Acoustic telemetry survey of the dusky grouper (Epinephelus marginatus) in the Marine Reserve of Cerbère-Banyuls: informations on the territoriality of this emblematic species

The Marine Reserve of Cerbère-Banyuls represents a refuge for dusky grouper populations (Epinephelus marginatus). Density survey and observation of the reproductive behavior of this species have been conducted there for the last 30 years. However, information on the behavior or habitat utilization for this species during winter time is limited. We conducted acoustic telemetry surveys from September 2005 to June 2006 in the Marine Reserve of Cerbère-Banyuls for a dusky grouper population. Six groupers were tagged and followed within the integral reserve and in the adjacent partial reserve. The results from the tracking of these individuals indicated that the largest dusky groupers are sedentary fishes with a high degree of site fidelity and a high sensitivity to variations of environmental conditions such as storms. This together with the life history characteristics of this species encourages the conservation and the protection of essential habitats of this species. Acoustic tracking coupled to the use of a fixed Kernel can be proposed to follow fish populations. To cite this article: J. Pastor et al., C. R. Biologies 332 (2009).     

Movement Patterns,Habitat Utilization,Home Range Size and Site Fidelity of Whitesaddle Goatfish,Parupeneus Porphyreus,In a Marine Reserve

Suitability of small (< 1km²) marine reserves for protecting a commercially important endemic Hawaiian goatfish, Parupeneus porphyreus, was examined by quantifying goatfish habitat use, home range size and site fidelity in an existing marine reserve (Coconut Island in Kaneohe Bay, Hawaii). Five goatfish equipped with acoustic transmitters were tracked for up to 93h each over 3–14 days. Daytime habitat use patterns of two of these fish were continuously monitored for one month using a fixed hydrophone hardwired to an onshore computer. Acoustically tagged fish showed consistent diel patterns of behavior, refuging in holes in the reef by day and moving over extensive areas of sand and coral rubble habitat at night. Remote monitoring of daytime habitat use by two goatfish revealed that the same daytime refuge was used by both fish for at least one month (the battery life of the transmitters). Home ranges of all fish were within the boundaries of the Coconut Island reserve suggesting that even small areas containing suitable habitat can make effective reserves for this species. A relatively low abundance of reproductive size P. porphyreus at Coconut Island in comparison with deeper areas may indicate an ontogenetic shift to deeper habitat in this species.     

Monitoring fish behaviour with a remote, combined acoustic/radio biotelemetry system

Biotelemetry is a powerful instrument for monitoring aquatic species in their natural environment. Using telemetry, animals can be monitored from a passive perspective, without the biases associated with conventional handling and sampling techniques. To monitor aquatic species in remote environments, with vast stretches of water, and in situations requiring both acoustic and radio transmissions (e.g. for diadromous fish), advances in telemetry are necessary. In this paper, a field-proven telemetry system based on a radio receiver and incorporating combined acoustic and radio smart transmitters, wireless hydrophones and two-way satellite communications is described. The system was first deployed in Bay d'Espoir, Newfoundland, Canada, in 1998. The purpose of this deployment was to determine whether aquaculture triploid steelhead trout ( Oncorhynchus mykiss Walbaum) (1.5–2.0 kg), experimentally released in the vicinity of a commercial aquaculture site, remained at the site (site fidelity) or dispersed. Two sets of fish releases, summer and winter, were performed to determine seasonal effects on the movement of aquaculture triploid steelhead trout in the wild. The results suggested strong site fidelity among steelhead trout when released during the growing season (summer). However, less fidelity was displayed for the winter released steelhead.     

Site fidelity and activity patterns of a humphead wrasse, Cheilinus undulatus (Labridae), as determined by acoustic telemetry

This study examines the short-term site fidelity, the home range size and the activity patterns of one specimen of the emblematic and threatened humphead wrasse, Chelinus undulatus. Four omnidirectional hydrophones were deployed for 7 months in the mooring area of Larégnère marine reserve (New Caledonia). The hydrophone network covered 50 ha. The monitored fish was caught in the study site and surgically implanted with an ultrasonic transmitter. The fish displayed a regular diurnal rhythm during 25 days before leaving the area. Different patterns of spatial use were identified. The temporal succession of these patterns indicates that the minimum distance covered by the fish every day ranged between 20 and 200 m. Its home range was at least 5 ha. A decrease of the detection was observed before the departure of the fish. This decrease coincided with the beginning of the reproduction period in New Caledonia and supports the hypothesis of a fish departure for the reproductive event. Despite the survey of only one specimen, the home range and movement calculated using acoustic telemetry are different in scale than the reported scuba-based visual estimations. Such information is essential for the development of management policies and conservation measures of large reef fish species highly vulnerable to disturbance and fishing pressure.     

A Methodological Framework to Estimate the Site Fidelity of Tagged Animals Using Passive Acoustic Telemetry

The rapid expansion of the use of passive acoustic telemetry technologies has facilitated unprecedented opportunities for studying the behavior of marine organisms in their natural environment. This technological advance would greatly benefit from the parallel development of dedicated methodologies accounting for the variety of timescales involved in the remote detection of tagged animals related to instrumental, environmental and behavioral events. In this paper we propose a methodological framework for estimating the site fidelity (“residence times”) of acoustic tagged animals at different timescales, based on the survival analysis of continuous residence times recorded at multiple receivers. Our approach is validated through modeling and applied on two distinct datasets obtained from a small coastal pelagic species (bigeye scad, Selar crumenophthalmus) and a large, offshore pelagic species (yellowfin tuna, Thunnus albacares), which show very distinct spatial scales of behavior. The methodological framework proposed herein allows estimating the most appropriate temporal scale for processing passive acoustic telemetry data depending on the scientific question of interest. Our method provides residence times free of the bias inherent to environmental and instrumental noise that can be used to study the small scale behavior of acoustic tagged animals. At larger timescales, it can effectively identify residence times that encompass the diel behavioral excursions of fish out of the acoustic detection range. This study provides a systematic framework for the analysis of passive acoustic telemetry data that can be employed for the comparative study of different species and study sites. The same methodology can be used each time discrete records of animal detections of any nature are employed for estimating the site fidelity of an animal at different timescales.     

The post‐spawning movements of migratory brown trout Salmo trutta L.

The post spawning behaviour of sea trout Salmo trutta was studied over a 2 year period in the river and estuary of the River Fowey, south‐west England. Forty‐five sea trout kelts were trapped immediately after spawning in December and intraperitoneally tagged with miniature acoustic transmitters. The subsequent emigration into coastal waters was monitored using acoustic receivers deployed throughout the river catchment. The levels of gill Na⁺K⁺ATPase activity in sea trout kelts sampled at the same time as the tagged fish were within the range of 2·5 to 4·5 μmol Pi per mg protein per h indicating that the post‐spawning fish were not physiologically adapted to salt water. The tagged kelts were resident in fresh water between 4 and 70 days before entering the estuary. Sixty two per cent of the tagged kelts subsequently migrated successfully into coastal waters, with a higher success rate for male fish (75%) than females (58%). There was a significant size related difference in the run‐timing of the kelts with the larger fish moving more quickly into coastal waters after spawning than smaller fish. Seaward migration within fresh water was predominantly nocturnal and generally occurred in conjunction with increasing river discharge and rising water temperature. Migration through the estuary continued to be predominantly nocturnal and occurred during an ebbing tide. Residency within the estuary varied amongst individuals although it was invariably short, with most fish moving out into coastal waters within one to two tidal cycles. Five tagged kelts returned from the coastal zone and re‐entered fresh water during April and June. Marine residence time varied between 89 and 145 days (mean 118 days) and the minimum estimated marine survival was c. 18%. One of these sea trout was subsequently recaptured after successfully spawning in the vicinity where it had been previously tagged demonstrating a degree of spawning site fidelity.     

Quantifying the activity and movement of perch in a temperate lake by integrating acoustic telemetry and a geographic information system

The horizontal movement patterns of perch (Perca fluviatilis L.) were studied by means of an automatic positioning system in a small Mediterranean temperate lake in northeastern Spain. Seven perch (247–265 mm in fork length, 243–271 g in weight) were implanted surgically with ultrasonic transmitters (38 mm long, 3.5 g in water) and their positions monitored approximately every 180 s using a radio-linked acoustic positioning (VRAP) system. Fish positions were integrated into a geographic information system database with information on date, time, slope and bottom depth. As a measure of the intensity of movement, the swimming speed was calculated. The Minimum Convex Polygon area was obtained as a measure of the area of activity. The data dispersion was calculated as r ² (the mean squared distance from the center of activity). The tagged perch showed individual variations in activity levels, but all had a circadian pattern, being less active at night (average speed 6.0 cm s^–1) than during the day (average speed 10.4 cm s^–1). They exhibited two peaks of activity, at sunrise and sunset. Two patterns of movement emerged, the first characterised by movement between the limnetic and the littoral zones, the second restricted to the shoreline. Fish appeared to follow the same path, reducing the area of activity to a limited part of the lake. Also, fish returned to the same place after movements, showing site fidelity but only for a few days. Overall, although perch could be very abundant in open waters (limnetic zone), they demonstrated a high dependence on the littoral zone.     

Movements,Home Range and Site Fidelity of Snapper (Chrysophrys auratus) within a Temperate Marine Protected Area

Understanding the movement dynamics of marine fish provides valuable information that can assist with species management, particularly regarding protection within marine protected areas (MPAs). We performed an acoustic tagging study implemented within the Port Stephens-Great Lakes Marine Park on the mid-north coast of New South Wales, Australia, to assess the movement patterns, home range and diel activity of snapper (Chrysophrys auratus; Sparidae); a species of significant recreational and commercial fishing importance in Australia. The study focused on C. auratus movements around Cabbage Tree Island, which is predominantly a no-take sanctuary zone (no fishing), with an array of acoustic stations deployed around the island and adjacent reefs and islands. Thirty C. auratus were tagged with internal acoustic tags in November 2010 with their movements recorded until September 2014. Both adult and juvenile C. auratus were observed to display strong site fidelity to Cabbage Tree Island with a mean 12-month residency index of 0.83 (range = 0 low to 1 high). Only three fish were detected on acoustic receivers away from Cabbage Tree Island, with one fish moving a considerable distance of ~ 290 kms over a short time frame (46 days). The longest period of residency recorded at the island was for three fish occurring regularly at the site for a period of 1249 days. Chrysophrys auratus displayed strong diurnal behaviour and detection frequency was significantly higher during the day than at night; however, there was no significant difference in detection frequency between different hours. This study demonstrates that even small-scale protected areas can benefit C. auratus during multiple life-history stages as it maintains a small home range and displays strong site fidelity over a period of 3 years.     

Movements and Site Fidelity of two Juvenile Fish Species Using Surf Zone Nursery Habitats Along The Southeastern North Carolina Coast

We examined the extent of movements of juvenile Florida pompano, Trachinotus carolinus, and gulf kingfish, Menticirrhus littoralis, along an open ocean beach. Fishes were collected by seine at three sites along Masonboro Island and Carolina Beach, NC between 7 June and 7 July 1995. All specimens 40 mm standard length (SL) were tagged with coded wire tags and released at the capture sites. Between 7 July and 9 August and on 15–16 September Masonboro Island and northern Carolina Beach were surveyed for tagged fish. A controlled tag mortality/retention study was conducted for both species. Overall, 1569 Florida pompano (40–135 mm SL) were tagged. Sixty-one (3.9%) of these were recaptured, and only eight moved away from the original tagging sites. The largest movements by two Florida pompano were 2.1 and 10.5 km. Many fish remained at their original tagging sites for 21–27 days. Of 488 gulf kingfish (36–158 mm SL) tagged, 16 (3.3%) were recaptured. Gulf kingfish also exhibited little movement away from tagging sites during the study, with individuals remaining at original tagging sites up to 21 days. Stock size estimates for Florida pompano ranged from 3354 to 4670 among the tagging sites, with densities ranging from 1.9 to 2.6 fish m^–2. The remarkable site fidelity exhibited by these two species suggests that resources were not limiting or that predation pressure was not high enough to cause large scale movements during the study. This implies that local disturbances could impact behavior or survival of juvenile fishes in the surf zone.     

The combined use of acoustic tracking and echosounding to investigate the movement and distribution of common bream (Abramis brama) in the River Trent,England

Spatial behaviour and distribution of fishes along a 7.6-km lowland reach of the River Trent, England, were examined using two complementary telemetry techniques: acoustic tracking to assess the movement and activity of common bream Abramis brama (L.) and quantitative echosounding for measuring the density and distribution of fish shoals. Nine adult bream (39.3–53.2 cm) were tracked by means of intraperitoneally implanted acoustic transmitters from 19 July to 12 September 2000. Home range size varied between 0.35 and 5.40 km of river length over this period. Bream were relatively inactive during daylight hours, began moving near dusk, and tended to move throughout the night. A distinct daytime residence area was occupied by most tagged fish on most occasions, while river use at night was more variable between individuals. Mobile echosounding surveys, with the transducer beaming horizontally across the river, conducted at night between July and September 2000, showed a highly contagious fish distribution within the study reach. For 200-m sections of river, there was a negative correlation between the relative frequency of acoustic tracking fixes at night and mean fish densities, as measured by echosounding for targets larger than –50 dB (c. 5-cm long). However, there was a highly significant positive rank correlation between the relative frequency of acoustic tracking fixes and acoustic targets larger than –30 dB (c. 22-cm long), most of which in this river are bream. This suggests that telemetry and echosounding can, in this part of the River Trent, be combined to provide valuable spatial information at individual and population scales for bream.     

Potential of a no‐take marine reserve to protect home ranges of anadromous brown trout (Salmo trutta)

The extent to which no‐take marine reserves can benefit anadromous species requires examination. Here, we used acoustic telemetry to investigate the spatial behavior of anadromous brown trout (sea trout, Salmo trutta) in relation to a small marine reserve (~1.5 km²) located inside a fjord on the Norwegian Skagerrak coast. On average, sea trout spent 42.3 % (±5.0% SE) of their time in the fjord within the reserve, a proportion similar to the area of the reserve relative to that of the fjord. On average, sea trout tagged inside the reserve received the most protection, although the level of protection decreased marginally with increasing home range size. Furthermore, individuals tagged outside the reserve received more protection with increasing home range size, potentially opposing selection toward smaller home range sizes inflicted on fish residing within reserves, or through selective fishing methods like angling. Monthly sea trout home ranges in the marine environment were on average smaller than the reserve, with a mean of 0.430 (±0.0265 SE) km². Hence, the reserve is large enough to protect the full home range of some individuals residing in the reserve. Synthesis and applications: In general, the reserve protects sea trout to a varying degree depending on their individual behavior. These findings highlight evolutionary implications of spatial protection and can guide managers in the design of marine reserves and networks that preserve variation in target species' home range size and movement behavior.     

Fish with Chips: Tracking Reef Fish Movements to Evaluate Size and Connectivity of Caribbean Marine Protected Areas

Coral reefs and associated fish populations have experienced rapid decline in the Caribbean region and marine protected areas (MPAs) have been widely implemented to address this decline. The performance of no-take MPAs (i.e., marine reserves) for protecting and rebuilding fish populations is influenced by the movement of animals within and across their boundaries. Very little is known about Caribbean reef fish movements creating a critical knowledge gap that can impede effective MPA design, performance and evaluation. Using miniature implanted acoustic transmitters and a fixed acoustic receiver array, we address three key questions: How far can reef fish move? Does connectivity exist between adjacent MPAs? Does existing MPA size match the spatial scale of reef fish movements? We show that many reef fishes are capable of traveling far greater distances and in shorter duration than was previously known. Across the Puerto Rican Shelf, more than half of our 163 tagged fish (18 species of 10 families) moved distances greater than 1 km with three fish moving more than 10 km in a single day and a quarter spending time outside of MPAs. We provide direct evidence of ecological connectivity across a network of MPAs, including estimated movements of more than 40 km connecting a nearshore MPA with a shelf-edge spawning aggregation. Most tagged fish showed high fidelity to MPAs, but also spent time outside MPAs, potentially contributing to spillover. Three-quarters of our fish were capable of traveling distances that would take them beyond the protection offered by at least 40–64% of the existing eastern Caribbean MPAs. We recommend that key species movement patterns be used to inform and evaluate MPA functionality and design, particularly size and shape. A re-scaling of our perception of Caribbean reef fish mobility and habitat use is imperative, with important implications for ecology and management effectiveness.     

Short-Term Fidelity,Habitat Use and Vertical Movement Behavior of the Black Rockfish Sebastes schlegelii as Determined by Acoustic Telemetry

The recent miniaturization of acoustic tracking devices has allowed fishery managers and scientists to collect spatial and temporal data for sustainable fishery management. The spatial and temporal dimensions of fish behavior (movement and/or vertical migrations) are particularly relevant for rockfishes (Sebastes spp.) because most rockfish species are long-lived and have high site fidelity, increasing their vulnerability to overexploitation. In this study, we describe the short-term (with a tracking period of up to 46 d) spatial behavior, as determined by acoustic tracking, of the black rockfish Sebastes schlegelii, a species subject to overexploitation in the Yellow Sea of China. The average residence index (the ratio of detected days to the total period from release to the last detection) in the study area was 0.92 ± 0.13, and most of the tagged fish were detected by only one region of the acoustic receiver array, suggesting relatively high site fidelity to the study area. Acoustic tracking also suggested that this species is more frequently detected during the day than at night in our study area. However, the diel detection periodicity (24 h) was only evident for certain periods of the tracking time, as revealed by a continuous wavelet transform. The habitat selection index of tagged S. schlegelii suggested that S. schlegelii preferred natural reefs, mixed sand/artificial reef bottoms and mixed bottoms of boulder, cobble, gravel and artificial reefs. The preference of this species for the artificial reefs that were recently deployed in the study area suggests that artificial seascapes may be effective management tools to attract individuals. The vertical movement of tagged S. schlegelii was mostly characterized by bottom dwelling behavior, and there was high individual variability in the vertical migration pattern. Our results have important implications for S. schlegelii catchability, the implementation of marine protected areas, and the identification of key species habitats, and our study provides novel information for future studies on the sustainability of this important marine resource in eastern China.     

Passive acoustic telemetry reveals highly variable home range and movement patterns among unicornfish within a marine reserve

Marine reserves are the primary management tool for Guam’s reef fish fishery. While a build-up of fish biomass has occurred inside reserve boundaries, it is unknown whether reserve size matches the scale of movement of target species. Using passive acoustic telemetry, we quantified movement patterns and home range size of two heavily exploited unicornfish Naso unicornis and Naso lituratus. Fifteen fish (N. unicornis: n = 7; N. lituratus: n = 4 male, n = 4 female) were fitted with internal acoustic tags and tracked continuously over four months within a remote acoustic receiver array located in a decade-old marine reserve. This approach provided robust estimates of unicornfish movement patterns and home range size. The mean home range of 3.2 ha for N. unicornis was almost ten times larger than that previously recorded from a three-week tracking study of the species in Hawaii. While N. lituratus were smaller in body size, their mean home range (6.8 ha) was over twice that of N. unicornis. Both species displayed strong site fidelity, particularly during nocturnal and crepuscular periods. Although there was some overlap, individual movement patterns and home range size were highly variable within species and between sexes. N. unicornis home range increased with body size, and only the three largest fish home ranges extended into the deeper outer reef slope beyond the shallow reef flat. Both Naso species favoured habitat dominated by corals. Some individuals made predictable daily crepuscular migrations between different locations or habitat types. There was no evidence of significant spillover from the marine reserve into adjacent fished areas. Strong site fidelity coupled with negligible spillover suggests that small-scale reserves, with natural habitat boundaries to emigration, are effective in protecting localized unicornfish populations.     

Opportunistic Visitors: Long-Term Behavioural Response of Bull Sharks to Food Provisioning in Fiji

Shark-based tourism that uses bait to reliably attract certain species to specific sites so that divers can view them is a growing industry globally, but remains a controversial issue. We evaluate multi-year (2004–2011) underwater visual (n = 48 individuals) and acoustic tracking data (n = 82 transmitters; array of up to 16 receivers) of bull sharks Carcharhinus leucas from a long-term shark feeding site at the Shark Reef Marine Reserve and reefs along the Beqa Channel on the southern coast of Viti Levu, Fiji. Individual C. leucas showed varying degrees of site fidelity. Determined from acoustic tagging, the majority of C. leucas had site fidelity indexes >0.5 for the marine reserve (including the feeding site) and neighbouring reefs. However, during the time of the day (09:00–12:00) when feeding takes place, sharks mainly had site fidelity indexes <0.5 for the feeding site, regardless of feeding or non-feeding days. Site fidelity indexes determined by direct diver observation of sharks at the feeding site were lower compared to such values determined by acoustic tagging. The overall pattern for C. leucas is that, if present in the area, they are attracted to the feeding site regardless of whether feeding or non-feeding days, but they remain for longer periods of time (consecutive hours) on feeding days. The overall diel patterns in movement are for C. leucas to use the area around the feeding site in the morning before spreading out over Shark Reef throughout the day and dispersing over the entire array at night. Both focal observation and acoustic monitoring show that C. leucas intermittently leave the area for a few consecutive days throughout the year, and for longer time periods (weeks to months) at the end of the calendar year before returning to the feeding site.     

Multi Year Observations Reveal Variability in Residence of a Tropical Demersal Fish,Lethrinus nebulosus: Implications for Spatial Management

Off the Ningaloo coast of North West Western Australia, Spangled Emperor Lethrinus nebulosus are among the most highly targeted recreational fish species. The Ningaloo Reef Marine Park comprises an area of 4,566 km² of which 34% is protected from fishing by 18 no-take sanctuary zones ranging in size from 0.08–44.8 km². To better understand Spangled Emperor movements and the adequacy of sanctuary zones within the Ningaloo Reef Marine Park for this species, 84 Spangled Emperor of a broad spectrum of maturity and sex were tagged using internal acoustic tags in a range of lagoon and reef slope habitats both inside and adjacent to the Mangrove Bay Sanctuary zone. Kernel Utilisation Distribution (KUD) was calculated for 39 resident individuals that were detected for more than 30 days. There was no relationship with fish size and movement or site fidelity. Average home range (95% KUD) for residents was 8.5±0.5 km² compared to average sanctuary zone size of 30 km². Calculated home range was stable over time resulting in resident animals tagged inside the sanctuary zone spending ∼80% of time within the sanctuary boundaries. The number of fish remaining within the array of receivers declined steadily over time and after one year more than 60% of tagged fish had moved outside the sanctuary zone and also beyond the 28 km² array of receivers. Long term monitoring identified the importance of shifting home range and was essential for understanding overall residency within protected areas and also for identifying spawning related movements. This study indicates that despite exhibiting stable and small home ranges over periods of one to two years, more than half the population of spangled emperor move at scales greater than average sanctuary size within the Ningaloo Reef Marine Park.     

Spatio-temporal movement patterns of Diplodus vulgaris (Actinopterygii, Sparidae) in a temperate marine reserve (Lampedusa, Mediterranean Sea)

The movements of a commercially important species, Diplodus vulgaris, were assessed in a marine-protected area to test whether their spatial and temporal activity patterns differ during and outside of their spawning season. Twelve adults were caught along the north-eastern coast of a small Mediterranean island, tagged with acoustic transmitters and released within or just outside the integral reserve. Fish detected, during both the seasons showed strong fidelity for the study area before and during the spawning season and their home range did not differ between seasons. Home ranges reached an asymptote between 12 and 174 days after release. Home range estimated by kernel utilization distributions ranged from 9,876 to 89,914 m², with core areas of 946 to 7,274 m². Temporal patterns frequently showed a dominant diel rhythm with most of detections occurring at daytime, independently of season. The variability in the movement patterns of D. vulgaris was lower between seasons (i.e., during and outside the spawning season) than at smaller temporal scale (i.e., between day and night) and was largely affected by inter-individual differences. Some conclusions arising from this and previous findings are useful to orient future studies on coastal fish movement and have direct implications for MPAs design.     

Use of Washington Estuaries by Subadult and Adult Green Sturgeon

Green sturgeon, Acipenser medirostris, are the most marine-oriented of North American sturgeons. However, their estuarine/marine distribution and the seasonality of estuarine use are largely unknown. We used acoustic telemetry to document the timing of green sturgeon use of Washington estuaries. In the summers of 2003 and 2004, uniquely coded acoustic transmitters were surgically implanted in green sturgeon captured using commercial gillnets. All sturgeon tagged were greater than 1.2 m total length. They were caught, tagged, and released in both Willapa Bay (n = 49) and Columbia River (n = 11) estuaries. We deployed an array of four fixed- site acoustic receivers in Willapa Bay to detect the estuarine entry and exit of these and any of over 100 additional green sturgeon tagged in other systems during 2003 and 2004. Green sturgeon occurred in Willapa Bay in summer when estuarine water temperatures exceeded coastal water temperatures by at least 2°C. They exhibited rapid and extensive intra- and inter- estuary movements and green sturgeon from all known spawning populations were detected in Willapa Bay. We hypothesize that green sturgeon optimize their growth potential in summer by foraging in the relatively warm, saline waters of Willapa Bay and we caution that altering the quality of estuarine habitats could negatively affect this species throughout its range.     

Does river of origin influence the early marine migratory performance of Salmo salar?

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 (Laerdal 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 Laerdal fish began migrating before the Flekke fish and had higher progression rates in the middle part of the fjord system. A greater number of Laerdal 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.     

Inter-annual Fidelity to Summer Feeding Sites in Arctic Grayling

Inter-annual fidelity to summer feeding sites was assessed in adult Arctic grayling, Thymallus arcticus, in the Kuparuk River, Alaska using long-term (15 years) records of individually tagged fish. The Kuparuk River has been the site of a long-term fertilization experiment which allowed us to evaluate the effects of habitat quality on site fidelity. Fidelity to the entire 5km experimental reach, the reference or fertilized zone of the river and to specific river locations was examined. On average, 32% of the arctic grayling caught in the experimental reach were recaptured within the reach in subsequent years. Grayling that returned to the reach displayed strong fidelity to river zones as well as to specific sites on the river. More than half of the fish were recaptured within 300meters of the site where they were captured in previous years. There was no significant difference in fidelity to either the reference or the more productive fertilized zone. Unexpectedly, fidelity was unrelated to fish size (29–43cm TL) or previous summers growth. Strong site fidelity appears to be an adaptation to a short summer during which sufficient resources must be acquired to sustain the fish through the long (9 month) Arctic winter leaving little time to explore alternative locations.