Research expedition aids understanding of fish movements, spawning locations

September 2012

Expedition scientists repaired and replaced 57 underwater listening stations used to detect fish outfitted with acoustic tags. Acoustic receivers allow scientists to map where fish travel.

Thanks to the technology and platform of the NOAA Ship Nancy Foster, researchers were able to safely conduct 214 science dives and use sonar technology to map 266 miles of seafloor.

Red dots represent the simulated distribution of larval fish particles 25 days after spawning in the sanctuary's Tortugas Ecological Reserve. Credit: University of Miami RSMAS and NOAA Fisheries

Since Tortugas Ecological Reserve protection in 2001, scientists have documented increases in mutton snapper and the return of a historic spawning aggregation. Credit: Chris Parsons

Scientist can use sound to "see" the ocean floor. Multibeam sonar, which can measure depth and seafloor features, was used to map 266 miles of the ocean during this research expedition.

To the untrained eye these dots on the screen might not seem like much, but it is a sonar image of gathering cubera snapper preparing to spawn in the Tortugas Ecological Reserve.

Teams of science divers used small boats to perform dives at many sites each day, repairing underwater listening stations and counting fish. Calm conditions enabled the divers to do 214 dives.

Scientists used a Remotely Operated Vehicle (an underwater vehicle with a camera) to observe fish and habitat deeper than the no-decompression limits of expedition scuba divers.

scientists from the Florida Keys National Marine Sanctuary and partner agencies recently completed a nine-day research expedition between Key West and the Dry Tortugas aboard the NOAA Ship Nancy Foster. During this expedition, scientists performed 214 scuba dives, mapped 266 miles of seafloor, and documented spawning behaviors of mutton snapper, cubera snapper and ocean triggerfish inside the sanctuary’s Tortugas Ecological Reserve.

During spawning, fish will gather or aggragate, often by the thousands, to simultaneously release their eggs and sperm. Eggs fertilized in the Tortugas region – 70 miles west of Key west – can ride the ocean currents and populate areas not only throughout the Florida Keys, but even up the west and east coasts of Florida. Reef fish species caught in Georgia and South Carolina may have originated in the Tortugas.

Many fish species return to the same location to spawn at times of the year linked to the lunar cycle. This predictability of timing and location makes the adult fish an easy catch for anglers. By the late 1990s, fishery surveys suggested that mass spawning aggregations of mutton snapper in the Tortugas had all but ceased due to overfishing. However, since the establishment of the Tortugas Ecological Reserve in 2001, and changes in fishery regulations, the numbers of mutton snapper observed in the area of the reserve have slowly increased annually. And during this summer’s expedition, scientists continued to document the return of mutton snapper and other species to the reserve to spawn.

In order to protect the value of spawning aggregations, scientists are trying to better understand where fish go to spawn, and what habitats they prefer. On this expedition, scientists used multibeam sonar to measure the depth and features of the seafloor to help find common characteristics between different spawning sites. Scientists also used advanced sonar technology similar to a high-tech “fish finder” to look for the presence of fish. Science divers would then enter the water to visually confirm fish species and their numbers, and whether they appeared to be gathering for a potential spawn. If the depths were beyond the no-decompression limits for diving, scientists used drop cameras or remotely operated vehicles to make these observations.

Scientists also want to know where fish go when they aren’t spawning. To do this, scientists with NOAA and Florida Fish and Wildlife Conservation Commission manage a network of 74 underwater acoustic receivers that detect specially-tagged fish. On this expedition, science divers retrieved, reprogrammed, and replaced 57 of these receivers inside the Tortugas Ecological Reserve, Dry Tortugas National Park, and sanctuary areas open to fishing.

Data gathered during the 2012 expedition will support future science and management decisions, including greater emphasis on protection of fish spawning aggregations — a recurring theme in the sanctuary’s recent public scoping period for its marine zoning and regulatory review.

The expedition included researchers from NOAA’s Office of National Marine Sanctuaries, NOAA’s National Centers for Coastal Ocean Science, Florida Fish and Wildlife Conservation Commission, Florida Department of Environmental Protection, the College of Charleston, and a seventh-grade science teacher participating in NOAA’s Teacher at Sea Program.

The NOAA Ship Nancy Foster provides the only platform in the NOAA fleet that has the required combination of unique physical capabilities, duration, and trained staff to safely conduct these scientific dives and echosounding surveys on a 24-hour cycle.