Re: Bahamas Grouper Studies
Jack, Sobel (SOBELJ at dccmc.mhs.compuserve.com)
Wed, 25 Sep 1996 18:26:21 -0400 (EDT)
I believe the study referred to by Carlton Ray as "dubious" regarding
groupers in the Bahamas Exuma Cays Land and Sea Park is work done by
Robert Sluka. Bob presented a paper on his findings entitled "The
Benefits of Marine Fishery Reserve Status for Nassau Grouper, Epinephelus
striatus in the Central Bahamas at the International Coral Reef Symposium
in Panama this summer. However, I do not believe either the paper or its
findings should be characterized as "dubious". Furthermore, I believe it
was mis-characterized in several other ways as well. The paper concluded
that (1) Groupers were much more abundant and spawning stock biomass much
greater within the Exumas Park than outside in similar habitats and that
the park appeared to be adequately protecting grouper resources; (2)
Habitat differences were relatively unimportant in affecting grouper
distributions within the study area and differences in habitat could not
easily explain these differences; and (3) Differences in abundance and
biomass declined with distance from the park indicating that it was
likely exporting biomass across its boundaries. Contrary to Carlton's
statements, the paper did look at habitat characteristics, but did not
draw conclusions regarding the fate of larvae spawned within the park.
However, it did legitimately state that grouper reproductive capacity was
being protected within the park. Designing perfect studies to prove the
fate of larvae and the efficacy of reserves for replenishing specific
areas through their export are indeed very difficult. Nonetheless, a
large and increasingly sophisticated set of studies documenting the
benefits of reserves continues to accumulate. There is now overwhelming
scientific evidence that reserves can play an important role in
increasing the populations, spawning stock biomass, and reproductive
potential of many harvested species, including groupers. While this does
not address the fate of larvae, protecting spawning stock biomass is not
a trivial benefit and the maximum dispersal capacity of larvae says
little about actual distance travelled. Certainly, larval dispersal
capacity does not contradict the notion that reserves can enhance fish
populations. In fact, a number of recent studies suggest that the bulk
of recruitment for many reef fish is a relatively local phenomenon and
that long distance dispersal may be relatively rare or of limited
importance. Protecting natural populations and spawning stock biomass
may not guarantee improved recruitment, but its certainly a positive step
with many additional benefits. At some point, failure to maintain
adequate spawning stocks does ensure reproductive/recruitment failure.
Jack Sobel
Center for Marine Conservation