Passive Integrated Transponder Antenna Research Articles

Predator presence influences survival and behavior of translocated stream fish in ponds

Abstract Small artificial impoundments such as farm ponds have recently been recognized as potential habitat for threatened native fish species. However, factors influencing translocation or colonization success into these environments, including connectivity to stream networks and interactions with existing fish community, are largely unknown. In this study we conducted a controlled experiment to quantify the influence of piscivorous Largemouth Bass Micropterus salmoides on the survival of a translocated native minnow species that we used as a surrogate for federally endangered Topeka Shiner Notropis topeka. We translocated or released 100 Bluntnose Minnow Pimephales notatus into each replicate treatment ponds with and without Largemouth Bass in the summers of 2020 and 2021. Each minnow was implanted with a passive integrated transponder (PIT) tag. Translocated populations were monitored using stationary and mobile passive integrated transponder antennas and estimates of apparent survival and probability of detection for each pond were derived from open population mark-recapture models. Apparent survival was nearly two times higher in ponds without bass suggesting predation by bass leads to higher mortality. Additionally, probability of detection was nearly 10 times higher in ponds without bass, suggesting reduced movement of translocated minnows when bass were present. While the direct effect of mortality impacts translocated populations, the indirect effect of altered behavior may also be impactful on translocation success. These results confirm that Largemouth Bass can limit the success of translocated minnow species.

Novel application of two- and four-lobed noise-canceling passive integrated transponder antennas for tracking fish in areas of high ambient electromagnetic interference.

Passive integrated transponder (PIT) technology is a leading tool for tracking fish in freshwater systems. PIT is highly applicable for assessing fish passage at anthropogenic infrastructure (e.g., dams and floodgates); however, there are often complications in operating PIT antennas near these structures due to the ambient electromagnetic interference of metal and power-supply equipment. We designed a PIT antenna that is resistant to the effects of ambient electromagnetic interference (AEMI). This design uses lobes with balanced polarity within the antenna to neutralize AEMI within the vicinity of the antenna. This novel PIT antenna provides a more effective and cost-efficient option for researchers tracking fish in environments with high AEMI.

Estimating migration timing and abundance in partial migratory systems by integrating continuous antenna detections with physical captures.

Many populations migrate between two different habitats (e.g. wintering/foraging to breeding area, mainstem-tributary, river-lake, river-ocean, river-side channel) as part of their life history. Detection technologies, such as passive integrated transponder (PIT) antennas or sonic receivers, can be placed at boundaries between habitats (e.g. near the confluence of rivers) to detect migratory movements of marked animals. Often, these detection systems have high detection probabilities and detect many individuals but are limited in their ability to make inferences about abundance because only marked individuals can be detected. Here, we introduce a mark-recapture modelling approach that uses detections from a double-array PIT antenna system to imply movement directionality from arrays and estimate migration timing. Additionally, when combined with physical captures, the model can be used to estimate abundances for both migratory and non-migratory groups and help quantify partial migration. We first test our approach using simulation, and results indicate our approach displayed negligible bias for total abundance (less than ±1%) and slight biases for state-specific abundance estimates (±1%-6%). We fit our model to array detections and physical captures of three native fishes (humpback chub [Gila cypha], flannelmouth sucker [Catostomus latipinnis] and bluehead sucker [Catostomus discobolus]) in the Little Colorado River (LCR) in Grand Canyon, AZ, a system that exhibits partial migration (i.e. includes residents and migrants). Abundance estimates from our model confirm that, for all three species, migratory individuals are much more numerous than residents. There was little difference in movement timing between 2021 (a year without preceding winter/spring floods) and 2022 (a year with a small flood occurring in early April). In both years, flannelmouth sucker arrived in mid-March whereas humpback chub and bluehead sucker arrivals occurred early- to mid-April. With humpback chub and flannelmouth sucker, movement timing was influenced by body size so that large individuals were more likely to arrive early compared to smaller individuals. With more years of data, this model framework could be used to evaluate ecological questions pertaining to flow cues and movement timing or intensity, relative trends in migrants versus residents and ecological drivers of skipped spawning.

Does release size into net‐pens affect survival of captively reared juvenile endangered suckers in Upper Klamath Lake?

AbstractObjectiveHigh juvenile mortality prevents recruitment into the adult populations of endangered Shortnose Sucker Chasmistes brevirostris and Lost River Sucker Deltistes luxatus in Upper Klamath Lake, Oregon. To address the lack of recruitment, the U.S. Fish and Wildlife Service implemented the Sucker Assisted Rearing Program (SARP). Managers developing the rearing program lack information about how length at release relates to survival. To determine how initial length affects survival of captively reared juvenile suckers, we introduced juvenile suckers from the SARP into three net‐pens in Upper Klamath Lake.MethodsThe juvenile suckers ranged from 102 to 284 mm standard length, and each fish was tagged with a passive integrated transponder (PIT) tag. Fish were monitored continuously by PIT antennas and mortality was inferred when movements ceased.ResultEstimated survival over 57 days was high in all net‐pens (0.79–1.00) and remained high at two net‐pens for 76 and 86 days. Adjusted survival curves resulting from a stratified Cox model with standard length as a covariate, indicated that length positively influenced predicted survival by as much as 41% at one site. During the study, pH and dissolved oxygen regularly exceeded no‐effect thresholds at two sites and briefly reached lethal thresholds at the same two sites but did not coincide with the observed mortalities. Slower growth and the lowest survival were observed at the third site, where water quality never exceeded thresholds.ConclusionA larger release size and the location of the net‐pen can improve the survivability of juvenile suckers in net‐pens in Upper Klamath Lake.

Body condition metrics explain fish movement in experimental streams

AbstractBody condition refers to an array of physiological or nutritious states in animals, but body condition is typically measured using a single metric in animal behavior studies. In this paper, we conducted a three‐day laboratory study to evaluate whether metrics of body condition affected movement of wild‐caught creek chub (Semotilus atromaculatus) at 16 and 22°C. Movement was counted between two circular tanks connected by a straight corridor, which was equipped with a pair of passive integrated transponder antennas. Fish movement was most frequent during periods of darkness in a simulated photoperiod, and more mobile individuals consistently moved more frequently across the 3 days. In general, individuals in better body condition were more mobile than those in poorer condition, and different metrics of body condition affected movement to different degrees. Specifically, per cent weight loss and dry matter content (ratio of wet versus dehydrated weight) were better predictors of movement than weight‐at‐length, which is most typically used as a surrogate of body condition in animals. In addition, body condition and length interacted to affect fish movement, where body condition affected movement of smaller individuals more significantly than that of larger individuals. Body condition effects on activity were similar at 16 and 22°C. This study demonstrates that body condition metrics may not always affect certain behavior in a similar way. Body condition metrics need to be carefully selected when used in the context of animal behavior, and more than a single metric should be tested when feasible.

Comparison of Electrofishing and PIT Antennas for Detection of Hatchery-Reared Roundtail Chub (Gila robusta) Stocked into a Desert Stream

Stocking of rare native fishes for conservation purposes is a common practice in the southwestern United States. Monitoring typically occurs after hatchery-reared fish are released to assess post-stocking movement and survival. We conducted a two-year study, in which tow-barge electrofishing and portable, flat-bed passive integrated transponder (PIT) antennas were used to monitor PIT-tagged, hatchery-reared roundtail chub (Gila robusta) following release into the upper Verde River in Arizona. Specifically, our study aimed to compare the performance of PIT antennas and electrofishing in detecting PIT tagged fish released in a small desert river and to examine the behavioral response of hatchery-reared roundtail chub after stocking. In both years, more fish were detected by antenna arrays (84%) than by electrofishing (30%). roundtail chub were significantly more likely to be detected by antennas than electrofishing each year; however, when antenna data were evaluated only during the few days in which electrofishing took place, there was no significant difference (Year 1, p=0.1784; Year 2, p=0.6295) in detection between gear types for the same time interval, suggesting that electrofishing and antennas are equally likely to detect fish during 48-72 hour time frames. Within 72 hours of release, antennas detected 100% of fish that moved upstream and 93.8% of fish that moved downstream from the stocking location. Overall, less than half (45.6% in Year 1; 41.1% in Year 2) of the stocked roundtail chub were detected using both methods in both years. Utilization of both active capture gear (electrofishing) and passive gear (antennae) had advantages over monitoring with a single method. PIT antennae can be especially useful for managers who lack the personnel or time to implement more intensive methods of capture but want to monitor post-stocking movement and survival of stocked fish.

Flow velocity preference of Schizothorax oconnori Lloyd swimming upstream

Schizothorax oconnori Lloyd is a local endemic species, one of the most frequently observed species in the Tibet plateau, China, and the representative species of cold-water fish in the Yarlung Zangbo River basin. Knowing the flow velocity preference of fish is essential for understanding the mechanics of their locomotion, and part of the biological foundation required for habitat restoration. The flow velocity preference of Schizothorax oconnori swimming upstream was investigated using a four-channel flume. The flow fields in each channel were nearly uniform, but the flow velocity varied by channel. Test fish swam upstream, of their own volition, into a channel and were recorded by PIT (Passive Integrated Transponder) antennas as they entered the channel. The proportion of fish entering each channel was recorded and changes in activity level during the experiment were analyzed to detect diurnal and nocturnal cycles of activity. The choice among channels made by the test fish differed significantly, indicating that Schizothorax oconnori display a preference for flow velocity. Furthermore, it was demonstrated that the preference for flow velocity varied by season, with a preference for relatively high velocity in late July and a relatively low velocity in late August. This variation in preference may be attributed primarily to different feeding strategies in the two seasons and to differing maximum flow velocities in the two experiments. Due to fatigue, or acclimation to the constant flow field, fish activity decreased significantly after 10 h. Schizothorax oconnori was more active at night than during the day, attributed to its benthic nature and the relatively high light level in the shallow flume. Based on our findings, we make the following recommendations for fish passage design: (1) The flow field should be non-uniform to accommodate a flow preference that varies with season, and which helps prevent fatigue; (2) Avoid excessively long fish passageways and provide a combination of water depth and shading that provides a satisfactory light level.

Wild juvenile salmonid abundance in Wisconsin tributaries indicates limited contributions to Lake Michigan fisheries

Natural reproduction of salmonids occurs in many Lake Michigan tributaries, yet little is known about abundance and the potential contribution of wild fish hatching in Wisconsin tributaries. The objectives of our study were to determine if: 1) abundance of wild juvenile salmonids (primarily adfluvial rainbow trout, Oncorhynchus mykiss, referred to as steelhead) varied among selected Wisconsin streams based on available spawning and age-0 habitat; 2) stream temperature regimes could limit survival of juvenile salmonids, and 3) wild juvenile salmonids outmigrate from Wisconsin tributaries into Lake Michigan or larger tributaries. In 2016 and 2017, juvenile salmonid abundance was estimated in six Wisconsin tributaries to Lake Michigan by multiple-pass depletion sampling using backpack electrofishing. Habitat assessments included steelhead redd surveys, age-0 habitat surveys, and stream temperatures were monitored using in-stream loggers. Passive integrated transponder (PIT) tagging and PIT antennas were used to detect outmigration from three streams (Willow, Stony and Hibbard creeks). Population estimates for individual streams ranged from 75 to 2276 for juvenile steelhead and from 0 to 243 for juvenile coho salmon, Oncorhynchus kisutch. No correlation was detected between juvenile steelhead abundance and quality age-0 habitat. Stream temperatures rarely exceeded the thermal limit for steelhead (27 °C). Outmigration rates for three streams ranged from 0.6% to 3.1%, but these estimates were considered minimum values. Low abundance of wild juvenile steelhead and coho salmon alone suggest that the contributions of these tributaries to Lake Michigan fisheries are likely small. Furthermore, relying on returns of wild steelhead produced in these streams is probably insufficient to maintain stream fisheries.

Passive Integrated Transponder Tag Monitoring Reveals Complex Migration and Life History Patterns in Mountain Whitefish in Upper Columbia River Tributaries

AbstractMountain Whitefish Prosopium williamsoni is a native salmonid distributed throughout the Columbia River basin, but little is known about the life history traits of tributary‐specific populations. We captured and tagged 129 Mountain Whitefish with passive integrated transponder (PIT) tags between 2010 and 2015 at a weir on the Twisp River, Washington, to assess migration patterns. Detection records suggested that two populations of Mountain Whitefish overlap in the Twisp River during spring: resident fish that spawn in the Twisp River (42% of fish) and migrant fish that spawn in the Okanogan River (58% of fish). The median entry day into the Twisp River was similar for resident (April 17) and migrant (April 16) populations, but median exit day was significantly earlier for migrant (July 2) than for resident fish (November 6). Migrant fish exited the Methow basin and traveled at 14.1 river kilometers per day, passing the lower Okanogan River PIT antenna with a median date of September 17. After spawning and overwintering in the Okanogan River with a median exit date of March 16, these fish returned to the Methow basin traveling at 22.1 river kilometers per day. These results improve our understanding of Mountain Whitefish life history and habitat use in tributaries upstream of Wells Dam, Washington.

Incorporating antenna detections into abundance estimates of fish

Autonomous passive integrated transponder (PIT) tag antennas are commonly used to detect fish marked with PIT tags but cannot detect unmarked fish, creating challenges for abundance estimation. Here we describe an approach to estimate abundance from paired physical capture and antenna detection data in closed and open mark–recapture models. Additionally, for open models, we develop an approach that incorporates uncertainty in fish size, because fish size changes through time (as fish grow bigger) but is unknown if fish are not physically captured (e.g., only detected on antennas). Incorporation of size uncertainty allows for estimation of size-specific abundances and demonstrates a generally useful method for obtaining state-specific abundances estimates under state uncertainty. Simulation studies comparing models with and without antenna detections illustrate that the benefit of our approach increases as a larger proportion of the population is marked. When applied to two field data sets, our approach to incorporating antenna detections reduced uncertainty in abundance substantially. We conclude that PIT antennas hold great potential for improving abundance estimation, despite the challenges they present.

Behavior outweighs body size in mediating male reproductive success in a nest-building fish, bluehead chub

In polygamy, individuals interact in a non-random manner to shape reproductive networks. However, relative importance of behavior versus individual physical traits (e.g., body size) in determining access to partners and reproductive success varies by species and is poorly understood in small-bodied aquatic species for which direct observations are challenging in the wild. Here, we coupled automated individual tracking and genetic parentage techniques to characterize reproductive networks and their consequences on reproductive success in bluehead chub (Nocomis leptocephalus), a nest-building stream fish native to the southeastern USA. Fish were marked with 12-mm passive integrated transponder (PIT) tags, and loop-shaped PIT antennas were deployed around 18 nests to monitor behavioral encounters of 311 individuals (34 males and 277 females and immature males) during the spawning season in 2017. After spawning, genetic samples of 326 young-of-the-year fish (i.e., offspring) were collected. The mating system was polygynandrous, and factors affecting access to partners and reproductive success differed between males and females. Male body size did not affect number of encounters with females and reproductive success, instead behavior indexing reproductive effort (number and size of nests occupied) explained variation in reproductive success. On the contrary, body size was a key determinant of female reproductive success. Fecundity (i.e., number of eggs) increased with body size, and higher encounters rates with males did not result in higher reproductive success. In males and females, mating with more partners led to higher reproductive success, which may have contributed to the evolution and maintenance of polygynandry in this species. Is bigger better? This question has been investigated with respect to animal mating behavior and reproductive success, and the answer appears to vary by species. Using an intensive individual-based approach with PIT antenna and molecular markers, we show that behavior outweighed body size in mediating reproductive success of males but not females of a nest-building stream fish. Males increased access to females and ultimately number of offspring by occupying larger and more nests, which are proxies of reproductive effort. In females, body size was more important than behavior in determining reproductive success, and behavior explained much less of variation in reproductive success. Diverse and complex reproductive patterns of males may explain why behavior outweighed body size in mediating reproductive success, a hypothesis that warrants further research across species with a gradient of mating systems and behavioral complexities.

Behavioural response of sea lamprey (Petromyzon marinus) to acoustic stimuli in a small stream

Sea lamprey (Petromyzon marinus) are invasive in the Laurentian Great Lakes and parasitically feed on valued fishes. Migration barriers and selective pesticides are used to control sea lamprey, but there is a desire to develop additional control tools such as traps with nonphysical deterrents. Sound has been used as a deterrent for other invasive species, but its potential for manipulating sea lamprey behavior in natural stream conditions remains untested. Here, behavioral responses of upstream-migrating adult sea lamprey in response to low frequency sounds of 70 or 90 Hz was tracked in a small stream (8 m wide) using passive integrated transponder (PIT) telemetry. The low frequency sounds shifted sea lamprey distribution, with up to 30% more sea lamprey detected on PIT antennas without sound compared with PIT antennas with sound playing. Future studies could continue testing low frequency sounds in larger rivers with larger speakers for use as a natural deterrent at sea lamprey barriers to push sea lamprey toward traps.

Fishway Effectiveness and Upstream Residency of Three Fish Species at Four Fishways in Prince Edward Island, Canada

We evaluated passage of Osmerus mordax (Rainbow Smelt), Salvelinus fontinalis (Brook Trout), and Alosa pseudoharengus (Alewife) at 4 fishways on Prince Edward Island, Canada. We implanted fish with passive integrated transponder (PIT) tags and recorded their movements using stationary PIT antennas. Passage at different fishway types was highly variable. Nature-like fishways passed over 96% of Brook Trout and a maximum of 41.8% of Rainbow Smelt. The latter percentage is the highest yet reported in the literature for Rainbow Smelt. Pool-and-weir fishways passed nearly 100% of Brook Trout, 13.2% of Rainbow Smelt, and only 5.6% of Alewife. After passing a fishway, upstream residency was highly variable both among species as well as among individuals within species. Rainbow Smelt were observed spawning within nature-like fishways, suggesting that this type of fishway may also provide spawning habitat. Results highlight the challenge of passing non-salmonid species and indicate nature-like fishways are more appropriate than technical designs for passing Rainbow Smelt.

High detectability with low impact: Optimizing large PIT tracking systems for cave-dwelling bats.

Passive integrated transponder (PIT) tag technology permits the “resighting” of animals tagged for ecological research without the need for physical re‐trapping. Whilst this is effective if animals pass within centimeters of tag readers, short‐distance detection capabilities have prevented the use of this technology with many species. To address this problem, we optimized a large (15 m long) flexible antenna system to provide a c. 8 m2 vertical detection plane for detecting animals in flight. We installed antennas at two roosting caves, including the primary maternity cave, of the critically endangered southern bent‐winged bat (Miniopterus orianae bassanii) in south‐eastern Australia. Testing of these systems indicated PIT‐tags could be detected up to 105 cm either side of the antenna plane. Over the course of a three‐year study, we subcutaneously PIT‐tagged 2,966 bats and logged over 1.4 million unique detections, with 97% of tagged bats detected at least once. The probability of encountering a tagged bat decreased with increasing environmental “noise” (unwanted signal) perceived by the system. During the study, we mitigated initial high noise levels by earthing both systems, which contributed to an increase in daily detection probability (based on the proportion of individuals known to be alive that were detected each day) from <0.2 (noise level ≥30%) to 0.7–0.8 (noise level 5%–15%). Conditional on a low (5%) noise level, model‐based estimates of daily encounter probability were highest (>0.8) during peak breeding season when both female and male southern bent‐winged bats congregate at the maternity cave. In this paper, we detail the methods employed and make methodological recommendations for future wildlife research using large antennas, including earthing systems as standard protocol and quantifying noise metrics as a covariate influencing the probability of detection in subsequent analyses. Our results demonstrate that large PIT antennas can be used successfully to detect small volant species, extending the scope of PIT technology and enabling a much broader range of wildlife species to be studied using this approach.

Beaver activity increases habitat complexity and spatial partitioning by steelhead trout

Freshwater habitat restoration is a major conservation objective, motivating efforts to restore habitat complexity and quality for fishes. Restoration based on the engineering activities of beavers (Castor canadensis) increases fish habitat complexity, but how this affects fish habitat use and movement behaviours is not well known. We used a network of passive integrated transponder antennas to quantify small-scale movement and microhabitat use of 175 individual juvenile steelhead (Oncorhynchus mykiss) in a stream channel with a complex bathymetric profile resulting from a beaver impoundment and in a simplified channel devoid of beaver activity. Our results show that juvenile steelhead exploit microhabitat heterogeneity by employing a range of behaviours that maximizes available habitat via spatial and temporal partitioning among individuals. These results suggest spatial resource partitioning as a potential mechanism for the previously established positive correlations among steelhead density, survival, and production with beaver-based restoration within the study watershed. More broadly, our findings provide insight as to how populations can exploit habitat complexity through spatial partitioning that can be informative for planning restoration and management actions.

Efficacy of 12‐mm Half‐Duplex Passive Integrated Transponder Tags in Monitoring Fish Movements through Stationary Antenna Systems

AbstractGlobally, many freshwater fishes are declining in distribution and abundance, but for many species conservation measures are hindered by a limited knowledge of their ecology. Recent development of 12‐mm half‐duplex (HDX) passive integrated transponder (PIT) tags has broadened the potential application of this technology for studying habitat selection and migration of freshwater fishes. However, the limited read range of the smaller 12‐mm PIT tags can limit their functionality in ecological studies. The present study used four migratory fish species to test the efficacy of different PIT antenna designs for detecting 12‐mm HDX tags in small‐ and medium‐sized rivers. Three types of pass‐through antennae were created and coupled to either a single reader or multiplexor board. Across single‐reader and multiplexor systems, the detection efficiencies for Giant Kokopu Galaxias argenteus, Shortfin Eel Anguilla australis, and New Zealand Longfin Eel Anguilla dieffenbachii ranged between 87% and 97%. Adult Pouched Lamprey Geotria australis also had a high detection rate of 74%, even though several other migration routes existed that were unmonitored. Overall, the present study shows that with appropriate antenna design, the 12‐mm HDX PIT tag can be effective for monitoring a variety of fish species. Although the antennae in the present study had a maximum width of 6.1 m, the spaced double‐coil antenna design may increase efficacy of the 12‐mm tag in larger rivers.Received April 27, 2017; accepted September 1, 2017 Published online October 30, 2017

Summer habitat and movements of juvenile salmonids in a coastal river of Washington State

AbstractWe investigated the summer ecology of juvenile steelhead trout Onchorhynchus mykiss and Chinook salmon O. tshawytscha in the context of habitat use and movement behaviour. The study area was a 14.8 km section of the Chehalis River, Washington, and is of particular interest due to recent proposals for both a flood retention dam and restoration actions in this watershed. Ten study reaches were paired in distance upstream and downstream from a central point where a passive integrated transponder antenna array was operated between late June and September 2014. Juvenile densities for each species were associated with reach‐scale habitat and temperature characteristics. Juvenile steelhead underwent upstream and downstream movements up to 7 km, although more fish from further away moved downstream than upstream. Juvenile steelhead repeated horizontal movements throughout the study period, but daily detections were not associated with temperature or flow. The majority (81%) of steelhead movements occurred between the hours of 04:00–07:00 and 18:00–21:00. Juvenile Chinook underwent a downstream migration that was nearly complete by the end of August. Most juvenile Chinook were detected just once and movements occurred on days with warmer stream temperature and higher flows. The majority of Chinook movements occurred at night. Although juvenile salmonids are often thought to have small home ranges during summer months, our results suggest that horizontal movements may be more prevalent than previously thought. Summer habitat should be defined by a network of suitable rearing reaches with connectivity available in both upstream and downstream directions.

Estimating disperser abundance using open population models that incorporate data from continuous detection passive integrated transponder arrays

Autonomous passive integrated transponder (PIT) tag antenna systems continuously detect individually marked organisms at one or more fixed points over long time periods. Estimating abundance using data from autonomous antennas can be challenging because these systems do not detect unmarked individuals. Here we pair PIT antenna data from a tributary with mark–recapture sampling data in a mainstem river to estimate the number of fish moving from the mainstem to the tributary. We then use our model to estimate abundance of non-native rainbow trout (Oncorhynchus mykiss) that move from the Colorado River to the Little Colorado River, the latter of which is important spawning and rearing habitat for federally endangered humpback chub (Gila cypha). We estimate that 226 rainbow trout (95% confidence interval: 127–370) entered the Little Colorado River from October 2013 to April 2014. We discuss the challenges of incorporating detections from autonomous PIT antenna systems into mark–recapture population models, particularly in regards to using information about spatial location to estimate movement and detection probabilities.

Estuarine fish behavior around slotted water control structures in a managed salt marsh

Estuaries are composed of multiple interconnected habitat types used by transient fish species during their period of estuarine residency. Structural marsh management restricts habitat connectivity and impedes the movement of fishes among these habitat types by limiting access via water control structures (WCSs) between the managed area and the rest of the estuary. While some general information on fish passage rates is available, species-specific information on passage through WCSs is lacking for salt marsh fishes. We monitored tagged fishes from March 2012 through November 2013 using passive integrated transponder antenna arrays at two identical WCSs in the Calcasieu Lake estuary, Louisiana, USA, to assess the effect of slotted WCSs on fish behavior. A total of 420 individuals of 15 species was tagged and released at the WCSs; of these, 145 individuals representing 11 species were later detected at the WCSs. Five species comprised most (93%) of the detected individuals: Elops saurus (n = 60), Mugil cephalus (n = 43), Sciaenops ocellatus (n = 20), Pogonias cromis (n = 7), and Ariopsis felis (n = 5). Passage rates were low, with most of the observed fishes (n = 80) passing only once through the structures. Other than E. saurus, which was only observed migrating out of the managed marsh, no clear pattern in swimming direction was observed for the other species. Detected species were all present primarily during the summer and fall, however, diel activity at the structures varied by species. The WCSs in our study area appeared to attract and congregate fishes, functioning more like ecological hotspots, rather than simply facilitating fish passage.

Performance of a Vertical‐Slot Fish Pass for the Sea Lamprey Petromyzon marinus L. and Habitat Recolonization

AbstractIn 2011, a vertical‐slot fish pass was built at the Coimbra Açude‐Ponte dam (Mondego River, Portugal), approximately 45 km upstream from the river mouth. The performance of this infrastructure for sea lamprey passage was evaluated between 2011 and 2015 using several complementary methodologies, namely radio telemetry [conventional and electromyogram (EMG)], passive integrated transponder (PIT) telemetry and electrofishing surveys. During the study period, the electrofishing revealed a 29‐fold increase in the abundance of larval sea lamprey upstream of the fish pass. Of the 20 radio‐tagged individuals released downstream from the dam, 33% managed to find and successfully surpass the obstacle in less than 2 weeks, reaching the spawning areas located in the upstream stretch of the main river and in one important tributary. Fish pass efficiency was assessed with a PIT antenna installed in the last upstream pool and revealed a 31% efficiency, with differences between and within migratory seasons. Time of day and river flow significantly influenced the attraction efficiency of the fish pass, with lampreys negotiating it mainly during the night period and when discharge was below 50 m3 s−1. Sea lampreys tagged with EMG transmitters took 3 h to negotiate the fish pass, during which high muscular effort was only registered during passage, or passage attempts, of the vertical slots. The use of complementary methodologies provided a comprehensive passage evaluation for sea lamprey, a species for which there is a considerable paucity of valuable data concerning behavioural, physiological and environmental influences on obstacle negotiation. Copyright © 2016 John Wiley &amp; Sons, Ltd. Copyright © 2016 John Wiley &amp; Sons, Ltd.