Conservation of a Prehistoric Fish

Latest update June 3, 2020 Started on January 1, 2013

Bonefish have inhabited shallow tropical habitats for more than 30 million years, and currently support economically and culturally important fisheries. Our research aims to inform conservation before more populations decline.

January 1, 2013
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In The Field

It's great to once again get access to the field report post. The big news is that we tracked a coastal, shallow water fish descending to 137 meters (452 feet) to spawn! This is information new to science. Check out the video we made about this exciting project that includes work in the field and lab.


Here is a video of a school of bonefish that are being held within a larger seine net on a shallow flat. We captured this school of fish and tagged all of them with dart tags so we can figure out which flats they return to after spawning (anglers tha catch these tagged fish let us know the location of recapture). We also surgically implanted acoustic tags in some of the fish so we could track them as they move offshore to spawn.

I am pleased to share that our expedition will be receiving a Trident Underwater Drone. Thanks to the many followers and those who have been tracking the blog. As we prepare for the first trip of the spawning season (early November), we'll continue to add updates.

The video below is fun to watch, but it is a good example of why we need the drone. You can see that we are limited to snorkeling - SCUBA bubbles scare the fish, and since some of their predators (large groupers and snappers) attack from below, even a rebreather is a challenge. Even with snorkeling, we can't really swim into the school, we have to drift into the school. And you can see that as a snorkelers we are exposed to even small wave action, which makes it tough to get steady video shots. Finally, even while snorkeling, you can see that the behavior of fish closer to the snorkeler is different than fish on the other side of the school. The fish on the other side of the school continue to porpoise and gulp air at the surface. Those closer to the snorkeler are more wary. The drone will allow us to obtain extensive footage of pre-spawning behavior.

You can read the latest on what we've learned so far about bonefish pre-spawning behavior on Dr. Andy Danylchuk's Researchgate page:

Regional conservation implications. Part 2 - Genetics

In addition to estimating the connectivity of bonefish populations in different areas by larvae being transported by ocean currents, BTT also collaborated with scientific colleagues to examine bonefish genetics. Recreational anglers and fishing guides collected fin tissue samples from more than 13,000 bonefish from Florida, The Bahamas, Cuba, Mexico, Belize, Cayman Islands, Honduras, Nicaragua, Puerto Rico, US Virgin Islands, Turks and Caicos. The results reflect the findings of the oceanographic study. On the broad scale, bonefish throughout the Caribbean share enough genetic similarities that we can consider the region to have a connected population.

This doesn’t mean, however, that locations are directly connected. For example, it’s highly unlikely that a larva spawned in Vieques reaches the Florida Keys, much less The Bahamas. Instead, the relationships are probably step-by-step: a larva spawned in Vieques, for example, reaches the Cayman Islands; a larva spawned in the Cayman Islands reaches Mexico or southwest Cuba; a larva spawned in Mexico or southwest Cuba reaches the Florida Keys. Thus, locations that are closer together are likely more connected – by closer together I mean close in space, like northern Cuba and the southern Bahamas, or seemingly made closer by strong currents (the stronger the currents the faster larvae are transported) like Mexico and the Florida Keys.

We can see some of these relationships on the map. Mexico/Belize have a close relationship with the Florida Keys. This is a one-way street, with larvae from spawning in Belize and Mexico reaching the Florida Keys. Mexico and Belize also have a strong relationship with Cuba – based on the oceanographic current models this is likely in the direction from Cuba to Mexico and Belize. Cuba has a moderate relationship with Florida – that could result from larvae from spawning in southwest Cuba reaching the Florida Keys, or from larvae that travel from Cuba to Belize and Mexico that then grow up to spawn and send larvae to the Florida Keys. And as you might expect, there is a genetic connection between The Bahamas and Cuba. Additional, ongoing analyses of the genetic and oceanographic, as well as future studies, will further reveal these relationships.

Below is a map showing some of the likely connections.

Next week we'll start talking about the upcoming research to track bonefish spawning offshore.


You can get up to speed on this and other important projects being conducted by Bonefish & Tarpon Trust and collaborators in this episode from the PBS series Changing Seas.


Regional Conservation Implications:
Part 1 - Oceanography.

Recent technological advances have allowed oceanographers to reach a much better understanding of ocean currents. BTT recently collaborated with a group of oceanographers to get a better idea of where bonefish larvae are likely to end up. We provided a map showing known and likely pre-spawning aggregation (PSA) sites for bonefish throughout the Caribbean. The known sites are where we had observed PSAs. The likely sites were either where PSAs had been reported by guides and anglers or where the geography matched what we had documented for the known sites. This included sites in The Bahamas, Cuba, Florida Keys, Belize, Mexico, Puerto Rico, U.S. Virgin Islands, and Vieques, Venezuela – all locations with known recreational bonefish fisheries.

The oceanographers then used computer models that are based on real readings of ocean currents to inject 100 ‘virtual bonefish larvae’ into the water at these sites at the full moons between November and April for a 5-year period, and kept the larvae in this virtual ocean for 53 days. This resulted in the paths of thousands of larvae being estimated by the computer models. The computer model study concluded that many larvae remain in the vicinity of where they were spawned, but that many are transported to distant location – the ratio of staying local vs distant travel differed among locations. In other words, to some extent, some local bonefish populations are responsible for a large portion of producing the next generation. But all populations receive larvae from other locations, and some populations receive a lot of larvae from other locations.

The oceanographic study results showed that Belize and Mexico likely provide a lot of larvae to the Florida Keys, and even the likelihood of larvae from southwest Cuba reaching the Keys. The study also estimated that depending on where bonefish in the Florida Keys spawn, the Keys bonefish population could depend almost entirely on larvae from elsewhere or provide a lot of its own larvae.

As you might expect, there is a high level of connectivity among the islands in The Bahamas, as well as between The Bahamas and the north coast of Cuba. And because the currents are so strong, it’s even likely that larvae from spawning in the eastern Caribbean, at Vieques, reached bonefish populations in the western Caribbean.

The first image below shows a bonefish larvae captured while sampling on a sand flat at the end of its planktonic stage, just before it metamorphoses into the juvenile form.

The second image shows the results of the oceanographic model estimating larval transport. The light blue dot is a bonefish spawning location on Andros, The Bahamas. The red is the hundreds of overlapping tracks of the larvae. The dark blue are the locations of the larvae after 53 days. You can see the amount of connectivity between Andros, other Bahamas islands, and the north coast of Cuba.

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Regional conservation implications. Because bonefish spawn offshore and their larvae live as plankton in the open ocean for so long, it’s highly likely that many of those larvae travel a long way before they metamorphose into juveniles. Recent research confirms this likelihood, which means that conservation of a spawning area has regional implications. There are two lines of evidence that show regional connectivity – oceanographic and genetics data. Tune in next week for the details.

The image below shows a day-old bonefish larvae ready to begin it's 2-month oceanographic journey.


Conservation success.
So far, our scientific data on bonefish has contributed to the creation of 5 new national parks in The Bahamas, and helped to justify the expansion of a 6th park. Our data have also been included in a recent proposal for more parks in The Bahamas that focus on habitat conservation.

The image below shows the parks that have already been aided by data on bonefish movements.


Why it Matters. Part 3.

Threats to fish spawning aggregations. Like bonefish, many marine fish form large aggregations to spawn. These large aggregations of fish are especially attractive to commercial fishermen because the high abundance of large fish in a small area makes catch rates very high. This has led to severe overfishing for many fish species, for which the poster-child is Nassau grouper. Like bonefish, adult Nassau grouper migrate long distances from their home ranges to a spawning site, where they formed large aggregations of thousands of fish. These aggregations were targeted by fishermen with traps, nets, and hook-and-line. Harvest rates were so high that Nassau grouper were fished to near-extinction in many locations. In fact, with a few exceptions where protections are in place, it’s extremely unlikely that a SCUBA diver on a Caribbean coral reef will see a Nassau grouper, a species that was once abundant on coral reefs. Similar stories can be told for other species of reef fishes, like snappers and groupers, that aggregate to spawn. Although not as important of a food fish as Nassau grouper, bonefish spawning is also threatened: by harvest with nets during their spawning migration and by coastal development at the pre-spawning sites and along the spawning migration pathways.

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Why it matters. Part 2.

Aids to overall conservation. The economic and social importance of bonefish provide leverage for conservation that is lacking for many other species. In addition, because bonefish use a wide array of coastal habitats during their life cycle, they’re a good Umbrella Species. Umbrella Species are species whose ecological requirements are broad enough to encapsulate the requirements of many additional species. In other words, by protecting bonefish habitats, we are also protecting habitats used by many other species, thus creating much broader conservation benefits.

The images below show red mangrove prop-roots (first image), small baitfish hiding from predators among mangrove prop-roots (image 2), and a healthy seagrass bed. Bonefish use all of these habitats, so protecting bonefish and their habitats provides broader habitat protections.

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Why it matters. Why should we care about bonefish? Why is it worthwhile to conduct research and advocate for conservation? The reasons are many.

  1. Economics and culture. Bonefish support economically important fisheries throughout their geographic range. An economic study in 2009, for example, found that the recreational bonefish fishery in The Bahamas has an annual economic impact greater than $141 million. The fishery is responsible for a high portion of the local economies on many of the Family Islands of The Bahamas. In fact, bonefish are so important to the Bahamas they are on the 10₵ coin: many years ago, bonefish were an important part of the local diet, especially on the outer islands, and now support these communities as a recreational fishery. The flats fishery for bonefish, tarpon, and permit) in the Florida Keys has an annual economic impact of more than $465 million, and more than $50 million in Belize. This supports many thousands of jobs, and is forms an important cultural component of these communities.

The image below shows a fishing guide and clients on a flat in search of bonefish.


Bonefish Life Cycle. Part 5.

Like most marine fishes, bonefish spawn by a method known as broadcast spawning. The aggregation is mixed males and females that eject their eggs and sperm into the water, where fertilization occurs. The eggs hatch in about 24 hours, and then the larvae that hatch from the eggs live as plankton in the open ocean for between 41 and 71 days. The larvae that are lucky enough to survive and make it inshore to shallow areas transform into miniature versions of what we would recognize as bonefish. Research in The Bahamas has shown that juvenile bonefish require protected bays with sandy or sandy-mud bottoms.

The photo below shows a newly hatched leptocephalus larvae.


Bonefish Life Cycle. Part 4.

Moving offshore to spawn. At dusk, the bonefish in the PSA migrate offshore. Over many hours, they slowly make their way into water that is thousands of feet deep, though they remain at the surface. When they are ready to spawn, they descend as deep as 200’. It is believed that spawning occurs at this depth or as the bonefish rush back toward the surface. They then head back to the PSA site, and either remain to go out and spawn again the next night, or head home. One reason we don’t yet know the details on the actual spawning act is that it occurs at night, in water thousands of feet deep, where plenty of large predators could potentially be feeding on these large aggregations. On a recent trip to track bonefish as they moved offshore to spawn, our boat was circled on two consecutive nights by tiger two sharks (one on each night) estimated to be 7’ and 9’ long. That’s a pretty strong deterrent to getting in the water to try to observe spawning. This is why we need to begin using ROVs like the Trident to study these offshore spawning movements.

The picture below show a pre-spawning aggregation getting ready to move offshore.

The graph below shows the track of a bonefish in the spawning school as the school moves offshore. They stay near the surface for hours as they meander into offshore waters thousands of feet deep. Then they dive to more than 60 meters (nearly 200 feet) to spawn near dawn. (To convert from meters to feet: 1 meter = 3.3 feet.)

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Bonefish Life Cycle. Part 3.

Pre-spawning aggregations. When bonefish finally reach the spawning area, they frequently stage on a flat for half a day or so, then move into deeper water (typically 4-20’ depth) and form what we call Pre-Spawning Aggregations (PSAs). These PSAs frequently have many thousands of bonefish. In the afternoon, the bonefish in the PSAs begin behaviors that we don’t see on the flats: they jump out of the water (called porpoising), and bump into other fish (called ventral nudging). There are numerous theories on what these behaviors mean – we’re working on that one, too.

The image below shows a pre-spawning aggregation circling around an acoustic receiver that is anchored at a pre-spawning site. This allows us to know when our tagged fish are present, and when they leave the site to move offshore to spawn. We can also detect when they return to the site to spawn at later dates.

But it's difficult to correlate the presence of the bonefish (as recorded by the acoustic receiver) with their behavior. This photo gives you a glimpse of how the Trident can be used. It's difficult for a snorkeler to stay with the school, and the bubbles from SCUBA disturb the school of bonefish. The Trident would allow us to record long-term observations of pre-spawning behavior as the bonefish prepare to move offshore to spawn.

In The Field

Bonefish Life Cycle, Part 2.

Spawning migrations. Adult bonefish break from this local existence when they migrate to spawn. Spawning season runs from late October through April, though it seems that peak spawning differs among locations. In The Bahamas, for example, the peak in Abaco appears to be October-November, while in South Andros it’s December-January. In Belize, the peak seems to be December-February. And though spawning most frequently occurs near the full moon, we have documented spawning occurring at other stages of the lunar cycle. This variability is confusing since bonefish from a wide geographic range travel to a spawning site – migrations of 70km from home range to spawning site, and then the return trip, are common. So how do bonefish from distant flats know when it’s time to migrate to spawn? That’s a question we don’t yet have the answer to, but we’re working on it.

The image below shows a large school of bonefish migrating from their home range on the flats to the pre-spawning site.

Interesting. How big do the schools get?
The migrating schools can range from 30 fishi to hundreds. Once they collect in the pre-spawning aggregations it's in the thousands. Stay tuned for a future post to see a photo of a pre-spawning aggregation.

The Bonefish Life Cycle, Part 1.
Home range and spawning migration. Tagging studies of bonefish in The Bahamas, Florida Keys, Belize, and Mexico show that adult bonefish live in relatively small areas for most of the year. For example, in Belize and Mexico, more than 70% of tagged bonefish that were recaptured were within 1km of where they were tagged. Results in The Bahamas were similar – 60-80% (depending on the island) of recaptured bonefish were within 5km of the tagging location. In other words, bonefish have what we might call relatively small home ranges, so if a flat is lost or degraded it’s unlikely bonefish “will just go somewhere else.”

The first image shows a bonefish that has been tagged after being caught by a recreational angler. The second image shows a tagged bonefish that has been recaptured by a recreational angler more than a year after the fish was originally tagged.

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The Bonefish Life Cycle. To set the stage for explaining how recent and ongoing research is leading us to regional conservation, it’s worth a brief overview of what we know about the bonefish life cycle. We’ll frequently circle back to this information to address the conservation consequences. The next few posts will summarize the bonefish life cycle.

This Expedition blog is all about the science being conducted to advance conservation of bonefish in the Caribbean Sea, with a focus on spawning. Our next research cruise to The Bahamas to study bonefish spawning will be November 2019. Our plan is to conduct 5 cruises during the 2019-2020 bonefish spawning season. I’ll post a few times a week between now and the first cruise to bring you up to speed on what we know about bonefish biology, why we are doing this research, what we’ve accomplished so far, and preparations for the coming research season. Once we’re on the research cruises. I’ll do some live posts to share our progress.


We are conducting this research throughout The Bahamas, as well as in Belize and Mexico. However, the actual locations of the research are not shared for two reasons: 1) the fishing guides who make their livelihoods by taking paying clients fishing are secretive about their fishing spots. We don't want to give away their livelihoods by posting locations; 2) we don't share the spawning locations because we are afraid of poachers taking advantage of having access to large groups of fish (often more than 10,000 bonefish are in a spawning school).

Expedition Background

Bonefish (Albula vulpes) support an economically important recreational, catch and release fishery throughout the Caribbean, including The Bahamas. Despite this economic importance, only recently have we begun to learn about bonefish biology. We've learned that adult bonefish have a relatively small home range, and live on shallow flats of sand, mud, seagrass, algae, and in mangrove creeks. However, during spawning season they migrate long distances to spawn - a 140 mile roundtrip from home range to spawning location is common. When they get to the spawning area, they gather in large pre-spawning aggregations, and then move offshore at night to spawn. Our research now is focused on identifying more pre-spawning and spawning areas, and working to get these important locations protected. We are also working to observe and understand the complex pre-spawning and spawning behaviors, and to observe the actual spawning event. Since bonefish spawn in offshore waters at night, we have not yet observed spawning, so we are hopeful that by using ROVs we will be able to observe spawning for the first time in the coming spawning season (October - March). The images below show a bonefish that has been tagged with a dart tag, which has a unique identification number. We recorded the date and location where we tagged the fish and the fish's size. The second photo is a tagged bonefish that was recaptured by a recreational fisherman and his fishing guide. They recorded the date and location they caught the fish. The information on the locations of fish tagging and recapture help us determine bonefish home ranges and movement patterns.

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