Richard Hedger | Norwegian Institute for Nature Research, NINA (original) (raw)

Papers by Richard Hedger

Research paper thumbnail of Improving abundance estimates from electrofishing removal sampling

ABSTRACT Estimates of fish abundance from electrofishing surveys depend on accurate estimation of... more ABSTRACT Estimates of fish abundance from electrofishing surveys depend on accurate estimation of capture probability. We examine in this paper how estimates of capture probability and abundance of Atlantic salmon from multi-pass removal sampling can be improved by comparing the results of an experimental programme of closed electrofishing sites within selected rivers in west-central Norway, and those obtained from open electrofishing sites established for monitoring long-term juvenile Atlantic salmon population abundance within the Burrishoole catchment, western Ireland. We first establish that the Carle & Strub method provides a more robust estimate of population abundance than the Zippin and Seber methods. We then show how prior information on capture probability may be used to improve the accuracy of the abundance estimate in open sites. We also show that the use of prior information with single-pass electrofishing may improve the accuracy of the abundance estimate so that it is comparable with that of multi-pass electrofishing in terms of stock prediction while requiring less sampling effort.

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

1. Environmental factors, such as wind, may have a strong influence on the detection probability ... more 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 significantly 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).

Research paper thumbnail of Effects of salmon lice infection on the behaviour of sea trout in the marine phase

Salmon lice Lepeophtheirus salmonis Krøyer may affect survival and growth of anadromous salmonids... more Salmon lice Lepeophtheirus salmonis Krøyer may affect survival and growth of anadromous salmonids through physiological stress and/or behavioural changes. Using acoustic telemetry tracking, we investigated the behaviour of 30 infected sea trout Salmo trutta throughout the summer in a fjord with very high salmon lice infection pressure. Most of the tracked sea trout adopted a movement pattern expected to suppress salmon lice infestation, as they showed a strong preference for fresh or brackish water, spending most of the time close to a river outlet or even migrating into the river. Highly infested sea trout preferred shallower depths, associated with lower salinity. The fish lost to predation stayed further away from the river outlet than non-predated fish, and were likely subjected to a stronger infection pressure. Half of the tracked group were treated with a salmon lice prophylaxis, emamectin benzoate. The effect of treatment on infestation was monitored in a separate group held in a sea cage and found to be moderate; the mortality in this group was associated with infestation by motile lice stages. In contrast, treatment was not found to have an effect on tracked fish behaviour. It is likely that some physiological and behavioural responses to high salmon lice infection pressure may be present even after a prophylaxis treatment, in particular when the treatment is given after exposure to salmon lice infection. We conclude that increased salmon lice infection pressure associated with altered salmon farming practice may have the potential to influence the marine behaviour and growth of sea trout.

Research paper thumbnail of Spatial dynamics of estuarine water surface temperature from airborne remote sensing

Estuarine, Coastal and Shelf Science, 2007

This paper examines the applicability of airborne remote sensing to the characterization and quan... more This paper examines the applicability of airborne remote sensing to the characterization and quantification of the spatial dynamics of water surface temperature (WST) within estuaries. For this, a series of successive airborne Thematic Mapper thermal images was acquired of Kirkcudbright Bay, an estuary in the United Kingdom, on two dates. Spatial dynamics were determined by two techniques: (1) qualitatively, which involved interpreting features 'by eye'; and (2) by the velocimetric technique of maximum cross correlation (MCC). Qualitatively, complex spatial dynamics were identified over a wide range of spatial and temporal scales, associated with the creation and dissipation of eddies, and the convergence and divergence of fronts, all of which were superimposed on the synoptic tidal flow. MCC was effective for producing synoptic velocity fields, but the minimum cell size was constrained by image noise, limiting the ability to analyze small-scale spatial dynamics. The effectiveness of MCC was related to the ratio of spatially correlated variance to spatially independent variance, as estimated from the variogram. Suggestions for optimizing the application of airborne remote sensing to estuarine spatial dynamics are presented.

Research paper thumbnail of <title>Spatial dynamics of chlorophyll-α and sea surface temperature in a coastal zone as revealed by high-resolution remote sensing</title>

Remote Sensing of the Ocean and Sea Ice 2002, 2003

ABSTRACT

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

International Journal of Remote Sensing, 2001

The study of surface water velocity éelds through in situ sampling is intrinsically diYcult becau... more The study of surface water velocity éelds through in situ sampling is intrinsically diYcult because they are highly variable in time and space. With airborne remote sensing, however, it is possible to determine changes in velocity éelds 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 éelds were estimated by the Maximum Cross Correlation technique. Complex patterns were found, conérming that the comprehensive coverage provided by airborne remote sensing is required for their analysis. The chlorophyll-a velocity éeld diVered from the SST velocity éeld, suggesting that these éelds are relevant to the water quality variable in question, and not necessarily the water body itself.

Research paper thumbnail of Airborne remote sensing for velocity field determination

Research paper thumbnail of Near-coastal surface water velocity field estimation using airborne remote sensing

The study of surface water velocity fields through in situ sampling is intrinsically difficult be... more 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 synoptic changes in velocity fields because spatially and temporally comprehensive data may be obtained. This paper 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 parameter in question, and not necessarily the water body itself.

Research paper thumbnail of Modelling the Horizontal Distribution of Algae in a Water Supply Reservoir

IAHR 28th. Bienneal Congress, …, 1999

Modelling the Horizontal Distribution of Algae in a Water Supply Reservoir. NILS REIDAR B. OLSEN.... more Modelling the Horizontal Distribution of Algae in a Water Supply Reservoir. NILS REIDAR B. OLSEN. Department of Hydraulic and Environmental Engineering. ... D. GLEN GEORGE. Institute of Freshwater Ecology. The Ferry House, Far Sawrey, Ambleside,. Cumbria LA22 0LP, UK. ...

Research paper thumbnail of Atferd hos rømt oppdrettslaks i Sunndalsfjorden

Research paper thumbnail of Spatial Dynamics in Lakes: Modelling Spatial Distributions of Phytoplankton and Their Causative Processes

Research paper thumbnail of Movements and dispersal of farmed Atlantic salmon following a simulated-escape event

Environmental Biology of Fishes, 2013

ABSTRACT One of the major challenges for understanding the ecological impact of escaped farmed At... more ABSTRACT One of the major challenges for understanding the ecological impact of escaped farmed Atlantic salmon (Salmo salar L.) is predicting their dispersal patterns after an escape event. Here, we quantify the behaviour of escaped farmed salmon using a simulated-escape experiment within a Norwegian fjord system. Thirty-seven individuals were tagged with acoustic transmitters and their spatial distribution, horizontal movements and diving behaviour was monitored throughout the fjord and accompanying rivers using 29 acoustic receivers. A rapid movement away from the release site occurred. There was no movement into the rivers feeding the fjord and there was no preference for residence at the fish farms: nearly a third of the individuals had a final detection in the outer part of the fjord and no detections occurred from approximately 2 months after release. As it is unlikely that all fish died or remained undetected within the study area it is reasonable to assume that a substantial proportion of the fish moved out of the fjord system. If a recapture program is not implemented immediately after an escape event, we recommend spreading potential recapture efforts over a relatively large area.

Research paper thumbnail of Net-biting and escape behaviour in farmed Atlantic cod Gadus morhua: effects of feed stimulants and net traits

Preventing farmed fish from escaping sea cages is a major challenge for developing sustainable aq... more Preventing farmed fish from escaping sea cages is a major challenge for developing sustainable aquaculture practices. In this study, the individual behaviour of Atlantic cod Gadus morhua to inspect and bite the net was investigated in 4 replicate multi-patch experiments, using underwater video techniques and behavioural event recording. The experimental system included a tank enclosure where cod were presented with 6 separate net panels: duplicate pairs of plain control nets and 2 different treatment panels. Four holes were made in the treatment panels, 3 of which were mended with different repair techniques including short and loose thread ends and contrasting colour repair threads. Behavioural effects of feed stimulants were studied before, during and after a feed source was placed outside the net. The cod inspected and bit the net systematically, significantly focusing on loose threads or minor damage on the net, and the fish were capable of causing severe net damage within a few days. The observed behaviours were related to hunger level and feed stimulation, and increased significantly during times when a feed source was present outside the net wall. Few bites were observed, and almost no measureable damage was recorded to plain control panels and the area around unrepaired holes during the treatment. Repairs made with white and black threads, and loose, long ends were significantly more damaged than repairs made with short thread ends and threads of similar colour as the net. The experiments demonstrated how a behavioural approach might be used in interpretation of a practical problem in aquaculture, and the results will be useful in the development of technology and escape mitigation strategies.

Research paper thumbnail of Improving abundance estimates from electrofishing removal sampling

Fisheries Research, 2013

ABSTRACT Estimates of fish abundance from electrofishing surveys depend on accurate estimation of... more ABSTRACT Estimates of fish abundance from electrofishing surveys depend on accurate estimation of capture probability. We examine in this paper how estimates of capture probability and abundance of Atlantic salmon from multi-pass removal sampling can be improved by comparing the results of an experimental programme of closed electrofishing sites within selected rivers in west-central Norway, and those obtained from open electrofishing sites established for monitoring long-term juvenile Atlantic salmon population abundance within the Burrishoole catchment, western Ireland. We first establish that the Carle &amp; Strub method provides a more robust estimate of population abundance than the Zippin and Seber methods. We then show how prior information on capture probability may be used to improve the accuracy of the abundance estimate in open sites. We also show that the use of prior information with single-pass electrofishing may improve the accuracy of the abundance estimate so that it is comparable with that of multi-pass electrofishing in terms of stock prediction while requiring less sampling effort.

Research paper thumbnail of Using optical and microwave, modelled 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... more 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

Research paper thumbnail of Near-coastal surface water velocity field estimation using airborne remote sensing

The study of surface water velocity fields through in situ sampling is intrinsically difficult be... more 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 synoptic changes in velocity fields because spatially and temporally comprehensive data may be obtained. This paper 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 parameter in question, and not necessarily the water body itself.

Research paper thumbnail of Dynamic modelling to simulate chlorophyll-a concentration in a remotely sensed image of Loch Leven

Research paper thumbnail of Spatial dynamics of chlorophyll-α and sea surface temperature in a coastal zone as revealed by high-resolution remote sensing

Research paper thumbnail of Automated feature discrimination for optimizing water supply networks

The traditional approach to delineating and extracting features from remotely sensed images relie... more The traditional approach to delineating and extracting features from remotely sensed images relies predominantly on manual interpretation, a procedure that is often time consuming and expensive. Automation offers the potential for reduced costs and wider utilization of remote sensing within the business community, but involves difficulty in representing the expertise of remote sensing scientists within a series of decision rules.

Research paper thumbnail of Wild salmon populations in a changing climate

Research paper thumbnail of Improving abundance estimates from electrofishing removal sampling

ABSTRACT Estimates of fish abundance from electrofishing surveys depend on accurate estimation of... more ABSTRACT Estimates of fish abundance from electrofishing surveys depend on accurate estimation of capture probability. We examine in this paper how estimates of capture probability and abundance of Atlantic salmon from multi-pass removal sampling can be improved by comparing the results of an experimental programme of closed electrofishing sites within selected rivers in west-central Norway, and those obtained from open electrofishing sites established for monitoring long-term juvenile Atlantic salmon population abundance within the Burrishoole catchment, western Ireland. We first establish that the Carle &amp; Strub method provides a more robust estimate of population abundance than the Zippin and Seber methods. We then show how prior information on capture probability may be used to improve the accuracy of the abundance estimate in open sites. We also show that the use of prior information with single-pass electrofishing may improve the accuracy of the abundance estimate so that it is comparable with that of multi-pass electrofishing in terms of stock prediction while requiring less sampling effort.

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

1. Environmental factors, such as wind, may have a strong influence on the detection probability ... more 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 significantly 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).

Research paper thumbnail of Effects of salmon lice infection on the behaviour of sea trout in the marine phase

Salmon lice Lepeophtheirus salmonis Krøyer may affect survival and growth of anadromous salmonids... more Salmon lice Lepeophtheirus salmonis Krøyer may affect survival and growth of anadromous salmonids through physiological stress and/or behavioural changes. Using acoustic telemetry tracking, we investigated the behaviour of 30 infected sea trout Salmo trutta throughout the summer in a fjord with very high salmon lice infection pressure. Most of the tracked sea trout adopted a movement pattern expected to suppress salmon lice infestation, as they showed a strong preference for fresh or brackish water, spending most of the time close to a river outlet or even migrating into the river. Highly infested sea trout preferred shallower depths, associated with lower salinity. The fish lost to predation stayed further away from the river outlet than non-predated fish, and were likely subjected to a stronger infection pressure. Half of the tracked group were treated with a salmon lice prophylaxis, emamectin benzoate. The effect of treatment on infestation was monitored in a separate group held in a sea cage and found to be moderate; the mortality in this group was associated with infestation by motile lice stages. In contrast, treatment was not found to have an effect on tracked fish behaviour. It is likely that some physiological and behavioural responses to high salmon lice infection pressure may be present even after a prophylaxis treatment, in particular when the treatment is given after exposure to salmon lice infection. We conclude that increased salmon lice infection pressure associated with altered salmon farming practice may have the potential to influence the marine behaviour and growth of sea trout.

Research paper thumbnail of Spatial dynamics of estuarine water surface temperature from airborne remote sensing

Estuarine, Coastal and Shelf Science, 2007

This paper examines the applicability of airborne remote sensing to the characterization and quan... more This paper examines the applicability of airborne remote sensing to the characterization and quantification of the spatial dynamics of water surface temperature (WST) within estuaries. For this, a series of successive airborne Thematic Mapper thermal images was acquired of Kirkcudbright Bay, an estuary in the United Kingdom, on two dates. Spatial dynamics were determined by two techniques: (1) qualitatively, which involved interpreting features 'by eye'; and (2) by the velocimetric technique of maximum cross correlation (MCC). Qualitatively, complex spatial dynamics were identified over a wide range of spatial and temporal scales, associated with the creation and dissipation of eddies, and the convergence and divergence of fronts, all of which were superimposed on the synoptic tidal flow. MCC was effective for producing synoptic velocity fields, but the minimum cell size was constrained by image noise, limiting the ability to analyze small-scale spatial dynamics. The effectiveness of MCC was related to the ratio of spatially correlated variance to spatially independent variance, as estimated from the variogram. Suggestions for optimizing the application of airborne remote sensing to estuarine spatial dynamics are presented.

Research paper thumbnail of <title>Spatial dynamics of chlorophyll-α and sea surface temperature in a coastal zone as revealed by high-resolution remote sensing</title>

Remote Sensing of the Ocean and Sea Ice 2002, 2003

ABSTRACT

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

International Journal of Remote Sensing, 2001

The study of surface water velocity éelds through in situ sampling is intrinsically diYcult becau... more The study of surface water velocity éelds through in situ sampling is intrinsically diYcult because they are highly variable in time and space. With airborne remote sensing, however, it is possible to determine changes in velocity éelds 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 éelds were estimated by the Maximum Cross Correlation technique. Complex patterns were found, conérming that the comprehensive coverage provided by airborne remote sensing is required for their analysis. The chlorophyll-a velocity éeld diVered from the SST velocity éeld, suggesting that these éelds are relevant to the water quality variable in question, and not necessarily the water body itself.

Research paper thumbnail of Airborne remote sensing for velocity field determination

Research paper thumbnail of Near-coastal surface water velocity field estimation using airborne remote sensing

The study of surface water velocity fields through in situ sampling is intrinsically difficult be... more 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 synoptic changes in velocity fields because spatially and temporally comprehensive data may be obtained. This paper 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 parameter in question, and not necessarily the water body itself.

Research paper thumbnail of Modelling the Horizontal Distribution of Algae in a Water Supply Reservoir

IAHR 28th. Bienneal Congress, …, 1999

Modelling the Horizontal Distribution of Algae in a Water Supply Reservoir. NILS REIDAR B. OLSEN.... more Modelling the Horizontal Distribution of Algae in a Water Supply Reservoir. NILS REIDAR B. OLSEN. Department of Hydraulic and Environmental Engineering. ... D. GLEN GEORGE. Institute of Freshwater Ecology. The Ferry House, Far Sawrey, Ambleside,. Cumbria LA22 0LP, UK. ...

Research paper thumbnail of Atferd hos rømt oppdrettslaks i Sunndalsfjorden

Research paper thumbnail of Spatial Dynamics in Lakes: Modelling Spatial Distributions of Phytoplankton and Their Causative Processes

Research paper thumbnail of Movements and dispersal of farmed Atlantic salmon following a simulated-escape event

Environmental Biology of Fishes, 2013

ABSTRACT One of the major challenges for understanding the ecological impact of escaped farmed At... more ABSTRACT One of the major challenges for understanding the ecological impact of escaped farmed Atlantic salmon (Salmo salar L.) is predicting their dispersal patterns after an escape event. Here, we quantify the behaviour of escaped farmed salmon using a simulated-escape experiment within a Norwegian fjord system. Thirty-seven individuals were tagged with acoustic transmitters and their spatial distribution, horizontal movements and diving behaviour was monitored throughout the fjord and accompanying rivers using 29 acoustic receivers. A rapid movement away from the release site occurred. There was no movement into the rivers feeding the fjord and there was no preference for residence at the fish farms: nearly a third of the individuals had a final detection in the outer part of the fjord and no detections occurred from approximately 2 months after release. As it is unlikely that all fish died or remained undetected within the study area it is reasonable to assume that a substantial proportion of the fish moved out of the fjord system. If a recapture program is not implemented immediately after an escape event, we recommend spreading potential recapture efforts over a relatively large area.

Research paper thumbnail of Net-biting and escape behaviour in farmed Atlantic cod Gadus morhua: effects of feed stimulants and net traits

Preventing farmed fish from escaping sea cages is a major challenge for developing sustainable aq... more Preventing farmed fish from escaping sea cages is a major challenge for developing sustainable aquaculture practices. In this study, the individual behaviour of Atlantic cod Gadus morhua to inspect and bite the net was investigated in 4 replicate multi-patch experiments, using underwater video techniques and behavioural event recording. The experimental system included a tank enclosure where cod were presented with 6 separate net panels: duplicate pairs of plain control nets and 2 different treatment panels. Four holes were made in the treatment panels, 3 of which were mended with different repair techniques including short and loose thread ends and contrasting colour repair threads. Behavioural effects of feed stimulants were studied before, during and after a feed source was placed outside the net. The cod inspected and bit the net systematically, significantly focusing on loose threads or minor damage on the net, and the fish were capable of causing severe net damage within a few days. The observed behaviours were related to hunger level and feed stimulation, and increased significantly during times when a feed source was present outside the net wall. Few bites were observed, and almost no measureable damage was recorded to plain control panels and the area around unrepaired holes during the treatment. Repairs made with white and black threads, and loose, long ends were significantly more damaged than repairs made with short thread ends and threads of similar colour as the net. The experiments demonstrated how a behavioural approach might be used in interpretation of a practical problem in aquaculture, and the results will be useful in the development of technology and escape mitigation strategies.

Research paper thumbnail of Improving abundance estimates from electrofishing removal sampling

Fisheries Research, 2013

ABSTRACT Estimates of fish abundance from electrofishing surveys depend on accurate estimation of... more ABSTRACT Estimates of fish abundance from electrofishing surveys depend on accurate estimation of capture probability. We examine in this paper how estimates of capture probability and abundance of Atlantic salmon from multi-pass removal sampling can be improved by comparing the results of an experimental programme of closed electrofishing sites within selected rivers in west-central Norway, and those obtained from open electrofishing sites established for monitoring long-term juvenile Atlantic salmon population abundance within the Burrishoole catchment, western Ireland. We first establish that the Carle &amp; Strub method provides a more robust estimate of population abundance than the Zippin and Seber methods. We then show how prior information on capture probability may be used to improve the accuracy of the abundance estimate in open sites. We also show that the use of prior information with single-pass electrofishing may improve the accuracy of the abundance estimate so that it is comparable with that of multi-pass electrofishing in terms of stock prediction while requiring less sampling effort.

Research paper thumbnail of Using optical and microwave, modelled 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... more 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

Research paper thumbnail of Near-coastal surface water velocity field estimation using airborne remote sensing

The study of surface water velocity fields through in situ sampling is intrinsically difficult be... more 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 synoptic changes in velocity fields because spatially and temporally comprehensive data may be obtained. This paper 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 parameter in question, and not necessarily the water body itself.

Research paper thumbnail of Dynamic modelling to simulate chlorophyll-a concentration in a remotely sensed image of Loch Leven

Research paper thumbnail of Spatial dynamics of chlorophyll-α and sea surface temperature in a coastal zone as revealed by high-resolution remote sensing

Research paper thumbnail of Automated feature discrimination for optimizing water supply networks

The traditional approach to delineating and extracting features from remotely sensed images relie... more The traditional approach to delineating and extracting features from remotely sensed images relies predominantly on manual interpretation, a procedure that is often time consuming and expensive. Automation offers the potential for reduced costs and wider utilization of remote sensing within the business community, but involves difficulty in representing the expertise of remote sensing scientists within a series of decision rules.

Research paper thumbnail of Wild salmon populations in a changing climate