Understanding Gulf Ocean Systems (UGOS) Initiative recently marked a significant milestone by collecting 10,000 profiles from these floats, making the Gulf one of the most intensively sampled water bodies in the world.  

These floats do not always have easy journeys. During their missions, some floats become ensnared by fishing vessels, encounter wildlife, or otherwise go missing and stop transmitting data. It is rare for a missing float to return to its mission, but one UGOS team experienced just that. Here, the UGOS team at the Woods Hole Oceanographic Institution recount the intrepid story of Float 7513.  

Argo Float 7513 was launched at [26.265N, 85.604W] in the Gulf of Mexico on September 27, 2019. One never knows where a float will go after deployment, but it is not typical for its mission to include two visits aboard fishing vessels!

Figure 1. Example of a label on an Argo Float that states that the float is scientific equipment. Image courtesy of Woods Hole Oceanographic Institution

For five years, the float was on a normal mission. It would drift for five days at 1500 meters below the surface of the ocean, collect profile data, surface, transmit the data, sink back to 1500 meters, and repeat. In July of 2024, the float was located south of the center of the Loop Current—a major current of warm water that plays a major role in the Gulf’s ecosystem, in hurricane formation, and in offshore oil and gas operations— and was providing important measurements for improving ocean and atmosphere forecasts.

From there it started moving south, in the opposite direction than what might be expected. By September of 2024, it had drifted to just off the western tip of Cuba. To make its way over the sill between Cuba and the Yucatán Peninsula and get around a seamount, the float moved in a rough figure 8 throughout October 2024.  

By December 2024, the float had begun heading southwest at a depth of 2000 meters, picking up speed the further off course it went. Throughout the rest of the winter, the float stuck around the 19th parallel north. In mid-April, we noticed that the float had stopped transmitting data, and we presumed it was nonfunctional.  

At this point, the float had been collecting data for over five and a half years, which is a good lifespan for an Argo float. We were content with the fact that the float lived a long life, provided us with valuable data, and gave us an interesting story by becoming the first UGOS float to exit the Gulf of Mexico by slipping between Cuba and the Yucatán Peninsula. However, we soon discovered that this was not the end of float 7513’s journey in the Gulf.

Figure 2. Map of Gulf of Mexico with trajectory of Float 7513 from July 2024 through May 2025, color coded by month. Image courtesy of Woods Hole Oceanographic Institution.

After a 20-day absence, Float 7513 started reporting data again. We believe that a fishing vessel caught the float and then released it back in the water off the Northeast coast of the Yucatán Peninsula. The floats are marked with labels explaining that they are used for ocean, weather and climate predictions, so perhaps the fishermen read it and decided to put it back in the ocean (see Figure 1). The water depth is only approximately 300 meters where it was released, much shallower than the 1500-meter drift depth the float is programmed for. Because of this, in May, a command was sent to the float to change the park depth to 200 meters so the float would stop skittering along the bottom and hopefully make its way back into the Gulf. However, on May 14th, 2025, we realized that the learning algorithm which should teach the float to park at 200 meters was not working and we were not sure why… 

Ten days later, on May 24th, we found out that while on the Yucatán shelf, the float was yet again captured by a bottom-fishing vessel. This time, the float was aboard for a day and a half, during which the vessel transited about 400 kilometers to the north. When the float started up again and was returned to the ocean, we saw it was back in the deep waters of the Gulf of Mexico. Still operating at a park depth of 200 meters, it was drifting fast and at risk of being quickly swept out of the Gulf through the Straits of Florida.  

The float pilot immediately uploaded a command to the float on May 24, 2025, to return it to the standard UGOS mission, with a parking depth of 1500 meters. As of June 13, 2025, Float 7513 reported from just north of the center of the Loop Current, with a parking depth of 1500 meters that will keep it safely inside the Gulf—at least for now!  

This is not the first time an Argo float has been picked up by a fishing vessel. In fact, of the 53 profiling floats deployed through UGOS, at least six have experienced encounters with fishing vessels (7513, 7518, 7542, 7543, 7544, 7584). This encounter rate of about 10% is much greater than that of the global Argo fleet. The best method to avoid this is through careful monitoring of the fleet and active adjustments to alter the mission when the float is in shallow water (<1000m) and spending a portion of its drift on the seafloor.  

Typically, we don’t want our instruments to be in the position where they could be fished up, but in the case of Float 7513, the fishing vessel aided in getting the float from the Caribbean back into the deep waters of the Gulf! Doing field research always involves risk, but through the efforts of scientists, the assistance of fishermen, and a little bit of luck, autonomous floats like Float 7513 continue to help us improve our understanding of the complex physical dynamics of the Gulf.  

Disclaimer

The views expressed in this perspective are those of the authors and not necessarily of the National Academies of Sciences, Engineering, and Medicine (the National Academies). This perspective is intended to help inform and stimulate discussion. It is not a report of the National Academies.