New Tech Reveals Bonefish Secrets

BY CHRIS HUNT

Bonefish have long been associated with the Florida Keys, the birthplace of flats fishing, but, up until very recently, their spawning activity in Florida waters had remained largely a mystery.

Building on previous work in the Bahamas, where Bonefish & Tarpon Trust has identified numerous bonefish pre-spawning aggregations (PSAs), BTT scientists are now homing in on areas in the Keys important to spawning, and have confirmed what many have suspected for decades: that Keys bonefish do what bonefish do in the Bahamas and other places across the Caribbean. They gather in these PSAs, gulp air to fill their swim bladders and migrate offshore at night during certain moon phases from November through March or April. They then dive hundreds of feet deep. As they return to the surface, the pressure changes in their swim bladders allow for the release of eggs and sperm, creating a broadcast spawning event.

And now, thanks to ever-evolving technology, Bonefish & Tarpon Trust knows even more about these clandestine romantic gatherings of bonefish schools that can number in the thousands. All it took was one fish to give up its secrets.

Thanks to a new monitoring tool called an archival data storage tag (ADST), Dr. Ross Boucek, BTT’s Florida Keys Initiative Manager, was able to better understand the bonefish mating ritual that, up until 2010, was a virtual mystery (that’s when PSAs were first discovered and documented). Boucek and his team—the first to ever use this technology—implanted four bonefish with

ADSTs, and were able to determine when the fish gathered, when they moved offshore and, within a 12- to 13-minute window, when the bonefish likely spawned.

Only one of the four tagged fish spawned, Boucek believes. Three of the tagged fish, according to data from their ADSTs, never moved offshore to deeper water. But that last fateful bonefish did its thing.

“It gathered at the PSA site and then it just kind of disappeared for 48 hours,” Boucek reported. “When it came back, the data we collected told us what likely happened.”

Here’s the rest of the love story.

When that one tagged fish moved offshore, likely with thousands of others gathered together in a PSA, it dove to a depth of 304 feet. As it ascended in the water column, it paused below 100 feet for more than 12 minutes. This is likely when it released its eggs (the fish was female). Then it returned to the surface and ventured back to the flats.

“We relocated this fish with a manual tracker nine days after it spawned, when the fish tracker detected it—it was almost in the same spot where I caught it and put the tag in,” Boucek said. How much time passed between when the fish was caught and tagged and when it turned up on its home flat after its romantic jaunt? Just about two months.

Bonefish are on the rebound in the Keys after a dismal decade that followed a declining trend. Now, Boucek said, there’s a growing population of bones around Key West and numbers continue to improve on the flats throughout the Keys. Why? Research into the question is ongoing, but it’s clear the population rebound coincided with a number of different events.

For instance, the state of Florida recently spent about $1 billion removing old and faulty septic systems in the Keys. When that effort concluded, fish numbers started to rise.

“It’s hard to ignore that,” Boucek said. “But there are a number of different mechanisms in play, including planetary-scale ocean phases and other events that could cause conditions to be more favorable for bonefish.”

Additionally, all the bonefish in Florida aren’t necessarily from Florida—BTT’s research shows that some larvae from spawning events in Mexico, Belize, and even southwest Cuba can drift on ocean currents to the Keys, where they mature and take up residence. The efforts of BTT and others in Belize, Mexico, and Cuba to reduce harvest of bonefish by artisanal and commercial fisheries might be having a positive impact on bonefish populations in Florida.

“We still have so much to learn,” Boucek said, “but we’re making great progress. There are so few opportunities to discover something new, so this recent detection meant a lot.”

What’s next? Well, if Boucek had his way, he’d be on hand for the next gathering of bonefish in a PSA in the Keys, and he’d do whatever he had to do to document the entire spawning process. And that may not be a pie-in-the-sky goal with the assistance of even more new tech—this one, a prototype receiver.

The receiver technology was initially used on surf beaches to warn swimmers and surfers in real-time when sharks were in the area. Boucek and BTT hope to know exactly when the next PSA starts to gather in the Florida Keys by using that same tech. The novel receiver was deployed in December 2022.

If the receiver alerts scientists in real time of a PSA starting to form, Boucek and team could drop everything and go witness this aggregation.

“If it works, we might be able to actually see a PSA in the Keys,” he said. “How cool would that be?”

Even cooler? If Boucek and his team find the PSA, they could use tag tracking gear to follow the bonefish as they move offshore to spawn. Not only would they get to witness a PSA, but they could essentially follow thousands of bonefish offshore to an actual spawning site.

“This project is really pushing the envelope with new technology,” Boucek said. “The goal is to be at the same place at the same time when these fish spawn.”

Chris Hunt is an award-winning journalist and author whose latest work includes The Little Black Book of Fly Fishing (with Kirk Deeter) and Catching Yellowstone’s Wild Trout. His work has appeared in Outdoor Life, Field & Stream, TROUT, The New York Times, Hatch Magazine, The Fly Fish Journal and other publications. He lives and works in Idaho Falls, ID.