Novel insights into the marine phase and river fidelity of anadromous twaite shad Alosa fallax in the UK and Ireland

© 2020 The Authors. Aquatic Conservation: Marine and Freshwater Ecosystems published by John Wiley & Sons Ltd Most research on anadromous fishes has been invested in their freshwater life-phases, resulting in a relatively sparse understanding of their spatial ecology during marine life-phases. However, understanding the marine dispersal of anadromous fishes is essential to identify threats and to implement conservation measures that fully encompass their lifecycle. The twaite shad Alosa fallax is an anadromous fish increasingly imperilled across its range due to pollution, harvesting, and impediments to freshwater migration, but little is known about its distribution and movements during its marine life-phase. Here, the application of acoustic telemetry provided novel insights into the coastal dispersal of twaite shad in the UK and Ireland during 2018–2019, and the freshwater entry of individuals during the 2019 spawning season. Of 73 twaite shad acoustic-tagged during their upstream migration in the River Severn in May 2018, 58 emigrated from the river. Twelve were subsequently detected 200 km to the south-west at the Taw–Torridge Estuary between July 2018 and April 2019, where estuarine movements up to 5.8 km inland occurred in summer, winter, and spring. One was subsequently detected in the Munster Blackwater Estuary (Ireland) and then in the River Severn, indicating a minimum movement distance of 950 km. Thirty-four (59%) of the emigrating individuals from 2018 re-entered fresh water in the rivers Severn (n = 33) and Wye (n = 2) in April and May 2019. These results suggest year-round use of estuarine and nearshore habitats by at least a subset of the twaite shad population during their marine phase, providing evidence of potential range overlap between populations that spawn in different areas in the UK and Ireland, which may be facilitated by substantial dispersal. The results also highlight the potential of telemetry for estimating freshwater and marine mortality, and the benefits of sharing detection data across networks

A protocol for stocking hatchery reared freshwater pearl mussel Margaritifera margaritifera

1.Freshwater pearl mussel (Margaritifera margaritifera L.) populations are under serious threat of extinction throughout their geographical range and only a few remnant populations are recruiting to adulthood. Consequently, M. margaritifera is classified as endangered on the International Union for Conservation of Nature Red List.2.Several institutions across many countries have set up Ark sites at hatcheries to culture and rear young M. margaritifera from population remnants, with the intention of stocking these juveniles into rivers. The release location must fulfill the habitat requirements for the full life-cycle of the species, so they can contribute to the next generation and thus the long-term recovery of the species. However, little research or advice exists about how to decide if river environments are suitable for stocking.3.A protocol is presented for determining whether a M. margaritifera population will benefit from stocking hatchery reared juveniles and how to identify suitable areas. Stocking locations are considered from catchment scale to microscale using water quality (reach), macrohabitat (site) and microhabitat, including physicochemical properties of the substratum (spots).4.A case study of the River Esk in north-east England, is incorporated to exemplify the myriad of considerations surrounding attempts to conserve M. margaritifera, and describes how implementation of the protocol can structure and assist stocking programmes

The habitat use of young-of-the-year fishes during and after floods of varying timing and magnitude in a constrained lowland river

Globally, channelisation and artificial levee construction have reduced rivers to single-thread channels isolated from their floodplains. These modifications may be particularly detrimental to fish during floods, because of increased severity of conditions in the main river channel, prevention of fish finding refuge in floodplain habitats, and stranding of fish when floodwaters recede after artificial levees are ‘over-topped’. Notwithstanding, few studies have examined the habitat use by young-of-the-year (YoY; age 0+ year) fish in constrained lowland rivers during floods in slackwaters (main channel with little or no discernible current) and after floods on floodplains. This study investigated the community structure and density of 0+ fish species before (main river), during and after floods of varying timing and magnitude in the River Yorkshire Ouse, a constrained lowland river in north-east England. Slackwaters provided refuge for high densities of mainly eurytopic 0+ fishes during floods and high densities of 0+ fishes were found stranded on floodplains after floods. Community composition in slackwaters during floods and on floodplains after floods was significantly different to the main river catches during average daily flows, possibly related to species-specific morphology and behavioural responses to elevated flow. Despite there being floods of greater magnitude during the winter, peak densities of 0+ fish stranded on floodplains occurred in the summer, and probably related to habitat use immediately prior to floods. Fish were also found stranded on floodplains actively managed to store floodwater to protect property and are presumed to permit safe egress for fish. The results are discussed in relation to lowland river rehabilitation, which is particularly important because of potential conflicts between obligations under various European directives to improve the status of fish populations in degraded rivers (Water Framework Directive) whilst at the same time minimise flooding of societal assets (Flood Directive)

Cumulative impacts of habitat fragmentation and the environmental factors affecting upstream migration in threatened sea lamprey Petromyzon marinus

1. Riverine ecosystems are often fragmented due to man-made structures, such as weirs. By impeding access to upstream spawning sites, the effects of these structures on anadromous species can be severe, ultimately leading to population declines. 2. This study focused on the freshwater spawning migration of sea lamprey Petromyzon marinus, a species threatened by habitat fragmentation across its native range. To quantify the cumulative impacts of multiple weirs on upstream-migrating adults, and explore the environmental factors affecting migratory movements, passive acoustic telemetry was applied to 56 individuals during their spawning migration in the heavily fragmented River Severn basin, UK. 3. While 89% of tagged sea lamprey passed the first weir upstream of the release site on the main river, only 4% passed the fifth. For 85% of migrants, the upstream extent of migration was immediately downstream of a weir. Individuals that passed weirs upstream of the release site (n = 50) took 21.6 ± 2.8 days to reach their most upstream location, experiencing cumulative passage times at weirs of 15.7 ± 2.8 days; these delays constituted a median of 84% of total upstream movement times. 4. Multistate models revealed that weir passage rates by sea lamprey in tidal and non-tidal areas increased significantly when downstream river level and discharge were elevated. Upstream-to-downstream changes in direction were frequent downstream of weirs, but rare in unobstructed river sections. 5. The results provided evidence for a cumulative effect of multiple weirs on sea lamprey movements, substantially delaying upstream migrants and limiting their spawning to atypical habitat; they also demonstrated the crucial roles of tides and elevated discharge events in enabling weir passage. While the Severn estuary features conservation designations for sea lamprey, this study reveals that barriers are inhibiting upstream migration, an issue which should be addressed to assist their conservation

Acoustic telemetry informs capture susceptibility of an anadromous fish

Information on movement ecology and susceptibility to fishing gears is becoming increasingly employed in the management of commercial fisheries. This study combined acoustic telemetry (n = 51 and 52) and a simple passive integrated transponder (PIT) tag (n = 1499 and 1113) mark-recapture study, across two successive years on a commercial river lamprey (Lampetra fluviatilis) fishery, to inform exploitation rates and the influence of conditional capture probability on expected catch-per-unit-effort (CPUE). The movements of acoustic-tagged lamprey were used to refine estimates of the number of PIT-marked individuals vulnerable to the fishery. In 2018, this increased the recapture rate estimation by 0.99% and reduced the estimated run size by 152,101 (21.6%; 95% CL, 148,683, 155,688) individuals, with corresponding values of 0.12% and 114,639 (25.0%; 95% CL, 112,900, 116,448) in 2019. Lamprey movements were similar between years, with the number of trap line encounters by individuals between trap lifts used to inform expected CPUE for each lift. Conditional capture probability was mainly dependent on environmental conditions (e.g., river flow) with most trap lifts in the expected CPUE range, although the impacts of behaviour on vulnerability to capture were difficult to disentangle. This study highlights how the incorporation of acoustic telemetry increased the accuracy of, validated, and complemented mark-recapture data, without which management decisions (e.g., quota size) would have been based upon over 100,000 more individuals (27.5% higher than the adjusted run size in 2018 and 33.3% higher in 2019), with potentially severe consequences for the population. These findings demonstrate the importance of understanding fish movement to improve and inform fishery management. The study also presents a framework to quantify conditional capture probability and its influence on CPUE; knowledge that is widely applicable across aquatic systems for management and sustainability of fisheries