Research Highlight: Shark research and conservation cruise in The Bahamas Shark Sanctuary

 

The islands of the Bahamas lie within a mosaic of marine habitats where the subtropical open ocean washes over vibrant coral reefs connected to shallow seagrass beds fringed by rich mangrove forests. Divers still see sharks there on a regular basis, which is unusual throughout most of the rest of the region. This stems from the nation’s extremely progressive policy on shark conservation. Initiating with a ban on commercial shark fishing gear in the 1990s and culminating in the establishment of a “Shark Sanctuary” in 2011, commercial shark fishing and trade is now prohibited throughout the country.

Stony Brook University’s School of Marine and Atmospheric Science and the Cape Eleuthera Institute are conducting a 6-week research cruise of The Bahamas Shark Sanctuary from May 7-June 15, 2013. Funded by a generous grant from The Moore Bahamas Foundation the expedition will be led by Dr. Demian Chapman and graduate student Mark Bond, from Stony Brook University. The cruise aims to locate areas where juvenile sharks are common, thus providing a foundation for future efforts to map critical breeding and nursery habitats for sharks within the sanctuary. The team will also study shark movements in relation to the borders of The Bahamas to determine how ongoing fishing of sharks in neighboring countries may affect their numbers in the sanctuary.

Collaborators from Microwave Telemetry Inc. will fit critically endangered oceanic whitetip sharks with satellite archival tags to learn about their migrations to distant mating and breeding grounds, while researchers from the University of Florida and University of North Florida will study their fine-scale hunting behavior and reproductive biology respectively. Researchers from the U.S. National Marine Fisheries Service will attempt to track the movements of critically endangered smalltooth sawfish and determine whether or not the species breeds in The Bahamas. The research team also plan on tracking the movements of endangered great hammerhead sharks.

Follow the progress of the expedition by returning to this page for daily updates.

Day 1

Arriving by sea or air and with most of our luggage, the expedition team has assembled at Port Howe, Cat Island in the Bahamas. Cat Island is arguably the best place in the North Atlantic to find oceanic whitetip sharks. A true pelagic or “blue water” animal, oceanic whitetips have a global distribution and grow to lengths approaching 3 meters. They typically feed on other blue water fish, such as mahi-mahi, tuna and marlin. They also dive deep (to over 1,000 meters, which is double the height of the Empire State Building), where it is thought that they capture squid. If you have read any of Cousteau’s books you will know that oceanic whitetips used to be extremely common. In the film “Blue Water White Death”, which was made in the late sixties, pioneering underwater filmmakers swam with scores of these sharks off the coast of South Africa. Today, it would be very difficult to replicate this feat. Oceanic whitetips have declined to a shadow of their former abundance, so much so that it is now illegal to catch them throughout most of the world. The reason for this decline is the growth of industrial blue water fishing. Although sharks did not start as the target of these fisheries, fishermen found a market for dried shark fins and so began taking sharks (or at least their fins) as well. The fins were used in parts of Asia to make the Chinese delicacy shark fin soup, a luxury dish that fetches upwards of $100 U.S. a bowl. This market ballooned as the Chinese economy boomed, driving a global shark hunt of epic proportions as the world’s fishing nations responded to this demand.

The Bahamas Shark Sanctuary remains a great place to study oceanic whitetips and learn more about their movements and conservation requirements. Our team has recently published a preliminary study of this nature and we are keen to learn more. Our primary research tool is the pop-off satellite archival tag or PSAT, a device that is attached to the shark for several months and collects environmental data that helps us determine where the shark travels over this period. During the first few weeks of this expedition we hope to fit 25 oceanic whitetips with PSATs and learn where they go to mate and give birth. This part of the Stony Brook-Moore Bahamas Foundation cruise is also supported by Microwave Telemetry, the Blue Ocean Institute and the Save Our Seas Foundation.

Day 2 and 3

The first step to tagging a shark is catching it. Scientists do not always make the best fishermen, but our method for catching oceanic whitetip sharks is simple to say the least. First, we drift along in the boat and several tethered crates filled with fish pieces. Then we wait. These sharks are adept at finding food in a vast, relatively empty ocean and when they arrive they are usually hungry. We are then, eventually, able to hook them and haul them alongside our small boat for tagging.

Each shark is first given an identification tag in the dorsal fin that can be read underwater. This enables divers who see the shark during tours run from the island to provide us with information about its whereabouts for many years. Divers have just e-mailed us photographs of four of our sharks tagged in 2011, proving that at least some of these animals return to Cat Island each year. Next, we measure the shark. Although they are not as big as, say, a great white shark, oceanic whitetips are certainly hefty animals. The typical shark we catch is more than seven feet long. Once the tape measure is rolled up we take a small piece of the fin no larger than the nail in your little finger. This tissue provides us with a sample of the animals DNA, which contains a treasure trove of information about the individual’s relationship to others we catch, as well as the history of the population it comes from and how the population is related to others around the world.

We then take a blood sample from the underside of the tail, which is the best spot to access a decent blood vessel. This is being used by researchers from the University of North Florida are developing a pregnancy test for sharks (more on this in a future post). Lastly, the PSAT is applied at the base of the dorsal fin. We usually manage to get all of this done in around 15 minutes. The hook used to catch the shark is then removed, together with any other old hooks the shark has picked up from stealing baits or fish from local anglers, and the shark is released back into the blue.

In the first two days of fishing we have managed to hit the shark bulls-eye. Somehow we begin our drifts right on top of small pockets of sharks. In fact, the most we have to wait to see the first animal is just 15 minutes. Even better, they are ready to eat right away and readily take the bait. This works for us because we have an ambitious 25 PSATs to put out during this expedition. Remarkably, by the end of the second day we have deployed 16 of them. In the next few days we hope to capture either a pregnant female so that we can find out where they go to give birth, or a mature male to see where they go to mate.

 

Day 4 and 5

The number of PSAT-carrying oceanic whitetips has grown to 20 individuals in another couple of productive fishing days. Importantly, several of them are mature males. The females outnumber the males by about 5 to 1 at Cat Island, so males are hard to come by. As is the pattern in most sharks, the males are shorter and more slender than the females. We hope that the PSATs will show us where the males go after leaving Cat Island, which happens in the middle of June. The adult females we have already tracked follow one of three rough patterns so far. Some meander around The Bahamas for nearly a year. Others go north and occupy open ocean areas between Cape Hatteras, North Carolina, and Bermuda for a few months. The remainder travel east to an area around Puerto Rico for a short period. What they all have in common is that they all return to The Bahamas after a few months. We think that these short term but long distance movements are related to reproduction. We hope that overlaying male movements on top of female movements will shed light on which of these areas are mating grounds, where males are likely to go to find non-pregnant females to mate with. If we can PSAT a pregnant female it will help resolve where they go to give birth.

As the number of tagged oceanic whitetip sharks grows so to does the list of other shark species that pay us a visit. Tiger sharks (Galeocerdo cuvier) are very common in The Bahamas but we have never seen one out in the blue with the oceanic whitetips until this expedition. Even more surprising is to see a blue shark (Prionace glauca), a species I would expect to see off New York as opposed to The Bahamas. Blue sharks like colder water but practice “tropical submergence”, swimming at deeper depths as they head towards the equator. Our bait attracts a female blue from the deep and she swims amongst the much more robust oceanic whitetips without a care. We catch her and fit her with a PSAT in order to learn more about their depth range in tropical waters. As we move along the reef each day we see an abundance of nurse (Ginglymostoma cirratum), lemon (Negaprion brevirostris) and Caribbean reef sharks (Carcharhinus perezi). We even catch a fleeting glance of a great hammerhead (Sphyrna mokarran) over white sand. These sightings reaffirm why The Bahamas is considered by many to be the shark dive capital of the world and a leader in global shark conservation efforts.

Days 6 – 10

After a couple of rough weather days that keeps us at the dock, we resumed our efforts to tag oceanic whitetip sharks. During the hiatus we were able to get our ducks in a row to be able to conduct ultrasounds on the female sharks in order to determine whether or not they are carrying young. Like all sharks of their genus, oceanic whitetips have a lengthy gestation period and actually develop a placental connection with each of the developing offspring (which can number up to 15 or 16). A key objective of this expedition is to determine if any of the females we are seeing are in the late stages of pregnancy and, if they are, to then track them to where they give birth.

It is not long after we are ready with the ultrasound that a great candidate arrives in the form of a massive female. As round as on oil drum, this is the largest shark we have yet seen at Cat Island. She deliberately approaches the boat and quickly begins feeding on small chunks of fish, as we prepare the gear needed to catch and tag her. After a few minutes she is hooked and then brought alongside our small work up boat. She measures in at 292 cm total length, or very close to 10 feet. As far as we know the largest oceanic whitetip ever measured was about 320 cm, so this animal is in an elite size class. And if that is not exciting enough as soon as the ultrasound is rubbed along her belly it reveals the spine of one of her offspring. She is definitely expecting. We work fast to apply the PSAT and gather the remaining samples before releasing her. She surges down into the blue water carrying our PSAT and the first opportunity to learn where these sharks go to give birth. In the subsequent days we get another PSAT out on a pregnant female and one out on one that is definitely not pregnant. The males are showing up as well and several more of them are fitted with PSATs. We close the Cat Island portion of the expedition with all 25 PSATs deployed, 24 on oceanic whitetips and 1 on a blue shark. We are now headed for a break in Nassau to resupply the boat and to conduct outreach activities.

Andros Day 1, the West side.

Following a busy five days in Nassau, New Providence conducting shark education and outreach programs with local schools the team welcomed new members for the next leg of the expedition. Joined by researchers from the Panama City laboratory of the U.S. National Marine Fisheries Service and Cape Eleuthera Institute the crew eagerly boarded a seaplane and departed for Andros. Andros, the largest of all the Bahamian Islands however one of the least populated is home to the world’s third largest Barrier reef. In addition it boasts miles of deserted beaches and freshwater lakes which play host to countless species of wildlife, marine life, flora and fauna, including sharks. Andros is covered with vast areas of wetlands that create channels perfect for exploring and searching for the elusive smalltooth sawfish (Pristis pectinata).

A victim of bycatch in gillnets, the smalltooth sawfish is critically endangered around the world with populations having declined by >90% and with this their genetic diversity. As with sharks their life-history characteristics mean that populations will be slow to recover, therefore identifying and protecting critical nursery habitat is a top priority. Andros has been identified as one of the few places in the world where Small tooth sawfish are found outside of the US. Our research objectives while on the West side of Andros are to fit sawfish with PSATs and determine their movement patterns in relation to The Bahamas EEZ. Check back here to find out how we get on!

Andros Days 2 and 3

Still on the west side of Andros the team began searching for the critically endangered smalltooth sawfish. Sawfish have the ability to sit on the bottom and ‘rest’ for large periods of time making them difficult to spot, especially in very shallow water which they frequently inhabit. One of the most successful techniques for finding the sawfish involves driving around suitable habitat and targeting them with a custom designed lasso.

Feeling somewhat like the ‘A-team’ we split into groups and took to two boats and a helicopter! The eyes in the sky enabled us to cover much of the very shallow sand flats and creeks, endemic to Andros. Shortly after leaving the dock one of the boats spotted a smalltooth sawfish, estimated to be eight feet in length, cruising alongside them. They sprang into action and attempted to corral the sawfish into a position where they could use the lasso. Despite their strange appearance sawfish have the ability to turn very quickly and due to the shallow depth of water they can easily out maneuver the boats. Despite a valiant attempt by the team, including two near misses merely inches away, unfortunately the sawfish managed to evade capture by using the clouded water stirred up by the boat to mask its escape. Although our ultimate goal is to capture and deploy a satellite tag on one of these fish, this sighting provides crucial data. Previous expeditions have failed to even sight one therefore its location, estimated size and the time of year all contribute to furthering our knowledge of their movements in order to better conserve them.

Andros Days 4 and 5

While the search for the small tooth sawfish may be the primary objective while the team visited Andros, Andros’s size and low population density provided a pristine environment to witness more wonders than just sawfish. One of the biggest obstacles researchers face in their attempts to protect shark species is the lack of basic life history information, such as when and where they mate. Identifying and protecting areas of the ocean where behaviors such as mating and birthing occur can be critical to ensuring a species’ survival. To date only two out of the more than 450 species of shark currently known to us have been observed mating in the wild, and by a select few. It was therefore with great excitement and amazement that while out searching for sawfish the team were able to witness a couple of mating pairs of nurse sharks (Ginglymostoma cirratum).
Sharks mate via internal fertilization and it is thought that sharks were historically the first organism still alive today to use this reproductive method. The mating pairs were observed in shallow water (<3ft deep) on the sandy flats surrounding the West side of Andros.  n most species female sharks develop thicker skin and muscle walls on their sides, compared to the males. Since sharks don’t have arms the males need to bite onto the females to enable copulation. The mouth of a nurse shark is located on the underside of their head and they have very small teeth therefore in nurse sharks the males are seen to pin the females to the ground and bite onto their pectoral fins. Given the shallow water and the type of sandy bottom mostly what was witnessed was a lot of splashing around with tails and fins slapping the water, but we knew what was going on!

Our departure from the West side of Andros was dictated by an approaching storm system. This meant we were on standby until a small break in the weather allowed us to board the seaplane and head back to Nassau. There we reconnected with our mothership where we intend to continue the expedition to other areas of Andros.

Andros Days 6 – 8

After being delayed in Nassau for a couple of days due to some rough seas and a torrential downpour of what the Bahamians refer to as ‘liquid sunshine’ we were able to depart for the northern and eastern parts of Andros. For the most part Andros is under-researched compared to other islands in the Bahamas, however colleagues of ours have led expeditions to the west side of Andros in the past. One of the most exciting aspects of research is exploring and fishing areas previously unexplored and this was the challenge that awaited us on our journey around the rest of Andros. Using satellite images and our knowledge of suitable habitats gained from working in other areas, we identified potentially productive sites to fish. Sometimes this trial and error approach was a huge success with sharks ready and waiting to be caught and tagged on our arrival. At other times we found ourselves in water too shallow to even access the target area!

In addition to satellite tagging small tooth sawfish, oceanic whitetip and great hammerhead sharks, another aim of the cruise is to identify areas where juvenile sharks are common. This will help to provide a foundation for future efforts to map critical nursery habitats for sharks within the Bahamas. The isolated mangrove creeks of Andros provide ideal nursery habitat for lemon and nurse sharks therefore we targeted creeks in search of the ‘little guys’! We had great success and managed to tag and release many juvenile lemon sharks including those who were newborns, born within 6 weeks of being captured. Like humans, lemon sharks are born with a placental attachment and so they are left with a ‘belly-button’ scar which heals up within six weeks of being born. Two of the juvenile sharks we caught still had the umbilical scar partially open which indicates they were very recently born. Juvenile sharks spend their early years in the protective mangroves therefore these newborns were native to Andros. DNA was collected from these juvenile lemon sharks, via a small fin clip, and will be compared to a catalogue of genetic samples collected annually since 1995 from Bimini and other locations around the Bahamas and Florida. This will allow us to determine whether these populations are breeding together or whether these populations are genetically distinct based on geographic location. This is valuable for conservation because a high genetic diversity is important for a species survival. If one geographic region is genetically unique it is important that it is adequately protected. This ensures that it is not depleted by fishing and those genes lost from the gene pool forever.

Andros Days 9 – 10

We continued our exploration of Andros but moved round to target the creeks and sand flats on the eastern side. Still dodging rain storms we journeyed back into the seemingly endless network of channels and mangroves. Although the habitat was similar to other areas where we had had success in recent days, the salinity of the water was very low. Andros is home to the only freshwater river in the Bahamas and we think this is what made such a difference to the salinity on the eastside compared to our other locations. Sharks are highly sensitive to changes in their environment and the conditions of the water such as temperature and salinity. So after a couple of unsuccessful attempts in the creeks where we didn’t even sight a shark we switched up our approach and headed out onto the reef. The barrier reef that runs along the east coast of Andros is the third largest in the world so knowing where to start was a challenge. Some local fishermen at the dock had tales of “monster sharks” preventing them from getting a fish to the boat the previous day so we thought this would be a good place to start!

The fishermen had been taking advantage of the snapper spawning aggregation which occurs when the snappers are condensed in large numbers to mate, typically around a full moon. It appeared that the sharks had the same idea as no sooner than we had arrived we hooked up a blacktip shark (Carcharhinus limbatus), the first of the expedition, followed by two Caribbean reef sharks (Carcharhinus perezi). It was an interesting scene with a chorus of cheers between the boats, ours when we caught, tagged and released a shark and the Bahamians meters away when they landed a snapper! This last day in Andros added a couple of new species to our list and brought a close to a very successful exploration of Andros. We are headed back to Nassau now to resupply the boat before journeying north to the Berry Islands.

 

Berry Islands Days 1 – 3

As the crew headed north east for the Berry Islands, we decided to stop at a marine navigational buoy to fish for bait. The pelagic ocean is a dangerous place for most fish species given that they are prey for other larger or faster fish. So much so that any type of structure can act as shelter providing relief from predation risk for a wide range of fish species. Fishermen have capitalized on this through the installation of Fish Attraction Devices (FADs) which act to concentrate fish in a particular area therefore making them easier to catch. Although the buoy served as a navigational aid it still provided a similar function and within a few minutes of having hooks in the water we were getting bites. Almost immediately after we had our first fish on the line we started seeing silky sharks (Carcharhinus falciformis) behind the boat. Attracted by the acoustic signals of the struggling fish, the sharks were hoping to score an easy meal themselves. They were attempting to take the caught fish off the line, a process known as depredation, before we could get them to the boat providing them a meal with limited effort. It is this type of behavior, an obvious nuisance for sport fishermen that helped the team to identify Cat Island as a hotspot for oceanic whitetip sharks, another pelagic predator. While simultaneously stocking up on bait fish we were able to catch two silky sharks and process them on the back of the boat. This added another new species for the expedition and we collected data on a species that is considered vulnerable in the region.

The Berry Islands are a chain of thirty barely populated islands and over 100 smaller cayes covering approximately thirty square miles. Referred to as the ‘fish bowl of the Bahamas’ because of its shape it provided the team another opportunity to survey areas previously not researched. Over our time at anchor we were able to add to our tally of lemon sharks including many juveniles and newborns the presence of which indicates that the islands’ creeks and mangroves provide more important nursery habitat. On one afternoon the importance of the role of mangroves at providing refuge for juvenile sharks was witnessed firsthand. In water < 2ft deep we caught three newborn lemon sharks in quick succession, none of which were longer then 65cm. After their release they quickly headed for the nearby shelter within the roots of the mangroves. No sooner than four minutes after we released the last newborn we saw a mature adult lemon shark (221cm in length) with both dorsal fins and some of his back out of the water searching the fringes of the mangroves right where we had last seen the newborns. The iconic image of a shark’s fin breaking the surface, the cause of many shark themed nightmares after the movie Jaws©, seemed to spark a similar reaction even from the newborn lemon sharks in this shark eat shark world!

While leaving the last fishing site we spotted an unusual sight on the horizon and so decided to investigate. We discovered a large fishing boat lying on one side of its hull, in merely a few inches of water. It seems like it isn’t only our crew that can misjudge the depth of water when attempting to fish new areas!  We are now departing the Berry Islands heading further north for the final leg of the expedition at Grand Bahama.

Grand Bahama Days 1 – 3

The team reached Grand Bahama and began the last leg of what has been a very exciting and productive research expedition. Grand Bahama is the fourth largest of the Bahamian islands and is composed of approximately 700 islands and 2400 smaller cayes. Known for excellent bonefishing the north shore of Grand Bahama is an extensive shallow flat with hundreds of small creeks and channels fringed with mangroves. With almost every item on the ‘what makes a suitable nursery area’ checklist checked off we expected it to be ‘sharky’… and it didn’t disappoint! We added valuable newborn and juvenile samples from both lemon and blacktip species to our genetic database in addition to documenting an extensive range of nursery habitat. We also added another new species to the expedition’s tally with the inclusion of bonnethead sharks (Sphyrna tiburo), one of the smallest members of the hammerhead family. Bonnetheads, also known as shovelhead sharks, have the signature ‘hammer’ head shape however they only reach a maximum length of 5ft (1.5m) which is dwarfed by that of the great hammerhead (Sphyrna mokarran) measured at 20ft (6m).

Despite being relatively accessible by people given its proximity to the major settlement of Freeport, we saw only one other boat while out on the north shore. This limited disturbance by humans contributes to the areas success as a viable and productive nursery habitat. The success was evident by the fact that at one location we had a school of approximately twenty juvenile sharks near our boat. The school which comprised of lemon, blacktip and bonnethead species freely swimming amongst each other was quite a sight and one rarely seen elsewhere.

The final event of the expedition took us to ‘Tiger Beach’ a known shark dive tourism site located off the western point of Grand Bahama. After working with predominantly smaller lemon sharks for the past couple of weeks it was an awesome sight to have up to twelve individuals all >6.5ft (2m) swimming behind the boat. It allowed us the opportunity to get in the water and appreciate the size and tenacity of these creatures while completely dispelling the myth that all sharks are ferocious man-eaters. It is through dive sites like Tiger Beach that tourists from around the world can experience sharks first hand which often leads to an appreciation of how unique they are with many former skeptics becoming advocates of shark conservation after such an experience. While in the water we noticed that all of the lemon sharks were female, which is an interesting point to note as we attempt to delineate their life history. We were briefly visited by a tiger shark but for fear of interrupting ‘lemon shark ladies night’ it did not stick around!

This brought a fitting conclusion to what has truly been an epic expedition around the northern parts of the Bahamas. With valuable science and outreach being conducted throughout the expedition we leave the beauty of the Bahamas with data in hand to start the process of analyzing it back at our respective institutions. With a list for the entire cruise totaling ten observed species of shark (oceanic whitetip, nurse, tiger, blue, silky, blacktip, great hammerhead, bonnethead and Caribbean reef) in addition to a small tooth sawfish and with the deployment of a myriad of tags we can attest to the abundance of the Bahamas’ shark populations. As researchers we were very fortunate to be able to conduct this work in the Bahamas where there is still a healthy population of sharks and so great thanks must again go to the Moore Charitable Foundation for providing the opportunity to conduct such a productive cruise.