Richard D. Hedger

Environmental influence on transmitter detection probability in biotelemetry: developing a general model of acoustic transmission

Summary 1. Environmental factors, such as wind, may have a strong influence on the detection probability and detection rate of acoustic telemetry tags. The effect of environmental factors may obscure biological effects and distort the interpretation of acoustic telemetry data. 2. This study was undertaken with fish internally tagged with acoustic transmitters containing depth sensors and monitored by an array of automatic receivers. The influence of environmental factors on the hourly detection rate was evaluated using environmental data from a nearby climate station. The signal detection probability was modelled within the framework of general theory of sound propagation in water. 3. Wind was found to have the strongest influence on the detection rate. Transmitter depth range and rain also contributed signif icantly to the variation in detection rate. 4. By modelling the attenuation coefficient as a function of wind speed, we show that the probability of detecting a free-swimming acoustically tagged animal can be successfully modelled using general sound propagation theory. 5. The approach of modelling detection probability as a function of the attenuation coefficient offers a wide applicability, as it implies a direct link between detection probability and physical characteristics of the water at the study site. Correcting for varying detection probability is in many cases extremely important to do, since rhythms in biological/behavioural factors are often confounded with environmental variables that influence detection probability (e.g. sea breeze, tide).

A quantitative approach for classifying fish otolith strontium: Calcium sequences into environmental histories

Zoning algorithms were used to quantitatively classify strontium:calcium otolith sequences into fish environmental histories. Otoliths were acquired from 162 American eels (Anguilla rostrata) caught in the Gaspe region of Quebec, Canada, and Sr:Ca ratios were determined at an interval of 10 µm along a transect from the core to the edge of each otolith (the otolith sequence) using an electron probe microanalyzer. Changes between freshwater and brackish water occupancy were determined with reference to a sample of non-anadromous species including brook char (freshwater) and Fundulus sp. (brackish water). Three algorithms were then applied separately to zone the sequences into environmental histories: (i) a local zoning algorithm, which used a split-moving window; (ii) a global zoning algorithm, which used a recursive method; and (iii) an optimization zoning algorithm, which maximized the combined value of selected statistics of the fitted model within a decision-rule framework. Zones were further classified into being of either freshwater or brackish water. All algorithms produced classifications that were not significantly different to those determined using the standard approach of qualitative interpretation, demonstrating the applicability of a quantitative approach. The advantages of the quantitative approach are that (i) the statistics of the model fit provide information on environmental history patterns that is generally not available from qualitative interpretation, and (ii) the parameters of the algorithm can be reported, allowing methodological consistency between different researchers, enabling the potential for more robust meta-analyses.

Coupling remote sensing with computational fluid dynamics modelling to estimate lake chlorophyll-a concentration

A remotely sensed image of Loch Leven, a shallow meso-eutrophic lake in Central East Scotland, UK, revealed a strong gradient in chlorophyll-a (chl-a) concentration. As a means of interpreting the spatial distribution of chl-a in this image, a combined three-dimensional computational fluid dynamics (CFD) and ecological model was run using estimates of the environmental and planktonic conditions concurrent with and preceding the time of image acquisition. The post facto modelling of the dynamics of the lake produced spatial distributions of surface chl-a that were consistent with that evident in the remotely sensed image. It is proposed that CFD modelling benefits the interpretation of remotely sensed images of water bodies in that it may be used to infer the causes of the spatial distributions evident in the remotely sensed imagery. This is because modelling extends the analysis into the temporal and vertical domains. However, the value of combining CFD with remote sensing is limited by the quality and quantity of data available through surface observation and remote sensing, and the implications of this to the integration of CFD with remote sensing are discussed.

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.

Ice-dependent winter survival of juvenile Atlantic salmon

Changes in snow and ice conditions are some of the most distinctive impacts of global warming in cold temperate and Arctic regions, altering the environment during a critical period for survival for most animals. Laboratories studies have suggested that reduced ice cover may reduce the survival of stream dwelling fishes in Northern environments. This, however, has not been empirically investigated in natural populations in large rivers. Here, we examine how the winter survival of juvenile Atlantic salmon in a large natural river, the River Alta (Norway, 70°N), is affected by the presence or absence of surface ice. Apparent survival rates for size classes corresponding to parr and presmolts were estimated using capture-mark-recapture and Cormack-Jolly-Seber models for an ice-covered and an ice-free site. Apparent survival (Φ) in the ice-covered site was greater than in the ice-free site, but did not depend on size class (0.64 for both parr and presmolt). In contrast, apparent survival in the ice-free site was lower for larger individuals (0.33) than smaller individuals (0.45). The over-winter decline in storage energy was greater for the ice-free site than the ice-covered site, suggesting that environmental conditions in the ice-free site caused a strong depletion in energy reserves likely affecting survival. Our findings highlight the importance of surface ice for the winter survival of juvenile fish, thus, underpinning that climate change, by reducing ice cover, may have a negative effect on the survival of fish adapted to ice-covered habitats during winter.

Modelling spatial distributions of Ceratium hirundnella and Microcystis spp. in a small productive British lake

The short-term relationships between the spatial distributions of phytoplankton and the environmental conditions of Esthwaite Water, a small eutrophic lake in the English Lake District, UK, were examined using a hydrodynamic model. Spatial distributions of phytoplankton were simulated on two occasions the first, when the population was dominated by dinoflagellates; and the second, when the population was dominated by cyanobacteria.Vertical motility of the dinoflagellate Ceratium hirundinellaand buoyancy of the cyanobacteria Microcystis ssprm.were estimated as functions of irradiance. Water velocity fields were estimated through solving the 3-D Navier–Stokes equations on a finite-volume, unstructured non-orthogonal grid. Simulated circulation patterns of water and phytoplankton were similar to those obtained through field observations. Near-surface drift currents were initiated by wind stress, which then generated return currents along the seasonal thermocline. Aggregations of motile Ceratiumthat existed near the thermocline were pushed upwind by the deep return currents and accumulated at upwelling areas. In contrast, near-surface aggregations of Microcystiswere pushed downwind by the surface currents and accumulated at downwelling areas. Horizontal and vertical phytoplankton distributions resulted from the interaction between the vertical motility of the phytoplankton (dependent upon the light environment) and the velocity vectors at the depths at which the phytoplankton accumulated (dependent upon wind stress and morphometry). Modelling showed that phytoplankton motility and buoyancy greatly affect phytoplankton spatial distributions.

Estimation of velocity fields at the estuary-coastal interface through statistical analysis of successive airborne remotely sensed images

The study of surface water velocity fields through in situ sampling is intrinsically difficult because they are highly variable in time and space. With airborne remote sensing, however, it is possible to determine changes in velocity fields because spatially and temporally comprehensive data may be obtained. This letter shows how changes in the statistical properties of successive remotely sensed images may be used to estimate velocity vectors associated with chlorophyll-a and sea surface temperature (SST). The study area is Kirkcudbright Bay, a small estuary in south-west Scotland. Multi-temporal imagery of the study area were acquired by the NERC Daedalus ADDS-1268 Airborne Thematic Mapper (ATM) and processed to show chlorophyll and thermal indices as substitutes for chlorophyll-a and SST. Velocity fields were estimated by the Maximum Cross Correlation technique. Complex patterns were found, confirming that the comprehensive coverage provided by airborne remote sensing is required for their analysis. The chlorophyll-a velocity field differed from the SST velocity field, suggesting that these fields are relevant to the water quality variable in question, and not necessarily the water body itself.

Using optical and microwave, modeled and airborne data to identify water leaks from rural aqueducts

The development of techniques for the detection of water leaks from underground pipelines is seen as a high profile activity by water companies and regulators. This is due to increasing water demands and problems with current leak detection methods. In this paper optical reflectance and microwave backscatter models (SAIL + PROSPECT and RT2) were used to try and identify optimal indices for detecting water leaks amongst a variety of different land cover types at different growth stages. Results suggest that red/near infrared and red/middle infrared ratios show potential for leak detection. Given the sensitivity of L-band radar to moisture, and the ability to separate contributions from canopy and ground surface, it is possible to detect saturated soils through vegetation canopies. The results of both approaches are used to infer limits of detection in terms of season and meteorological conditions for a range of land covers. Preliminary findings suggest that leaks may be optimally detected when canopy height is low, surrounding soil is dry, and the leak has been present for more than 14 days. The modelled data is compared with L - band fully polarimetric E-SAR data, and 200 channel HYMAP hyperspectral airborne data which were acquired over an 8km section of the Vrynwy aqueduct (UK), which included a high concentration of leaks. Data was acquired as part of the British National Space Centre (BNSC) and Natural Environmental Research Council (NERC), SAR and Hyperspectral Airborne Campaign (SHAC) in June 2000. The results from this work suggest that remote sensing is both an effective and feasible tool for leak identification.

Modelling climate change effects on Atlantic salmon: Implications for mitigation in regulated rivers

Climate change is expected to alter future temperature and discharge regimes of rivers. These regimes have a strong influence on the life history of most aquatic river species, and are key variables controlling the growth and survival of Atlantic salmon. This study explores how the future abundance of Atlantic salmon may be influenced by climate-induced changes in water temperature and discharge in a regulated river, and investigates how negative impacts in the future can be mitigated by applying different regulated discharge regimes during critical periods for salmon survival. A spatially explicit individual-based model was used to predict juvenile Atlantic salmon population abundance in a regulated river under a range of future water temperature and discharge scenarios (derived from climate data predicted by the Hadley Centres Global Climate Model (GCM) HadAm3H and the Max Plank Institutes GCM ECHAM4), which were then compared with populations predicted under control scenarios representing past conditions. Parr abundance decreased in all future scenarios compared to the control scenarios due to reduced wetted areas (with the effect depending on climate scenario, GCM, and GCM spatial domain). To examine the potential for mitigation of climate change-induced reductions in wetted area, simulations were run with specific minimum discharge regimes. An increase in abundance of both parr and smolt occurred with an increase in the limit of minimum permitted discharge for three of the four GCM/GCM spatial domains examined. This study shows that, in regulated rivers with upstream storage capacity, negative effects of climate change on Atlantic salmon populations can potentially be mitigated by release of water from reservoirs during critical periods for juvenile salmon.

Modelling the effect of hydropeaking-induced stranding mortality on Atlantic salmon population abundance: Effect of hydropeaking stranding mortality on Atlantic salmon population abundance

Norwegian Institute for Nature Research, Trondheim NO‐7485, Norway Sweco Norway, Trondheim NO‐7030, Norway SINTEF, Trondheim NO‐7465, Norway Correspondence Richard D. Hedger, Norwegian Institute for Nature Research, Trondheim NO‐7485, Norway. Email: richard.hedger@nina Present Address Julian Sauterleute, Dr. Blasy ‐ Dr. Øverland, Beratende Ingenieure GmbH & Co. KG, Moosstraße 3, 82279 Eching am Ammersee, Germany