Remediation measures for the Baltic sturgeon: status review and perspectives

Abstract

More than one century ago, sturgeons were prevalent species in the fish communities of all major German rivers both in the North and the Baltic seas drainages. Since then, the populations declined rapidly due to river damming, overfishing and pollution. The last sturgeon catches in the Baltic drainage system occurred during the late 1960ies. Only a few individual captures have been reported during the last 30 years with the most recent records in the Lake Ladoga (Russia), where the last confirmed catch was recorded in 1984, and a single individual caught off Estonia in 1996. Today, sturgeons are considered missing or extinct in German waters. First attempts for remediation of the species were undertaken in the mid 1990ies. Subsequently, phylogenetic and population genetic analyses of the species were carried out using mtDNA, microsatellites, and nuclear markers (SNPs). These genetic analyses using recent and historic material have proven the existence of two different species in the Baltic Sea in what was previously considered to represent the European Atlantic sturgeon only. In the Baltic Sea, the American Atlantic sturgeon (A. oxyrinchus) succeeded to colonize this brackish water system during the Middle Ages. In the North Sea, the European Atlantic sturgeon (A. sturio) is considered to be the endemic species. These results led to the separation of the remediation activities in the North Sea and the Baltic Sea tributaries. Further studies on the mechanism that lead to the extinction of A. sturio in Germany and the subsequent succession of the A. oxyrinchus mtDNA haplotype are currently been carried out. Broodstock development using the northernmost populations of A. oxyrinchus is currently under way. As a further prerequisite to re-introduce this species into the Baltic, the evaluation of the status of critical habitats for the early life stages of the American Atlantic sturgeon in the River Odra has been performed in collaboration with the Institute for Inland Fisheries of Poland. Alternative fisheries techniques, based on the data of by-catch of exotic sturgeons in the fishery, are presently developed in close cooperation with the fishery to reduce fisheries related mortality in juvenile sturgeons upon release. Monitoring of habitat utilization and migration characteristics of juvenile fish upon experimental release will have to be carried out shortly, using acoustic telemetry, with the aim to follow the fate of the released fish and to determine the best time-sizerelease-window for future release programmes. Historic range, fisheries and stock decline Historic rangeHistorically, the European Atlantic sturgeon -previously referred to as A. sturio -ranged from the Black Sea via the Mediterranean

Retrospective weight-of-evidence analysis identifies substrate change as the apparent cause of recruitment failure in the upper Columbia River white sturgeon (Acipenser transmontanus)

“…The sensitivity of long-lived species to habitat disturbances (Winemiller and Rose 32 1992; Olden et al 2007) and strong recruitment declines for many species (e.g., Minkley 1991;33 Wei et al 2009) also suggests that long-lived fish represent a particularly vulnerable group 34 whose conservation would benefit from improved methods for retrospective evaluations of 35 population declines. 38 Sturgeon population declines are broadly attributed to overfishing and anthropogenic 39 habitat change (Birstein 1993;Pikitch et al 2005) and habitat impacts caused by river 40 channelization, dams and flow regulation (collectively referred to as river regulation) are 41 widely identified (e.g., Williot et al 2002;Gessner et al 2006). 38 Sturgeon population declines are broadly attributed to overfishing and anthropogenic 39 habitat change (Birstein 1993;Pikitch et al 2005) and habitat impacts caused by river 40 channelization, dams and flow regulation (collectively referred to as river regulation) are 41 widely identified (e.g., Williot et al 2002;Gessner et al 2006).…”

Downstream migration patterns of one-year-old hatchery-reared European sturgeon (Acipenser sturio)

“…Studies on juvenile in the field have mainly concerned large juveniles (above 60 cm long or greater than 2 years of age) such as the Gulf sturgeon (Acipenser oxyrinchus desotoi) (Harris et al, 2005;Sulak et al, 2009), the green sturgeon (Acipenser medirostris) (Lindley et al, 2011) or the white sturgeon (Acipenser transmontanus) (Parsley et al, 2008). Knowledge is poorly developed in our understanding of habitat use and migration tactics in juveniles, and telemetry studies on released fish could improve our understanding of sturgeon life histories and stocking program sustainability (Gessner et al, 2006).…”

Research Tools to Investigate Movements, Migrations, and Life History of Sturgeons (Acipenseridae), with an Emphasis on Marine-Oriented Populations

“…Acoustic telemetry has been used to study young European Sturgeon in the Gironde River estuary and the influence of tidal cycles on their movement [52]. [53] used acoustic telemetry to monitor reintroduction trials for American Atlantic Sturgeon ( A. oxyrinchus oxrinchus ) to the Baltic Sea and European Sturgeon to the Elbe River in Germany, providing key information on food selectivity, migration patterns, and potential sources of mortality. This study was important to the success of reintroduction efforts (2,000–5,000 tagged fish released per year) and in guiding planned restoration and habitat protection efforts.…”