Browsing by Author "Kennedy, Richard"

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Open Access
Assessing the potential of acoustic telemetry to underpin the regional management of basking sharks (Cetorhinus maximus)
(BMC, 2024-07-12) Thorburn, James; Collins, Patrick C.; Garbett, Amy; Vance, Heather; Phillips, Natasha; Drumm, Alan; Cooney, Joseph; Waters, Catherine; Ó’Maoiléidigh, Niall; Johnston, Emmett; Dolton, Haley R.; Berrow, Simon; Hall, Graham; Hall, Jackie; Delvillar, Diego; McGill, Ross; Whoriskey, Fred; Fangue, Nann A.; McInturf, Alexandra G.; Rypel, Andrew L.; Kennedy, Richard; Lilly, Jessie; Rodger, Jessica R.; Adams, Colin E.; van Geel, Nienke C. F.; Risch, Denise; Wilkie, Lorna; Henderson, Suzanne; Mayo, Paul A.; Mensink, Paul J.; Witt, Matthew J.; Hawkes, Lucy A.; Klimley, A. Peter; Houghton, Jonathan D. R.; Fisheries and Aquatic Ecosystems
Abstract Acoustic telemetry can provide valuable space-use data for a range of marine species. Yet the deployment of species-specific arrays over vast areas to gather data on highly migratory vertebrates poses formidable challenges, often rendering it impractical. To address this issue, we pioneered the use of acoustic telemetry on basking sharks (Cetorhinus maximus) to test the feasibility of using broadscale, multi-project acoustic receiver arrays to track the movements of this species of high conservation concern through the coastal waters of Ireland, Northern Ireland, and Scotland. Throughout 2021 and 2022, we tagged 35 basking sharks with acoustic transmitters off the west coast of Ireland; 27 of these were detected by 96 receiver stations throughout the study area (n = 9 arrays) with up to 216 detections of an individual shark (mean = 84, s.d. 65). On average, sharks spent ~ 1 day at each acoustic array, with discrete residency periods of up to nine days. Twenty-one sharks were detected at multiple arrays with evidence of inter-annual site fidelity, with the same individuals returning to the same locations in Ireland and Scotland over 2 years. Eight pairs of sharks were detected within 24 h of each other at consecutive arrays, suggesting some level of social coordination and synchronised movement. These findings demonstrate how multi-project acoustic telemetry can support international, cost-effective monitoring of basking sharks and other highly mobile species. Decision support tools such as these can consolidate cross-border management strategies, but to achieve this goal, collaborative efforts across jurisdictions are necessary to establish the required infrastructure and secure ongoing support.
Open Access
Atlantic salmon smolts in the Irish Sea: First evidence of a northerly migration trajectory
(Wiley, 2020-06-09) Barry, James; Kennedy, Richard; Rosell, Robert S.; Roche, William K.; Fisheries and Aquatic Ecosystems
Results from an acoustic telemetry study revealed for the first time a northerly migration route for Atlantic salmon (Salmo salar L.) smolts leaving the east coast of Ireland. Atlantic salmon smolts were tagged in spring 2019 in the Castletown and Boyne rivers. Three tagged smolts registered on disparate deep‐water offshore marine receivers as they travelled northwards out of the Irish Sea through the North Channel. One fish had migrated an estimated 250 km in a period of 32 days. The remaining two individuals were detected on receivers located off the Northern Ireland coast, further corroborating the northward migration of salmon smolts through the Irish Sea.
Open Access
Behavioural traits of rainbow trout and brown trout may help explain their differing invasion success and impacts
(Nature Research (Springer), 2022-02-02) McGlade, Ciara L. O.; Dickey, James W. E.; Kennedy, Richard; Donnelly, Shannon; Nelson, Clare‑Ann; Dick, Jaimie T. A.; Arnott, Gareth; Fisheries and Aquatic Ecosystems
Animal behaviour is increasingly recognised as critical to the prediction of non-native species success and impacts. Rainbow trout and brown trout have been introduced globally, but there appear to be differences in their patterns of invasiveness and ecological impact. Here, we investigated whether diploid rainbow trout and diploid and triploid brown trout differ among several key behavioural measures linked to invasiveness and impact. We assessed activity, boldness, aggression, and feeding, using open field, novel object, shelter, mirror, feeding, and functional response experiments. We also tested within each fish type for behavioural syndromes comprising correlations among activity, boldness and aggression. Rainbow trout were more active and aggressive but less bold than diploid and triploid brown trout. In small groups, however, rainbow trout were bolder than both types of brown trout. Diploid brown trout were more active and bolder than triploids when tested individually, and had a higher functional response than both rainbow trout and triploid brown trout. In terms of behavioural syndromes, there was no association between activity and boldness in rainbow trout, however, there was in both brown trout types. The increased activity and aggression of rainbow trout may reflect an increased stress response to novel situations, with this response reduced in a group. These results suggest that rainbow trout do not manage their energy budgets effectively, and may explain why they have limited survival as invaders. In addition, the lower functional response of rainbow trout may explain why they are implicated in fewer ecological impacts, and the triploidy treatment also appears to lower the potential impact of brown trout. Comparative analyses of multiple behaviours of invasive species and genetic variants may thus be key to understanding and predicting invader success and ecological impacts.
Open Access
A comparison of the behaviour and survival of angling vs. trap-sampled S. salar smolts.
(Wiley, 2022-06-15) Kennedy, Richard; Rosell, Robert S.; Campbell, Warren; Allen, Michelle M.; Del Villar-Guerra, diego; Fisheries and Aquatic Ecosystems
An experiment was undertaken, using acoustic telemetry, to compare the survival and migratory timing of Salmo salar L. smolts sampled, under optimal conditions, in a traditional fixed Wolf trap against a sample of rod-caught fish captured using a sensitive angling technique. No significant difference was evident in survival with 83% of both samples detected in the river outflow, 67% of the trap and 76% of the rod samples were detected in coastal waters and finally 43% of the trap and 35% of the rod samples were detected on an offshore array c. 50 km from the river outlet. No significant difference was evident in the time taken for trap- and rod-sampled fish to reach either the river outflow, coastal or offshore waters. Angling, if undertaken sensitively, can provide an effective, resource-efficient and ethically justifiable sampling tool for juvenile salmonid age classes.
Open Access
Determinants of riverine migration success by Atlantic salmon (Salmo salar) smolts from rivers across the UK and Ireland
(Wiley, 2024-08-12) Rodger, Jessica R.; Guthrie, Jemma; Honkanen, Hannele M.; Lothian, Angus J.; Lilly, Jessie; Walters, Marcus; Miller, Richie; Hawkins, Lorraine; Reeve, Al; Ribbens, Jamie; Henderson, Jim; Parke, Debbie; Green, Amy; Shields, Brian A.; Ramsden, Philip; Fletcher, Melanie; Kettle-White, Alan; Shaw, Brian; Burns, Stephen; Laughton, Robert; Conroy, Chris; Daphne, Chris; Williams, Keith; Robertson, Sean; Bean, Colin W.; del Villar, Diego; Waters, Catherine; Rosell, Robert; Cotter, Deirdre; Smith, Melanie; Ó. Maoiléidigh, Niall; Kennedy, Richard; Adams, Colin E.; Fisheries and Aquatic Ecosystems
There is some evidence that the river migration success of Atlantic salmon smolts, on their first migration to sea, varies both spatially and temporally. However, we have only a poor understanding of what may be driving this variation. In this study, we used acoustic telemetry to quantify the spatial and temporal variations in river migration success in Atlantic salmon smolts on their first migration to sea. In total 4120 Atlantic salmon smolts migrating through 22 rivers in Scotland, England, Ireland, and Northern Ireland over multiple years were included in the study. Individuals were defined as successful migrants if detected leaving the river to enter marine waters. The results show significant temporal (up to 4 years) and spatial (river) variations in migration success, with overall between-river migration success varying from 3.4% to 97.0% and between years from 3.4% and 61.0%. Temporal variation in migration success was river specific, with some rivers being more temporally stable (exhibiting little variation between years) than others. Across all rivers and years, individual migration success was predicted positively by body condition and negatively by tag burden. The rate of migration success for a population (migration success standardized to a common river distance [proportion km−1]) was predicted by a number of environmental factors. The proportion of river catchment that comprised wetland and woodland positively predicted migration success, whereas the proportion of grassland and peatland in a catchment negatively predicted the rate of migration success. Although the mechanisms through which these effects may be operating were not directly examined in this study, we discuss some potential routes through which they may occur.
Embargo
Does phenology influence predation rate on Salmo trutta parr during lake migration?
(Wiley, 2024-03-16) Kennedy, Richard; Barry, James; Boyd, Adele; Allen, Michelle; Fisheries and Aquatic Ecosystems
Acoustic tags fitted with predation sensors, which trigger following ingestion by piscivorous predators, were used to compare direct predation rates during downstream migration (out-migration) of potamodromous (freshwater) brown trout (Salmo trutta L.) parr from their natal river into a large freshwater lake system during spring and autumn. Thirty-eight spring migrants were tagged across two study years (2021 and 2022) of which 13 individuals (34%) were predated. By contrast 40 autumn migrants were tagged (2020 and 2021) of which three individuals (7.5%) experienced predation. The overall predation loss rate for spring migrants was 0.342% day−1 and was 0.075% day−1 for autumn migrants. Most predation events during spring (77%) occurred within the lower river before tagged fish entered the lake, whilst no predation events were recorded within the river in the autumn. Predation events were significantly linked to tagging season (spring or autumn), with the probability of tags remaining untriggered (as a proxy for survival) being higher 93% (95% confidence interval [CI] [87%, 100%]) in autumn than in spring 66% (95% CI [53%, 83%]). The spring migration periods showed significantly lower river discharge (0.321 m3/s mean daily discharge, April 1 to May 31) to those measured during autumn (1.056 m3/s mean daily discharge, October 1 to November 30) (Mann–Whitney U-test, U = 1149, p < 0.001). Lower flows, clearer water, and longer sojourn in the river may have contributed to greater predation losses in the spring relative to the autumn.
Open Access
Does rod catch reflect the background size structure of the sea trout stock in a small coastal river?
(Wiley, 2020-11-21) Kennedy, Richard; Rosell, Robert; Fisheries and Aquatic Ecosystems
Open Access
Evidence of Long-Distance Coastal Sea Migration of Atlantic Salmon, Salmo Salar, Smolts from Northwest England (River Derwent).
(Springer, 2022-01-26) Green, Amy; Honkanen, Hannele M.; Ramsden, Philip; Shields, Brian; Villar-Guerra, Diego del; Fletcher, Melanie; Walton, Silas; Kennedy, Richard; Rosell, Robert S.; O'Maoileidigh, Niall; Barry, James; Roche, William; Whoriskey, Fred; Klimley, Peter; Adams, Colin E.; Fisheries and Aquatic Ecosystems
Background Combining data from multiple acoustic telemetry studies has revealed that west coast England Atlantic salmon (Salmo salar L.) smolts used a northward migration pathway through the Irish Sea to reach their feeding grounds. Hundred Atlantic salmon smolts were captured and tagged in May 2020 in the River Derwent, northwest England as part of an Environment Agency/Natural England funded project. Results Three tagged smolts were detected on marine acoustic receivers distributed across two separate arrays from different projects in the Irish Sea. One fish had migrated approximately 262 km in 10 days from the river mouth at Workington Harbour, Cumbria to the northernmost receiver array operated by the SeaMonitor project; this is the longest tracked marine migration of an Atlantic salmon smolt migrating from the United Kingdom. This migrating fish displayed behaviours which resulted in fast northward migration. The remaining two fish were detected on a receiver array operated by a third project: the Collaborative Oceanography and Monitoring for Protected Areas and Species (COMPASS). Conclusion These detections further provide evidence that migration to reach marine feeding grounds of at least a proportion of salmon smolts from rivers draining into the Irish Sea is northerly, though without a southern marine array it is impossible to conclude that this is the only route. The pattern of these detections would not have been possible without the collaborative efforts of three distinct and separately funded projects to share data. Further work is required to fully understand migration trajectories in this species on the west coast of the British Isles.
Open Access
In-river behaviour and freshwater return rates of sea trout, Salmo trutta L., from two coastal river populations
(Wiley, 2022-07-22) Kennedy, Richard; Barry, James; Roche, William; Rosell, Robert S.; Allen, Michelle M.; Fisheries and Aquatic Ecosystems
The effective management of anadromous Salmo trutta resources is challenging because long-term data on life history, phenology and survival are sparse and most stocks across the range are highly diverse and data-limited. The current study employed acoustic telemetry to tag 448 sea trout across three life stages, to describe the phenology, spawning behaviour and return rates of smolts, finnock (0+ sea age) and adult (≥1+ sea age) sea trout in two Irish river systems during 2018–2021. Tagged smolts (n = 206) exhibited river to sea transition rates of 78%–92% and a number of surviving smolts returned to their natal river as 0+ sea age finnock, exhibiting overall smolt to finnock return rates of between 6% and 17%. Short-term vagrancy occurred among smolts, and 14 individuals were detected in adjacent nonnatal rivers. Finnock tagged during the late summer (n = 205) exhibited a range of behaviours with a minority (<30%) ascending upstream to spawning areas. Tagged adult sea trout (n = 37) ascended upstream to the spawning grounds and between 50% and 80% successfully returned to sea as kelts after spawning. Subsequent return rates of kelts back to the river in the following year ranged from 9% to 40%. The current study indicated that body size was an influential predictor of behaviour and survival across all three life stages. Increased body size was positively associated with marine transition success in smolts, long-term marine survival in kelts and spawning behaviour in finnock. This work further demonstrates the complexity of sea trout life-history dynamics and provides a comparative perspective across different age classes. An understanding of life-history variation, behaviour and survival is f
Open Access
Inshore and offshore marine migration pathways of Atlantic salmon post-smolts from multiple rivers in Scotland, England, Northern Ireland, and Ireland
(Wiley, 2024-04-28) Rodger, Jessica R.; Lilly, Jessie; Honkanen, Hannele M.; del Villar, Diego; Kennedy, Richard; Ó. Maoiléidigh, Niall; Boylan, Patrick; Rosell, Robert; Morris, David J.; O'Neill, Ross; Waters, Catherine; Cotter, Deirdre; Wilkie, Lorna; Barkley, Andrea; Green, Amy; Beck, Samantha V.; Ribbens, Jamie; Henderson, Jim; Parke, Debbie; Kettle-White, Alan; Ballantyne, Lucy; Marshall, Shona; Hopper, Paul; Gauld, Niall; Godfrey, Jason D.; Chapman, Lauren E.; Thorburn, James; Drumm, Alan; Whoriskey, Fred; Shields, Brian; Ramsden, Philip; Barry, James; Millane, Michael; Roche, William; Armstrong, John D.; Wells, Alan; Walton, Silas; Fletcher, Melanie; Bailey, David M.; Whyte, Bill; McGill, Ross; Bilsby, Mark; Whelan, Ken; Bean, Colin W.; Adams, Colin E.; Fisheries and Aquatic Ecosystems
The migratory behavior of Atlantic salmon (Salmo salar) post-smolts in coastal waters is poorly understood. In this collaborative study, 1914 smolts, from 25 rivers, in four countries were tagged with acoustic transmitters during a single seasonal migration. In total, 1105 post-smolts entered the marine study areas and 438 (39.6%) were detected on a network of 414 marine acoustic receivers and an autonomous underwater vehicle. Migration pathways (defined as the shortest distance between two detections) of up to 575 km and over 100 days at sea were described for all 25 populations. Post-smolts from different rivers, as well as individuals from the same river, used different pathways in coastal waters. Although difficult to generalize to all rivers, at least during the year of this study, no tagged post-smolts from rivers draining into the Irish Sea were detected entering the areas of sea between the Hebrides and mainland Scotland, which is associated with a high density of finfish aquaculture. An important outcome of this study is that a high proportion of post-smolts crossed through multiple legislative jurisdictions and boundaries during their migration. This study provides the basis for spatially explicit assessment of the impact risk of coastal pressures on salmon during their first migration to sea.
Open Access
Investigating the phenology of juvenile potamodromous brown trout (Salmo trutta L.) in two large lake catchments
(Wiley, 2022-01-05) Kennedy, Richard; Rosell, Robert; Allen, Michelle; Fisheries and Aquatic Ecosystems
There is growing interest in the phenology of juvenile Salmo trutta and evidence of significant downstream migration during the autumn in some anadromous populations. The present study used acoustic telemetry to examine the phenology of potamodromous trout parr across a region encompassing two large lake catchments. One hundred sixty-seven trout parr were tagged in late summer across four lake tributaries between 2018 and 2020. In total, 75 tagged parr migrated into the lakes with 67 (89%) migrating between September and December and 8 (11%) migrating between March and June. Autumn migration was highly prevalent across all the tributaries, with 16%–66% of each tagged sample exhibiting autumn migration, and 0%–15% of each tagged sample exhibiting spring migration. Autumn migrants were significantly longer and heavier than spring migrants, but condition factor was similar. Autumn migrants were associated with higher river discharge levels and lower water temperatures than spring migrants. The management challenges posed by extensive autumn migration behaviour in migratory trout stocks are examined and discussed.
Open Access
Long term abundance patterns of potamodromous brown trout in a large lacustrine catchment in County Fermanagh
(Royal Irish Academy, 2021-09-29) Kennedy, Richard; Rosell, Robert S.; McElarney, Yvonne; Gallagher, Kevin; Allen, Michelle M.; Fisheries and Aquatic Ecosystems
Long-term survey data detailing brown trout abundance in the Lough Erne catchment in Co. Fermanagh were tabulated from 1968–2016. These data included redd counts and electric fishing surveys across three key spawning tributaries in addition to gill-net surveys of the lake. The abundance of spawning adults fluctuated widely across the time-series and were examined in relation to various pressures, including a major disease epidemic and the invasion of the catchment by zebra mussels. A functional stock-recruitment relationship between adult spawners and young-of-year juveniles in the spawning tributaries was identified and described. Redd counts were significantly lower for the post-zebra mussel time-series (2000–16) than the pre-zebra mussel time-series (1968–99). The post-zebra mussel invasion period was associated with increased water clarity, reduced plankton productivity and changes to the balance of coarse fish species in the lake. The significance of these changes is discussed in relation to the trout stock.
Open Access
Long term retention of dummy acoustic transmitters in adult brown trout
(Wiley, 2020-08-26) Kennedy, Richard; Evans, Derek W.; Allen, Michelle M.; Fisheries and Aquatic Ecosystems
A group of 36 1+ age class Salmo trutta were surgically implanted with dummy acoustic tags and monitored for 370 days. In total 13 tags were expelled through-out the experiment with an overall tag loss rate of c. 0.035 tag/d. Fish length was the only explanatory variable which had a significant association with subsequent tag expulsion. The estimated probability of retaining a tag for a year for a fish of length 32 cm was 0.76, 34 cm was 0.60 and 36 cm was 0.38. The long term tag loss patterns were examined and discussed.
Open Access
Migration patterns and navigation cues of Atlantic salmon post-smolts migrating from 12 rivers through the coastal zones around the Irish Sea
(Wiley, 2023-10-16) Lilly, Jessie; Honkanen, Hannele H.; Rodger, Jessica R.; del Villar, Diego; Boylan, Patrick; Green, Amy; Pereiro, Diego; Wilkie, Lorna; Kennedy, Richard; Barkley, Andrea; Rosell, Robert; Maoiléidigh, Niall Ó.; O'Neill, Ross; Waters, Catherine; Cotter, Deirdre; Bailey, David; Roche, William; McGill, Ross; Barry, James; Beck, Samantha V.; Henderson, Jim; Parke, Debbie; Whoriskey, Frederick G.; Shields, Brian; Ramsden, Philip; Walton, Silas; Fletcher, Melanie; Whelan, Ken; Bean, Colin W.; Elliott, Sophie; Bowman, Adrian; Adams, Colin E.; Fisheries and Aquatic Ecosystems
The freshwater phase of the first seaward migration of juvenile Atlantic salmon (Salmo salar) is relatively well understood when compared with our understanding of the marine phase of their migration. In 2021, 1008 wild and 60 ranched Atlantic salmon smolts were tagged with acoustic transmitters in 12 rivers in England, Scotland, Northern Ireland and Ireland. Large marine receiver arrays were deployed in the Irish Sea at two locations: at the transition of the Irish Sea into the North Atlantic between Ireland and Scotland, and between southern Scotland and Northern Ireland, to examine the early phase of the marine migration of Atlantic salmon smolts. After leaving their natal rivers' post-smolt migration through the Irish Sea was rapid with minimum speeds ranging from 14.03 to 38.56 km.day−1 for Atlantic salmon smolts that entered the Irish Sea directly from their natal river, to 9.69–39.94 km.day−1 for Atlantic salmon smolts that entered the Irish Sea directly from their natal estuary. Population minimum migration success through the study area was strongly correlated with the distance of travel, populations further away from the point of entry to the open North Atlantic exhibited lower migration success. Post-smolts from different populations experienced different water temperatures on entering the North Atlantic. This was largely driven by the timing of their migration and may have significant consequences for feeding and ultimately survivorship. The influence of water currents on post-smolt movement was investigated using data from previously constructed numerical hydrodynamic models. Modeled water current data in the northern Irish Sea showed that post-smolts had a strong preference for migrating when the current direction was at around 283° (west-north-west) but did not migrate when exposed to strong currents in other directions. This is the most favorable direction for onward passage from the Irish Sea to the continental shelf edge current, a known accumulation point for migrating post-smolts. These results strongly indicate that post-smolts migrating through the coastal marine environment are: (1) not simply migrating by current following (2) engage in active directional swimming (3) have an intrinsic sense of their migration direction and (4) can use cues other than water current direction to orientate during this part of their migration.
Open Access
Patterns of declining zooplankton energy in the northeast Atlantic as an indicator for marine survival of Atlantic salmon
(Oxford University Press, 2024-06-22) Tyldesley, Emma; Banas, Neil S; Diack, Graeme; Kennedy, Richard; Gillson, Jonathan; Johns, David G; Bull, Colin; Fisheries and Aquatic Ecosystems
Return rates of Atlantic salmon (Salmo salar) from the sea to European rivers have declined in recent decades. The first months at sea are critical for growth and survival; recent evidence suggests that reduced food availability may be a contributory factor to the observed declines. Here, zooplankton abundance data are used to derive a measure of prey energy available to forage fish prey of salmon during early marine migration. This zooplankton prey energy has significantly and dramatically declined over much of the northeast Atlantic, and specifically within key salmon migration domains, over the past 60 years. Marine return rates from a set of southern European populations are found to exhibit clustering not entirely predictable from geographical proximity. Variability in grouped return rates from these populations is correlated with zooplankton energy on a range of scales, demonstrating the potential use of zooplankton energy as an indicator of salmon marine survival. Comparison with environmental variables derived from ocean model reanalysis data suggests zooplankton energy is regulated by a combination of climate change impacts on ecosystem productivity and multi-decadal variability in water mass influence along the migration routes.
Open Access
Programmed acoustic tags reveal novel information on late-phase marine life in Atlantic salmon, Salmo salar
(Wiley, 2022-12-30) Kennedy, Richard; Rosell, Robert; Hunter, Ewan; del Villar-Guerra, Diego; Fisheries and Aquatic Ecosystems
This pilot study used programmed acoustic tags implanted into Salmo salar smolts, in conjunction with an extensive offshore marine receiver array, to investigate latestage migratory behaviour and survival of returning adult salmon. A total of 100 smolts were tagged in 2020, and a number of individuals were successfully detected as returning adults in 2021. After detection efficiency was accounted for, 5–9 adults were estimated to have returned to the offshore array c. 45 km from the river mouth. A total of three fish were subsequently detected in the river. Losses of between 40% and 66% were evident during the final stages of ocean migration, and one tagged fish provided direct evidence of a predation event.
Open Access
River lamprey present an unusual predation threat to Atlantic salmon smolts in Lough Neagh, Northern Ireland.
(Wiley, 2020-09-18) Kennedy, Richard; Campbell, W.; Gallagher, K.; Evans, Derek W.; Fisheries and Aquatic Ecosystems
A new monitoring programme on the Lough Neagh catchment has documented a high incidence of river lamprey, Lampetra fluviatilis L., predation on Atlantic salmon smolts, Salmo salar L.,. In total 470 smolts were examined during the 2020 emigration period with 168 fish (36%) exhibiting lamprey scars of which 57 were lightly scarred and 111 were classed as heavily scarred. Lamprey predation was not size selective on Lough Neagh S. salar smolts.
Open Access
Some observations on the behaviour of lake-dwelling brown trout in Lower Lough Erne
(Royal Irish Academy, 2021-02-23) Kennedy, Richard; Rosell, Robert S.; Allen, Michelle M.; Fisheries and Aquatic Ecosystems
Acoustic telemetry was utilised to track a sample of 80 adult wild brown trout across an extensive array of 30 receivers in Lower Lough Erne during 2016 and 2017. The mean detection duration across the array was 142 days, and the majority of tagged fish were detected consistently in the northern basin of the lake. One year after tagging, c.40% of larger fish (>45cm LF) were still actively detected, while only 5-10% of smaller fish (<45cm LF) were detected on the array. In total, nine trout were recaptured by anglers between 2 and 1,152 days post-tagging, with a mean liberty time of 152 days, and a minimum angling exploitation rate of 11.25%. A high proportion of surviving tagged trout (>50%) did not undertake spawning migrations into an influent tributary and remained active within the lake during the reproductive period in November. In total, fourteen tagged trout undertook spawning migrations into a range of tributaries; the mean spawning sojourn was 54 days, and five fish (36%) did not return to the lake post spawning.
Open Access
The effect of trapping on the migration and survival of Atlantic salmon smolts
(Wiley, 2024-07-15) Sortland, Lene Klubben ; Jepsen, Niels; Kennedy, Richard; Koed, Anders; del Villar-Guerra, Diego; Lennox, Robert J.; Birnie-Gauvin, Kim; Aarestrup, Kim; Fisheries and Aquatic Ecosystems
Electronic tags are often used to track the freshwater-marine migrations of smolts, where smolts are captured for tagging pre-migration (e.g., via electrofishing) or during-migration (e.g., via traps). Pre-migration capture allows smolts to initiate and complete their downstream migration unhindered, but risks smolt loss before the migration commences. The contrary is the case for during-migration trap-caught smolts, but trapping smolts temporarily halts their seaward journey which may negatively impact their progress. This study investigated the effect of trapping on the behaviour and survival of migrating Atlantic salmon (Salmo Salar) smolts using acoustic telemetry. We compared the movements and survival of smolts tagged before the smolt run captured by electrofishing (“comparator”) with smolts trapped and tagged during the smolt run (“trapped”). A total of 478 smolts were tagged and released in River Skjern (2020 and 2022), Denmark, and 82 smolts in River Ballycastle (2022), Northern Ireland, and their seaward movements were monitored using acoustic receivers deployed in the river, fjord, and coastal area. In River Skjern in 2022, comparator smolts migrated earlier than trapped smolts, likely because these constituted more of the larger-sized, earlier migrating individuals. We found no differences in descent trajectories, diel patterns, progression rates, or survival between trapped smolts and comparator smolts in any of the rivers or study years. Thus, our results support the use of during-migration trapping as a low-impact method to capture smolts for telemetry studies, with trapped samples (if held <24 h) yielding comparable results in terms of behaviour and survival with non-delayed pre-migration tagged fish.