Diel differences in blue whale (Balaenoptera musculus) dive behavior increase nighttime risk of ship strikes in northern Chilean Patagonia

Abstract

The northern Chilean Patagonia region is a key feeding ground and a nursing habitat in the southern hemisphere for blue whales (Balaenoptera musculus). From 2014 to 2019, during 6 separate research cruises, the dive behavior of 28 individual blue whales was investigated using bio-logging tags (DTAGs), generating ≈190 h of data. Whales dove to significantly greater depths during the day compared to nighttime (day: 32.6 ± 18.7 m; night: 6.2 ± 2.7 m; P < 0.01). During the night, most time was spent close to the surface (86% ± 9.4%; P < 0.01) and at depths of less than 12 m. From 2016 to 2019, active acoustics (scientific echosounders) were used to record prey (euphausiids) density and distribution simultaneously with whale diving data. Tagged whales appeared to perform dives relative to the vertical migration of prey during the day. The association between diurnal prey migration and shallow nighttime dive behavior suggests that blue whales are at increased risk of ship collisions during periods of darkness since the estimated maximum ship draft of vessels operating in the region is also ≈12 m. In recent decades, northern Chilean Patagonia has seen a large increase in marine traffic due to a boom in salmon aquaculture and the passenger ship industry. Vessel strike risks for large whales are likely underestimated in this region. Results reported in this study may be valuable for policy and mitigation decisions regarding conservation of the endangered blue whale.

Environmental cycles and individual variation in the vertical movements of a benthic elasmobranch

“…They extend across ecological timescales, from the cycles of the tides (Gibson 2003;Krumme 2009) to those of the seasons (Hyndes et al 1999;Milligan et al 2020) and those exhibited over ontogenetic development (Grubbs 2010;Frank et al 2018). They are also prevalent across trophic levels, from the diel vertical migration (DVM) of plankton (Hays 2003;Bianchi and Mislan 2016) to the diving patterns of cetaceans (Keen et al 2019;Caruso et al 2020) and pelagic sharks (Papastamatiou and Lowe 2012;Schlaff et al 2014). An important area of research in marine ecology is to understand the drivers of these trends.…”

Research on whales, dolphins, and porpoises

“…In this volume, Caruso et al . (2021) used non‐invasive digital acoustic recording tags (D‐Tags) to study the dive behavior of 28 blue whales in the northern Chilean Patagonia. Their results showed that Chilean blue whales dove to significantly greater depths during the day compared to night‐time, when most time was spent close to the surface.…”

“…In recent decades, biologging technology has become increasingly applicable, which allows researchers to take different types of measurements, such as GPS location, speed, and/or physiological parameters of animal, and depth, temperature, or salinity of environment (McIntyre 2014). In this volume, Caruso et al (2021) used non-invasive digital acoustic recording tags (D-Tags) to study the dive behavior of 28 blue whales in the northern Chilean Patagonia. Their results showed that Chilean blue whales dove to significantly greater depths during the day compared to night-time, when most time was spent close to the surface.…”

A sampling, exposure and receptor framework for identifying factors that modulate behavioural responses to disturbance in cetaceans

“…whether a species is nocturnal or diurnal) and seasonal (e.g. whether an individual is breeding or moulting) patterns can modulate sensitivity to disturbance, the severity of response, and the likelihood of exposure (Caruso et al, 2020 ). Some fish species have been observed to respond more strongly to disturbance at night (Neo et al, 2018 ).…”