Life at Sea

How One Tagged Specimen Completes the Picture

Don Hammond October 1, 2015

On June 3, 2014, members from the Cooperative Science Service’s Dolphinfish Research Program were invited aboard My Three Sons. The goal, which was accomplished with an estimated 20-pound bull dolphin labeled GHOF-01 in recognition of the Guy Harvey Ocean Foundation, was to deploy a satellite tag on a mature dolphin off Charleston, South Carolina. The archival tag was programmed to monitor the fish’s movement multiple times per day for an entire six-month period—a first of its kind. Considering dolphin mortality rate is as high as 99.7 percent, tagging a fish that would survive for an entire 180 days without falling victim to predation seemed like a needle in a haystack.

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Photo: Don Hammond

Since the Dolphinfish Research Program’s inception over 14 years ago, previous tagging data provided distance traveled from Point A to Point B in a given time period and estimated growth rates, but little else. Satellite tags are very different than typical streamer tags. These high-tech instruments study fish behavior to the hour…it’s a comprehensive and expensive research effort solely made possible by a grant from the Guy Harvey Ocean Foundation. The study, now in its second phase, is directed at mapping the routes that dolphinfish travel along the Eastern Seaboard.

On October 31, 2014, GHOF‑01 turned south and never looked back, passing just 27 miles northwest of Rincon, Puerto Rico, on November 30.

Our heroic fish that has gone on to teach us so much released its archival tag on December 2, 2014, and the tag made first contact with a satellite the following day approximately 44 miles northeast of Punta Cana, Dominican Republic. As the satellite tag drifted southwest into the open Caribbean Sea, it would spend the next 23 days downloading vital data via the ARGOS satellite system.

In an effort to provide a smoother track, the daily positions of the fish were averaged and the distance between positions from one day to the next was considered the daily distance traveled. Of significant importance, the maximum daily distance traveled between consecutive days was 152 miles. During its first month at large, GHOF-01 traveled 982 miles, but even more astounding is that the fish traveled 8,000 miles in six months! This does not account for vertical movement, so the tagged fish actually traveled significantly farther than what is shown.

After the satellite tag was affixed on June 3, 2014, GHOF-01 swam east for four days to a point 190 miles southeast of Charleston before turning north. The bull dolphin put itself at risk on June 14, when it passed only 74 miles off Beaufort Inlet, North Carolina. From this location, GHOF-01 headed east for open water. It spent the last week of June 340 miles east of Oregon Inlet, North Carolina, likely riding a warm water eddie.

By the first of July it was well out into international waters, and by July 16 it reached a point 590 miles east of Nantucket Island, Massachusetts. GHOF-01 likely encountered another large rotating water mass, as it spent the remainder of July traveling around in a 174-mile diameter circle.

During the month of August, our lucky loaner clearly showed it was happy where it was. The fish spent the entire month moving in zigzag patterns, probably in a large eddie 680 miles southeast of Nantucket.

On September 4, our tagged fish returned to an easterly track that carried it to a point 1,175 miles southeast of Nantucket Island. At this point the fish turned south and traveled in a 263-mile diameter arc. At the end of the month it found another place it liked, because it spent the last three days of the month traveling in a loose pattern.

During most of October, GHOF-01 would travel 1,238 miles, zigzagging in a rectangular area that was 122 miles wide and 164 miles long. In the last four days of the month, it appeared to begin breaking away from the zigzag life it had been enjoying, heading in a more southerly direction. After one last 40-mile jog to the east on October 30, the dolphin decided it was time to head to the Caribbean, approximately 1,600 miles away. On October 31, 2014, GHOF-01 turned south and never looked back, passing just 27 miles northwest of Rincon, Puerto Rico, on November 30.

It spent the next three days at the entrance to the passage between Puerto Rico and the Dominican Republic. Unfortunately, we don’t know if the fish would have entered the Caribbean or continued westward in the Old Bahamas Channel toward the Florida Straits because the satellite tag released itself from the fish, which by now had very likely surpassed 40 pounds in weight.

Observed Movements of
Dolphin GHOF-01

June
Monthly Distance (Miles): 982
Daily Maximum Distance (Miles): 138
Daily Average Distance (Miles): 35.7

July
Monthly Distance (Miles): 1,335
Daily Maximum Distance (Miles): 152
Daily Average Distance (Miles): 43.1

August
Monthly Distance (Miles): 1,571
Daily Maximum Distance (Miles): 129
Daily Average Distance (Miles): 50.7

September
Monthly Distance (Miles): 1,539
Daily Maximum Distance (Miles): 132
Daily Average Distance (Miles): 51.3

October
Monthly Distance (Miles): 1,238
Daily Maximum Distance (Miles): 68
Daily Average Distance (Miles): 39.9

November
Monthly Distance (Miles): 1,654
Daily Maximum Distance (Miles): 119
Daily Average Distance (Miles): 55.1

The 8,000-mile journey traveled by GHOF-01 is the very first documented migration track for the species in the western North Atlantic Ocean. However, it most likely is not the only route used by the species. It will take many more documented migrations to establish their primary pattern(s).

Having a known route from the U.S. East Coast through the open North Atlantic Ocean down to the Caribbean, we can now combine it with knowledge we have gained from the Dolphinfish Tagging Program for a complete picture of a migratory route. This gives us a better understanding of the real and potential fishing pressure being exerted on the same stock of fish relied upon by U.S. recreational anglers. It also raises concerns about the two specific areas where GHOF-01 spent extended periods, which if commonly used by dolphin year after year, could expose massive numbers of fish to international commercial exploitation that would be completely unknown to U.S. fisheries management.

As a research biologist who has been studying dolphinfish for the better part of two decades, I consider GHOF-01 an absolute dream come true. It’s important to keep in mind that studying any wild animal that covers such amazing distances requires a long term dedicated study—you simply can’t do it in a year or two. Nor can you do it under any sort of governmental grant that comes with political restrictions and time limitations. For recreational anglers, the Dolphinfish Research Program represents our best chance to understand a vitally important fishery crucial not only to countless recreational anglers along the entire Eastern Seaboard, but also to such a wide range of blue water predators. While we’ve learned so much from GHOF-01, the fish’s impressive migration route also leaves us with many unanswered questions.

The Dolphinfish Research Program

The Dolphinfish Research Program is a scientific project for fishermen by fishermen. Virtually all fieldwork is carried out by recreational anglers. Concerned conservationists spend their time and money to catch and tag dolphin, and complete the necessary paperwork. It is also the private angler who makes the effort to report the recovery of tagged fish.

Dolphin are extremely challenging to study since the fish travel several thousand miles in a year, including the entire western North Atlantic, Caribbean Sea and Gulf of Mexico, and only two or three out of every 100 tagged fish are likely to be recovered.

Since its inception, more than 1,100 boats and 2,200 anglers from 40 states and 10 foreign countries have participated, tagging 18,000 dolphin, resulting in the recovery of more than 500 tags. Through the Dolphinfish Research Program we’ve learned…

1. Dolphin never stop moving.
2. Dolphin exceed 30 pounds in their first 12 months.
3. Dolphin have a daytime menu consisting primarily of flying fish, jacks and other forage that associate with sargassum weed.
4. Dolphin have a nighttime menu consisting of squid and shrimp, often diving hundreds of feet into prime feeding zones where the fish spend minimal amounts of time before returning to the surface to warm up.
5. Dolphin ride ocean currents, and eddies are definitive feeding zones.
6. Dolphin are considered “offshore herring” as all offshore species rely upon them as a food source, especially mako sharks.
7. Dolphin most likely see color as indicated by the brilliant colors they wear, and alter the pigmentation of their skin to communicate.

There is still a tremendous amount to be discovered about this incredible fish and the Dolphinfish Research Program needs your help. To learn more about a tax deductable financial contribution or to obtain a free tagging kit, visit dolphintagging.homestead.com.

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