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In this study, 34 anadromous brown trout (sea trout) Salmo trutta were equipped with acoustic transmitters in order to examine whether they performed avoidance behaviour in response to a CFT Legumin (rotenone) treatment in the Norwegian River Vefsna. Migratory behaviour of the S. trutta was monitored by use of 15 automatic listening stations and manual tracking in the lower part of the river, in the estuary and in the fjord. None of the studied S. trutta survived the rotenone treatment and no indications of successful avoidance behaviour were observed. [ABSTRACT FROM AUTHOR]

Sharks have been shown to benefit from the protection of marine protected areas (MPAs). There is, however, little information on the degree of protection by MPAs to shark populations. The movements of individual smoothhound sharksMustelus mustelusin, and adjacent to, a small (34 km2) no-take MPA (Langebaan Lagoon Marine Protected Area; LMPA) situated on the west coast of South Africa were investigated over two years using acoustic telemetry. Sharks spent the majority of the time (in hours, average 79%) inside the reserve, and some sharks (n= 2 of 15 recorded during a full year) did not leave the reserve during the study period. Time spent inside the LMPA and the number of crossings of its boundary were strongly influenced by season. Sharks concentrated inside the LMPA during summer, whereas they were widely distributed throughout the study area during winter. Six sharks left the Saldanha Bay embayment during spring and winter for durations ranging from two to 156 days (median = 111 days). All returned to the bay within the study period. Individuals recorded over two years showed consistency in behavioural patterns and protection by the LMPA between years, and spent an average of 74% and 80% of the time inside the LMPA during the two study years respectively. The extended residency of smoothhound sharks within the LMPA suggests that no-take area protection may be a viable management option. [ABSTRACT FROM AUTHOR]

Summary The aim of this study was to assess escapement success of silver eels, Anguilla anguilla (L.), in a lowland river while passing a reservoir and a hydropower station. It was hypothesized that passage success would be lowest at the hydropower station and that survival and migration speed would be highest in the free-flowing river section upstream the reservoir. Forty-five female silver eels 56-86 cm in length were tagged with acoustic transmitters and released in November 2006. Their migration was monitored via automatic listening stations (ALS) in various sections of the river, covering a total migration distance of 64 km. Survival and progression rate of downstream migration was highest in the upstream river section and significantly lower in the reservoir. The eels apparently had trouble finding their way past the turbines and spent between 1.5 and 35 h in the forebay. The results show that within the study period, only 23% of the tagged eels reached the tidal limit, mainly due to difficulties in passing the hydropower dam. With such high loss-rates, the escapement goals set in the management plan cannot be achieved. [ABSTRACT FROM AUTHOR]

The early marine migratory behaviour of two populations of hatchery-reared Atlantic salmon Salmo salar was compared in a common-garden experiment. Post-smolts from a river in a long fjord (Lærdal River, 144 km from the open coastline, n = 79) and a short fjord (Flekke River, 20 km from the open coastline, n = 80) in western Norway were tagged with acoustic transmitters and released during the spring of 2005 and 2006 in the inner part of the Hardangerfjord system (Opo River mouth, 179 km from the open coastline). The migratory behaviour of the tagged fish was monitored by acoustic listening stations in the fjord system up to 167 km from the release site. The Lærdal fish began migrating before the Flekke fish and had higher progression rates in the middle part of the fjord system. A greater number of Lærdal fish was detected along the most direct migratory route and in the outermost part of the Hardangerfjord system, which is indicative of a higher survival. The results from this study demonstrate differences in early marine migratory behaviour between S. salar from two different stocks and suggest that the distance a S. salar population travels to reach the open coastline may influence its early marine migratory behaviour and performance. The selective pressures of marine predation and arrival time at feeding areas in the ocean may be stronger for stocks with a longer inshore migration, creating more efficient migrants over time. [ABSTRACT FROM AUTHOR]

Eight hatchery-reared Atlantic salmon Salmo salar post-smolts, implanted with acoustic depth sensing transmitters and manually tracked for 5–12 h in the Hardangerfjord (Norway), spent most of their time (49–99%) at 1–3 m depth during the day, whereas four of seven fish tracked were found close (<0·5 m) to the surface at night, with a strong negative cross-correlation between general swimming depth and surface light intensity. Hence, the actual swimming depth of post-smolts during their early marine migration may depend on the light conditions, although the individual variation in vertical movement pattern was large. No cross-correlations were found between light intensity and swimming depth during daytime periods with rapid changes in light intensity, indicating that other factors than light intensity were important in initiating the irregular dives that were recorded down to 6·5 m depth. [ABSTRACT FROM AUTHOR]

By combining behavioural observations on adult resident brown trout Salmo trutta in the laboratory with radio telemetry studies in a natural stream, information on movement and space use in relation to social status was obtained. Dominant individuals moved longer distances and also tended to have larger home ranges than subordinates during the summer. In general, home ranges were larger during daytime than at night. Fish were not strictly territorial since the average overlap in interquartile range was 36% during the summer. During the spawning period, the brown trout moved to specific spawning areas resulting in an increased overlap (89%) in space use. Subordinate individuals now tended to increase both home range and interquartile range and were also less frequently observed in spawning areas relative to dominants. [ABSTRACT FROM AUTHOR]

The article features a study on the Atlantic salmon. The development of small-sized acoustic transmitters that could be applied to wild Atlantic salmon smolts makes it possible to access information such as swimming speeds, migration efficiency and orientation that is essential for understanding the factors affecting salmons. The study also focuses in recording the observed and actual swimming speeds and directions of wild Atlantic salmon post-smolts based on simultaneous recordings of fish movements and water current, and to compare these with results from larger hatchery-reared post-smolts.

Radio tagged wild Atlantic salmon Salmo salar( n = 30) and sea trout Salmo trutta( n = 19) were simultaneously released from a sea pen outside the mouth of the River Lærdalselva and their migration to spawning areas was recorded. The distance from the river mouth to a position held at spawning ranged from 2 to 24 km and did not differ between the species (mean ± s. d. 15·9 ± 4·3 and 14·9 ± 5·2 km for Atlantic salmon and sea trout, respectively). The duration of the migration phase, however, was significantly shorter for Atlantic salmon than for sea trout (8–12 days, respectively). All Atlantic salmon migrated straight to an area near the spawning ground, whereas 50% of the sea trout had a stepwise progression with one or more periods with erratic movements before reaching the spawning area. After the migration phase, a distinct search phase with repeated movements up- and downstream at or close to the position held at spawning was identified for the majority of the fishes (75%, both species). This search phase was significantly shorter for Atlantic salmon than for sea trout (mean 13–31 days, respectively). Mean ± s. d. length of the river stretch used during the search phase was larger for sea trout (3·3 ± 2·5 km) than for Atlantic salmon (1·2 ± 0·9 km). A distinct holding phase, with no movements until spawning, was also observed in the majority of the Atlantic salmon (80%, mean duration 22 days) and sea trout (65%, mean duration 12 days). For both species, a weak, non-significant trend was observed in the relationship between time spent on the migration phase, and time spent on the search ( r2 = 0·43) and holding phase ( r2 = 0·24). There was a highly significant decrease, however, in the duration of the holding phase with an increase in the time spent on the search phase ( r2 = 0·67). [ABSTRACT FROM AUTHOR]

Økland F, Thorstad EB, Hay CJ, Næsje TF, Chanda B. Patterns of movement and habitat use by tigerfish (Hydrocynus vittatus) in the Upper Zambezi River (Namibia).Ecology of Freshwater Fish 2005.© Blackwell Munksgaard, 2005During 6 November to 24 December 2000, 23 tigerfish [(Hydrocynus vittatus), 30–54 cm] were tagged with radio transmitters in the Zambezi River (Namibia) to record habitat utilisation during low, rising and high water levels. The fish were tracked, on average, every fourth day during 23 November to 18 May. Two movement patterns were detected. Approximately 50% of the fish moved<1000 m among tracking surveys, staying within‘defined’ home ranges. The remaining fish showed consistent site fidelity for periods, with long distance movements (>1000 m) to new areas among residency periods. Overall, mean distance moved between tracking surveys was 1447 m. Home range size varied among individuals, with a 95% probability of localisation within an average area of 276,978 m2. The fish utilised a mean river stretch of 18,836 m (range = 90–71,840). All the fish were recorded in the main stem, and on average, 95% of the fixes were in the main stem during low water. However, the fish used temporary flooded areas to an increasing extent during the rising and high water period, but did not undertake long-distance migrations into the floodplains. Fish were sometimes near vegetation, but were never recorded into or under vegetation. [ABSTRACT FROM AUTHOR]

Thirty Atlantic salmonSalmo salarparr(mean 135 mm total length,LT) in the River Alta, Norway, were radio-tagged and tracked during a 11–13 day period. The parr stayed within defined home ranges with a 95% probability of localization within an average area of 1286 m2(241–3484 m2). On average, each parr had overlapping home ranges with 7·7 other parr, and the overlap between pairs of fish covered on average 24% of their home range areas. Mean length of the river stretch used was 90 m(22–383 m). On average, during 38%(16–77%) of the tracking surveys, the fish had moved>10 m since the previous survey. Mean total distance moved during the whole study was 402 m(208–862 m). The Atlantic salmon were most often recorded in riffles, but 27% of the parr alternated between riffles and pools. The extensive movements, flexible habitat utilization and relatively large home ranges, together with the fact that all the parr had home ranges partly overlapping with other radio-tagged parr, indicate a flexible and variable behaviour and, thereby, a more complex social structure than a rigid defence of a fixed territory. Thus, Atlantic salmon production seems not to be limited by the highest potential number of territories for large parr in a given area. [ABSTRACT FROM AUTHOR]

Fifty-three one-sea-winter Atlantic salmon Salmo salar (45–63 cm LT) were radio-tagged in the Tana fjord, Barents Sea, in 1995. Thirty-seven fish (70%) entered the freshwater zone of the River Tana in an average of 3 days after release in the fjord. The migration speeds in the lowest river section below the first riffle area were significantly higher than in the subsequent river section below the second riffle area. Similarly, the observed time spent in the first riffle area was significantly lower than in the next riffle area. The majority of Atlantic salmon entered the river during the hours of high tide and the subsequent ebb tide. In addition, most river entries were recorded around midnight. No effects of river flow on the river entry or migration speed were detected, but the migration speed of Atlantic salmon in both river sections examined was greater at lower temperatures. Twenty-eight fish (72%) were recaptured in the river, 71% of them with weirs and gillnets, and 29% by rod and line. Over half of the Atlantic salmon (54%) were recaptured within 3 weeks following river entry, and within the first 100km of the river (56%). The results are discussed in relation to earlier studies on multi-sea-winter Atlantic salmon in the River Tana. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate effects of the ban on the Norwegian coastal drift net fishery in 1989 on the spawning run of Atlantic salmon (Salmo salar) populations in four Norwegian and four Russian rivers. Catches/escapements, size distribution, sea-age proportions, and mean weights of different sea-age groups were collected from official catch statistics and analyses of scale samples. In three of the Norwegian rivers, catches of grilse (1SW) increased significantly after the ban on the drift net fishery. No changes were recorded for multi-sea-winter (MSW) fish. In addition, the proportion of grilse increased in all the Norwegian rivers, and 2SW salmon increased in three of them. The mean weight of grilse increased in all four Norwegian rivers, whereas the mean weight of 2SW fish decreased in the two rivers in southern Norway. The size of 3SW fish did not change. These changes correspond well to actual net selection curves and reported mean weight of drift net catches in different parts of Norway. Trends in the Russian populations were more varying. In the three rivers draining to the Barents Sea, changes were similar to those in the Norwegian rivers. However, these changes were less obvious than those observed in Norwegian populations. The authors conclude that the ban of the drift net fishery significantly affected the structure of the spawning run in Norwegian Atlantic salmon populations. Furthermore, the results indicate that the drift net fishery affected Russian salmon populations in rivers draining to the Barents Sea to a lesser extent than Norwegian salmon, and had no effect in rivers draining to the White Sea. [ABSTRACT FROM PUBLISHER]

The article discusses observations of predatory behavior of salmon and trout smolts in a river mouth. Visual observations revealed that gulls attacked the school of smolts when they left the river especially in the shallow water. They were attacked by cod and saithe as they were moving out over the edge of the deeper water. Observations from the mouth of the River Eira revealed that the tagged smolts were eaten by predatory fishes and gulls in their descent. The predators took advantage of the smolts' apparent vulnerability.

Behaviour observations of the endangered native marble trout (Salmo marmoratus, Cuvier, 1829) and introduced rainbow trout (Oncorhynchus mykiss, Walbaum, 1792) in the laboratory and in a tributary to the Idrijca River in Slovenia were combined to study the movements and dominance relationships between individuals of the two species in an open field test. Under laboratory conditions, no difference between the species was detected for neither time spent actively or distance moved. In species paired tests, rainbow trout initiated more aggressive behaviours towards marble trout than vice versa, and rainbow trout were clearly the dominant individuals. After simultaneous release in the river, marble trout immediately left the release area and spent twice as long time as rainbow trout until they settled in an area of the river; therefore, the release site was immediately occupied exclusively by rainbow trout. Thus, the dominant and aggressive behaviour of rainbow trout seen in the laboratory before release might have influenced marble trout's subsequent behaviour in the river, by marble trout leaving the areas occupied by rainbow trout and moving to locations further away from the release site. In the field, the marble trout occupied sites individually, whereas rainbow aggregated at a few locations. Rainbow trout showed higher movement activity in the morning compared to marble trout. There was a positive correlation between swimming speed in the laboratory and movement in the field for marble trout but not for rainbow trout. In conclusion, the results in this study support the need to end stocking of rainbow trout in rivers with native marble trout. To better understand the interaction between the species, and to develop efficient management plans to protect the native marble trout, reference behaviours should first be understood, and future research in sites where the two species do not co-exist is needed. This is especially important for marble trout for which behavioural research and data are lacking., (© 2023 Fisheries Society of the British Isles.)

The global population of European eel (Anguilla anguilla) is rapidly declining, and migration barriers in rivers are believed to be one of several key causes. While progress has been made in the development of bypass solutions, they are often constructed based on a limited knowledge of swimming behaviour. A bypass close to the stream bed is often recommended at fish passage facilities to accommodate downstream eel migration. The results of this recommendation are poorly studied, and the few studies that exist show varying bypass efficiencies. The current study used acoustic telemetry with depth sensors to explore the three-dimensional migratory behaviour of downstream-migrating silver eels. The eels were tracked as they approached a hydropower plant with a state-of-the-art angled bar rack and full-depth bypass. Downstream and upstream swimming differed in preferred vertical and lateral positions. During periods of local downstream movement, the density of observations was largest in the upper middle section, away from the river boundaries and in higher velocities. Conversely, when moving upstream, eels tended to avoid the upper layers of the middle part of the river, swimming closer to the riverbed and using the bank areas to a greater extent. Downstream-moving fish swam higher in the water column during night and in turbid conditions (high discharge). When approaching the impassable bar rack and the full-depth bypass, the eels searched most intensely but not exclusively along the bottom third of the rack, often exploring at new depths after changing direction. The impediment passage efficiency was 100% when both bypass solutions were considered. The study provides knowledge of the swimming behaviour of silver eels, which is relevant for the design of bypass solutions for eels at migration barriers., (© 2022 The Authors. Journal of Fish Biology published by John Wiley & Sons Ltd on behalf of Fisheries Society of the British Isles.)

The European eel's singular spawning migration from European waters towards the Sargasso Sea remains elusive, including the early phase of migration at sea. During spawning migration, the movement of freshwater resident eels from river to sea has been thought to be irreversible. We report the first recorded incidents of eels returning to the river of origin after spending up to a year in the marine environment. After migrating to the Baltic Sea, 21% of the silver eels, tagged with acoustic transmitters, returned to the Narva River. Half returned 11-12 months after moving to the sea, with 15 km being the longest upstream movement. The returned eels spent up to 33 days in the river and migrated to the sea again. The fastest specimen migrated to the outlet of the Baltic Sea in 68 days after the second start-roughly 1300 km. The surprising occurrence of returning migrants has implications for sustainable management and protection of this critically endangered species.

Structural complexity is known to influence prey behaviour, mortality and population structure, but the effects on predators have received less attention. We tested whether contrasting structural complexity in two newly colonised lakes (low structural complexity lake-LSC; high structural complexity-HSC) was associated with contrasting behaviour in an aquatic apex predator, Northern pike (Esox lucius; hereafter pike) present in the lakes. Behaviour of pike was studied with whole-lake acoustic telemetry tracking, supplemented by stable isotope analysis of pike prey utilization and survey fishing data on the prey fish community. Pike displayed increased activity, space use, individual growth as well as behavioural differentiation and spent more time in open waters in the LSC lake. Despite observed differences between lakes, stable isotopes analyses indicated a high dependency on littoral food sources in both lakes. We concluded that pike in the HSC lake displayed a behaviour consistent with a prevalent ambush predation behaviour, whereas the higher activity and larger space use in the LSC lake indicated a transition to more active search behaviour. It could lead to increased prey encounter and cause better growth in the LSC lake. Our study demonstrated how differences in structural complexity mediated prominent changes in the foraging behaviour of an apex predator, which in turn may have effects on the prey community., (© 2021. The Author(s).)

Determining the mechanisms driving range-wide reductions in Atlantic salmon marine survival is hindered by an insufficient understanding of their oceanic ecology and distribution. We attached 204 pop-up satellite archival tags to post-spawned salmon when they migrated to the ocean from seven European areas and maiden North American salmon captured at sea at West Greenland. Individuals migrated further north and east than previously reported and displayed increased diving activity near oceanographic fronts, emphasizing the importance of these regions as feeding areas. The oceanic distribution differed among individuals and populations, but overlapped more between geographically proximate than distant populations. Dissimilarities in distribution likely contribute to variation in growth and survival within and among populations due to spatio-temporal differences in environmental conditions. Climate-induced changes in oceanographic conditions will alter the location of frontal areas and may have stock-specific effects on Atlantic salmon population dynamics, likely having the largest impacts on southern populations.

Ferox trout are large, long-lived, piscivorous trout normally found in deep lakes; they are highly prized by trophy anglers. Lough Corrib and Lough Mask, Western Ireland, have recorded the majority of Irish specimen ferox trout since angling records began. Little was known regarding the spawning location of ferox trout relative to sympatric brown trout, and a radio telemetry study was initiated in both catchments in 2005. Over the period 2005-2009, 79 ferox were captured by angling and radio tagged in Lough Corrib, while 55 ferox were tagged in Lough Mask. Manual and helicopter tracking were carried out on all spawning streams entering both lakes over the autumn/winter period to detect tagged fish. Overall, 37 radio-tagged trout (46.8%) were detected in Lough Corrib streams and 21 tagged trout (38.2%) were recorded from Lough Mask streams. Results from radio tracking indicate that the majority (92%) of ferox trout tagged in Lough Corrib spawned in a single spawning stream, the Cong river, while the majority (76%) of ferox trout tagged in Lough Mask spawned in the Cong canal and Cong river. These results suggest that these streams are most likely the principle spawning locations of ferox trout in both lakes. The occurrence of ferox trout predominantly in single spawning rivers in both catchments highlights the vulnerability of the study ferox populations. As a result of these findings, conservation measures were introduced for ferox trout in both catchments., (© 2020 Fisheries Society of the British Isles.)

Potamodromous fishes require safe migration routes between spawning, feeding and wintering habitats to complete their life cycle. As knowledge on asp migrations is restricted, this work investigated the movements of adult asp tagged with acoustic transmitters for 3 years in the large Peipsi-Emajõgi-Võrtsjärv lake-river system, Estonia, which is free of migration barriers. Asp showed complex migration patterns, moving between and within different waterbodies (lakes, river, tributaries) in all seasons, but with a tendency to repeat habitat use patterns between years. Lakes were mainly used for feeding during spring and summer (after spawning 65% of the fish migrated to Lake Peipsi), and more so by large fish. The majority (80-96%) of the fish spent the winter in the rivers, mostly close to their subsequent spawning area. Spawning areas were in swift-flowing waters in tributaries and the main river. The results indicate that asp may benefit from an extensive and diverse complex of habitats, and any migration barrier during any season may restrict the natural habitat use by asp. Maintenance and restoration of habitat heterogeneity and connectivity is critical to protect behaviourally diverse fish populations and increase resilience in rivers negatively impacted by various human activities., (© 2020 Fisheries Society of the British Isles.)

Anthropogenic structures in rivers are major threats for fish migration and effective mitigation is imperative given the worldwide expansion of such structures. Fish behaviour is strongly influenced by hydrodynamics, but little is known on the relation between hydraulics and fish fine scale-movement. We combined 3D Computational fluid dynamics modelling (CFD) with 2D and 3D fish positioning to investigate the relation between hydrodynamics and the downstream movement of Atlantic salmon smolts (Salmo salar). We show that fish use fine-scale flow velocity and turbulence as navigation cues of fine-scale movement behaviour. Tri-dimensional swimming speed and swimming direction can be explained by adjustments of fish to flow motion, which are linked to fish swimming mode. Fish diverge from the flow by swimming at speeds within or higher than their prolonged speeds (0.38-0.73 m s - 1 ). Flow direction plays a pivotal role on fish swimming performance, with high upstream and downwards velocities impacting swimming the most. Turbulence is also influential, by benefiting swimming performance at low TKE (< 0.03 m 2  s - 2 ) or constraining it at higher levels. We show that fish behaviour is affected by interactions of several hydraulic variables that should be considered jointly., (Copyright © 2018 The Authors. Published by Elsevier B.V. All rights reserved.)

Aquatic positional telemetry offers vast opportunities to study in vivo behaviour of wild animals, but there is room for improvement in the data quality provided by current procedures for estimating positions. Here we present a novel positioning method called YAPS (Yet Another Positioning Solver), involving Maximum Likelihood analysis of a state-space model applied directly to time of arrival (TOA) data in combination with a movement model. YAPS avoids the sequential positioning-filtering-approach applied in alternative tools by using all available data in a single model, and offers better accuracy and error control. Feasibility and performance of YAPS was rigorously tested in a simulation study and by applying YAPS to data from an acoustic transmitter towed in a receiver array. Performance was compared to an alternative positioning model and proprietary software. The simulation study and field test revealed that YAPS performance was better and more consistent than alternatives. We conclude that YAPS outperformed the compared alternative methods, and that YAPS constitute a vast improvement to currently available positioning software in acoustic telemetry. Additionally, in contrast to vendor-supplied solutions, YAPS is transparent, flexible and can easily be adapted and extended for further improvements or to meet study specific requirements such as three-dimensional positioning.

The spawning migration of the European eel ( Anguilla anguilla L.) to the Sargasso Sea is one of the greatest animal migrations. However, the duration and route of the migration remain uncertain. Using fishery data from 20 rivers across Europe, we show that most eels begin their oceanic migration between August and December. We used electronic tagging techniques to map the oceanic migration from eels released from four regions in Europe. Of 707 eels tagged, we received 206 data sets. Many migrations ended soon after release because of predation events, but we were able to reconstruct in detail the migration routes of >80 eels. The route extended from western mainland Europe to the Azores region, more than 5000 km toward the Sargasso Sea. All eels exhibited diel vertical migrations, moving from deeper water during the day into shallower water at night. The range of migration speeds was 3 to 47 km day -1 . Using data from larval surveys in the Sargasso Sea, we show that spawning likely begins in December and peaks in February. Synthesizing these results, we show that the timing of autumn escapement and the rate of migration are inconsistent with the century-long held assumption that eels spawn as a single reproductive cohort in the springtime following their escapement. Instead, we suggest that European eels adopt a mixed migratory strategy, with some individuals able to achieve a rapid migration, whereas others arrive only in time for the following spawning season. Our results have consequences for eel management.

Catadromous anguillid eels (Genus Anguilla ) migrate from their freshwater or estuarine habitats to marine spawning areas. Evidence from satellite tagging studies indicates that tropical and temperate eel species exhibit pronounced diel vertical migrations between 150 to 300 m nighttime depths to 600 to 800 m during the day. Collections of eggs and larvae of Japanese eels ( A. japonica ) show they may spawn at these upper nighttime migration depths. How anguillid eels navigate through the ocean and find their spawning areas remains unknown, so this study describes the salinity, temperature and geostrophic currents between 0 and 800 m depths within two confirmed and three hypothetical anguillid spawning areas during likely spawning seasons. Within all four ocean gyres many eels would encounter subducted 'Subtropical Underwater' during their nighttime ascents that could provide odor plumes as signposts. Four spawning areas are located near the western margins of where subducted water masses form cores of elevated salinities (~35.0 to 36.8) around 150 m depths, while one is found near the center of subduction. Low salinity surface waters and fronts are present in some of the areas above the high-salinity cores. Spawning may occur at temperatures between 16 to 24°C where the thermocline locally deepens. At spawning depths, weak westward currents (~0 to 0.1 m s -1 ) prevail, and eastward surface countercurrents are present. Anguillid eels possess acute sensory capabilities to detect these hydrographic features as potential signposts guiding them to where they spawn.

The application of no-take areas in fisheries remains controversial. Critics argue that many targeted species are too mobile to benefit from area protection and that no-take areas are only appropriate for resident species. The degree of protection does not depend on the size of the no-take area but rather on the time fish reside inside its boundaries during key life-history events (i.e., spawning) and during periods of peak fishing activity. We evaluated the potential of a small no-take marine protected area (MPA) inside a coastal embayment as a harvest refuge for a mobile, possibly migratory, long-lived fish species. We used acoustic telemetry to track movements of 30 transmitter-tagged white stumpnose (Rhabdosargus globiceps) across and on both sides of the boundary of a small (34 km(2)) no-take area over a full year. Being landlocked on 3 sides, the location of the MPA inside the lagoon made it practical to detect all boundary crossings and to calculate the time individual fish used the MPA. We detected frequent movements across the boundary, with strong seasonal and individual variations. There were significant differences in MPA use patterns between fish from different release areas. The time spent in the MPA by individual fish during summer (mean 50%; max 98%) was out of proportion with the size of that area (4% of total habitat). Summer coincided with peak recreational fishing activity and with the spawning season of this species. The small MPA provided a refuge for a part of the spawning stock of white stumpnose. Our findings suggest that if strategically placed, a small no-take area can be effective in protecting mobile species and that models of spillover from no-take areas should account for seasonal and individual variation in area use and the spatiotemporal distribution of fish and fishers., (©2008 Society for Conservation Biology.)