Estuarine phase during seaward migration for allis shad Alosa alosa and twaite shad Alosa fallax future spawners

Abstract –  The timing and duration of the estuarine phase during seaward migration were addressed for allis shad and twaite shad, closely related sympatric species in the Gironde system. Otolith Sr:Ca and daily growth increments were used to retrospectively estimate the age at entrance in the estuary, the time spent in estuary and the age at seaward exit from returning adults. The two species exhibited different seaward migration strategies: allis shad entered the estuary at an older age than twaite shad (88 days vs. 59 days), stayed shorter in the estuary (11 days vs. 17 days) and exited to the sea at an older age (99 days vs. 77 days). In the Gironde system, the estuarine phase is very short and occurs within a particular time 'window' for the juveniles that will become future spawners. In this context, it might be suggested that the estuarine phase is a bottleneck for these sympatric shad populations.     

Diel and seasonal changes in nutritional condition of the anadromous twaite shad Alosa fallax fallax (Lacépède, 1803) larvae

Abstract –  In this work we aim to study: (i) the diel and seasonal changes in nutritional condition, herein RNA/DNA ratios, of twaite shad ( Alosa fallax fallax ) larvae and (ii) the influence of environmental and biological covariates on those changes. Samples were collected in the River Mira (Portugal) from February 1998 to July 2000. The RNA/DNA ratios were significantly lower than average during dawn and dusk hours. This pattern can be attributed to: the absence of better-fit specimens escaping the net; a nightly increase in the RNA content in response to circadian rhythm; and/or nucleic acids of prey items remaining in the gut of larvae during daylight. Thus, the time of day is important when examining RNA/DNA ratios of twaite shad. Generalised additive model of seasonal data showed that water temperature, freshwater pulses and/or turbidity largely contribute to create adequate environments. These might enhance the nutritional condition of twaite shad larvae during the period that they remain in the upper reaches of River Mira.     

Modeling environmental,temporal and spatial effects on twaite shad (Alosa fallax) by‐catches in the central Mediterranean Sea

Modeling the relationships between environmental factors and the distribution at sea of species of conservation interest can be useful in predicting their occurrence from a local to a regional scale. This information is essential for planning management and conservation initiatives. In this study, generalized additive models (GAMs) were applied to investigate the influence of environmental, temporal and spatial variables on the catch rates of the twaite shad Alosa fallax (Lacepède) by the pelagic trawl fishery in the north‐central Adriatic Sea. Presence/absence and abundance [catch per unit effort (CPUE)] data between 2006 and 2012 were separately modeled, and the two models were then validated using a test data set. The most important factor influencing the presence and abundance of adult twaite shads was the spatial predictor (latitude × longitude). Two areas of major shads aggregations were observed, the most important of which being located near the estuaries of three main river systems of northern Italy. The twaite shad presence was also significantly affected by season, the largest and lowest occurrences being observed in autumn and spring, respectively. Among the environmental variables tested, only sea surface temperature was included in both models. Alosa fallax showed a wide thermal tolerance (6–27°C) with preference for temperature around 23°C. The model developed from the abundance data showed a moderate predictive power, whereas the accuracy of the presence/absence model was rather low. Some conclusions on the ecological requirements of A. fallax at sea arising from this study are useful to orient future monitoring and research programs and to develop effective conservation actions.     

Atlantic salmon living on the edge: Smolt behaviour and survival during seaward migration in River Minho

The Atlantic salmon (Salmo salar) population of the River Minho represents the southern natural distribution edge of the species. In line with the general trend for Atlantic salmon, this population has been declining over the years and is now at a critically low level. With river connectivity compromised by a large dam just 80 km upstream the River Minho's outlet, and an expected deterioration of climatic conditions, it is urgent to increase our knowledge of this population and identify survival bottlenecks that can be addressed. In this study, we used radio and acoustic telemetry to track Atlantic salmon smolts during their migration towards the sea and record both survival rates and possible causes of mortality. The recorded survival for the tagged migrating Atlantic salmon remained below 55% in the three studied years, indicating that the in‐river loss of smolts is likely a strong constraint to this population. From the smolts to which a likely cause of mortality could be attributed (34%), most appear to have been removed from the river (25%), with two confirmed events of bird predation and one of mammal predation. Interestingly, eight tags were recorded moving back upstream, likely indicating predation by larger fish. Increasing predator populations (e.g. cormorants, Phalacrocorax carbo) and invasive predators (e.g. American mink, Neovison vison) lead to elevated predation pressure on this already strained Atlantic salmon population, and further studies quantifying their impact in more detail could prove crucial for future management considerations.     

The effect of migration distance and timing on metabolic enzyme activity in an anadromous clupeid, the American shad (Alosa sapidissima)

The American shad (Alosa sapidissima) is a common anadromous fish species with ecological and economic importance on the east coast of North America. This iteroparous species undergoes an energetically costly upriver spawning migration in spring. To evaluate metabolic changes associated with this migration, we assessed the maximum activity of five metabolic enzymes (citrate synthase (CS), phosphofructokinase (PFK), lactate dehydrogenase (LDH), -hydroxyacyl coenzyme A dehydrogenase (HOAD), alanine aminotransferase (GPT)) in liver, red muscle and white muscle during upstream migration in two successive years in the Connecticut River. For aerobic capacity (CS), glycolytic capacity (LDH) and utilization of stored lipid and protein energy (HOAD and GPT), there is a general pattern of increasing activity with a subsequent decline at the most upriver sites. Red muscle CS activity increased by as much as 40% during the migration while white muscle CS activity was 120% higher in the river than in the ocean. In contrast, muscle anaerobic capacity, indicated by PFK, was low as fish entered the river and then increased 5-fold at the most upriver sites. White muscle HOAD increased 30% while red muscle HOAD and muscle GPT increased as much as 60%. There were interannual and sex-associated differences in enzyme activity during upstream migration and through time at a single location. In some cases interannual differences can be larger than those seen during upriver migration as in the case of red muscle CS where sampling years differed by 125%. These interannual differences may be a result of differing river conditions that affect migratory effort. We have demonstrated that American shad use tissue and sex-specific regulation of enzyme activity during migration and we suggest that American shad metabolically acclimate to upstream migration.     

Environmental DNA reveals the temporal and spatial extent of spawning migrations of European shad in a highly fragmented river basin

1. Artificial barriers on lowland rivers impede the spawning migrations of anadromous fishes, preventing access to historical spawning areas. In the cryptic European shads Alosa alosa and Alosa fallax (‘shad’ hereafter), this has resulted in population declines across their range. Conservation programmes aim to facilitate the passage of migrators over these barriers and so require baseline information on the spatial and temporal extent of current migrations.
2. Here, a shad-specific environmental DNA (eDNA) assay was used to quantify the spatial extent of shad spawning migrations in the River Severn basin, western England. This basin is characterized by the presence of multiple barriers in the lower catchment. In 2017, the eDNA assay was piloted in the River Teme, an important shad spawning tributary, and then applied in 2018 and 2019 across the lower Severn basin.
3. In all years, shad DNA was detected between mid-May and mid-June, with the maximum spatial extent of shad distribution being in early June when shad eDNA was detected upstream of weirs that were generally considered as impassable. In 2018, this included the detection of shad above the most upstream weir on the main River Severn that required individual fish to have passed six weirs.
4. Although barriers inhibit the spawning migrations of shad, this eDNA assay showed that some highly vagile individuals might be able to ascend these barriers and migrate considerable distances upstream. This suggests that efforts to increase the permeability of these barriers could result in relatively high numbers of migrating shad reaching upstream spawning areas. These results demonstrate that this eDNA assay could also be used across their range, to further quantify the spatial extent of their spawning, including in highly fragmented rivers and those where shad are believed to spawn only occasionally and are rarely observed.

     

Review of climate change impacts on marine fisheries in the UK and Ireland

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Behaviour,escapement and mortality of female European silver eels within a regulated lowland river draining into the Baltic Sea

Migration patterns of 146 female silver eels on their way through fresh and brackish water stretches of the Warnow River into the Baltic Sea were studied using acoustic telemetry. The majority of eels (77%) regained their expected downstream migration behaviour after a median rehabilitation time of 2 days. Positive rheotactic behaviour was observed for 23% of tagged eels after release, probably influenced by experimental procedures. The observed silver eel escapement rate was 63%. Two migratory groups were classified by significantly different migratory speed, time of residence in brackish waters and biometric silvering characteristics. Although the classification of silvering stages is based on these measures, the proportions of these stages did not reflect the observed differences in migratory behaviour. In the context of a permanent silver eel descent in the freshwater part of the Warnow River, a permanent escapement was likewise occurring into the Baltic Sea.     

Review of climate change impacts on marine aquaculture in the UK and Ireland

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Review of climate change impacts on marine fish and shellfish around the UK and Ireland

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Evaluation of the removal of impassable barriers on anadromous salmon and steelhead in the Columbia River Basin

Despite the popularity of barrier removal as a habitat restoration technique, there are few studies that evaluate the biological effects of restored stream crossings. An extensive post‐treatment study design was used to quantify fish populations (e.g. species, life stage, abundance) and habitat attributes (e.g. gradient, geomorphic channel units) at 32 culvert removal or replacement projects to determine their effectiveness in restoring habitat access for juvenile salmon, Oncorhynchus spp., and steelhead, O. mykiss (Walbaum), in the Columbia River Basin, USA. Anadromous fish (steelhead, Chinook salmon O. tshawytscha [Walbaum]) abundance, juvenile steelhead abundance and habitat conditions were not significantly different between paired reaches (i.e. upstream and downstream of former barrier sites), suggesting these sites are no longer full barriers to movement. This suggests that barrier removal projects on small Columbia Basin streams provide adequate fish passage, increased habitat availability and increased juvenile anadromous fish abundance immediately upstream of former barriers.     

Upstream migration of the anadromous sea lamprey (Petromyzon marinus Linnaeus, 1758) in a highly impounded river: Impact of low‐head obstacles and fisheries

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How pathogens affect the marine habitat use and migration of sea trout (Salmo trutta) in two Norwegian fjord systems

Wild fish are confronting changing pathogen dynamics arising from anthropogenic disturbance and climate change. Pathogens can influence animal behaviour and life histories, yet there are little such data from fish in the high north where pathogen dynamics may differ from comparatively southern regions. We aimed to compare the pathogen communities of 160 wild anadromous brown trout in two fjords in northern Norway and to determine whether pathogens influenced area use or return to spawn. Application of high-throughput qPCR detected 11 of the 46 pathogens screened for; most frequently encountered were Ichthyobodo spp., Flavobacterium psychrophilum and Candidatus Branchiomonas cysticola. The rate of returning to freshwater during the spawning season was significantly lower for the Skjerstadfjord fish. Piscichlamydia salmonis and F. psychrophilum were indicator species for the Skjerstadfjord and pathogen communities in the two fjords differed according to perMANOVA. Individual length, Fulton's condition factor and the time between first and last detection of the fish were not related to the presence of pathogens ordinated using non-metric multidimensional scaling (NMDS). However, there was evidence that pathogen load was correlated with the expression of smoltification genes, which are upregulated by salmonids in freshwater. Correspondingly, percentage of time in freshwater after release was longer for fish with greater pathogen burdens.     

Migration and movement profiles of a potadromous fish (Brachymystax lenok Pallas 1773) in a highly connected river system (Mongolia)

Understanding a species’ spatial and temporal movements along with the way these shift under extreme environmental conditions is vital for developing scientifically sound conservation and management strategies. The aim of this research was to describe and quantify the seasonal migration patterns and fine‐scale movement profiles of Brachymystax lenok, a threatened, potadromous salmonid that inhabits the highly connected, boreal river basins of Siberia and northern Asia. During this study 21 mature individuals were monitored over a 15 month period in the upper Eroo River basin, Mongolia, using passive acoustic telemetry. Mean (±SD) B. lenok home ranges were 19.1 ± 15.1 km (median = 11.5 km), with maximum longitudinal movements detected > 45.3 km. Two periods of increased movements were identified; the first in late summer/early autumn when 10 B. lenok moved into deeper, overwintering pools, with the second period occurring in late spring and early summer when nine B. lenok were detected entering the surrounding tributaries. Diel activity and depth typically increased during daylight hours followed by decreased activity or resting periods in shallower river sections at night. These results highlight the need to maintain a high level of river connectivity and adequate fishing season closures by implementing and enforcing an expansive spatiotemporal management plan that can better protect and recover the Mongolian B. lenok populations. Such measures should be transferable to other threatened, potadromous fish species residing throughout the world's boreal river basins.     

Migration pathways,speed and mortality of Atlantic salmon (Salmo salar) smolts in a Scottish river and the near‐shore coastal marine environment

Long‐distance migration of Atlantic salmon (Salmo salar) is known to result in high levels of mortality. For a species experiencing global population decline, it is thus vital to better understand migration behaviour, both in the river and marine stages. Atlantic salmon smolts (n = 50) were tracked using acoustic telemetry in the River Deveron, Scotland, and adjacent coastal area. Higher rates of mortality were observed in the river (0.77% per km) than the early marine stage of migration (0.0% per km). Mortality likely resulted from predation. Higher swim speeds were recorded in the early marine stage compared with the river (marine = 7.37 ± 28.20 km/day; river = 5.03 ± 1.73 km/day [mean ± SD]), a potential predator avoidance behaviour. The majority of smolts leaving the river did so in darkness and on a flooding tide. Overall river and marine migration success were linked to nights of lower lunar brightness. Marine migration speed decreased with increasing environmental noise levels, a finding with implications for fisheries management. The migration pathway in the early marine environment did not follow obvious geographical features, such as the coastline. Thus, we suggest that early marine environment pathways are more influenced by complex water currents. These findings highlight factors that influence smolt migration survival and behaviour, areas on which future research should focus.     

Río de la Plata voyagers: Deciphering the migration ecology of a vulnerable marine catfish (Genidens barbus) in a large subtropical river (lower Uruguay River)

1. Genidens barbus is a vulnerable marine migrant catfish with low fecundity, a complex life cycle (i.e. mouth breeding), and is the target of industrial and artisanal fisheries of several countries. This species regularly migrates from marine to freshwater environments of the south-western Atlantic.
2. The aim of this work was to delve deeper into the migration ecology of G. barbus, characterizing both its timing and potential environmental drivers. Furthermore, aspects of the population structure and reproduction of migrants in the lower Uruguay River were studied and the presence of juveniles in the adjacent estuarine recruitment area was evaluated.
3. Data from 11 years (2008–2018) of records of adult G. barbus captured by artisanal fisheries were used alongside relevant environmental variables that were recorded monthly. Reproductive biology (i.e. sex ratio, gonadosomatic index, fecundity, and oocyte size) was analysed for a period of 3 years (2016–2018). The juvenile abundance in the Río de la Plata estuary was evaluated seasonally.
4. A total of 935 adult individuals of G. barbus were captured, representing a total biomass of 3,123 kg. The migration timing was from early spring to early summer. The abundance of migrants strongly increased with river discharge, suggesting that this variable regulates the upriver migration. Furthermore, pre- and post-spawn females and males displaying mouth breeding were recorded during the study period, confirming G. barbus reproduction in the lower Uruguay River.
5. The results obtained suggest that G. barbus ascend to spawn in the freshwater environments upstream from the mouth of the Uruguay River. Then, adult males incubate and carry the embryos downstream, releasing juveniles in the Río de la Plata estuary.
6. This relevant information will help with the implementation of effective management polices (e.g. fishing restrictions during the reproductive period) for the presently unregulated fishery of this vulnerable species in the lower Uruguay River.

     

Site fidelity,diel and seasonal activities of yellow‐phase Japanese eels (Anguilla japonica) in a freshwater habitat as inferred from acoustic telemetry

Japanese eels (Anguilla japonica) perform large‐scale oceanic migrations between their spawning ground and growth habitats in continental waters during life history. However, between these migrations, they spend most of time in growth habitats such as rivers. To investigate the diel and seasonal activities, homing behaviour and home range of yellow‐phase Japanese eels in the lower reach of the Tone River, we tracked them throughout a year using a fine‐scale positioning system (VPS) based on acoustic telemetry. The tracked eels were generally nocturnal, but not exclusively. They were mainly mobile from spring to autumn, with little or no activity observed during winter. A transport‐release experiment showed that most eels returned to their original capture area within 13 days after release. The eels had very small home ranges (mean ± SD = 0.085 ± 0.068 km²), core areas (0.014 ± 0.014 km²) and linear home ranges (744 ± 268 m). They also tended to be distributed on one particular side of the river (right or left bank) and in one particular shore type (revetment or vegetation), rarely moving from one to the other. This study provides evidence for nocturnal, dormancy, homing behaviours, limited habitat use and small home range size in Japanese eels. The eels clearly showed strong fidelity to a “familiar” site, which contrasts with the long distances travelled during upstream and downstream migration phases in the river, and during spawning migrations in the ocean.     

Size isn't everything: movements,home range,and habitat preferences of eastern blue gropers (Achoerodus viridis) demonstrate the efficacy of a small marine reserve

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Establishing survey and monitoring protocols for the assessment of conservation status of fish populations in river Special Areas of Conservation in the UK

• 1. Under the EC Habitats Directive (92/43/EEC), several rivers in the UK have been designated Special Areas of Conservation (SACs) because they support important populations of fish species. Several factors need to be considered when establishing survey protocols to assess the conservation status of fish species in these rivers.
• 2. It is important to understand the biology and habitat requirements of fish species and to design appropriate monitoring surveys that adequately assess the status of the fish populations. This information can, in turn, provide the basis for establishing sustainable conservation targets for specific stocks, a process known as condition assessment.
• 3. Favourable condition of fish species in SAC rivers is assessed using three criteria. The first relates to density of fish in various life stages against pre‐set targets, assuming that an appropriate number of sites is surveyed to account for natural spatial and temporal variations in fish populations. The second is evaluation of the demographic structure to demonstrate continued recruitment success. Third, by mapping the distribution of the target species in individual rivers and where favourable condition is only achieved where there has been no reduction in the distribution range river between surveys.
• 4. The framework described was developed from limited survey data. As more monitoring and assessment data become available, the threshold criteria for favourable condition for each species should be improved, and uncertainty in the procedures reduced.

Copyright © 2008 John Wiley & Sons, Ltd.