Noninvasive unmanned aerial vehicle provides estimates of the energetic cost of reproduction in humpback whales

Abstract

Abstract. An animal's body condition will affect its survival and reproductive success, which influences population dynamics. Despite its importance, relatively little is known about the body condition of large whales and its relationship to reproduction. We assessed the body condition of humpback whales (Megap tera novaeangliae) at a breeding/resting ground from aerial photographs recorded using an unmanned aerial vehicle (UAV). Photogrammetry methods were used to measure the surface area of individual whales, which was used as an index for body condition. Repeated measurements of the same individuals were not possible; hence, this study represents a cross-sectional sample of the population. Intraseasonal changes in the body condition of four reproductive classes (calves, immature, mature, and lactating) were investigated to infer the relative energetic cost that each class faces during the breeding season. To better understand the costs of reproduction, we investigated the relationship between female body condition (FBC) and the linear growth and body condition of their dependent calves (CBC). We documented a linear decline in the body condition of mature whales (0.027 m 2 /d; n = 20) and lactating females (0.032 m 2 /d; n = 31) throughout the breeding season, while there was no change in body condition of immature whales (n = 51) and calves (n = 32). The significant decline in mature and lactating female's body condition implies substantial energetic costs for these reproductive classes. In support of this, we found a positive linear relationship between FBC and CBC. This suggests that females in poorer body condition may not have sufficient energy stores to invest as much energy into their offspring as better conditioned females without jeopardizing their own body condition and survival probability. Measurement precision was investigated from repeated measurements of the same animals both from the same and different photographs, and by looking at residual errors in relation to the positioning of the whales in the photographs. The resulting errors were included in a sensitivity analysis to demonstrate that model parameters were robust to measurement errors. Our findings provide strong support for the use of UAVs as a noninvasive tool to measure the body condition of whales and other mammals.

Inexpensive Aerial Photogrammetry for Studies of Whales and Large Marine Animals

“…Durban et al (2015), whose APH-22 hexacopter estimates altitude from logged measurements of air pressure, report similar mean accuracy in measurements of fixed targets (mean errors; theirs = 0.7%, ours = 1.0%), but much worse precision (their CV = 4.5%; our CV = 1.8%). Their approach, and that of Christiansen et al (2016), makes no allowance for any lens/camera distortions. Six individual blue whales they measured 4-7 times showed ranges of measurements within 5% of the mean for each individual (Durban et al, 2016).…”

“…We also took along an APH-22 hexacopter equipped with an Olympus E-PM2 and 25 mm f1.8 lens (Durban et al, 2015) and two Swellpro Splashdrones equipped with Canon D30 waterproof point-and-shoot cameras programmed to take images every 2 s (Christiansen et al, 2016). The APH-22 flew well and collected data for 2 days, but crashed into the water when the velcro strap holding its battery in place failed.…”

“…The simplest approach is to include in the image an object of known size, typically a boat (e.g., Whitehead and Payne, 1981;Christiansen et al, 2016), or projected laser dots a known distance apart (e.g., Durban and Parsons, 2006;Rowe and Dawson, 2008). Having a boat in the image involves the potential for disturbance, and our trials with lasers indicated that the dots may not show up on whales at the ranges required, and raised questions about eye-safety.…”

The Use of Unmanned Aerial Systems in Marine Mammal Research

“…In addition, Pomeroy et al [13] pointed out that in absence of wind the aircraft noise is not masked and is more obvious. Christiansen et al [4] tested a small waterproof quadcopter (Splashdrone, www.swellpro.com, Figure 3) in Western Australia to measure humpback whales. The authors demonstrated that high resolution aerial photographs of whales can be used to assess the body condition of whales and estimate the energetic cost of reproduction.…”

“…In particular, UAS have been proposed as a tool for marine mammal surveys, as they allow researchers to reach remote areas and observe animals from an advantageous perspective, being less invasive than standard aircraft [3][4][5][6][7][8][9]. Despite the challenges of operating at sea [10], UAS have been used for a number of marine mammal research applications, from abundance surveys [8,[11][12][13][14][15][16][17] to the measurement of…”