Over the past 50 years, Caribbean coral reefs and fish populations have undergone major declines. Hundreds of marine protected areas have been established to restrict fishing across the Caribbean, but with little knowledge of fish movements to guide their design or assess their effectiveness.
An open access study from the National Oceanic and Atmospheric Administration and a cadre of international university scientists followed fish movement in the Caribbean Sea to determine if marine protected areas are doing their job and how they might be improved.
“The fish tracking project grew out of a long-term collaboration between the NOAA Biogeography Branch and the U.S. National Park Service,” said Simon Pittman, a marine ecologist at NOAA and the University of the Virgin Islands. “It became evident that we needed to gain a better understanding of fish movements to determine if the fishes were staying in the protected areas.”
Turning to tracking technology for assistance, the researchers used miniature acoustic transmitters and an array of fixed acoustic receivers to answer three questions: How far do Caribbean fish travel? Are adjacent marine protected areas truly connected? And are the areas large enough to protect the fish that swim within and between them?
The researchers studied 18 species from July 2006 to July 2008 and tagged 184 individual specimens — 21 of which were never detected. Before tagging, the fish were caught with locally made traps of traditional design. Researchers took the captured fish back to a field station for a quick bit of surgery, implanting the acoustic transmitter and suturing the wound with standard surgical equipment. The fish spent the night at the field station, underwent a postoperative check-up and were discharged back into the reef.
With more than 40 acoustic receivers continuously listening for tagged fish across the Puerto Rican shelf, there was plenty of routine equipment maintenance to perform.
“If we were downloading data from the acoustic receivers, then an average day would include 10 or more short SCUBA dives to clean the growth off the mooring lines where the receivers are attached,” Pittman said. The receivers would then be removed and taken to a boat where the researchers downloaded any data onto a computer before replacing the receiver.
Submerged mooring floats occasionally went missing, only to be found gouged and lacerated on the seafloor. Whispers of possible sabotage spread through the team, only to be assuaged months later, when a receiver picked up an unknown tag ID. After consulting a number of other research groups, it was determined that a 12-foot female tiger shark — tagged by the Guy Harvey Research Institute — had taken a liking to the floats.
“She must have been a little disappointed, as plastic is unlikely to be as tasty as her usual prey,” Pittman said.
While most of the fish were tracked automatically, researchers monitored 20 tagged fish manually, recording their position every 15 minutes over the course of a day. A rotation of three or four researchers took eight-hour shifts to accomplish the task, which Pittman called the study’s biggest challenge.
“We had to draw straws for the 1 a.m. to 9 a.m. shift, which was the hardest even with free pizza and drinks provided,” Pittman said. “Any field work at sea has its challenges, but working at night can be tricky.”
Long nights and fatigue weren’t the study’s only obstacles. Pittman recalled an instance where a Coast Guard patrol boat stealthily approached him and a student, ordering the two to keep their hands on their heads until they explained their business on the shore at 2 a.m.
In spite of the challenges involved, the study provided plenty of valuable data showing that fish often travel between and out of marine protected areas, and in some cases travel tens of kilometers away from their home range to spawn. One lane snapper arrived in the bay at sunrise and left along the same pathway at sunset, a behavior that Pittman described as clocking in and clocking out.
The study’s findings suggest that many marine protected areas, or MPAs, should be larger, and that managers should be mindful of activities outside of their jurisdiction. Furthermore, MPAs should be designed with attention to shape as well as size.
“Most MPAs are designed to protect nearshore resources, yet fish may need to cross the shelf at specific times of the life cycle to spawn or shift to deeper reefs with maturity,” Pittman said. “Our data highlights a potential problem that many MPAs are designed without any knowledge of the movements patterns of the species they intend to protect.”
Pittman and the other researchers have returned to the Virgin Islands to track key species that they previously missed, such as parrotfish. In the new study, the team will expand their acoustic network to examine connectivity between important spawning sites.