Physiological Resilience in Mammalian Divers: Assessing the role of vascular conflict and control in recovery from anthropogenic disturbances
Abstract
Underwater noise, most notably from shipping, seismic activities and naval sonars, has emerged as one of the most important and controversial stressors on marine mammal populations worldwide. Despite geo-spatial and temporal evidence linking such anthropogenic disturbances to mass stranding events by deep-diving cetaceans, causal mechanisms between oceanic noise and lethal or sublethal injuries have been difficult to identify. Currently, the leading hypotheses suggest a combination of extreme behavioral flight responses, cardiovascular instability and decompression syndromes. However, the question remains, what factors differentiate when an escape response by cetaceans due to noise exposure leads to benign avoidance or to death? An understanding of two critical elements of the escape response, physiological resiliency and recovery, are required to answer this question. To date, neither has been studied for any integration of key behavioral (dive duration, exercise level), environmental (water temperature), physiological (heart rate, metabolic demand, respiratory rate, heat flow), and biochemical (pH, lactate, blood oxygen, carbon dioxide, catecholamines/cortisol) triggers that control the three Rs of escape reactions in mammalian divers - response, resilience and recovery. We will focus on four physiological pathways to assess resiliency and recovery via the cardiovascular system, 1) thermal and metabolic homeostasis, 2) metabolite control, 3) neurological protection, and 4) behavioral-respiratory integration. This will be accomplished by pairing our current physiological and blood chemistry monitors with newly available, portable near-infrared spectroscopy (NIRS) monitors, heat flux tags and doppler ultrasound technology for assessing tissue blood flow. Using this multi-variable approach with trained cetaceans (bottlenose dolphins, beluga whales) performing controlled swims and dives, we will determine the hierarchy of blood flow to central and peripheral body sites to support local oxygenation and thermoregulation during submersion and surface recovery. Independent and sequential dives will be compared. Particular focus will be on central and peripheral thermal windows, and the hypoxia-sensitive vascular master switch, the brain. By correlating vascular events and blood chemistries with common physiological and behavioral markers used for recovery (i.e., breathing frequency, heart rate, stroke frequency, dive duration) in trained cetaceans under controlled conditions we will develop predictive metrics for determining the timeline for re-establishment of thermal, cardiovascular and metabolic homeostasis in wild diving mammals. This will be tested on both new and previously archived data for the elite deep diver, the narwhal, during control and noise-exposed periods in the wild. This project will be the most comprehensive analysis of diving physiology for cetaceans exposed to unanticipated noise to date. For the first time the cardiac, respiratory, and energetic responses of noise-impacted wild, deep-diving cetaceans will be followed throughout escape and recovery. As such, the study will provide a comparative foundation and key physiological metrics applicable to evaluating the effect of fear and submerged exercise on other marine mammal species and even human divers. Ultimately, these metrics will enable Navy personnel to, 1) develop environmentally-sensitive schedules for acoustic activities that account for the most likely lethal and sub-lethal effects on marine mammal populations, and 2) instigate measures that will promote rapid recovery and resumption of normal behaviors by affected animals.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 31, 2020
- Source ID
- N000142012762
Entities
People
- Terrie M. Williams
Organizations
- Office of Naval Research
- United States Navy
- University of California, Santa Cruz