Sea turtles are measured by length so we can have a deeper understanding of their biology, identity, and health, similar to how humans are measured by height for identification and medical purposes. For our research projects, we measure the length of a sea turtle to relate their body size or age class to their behaviors, such as nesting, foraging, and basking. Although you will identify individual basking sea turtles by photo-ID, it is helpful if you can also record morphometric data, including the turtle's body size.
Traditionally, sea turtles are captured and restrained to collect accurate measurements of their body size through standardized Techniques for Measuring Sea Turtles. One of the more invasive methods of capturing turtles for research purposes involve chasing after them and then grabbing them abruptly out of the water; if this was done without permits, this would be a violation of federal law as it would constitute harassment of an endangered species. This methodology is practiced by some researchers and is known as Turtle Rodeo.
Since animal welfare is very important to the mission of Sea Turtles 911, we do NOT want to capture and restrain animals to measure them as many institutions do. Thus, as a researcher for Sea Turtles 911, you are always advised to use minimally-invasive methods to collect data on sea turtles without disturbing them. One of the ways we measure sea turtles in a non-invasive manner is through a technique which uses laser photogrammetry. To do this, you will have access to these FDA-approved laser pointers. However, we do not have a chassis / mount for these lasers, including an easy way to attach a camera on the chassis. To help advance this non-invasive research methodology here in Hawaii, your next step as a team is to construct a chassis with materials from local hardware stores or online. Please propose a design with estimated costs to your program leaders.
This photo is an example of an underwater-based chassis. For your basking sea turtle project, a terrestrial-based chassis would suffice at this time. Please review the following research publications for more information on how to implement methods to ensure your research is conducted non-invasively.
How to Non-Invasively Measure Body Size of Animals with Photogrammetry
- Araujo (2016) Using minimally invasive techniques green turtle life history.
- Araujo (2019) In-water-stereo photogrammetry population dynamics foraging green turtles Philippines.
- Deakos (2010) Paired-laser photogrammetry manta rays.
- Harvey (1995) System for Stereo-Video Measurement of Sub-Tidal Organisms.
- Meise (2014) Applicability Photogrammetry Body Dimensions Pinnipeds Galapagos Sea Lions.
- Monkman (2019) Accurate estimation of fish length in single camera photogrammetry.
- Morisaka (2016) A Simple and Non-invasive Measurement Method Important for Conserving Large Animals Underwater.
- Parsons (2006) Laser-metrics of free-ranging killer whales.
- Rohner (2011) How large is the worlds largest fish.
- Rohner (2015) Laser photogrammetry improves estimates whale sharks.
- Siegfried (2021) Validating use stereo video cameras measurements sea turtles.
- Webster (2010) A simple laser photogrammetry technique for measuring dolphins.
- Wong (2018) Using laser photogrammetry to measure pilot whales.