When Captain Jesus Duran and mate Dagobuerto Rodriquez of Boquerón, Puerto Rico, posed for a picture with a popup satellite archival transmitter (PSAT) on March 25th, 2019, we didn’t think we would ever see the tag again. That day, while fishing 20 miles south of Cabo Rojo Lighthouse, they attached the PSAT to a beautiful 47” male dolphinfish. The fish was hooked on a ballyhoo that was left drifting behind Yadimar, a 25’ Grady-White, by photographer Anthony Dooley of Rincón, while at the same time we fought, landed, and tagged a 38” female dolphinfish with another PSAT. Over the past decade, with funding from Puerto Rico’s Department of Natural and Environmental Resources, our tagging program, known internationally as the Dolphinfish Research Program, has deployed more than 20 PSATs on adult dolphinfish around the island. Attaching the devices to these fish allows us to garner a glimpse into their daily behavior as well as short and long-term migration patterns, information that is useful for improving dolphinfish management and advancing species conservation. The process of deployment, however, is nerve-wracking. Generally, once the fish is revived and released, you can be certain that the costly tag you just attached to your fish will never be in your possession again. Well, that is, at least, what we thought. A few months after we tagged our 47” bull, we noticed that tag was transmitting from land. How could that be? Well, simply put, another fishermen caught it and they brought the tag home! For the first time in this
20-year study, we were able to successfully recover a PSAT. In most cases, having a fish captured that is carrying a PSAT is not advantageous to our research. However, in this case, the fish carried the tag for 57 days, and by retrieving the tag, we acquired a more detailed record of the behavior of the fish over that time period than if the tag had not been recovered. Typically, a tag detaches from a fish after a monitoring period that we set (e.g., 30, 90, or 180 days) and we retrieve a portion of data recorded on the device while attached to the fish via satellite uplink. In the case of our recovered PSAT, we were able access the tag’s hard-drive to download the entire dataset. This occurrence, to the best of our knowledge, is the first-time a PSAT has been recovered on a dolphinfish, and it represents one of the most detailed daily records of a bull dolphinfish in our world’s oceans. This information is critical in order to better understand how large dolphin behave in the Caribbean Sea, a region that lacks this information, and to ultimately ensure the long-term sustainability of the dolphin fishery throughout the region.
While not considered a broad-scale movement, the 445-mile long track showed us that this bull used a variety of habitats throughout the region at a varied pace. For the first six days, the fish lingered within a few miles of the shelf edge off La Parguera before moving northwest into the Mona Passage on March 31st. Once in the Mona Passage, the fish meandered for 12 more days off the western insular platform, due west of Boquerón Bay and within the vicinity of Abrir La Sierra, an important shelf-edge reef system off the west coast. After the fish utilized the shelf and open ocean coastal waters off southwestern Puerto Rico for 18 days, it began more direct and transitory movements toward the northwest bisecting the Mona Passage in seven days. The fish swam an average of 12 miles per day in the middle of the Mona Passage and then slowed to an average of six once the fish arrived off Punta Cana on April 17th. The fish then swam south along the eastern coast of the Dominican Republic before heading back into the Caribbean Sea southeast of Isla Saona on April 26th, four days shy of spending the entire month of April in the Mona Passage. For the remaining 24 days of the track, the fish occupied a 2000 square kilometer area south of La Romana, DR, which was half as much area covered during the first part of the track off PR and while in the Mona Passage. Within DR coastal waters, the fish revisited previously visited areas at 3 to 20 day intervals. The fish was captured at a fish aggregating device (FAD) south of Isla Saona on May 20th.
During the 18 days the fish was off southwestern Puerto Rico, it experiences its deepest and most complex diving behaviors. On March 28th, a day when the bull was estimated to be right along the shelf break off La Parguera, the bull’s average daily depth was only 14 meters but during night average depth use extended to 51 meters with several dives taken between 100 and 142 meters. During sunrise and sunset the bull was also observed to dive to 57 and 116 meters with the brightest time of day spent in depths less than 36 meters.
While along the west coast of Puerto Rico on April 6th, the bull dove to its deepest depth, 149.3 meters, of the entire 57-day. Two days later, the fish displayed similar diving behavior as observed off La Parguera while the bull was estimated to be off the shelf edge west of Boquerón Bay. On that day, the deepest depths to 129 meters were registered around sunrise.
The bull’s deep diving behaviors during sunrise, sunset, and night continued through the middle section of the Mona Passage near el Pinchincho, but when the fish arrived off Punta Caña and the eastern shores of the Dominican Republic (DR) on April 17th, depth use had decreased to a daily average of 2 meters and the fish only ventured to depths below 50 meters during 20 dives over a two-week period. The majority of those dives also occurred once the fish was estimated to be off the southeastern coast of DR, where the continental shelf habitat protrudes into the southern portion of the Mona Passage from Isla Saona.
The majority of those dives also occurred once the fish was estimated to be off the southeastern coast of DR, where the continental shelf habitat protrudes into the southern portion of the Mona Passage from Isla Saona. For the remainder of the track while the fish was south of La Romana, crepuscular and night-time diving behaviors were extensive but rarely exceeded 100 meters like the dives observed off southwestern PR.
During the 57-day monitoring period, the bull experienced three full and two new moon phases. Depth use during these periods did not show a pattern or trend. Depth use during the full moon phases varied from deep during the first phase, shallow during the second, and back to deep during the third. During the new moon phases, diving behavior was shallow during the first phase but deep during the second phase. In terms of patterns or trends observed over the period, both night and the presence of extensive shelf habitat, which likely affect differences in foraging habits for prey, appeared to be drive changes in the vertical movements of this animal.
Another remarkable facet of this dolphinfish tracking event, as well as others that our program has logged around Puerto Rico, is the collaboration of the parties involved to help deploy tags as well as retrieve the tag that was the focus of this article. The tag was retrieved through the help and assistance of Chris Whitley and Rick Alvarez, anglers who have extensive fishing experience in the Dominican Republic, as well as Oscar Paredes, Harbor Master at Marina Casa de Campo, who contacted fishermen in the local artisanal fishing co-op to locate the tag, and then helped ship it to our HQ. This event also would not have occurred without the assistance of Captain Duran, mate Rodriquez, and photographer Dooley. Over the past decade, six different captains and fishing teams have helped deploy satellite transmitters around the island, with the most recent being Captain Alexis and Sein Lopez of Aguadilla whom helped deploy a PSAT on a 34” bull on April 21st, 2021. A special thanks to everyone involved in the deployment of satellite tags on dolphinfish in Puerto Rico. It is simply amazing how this event and the study of this species have brought together so many people on the island for the vital purpose to better understand and manage the most landed pelagic species on the island.
Captain Colt Cook and angler Duncan Wright aboard Hook n Cook tagged and released a 20″ dolphin north of St. Croix in the southwestern portion of the Anegada Passage on August 3rd, 2020. On September 23rd, 2020, artisanal fishermen Alido Baez of Bayahibe, Dominican Republic, recaptured Hook n Cook’s fish aboard La Fiera, which had grown 5″. This is the 11th within-region Caribbean Sea conventional recovery and first from north of St. Croix to south of Saona Island, DR, spanning the entire USVI/PR continental shelf corridor to the southwestern edge of the Mona Passage. When combined with the other recoveries reported south of PR and DR since 2011, the average movement rate is 8.93 miles per day. In the image to the left the numbers represent days at liberty for 7 of the 11 recoveries. The only other recovery generated from the Anegada Passage was tagged and released aboard World Class Anglers by Captain Josh Slayton and was recaptured in the northwestern portion of the Mona Passage by Captain Matthew Bierley, showing that fish can move through the Mona Passage from the Caribbean Sea toward the Tropical Atlantic.
Straight-line distance between tag and recapture sites = 257.58 miles; Straight-line movement rate = 5.05 miles per day; Days at liberty = 51; Growth rate = .098″/day or .68″/week.