Predicting physiological impacts of disturbance on marine mammals: Implications for population-level effects

The increasing urbanisation of marine environments poses a risk for marine populations. The Population Consequences of Disturbance (PCoD) model is a conceptual modelling framework that aims to predict the mechanistic effects of anthropogenic disturbance on the behaviour and physiology of marine populations, including marine mammals. Currently, the primary metrics for quantifying disturbance are behavioural changes, meaning there is a lack of empirical data to parameterise physiological health consequences in the PCoD model. Marine mammals have specialised anatomical and physiological adaptations to endure long periods of apnoea (i.e. breath-holding) making them sensitive to disturbance, as it could challenge physiological homeostasis and affect their ability to dive, forage, and recover. Previous research suggests that marine mammals may experience a simultaneous fight and flight response following a disturbance event in which oxygen is required for exercise, but the necessary cardiovascular responses to accommodate the oxygen demand do not occur. This paradoxical response may result in hypoxia (low blood oxygen) and hypercapnia (increased carbon dioxide); collectively called asphyxia. Given the limited technological and logistical capabilities for physiological monitoring, the consequences of asphyxia in response to disturbance of marine mammals are unknown. This project aims to inform this knowledge gap by measuring physiological consequences of disturbance to marine mammals and their interaction with behaviour and foraging energetics in order to integrate physiological and health components to population modelling frameworks.

The data will be collected using voluntarily diving, temporarily captive, grey seals at the Sea Mammal Research Unit's pool facility, in which seals make repeated dives to a feeder and back to the surface to breathe. The physiological state of the seals will be manipulated without exposing seals to disturbance stimuli by using a breathing chamber to control exposure to respiratory gas mixes: ambient, hypoxic, and hypercapnic. The effect of changing blood gases on (1) cardiovascular regulation and organ function and (2) energetics will be measured using this experimental setup.
Cardiovascular function and blood gases will be measured by wearable, non-invasive continuous-wave near infrared spectroscopy (NIRS) tags. Additionally, venous blood sampling before and after diving trails will provide blood biomarkers of mild traumatic brain injury, oxidative stress, and inflammation to be combined with NIRS data to investigate changes to organ and tissue homeostasis. Energy expenditure required to dive and consume prey will be calculated using dive and recovery interval durations, as well as total oxygen consumption and carbon dioxide production calculated from open-flow respirometry. Together, these metrics will allow for testing and calibration of metrics for energy expenditure that can be incorporated into onboard data processing of NIRS tags for future field deployments. Finally, the physiological and energetic outcomes will be incorporated to existing PCoD models to predict individual and population level consequences of disturbance.