Field trials of a new physiological data logger in active fishes

Abstract

We have designed and constructed implantable data loggers that measure heart rate (HR) and body temperature of free‐ranging animals. We present data from the first field trials of these loggers in penned southern bluefin tuna (Thunnus maccoyii) under aquacultural conditions, and in spawning sockeye salmon (Oncorhynchus nerka) under natural conditions. Bluefin tuna (~ 15.2kg) maintained visceral temperature (VT) between 0.4 – 2.6°C above ambient water temperature (18.5°C) during non‐digesting periods, while HR ranged from 33 – 74 beats/min. VT rose to 1.4 – 6.5°C above ambient at the peak of the digestive period, and the magnitude of this increase was dependent on ration size. HR followed a similar trend during the digestive period, reaching levels of 52 – 117 beats/min and implying that the postprandial increase in oxygen consumption is assisted largely by an increase in HR. The duration of digestion ranged from 10.7 to 30.9 h depending on ration size.Sockeye salmon were implanted with data loggers in October 2007 when they had migrated from the ocean to their natal stream to spawn and subsequently die. Data analyses are ongoing, but it has been confirmed that salmon carrying data loggers do not have a reduced lifetime on the spawning ground, implanted salmon display normal courting and mating behaviours, and implanted salmon completed their lifecycle normally by spawning before death.