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1. Movement patterns of juvenile Atlantic tarpon (Megalops atlanticus) in Brewers Bay, St. Thomas, U.S. Virgin Islands

   https://doi.org/10.1186/s40317-021-00239-x  

   Duffing Romero, Mareike D. ; Matley, Jordan K. ; Luo, Jiangang ; Ault, Jerald S. ; Pittman, Simon J. ; Nemeth, Richard S. ( May 2021 , Animal Biotelemetry)

   Atlantic tarpon (Megalops atlanticus) are a highly migratory species ranging along continental and insular coastlines of the Atlantic Ocean. Due to their importance to regional recreational and sport fisheries, research has been focused on large-scale movement patterns of reproductively active adults in areas where they are of high economic value. As a consequence, geographically restricted focus on adults has left significant gaps in our understanding of tarpon biology and their movements, especially for juveniles in remote locations where they are common. Our study focused on small-scale patterns of movement and habitat use of juvenile tarpon using acoustic telemetry in a small bay in St. Thomas, US Virgin Islands.

   Four juvenile tarpon (80–95 cm FL) were tracked from September 2015 to February 2018, while an additional eight juveniles (61–94 cm FL) left the study area within 2 days after tagging and were not included in analysis. Four tarpon had > 78% residency and average activity space of 0.76 km²(range 0.08–1.17 km²) within Brewers Bay (1.8 km²). Their vertical distribution was < 18 m depth with occasional movements to deeper water. Activity was greater during day compared to night, with peaks during crepuscular periods. During the day tarpon used different parts of the bay with consistent overlap around the St. Thomas airport runway and at night tarpon typically remained in a small shallow lagoon. However, when temperatures in the lagoon exceeded 30 °C, tarpon moved to cooler, deeper waters outside the lagoon.

   Our results, although limited to only four individuals, provide new baseline data on the movement ecology of juvenile Atlantic tarpon. We showed that juvenile tarpon had high residency within a small bay and relatively stable non-overlapping daytime home ranges, except when seasonally abundant food sources were present. Fine-scale acoustic tracking showed the effects of environmental conditions (i.e., elevated seawater temperature) on tarpon movement and habitat use. These observations highlight the need for more extensive studies of juvenile tarpon across a broader range of their distribution, and compare the similarities and differences in behavior among various size classes of individuals from small juveniles to reproductively mature adults.

    

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2. Trophic interactions among algal blooms, macroinvertebrates, and brown trout: Implications for trout recovery in a restored river

   https://doi.org/10.1002/rra.3523  

   Peipoch, Marc ; Valett, Herbert Maurice ( August 2019 , River Research and Applications)

   Positive correlation between trout abundance and dissolved metal concentrations along the Upper Clark Fork River (UCFR; Montana, USA) have forced restoration practitioners to seek underlying causes of reduced fish density beyond heavy metal contamination. Throughout the river, nutrient enrichment and summer algal blooms may be hindering full recovery of trout populations. In this study, we evaluated the community structure and metal body burdens of benthic invertebrates and characterized existing trophic linkages between brown trout and dominant invertebrate taxa before and during summer algal blooms in a downstream reach of the UCFR where fish densities are low (20–30 trout/km), and where metal contamination is relevant but minimal compared with upstream. In spring, estimated invertebrate abundance was 1,727 ± 217 individuals/m²and dominated by Ephemerellidae and Baetidae families. During summer algal bloom, invertebrate abundance increased 15‐fold (20,580 ± 3,510 individuals/m²) mostly due to greater abundance of Chironomidae, Hydropsychidae, and Simulidae. Copper body burdens (130 ± 42 ppm) were higher than any other heavy metal regardless of season, but detectable concentrations of arsenic, cadmium, and lead were also found. A Bayesian mixing model combining metal burdens and stable isotopes showed that in the spring, trout of average size (355 ± 65 g) relied mostly on epibenthic taxa (Ephemerellidae and Hydropsychidae), contrasting with small (<100 g) and large (>400 g) trout relying heavily on Baetidae, a major component of invertebrate drift. Foraging segregation related to trout size did not occur during summer algal blooms, which may reflect increasing influence of benthic algal proliferation or indicate the indiscriminate use of pool habitats as thermal refugia over summer conditions by trout of different ages.

    

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3. Landscape geomorphology and local‐riverine features influence Broad Whitefish ( Coregonus nasus ) spawning habitat suitability in Arctic Alaska

   https://doi.org/10.1111/eff.12657  

   Leppi, Jason C. ; Falke, Jeffrey A. ; Rinella, Daniel J. ; Wipfli, Mark S. ; Seitz, Andrew C. ; Whitman, Matthew S. ( March 2022 , Ecology of Freshwater Fish)

   Landscape‐level geomorphic processes influence the spatial and temporal arrangement of fish habitats in freshwater ecosystems and fishes move across riverscapes, selecting a suite of habitats to maximise fitness. Here, we explore the influence of geomorphology on stream channel attributes and assess Broad Whitefish (Coregonus nasus) spawning habitat potential in the Colville River in Arctic Alaska. Using high‐resolution digital surface models (5 m²), we quantified the stream network extent and summarised channel habitat attributes continuously across the drainage network. Next, we developed an intrinsic potential (IP) model for Broad Whitefish by using geomorphic channel parameters previously understood to be associated with spawning habitats (channel width, median substrate size and channel braiding) to estimate the potential of streams across the Colville River watershed to provide spawning habitat. Our model results show the majority of habitat with high IP (≥0.6) was located within the braided sections of the main channel, which encompass >1548 km, but only 2% of the total channel network. The IP model was tested by tracking radio‐tagged Broad Whitefish using aerial surveys. Prespawn fish moved into the watershed starting mid‐July and mostly used habitat with moderate to very high IP in the middle and lower watershed. Several individuals were relocated in smaller multichannels with vegetated bars that contained very low IP (≤0.2), suggesting that other factors, such as hyporheic flow, may also influence spawning habitat selection. Our study demonstrates that IP modelling offers a useful method to quantify spawning habitat potential in data‐poor riverscapes, providing useful information for managers to assess potential anthropogenic impacts and develop conservation plans to protect essential Broad Whitefish habitat.

    

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4. Quantifying thermal refugia connectivity by combining temperature modeling, distributed temperature sensing, and thermal infrared imaging

   https://doi.org/10.5194/hess-23-2965-2019  

   Dzara, Jessica R. ; Neilson, Bethany T. ; Null, Sarah E. ( January 2019 , Hydrology and Earth System Sciences)

   Abstract. Watershed-scale stream temperature models are often one-dimensional because they require fewer data and are more computationally efficient than two- or three-dimensional models. However, one-dimensional models assume completely mixed reaches and ignore small-scale spatial temperature variability, which may create temperature barriers or refugia for cold-water aquatic species. Fine spatial- and temporal-resolution stream temperature monitoring provides information to identify river features with increased thermal variability. We used distributed temperature sensing (DTS) to observe small-scale stream temperature variability, measured as a temperature range through space and time, within two 400 m reaches in summer 2015 in Nevada's East Walker and main stem Walker rivers. Thermal infrared (TIR) aerial imagery collected in summer 2012 quantified the spatial temperature variability throughout the Walker Basin. We coupled both types of high-resolution measured data with simulated stream temperatures to corroborate model results and estimate the spatial distribution of thermal refugia for Lahontan cutthroat trout and other cold-water species. Temperature model estimates were within the DTS-measured temperature ranges 21 % and 70 % of the time for the East Walker River and main stem Walker River, respectively, and within TIR-measured temperatures 17 %, 5 %, and 5 % of the time for the East Walker, West Walker, and main stem Walker rivers, respectively. DTS, TIR, and modeled stream temperatures in the main stem Walker River nearly always exceeded the 21 ∘C optimal temperature threshold for adult trout, usually exceeded the 24 ∘C stress threshold, and could exceed the 28 ∘C lethal threshold for Lahontan cutthroat trout. Measured stream temperature ranges bracketed ambient river temperatures by −10.1 to +2.3 ∘C in agricultural return flows, −1.2 to +4 ∘C at diversions, −5.1 to +2 ∘C in beaver dams, and −4.2 to 0 ∘C at seeps. To better understand the role of these river features on thermal refugia during warm time periods, the respective temperature ranges were added to simulated stream temperatures at each of the identified river features. Based on this analysis, the average distance between thermal refugia in this system was 2.8 km. While simulated stream temperatures are often too warm to support Lahontan cutthroat trout and other cold-water species, thermal refugia may exist to improve habitat connectivity and facilitate trout movement between spawning and summer habitats. Overall, high-resolution DTS and TIR measurements quantify temperature ranges of refugia and augment process-based modeling. 

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5. Characterization of acoustic detection efficiency using a gliding robotic fish as a mobile receiver platform

   https://doi.org/10.1186/s40317-020-00219-7  

   Ennasr, Osama ; Holbrook, Christopher ; Hondorp, Darryl W. ; Krueger, Charles C. ; Coleman, Demetris ; Solanki, Pratap ; Thon, John ; Tan, Xiaobo ( December 2020 , Animal Biotelemetry)

   null (Ed.)

   Abstract Background Autonomous underwater vehicles (AUVs) and animal telemetry have become important tools for understanding the relationships between aquatic organisms and their environment, but more information is needed to guide the development and use of AUVs as effective animal tracking platforms. A forward-facing acoustic telemetry receiver (VR2Tx 69 kHz; VEMCO, Bedford, Nova Scotia) attached to a novel AUV (gliding robotic fish) was tested in a freshwater lake to (1) compare its detection efficiency (i.e., the probability of detecting an acoustic signal emitted by a tag) of acoustic tags (VEMCO model V8-4H 69 kHz) to stationary receivers and (2) determine if detection efficiency was related to distance between tag and receiver, direction of movement (toward or away from transmitter), depth, or pitch. Results Detection efficiency for mobile (robot-mounted) and stationary receivers were similar at ranges less than 300 m, on average across all tests, but detection efficiency for the mobile receiver decreased faster than for stationary receivers at distances greater than 300 m. Detection efficiency was higher when the robot was moving toward the transmitter than when moving away from the transmitter. Detection efficiency decreased with depth (surface to 4 m) when the robot was moving away from the transmitter, but depth had no significant effect on detection efficiency when the robot was moving toward the transmitter. Detection efficiency was higher when the robot was descending (pitched downward) than ascending (pitched upward) when moving toward the transmitter, but pitch had no significant effect when moving away from the transmitter. Conclusion Results suggested that much of the observed variation in detection efficiency is related to shielding of the acoustic signal by the robot body depending on the positions and orientation of the hydrophone relative to the transmitter. Results are expected to inform hardware, software, and operational changes to gliding robotic fish that will improve detection efficiency. Regardless, data on the size and shape of detection efficiency curves for gliding robotic fish will be useful for planning future missions and should be relevant to other AUVs for telemetry. With refinements, gliding robotic fish could be a useful platform for active tracking of acoustic tags in certain environments. 

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