PNNL

Abstract

The current minimum size for tagging Chinook Salmon Oncorhynchus tshawytscha with acoustic transmitters is = 95 mm fork length (FL). Using a new injectable acoustic transmitter (AT), our objective was to determine a minimum size for tagging Chinook Salmon. We measured survival and transmitter and tissue retention after exposure to rapid pressure changes (n = 399) or shear forces (n = 308). Fish (69–107 mm FL) were implanted with an AT (0.22 g; AT-only) or an AT and a passive integrated transponder (PIT; 0.10 g; AT+PIT) tag through a 3-mm incision with no sutures, or did not receive an incision or tag (control). Survival and transmitter and tissue retention following pressure changes was significantly lower for AT-only (0.70) and AT+PIT (0.54) fish compared to controls (0.85). No transmitters were expelled but 2.2% of AT-only and 12.5% of AT+PIT fish had tissue or a transmitter protruding. Following shear exposure, survival and transmitter and tissue retention was significantly lower for AT-only (0.70) and AT+PIT (0.61) fish compared to controls (0.98). Tissue expulsion described 87% of AT-only and 80% of AT+PIT mortalities. In both tests fish larger than 85–88 mm FL had a higher probability of survival and tissue and transmitter retention than smaller fish. We recommend the minimum size for tagging continue to be 95 mm FL, using a 3-mm incision with no sutures.