THE GROUPER MOON PROJECT
Acoustic Research Project
A collaborative
conservation program between REEF and
the Cayman Islands Department of the Environment
FEATURED CONTENT
Grouper Moon video documentary (click
here)
Fish Movement Videos (click
here)
ABOUT THE GROUPER MOON ACOUSTIC PROJECT
In 2003 the Cayman Island Marine Conservation Board instituted an 8-year
total fishing ban on all known Nassau grouper (Epinephelus
striatus) aggregation sites in the Cayman Islands.
Of the eight known (and now protected) aggregation sites, six
appear to be inactive due to over fishing.
Only one protected aggregation, at the west end of Little Cayman
Island, maintains annual aggregations of more than 1,000 grouper.
In order to justify the no-take status of aggregation sites, and in
order to assess the likelihood that the closures are effective, the Cayman
Islands Department of the Environment needs a clearer understand of how
local populations of Nassau grouper use aggregation sites.
We have acoustically tagged Nassau grouper both on and off the
Little Cayman west end aggregation site, and are now monitoring movements
of the tagged fish over a two year period using an array of passive
autonomous hydrophones surrounding the island. Fish tagged on the aggregation site will allow us to
determine where fish go after they leave the aggregation. Fish tagged
around Little Cayman outside of the aggregation season will allow us to
determine the proportion of fish from the Island that attend aggregations,
and the frequency of aggregation attendance by individual fishes as a
function of demography. Ultimately,
this information will allow us to assess the current and future impacts of
protections afforded Cayman’s spawning aggregations.
Moreover, the study will define an aggregation’s
“sphere of influence” both geographically and demographically
and will thus aid in the management of aggregations throughout the
Caribbean and elsewhere.
PROJECT
NEED:
Nassau grouper (Epinephelus
striatus) migrate to specific sites during the winter full moons in
order to reproduce in mass aggregations (Domeier & Colin 1997, Bolden
2000, Sala et al. 2001). The Nassau grouper is listed as ‘threatened’
by the International Union for Conservation of Nature and Natural
Resources (IUCN 2002). Intense
harvesting of spawning aggregations is the primary cause of the
precipitous decline in populations throughout the Caribbean (Beets &
Hixon 1994, Sadovy & Eklund 1999).
In recent years, several Caribbean governments have instituted
marine protected areas at known Nassau grouper aggregation sites in
response to chronic declines in catch.
Spawning
aggregations of reef fishes are of concern to fisheries management because
1) they result in the concentration of individuals from stocks that are
otherwise at low densities, and 2) aggregations are disproportionately
responsible for the reproductive output of many economically valuable and
ecologically important species (Domeier and Colin 1997).
Because aggregations are site specific, designating aggregation
sites as marine protected areas is likely to be a successful conservation
measure. It is important,
however, to evaluate the scope of protections afforded stocks through the
protection of spawning grounds since such management actions alone may not
be sufficient to protect at risk species.
OBJECTIVES:
In 2003 the Cayman Island Marine Conservation Board instituted an
8-year total fishing ban on all known Nassau grouper aggregation sites
through the Restricted Marine Areas (Designation) Regulations legislation.
Before these areas were protected, fishers took
>90% of all harvested Nassau grouper from aggregations.
Eight Nassau grouper spawning aggregations have been documented in
the Cayman Islands: east end Little Cayman, west end Little Cayman, west
end Cayman Brac, east end Cayman Brac, and four on Grand Cayman (Tucker et
al. 1993). Six of these aggregations apparently no longer exist due to
intense fishing. Only one of
the remaining aggregations, on the west end of Little Cayman, maintains
annual aggregations of more than 1,000 grouper. In order to justify the
no-take status of the aggregation sites, and in order to assess the
likelihood that the closures are effective, the Cayman Islands Department
of the Environment (CIDOE) needs answers to the following questions:
1) What proportion of Nassau grouper on the Cayman Islands use the aggregation sites receiving protection?
2) Are there any undiscovered (and thus unprotected) aggregation sites?
3) How often do individual fish participate in aggregations?
4) Where do aggregating individuals come from and where do they go afterward?
5)
Does demographic status (sex and size) influence participation in
aggregations?
To our knowledge, these questions have not been systematically addressed in relation to specific grouper aggregations anywhere in the Caribbean. We are addressing these questions by acoustically tagging Nassau grouper both on and off the Little Cayman west end aggregation site, and subsequently monitoring the movements of the tagged fish over a two year period using an array of passive autonomous hydrophones. By tagging fish on the aggregation we will be able to determine where fish go after aggregating. The behavior of fish tagged at sites around Little Cayman prior to the aggregation will provide insight into the proportion of fish from the Island that attend aggregations, and the frequency of aggregation attendance by individual fishes as a function of demography. This information will allow the assessment of current and future impacts of the marine protected areas on Cayman’s spawning aggregations; moreover, the study will define an aggregation’s “sphere of influence” both geographically and demographically and will thus aid in the management of aggregations and populations generally.