Abstract
BackgroundAdvances in biologging technology allow researchers access to previously unobservable behavioral states and movement patterns of marine animals. To relate behaviors with environmental variables, features must be evaluated at scales relevant to the animal or behavior. Remotely sensed environmental data, collected via satellites, often suffers from the effects of cloud cover and lacks the spatial or temporal resolution to adequately link with individual animal behaviors or behavioral bouts. This study establishes a new method for remotely and continuously quantifying surface ice concentration (SIC) at a scale relevant to individual whales using on-animal tag video data.ResultsMotion-sensing and video-recording suction cup tags were deployed on 7 Antarctic minke whales (Balaenoptera bonaerensis) around the Antarctic Peninsula in February and March of 2018. To compare the scale of camera-tag observations with satellite imagery, the area of view was simulated using camera-tag parameters. For expected conditions, we found the visible area maximum to be ~ 100m2 which indicates that observations occur at an equivalent or finer scale than a single pixel of high-resolution visible spectrum satellite imagery. SIC was classified into one of six bins (0%, 1–20%, 21–40%, 41–60%, 61–80%, 81–100%) by two independent observers for the initial and final surfacing between dives. In the event of a disagreement, a third independent observer was introduced, and the median of the three observer’s values was used. Initial results (n = 6) show that Antarctic minke whales in the coastal bays of the Antarctic Peninsula spend 52% of their time in open water, and only 15% of their time in water with SIC greater than 20%. Over time, we find significant variation in observed SIC, indicating that Antarctic minke occupy an extremely dynamic environment. Sentinel-2 satellite-based approaches of sea ice assessment were not possible because of persistent cloud cover during the study period.ConclusionTag-video offers a means to evaluate ice concentration at spatial and temporal scales relevant to the individual. Combined with information on underwater behavior, our ability to quantify SIC continuously at the scale of the animal will improve upon current remote sensing methods to understand the link between animal behavior and these dynamic environmental variables.
Highlights
Advances in biologging technology allow researchers access to previously unobservable behavioral states and movement patterns of marine animals
Our results indicate that Antarctic minke whales in the coastal bays around the West Antarctic Peninsula occupy low ice content areas for the majority of the time during which video was recorded, with 84.36% of observations in ≤ 20% ice cover (Table 3)
Our method for describing surface ice concentration at such fine spatiotemporal scales, with continuous reliable information on behavioral state from motion-sensing tags, will allow greater quantification of how the behavior of this species is affected by ice in the environment
Summary
Advances in biologging technology allow researchers access to previously unobservable behavioral states and movement patterns of marine animals. While the spatial resolution may be appropriate to link ice to animal behavior at submesoscales, the likelihood of timely satellite images coinciding with data collection are low, and in many cases tasking SAR instruments to collect synoptic imagery is expensive (e.g., RADARSAT) and may still not capture appropriate scenes if field operations are out of phase due to local conditions. These challenges necessitate new tools to more accurately determine associations between animals and their surrounding ice environment in polar regions
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