Bush, P.G.

Gibb, J.

Heppell, S.A.

Heppell, S.S.

Johnson, B.C.

McCoy, C.M.

Paris, C.

Pattengill-Semmens, C.V.

Semmens, B.X.

Aquatic Commons

Tracking potential larval dispersal patterns from Nassau grouper aggregation sites: evidence for local retention and the “importance of place”

 Proceedings of the 61st  Gulf and Caribbean Fisheries Institute     November 10 - 14, 2008   Gosier, Guadeloupe, French West Indies 
Tracking Potential Larval Dispersal Patterns from Nassau grouper Aggregation Sites:  
Evidence for Local Retention and the “Importance of Place” 
 
HEPPELL, S.A.1, B.X. SEMMENS2,3, C.V. PATTENGILL-SEMMENS3, P.G. BUSH4, B.C. JOHNSON4,  
C.M. MCCOY4, C. PARIS5, J. GIBB4, and S.S. HEPPELL1 
1Department of Fisheries and Wildlife, 104 Nash Hall, Oregon State University, Corvallis, Oregon 97331 USA 
2NOAA Northwest Fisheries Science Center 4726 38th Ave. NE Seattle, Washington 98105 USA 
3Reef Environmental Education Foundation (REEF), PO Box 246, Key Largo, Florida 33037 USA 
4Department of Environment, Cayman Islands Government, P.O. Box 486GT,  
Grand Cayman, Cayman Islands 
5Rosenstiel School of Marine and Atmospheric Science, Division of Applied Marine Physics, 4600 
Rickenbacker Causeway, Miami, Florida 33149 USA 
 
ABSTRACT 
Nassau grouper spawn in large aggregations at specific locations 1-3 times each winter.  The fate of the larvae between birth 
and the time they settle out is virtually unknown, yet the location of the aggregation site itself must be important in determining their 
fate. In order to investigate the “importance of place” for aggregation-spawning species, during the winter of 2008 we deployed 
Surface Velocity Profile drifters at the Nassau grouper spawning aggregation site on Little Cayman Island.  A single drifter was 
deployed each night for five nights following the January full moon, then subsequently recovered after 12 hours to determine initial 
trajectory paths.  On the 6th night, when peak spawning was observed, three drifters were deployed simultaneously and tracked for 
35 days.  The drifters released on the night of spawning showed substantial eddy formation near the aggregation site, in contrast to 
the largely linear paths taken on nights prior to spawning. This suggests an oceanographic-based “importance of place” for the 
aggregation site that may result in local recruitment. This would mean that local aggregations of fish are directly responsible for the 
long-term survival of local populations.  We plan to continue our work in 2009.  This work will give substantial credence to the need 
to protect specific locations because they are unique and critical to the long-term survival of the many species that aggregate there, 
including the important and endangered Nassau grouper. 
 
KEY WORDS:  Nassau grouper, spawning, dispersal, satellite drifters 
 
 
El Seguimiento de Patrones Larvales Potenciales de la Dispersión de la Agregación del Mero de 
Nassau Localiza: ¿ Evidencia de la Retención Local? 
 
La freza del mero de Nassau en agregaciones grandes en las localizaciones específicas 1-3 mide el tiempo de cada invierno. El 
sino de las larvas entre el nacimiento y el tiempo que deciden es virtualmente desconocido, con todo la localización del sitio de la 
agregación sí mismo debe ser importante en la determinación de su sino. Para investigar la “importancia del lugar” para la especie de 
agregación-freza, durante el invierno de 2008 desplegamos las traineras superficiales del perfil de la velocidad en el mero de Nassau 
que frezaba el sitio de la agregación en la pequeña isla del caimán. Una sola trainera fue desplegada cada noche por 5 noches que 
seguían la Luna Llena de enero, después recuperada después de 12 horas para determinar las trayectorias iniciales de la trayectoria. 
En la 6ta noche, cuando la freza del pico fue observada, tres traineras fueron desplegadas simultáneamente y seguidas por 35 días. 
En contraste con las trayectorias adquiridas noches antes de la freza, las traineras lanzadas en la freza del pico demostraron la 
formación substancial del remolino cerca del sitio de la agregación. Esto sugiere una “importancia oceanográfico-basada del lugar” 
para el sitio de la agregación que puede dar lugar al reclutamiento local. Esto significaría que las agregaciones locales de pescados 
son directamente responsables de la supervivencia de largo plazo de poblaciones locales. Planeamos continuar nuestro trabajo en 
2009 en la pequeña isla del caimán, pero propondremos más importantemente el organizar de un lanzamiento multinacional, Del 
Caribe-ancho, coordinado de las traineras del SVP para evaluar patrones lavabo-anchos en transporte larval de sitios conocidos de la 
agregación. Esto dará crédito substancial a la necesidad de proteger localizaciones específicas porque son únicas y críticas a la 
supervivencia de largo plazo de las muchas especies que agregan allí.  
 
PALABRAS CLAVES:  Mero de Nassau, frezando, dispersión, basadas en los satellites 
  
Le Cheminement des Modèles Larvaires Potentiels de Dispersión de L’agregation de Mérou de 
Nassau Situé: Évidence pour la Conservation Locale? 
 
Le frai de mérou de Nassau dans de grandes agrégations aux endroits spécifiques 1-3 chronomètre chaque hiver. Le destin des larves 
entre la naissance et le moment où elles se précipitent est pratiquement inconnu, pourtant l'endroit de l'emplacement d'agrégation lui-
même doit être important en déterminant leur destin.  Afin d'étudier la « importance de l'endroit » pour des espèces de agrégation-frai, 
pendant l'hiver de 2008 nous avons déployé les pêcheurs extérieurs de profil de vitesse au mérou de Nassau engendrant l'emplacement 
d'agrégation sur la petite île de caïman.  Un pêcheur simple a été déployé chaque nuit pendant 5 nuits suivant la pleine lune de janvier, 
puis récupéré après 12 heures pour déterminer les chemins initiaux de trajectoire.  La 6ème nuit, quand on a observé le frai de crête, trois 
pêcheurs ont été déployés simultanément et dépistés pendant 35 jours. Contrairement aux chemins pris des nuits avant d'engendrer, les 
pêcheurs libérés au frai de crête ont montré la formation substantielle de remous près de l'emplacement d'agrégation.  Ceci suggère une « 
importance océanographique-basée d'endroit » pour l'emplacement d'agrégation qui peut avoir comme conséquence le recrutement local.  
  Page 326   61st Gulf and Caribbean Fisheries Institute  
 
Ceci signifierait que les agrégations locales des poissons 
sont directement responsables de la survie à long terme 
des populations locales.  Nous prévoyons de continuer 
notre travail en 2009 sur la petite île de caïman, mais 
d'une manière primordiale nous proposerons d'organiser 
un dégagement multinational,  Des Caraïbes-large, 
coordonné des pêcheurs de SVP pour évaluer les modèles 
bassin-larges dans le transport larvaire des emplacements 
connus d'agrégation.  Ceci donnera la créance substan-
tielle à la nécessité de protéger des endroits spécifiques 
parce qu'ils sont uniques et critiques à la survie à long 
terme des nombreuses espèces qui agrègent là. 
 
MOTS CLÉS:  Mérou de Nassau, engendrant, dispersion, 
pêcheurs satellites 
 
BACKGROUND 
Nassau grouper aren’t just icons of the Caribbean— 
they are a social and ecological cornerstone of the region’s 
coral reefs.  Reports from the 19th century describe Nassau 
grouper as an abundant species on Caribbean reefs and a 
critically-important component of commercial fisheries.  
By the 1990s, the number of Nassau grouper had dropped 
so significantly that they became the first Caribbean reef 
fish to be listed as endangered by the International Union 
for the Conservation of Nature (IUCN).  In Bermuda and 
the United States, harvest of Nassau grouper has been 
completely prohibited for more than two decades in an 
attempt to recover the species; unfortunately without any 
sign of recovery.  As stocks continue to dwindle through-
out the Caribbean and southeast Atlantic, managers are in 
desperate need of a new approach for the conservation of 
this critically important species.  With our work in the 
Cayman Islands we have provided both the scientific basis 
to justify Nassau spawning aggregation protections and the 
data to demonstrate that they can work if governments 
make swift and decisive decisions to protect this important 
natural resource. 
Five years ago, in response to what they identified as a 
critical conservation need, the Cayman Islands government 
protected all known Nassau grouper spawning sites in the 
Cayman Islands.  This watershed event was motivated by 
the 2001 discovery and subsequent fishing-induced rapid 
depletion of a large (~7000 fish) spawning aggregation on 
the west end of Little Cayman Island.  The government’s 
rapid legislative response, driven in part by the results of a 
potent collaboration between the Cayman Islands Depart-
ment of Environment (CIDOE) and the Reef Environ-
mental Education Foundation (REEF), protected the last 
functional Nassau grouper aggregation left in the Cayman 
Islands, before all the fish were taken.  The west-end site is 
now home to one of the largest fully-protected spawning 
aggregations left in the entire Caribbean, and works to 
preserve this endangered, economically and ecologically 
important reef fish.  It should be noted, however, that the 
Cayman Islands spawning site protections were established 
under a ‘sunset’ provision, and their effectiveness must be 
demonstrated in the years leading up to 2011 or they will 
be revoked.  The 8-year ban on fishing Cayman aggrega-
tions was enacted with the understanding that any exten-
sion to this ban would be contingent on a comprehensive 
assessment of the status of the Cayman Island’s Nassau 
grouper spawning population.  For our work this entails 
describing the spatial ecology of adult Nassau grouper and, 
more specifically aggregation site usage as a function of 
demography, as well as understanding the reproductive 
output from this aggregation.  Integrating both adult and 
offspring components will be important to the comprehen-
sive assessment of the fishing ban protections and the 
decision making process for management of reserves of the 
Cayman Islands and elsewhere. 
At the beginning of this process, the Grouper Moon 
Project, a cooperative research and monitoring program 
between CIDOE and REEF, provided the aggregation 
monitoring and fisheries statistics and analysis that 
motivated the legislative decision.  Following the enact-
ment of the new law, the Grouper Moon Project focused on 
efforts aimed at demonstrating the efficacy of the aggrega-
tion-site no-take legislation and in documenting recovery 
of the aggregation.  Since 2002, Grouper Moon researchers 
have:  
i) Carried out a multi-year electronic tagging project 
on Little Cayman island that tracks the move-
ments of adult grouper as they migrate to and 
from the aggregation site, 
ii) Developed and currently maintain a fisheries-
independent monitoring program that tracks 
spawning frequency, changes in observed 
abundance on the aggregation site, and shifts in 
the size distribution of spawning adults, and 
iii) The subject of this talk, have recently started 
tracking potential larval dispersal patterns from 
the spawning aggregation. This dispersal work is 
designed to evaluate local larval retention and 
identify why multiple species aggregate in a 
specific location each winter full moon (up to 22 
other species of fish use this exact same location 
to spawn during the winter full moon) –what we 
call “the importance of place”.  
 
All of this work is performed with the overall goal of 
establishing the role that spawning aggregations play in the 
population dynamics of Nassau grouper and that protecting 
the Nassau grouper spawning aggregations in the Cayman 
Islands can lead to protection and recovery of this species. 
 
RESEARCH 
Our tracking of adults has demonstrated the surpris-
ingly insular influence of the spawning site; all fish 
attending the west end Little Cayman spawning site are 
from the Island of Little Cayman.  Additionally, our 
research shows that all reproductive aged fish from the 
island attend the aggregation each year.  Put simply, the 
tracking research clearly demonstrates that the sum total of 
Nassau grouper spawning stock on Little Cayman is 
  Heppell, S.A.  et  al.    GCFI:61   (2009)   Page 327 
 
concentrated into a tiny piece of ocean each winter, making 
them extremely vulnerable to exploitation during this time. 
This has in fact been the downfall of Nassau throughout 
their entire range. 
Now that we understand the spatial ecology of adults 
at the spawning aggregation site, we are working to 
identify the connectivity of the system with regard to larval 
output and local recruitment.  There is evidence that even 
within open ocean systems there can be a substantial 
amount of local larval retention.  This means that local 
adults may be crucial to the long-term sustainability of 
local populations, counter to the sometimes proposed 
concept that larvae are transported in from other locations 
and therefore local adults are not important for local 
recruitment.  In spite of the importance of this recruitment 
work, this concept has not been tested within the Cayman 
Islands, nor has it to our knowledge been tested anywhere 
specifically for grouper aggregations. 
In late January 2008, we released a single Pacific Gyre 
Surface Velocity Profile (SVP) drifter at the west end of 
Little Cayman Island, directly over the aggregation site, on 
each of the six nights prior to Nassau grouper spawning, 
and recovered it on each of the following mornings.  We 
then released three drifters on the night we observed peak 
spawning, allowed these drifters to move freely with the 
currents, and tracked them for a subsequent 30 days.  For 
the six nights prior to spawning, the SVP drifter would 
move in a more or less linear or slightly curvilinear manner 
for the 12 hours it was at liberty.  Following the night of 
spawning, however, instead of a linear path, all three 
drifters entered an eddy loop and spun in a counter-
clockwise direction for almost three days as they moved 
slowly southeast of the island.  Formation of eddies near 
the edge of the continental shelf has been postulated as the 
means by which larvae are retained near the areas where 
they are spawned.  By the end of the 30 days at large, the 
drifters had made a large excursion south towards the 
Jamaican shelf, turned around when they encountered the 
Nicaraguan rise, and returned to the same latitude as that of 
their release off the east end of Cayman Brac. 
Overall, these results indicate:  
i) The fish spawned on a night when oceano-
graphic current conditions were substantially 
different than they were on the six nights 
previous to spawning,  
ii) There is a substantial chance for local larval 
retention based on the eddy formation during 
the first few days that larvae were in the 
water column, and  
iii) There appear to be biophysical barriers that 
limit dispersal of Nassau larvae from one 
location to another.  
 
Taken together, protection of local spawning aggrega-
tions is likely very important for local recruitment, and 
aggregation sites likely have unique oceanographic features 
that lend an “importance of place” to those locations.  
These locations therefore should be afforded special 
protections to act as conservation sites for all the species 
that spawn there. 


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Tracking potential larval dispersal patterns from Nassau grouper aggregation sites: evidence for local retention and the “importance of place”

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