Facilitating behavioural adaptation in Atlantic salmon to improve welfare in depth modified cages
Atlantic salmon require surface access to refill their swim bladder and regulate buoyancy. As depth-modified cages aimed at sea lice prevention increase in popularity, salmon are forced to adapt to complex rearing environments. In a new sea-cage, the submerged air-dome cage, salmon must learn to refill their swim bladder underwater at an air-dome or will become negatively buoyant. We plan to investigate (1) whether habituation to air-domes during the freshwater phase of production can facilitate adaptation to air-dome sea-cages and (2) whether air-dome experienced fish can ‘teach’ air-dome naïve fish to use domes for refilling via social learning. We propose to use 10500 fish in total in a two-part study to explore whether behavioural adaptation is a commercially viable welfare improvement tool for salmon in depth-modified cages.
Study 1 requires a total of 6000 fish split between 6 freshwater tanks (1000 fish per tank), and 170 fish of those having been PIT tagged and externally tagged prior to transfer. 3 replicate tanks will have miniature air-domes (treatment) and 3 tanks will be replicate controls (full surface access). After 4 weeks in tanks, fish will be transferred to six 12x12 m sea-cages fitted with air-domes (fitted with cameras and PIT antenna) submerged at 3m. Before sea transfer, 170 fish per tank will have length, weight and SWIM scores measured to enable welfare and behaviour monitoring. Swimming behaviour via underwater cameras, echo sounder data, and PIT registration in the dome will be monitored daily. To investigate the short-term effect of habituation: after four weeks at sea, 100 fish per cage will be captured, resurfaced, anaesthetized and have length, weight and SWIM scores measured before being returned to the sea cage. To investigate the long-term effect of habituation: after another four weeks, the cages will be resurfaced and 100 fish per cage will be measured (length, weight, SWIM).
Study 2 will compare the welfare and performance of groups of salmon with different ratios of air-dome experienced: naïve fish in air-dome sea-cages to explore what size of pioneer group is required for social transfer of air dome refilling skills to occur in the naïve population. Study 2 requires an additional 4500 fish (1500 fish reused from Study 1) that are air-dome naïve. Fish will be sourced from a stock cage nearby and come from the same cohort as experimental fish. A total of 500 of the new fish will be PIT tagged and externally tagged. Using the same air-dome sea-cages used in Study 1, there will be a total of 1000 fish per sea-cage. The following ratios of air-dome experienced fish: air dome naïve fish will be 0:100, 5:95, 10:90, 15:85, 20:80, 100:0. 100 fish of each naïve group per sea-cage (if present) will be PIT tagged prior to the trial. Daily monitoring of refilling and swimming behaviour and echo sounder data will be monitored. After four weeks, cages will be re-surfaced, and 100 fish per experience level in each sea-cage will be sampled for length, weight and SWIM scores.
Study 1 requires a total of 6000 fish split between 6 freshwater tanks (1000 fish per tank), and 170 fish of those having been PIT tagged and externally tagged prior to transfer. 3 replicate tanks will have miniature air-domes (treatment) and 3 tanks will be replicate controls (full surface access). After 4 weeks in tanks, fish will be transferred to six 12x12 m sea-cages fitted with air-domes (fitted with cameras and PIT antenna) submerged at 3m. Before sea transfer, 170 fish per tank will have length, weight and SWIM scores measured to enable welfare and behaviour monitoring. Swimming behaviour via underwater cameras, echo sounder data, and PIT registration in the dome will be monitored daily. To investigate the short-term effect of habituation: after four weeks at sea, 100 fish per cage will be captured, resurfaced, anaesthetized and have length, weight and SWIM scores measured before being returned to the sea cage. To investigate the long-term effect of habituation: after another four weeks, the cages will be resurfaced and 100 fish per cage will be measured (length, weight, SWIM).
Study 2 will compare the welfare and performance of groups of salmon with different ratios of air-dome experienced: naïve fish in air-dome sea-cages to explore what size of pioneer group is required for social transfer of air dome refilling skills to occur in the naïve population. Study 2 requires an additional 4500 fish (1500 fish reused from Study 1) that are air-dome naïve. Fish will be sourced from a stock cage nearby and come from the same cohort as experimental fish. A total of 500 of the new fish will be PIT tagged and externally tagged. Using the same air-dome sea-cages used in Study 1, there will be a total of 1000 fish per sea-cage. The following ratios of air-dome experienced fish: air dome naïve fish will be 0:100, 5:95, 10:90, 15:85, 20:80, 100:0. 100 fish of each naïve group per sea-cage (if present) will be PIT tagged prior to the trial. Daily monitoring of refilling and swimming behaviour and echo sounder data will be monitored. After four weeks, cages will be re-surfaced, and 100 fish per experience level in each sea-cage will be sampled for length, weight and SWIM scores.