Abstract
BackgroundAcoustic telemetry is a widely used tool to study the movement and survival of juvenile fish and often requires a surgical procedure to implant the transmitter, which may impact overall fitness and survival following release. This is an important consideration when implementing large-scale acoustic telemetry projects aimed at estimating outmigration survival. The objective of this study was to examine the effects of water temperature, tag type, size at tagging, and surgeon experience on tag retention and growth rate of juvenile Chinook salmon (Oncorhynchus tshawytscha). We tagged 128 spring-run Chinook salmon (81–97 mm fork length, 5.2–10.0 g, tag burden 2.4–6.0%) with one of two types of acoustic transmitters; a shorter, heavier model (‘standard’) and a longer, lighter model (‘injectable’). Fish were tagged by either a novice or experienced surgeon. An additional 64 untagged fish served as a control group and were split between temperature treatments. Fish were reared in either cool (mean 13.4 °C) or warm (mean 17.8 °C) water for 60 days, prior to being euthanized, weighed and measured.ResultsTag retention was similar for both transmitter types, but varied with water temperature, with significantly higher tag loss in the warm treatment (21.9%, 14 tags expelled), compared to the cold treatment (7.8%, 5 tags expelled). In the warm treatment, fish growth in the injectable tag group was significantly lower compared to the control group, and lower than the standard tag group, but not significantly lower. There was no significant difference between the control and standard tag groups for the warm treatment. In the cool temperature treatment, fish growth was not significantly different among any of the factors tested. Surgery time differed between surgeons; however, surgeon experience did not significantly affect tag shedding or growth.ConclusionTotal tag loss was 14.8% over the 60-day trial, with higher and earlier loss in the warmer treatment. Tag length may be a more important factor than tag weight in smaller size fish. This suggests that tag shedding is a significant factor to consider when estimating survival, as the actual survival rate may be higher than estimates based solely on receiver detections.
Highlights
Acoustic telemetry is a widely used tool to study the movement and survival of juvenile fish and often requires a surgical procedure to implant the transmitter, which may impact overall fitness and survival following release
We examined four factors known to exacerbate tagging effects following tag implantation in juvenile Chinook salmon, which included: water temperature [8, 18, 37, 51], surgeon experience [12, 18], size at tagging [5, 27, 50], and tag type [17, 25]
Fish were selected to provide a range in sizes that are similar to the mean fork length (FL) of 88.5 mm for trawl caught juvenile Chinook salmon leaving the Sacramento–San Joaquin Delta (“Delta Juvenile Fish Monitoring Program—Chipps Island trawls CHN-POD species 2012– Present” n.d. [15])
Summary
Acoustic telemetry is a widely used tool to study the movement and survival of juvenile fish and often requires a surgical procedure to implant the transmitter, which may impact overall fitness and survival following release. Acoustic telemetry has been used to monitor the movement and survival rates of many fish species including sturgeon [3, 30, 38], rays [4, 9, 41], and sharks [22, 24, 46] It is one of the most effective methods to study the movement and survival of juvenile Chinook salmon (Oncorhynchus tshawytscha) out-migrating from freshwater rearing areas to the Pacific Ocean [13, 32, 36, 53]. Further development resulted in a JSATS transmitter that was lighter and could be implanted by needle injection [16], potentially allowing studies to track movement patterns and estimate survival of even smaller fish (between 54 and 99 mm fork length) [19]
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