Caribbean Sea | Dolphinfish Research Program | Mahi-Mahi | Mahi | Dorado | Dolphin | Dolphinfish
mahi mahi, dolphinfish, dolphin, dorado, fisheries, FADs, tag and release
mahi mahi, dolphinfish, dolphin, dorado, fisheries, FADs, tag and release
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Caribbean Sea

Geolocation Movement for 44" Female Recaptured

July 2023

By: Wessley Merten


In 2019, we resumed a study to document the movements of dolphinfish in the Caribbean Sea by deploying satellite tags on adult dolphinfish during the spring run off the Southwest Coast of Puerto Rico (SW PR).  This research builds on earlier tagging work we did in the same area between 2011 and 2014 in which three satellite tags were deployed.  In total, 15 satellite tags have been deployed, with 12 deployed since 2019.  Of those 12, two were recaptured south of the Dominican Republic, which equates to a 16% recovery rate.  Even if we assess the recovery rate based on all PSATs deployed off SW PR, since 2011, two of 15 tags recovered equates to a 13% recovery rate.  Both tags were recaptured by anglers fishing FADs south of DR, and in both instances, we awarded those anglers with several hundred dollars to successfully ship us the tags.  Aside from the importance of documenting the recovery rate of satellite tagged fish moving west from PR waters, the information gleaned from these tags as well as our ability to refurbish and redeploy the tags enhances our ability to learn more about this important pelagic fish and the dolphinfish fishery in the region.  Interestingly, the 44″ female followed a similar track as the 47″ male recaptured in 2019 (click here

Most probable track for a 44" adult female dolphinfish fitted by unscented Kalman filtering with satellite-derived sea surface temperature (UKFSST; solid line). The fish was released off Cabo Rojo, Puerto Rico and remained at liberty for 22 days until the fish was recaptured at a fish aggregating device (FAD) south of Barahona, Dominican Republic, on April 21st, 2022. The numbered red boxes correspond to 3 regions of interest: #1 Rincon, #2 southern Mona Passage shelf, #3 Barahona. The depth use for these areas are depicted in the section below. This fish was tagged and released aboard Lalooli.
Animated most probable track for a 44" adult female dolphinfish.

or that story).  Similar to the bull’s movement, while not considered a broad-scale movement, the 625-mile long track showed us that this cow used a variety of habitats throughout the region at a varied pace.  Following a rapid daily movement northwest into the Mona Passage after being released, the succeeding four days were spent just offshore Rincon, Puerto Rico, and northeast of Isla Desecheo from April 1st until April 4th.   The fish then moved northwest into the tropical Atlantic before moving back south through the Mona Passage at a steady pace of 27 miles per day.  The cow moved from the tropical Atlantic in the northern part of the Mona Passage to the Caribbean Sea in the southern part of the Mona Passage in three days.  From here, the cow moved westward and seemed to orient relative to deep depth contours associated with the continental shelf.  Prior to the six-day westward movement to the recapture site, there were three instances when the fish moved southeast for one to two days moving against the prevailing southeasterly tradewinds.  Anglers fishing south of Puerto Rico have provided accounts of outings where they seemed to follow schools, called cardumens in Puerto Rico, east.  These short jaunts confirm that this cow was making short easterly movements, but it is unknown whether or not the cow was schooling.  After the final short southeasterly movement, the fish moved west 150 miles in one day, which is the fastest daily movement obtained over the monitoring period.  That distance traveled in one day equates to an hourly movement rate of 6.25 miles per hour.  However, when the cow was south of DR, the average daily movement rate slowed down to 21 miles per day before the fish was recaptured a FAD south of Barahona, DR.  Total time at liberty between deployment and recapture was 21.97 days.

In terms of depth use, the female’s vertical habitat use was a stark contrast to the habitat use observed for the 47″ male tracked in the same area in 2019.  For the female, aside from repetitive deep diving behavior off Rincon for a few days, deep dives for extended periods of time were lacking for the cow.  While the deepest observed depth for the cow was 150.6 meters, similar to the 149.3 meters observed for the big bull, vertical water column use ranged from 0-50% of that depth.  The female did show deeper diving behavior at night, which was similar to the 2019 bull, but the bull consistently dove to depths at or near the maximum depth during the 55-day track.  This is the first time our program has acquired geolocation tracks that were similar in path in the same area between sexes for dolphinfish which makes these datasets a unique glimpse into behavioral differences between adult male and female dolphinfish.  One caveat to disclose is the entire dataset was acquired for the 47″ bull.  This led to a very precise depth record for where the bull was at any given time during the monitoring period.  For the cow, we opted for the 15-minute standard rate dataset to allow for more timely and less costly tag refurbishment.  Despite the major differences in sampling rate between datasets, depths recorded at 15-minute intervals would still show extensive depth use, which was not the case for the female’s record.  These records and observations obtained excite us as we forge ahead to tag and release more healthy adult dolphinfish off Southwest, Puerto Rico, in the future.  The anglers involved in this work off Southwest, PR, are as follows:  Captain Manuel Botello (2011); Captain Milton Carlo (2011-2014); Anibal Santiago (2011-2014); Captain Jesus Milo Duran (2019-present); Captain Dan Hack (2021-present); Captain Yunyi Gonzalez (2022-present); Anglers Dagobuerto Rodriquez, Emmanuel Markham, Jose Lebron, Irving Baez, Alexis Alfalla.

Most probable geolocation track and depth use for a 47" bull tracked in March to May, 2019, versus a 44" cow monitored from March through April 2022. The red boxes indicate areas of interest to examine vertical water column use.
Depth use (relative depth % of max) scatterplots for a 47" bull and a 44" female tracked in the same area but during different years. The female's record was for 21.97 days (typo on plot) versus 55.83 days. Only the standard rate for depth use was obtained for the female but despite this the patterns between these individuals are evident.
New Recoveries off the Dominican Republic

October 2022

By: Wessley Merten

Data collection on highly migratory fish stocks (HMS) is difficult.  For dolphinfish, while not officially recognized by regional fishery management bodies as an HMS species, it is no different.  To collect data on dolphinfish, for the past two decades, the Dolphinfish Research Program (DRP) has distributed more than 60,000 tags to thousands of anglers throughout the Atlantic, Pacific, and Indian Oceans to compile basic statistics on distribution, occurrence, movements, and growth.  In August 2021, the Sandman Fishing Team reached out to us to get involved.  While their fishing team was one of 366 vessels to receive tags from the DRP in 2021, it was the only new tagging vessel to generate eight recoveries through their dedication to tagging over the past year.  Last October, we showcased their efforts in our monthly newsletter (click here for that story), and over the last month, four additional Sandman tagged fish have been recovered.  The following summarizes all recoveries:

Figure - Conventional dolphinfish recaptures generated by the Sandman Fishing Team. DAL= Days at Liberty
  • All occurred within Dominican Republic (DR) waters in the fall
  • All were reported by DR commercial anglers
  • 7 of 8 recaptures occurred at fish aggregating devices (FADs)
  • All recovered fish were originally tagged at FADs
  • Tagged fish in DR waters, on average, grew 2″ while at liberty
  • One tagged off Florida grew 10″ in 200 days and moved to DR
  • Movements were to the northwest, averaging 13.52 miles/day
  • Sandman’s recapture rate is 6.5% (8 of 122 tagged)
Figure: The Sandman Fishing Team has generated 8 new dolphin recaptures over the past two years of participation. Sandman has tagged 122 fish. Numbers equal days at liberty.

Sandman’s high recapture rate rivals our top tagging teams (Killin Time II and WamJam) in the Florida Keys, and like in the Keys, is indicative of high fishing pressure but off the north coast of DR.  Another factor that could be contributing to the high recapture rate may be due to horizontal compression of the species due to the high number of FADs distributed around DR.  Wilson et al. (2020), estimated that 2,500 FADs were active off DR, which is the highest number of FADs present in any Caribbean Island nation by fourfold.  Is it then coincidental that commercial dolphinfish landings in DR have increased 70% since 2014 during the time period in which FAD use has proliferated?

Figure: Annual dolphinfish commercial landings in the Western Central Atlantic Ocean acquired from the FAO for the top three (FR = France; VZ = Venezuela; DR = Dominican Republic) and the 9th (US = United States) commercial harvester since 1992. According to the FAO dataset, France recorded 2200 pounds of dolphinfish landings in 2016, and no landings in 2017. These values are inconsistent with previous and recent annual levels of landings so likely are incorrect.

In the most recent year (2019) of reported landings to the Food and Agricultural Organization (FAO), the Dominican Republic ranked second in terms of commercial dolphinfish harvest, but 3 times lower than France, the top commercial dolphinfish fleet in the Western Central Atlantic Ocean (WCA).  The U.S. directed dolphinfish fleet ranked 9th in the WCA and was 4 times lower than DR and 13 times lower than France.  This information is reported here because, recently there have been several articles published that blame the U.S. directed commercial dolphinfish fleet for the decrease in abundance and size of dolphinfish in the Florida Keys/South Florida region.  What these articles failed to report, quote, or cite, however, is that less than 1,000 miles away, dolphinfish landings have increased dramatically during the same time period.  Even more shocking is these skewed reports failed to mention that the U.S. recreational (for-hire and private) fleet landed 13,053,698 pounds of dolphinfish in 2019, 4.4 times higher than the largest commercial harvester of the species in the WCA (France at 2,949,781 pounds), nearly 13 times the Dominican Republic commercial industry, and 57 times the U.S. commercial fleet.

Photo: Jeffrey Liederman pauses to showcase the release of a beautiful DR dorado aboard Sandman in 2021.

While there remain several key unknowns with regards to the harvest of dolphinfish in the region (click here for that analysis), what some recent calls to action fail to take into account are the biological attributes of dolphinfish.  Many of these attributes, such as an early age of maturation, high reproductive capacity, fast growth, large size at maturity and short lifespan, suggest it can sustain considerable rates of exploitation if the population is managed properly.  But, in DR, there is no management plan for dolphinfish.  Across the Caribbean Sea, there is no management plan for dolphinfish.  In the Gulf of Mexico, there is no management plan for dolphinfish.  From North Carolina north, and throughout the Caribbean Sea and Gulf of Mexico, any size dolphinfish can be harvested.  The use of j-hooks and dropback techniques, both of which are detrimental to the species, remain prolific among recreational and artisanal anglers throughout the region.  Additionally, there remains a lack of participation among anglers to provide relevant data for scientists and managers to consider to examine fishing pressure and dynamics exuded on the WCA stock, data that is needed to better manage the species.


Sandman’s recent participation and results showcase how individuals can make a difference through our tagging program on the knowledge of the WCA dolphinfish stock.  Their participation sheds light on real issues that face the WCA stock and can be used as evidence to drive constructive management of the species for the future and for all stakeholders.

Another Satellite Tag Recovered South of the Dominican Republic

May 2022

In 2019, our tagging program reinitiated a study to describe the movements of dolphinfish within the broader Caribbean Sea by deploying more satellite tags off the southwest coast of Puerto Rico.  Building off of work that began in the area in 2011, we deployed three  satellite tags in 2019, and one of them was recaptured at a fish aggregating device (FAD) south of Isla Sanoa, DR, on May 20th, 2019.  That was the first time a satellite tag had been recovered for our tagging program, and we were able to successfully retrieve the tag and acquire a very detailed record of the movement of the 47″ bull.  Click here for that story.  Recently, we deployed five tags in the same area, and another was recovered at a FAD, but this time 20 miles southeast of Barahona, DR.  Thankfully, we were able to compensate the anglers who recovered the 44″ female (pictured below being released), and they shipped the geolocating tag back to us.  While we have not yet processed the track, with this article we share the 21-day point-to-point movement as well as some details on the vertical behavior of this female while at large.  During the first 12 days post-release the female made frequent and repetitive dives  deeper than 75 meters.  During the last 9 days before being recovered, however, the female only exceeded a depth of 25 meters three times.  Aside from the fact that two out of 14 spring satellite tags deployed off southwest PR since 2019 were recovered within 30 miles of each other at FADs south of DR, a trend of decreasing depth use from east to west is similar to that of the bull, which suggests that FAD presence may have an effect on the vertical movements of dolphinfish monitored in this region.  A special thanks to Lalooli and Liqueo fishing teams (pictured above) based out of Boqueron, Puerto Rico, for their help with the recent tag deployments.

A 44" female released back to the wild with a geolocating satellite tag.
Point-to-point movement of a 44" female recaptured at a FAD south of DR. The satellite tag was successfully recovered from the anglers.
Raw vertical movement data for a 44" female recaptured at a FAD south of DR on April 20, 2022.
Caribbean Sea Sat Tag Deployments

April 2022

Our quest to describe the movements of dolphinfish within the Caribbean Sea continued in April with the Lalooli and Liqueo fishing teams based out of Boqueron, Puerto Rico.  Those crews deployed a total of five popup satellite archival transmitters on adult male and female dolphinfish ranging in size from 38″ to 48″ fork-length.  This work began nearly a decade ago, and so far, we have successfully deployed 16 satellite tags and have received several conventional  recoveries. Of the tags recently deployed, one popped up on its scheduled date and another was recaptured at a fish aggregating device southeast of Barahona, Dominican Republic.  Updates on these movement records will be posted soon.

Fishing aboard Liqueo with Captain Efrain Gonzalez, mates Dago Rodriquez, Jesus Duran, and Jose Lebron, pass a 42" female dolphinfish in a cradle to be revived in the water and set free. Photo: W. Merten

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


47" bull tagged and released while fishing aboard Yadimar with Captain Jesus Duran and mate Dagobuerto Rodriquez.

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.

Most probable track for a 47" adult male dolphinfish fitted by unscented Kalman filtering with satellite-derived sea surface temperature (UKFSST; solid line). The fish was released off La Parugera, Puerto Rico and remained at liberty for 57 days until the fish was recaptured at a fish aggregating device (FAD) south of Isla Saona, Dominican Republic, on May 20th, 2019. The numbered red boxes correspond 4 regions of interest: #1 La Parguera, #2 Boqueron, #3 Punta Cana, #4 La Romana. The animals depth use for these areas are depicted in the section below.

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.

Geolocation, most probable track, and depth use for movements of a 47" bull monitored off La Parguera, Puerto Rico.
Geolocation, most probable track, and depth use for movements of a 47" bull monitored off Boqueron, Puerto Rico.

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.

Geolocation, most probable track, and depth use for movements of a 47" bull monitored off Punta Cana, Dominican Republic.
Geolocation, most probable track, and depth use for movements of a 47" bull monitored off La Romana, Dominican Republic.

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.

St. Croix to the Dominican Republic

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.

Merten, W.B., Appeldoorn, R.S., Hammond, D.L. 2016. Movement dynamics of dolphinfish (Coryphaena hippurus) in the northeastern Caribbean Sea: Evidence of seasonal re-entry into domestic and international fisheries throughout the western central Atlantic. 175, 24-34. Click Here for the PDF

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