The use of native piscivorous fishes for the eradication of the invasive Chinese Sleeper, Perccottus glenii

The chief aim of invasive species management is to prevent biological invasions by taking measures for suppressing or eradicating potential invaders. Biological control as a management tool is frequently implemented to reduce the population size, adverse ecological impacts, and dispersal of invasive species. The efficacy of biological control measures in managing the Perccottus glenii population was assessed in four small lakes of Lithuania. The biocontrol was carried out by introducing the native piscivorous fishes Esox lucius and Perca fluviatilis into the invaded water bodies for two successive reproductive seasons. The stocking of these fishes led to an instant reduction in P. glenii abundances, and the outcome of the repeated stocking was complete disappearance of the species from the water bodies investigated. Our study proves that native predator fishes can be successfully used for eradicating well-established P. glenii populations in small eutrophic lakes. We hope the current study results will contribute to developing risk-commensurate methodologies for the control of invasive P. glenii populations in small water bodies

Impact of small hydro-power plants on salmonid fishes spawning migrations

In 2000 and 2005, fish ladders were built in Vilnia and Siesartis rivers providing fish access to another 10 and 25 km of the rivers respectively. The analysis of redd distribution and abundance in both rivers revealed that the construction of fish ladders significantly increased the number and share of redds above dams, however, a significant increase in redds above the dam occurred 2-4 years after fish ladders construction supporting homing behaviour as one of the most important factors for the recolonization of the newly accessible habitats. The tracking of radio tagged salmon and sea trout revealed that statistically, significantly more time, fishes spent in the middle part of fish ladders. Assessed fish ladders efficiency for migrating salmonids made 66%. Minor construction defects and lack of protection were the main factors reducing fishway efficiency. Based on radio tracking data, recommendations are given for minor changes in fish ladders construction and operating schedule to increase the efficiency of fish ladders. Mažųjų hidroelektrinių įtaka lašišinių žuvų neršto migracijai Santrauka. Siekiant sukurti palankias žuvų migracijos sąlygas ir atverti migracijos kelius į upių aukštupius Vilnios ir Siesarties upėse 2000 ir 2005 m. atitinkamai buvo pastatyti kaskadinio tipo žuvitakiai. Abiejose upėse atlikti lašišinių žuvų nerštaviečių tyrimai parodė, kad įrengti žuvitakiai padarė didelę įtaką lizdų sklaidai upėje – jų labai padaugėjo praėjus 2–4 metams po žuvitakių įrengimo aukščiau patvankos. Tai galėtų būti aiškinama „homingo“ ir naujų nerštui tinkamų plotų atradimu. Valtūnų žuvitakio efektyvumo tyrimai, taikant radijo telemetrinius metodus, parodė, kad didžiąją dalį laiko, įveikdamos žuvitakį, žuvys sugaišta vidurinėje jo dalyje. Nustatytas žuvitakio efektyvumas siekė 66 %. Straipsnyje pateikti pagrindiniai nustatyti žuvitakių trūkumai, kurių esmė – nedideli techniniai statinio trūkumai ir menka žuvitakių apsauga žuvų migracijos metu. Pateiktos rekomendacijos žuvitakių efektyvumui pagerinti. Reikšminiai žodžiai: radijo telemetrija, žuvitakiai, Baltic salmon, Sea trout

Migration patterns and survival of stocked Atlantic sturgeon (Acipenser oxyrinchus Mitchill, 1815) in Nemunas Basin, Baltic Sea

The restoration of the Atlantic sturgeon Acipenser oxyrinchus in Lithuania started in 2011. Two rivers (Neris and Šventoji) were chosen for reintroduction in the Nemunas river basin based on historical data and ecological conditions. Since 2011, more than 116 thousand of sturgeon juveniles have been stocked in Lithuania. In order to achieve successful population restoration, it is vital to evaluate the efficiency of performed artificial stocking. Analysis of post-stocking survival, migration patterns, predation pressure, fisheries-related mortality and possible aggregation zones are all important to understand the main threats and prepare possible mitigation measures necessary for population establishment during the initial phase of restoration. Therefore, conventional and radio tagging studies were performed during the initial restoration phase in Lithuania. Atlantic sturgeon downstream migration was divergent in summer and appeared to have no significant associations with fish size, river quality or hydrophysical parameters, but in autumn migration speed and even survival in small rivers seemed to depend on flow velocity and water discharge. The distribution of recaptured tagged juveniles coincided with dominant currents in the Curonian Lagoon and Baltic Sea. Some tagged specimens migrated long distances, with two sturgeons from Lithuania being caught in Estonian and Finnish territorial waters at up to 800 km from their release site. Tag recapture analysis and mortality rate of tagged fish clearly indicate that annual fisheries-related mortality exceeds the required threshold of 5% for population establishment. High survival in rivers indicates that the main threat for a successful sturgeon reintroduction program is commercial fishing in the Curonian Lagoon and Baltic Sea coastal zone

Survey-based assessment of recapture data for Atlantic sturgeon (Acipenser oxyrinchus) in Lithuanian fisheries

Against the background of ongoing European activities since the mid-1990s to restore stocks of the extinct Atlantic sturgeon in the Baltic Sea region, from 2011-2018, a total of 6366 sturgeon have been tagged in Lithuania. Despite an information campaign, there has been a drastic decline of reported recaptures within this national, non-reward tagging study. Similar trends have been observed across the whole Atlantic sturgeon distribution area in the Baltic Sea. As commercial fisheries account for most recaptured tagged sturgeon, a survey of Lithuanian fisheries and analysis of fish landings during the 2014-2018 period was performed to evaluate conventional tagging study results. The survey data revealed that reporting rates of tagged sturgeon in Lithuanian territorial waters were 13.3% of the true numbers recaptured in the Curonian Lagoon and 19.3% in coastal Baltic waters. The results showed a marked difference between fishing gear types as the sturgeon bycatch in gill nets was up to eight times higher than in fyke nets. This study emphasized the vulnerability of stocked sturgeon to commercial fishing. The increasing use of fyke nets in conjunction with its lower bycatch of sturgeons could be a strong argument to limit gill net usage in order to reduce fishery-related mortality of sturgeon to safe limits

The use of native piscivorous fishes for the eradication of the invasive Chinese Sleeper,

The chief aim of invasive species management is to prevent biological invasions by taking measures for suppressing or eradicating potential invaders. Biological control as a management tool is frequently implemented to reduce the population size, adverse ecological impacts, and dispersal of invasive species. The efficacy of biological control measures in managing the Perccottus glenii population was assessed in four small lakes of Lithuania. The biocontrol was carried out by introducing the native piscivorous fishes Esox lucius and Perca fluviatilis into the invaded water bodies for two successive reproductive seasons. The stocking of these fishes led to an instant reduction in P. glenii abundances, and the outcome of the repeated stocking was complete disappearance of the species from the water bodies investigated. Our study proves that native predator fishes can be successfully used for eradicating well-established P. glenii populations in small eutrophic lakes. We hope the current study results will contribute to developing risk-commensurate methodologies for the control of invasive P. glenii populations in small water bodies

Study area illustrating locations of beaver dams in the streams Šašuola and Plaštaka.

<p>Beaver dams, constructed in 2012 are indicated by an asterisk.</p

Fish metrics, significantly differing in downstream (D), middle stream (M) and upstream (U) sections (Kruskal-Wallis ANOVA and Mann-Whitney U-test for pair-wise comparisons; significantly differing sections are indicated in superscript).

<p>Fish metrics, significantly differing in downstream (D), middle stream (M) and upstream (U) sections (Kruskal-Wallis ANOVA and Mann-Whitney U-test for pair-wise comparisons; significantly differing sections are indicated in superscript).</p

Number of tagged sea trout individuals (ind. 100 m-1) in the Šašuola Stream at the sites of capture and release on August-September (A), sites of recapture on October (B), and sites of recapture on November (C).

<p>Dotted lines denote position of beaver dams. X axis represents distance from river confluence divided in to 100 meter sections.</p

Density of individuals (per 100 m² area), number of species, Shannon diversity (<i>H</i>’) and evennes (<i>J</i>’) in the Šašuola and Plaštaka downstream (D), middle stream (M) and upstream (U) sections.

<p>Data is presented as mean ± SD of all electrofishing surveys.</p><p>Density of individuals (per 100 m² area), number of species, Shannon diversity (<i>H</i>’) and evennes (<i>J</i>’) in the Šašuola and Plaštaka downstream (D), middle stream (M) and upstream (U) sections.</p

Impact of Beaver Dams on Abundance and Distribution of Anadromous Salmonids in Two Lowland Streams in Lithuania

European beaver dams impeded movements of anadromous salmonids as it was established by fishing survey, fish tagging and redd counts in two lowland streams in Lithuania. Significant differences in abundancies of other litophilic fish species and evenness of representation by species in the community were detected upstream and downstream of the beaver dams. Sea trout parr marked with RFID tags passed through several successive beaver dams in upstream direction, but no tagged fish were detected above the uppermost dam. Increase in abundances of salmonid parr in the stream between the beaver dams and decrease below the dams were recorded in November, at the time of spawning of Atlantic salmon and sea trout, but no significant changes were detected in the sections upstream of the dams. After construction of several additional beaver dams in the downstream sections of the studied streams, abundance of Atlantic salmon parr downstream of the dams decreased considerably in comparison with that estimated before construction