Dolphin population photogrammetry (DoPoGram): Assessing feasibility of generalizable method to determine delphinid population health.
Abstract
The Population Consequences of Disturbance (PCoD) framework provides a conceptual model to forecast a plausible range of outcomes following exposure to noise on individuals/populations in marine mammals. Yet, the data to inform this model is often limited and while efforts are underway to fill these data gaps, it might take decades before robust population assessments are available using traditional line transect and mark-recapture surveys (Taylor et al. 2007). Thus, there is a need for assessments which provide a more rapid indication of population trajectory and health status. For healthy populations, a stable age distribution is generally assumed. It follows that deviances from a stable age distribution would signify an unhealthy population. Until now, it has not been feasible to quantify the age structure of free-ranging delphinid populations without years of intensive field work efforts or access to large numbers of dead specimens from a given population. Recently, Booth et al. (2018) used existing PCoD models to explore the most suitable demographic variables to monitor as early warnings of population decline. They found certain demographic variables are strongly correlated with changes in abundance or population status, and can therefore provide some early warning of future changes in abundance. In particular, the proportion of immature animals in a population might provide a reasonable early indicator of population decline. Therefore, we propose to assess the feasibility of using multi-rotor unoccupied aerial vehicles (UAVs) to rapidly determine delphinid group age-composition and population age-structure in order to provide a means by which to assess a delphinid population trajectory and health status. The specific goals of our project are to: 1. Estimate length of free-ranging spinner dolphins off the Kona Coast off the Island of Hawaii We will collect vertical photogrammetry images of spinner dolphins via multi-rotor UAVs off the Kona Coast of Hawaii Island. The lead-PI has been studying this population of spinner dolphins for a decade, and much is known about their abundance, habitat use, social structure and exposure to human activities. Multi-rotor UAVs equipped with custom-built height sensors will be launched from both land and small research vessels and flown over groups of spinner dolphins within and outside of their four main resting bays (Makako Bay, Kealakekua Bay, Honaunau Bay and Kauhako Bay, Hawaii Island). 2. Develop age-length growth curves for Hawaiian spinner dolphins In order to utilize photogrammetric methods to assign animals to age classes, it is important to have auxiliary information, i.e. length-at-age growth curves and life history information such age of weaning and sexual maturity. It is then possible to classify animals into age stages according to their length. Length-at-age growth curves exist for a wide range of marine mammal species including delphinids. Growth curves will be informed for Hawaiian spinner dolphins from two data sources: a) published literature on by-caught eastern spinner dolphins from the Eastern Tropical Pacific (ETP) tuna fishery and b) available stranding specimens of Hawaiian spinner dolphins (n=30). The former (a) will rely on data on eastern spinner dolphins.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 31, 2020
- Source ID
- N000142012624
Entities
People
- Lars Bejder
Organizations
- Office of Naval Research
- United States Navy
- University of Hawaiʻi System