Transcript Marshak Marine Ecol Conch Lecture

GIS mapping and analysis of queen conch (Strombus gigas)
stock abundance surveys in Puerto Rico
Anthony R. Marshak and Richard S. Appeldoorn
Department of Marine Sciences
University of Puerto Rico – Recinto de Mayagüez
Queen Conch (Strombus gigas)
• One of the most important commercial species within the Caribbean,
especially in Puerto Rico.
• Greatly overfished within most Caribbean waters, with severe population
declines throughout the region
Queen conch in Puerto Rico

Most PR queen conch landings
concentrated in the E and W
coasts, primarily SW insular
platform.

Conch depletion within
shallow seagrass beds, and
fishing effort has moved into
deeper habitats.
Queen conch stock surveys
 Fisheries
independent stock abundance surveys:
• Estimate average densities within a variety of habitats
over a large area using strip transects and underwater
scooters
• May collect in-situ size and stage information over time.
•Many management applications for monitoring the
population, or its response to any mgmt action
GIS Conch Plotting
 Determine exact conch locations with GPS recorded transect start and endpoints
Divers record start and end time; time of encounter of conch and habitat/depth
Habitat, depth, conch size, stage incorporated into GIS accessory data.
Spatial Analyst Density calculator gives overall distribution and aggregation patterns.
Survey Results of the Puerto Rico
West Insular Platform
Three Surveys over a ten-year period
(1995-96, 2001-02, 2006)
Habitat Density Results: Total Conch
Density (conch/ha)
25
20
1995-96 Survey
15
2001-02 Survey
10
2006 Survey
5
0
Algae
Hardbottom
Reef
Sand
Seagrass
Habitat Density Results by Age Class
Density (conch/ha)
Seagrass
25
20
1995-96 Survey
15
2001-02 Survey
10
2006 Survey
5
0
Conch
Juvenile
Adult
Old
Very Old
Sum all area surveyed per habitat and number of conch
encountered to get densities
Spatial Patterns along the West Coast
of Puerto Rico
Juveniles 5000 m2 radius, 1995-1996 Survey
Juveniles 5000 m2 radius, 2001-2002 Survey
Juveniles 5000 m2 radius, Jul-Sep 2006 Survey
Adults 5000 m2 radius, 1995-1996 Survey
Adults 5000 m2 radius, 2001-2002 Survey
Adults 5000 m2 radius, Jul-Sep 2006 Survey
Old 5000 m2 radius, 1995-1996 Survey
Old 5000 m2 radius, Jul-Sep 2006 Survey
Very Old 5000 m2 radius, Jul-Sep 2006 Survey
Conclusions

Highest densities of juveniles and adults in all surveys within shallow seagrass



Other juv’s and adults clustered in smaller numbers in deeper algal sand habitats
Densities of 2006 survey higher than in previous surveys
Recurring large-scale conch concentrations exist along the western shelf.


These may be classified by habitats and depths
More pronounced conc’s in the SW shelf due to expansive seagrass habitat

Current patterns, habitat type, and the attraction of conspecifics are likely playing a
role in the recruitment of individuals to these areas.

Juveniles are settling/recruiting into both shallow seagrass and deeper algal sand
habitats, but higher proportions and densities are found within seagrasses.

Adults and older conch are somewhat more restricted in location along the shelf and
lower in number.
Conclusions

GIS mapping of surveys permits high understanding of large scale habitat
connectivity in queen conch.

Distinct regions and their concentrations may be identified to aid in future
management, and to complement stock abundance montioring



It would appear that the seasonal closures were effective in allowing for population increase, but
still a long way to go.
Alee Effect at <48 conch/ha, where reproduction ceases
Future Applications:

Essential Fish Habitat

Population Dynamics

Comparison to fishermen data

Ecosystem based management

Biological and Management applications

Seasonal survey periodicity and stratification

Future studies
BREAK TIME!!!
(5 Minutes)