Movement and Seasonal Energetics Mediate Vulnerability to Disturbance in Marine Mammal Populations

Abstract

In marine environments noise from human activities is increasing dramatically, causing animals to alter their behavior and forage less efficiently. These alterations incur energetic costs that can result in reproductive failure, death, and may ultimately influence population viability; yet the link between population dynamics and individual energetics is poorly understood. We present an energy budget model for simulating effects of acoustic disturbance on populations. It accounts for environmental variability and individual state, while incorporating realistic animal movements. Using harbor porpoises (Phocoena phocoena) as a case study, we evaluated population consequences of disturbance from seismic surveys and investigated underlying drivers of vulnerability. The framework reproduced empirical estimates of population structure and seasonal variations in energetics. The largest effects predicted for seismic surveys were in late summer and fall, and were unrelated to local abundance, but instead to lactation costs, water temperature, and body fat. Our results demonstrate that consideration of temporal variation in individual energetics and their link to costs associated with disturbances is imperative when predicting disturbance impacts. These mechanisms are general to animal species, and the framework presented here can be used for gaining new insights into the spatiotemporal variability of animal movements and energetics that control population dynamics.

Emerging themes in Population Consequences of Disturbance models

“…However, the proportion of the population exposed will depend on the spatial extent of the disturbance relative to the population's range. Because foraging grounds and reproductive areas spatially overlap for both resident and nomadic populations, PCoD modelling shows that the behaviours potentially disrupted will depend on the timing of the disturbance event [ 32 ].

Figure 2 ( a ) A population's movement patterns can help determine the degree of exposure to a disturbance-inducing activity.

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Agent‐based models to investigate sound impact on marine animals: bridging the gap between effects on individual behaviour and population level consequences

“…As a final remark, we like to emphasise that the validity of ABMs heavily depends on the quality of empirical data and the availability of quantitative data for parameters that turn out to be critical for population consequences in sensitivity analyses (Soudijn et al 2020, Gallagher et al 2020). The fact that it is for example often very difficult to get a species‐specific dose‐response threshold or curve for particular behavioural or physiological responses is a major concern (Harris et al 2018, van der Knaap et al 2021).…”

“…The studs by van Beest et al (2017) and Nabe‐Nielsen et al (2018) are, in our view, currently the most advanced examples of ABM applications for spatially explicit analyses to estimate population consequences of acoustic disturbances through effects on animal movement and bioenergetics. They recently followed‐up with an additional study at this advanced level (Gallagher et al 2020), in which they evaluated population consequences of disturbance from the spatially variable impact of seismic surveys on harbour porpoise. They investigated underlying drivers of vulnerability, which varied with season and were largely determined by lactation costs, water temperature and amount of body fat reserves.…”

From theory to practice in pattern‐oriented modelling: identifying and using empirical patterns in predictive models

“…in grams), or energy gained (e.g. in joules) per unit time, often a day (Roese, Risenhoover & Folse, 1991;Testa et al, 2012;Chudzi nska et al, 2016;Gallagher et al, 2021). Semeniuk et al (2012) estimated daily net energy intake in megajoules of woodland caribou (Rangifer tarandus) using empirical ingestion rates of lichen in kilograms and then converted to energy using a literature-derived energetic conversion factor.…”

“…Alternatively, indirect measures may serve as proxies for energy requirements, such as patterns in ventilation rates, heat loss, or body temperature (Jager & Ravagnan, 2016;Beltran, Testa & Burns, 2017;Malishev, Bull & Kearney, 2018;Desforges et al, 2020) and potentially movement metrics such as dynamic body acceleration (Qasem et al, 2012;Chimienti et al, 2020). Changes in mass or stored energy, particularly individual growth rates or body composition changes, can also provide insight on individual energy use or balance (Mueller et al, 2012;Dey et al, 2017;Boyd et al, 2018;Gallagher et al, 2021 with seasonal shifts in mass or body composition at different life-history events [e.g. reproduction or maturity (Beltran et al, 2017, Heinänen et al, 2018, Desforges et al, 2019].…”