Assessment of the environmental drivers of European glass eel (Anguilla anguilla) recruitment in transitional waters

O’Leary, Ciara; Healy, Sarah; Cruikshanks, Robert; Kelly, Karen; Gargan, Patrick

doi:10.1007/s10641-022-01340-7

Cited by 5 publications

(1 citation statement)

References 64 publications

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“…To quantify the local abundance of glass eel at the outlet locations, we used one group of tagged glass eel using Lincoln-Peterson with an estimated daily number of tagged glass eel present at the site to calculate the total seasonal abundance corrected for delay. Other studies, however, suggest using multiple groups for abundance estimates [ 62 , 63 ], which is wise to correct for the variability of environmental factors (e.g., turbidity, moon phase, water temperature) related to glass eel recruitment dynamics [ 47 , 64 – 66 ]. Moreover, the position of the barrier (e.g., location C showed more redistribution compared to other locations), the presence or alternative migratory routes (e.g., fish passages or adjacent shiplocks), the water velocity derived from pumping stations and the frequency of pump activity all may vary throughout the season.…”

Section: Discussionmentioning

confidence: 99%

Glass eel migration in an urbanized catchment: an integral bottleneck assessment using mark-recapture

Griffioen,

Wilkes,

van Keeken

et al. 2024

Mov Ecol

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Diadromous fish such as the European eel (Anguilla anguilla L.) are hampered by a high density of barriers in estuaries and freshwater systems. Modified and fragmented waterbodies lack tidal flows, and habitat may be less accessible and underutilized compared to free-flowing rivers and estuaries. With rising sea levels and increased occurrence of droughts, the number of barriers may further increase, implying that the need to study migration in such areas may even become more urgent worldwide. To study glass eel migration and behaviour in such highly modified water systems, a mark-recapture study was carried out in the North Sea Canal (NSC) basin, which drains into the North Sea via a large sluice complex. In total, eight uniquely tagged groups (3,797 glass eels) were released near the sluice complex, and 11 groups (2,663 glass eels) were released at inland barriers upstream over a 28 km long stretch in the NSC in spring 2018. The sluice complex attracted 10.3 million glass eel and did not block or delay their immigration. The large and diurnally intensively used coastal ship locks and allowings some saltwater intrusion, efficiently facilitated glass eel migration. Once in the NSC, water outlets from adjacent polders attracted glass eels relative proportional to the discharge of pumping stations. In the NSC, average migration speeds of 0.7 km/day (max. 1.8 km/day) were measured, and this increased with higher temperatures. Redistribution of glass eel from accumulations at inland barriers to other outlet locations was observed in both upstream and downstream directions in the NSC. Passage success and residence time (‘delays’ of 4.1–13.7 days) varied between the different inland barriers. Most of the glass eel, however, appears to settle in the easily accessible habitats within the brackish NSC catchment. This study combined an integral assessment of successive bottlenecks in a modified inland water system.

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Section: Discussionmentioning

confidence: 99%

Glass eel migration in an urbanized catchment: an integral bottleneck assessment using mark-recapture

Griffioen,

Wilkes,

van Keeken

et al. 2024

Mov Ecol

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Glass eels at the continental edge of Europe: revisiting catchment recruitment at the international River Minho/Miño

Stratoudakis,

Domingos,

Antunes

2024

Hydrobiologia

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The glass eel catch from the international River Minho, western Iberian Peninsula, forms the southernmost Atlantic series in the composite index outside the North Sea assessing European eel recruitment. Here, new experimental yield data from the lower estuary (1981–2022) and fishers´ daily records (1990–2022) were modelled to describe and compare seasonal and interannual trends. Seasonality matched river discharge climatology, possibly a more general feature in the southern range of the species distribution, with the difference between high and low season becoming less marked in recent periods of lower abundance. Glass eel yield showed a sharp decline during the 1980s, in line with the recruitment index outside the North Sea and with total Minho catch, but not with recent local estimates of catch per unit effort. This decline is corroborated by trends in fishers´ daily records, suggesting that the reduction in effort in the Minho was the consequence of a gradual adjustment to recruitment in the catchment mediated by progressively tighter local management measures. The inefficiency of fisheries regulatory measures to guarantee stock recovery alone calls for more comprehensive measures to reverse anthropogenic impacts on continental eel populations, but the task seems Herculean.

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Environmental influences on the phenology of immigrating juvenile eels over weirs at the tidal limit of regulated rivers

Boardman,

Pinder,

Piper

et al. 2024

Hydrobiologia

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Recruitment of the catadromous and critically endangered European eel Anguilla anguilla in Europe has declined substantially since the 1980s, with considerable knowledge gaps remaining in many aspects of their life cycle. The aim was to assess eel migration phenology in three regulated rivers in England between 2009 and 2019 through analyses of eel numbers using passes at their tidal limits, with calculation of the annual timings of migration initiation (10% of all eels passed, T10), peak (50%, T50) and conclusion (90%, T90). Across the three rivers, T10 varied between Julian Day (‘Day’) 94 and 173. Years of earlier T10 had significantly earlier T50, where T50 varied between Day 105 and 200. The considerable inter-annual variability in migration timings was associated with environmental variables; earlier T10 and T50 occurred in years of warmer river temperatures (RTs) and cooler sea surface temperatures (SST), and in years where RTs were higher than SSTs. No environmental variables were significant predictors of T90. These results indicate that whilst there is annual variability in the timing of eel migration initiation and peak into freshwaters, this variability is predictable according to differences in environmental conditions. As many of these conditions associated with annual variability in temperature and precipitation then climate change has the potential to shift these migration timings.

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Assessment of the environmental drivers of European glass eel (Anguilla anguilla) recruitment in transitional waters

Cited by 5 publications

References 64 publications

Glass eel migration in an urbanized catchment: an integral bottleneck assessment using mark-recapture

Glass eel migration in an urbanized catchment: an integral bottleneck assessment using mark-recapture

Glass eels at the continental edge of Europe: revisiting catchment recruitment at the international River Minho/Miño

Environmental influences on the phenology of immigrating juvenile eels over weirs at the tidal limit of regulated rivers

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