Acoustic telemetry is widely used to investigate aquatic animal movement. Pulse position modulati... more Acoustic telemetry is widely used to investigate aquatic animal movement. Pulse position modulation (PPM) is an acoustic telemetry method that allows multiple unique identification codes to be transmitted at a single acoustic frequency, typically in the 69 kHz range. However, because the potential number of unique identification codes (i.e. tags) is ultimately limited by the number of pulses in the PPM signal, this poses a practical limitation. In addition, different manufacturers have developed different approaches to encoding the transmitted data, hampering compatibility across brands. A lack of broad compatibility across telemetry systems restricts users to a single manufacturer and operating system, reduces market competition and limits innovation. As the aquatic animal tracking research community organises towards networks of devices and data, incompatibility becomes more problematic and jeopardizes the unique scientific benefits offered by the networking approach. Here, we mak...
ABSTRACT It has been shown that sharks may benefit from the protection of marine protected areas ... more ABSTRACT It has been shown that sharks may benefit from the protection of marine protected areas (MPAs), however, the degree of protection has not been quantified for a commercially valuable elasmobranch species. The movement of 24 smoothhound sharks (Mustelus mustelus) in and adjacent to a small (34 km2) no-take MPA situated on the West Coast of South Africa were investigated over two years using acoustic telemetry. The sharks spent the majority of thier time (average 79%) inside the reserve and some sharks (n=5 of 15) did not leave the MPA during the observation period. Time spent inside the MPA and the number of crossings of the MPA boundary was strongly influenced by season. The sharks concentrated inside the MPA during summer and were widely distributed throughout the study area during winter months. Six sharks left the Saldanha Bay embayment during spring and winter periods for durations ranging from two to 156 days (meian=111 days). All sharks returned to the bay within the study period. During 2007 and 2008, the sharks spent an average of 74% and 80% inside the MPA, respectively. The extended residency of smoothhound sharks within the MPA suggests that no-take area protection is a viable management option for this species.
Repeat spawners constitute an important component of Atlantic salmon populations, but survival of... more Repeat spawners constitute an important component of Atlantic salmon populations, but survival of post-spawning individuals (kelts) are often compromised by anthropogenic structures such as hydropower plants (HPPs). Potential effects of HPPs include migration delays and associated increased energy depletion, which potentially results in increased overall mortality. We combined a detailed 3D hydraulic model with high-resolution 3D tracking of tagged kelts (length 73–104 cm) to obtain estimates of kelt movement through water. These estimates were then used in an energetics model to estimate hourly energy expenditure while negotiating the HPP area. Hourly kelt energy expenditure varied between 0.8 and 10.1 kJ × h−1 and was dependent on kelt length. Degree of additional energy depletion can amount to several percent of remaining energy content (our study indicates 4–5 percentage points) potentially leading to reduced post-spawning survival. In turn, this can nullify the iteroparous bree...
The spawning migration of the European eel (Anguilla anguilla L.) to the Sargasso Sea is one of t... more The spawning migration of the European eel (Anguilla anguilla L.) to the Sargasso Sea is one of the greatest animal migrations. However, the duration and route of the migration remain uncertain. Using fishery data from 20 rivers across Europe, we show that most eels begin their oceanic migration between August and December. We used electronic tagging techniques to map the oceanic migration from eels released from four regions in Europe. Of 707 eels tagged, we received 206 data sets. Many migrations ended soon after release because of predation events, but we were able to reconstruct in detail the migration routes of >80 eels. The route extended from western mainland Europe to the Azores region, more than 5000 km toward the Sargasso Sea. All eels exhibited diel vertical migrations, moving from deeper water during the day into shallower water at night. The range of migration speeds was 3 to 47 km day(-1). Using data from larval surveys in the Sargasso Sea, we show that spawning lik...
ABSTRACT Radio tagged wild Atlantic salmon Salmo salar (n = 30) and sea trout Salmo trutta (n = 1... more ABSTRACT Radio tagged wild Atlantic salmon Salmo salar (n = 30) and sea trout Salmo trutta (n = 19) were simultaneously released from a sea pen outside the mouth of the River L ae rdalselva and their migration to spawning areas was recorded. The distance from the river mouth to a position held at spawning ranged from 2 to 24 kin and did not differ between the species (mean +/- S.D. 15(.)9 +/- 4(.)3 and 14(.)9 +/- 5(.)2 km for Atlantic salmon and sea trout, respectively). The duration of the migration phase, however, was significantly shorter for Atlantic salmon than for sea trout (8-12 days, respectively). All Atlantic salmon migrated straight to an area near the spawning ground, whereas 50% of the sea trout had a stepwise progression with one or more periods with erratic movements before reaching the spawning area. After the migration phase, a distinct search phase with repeated movements up- and downstream at or close to the position held at spawning was identified for the majority of the fishes (75%, both species). This search phase was significantly shorter for Atlantic salmon than for sea trout (mean 13-31 days, respectively). Mean +/- S.D. length of the river stretch used during the search phase was larger for sea trout (3(.)3 +/- 2(.)5 km) than for Atlantic salmon (1(.)2 +/- 0(.)9 km). A distinct holding phase, with no movements until spawning, was also observed in the majority of the Atlantic salmon (80%, mean duration 22 days) and sea trout (65%, mean duration 12 days). For both species, a weak, non-significant trend was observed in the relationship between time spent on the migration phase, and time spent on the search (r(2) = 0.43) and holding phase (r(2) 0.24). There was a highly significant decrease, however, in the duration of the holding phase with an increase in the time spent on the search phase (r(2) = 0.67). (c) 2005 The Fisheries Society of the British Isles.
An overview of electronic tags that can be used in fish research is given, including radio and ac... more An overview of electronic tags that can be used in fish research is given, including radio and acoustic transmitters, data storage tags (DST, also termed archival tags), pop-up satellite archival tags (PSAT) and passive integrated transponder tags (PIT-tag). Fish telemetry is a term used to describe the application of these methods. Typically, an electronic tag is attached to a free-swimming fish, and information on position, movements and/or measurements of environmental and physiological parameters can be recorded wirelessly by use of a mobile receiver or stationary loggers. For most methods, the fish need not to be recaptured to achieve data. However, DSTs record and store information on environmental and/or physiological parameters in the tag, and therefore need to be retrieved for downloading data. In the case of PSATs, stored data is transferred to satellites when the tag loosens from the fish and pops up to the surface, and in addition, the pop up position is recorded. The de...
Acoustic telemetry is widely used to investigate aquatic animal movement. Pulse position modulati... more Acoustic telemetry is widely used to investigate aquatic animal movement. Pulse position modulation (PPM) is an acoustic telemetry method that allows multiple unique identification codes to be transmitted at a single acoustic frequency, typically in the 69 kHz range. However, because the potential number of unique identification codes (i.e. tags) is ultimately limited by the number of pulses in the PPM signal, this poses a practical limitation. In addition, different manufacturers have developed different approaches to encoding the transmitted data, hampering compatibility across brands. A lack of broad compatibility across telemetry systems restricts users to a single manufacturer and operating system, reduces market competition and limits innovation. As the aquatic animal tracking research community organises towards networks of devices and data, incompatibility becomes more problematic and jeopardizes the unique scientific benefits offered by the networking approach. Here, we mak...
ABSTRACT It has been shown that sharks may benefit from the protection of marine protected areas ... more ABSTRACT It has been shown that sharks may benefit from the protection of marine protected areas (MPAs), however, the degree of protection has not been quantified for a commercially valuable elasmobranch species. The movement of 24 smoothhound sharks (Mustelus mustelus) in and adjacent to a small (34 km2) no-take MPA situated on the West Coast of South Africa were investigated over two years using acoustic telemetry. The sharks spent the majority of thier time (average 79%) inside the reserve and some sharks (n=5 of 15) did not leave the MPA during the observation period. Time spent inside the MPA and the number of crossings of the MPA boundary was strongly influenced by season. The sharks concentrated inside the MPA during summer and were widely distributed throughout the study area during winter months. Six sharks left the Saldanha Bay embayment during spring and winter periods for durations ranging from two to 156 days (meian=111 days). All sharks returned to the bay within the study period. During 2007 and 2008, the sharks spent an average of 74% and 80% inside the MPA, respectively. The extended residency of smoothhound sharks within the MPA suggests that no-take area protection is a viable management option for this species.
Repeat spawners constitute an important component of Atlantic salmon populations, but survival of... more Repeat spawners constitute an important component of Atlantic salmon populations, but survival of post-spawning individuals (kelts) are often compromised by anthropogenic structures such as hydropower plants (HPPs). Potential effects of HPPs include migration delays and associated increased energy depletion, which potentially results in increased overall mortality. We combined a detailed 3D hydraulic model with high-resolution 3D tracking of tagged kelts (length 73–104 cm) to obtain estimates of kelt movement through water. These estimates were then used in an energetics model to estimate hourly energy expenditure while negotiating the HPP area. Hourly kelt energy expenditure varied between 0.8 and 10.1 kJ × h−1 and was dependent on kelt length. Degree of additional energy depletion can amount to several percent of remaining energy content (our study indicates 4–5 percentage points) potentially leading to reduced post-spawning survival. In turn, this can nullify the iteroparous bree...
The spawning migration of the European eel (Anguilla anguilla L.) to the Sargasso Sea is one of t... more The spawning migration of the European eel (Anguilla anguilla L.) to the Sargasso Sea is one of the greatest animal migrations. However, the duration and route of the migration remain uncertain. Using fishery data from 20 rivers across Europe, we show that most eels begin their oceanic migration between August and December. We used electronic tagging techniques to map the oceanic migration from eels released from four regions in Europe. Of 707 eels tagged, we received 206 data sets. Many migrations ended soon after release because of predation events, but we were able to reconstruct in detail the migration routes of >80 eels. The route extended from western mainland Europe to the Azores region, more than 5000 km toward the Sargasso Sea. All eels exhibited diel vertical migrations, moving from deeper water during the day into shallower water at night. The range of migration speeds was 3 to 47 km day(-1). Using data from larval surveys in the Sargasso Sea, we show that spawning lik...
ABSTRACT Radio tagged wild Atlantic salmon Salmo salar (n = 30) and sea trout Salmo trutta (n = 1... more ABSTRACT Radio tagged wild Atlantic salmon Salmo salar (n = 30) and sea trout Salmo trutta (n = 19) were simultaneously released from a sea pen outside the mouth of the River L ae rdalselva and their migration to spawning areas was recorded. The distance from the river mouth to a position held at spawning ranged from 2 to 24 kin and did not differ between the species (mean +/- S.D. 15(.)9 +/- 4(.)3 and 14(.)9 +/- 5(.)2 km for Atlantic salmon and sea trout, respectively). The duration of the migration phase, however, was significantly shorter for Atlantic salmon than for sea trout (8-12 days, respectively). All Atlantic salmon migrated straight to an area near the spawning ground, whereas 50% of the sea trout had a stepwise progression with one or more periods with erratic movements before reaching the spawning area. After the migration phase, a distinct search phase with repeated movements up- and downstream at or close to the position held at spawning was identified for the majority of the fishes (75%, both species). This search phase was significantly shorter for Atlantic salmon than for sea trout (mean 13-31 days, respectively). Mean +/- S.D. length of the river stretch used during the search phase was larger for sea trout (3(.)3 +/- 2(.)5 km) than for Atlantic salmon (1(.)2 +/- 0(.)9 km). A distinct holding phase, with no movements until spawning, was also observed in the majority of the Atlantic salmon (80%, mean duration 22 days) and sea trout (65%, mean duration 12 days). For both species, a weak, non-significant trend was observed in the relationship between time spent on the migration phase, and time spent on the search (r(2) = 0.43) and holding phase (r(2) 0.24). There was a highly significant decrease, however, in the duration of the holding phase with an increase in the time spent on the search phase (r(2) = 0.67). (c) 2005 The Fisheries Society of the British Isles.
An overview of electronic tags that can be used in fish research is given, including radio and ac... more An overview of electronic tags that can be used in fish research is given, including radio and acoustic transmitters, data storage tags (DST, also termed archival tags), pop-up satellite archival tags (PSAT) and passive integrated transponder tags (PIT-tag). Fish telemetry is a term used to describe the application of these methods. Typically, an electronic tag is attached to a free-swimming fish, and information on position, movements and/or measurements of environmental and physiological parameters can be recorded wirelessly by use of a mobile receiver or stationary loggers. For most methods, the fish need not to be recaptured to achieve data. However, DSTs record and store information on environmental and/or physiological parameters in the tag, and therefore need to be retrieved for downloading data. In the case of PSATs, stored data is transferred to satellites when the tag loosens from the fish and pops up to the surface, and in addition, the pop up position is recorded. The de...
Uploads
Papers by F. Økland