Extremely low seasonal prey capture efficiency in a deep-diving whale, the narwhal

Successful foraging is essential for individuals to maintain the positive energy balance required for survival and reproduction. Yet, prey capture efficiency is poorly documented in marine apex predators, especially deep-diving mammals. We deployed acoustic tags and stomach temperature pills in summer to collect concurrent information on presumed foraging activity (through buzz detection) and successful prey captures (through drops in stomach temperature), providing estimates of feeding efficiency in narwhals. Compared to the daily number of buzzes (706.9 ± 368), the daily rate of feeding events was particularly low in summer (19.8 ± 8.9), and only 8–14% of the foraging dives were successful (i.e., with a detectable prey capture). This extremely low success rate resulted in a very low daily food consumption rate (< 0.5% of body mass), suggesting that narwhals rely on body reserves accumulated in winter to sustain year-round activities. The expected changes or disappearance of their w..., Data collected
Between summer 2012 and summer 2016, live-capture operations of narwhals were conducted in collaboration with Inuit hunters in Scoresby Sound fjord, South-eastern Greenland. Following Heide-Jørgensen et al.’s method (2014), 14 narwhals were instrumented with stomach temperature pills (STPs), while three of these individuals were simultaneously equipped with acoustic tags (AcousondeTM) as described in Blackwell et al. (2018). From the Acousondes, two variables from that analysis are of interest here: animal depth (every second), and the start time of terminal buzzes, which are believed to indicate prey capture attempts (i.e. foraging dives) (Blackwell et al 2018).
Data analysis
Estimation of prey capture success
The buzz database used in this study is the one generated in Blackwell et al. (2018) and includes the depth every second, as well as the start time of each buzz for three females (Frida, Thora and Eistla). Statistical analyses were conducted on R software version 4...,