By Leila Lemos, Ph.D. Student, Department of Fisheries and Wildlife, OSU.
Hello everybody with the first post of the year from the GEMM Lab!!
The year of 2016 has just begun and with that comes new projects and great expectations about my PhD project.
During this week I am going to learn how to measure gray whales (Eschrichtius robustus) using aerial images that were captured during last summer’s pilot field season along the Oregon Coast led by my advisor Dr. Leigh Torres.
Dr. Torres aimed to test the methodology for our project that will combine these whales’ measurements data with hormonal analysis to assess the overall health of gray whales.
The aerial videos and images were taken through an unmanned aerial system (UAS) that is composed of a flying unit and an on-board camera. An example of this system can be seen below, in Figure 1.
Figure 1: Dr. Leigh Torres re-captures the UAS (DJI Phantom 3) while at sea after an over flight of a gray whale.
Source: Leigh Torres, 2015.
The measurement of the whales through aerial images is known as “photogrammetry” and this method can give us important information about the whales through this unique overhead perspective, such as individual identification using natural markings, sex and reproductive condition based on size estimation, and individual-based changes in growth, health and body condition (nutritive condition) over time through replicate samples.
Perryman and Lynn (2002) used images captured from planes and adopted four different measurements for each photographed whale: the total length (Lt), the width of the whale at its widest point (Wm), the distance from the tip of the rostrum to the widest point (RWm), and the width of the flukes (Fw), as shown in the Figure 2. Using these methods, this study was able to identify pregnant females and found that southbound migrating gray whales were significantly wider than northbound whales.
Figure 2: Features measured on vertical photographs in gray whales
Source: Perryman and Lynn, 2002.
We plan to build upon this established method by measuring width at multiple points along the whale’s body, in addition to the total length.
Images taken of the same individuals during different temporal periods can reveal variations in their body condition.
We aim to collect images of the same individuals at the beginning and end of a foraging season and hypothesize that due to weight gain and increased blubber mass the width of animals will increase. Additionally, when images of indiviudals are compared between years we hypothesize that body condition changes due to major events such as pregnancy, entanglements, skin lesions, and predation events, will be linked to changes in body condition.
We will relate these photogrammetry data to hormonal data on stress and reproductive status in order to describe individual stress variation as it relates to size, health, location, year, reproductive status and ocean noise levels.
During the pilot field season, six gray whale fecal samples were collected and hormonal levels in these samples were analyzed showing positive results. Based on the success of the pilot field season, I believe my PhD project will produce exciting and informative data about gray whale ecology by linking physiology and morphometrics.
I am excited to begin my thesis research and, until my field season starts next summer, you can find me measuring gray whales!
To illustrate, below are a few aerial images taken of gray whales off Newport, Oregon, using a UAS, which we will use to conduct photogrammetry (all photos taken under NMFS permit 16111 issued to John Calambokidis).
And, just for fun, here is a UAS clip of a foraging gray whale in a kelp bed off the coast of Oregon to give a sense of the unique perspective we can get on animal behavior.
* Taken under NMFS permit 16111 issued to John Calambokidis.
This research is facilitated through the collaboration with OSU’s Aerial Imaging Systems Lab (http://ais.forestry.oregonstate.edu/), and Cascadia Research Collective (http://www.cascadiaresearch.org/).
Until next time and thanks for reading!
Perryman WL, Lynn MS. 2002. Evaluation of nutritive condition and reproductive status of migrating gray whales (Eschrichtius robustus) based on analysis of photogrammetric data. J. Cetacean Res. Manage. 4(2):155-164.