December 13, 2019 3 min read
Researchers from GHRI deployed the first accelerometer on a sailfish in Panama, as part of the Eastern Tropical Pacific Seascape Program
In addition to being popular gamefish, billfish are upper level predators in the oceans and, therefore, have the potential to help control ecosystems by influencing prey populations. Because of their important role in ecosystems, it is important to understand billfish movements and behaviors as this informs us where and when billfish are going to have the biggest effect on and how they connect ecosystems.
Over the last 20 years, advances in tagging technology have allowed researchers to follow the paths of billfish for up to a year and across ocean basins by using tags that send information to satellites (satellite tags). These satellite tags can now also provide information on the water depths that these fish are using. Although these tags can tell us where the fish is and how often the dive, they cannot provide us detailed information on what the fish is doing as it swims. New tagging technology, called accelerometers, provide a way to elucidate these fine-scale behaviors billfish undertake as they swim. This is the same technology that allows smartphones to flip the screen if the phone is rotated and is used in activity loggers like Fitbits. And just like we can use a Fitbit to measure our activity, accelerometers can be used to monitor fish activity. By measuring changes in acceleration across three-dimensions, changes in behavior can be identified, such as burst swimming to capture prey or avoid predators, and even individual tailbeats. It may even be possible to identify the lateral slashing of a marlin or sailfish’s bill as it attempts to immobilize its prey. In addition to the accelerometers, our new tags also contain a speed sensor to allow us to accurately measure routine cruising and burst speeds of these highly athletic fish for the very first time. Finally, a miniaturized video camera gives us never-before seen footage of the environment these fish use from their point of view, and the ability to ground-truth behavior seen in the acceleration data for these elusive fish. This information will provide a more detailed look at energy expenditure, when, where, and how often billfish forage, helping us to determine the impact they can have and how important they are in ocean food webs.
The information from accelerometers can also help us to protect billfish. Currently used satellite tags show us that when handled properly, billfish survive catch and release fishing. These tags, however, cannot provide much information on the recovery period immediately after release. Because accelerometers provide detailed behavioral information, the billfish recovery period after being caught and released can be examined and related to handling methods and gear used to catch the fish. Practices that reduce recovery times can then be identified and adopted, increasing billfish post-release survival.
Because of the amount of information being collected by these tags (50 data points every second) and 10 hours of video, they cannot transmit the data to a satellite like the satellite tags,
and must be physically recovered in order to download the data and video. This is accomplished by attaching the tag to the fish with a link that begins to dissolve when exposed to seawater, and the thickness of the link determines how long it will take to completely dissolve (1-3 days). Once the tag detaches from the fish, it floats to the surface, at which point it begins transmitting its location to the satellites. We can then run out to that location, and then use a handheld receiver and antenna to pinpoint the exact location to pick it up!
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