Using Satellite Technology to Study Dolphinfish
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The use of pop-off archival satellite telemetry tags as an effective tool in the study of fish behavior and movements has been demonstrated in studies of billfish, bluefin and yellowfin tuna, swordfish and several species of sharks. Over many years of use, these high-tech instruments have shown bluefin tunas found off the U. S. East Coast will make transatlantic crossing’s and then return to the place they were tagged. White sharks found along the California coast have been shown to travel westward to areas beyond the Hawaiian Islands and then return to the same coastal area along California. These instruments, which monitor temperature and pressure, have shown these pelagic fish to regularly utilize waters hundreds of feet deep and to enter waters with much lower temperatures than previously known. Now, for the first time, these instruments are being used to look into the watery world of the dolphinfish.
These instruments feature amazing technology. Capable of withstanding water pressure to 5,000 feet deep, the instruments record time-specific water temperature and pressure as frequently as every three minutes. They will record and store the data for as long as 500 days; however, each unit is preprogrammed to remain with the fish for a specific period ranging from a few days to more than a year. At that time, the instrument releases itself from the tether that connects it to the fish by electrolysis of the thin attachment wire and floats to the surface. Once at the surface, the unit makes contact with an Argos satellite and begins to download the archived data, sending it to Argos headquarters, which forwards it to the appropriate researcher. It can require as much as 30 days of transmissions to complete downloading the data file.
Photo Courtesy of Richard DeLizza
Archival tags offered science the first opportunity for long-term monitoring of fish in the wild. These devices record the water temperature and pressure at regular intervals along with the time of sunrise and sunset. This allows the fish to be tracked as it moves up and down in the water column while at the same time showing the range of temperatures that the fish naturally uses. While the data recorded on the capture of individual fish give a reading for one instance in the fish’s life, these tracks show the full range of all temperatures and depths naturally used by the fish over an extended period. This in-depth information allows scientists to discern behavior patterns as well as more accurately identify and define the essential habitat for the species.
Archival satellite telemetry instruments also offer the ability to track the path fish take during the monitored period. This feature is available in the standard program units but not in the high resolution program units, used so far on dolphin, that focus data collection on pressure and temperature. Each instrument manufacturer has developed proprietary software to calculate the daily latitude and longitude of the fish using temperature, depth and time of sunrise. However, there is a large margin of error of plus or minus two degrees of latitude and one degree of longitude. This renders the track of just one fish very questionable, but if you have ten or twenty tracks showing similar movements, then you can build confidence in that movement pattern. Initial results already show that dolphin use more of the water column than expected, diving to depths of at least 400 feet, and engage in deep diving more frequently at night.
Microwave Telemetry, Inc. (MTI) has advanced its technology in archival satellite telemetry tags. New technology has allowed the miniaturization of its PTT-100 satellite tag (left). Its new X model satellite tag (right) is roughly half the size of the old instrument that it replaces. The main unit of the new X tag is 4.75 inches long and weighs a mere 1.4 ounces.
Initial results already show that dolphin use more of the water column than expected, diving to depths of at least 400 feet, and engage in deep diving more frequently at night.
In a preliminary study funded by the South Carolina Department of Natural Resources (SC DNR) and the SC Sea Grant Consortium (SC SGC), the Dolphinfish Research Program has revealed many new facts about the life and behavior of dolphin using archival tags with satellite telemetry capability. These great game fish have been found to utilize waters at least as deep as 400 feet (120m) on occasion. and will regularly use waters between 100 and 200 feet deep (30 to 60m). Such deep diving behavior was found to be more common at night time than in the day. Dolphin were found to remain below 100 feet deep for as long 4.9 hours in a single dive. This may explain those beautiful Sargassum lines that fishermen find offshore that appear perfect but are void of fish.
Being able to track an individual fish’s dives from day to day allows scientists to compare behavior of fish within and between regions. Data have already indicated a possible universal behavior among all fish in which they rise to the surface at first light each morning. Data also show that fish off south Florida and those off South Carolina may have distinctly different daytime deep diving behavior. Fish off the Carolinas have been shown to engage in deep diving during the day 2 to 3 times more frequently than the fish off south Florida. Diving patterns among the initial study subjects suggests that dolphin may use the night to feed on a different group of prey species than those targeted during the day.
Comparison of diving behavior indicated that dolphin off south Florida engaged in deep diving during the day on an average of 1 out of every 4 days while fish off the Carolinas made deep dives an average of 3 out of 4 days.
The coldest waters utilized by dolphin were associated with the lower water layers entered during their deep dives. Fish seldom spent more than 15 minutes in waters below 70oF before returning to warmer waters.
Thermal tracks from monitored fish have begun identifying their thermal habitat preference. These tracks have shown dolphinfish to use a wide range of temperatures, varying as much as 26.4oF (61.2 to 87.6oF). Dolphin were found to utilize temperatures varying more than 22oF (61 to 83oF) within a 24 hour period. Data from the first round of monitoring also suggests that dolphin utilize different thermal ranges in different regions. The preliminary study found that overall the fish occupied waters of 79 to 84oF more than 80% of the time.
Technology costs, and these smart tags are no exception. Costing over $4,000 per unit plus another $1,000 for satellite time, science pays a hefty price for each unit. But these units are actually cost effective. The alternative devices recording similar information cost $1,100 to $1,500 but require recovery to acquire the data. This study has shown a recovery rate for tagged dolphin to be between 2 and 3%. This means that if 100 of the alternative tags ($110,000 to $150,000 in cost) were deployed, we would expect to recover 2 or 3. This would translate to a cost of $36,700 to $50,000 per instrument recovered.
The CSS Dolphinfish Research Program is committed to continuing the use of satellite telemetry-capable archival tags to study dolphinfish. It is critical to the future management of the species that we gain a better understanding of its habitat needs and movement patterns. The South Carolina DNR and Sea Grant Consortium have provided a small grant to allow this study to continue in 2007 and 2008. Additional funding for this research was also provided by Grady-White Boats, Inc. of Greenville, North Carolina, Central Florida Offshore Anglers of Orlando, Florida, and the Florida Sports Fishing Association of Cocoa Beach, Florida. Private sponsorship of satellite tags will play a major role in the future continuation of dolphin research using this cutting edge technology. Visit the “Study Results” page to view reports on the results from these initial studies.
Report: Use of Pop-off Satellite Archival Tags to Monitor
Cobia Utilizing Port Royal Sound, South Carolina
and Dolphinfish Present off the East Coast of the U. S.
Abstract: Cobia, Rachycentron canadum, and dolphinfish, Corypheana hippurus, are important species in the marine recreational fisheries of South Carolina as well as the South Atlantic Bight and Gulf of Mexico. Little information is available on the movements, associated water temperatures encountered and water depths occupied by these two species. The Microwave Telemetry’s model PTT-100 pop-off satellite archival tag (PSAT) was used to monitor temperature, pressure and, on certain instruments, geo-position information. These were attached to 5 dolphinfish off the U.S. East Coast and western Caribbean Sea and 4 cobia in or adjacent to Port Royal Sound, SC. Data were received from 4 instruments placed on dolphinfish and 3 attached to cobia. Dolphinfish were monitored for periods up to 23 days while cobia were monitored for as long as 92 days. Data received from the instruments showed that cobia used waters as deep as 70m and rose to the surface more frequently during May/June than July/August. Cobia were observed to utilize water temperatures from 20.7 to 29.33C but spent the majority of their time in waters from 22.0 to 26.99C. Dolphinfish were shown to utilize ocean waters with temperatures ranging from 16.0 to 30.5C. The highest temperatures were recorded by fish off south Florida while those off South Carolina entered the coldest waters. Dolphinfish off south Florida spent most their time in surface waters of 27.2 to 28.9C while fish off South Carolina spent most of their time in surface waters of 26.3 to 27.2C. Data showed that dolphinfish spend the majority of their time in the top 10 m of the water column but regularly made dives below 30 m going as deep as 124 m. Deep diving behavior was
shown to be most prevalent at night.
Click HERE for a completion report on the use of pop-off satellite archival tags to monitor cobia utilizing Port Royal Sound, South Carolina and dolphinfish present off the East coast of the U. S.
Made possible by a grant from the Guy Harvey Ocean Foundation.