Adult Nassau grouper at a cleaning station
on a coral reef. (Photo by C. Dahlgren)
Around the world, tropical marine fishery species
such as groupers (Family: Serranidae) are being overfished,
with devastating ecological and economic consequences to coral reefs.
Preventing these harmful effects requires management measures based
on the best available information about these stocks, and the causes
and consequences of overfishing them. The Caribbean Marine Research
Center, NOAA's Undersea Research Program's (NURP) Center for the
wider Caribbean region, is working in collaboration with scientists
from North Carolina State University and the National Marine Fisheries
Service's Southeast Science Center to study Nassau grouper population
dynamics to enhance our ability to manage this important but threatened
The Nassau grouper, a large predatory fish inhabiting
coral reefs throughout the tropical western Atlantic, including
the Caribbean Sea, Florida Keys and Gulf of Mexico, is among the
most important fish species on coral reefs throughout the region.
In addition to being important predators on coral reefs, they were
also one of the most important fishery species in the region. Overfishing,
however, has driven Nassau grouper stocks below sustainable levels
and has even eliminated them from much of their historic range.
Nassau grouper are currently protected in state and federal waters
where they occur, and are a candidate species for listing under
the Endangered Species Act. To improve our ability to re-build Nassau
grouper stocks to sustainable levels in US waters, NURP funded researchers
from the Caribbean Marine Research Center (Dr. Craig Dahlgren),
National Marine Fisheries Service (Drs. Anne-Marie Eklund and Stephania
Bolden) and North Carolina State University (Dr. David Eggleston,
the project's principle investigator, Dr. Peter Rand and Dr. Joe
Hightower) are currently studying critical aspects of Nassau grouper
biology in an area where these fish are still fairly common and
fisheries remain active, The Bahamas.
Stereo-paired images of grouper aggregation
at South Point, Long Island, Bahamas. Images were recorded
at approximately 16:25 on 10 December 2000. (Photo by P. Rand)
Most of this research focuses on large spawning aggregations,
at which thousands of Nassau grouper gather each year during one
or more winter full moons. This stage in the life cycle of the Nassau
grouper is particularly important to understand since the entire
annual reproduction for a region is concentrated at a few particular
spots where aggregations occur, for only a few days each year. Furthermore,
because fishers often know where and when these spawning aggregations
occur, the fish are usually subject to the greatest fishing pressure
at these times. In many instances, entire regional stocks have been
wiped out due to intense fishing pressure on spawning aggregations.
Stocks may take several decades to recover from such intense exploitation.
Adult Nassau grouper with surgically implanted
telemetry tag and external tag prior to release. (Photo Courtesy
of J. Hightower)
Although still in progress, preliminary results from
this collaborative research effort have yielded much information.
Through tagging fish that are captured in the fishery and ultrasonic
telemetry, this research has shown that fish may migrate over 100
miles to spawning aggregations, and may spend only a few days at
these aggregations. This highlights the importance of sustaining
spawning aggregations for protecting stocks throughout an entire
region. Furthermore, a comparison of the characteristics of fish
at current spawning aggregations to characteristics of fish at the
same spawning aggregations over 10 years ago, indicates that even
moderate fishing pressure on spawning aggregations over a decade
may have a large effect on fish stocks such as a reduction in the
number of fish at spawning aggregations, a reduction in the size
of fish at spawning aggregations, and a skewed ratio of males to
females at spawning aggregations.
Based on what we learn from Nassau grouper stocks
in The Bahamas, this research will contribute to the rebuilding
of Nassau grouper stocks in U.S. waters and throughout the wider
Caribbean region and assist fishery managers with the management
of a sustainable fishery when stocks are healthy enough for the
fishery to be reopened.