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Pelagic

You are what you eat… and what your dinner eats, too!

As any angler will tell you, fresh fish is the best fish (Fig. 1)! Even non-anglers would insist that grilled wahoo, dockside yellowfin sashimi, or fried dolphinfish fingers are best when fresh from the sea. Knowing your fish is wild-caught means there are no questions about the quality of the fillet, or the fish’s diet – right? Wahoo (top) and dolphinfish (bottom) are highly sought after sportfish, and are targeted for their fighting ability and table quality meat. These species, together with tunas and billfish, drive the economically valuable Bahamian sportfish economy.

Fig. 2: A sugar bag originating from the Dominican Republic. Within a few years this bag will break up into tiny microplastics, easily available for accidental consumption by marine fishes.

Each year, between 8-12 million tons of plastic end up in the world's oceans, ranging in size from large pieces of floating trash or small (< 5mm) microplastics barely visible to the naked eye (Fig. 2). Some of this debris may result in the entanglement and death of marine mammals, or can be ingested by birds, sea turtles, and fish with severe health consequences. Even more concerning is that plastic debris acts as a magnet for persistent organic pollutants (POPs) such as PCBs or DDT – chemicals known to disrupt hormones or have carcinogenic effects in humans and animals. Thus, identifying whether plastic debris is consumed by recreationally and commercially important fish species should be of concern to any angler or sushi-lover.

Fig. 3: Island School students remove the stomach from a dolphinfish in preparation for a stomach dissection.

CEI researcher Zach Zuckerman, along with 6 Island School students, are investigating how marine debris - particularly plastic - is affecting the marine food web of The Bahamas.  Zuckerman and his team have collected over 100 dolphinfish, wahoo, and yellowfin tuna carcasses from anglers at Cape Eleuthera Resort and Marina and Davis Harbour Marina, both located near CEI’s campus on South Eleuthera. The location at which each fish is captured is recorded, and the stomachs removed at CEI’s wetlab to be dissected in search of plastic debris. To identify microplastics, the team runs the contents of each fish’s stomach through a sieve, or a series of increasingly smaller screens, to separate prey and debris by size (Fig. 3).

Fig. 4: This large hair bead and piece of trash bag were discovered in a dolphinfish and wahoo (top), while these 14 small pieces of clear plastic film were discovered after sieving the stomach contents of a single yellowfin tuna.

Preliminary results indicate that 19% of wahoo, 23% of dolphinfish, and 20% of yellowfin tuna captured in Eleuthera’s waters contain plastic in their stomachs. Some of this is easily identifiable by eye such as pieces of plastic bag! Most of the debris, though, is less than 5mm in size and identifiable only through the sieving process such as the 14 small pieces of clear plastic found in a single yellowfin tuna (Fig. 4)!.

These preliminary results are quite startling; past gut content analysis of fish harvested near the Pacific Garbage Patch suggests much lower occurrences of plastic ingestion by recreational species, with only 2% of dolphinfish and no yellowfin tuna having been found with plastic in their stomachs. These researchers, though, only searched the gut by eye and did not sieve the stomach contents. Many anglers claim to have never seen plastic inside a fish, yet it would seem that most have never looked quite close enough!

Please follow this research as we increase our sample size, add new recreational species to the study, and quantify concentrations of free-floating plastic around Eleuthera by sampling the Exuma Sound with a plastic trawl (blog coming soon). Contact zachzuckerman@ceibahamas.org with questions or to support our research efforts.

 

Lyford Cay International School visits the Cape Eleuthera Institute

Students engaged in plastic pollution research getting up close with a mahi mahi dissection

Lyford Cay International School in New Providence brought 25 bubbly 5th graders down for a 3 day sustainability program at the Cape Eleuthera Institute. Besides learning about topics such as Bahamian ooidic limestone, ocean pollution, and permaculture, students also learned first hand how biodiesel is made from used cooking oil by making a “test batch” in the lab.

The Grade 5's post The Island School's youngest RUN-SWIM EVER!!!!!

This group of students was the youngest group to ever do a run-swim! A run-swim is a morning exercise where students go through a series of short runs and short swims before climbing a sea wall, jumping off a cliff and run-swimming back to campus. Run-swims are always a highlight for visitors and of course a great way to start your day off on the right foot!

Lyford will be returning in the fall with more grades, more science, more fun and more learning!

Student assisting Samuel our bio-diesel technician making a batch in the lab

Although one of our youngest overnight programs, Lyford Cay 5th grade students blew us away with their prior knowledge on sustainability as well as their excitement to learn even more through experience! 

 

Bull Shark Tags Provide Clues to Migratory Movements

The Cape Eleuthera Institute’s Shark Research and Conservation Program has just started to receive data back from the satellite tags deployed last winter onto five female bull sharks. These transient sharks come to The Cape Eleuthera Marina each November and spend around four months inhabiting the shallow marina waters where fishermen clean their daily catches. Their habitat occupation and use of space beyond Cape Eleuthera has remained a mystery until now. Bull Shark Blog Images together

The migratory routes of these animals has been speculated due to the necessity for females to seek freshwater in order to pup, however, the first track we have received reveals a long and exciting journey via Cuba and the Florida Keys. The highly migratory nature of this species creates challenges for conservation and management efforts as they travel across international boundaries with differing levels of protection.

Research efforts at The Cape Eleuthera Institute in collaboration with Microwave Telemetry will increase our understanding of the species by elucidating critical information about their use of space and seasonal habitat occupancy.

Dolphinfish tagging update

Fig. 1. Anglers target mahi for their strong fight, showy leaps, tasty fillets, and beautiful colors. Dolphinfish (aka mahi mahi or dorado) are a highly sought after sportfish targeted by offshore anglers, and they also support commercial fisheries in the Caribbean and US. Until recently, little was understood about their movements, stock ranges, and population structure. Recent findings suggest that these fish complete long-distance migrations and are quick to mature. However, little information exists about dolphinfish movements or harvest in The Bahamas – a location identified by the South Atlantic Fisheries Management Council  in critical need of further stock assessment.

Fig. 2. A tagged dolphinfish ready for release. Note the orange tag, printed with contact information for reporting a recapture of this fish.

The Cape Eleuthera Institute has been working with the Cooperative Science Services’ Dolphinfish Research Program (DRP; http://www.dolphintagging.com/) to mark dolphinfish in The Bahamas with external tags (fig. 2). After recording the fish’s size and location of capture, the fish is tagged and released to be captured again by an angler or commercial fisherman. Upon recapture, essential information such as distance travelled and growth of the fish can be determined.

Recent recaptures in the Bahamas have further demonstrated both the distances travelled by dolphinfish, as well as the large geographic range of the north Atlantic stock. One fish tagged in Florida last year was recaptured 309 days off Rum Cay in the southern Bahamas. It is estimated that the fish travelled up the East Coast of the US before swimming back to the Bahamas – a total of nearly 4,000 miles (fig. 3)!

A potential dolphinfish migration route. This individual dolphinfish grew in length from 18 to 53 inches in the 309 days between initial tagging and recapture, and might have travelled nearly 4,000 miles (map courtesy of DRP).

These findings are critical to protecting the Atlantic mahi fishery. By quantifying movements of dolphinfish across political boundaries (i.e., US, Bahamas, Puerto Rico, and other Caribbean nations), a regional management plan can be devised and enforced, ensuring a sustainable fishery for all countries.

If you will be fishing in the Bahamas and are interested in tagging dolphinfish, contact zachzuckerman@ceibahamas.org, or visit the DRPs website. Many anglers release small dolphinfish; tagging is a great way to contribute to our increasing knowledge of this economically important species!

Dolphinfish regulations in the Bahamas are not based on current stock assessments. Collecting data on recreational harvest and movements can ensure proper management of the fishery.

Tag and release small dolphinfish, or those too large for you cooler. Tagging is also a great way to enjoy fishing if you have reached your limit of fish. This dolphinfish smiles at the camera as it is being released.