and potential impact of environmental factors on the eel during this critical life stage.Out of 399 female eels tagged with acoustic transmitters, only 28% demonstrated clear downstream migratory behaviour. Fifty-five percent were detected exhibiting no downstream migration behaviour and 17% were not detected at any monitoring station. Movement patterns of downstream-migrating (silver) eels were characterized by nocturnal activity and seasonal migration, with distinct peaks in autumn and spring. Migration was often discontinuous and exhibited phases of active locomotion and expanded stopovers. The most important determinants of movement activity were water temperature, cumulative precipitation and moonlight, although the significance varied by season and location in the river basin.Our results evidence a discontinuous, stepwise migration over an extended period. Furthermore, our findings indicate that migration success depends on holding duration prior to tagging and environmental predictors with varying importance depending on the season, as well as the locations of capture, tagging and release.

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Section: Study Site Eel Capture and Taggingmentioning

confidence: 99%

Downstream Migration of the European Eel (Anguilla Anguilla) in the Elbe River, Germany: Movement Patterns and the Potential Impact of Environmental Factors

et al. 2015

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“…Transmitters were surgically implanted into the body cavity as described in Thorstad, Rikardsen, Alp, and Økland (). The fish were placed ventral side up, and a 13‐mm long incision was made on the ventral surface 3.5–4.0 cm in front of the anus, as recommended by Økland and Thorstad (). The Teflon coated antenna was folded together, and the antenna and radio transmitter were inserted into the incision and pushed anteriorly.…”

Section: Methodsmentioning

confidence: 99%

Mortality of downstream migrating European eel at power stations can be low when turbine mortality is eliminated by protection measures and safe bypass routes are available

Økland

Havn

Thorstad

et al. 2019

Internat Rev Hydrobiol

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The abundance of the European eel has seriously declined during recent decades. Hydropower production is one of the main threats, and solutions at power stations are needed to reduce the mortality of the downstream migrating silver eel. We examined the mortality, migration routes, and behavior of silver eel at a power station in Germany, after the power station was rebuilt to reduce the mortality of downstream migrating fish. Of 270 eels implanted with radio transmitters and released upstream of the power station, 222 eels passed the power station, primarily in October and November, although some descended during winter and spring. Most eels followed the main flow and passed over the spillway gate (59% and 49% in the 2 study years) or followed the route toward the bar racks in front of the turbines (24% and 27%), where they were guided to a route outside the turbines via the flushing channel. Some eels used the vertical slot fish passage (12% and 8%), whereas few used a nature‐like fishway, canoe pass, or custom‐made bypasses for eel. The eels showed large individual variation in migration timing, migration speeds, and choice of bypass. No eels were killed in the turbines, as none passed through them, likely due to the narrow bar spacing of the racks (10 mm). The results demonstrated that the mortality of eel passing power stations can be low (0–4% and 0–8% in the 2 study years) when the turbine intake is covered by racks hindering eels from entering turbines and safe bypass routes are available. Mortality estimates are given as ranges because the fate of 4% and 8% of the individuals could not be determined. Potential mortality could have been related to injuries in the bypass routes or increased predation risk, but there were no indications of injuries caused by installations in any of the bypass routes.

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“…minimize air exposure and handling, appropriate collection methods, minimizing captivity durations, ideal anaesthesia dosages [27,[81][82][83]) and that pilot trials be conducted to ensure that tagging conditions are optimized for fish welfare (i.e. selecting appropriate tag size, tag insertion location, and recovery periods [27,[84][85][86]). While there remains uncertainty regarding the physiological drivers surrounding post-tagging mortality, ensuring that stress is minimized should help enhance survival of tagged fish.…”

Section: The Effects Of Tagging In Modulating Mortality Ratesmentioning

confidence: 99%

The fate of intracoelomic acoustic transmitters in Atlantic Salmon (Salmo salar)post-smolts and wider considerations for casual factors driving tag retention and mortality in fishes

Lawrence,

Wilson,

Reid

et al. 2023

Preprint

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Acoustic telemetry is a widely used method in assaying behavioural dynamics in fishes. Telemetry tags are often surgically implanted in the coelom of the animal and are assumed to have minimal rates of post-release mortality and tag shedding. However, fish are capable expelling tags and mortalities do occur following release, with the mechanism(s) underlying these effects not well understood. The purpose of this research was to address causal factors underlying tagging mortality and tag expulsion in fishes. We conducted an empirical assessment of tag retention and post-surgical mortality rates in post-smolt Atlantic salmon (Salmo salar) fitted with a dummy acoustic tag over a 92 day monitoring period. This was complimented with a meta-analysis of factors affecting tag retention and post-surgical mortality rates in the wider literature. Post-smolt salmon exhibited low rates of mortality following tag implantation (≤ 5.1%) but had high rates of tag expulsion (54.8%) and impaired growth and a foreign body response was evident. The meta-analysis showed that mortality was generally low across all studies (12.4%) and was largely unaffected by model cofactors. Tag retention rates were high among the studies investigated here (86.7%) and had a weak negative relationship with tag:body mass ratios. Our results suggest that while mortality is often low among tagging studies, including this one, caution must be exercised in assessing stationary tags as they may represent an expelled tag rather than a mortality event. Our results also indicate that tag dimensions are not nearly important as the tag:body mass ratio.

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Recommendations on size and position of surgically and gastrically implanted electronic tags in European silver eel

Cited by 11 publications

References 25 publications

Downstream Migration of the European Eel (Anguilla Anguilla) in the Elbe River, Germany: Movement Patterns and the Potential Impact of Environmental Factors

Downstream Migration of the European Eel (Anguilla Anguilla) in the Elbe River, Germany: Movement Patterns and the Potential Impact of Environmental Factors

Mortality of downstream migrating European eel at power stations can be low when turbine mortality is eliminated by protection measures and safe bypass routes are available

The fate of intracoelomic acoustic transmitters in Atlantic Salmon (Salmo salar)post-smolts and wider considerations for casual factors driving tag retention and mortality in fishes

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