Association of Large Juvenile Red Drum, Sciaenops ocellatus, with an Estuarine Creek on the Atlantic Coast of Florida

Seasonal abundance, size distribution, year-class presence, residence duration, and migrational patterns of red drum, Sciaenops ocellatus, in an estuarine marsh creek in the northern Indian River Lagoon, Florida, were investigated during a study in which gill net samples were collected monthly from August 1991 to March 1996. A total of 282 large juvenile red drum were collected, of which 161 were tagged and released and 68 were sacrificed for age determination. Although red drum were collected in the creek throughout the year, abundance levels were negatively correlated with water temperatures and reached maximum levels during the winter months. Significant correlations between fish abundance and salinity or dissolved oxygen levels were not detected. The majority (90%) of the fish collected were large juveniles (260–450mm standard length) that were estimated to be from 10 to 26 months old. The oldest red drum we examined from the creek was estimated to be 37 months old. Tag-recapture data indicated that some fish repeatedly used or were associated with the creek for periods of up to 18 months after release. Estuarine creeks in this region provide exploitable habitat for large juvenile red drum (相似文献   

A modified stepping-stone model of population structure in red drum, Sciaenops ocellatus (Sciaenidae), from the northern Gulf of Mexico

Genetic studies of population or stock structure in exploited marine fishes typically are designed to determine whether geographic boundaries useful for conservation and management planning are identifiable. Implicit in many such studies is the notion that subpopulations or stocks, if they exist, have fixed territories with little or no gene exchange between them. Herein, we review our long-term genetic studies of red drum (Sciaenops ocellatus), an estuarine-dependent sciaenid fish in the Gulf of Mexico and western Atlantic Ocean. Significant differences in frequencies of mitochondrial DNA haplotypes and of alleles at nuclear-encoded microsatellites occur among red drum sampled across the northern Gulf of Mexico. The spatial distribution of the genetic variation, however, follows a pattern of isolation-by-distance consistent with the hypothesis that gene flow occurs among subpopulations and is an inverse (and continuous) function of geographic distance. However, successful reproduction and recruitment of red drum depend on estuarine habitats that have geographically discrete boundaries. We hypothesize that population structure in red drum follows a modified one-dimensional, linear stepping-stone model where gene exchange occurs primarily (but not exclusively) between adjacent bays and estuaries distributed linearly along the coastline. Gene flow does occur among estuaries that are not adjacent but probabilities of gene exchange decrease as a function of geographic distance. Implications of our hypothesis are discussed in terms of inferences drawn from patterns of isolation-by-distance and relative to conservation and management of estuarine-dependent species like red drum. Based on estimates of the ratio of genetic effective population size and census size in red drum, observed patterns of gene flow in red drum may play a significant role in recruitment.     

Effect of predator exposure on the performance and survival of red drum (<Emphasis Type="Italic">Sciaenops ocellatus</Emphasis>)

The influence of predator exposure on the survival of hatchery red drum, Sciaenops ocellatus was investigated under laboratory conditions. Several prey-capture (attack distance, mean attack velocity, capture time, and gape cycle duration) and anti-predator (reaction distance, response distance, mean velocity, and maximum velocity) performance variables were quantified using high-speed video for juvenile red drum (25–30 mm standard length, L _S ) reared with and without predators (pinfish, Lagodon rhomboides). Univariate contrasts of prey-capture events demonstrated that attack distance (mean ± s.e.) was significantly greater in red drum reared with (1.20 ± 0.16 mm) versus without (0.65 ± 0.09 mm) pinfish predators. During anti-predator events, red drum reared with predators had approximately 300% greater reaction distance and 20%–30% greater response distance, mean velocity and maximum velocity versus fish reared without predators; however, these differences were not statistically significant. Following video assessments, a series of mortality experiments were conducted using free-ranging pinfish predators. Mortality rates (Z) ranged from 0.047 to 0.060 (Z/hr/predator) and did not differ significantly among treatments.     

Movement patterns of small benthic fish in lowland headwater streams

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Habitat-related predation on juvenile wild-caught and hatchery-reared red drum Sciaenops ocellatus (Linnaeus)

We examined the patterns of habitat-specific mortality for newly settled red drum (Sciaenops ocellatus) using an experimental mesocosm approach. Experiments were designed to analyze prey vulnerability and fish rearing-type (wild-caught or hatchery-reared) in estuarine habitats of varying structural complexity including marsh (Spartina alterniflora Loisel), oyster reef (Crassostrea virginica Gmelin), seagrass (Halodule wrightii Aschers), and nonvegetated sand bottom. We used two different predators, pinfish (Lagodon rhomboides Linnaeus) and spotted seatrout (Cynoscion nebulosus Cuvier). For both predators, vulnerability of wild-caught red drum was significantly lower in structurally complex habitats such as seagrass and oyster reef; the highest vulnerability was associated with the nonvegetated bottom. This habitat effect was not apparent for hatchery-reared prey. In trials using a combination of both rearing-types, there was no significant habitat effect on prey selection, but hatchery-reared red drum suffered higher overall mortality than wild-caught fish from pinfish predators. In these trials, spotted seatrout did not select for either prey type. Differences we observed in prey vulnerability were likely caused by behavioral differences between wild-caught and hatchery-reared red drum. Our results reinforce the conclusion that structural complexity in estuarine habitats increases survival of newly settled fishes. Our data also suggest that hatchery-reared red drum may be more vulnerable to predation than natural fishes, and that survival of stocked fish may be enhanced through habitat-related behavior modification.     

Use of deuterium oxide (2H2O) to assess muscle protein synthesis in juvenile red drum (Sciaenops ocellatus) fed complete,and valine-deficient diets

The use of ²H₂O in tank water to assess protein synthesis rates in fish is a relatively novel methodology that could allow for a better understanding of the effects of particular nutritional and environmental variables on rates of protein accretion. As such, this study involved an assessment and comparison of protein synthesis rates in the muscle of juvenile red drum fed a control diet (nutritionally complete) versus a valine (Val)-deficient diet. Six groups of 12 juvenile red drum, initially weighing ~ 4.5 g/fish, were stocked in six separate 38-L aquaria operating as a recirculating system. Fish were acclimatized to experimental conditions for 2 weeks while being fed the control diet. Just prior to initiating the protein synthesis assay, one aquarium of fish was fed the control diet while a second aquarium of fish was fed the Val-deficient diet. Immediately after consuming the experimental diets, each group of fish was moved to an independent aquarium containing ²H₂O, and the fractional synthetic rate (FSR) of protein synthesis was obtained at 12, 24, 36 and 48 h after feeding by collecting two fish per treatment at each time point. This protein synthesis assay procedure was performed in three separate sessions, and considered as replicates over time (n = 3) for fish fed the control or Val-deficient diets immediately before initiating the session. Results indicated that a one-time feeding of a diet deficient in Val significantly reduced protein synthesis rates in the muscle of red drum. In addition, a significant effect of time after feeding was found, where observed FSR values peaked at 12 h after feeding and decreased as time progressed. In conclusion, deuterium methodologies were applicable to red drum, and this approach had the sensitivity to assess differences in protein synthesis rates when dietary perturbations were introduced.

     

Conventional tagging and acoustic telemetry of a small surgeonfish, <Emphasis Type="Italic">Zebrasoma flavescens</Emphasis>, in a structurally complex coral reef environment

Passive acoustic telemetry and conventional tag/re-sight techniques were used to study daily movement patterns of adult yellow tang, Zebrasoma flavescens, over a period of months. Range testing and visual observations revealed the limitations of using small acoustic transmitters to monitor movements of small coral reef fish in a topographically complex and noisy coral reef environment. Visual observations of conventionally tagged and albino fish suggest individuals return each day to forage over the same few hundred m² of shallow, turf algae dominated boulder and reef flat habitat for periods of at least weeks to months. Acoustic telemetry data suggest lower frequency of repeated use of daytime foraging, nighttime refuge and sunset spawning sites. However, integration of observation and acoustic telemetry data revealed that many fish were not detected while they were within the empirically tested range of the receivers. These observations indicate that data from passive acoustic telemetry can underestimate the frequency and duration of repeated use of specific areas. Yellow tang adults made daily crepuscular migrations of up to 600 m between foraging and spawning or sheltering sites at consistent times relative to sunset and sunrise. While there was high individual variability in migration distance, almost all individuals moved in the same direction (from south to north) at sunset. This study provided valuable information for evaluating ongoing fishery management efforts using marine protected areas in Hawaii.     

The influence of tidal cycles and freshwater inflow on the distribution and movement of an estuarine resident fish Acanthopagrus butcheri

Movement patterns and habitat utilization by black bream Acanthopagrus butcheri (Sparidae), an estuarine resident species, were investigated using acoustic telemetry in a small estuary on the east coast of Tasmania, Australia. Thirty‐four adult A. butcheri were tracked for periods of up to 187 days between August 2005 and January 2006. Although able to tolerate a wide range of salinities, the fish spent most of the time within the upper and middle regions of the estuary, where brackish conditions dominated. The species exhibited extensive movements linked to tidal cycles, with small‐scale upstream movements during incoming tides and downstream movements during out going tides. The extent of these movements was positively correlated with the tidal height difference between consecutive tidal peaks and troughs. Freshwater inflows and resultant changes in salinity also significantly influenced distribution and movement patterns. Fish moved downstream during the periods of heavy inflows, returning upstream as salinities increased to c. >10. During the peak of spawning period (November to December) fish moved into the upper region of the estuary, where they aggregated to spawn. Periodic increases in freshwater discharge, however, resulted in fish leaving the spawning grounds and moving downstream. Towards the end of the spawning season (January), the fish became more dispersed throughout the entire estuarine system.     

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.     

Validation of annual periodicity in otoliths of red snapper, <Emphasis Type="Italic">Lutjanus campechanus</Emphasis>

The periodicity of otolith growth increments (opaque and translucent zones) from adult red snapper (Lutjanus campechanus) was examined through a mark and recapture study (2005–2010), and laboratory holding of hatchery reared red snapper over a 2 year period (2002–2004). Wild red snapper (n = 295) were caught hook-and-line, marked with anchor tags, injected with oxytetracycline dihydrate (OTC), and released in the Gulf of Mexico 15–40 km south of Dauphin Island, Alabama. Marked fish were recaptured up to 2.8 years after release (n = 35) and sagittal otoliths were dissected, sectioned and examined under white and blue-violet light. The number of opaque growth zones past the OTC mark was compared to time at liberty for each fish and supported an annual periodicity of growth increment formation. Also, most (87%) of the hatchery reared fish showed two opaque zones that supported an annual increment formation rate. However, an unusual timing of opaque zone formation was shown for mark-recaptured fish. Based on known timing of OTC marking, otoliths from mark-recapture fish showed opaque zone formation from late summer (August) to early winter (December). This fall formation of opaque zones is in contrast to previous studies and its timing may relate to the end of spawning for this species.     

Characterizing the trophic niches of stocked and resident cyprinid fishes: consistency in partitioning over time,space and body sizes

Hatchery‐reared fish are commonly stocked into freshwaters to enhance recreational angling. As these fishes are often of high trophic position and attain relatively large sizes, they potentially interact with functionally similar resident fishes and modify food‐web structure. Hatchery‐reared barbel Barbus barbus are frequently stocked to enhance riverine cyprinid fish communities in Europe; these fish can survive for over 20 years and exceed 8 kg. Here, their trophic consequences for resident fish communities were tested using cohabitation studies, mainly involving chub Squalius cephalus, a similarly large‐bodied, omnivorous and long‐lived species. These studies were completed over three spatial scales: pond mesocosms, two streams and three lowland rivers, and used stable isotope analysis. Experiments in mesocosms over 100 days revealed rapid formation of dietary specializations and discrete trophic niches in juvenile B. barbus and S. cephalus. This niche partitioning between the species was also apparent in the streams over 2 years. In the lowland rivers, where fish were mature individuals within established populations, this pattern was also generally apparent in fishes of much larger body sizes. Thus, the stocking of these hatchery‐reared fish only incurred minor consequences for the trophic ecology of resident fish, with strong patterns of trophic niche partitioning and diet specialization. Application of these results to decision‐making frameworks should enable managers to make objective decisions on whether cyprinid fish should be stocked into lowland rivers according to ecological risk.     

Lipid acquisition and retention in tissues of spawning adult paddlefish Polyodon spathula (Walbaum, 1792) in relation to extended and compressed life history patterns in two river‐reservoir systems

Data from recreationally caught adult paddlefish from North Dakota and Oklahoma, USA, was used in an initial attempt to explain variation in lipid content in adult wild paddlefish Polyodon spathula (Walbaum, 1792) by stock and by sex. The objectives of this study were to describe the relative importance of three distinct paddlefish tissues [white muscle, red muscle, and gonadal fat body (GFB)] for lipid storage, and compare lipid content of these tissues between stock and sex. It was hypothesized that lipid content of the three tissue types would be related to each other within individual fish; and that, consistent with previously documented life history differences, lipid concentrations for all tissues would be sex‐ and stock‐specific. Paddlefish were sampled in April and May 2012 from the Grand Lake, Oklahoma, USA (GL) and Yellowstone‐Sakakawea, North Dakota (SAK) stocks. Three tissue types were collected from SAK fish, including white muscle (N = 137; 83M, 54F), red muscle (N = 74; 36M, 38F), and GFB (N = 164; 105M, 59F). Samples from GL fish included white muscle (N = 60; 36M, 24F), and GFB (N = 42; 41M, 1F). Proximate analysis was used to quantify the percentage of lipid, water, ash, and protein in tissue samples. The lipid component of proximate analysis was completed using the ANKOM method of lipid extraction which uses heated petroleum ether to extract lipid. Also investigated were lipid accumulation and storage in adult paddlefish in relation to tissue type: white muscle, red muscle, gonadal fat bodies (GFB) within individual fish, between the sexes, and between the two different stocks. White muscle was significantly correlated with both red muscle and GFB lipid, but red muscle lipid was not significantly correlated with GFB lipid. White muscle lipid content differed by stock and sex, with the more northerly stock having higher lipid content than the more southerly stock. Females had higher white muscle lipid content (SAK F = 17.18, M = 9.09; GL F = 6.74, M = 4.99) and red muscle (SAK F = 47.72, M = 30.93) than males. In contrast, GFB lipid differed by sex but not stock, with females having lower lipid content (SAK = 79.79, GL = 89.08) than males (SAK = 89.08; GL = 91.72). Life history differences, growing season, and the role of metabolism may help explain the differences in concentrations of lipids observed between stocks and between the sexes for all three tissues. It was hypothesized that different tissues may be used for different metabolic processes and that although metabolism likely strongly influences muscle tissue lipid, GFB lipid is probably linked more closely to reproductive demands associated with gonad development.     

Migration patterns of juvenile Lutjanus argentimaculatus in a mangrove estuary in Trang province, Thailand, as revealed by ultrasonic telemetry

Migrational patterns of mangrove jack Lutjanus argentimaculatus were studied in a mangrove estuary in Trang province, Thailand, using ultrasonic telemetry. Ultrasonic coded transmitters were surgically implanted in 18 fish and 16 of them were subsequently monitored by nine fixed receivers installed along Sikao Creek estuary in June and November 2006. Due to technical limitations all of the individuals were released in the middle of the creek. Their movements were monitored for a period of up to 1 month, the data being used to describe short term migration of juvenile Lutjanus argentimaculatus in the creek and to find possible environmental cues for the observed movements. All of the individuals showed a tide related movement pattern, suggesting foraging in the small mangrove channels and/or mangrove forest during high tides. 50% of the fish left the study area for the open coast area within a short time following release, indicating that a part of juvenile L. argentimaculatus may move in between estuarine habitats instead of being site attached. As the fish were reared in fish cages for a certain period of time before the study this behavior could partly be explained by the time spent in captivity. It was found that L. argentimaculatus showed higher movement activity during night high tides possibly explained by an increased availability of the sough after food items.     

Movements of bonnetheads, <Emphasis Type="Italic">Sphyrna tiburo</Emphasis>, as a response to salinity change in a Florida estuary

The movement of bonnetheads, Sphyrna tiburo, within an estuarine system on the Gulf of Mexico coast of Florida was examined to define response to salinity change. Shark presence and movements were evaluated by acoustic monitoring and gillnet sampling. Acoustic monitoring data were used to investigate active selection of different zones within the estuary based on differences in salinity among zones. Sharks were monitored for 187 days in 2003 and 217 days in 2004 in salinities ranging from 11.0 to 31.0 ppt in 2003 and 15.8 to 34.6 ppt in 2004. Monitoring data supported the hypothesis that salinity played a role in the distribution and movement of S. tiburo. Catch per unit effort (CPUE) data obtained from gillnet sampling from 1995 to 2004 were examined to determine affinity or avoidance of specific salinities within the study site as calculated using an electivity index. Electivity analysis showed almost no affinity or avoidance for specific salinity values. The difference in results between the CPUE and acoustic monitoring in relation to the potential effects of salinity likely relate to the nature of the data, with acoustic monitoring providing continuous data and CPUE providing snapshot location data. The results of this study suggest that although S. tiburo are collected within a wide range of salinity levels, salinity may affect movement and distribution. Salinity effects may be more pronounced during periods of prolonged and/or large changes in salinity as detected by long-term monitoring.     

Spawning Site Selection and Contingent Behavior in Common Snook,Centropomus undecimalis

Reproductive behavior affects spatial population structure and our ability to manage for sustainability in marine and diadromous fishes. In this study, we used fishery independent capture-based sampling to evaluate where Common Snook occurred in Tampa Bay and if it changed with spawning season, and passive acoustic telemetry to assess fine scale behavior at an inlet spawning site (2007–2009). Snook concentrated in three areas during the spawning season only one of which fell within the expected spawning habitat. Although in lower numbers, they remained in these areas throughout the winter months. Acoustically-tagged snook (n = 31) showed two seasonal patterns at the spawning site: Most fish occurred during the spawning season but several fish displayed more extended residency, supporting the capture-based findings that Common Snook exhibit facultative catadromy. Spawning site selection for iteroparous, multiple-batch spawning fishes occurs at the lifetime, annual, or intra-annual temporal scales. In this study we show colonization of a new spawning site, indicating that lifetime spawning site fidelity of Common Snook is not fixed at this fine spatial scale. However, individuals did exhibit annual and intra-seasonal spawning site fidelity to this new site over the three years studied. The number of fish at the spawning site increased in June and July (peak spawning months) and on new and full lunar phases indicating within population variability in spawning and movement patterns. Intra-seasonal patterns of detection also differed significantly with sex. Common Snook exhibited divergent migration tactics and habitat use at the annual and estuarine scales, with contingents using different overwintering habitat. Migration tactics also varied at the spawning site at the intra-seasonal scale and with sex. These results have important implications for understanding how reproductive behavior affects spatio-temporal patterns of fish abundance and their resilience to disturbance events and fishing pressure.     

Characterization of the 5′-to-5′linked adult α- and β-globin genes from three sciaenid fish species (Pseudosciaena crocea, Sciaenops ocellatus, Nibea miichthioides)

Recently, we cloned the adult α-globin genes from large yellow croaker Pseudosciaena crocea, cuneate drum Nibea miichthioides and red drum Sciaenops ocellatus. All these α-globins have a unique Gly insertion at the 47th residue. In this paper, the three sciaenid globin complexes were identified and compared in detail. Linkage analysis indicated that the sciaenid α- and β-globin genes were oriented head-to-head relative to each other. The sciaenid intergenic regions between the linked α- and β-globin genes were the smallest in reported fish globin gene complexes to date. Classical promoter elements were condensed and the CCAAT box unstable duplication was found in these regions. The promoter function of the intergenic region from large yellow croaker was tested by transient expression of EGFP in Vero cells. We also described a method for studying luciferase reporter gene transient expression in primary fish erythrocytes. We used the method to assess the promoter strength of the three intergenic regions between the sciaenid α- and β-globin genes.     

Physiological responses of Pacific halibut, <Emphasis Type="Italic">Hippoglossus stenolepis</Emphasis>, to intracoelomic implantation of electronic archival tags,with a review of tag implantation techniques employed in flatfishes

Management of Pacific halibut (Hippoglossus stenolepis), a long-lived flatfish, is complicated by possible ontogenic and sex-specific variation in migration. Archival tags promise the ability to help uncover long-term movement patterns at the individual level, if the tags can be retained and recovered from healthy fish. We examined fifteen individuals (69–90 cm fork length) for long-term physiological response to intracoelomic implantation of three types of archival tags: fully internal, internal with right angle protruding light stalk, and internal with straight protruding light stalk. Tags represented 0.05–0.16% of initial fish weights. Fish were reared at 10.8 ± 1.1°C for 59 weeks post-surgery. One fish died after 39 weeks from thermal stress unrelated to the surgical procedure. Temporal variation in behavior of tagged fish was indistinguishable from that of controls (n = 15 tagged, 5 controls). Treatment and control-group fish grew at similar rates. No tag expulsion or physiological response was evident in the individual that died at 39 weeks, but nine of eleven individuals dissected at the end of 59 weeks had developed internal responses. These responses ranged from deposition of fibrous protein and/or calcitic material on tag surfaces to partial or full tag encapsulation in either the visceral peritoneal layer (fully-internal tags) or the intestinal mesenteries (stalk-bearing tags). The responses were within the range reported for other pleuronectids implanted with tags of similar configuration and may have implications for design and interpretation of long-term tagging studies. Encapsulation may reduce the probability of tag recoveries even in the absence of tag expulsion, especially in species eviscerated at sea.     

Selection of Estuarine Nursery Habitats by Wild-caught and Hatchery-reared Juvenile Red Drum in Laboratory Mesocosms

We examined patterns of habitat selection in wild-caught and hatchery-reared early juvenile red drum, Sciaenops ocellatus, using mesocosm experiments. Experiments were performed in the presence and absence of a pinfish, Lagodon rhomboides. We hypothesized that newly recruited red drum would have distinct patterns of habitat selection, and these patterns could be influenced by the presence of a pinfish predator. Red drum were introduced to replicate mesocosms containing all possible pair-wise comparisons of four different habitat types: marsh Spartina alterniflora, non-vegetated bottom/sand, oyster reef Crassostrea virginica, and seagrass Halodule wrightii. Wild-caught and hatchery-reared red drum showed distinctively different patterns of habitat selection. In general, wild-caught red drum selected structured habitats, while hatchery-reared fish did not show strong selection for any habitat type. When a predator was present, wild-caught red drum either changed habitat selection or showed significant selection for other structured habitats. This predator effect was similar albeit weaker for hatchery-reared red drum, but as in the trials without a predator, overall habitat selection was reduced compared to wild-caught red drum. Our results suggest that in the absence of seagrass, other habitat types such as marshes and oyster reefs may be important recruitment habitat for red drum. Additionally, hatchery-dependent behaviors may need to be assessed in designing stock enhancement programs.     

Daily movement behavior of two Neotropical armored catfish species (Ancistrus aff. cirrhosus Valenciennes, 1836 and Hypostomus ancistroides Ihering, 1911) at a road‐stream crossing culvert

We hypothesized that the use of habitat by two armored catfish species, Ancistrus aff. cirrhosus and Hypostomus ancistroides, which share the same stream reach, is temporally segregated. To test this, fish residence time within a culvert and fish movements through the culvert were analyzed in relation to the daily hours, lunar cycle and discharge using Passive Integrated Transponder telemetry. The residence time for A. aff. cirrhosus conducting upstream movements was longer than H. ancistroides. Both species exhibited high nocturnal activity, although at different periods: A. aff. cirrhosus was most active at dawn (00:00–05:59 hr), while H. ancistroides exhibited intense activity at night (18:00–23:59 hr), indicating temporal segregation of movement behavior between species. In addition, A. aff. cirrhosus was most active in the new moon phase and when there was high water discharge, while H. ancistroides was most active only when there was high water discharge. This study elucidates the patterns of daily movement behavior and temporal habitat use of these fish species.     

River and estuary movements of yellow‐stage American eels Anguilla rostrata,using a hydrophone array

Patterns of summertime movement and habitat use of yellow‐stage American eels Anguilla rostrata within York River and estuary and Gaspé Bay (Gaspesia, Québec, Canada) were examined using acoustic telemetry. Fifty fish were tagged with acoustic transmitters and released, either in the river or in the upper estuary, and their patterns of movement and habitat use were monitored at short spatial and temporal scales during the summer months using a dense hydrophone array. Approximately half of the fish released in the river swam to the estuary; two‐thirds of the fish released within the estuary did not move out of the estuary. Anguilla rostrata were detected more frequently and had a greater areal range of detections during night, suggesting greater nocturnal activity. Longitudinal movements within the estuary tended to occur nocturnally, with upstream movements from early to late evening, and downstream movements from late evening to early morning. Approximately one‐third of fish showed a regular pattern of movement, tending to reside in the deeper, downstream part of the estuary during day and in the shallower, more upstream part of the estuary during night. Approximately a quarter of fish, located in the upper estuary, remained upstream during both night and day. The remaining fish showed patterns intermediate between these two.