Abstract
The live release of wild adult Pacific salmon (Oncorhynchus spp.) following capture is a management tactic often used in commercial, aboriginal, and recreational fisheries. Fisheries capture and handling can be both exhausting and stressful to fish, which can limit their ability to swim and survive after release. As a result, researchers have assessed methods intended to improve post-release survival by assisting the flow of water over the gills of fish prior to release. Such approaches use recovery bags or boxes that direct water over the gills of restrained fish. This study evaluated a method of assisting ventilation that mimics one often employed by recreational anglers (i.e. holding fish facing into a current). Under laboratory conditions, wild Fraser River sockeye salmon (Oncorhynchus nerka) either received manual ventilation assistance for 1 min using a jet of water focused at the mouth or were left to recover unassisted following a capture-and-release simulation. A control group consisted of fish that were not exposed to the simulation or ventilation assistance. The experiment was conducted at 16 and 21°C, average and peak summer water temperatures for the Fraser River, and fish survival was monitored for 33 days. At 21°C, all fish perished within 3 days after treatment in all experimental groups, highlighting the consequences of handling adult sockeye salmon during elevated migration temperatures. Survival was higher at 16°C, with fish surviving on average 15-20 days after treatment. At 16°C, the capture-and-release simulation and ventilation assistance did not affect the survival of males; however, female survival was poor after the ventilation assistance compared with the unassisted and control groups. Our results suggest that the method of ventilation assistance tested in this study may not enhance the post-release survival of adult Fraser River sockeye salmon migrating in fresh water.
Highlights
Understanding the physiological demands placed on a fish during fisheries capture through to recovery are key to evaluating conservation-driven attempts to aid recovery processes and reduce post-release mortality
We focused our survival analyses at 10 and 15 days after the simulated capture-and-release treatment because these durations reflect a range of times it would take Early Summer and Summer-run sockeye salmon to reach their natal tributaries from our capture locale (Gilhousen, 1990)
The method of ventilation assistance used here did not enhance the survival of sockeye salmon after the simulated capture-and-release event
Summary
Understanding the physiological demands placed on a fish during fisheries capture through to recovery (assuming it is to be released) are key to evaluating conservation-driven attempts to aid recovery processes and reduce post-release mortality. Fisheries capture and handling results in a stress response and physiological exhaustion associated with both aerobic and anaerobic metabolic activity. The physiological stress response is initiated with the release of catecholamines and corticosteroids, which stimulate cardiorespiration to meet mounting tissue oxygen requirements (Pickering and Pottinger, 1995). Encounters with fisheries gear often trigger anaerobic responses, which tend to be faster and result in an oxygen deficit as tissue energy demands rapidly exceed that which can be produced aerobically (Pickering and Pottinger, 1995). Physiological recovery requires oxygen in excess of basal metabolic needs for processes such as highenergy phosphate replenishment, lactate clearance, and glycogen resynthesis (Wood, 1991). Homeostasis can be regained, the stress of and recovery from fisheries captureand-release events can place a considerable physiological load on fish that may directly affect their survival
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