Expedition offers deep insights into fish use of waters near Tortugas and Marquesas
December 2014
When it comes to the question of how fish populations are faring in the Florida Keys National Marine Sanctuary, fish tales are always easier to come by than hard scientific data. As the sanctuary is reviewing its marine zoning and regulations, however, many stakeholders have called for more information on how to effectively protect fish spawning aggregations.
For two weeks this past September, NOAA scientists set out with state and university partners on a two-part mission to peer into some of the sanctuary’s most remote regions. The expedition was a collaborative effort between NOAA’s National Ocean Service, NOAA Fisheries, and Florida Fish and Wildlife Research Institute (FWRI)—building on a series of research studies from 2009, 2011, and 2012 that looked at how reef fishes use various parts of the sanctuary during their migrations to spawn.
Initial insights from the first leg of the cruise, which featured videos of amberjack, black grouper, snapper, and goliath grouper aggregations in the Tortugas Ecological Reserve, were posted throughout the cruise in near-real time on the sanctuary’s Facebook page. These images were taken from the remotely operated vehicle (ROV) Mohawk, which enabled scientists to explore to depths of 400 feet in areas with high currents. In another video clip, scientists performed an underwater surgery, inserting a tag into a scamp grouper to track its movements. All told, scientists implanted eight of these transponders into fish, while also servicing several of the receivers which capture the signals. More than 14 hours of ROV video was captured underwater, resulting in 957 digital stills of fish and benthic habitats.
The Tortugas’ fish aggregations are associated with spawning events and provide insights into the types of habitats needed to support fish populations. Tracking data will allow scientists and managers to understand how fish rely on more than one part of the sanctuary, through migrations from shallow reefs to deeper waters for spawning. To complement these observations, scientists use multibeam sonar to create detailed maps of the complexity and relief of the seafloor to identify areas that are likely prime fish habitats. One hypothesis is that multiple species of fishes are attracted to sites with high relief structures that are at shelf edges adjacent to deep waters.
The second leg of the expedition focused on reef areas south of the Marquesas Keys. Like in the Tortugas, scientists were looking for fish aggregations and mapping deep-water habitats, but they also surveyed shallower habitats for juvenile fish using seine nets. In the flats near the Marquesas, they netted 280 fish of 18 different species during 5 seine pulls. They also logged 40 dives to conduct a Reef Visual Census (RVC) at 11 sites. In an RVC, divers assess the numbers and types of fishes as well as the cover of algae and coral on the reefs. This methodology came out of a multi-agency effort to develop a standard protocol for assessing coral reef ecosystems of the Florida reef tract, so the data collected allows state, federal, and university scientists to work together to monitor the health of the reefs.
FWRI scientists also surveyed local populations of queen conch, a protected species which was once a delicacy. In 14 surveys, they measured 57 conch, including two females laying eggs and one egg mass – promising signs of a healthy, reproducing conch population. Back in 1966, roughly a quarter of a million conchs per year were landed in Key West, but by the 1980s, there were precipitous declines in the stock that led to a complete ban on harvest in state and federal waters. Work by a team of state and university scientists found that the failure was attributable, at least in part, to endocrine disrupters causing reproductive failures.
Both legs of the cruise explored how various management and zoning schemes affect the marine ecosystem, an important question as the sanctuary prepares to enter the next phase of the zoning and regulatory review. Even as the first wave of observations has been made public, there will be much deeper insights to look forward to as scientists and sanctuary staff conduct their review of the research findings.