Mote scientists use iPhone-quality motion sensors to study survival of caught-and-released sharks
Mote Marine Laboratory scientists have received a $192,310 federal grant to continue studies using iPhone-quality motion sensors to examine survival and recovery rates of several shark species after they are caught and released by Florida’s commercial fishers.
After fishers catch and release a shark, it is relatively unknown how the animal is affected, how long it takes to recover or if it will survive after release. This is vital information for resource managers seeking to assess shark stocks and maintain healthy shark populations, preserving the top predators that help keep ecosystems in balance.
Past Mote research has helped reveal that different shark species can have different post-release survival and recovery rates. This new study, a team effort among scientists and fishers, will expand data for multiple shark species, including some prohibited species that may be caught accidentally as bycatch.
Mote Staff Scientist Dr. Nick Whitney was recently awarded the new Cooperative Research Program (CRP) grant by the National Oceanic and Atmospheric Administration’s National Marine Fisheries Service (NMFS) to study post-release mortality rates of commercially caught-and-released Carcharhinid sharks, which include sandbar, blacktip, bull and tiger sharks.
CRP competitive grants provide federal funding for projects seeking to increase and improve the working relationships among NMFS scientists and collaborating researchers, state fishery agencies, universities and fishers.
In this project, Whitney will tag and study sharks caught and released by participating longline fishers in the Gulf of Mexico. The sharks will be tagged with acceleration data loggers (ADLs), or accelerometer tags, which use the same type of motion-sensing technology found in the iPhone or Fitbit, a wearable activity tracker that counts steps walked.
For sharks, the motion-sensing ADL will count tail beats and detect other fine-scale movement patterns such as acceleration amplitude, rolling or inability to remain upright. Such ADL results will provide detailed information about the shark’s survival or mortality, swimming abnormalities and recovery time.
“When we are trying to figure out the population numbers and manage the population of sharks, it is important that we understand the implication of catching and releasing sharks," Whitney said. “We know that there are a certain percentage of those animals that will die after release either from stress or injuries that they sustained during capture, and it is really difficult to figure out what that percentage is. That is what we’re trying to find out.”
The grant will support one year of research starting Sept. 1, 2015. It builds upon a 2013-2014, CRP-funded Mote study that was the first to quantify post-release mortality and behavioral effects of capture in sandbar and blacktip sharks caught in Florida’s commercial shark fishery, as well as other species including spinner, bull, tiger, blacknose and hammerhead sharks.
This study will not only expand a novel line of research with motion-sensing tags on sharks; it will also look for signs of capture stress using blood samples from caught-and-released sharks.The researchers will examine how tag and blood sample results relate to each other and to shark size, time on the hook and body condition at release, using their detailed data to create a species-specific post-release survival index. In essence, that’s numerical information valuable for science and management.
“The work Dr. Whitney has done to date with accelerometers to examine post-release mortality has been extremely impressive and has provided, without question, the most robust species-specific estimates available of this elusive parameter,” said Dr. William B. Driggers Ill, NMFS Research Fishery Biologist. “His success in applying this technology in assessing post release mortality of blacktip, tiger and sandbar sharks demonstrated the value of accelerometers to answer a historically unyielding question of the utmost importance to stock assessments.”
Whitney has been refining use of ADLs for shark research for the past few years. ADLs are quarter-sized chips that store 100 data points every second — too much to transmit back via satellite. The data are stored to memory, and to retrieve them, scientists must recover the tag.
Mote scientists designed a float package to carry the ADLs and allow for retrieval. The package is placed on the shark’s dorsal fin with a strap called a galvanic release. In seawater, the strap corrodes over a few days, releasing bubbles like Alka-Seltzer and ultimately releasing the package, which floats to the surface. To retrieve the tag, scientists search by boat, using a big antenna to “listen” for a radio transmitter in the float package. Within 10 or 12 miles of the tag, they can hear it ping.
“The companies that sell these accelerometer tags don’t give you any way to get them back. We designed a float system as a way to retrieve the tag and we’re the only institution that has perfected this specific way of retrieving the tags,” Whitney said. “Historically, this kind of work was done with satellite tags, which can cost between $3,000 and $4,000 per tagged shark to get the data and that tag can only be used once. We’re getting our data for around $600 per shark. So we’re able to get larger samples sizes for a fraction of the cost.”
Although ADLs are lower-cost, they collect different data than satellite tags, which provide geographic position data over longer time periods. For this reason, Whitney will also tag a portion of the sharks in this study with pop-up satellite archival tags, which track the shark’s position as it moves through the sea, pop up and float to the surface, and then transmit the data via satellite.
“I often refer to the accelerometers (ADLs) as the ‘what are they doing’ tags and satellite transmitters as ‘where did they go’ tags,” Whitney said.
“To validate our results from the ADLs, which are only attached for a few days, the PSATs will stay attached to the sharks for about a month. This will make sure that the animals that survive with the ADLs will also survive a month later. This validates our early survival results but costs less than tagging all the sharks with PSATs,” Whitney said.