GIS mapping and analysis of queen conch (GIS mapping and analysis of queen conch (Strombus gigasStrombus gigas) ) stock abundance surveys in Puerto Ricostock abundance surveys in Puerto Rico

Anthony R. Marshak and Richard S. AppeldoornAnthony R. Marshak and Richard S. AppeldoornDepartment of Marine SciencesDepartment of Marine Sciences

University of Puerto Rico – Recinto de MayagUniversity of Puerto Rico – Recinto de Mayagüüezez

Queen Conch (Queen Conch (Strombus gigasStrombus 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

Most PR queen conch landings Most PR queen conch landings concentrated in the E and W concentrated in the E and W coasts, primarily SW insular coasts, primarily SW insular platform.platform.

Conch depletion within Conch depletion within shallow seagrass beds, and shallow seagrass beds, and fishing effort has moved into fishing effort has moved into deeper habitats.deeper habitats.

Queen conch in Puerto RicoQueen conch in Puerto Rico

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

Queen conch stock surveysQueen conch stock surveys

Determine exact conch locations with GPS recorded transect start and endpoints

Divers record start and end time; time of encounter of conch and habitat/depthHabitat, depth, conch size, stage incorporated into GIS accessory data.

Spatial Analyst Density calculator gives overall distribution and aggregation patterns.

GIS Conch PlottingGIS Conch Plotting

Survey Results of the Puerto Rico Survey Results of the Puerto Rico West Insular PlatformWest Insular Platform

Three Surveys over a ten-year periodThree Surveys over a ten-year period(1995-96, 2001-02, 2006)(1995-96, 2001-02, 2006)

Habitat Density Results: Total ConchHabitat Density Results: Total Conch

0

5

10

15

20

25

Algae Hardbottom Reef Sand Seagrass

Den

sity

(co

nch

/ha)

1995-96 Survey

2001-02 Survey

2006 Survey

Habitat Density Results by Age ClassHabitat Density Results by Age Class

Seagrass

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5

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15

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25

Conch Juvenile Adult Old Very Old

Den

sity

(con

ch/h

a)

1995-96 Survey

2001-02 Survey

2006 Survey

Sum all area surveyed per habitat and number of conch encountered to get densities

Spatial Patterns along the West Coast Spatial Patterns along the West Coast of Puerto Ricoof 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

Highest densities of juveniles and adults in all surveys within shallow seagrassHighest densities of juveniles and adults in all surveys within shallow seagrass Other juv’s and adults clustered in smaller numbers in deeper algal sand habitatsOther juv’s and adults clustered in smaller numbers in deeper algal sand habitats Densities of 2006 survey higher than in previous surveysDensities of 2006 survey higher than in previous surveys

Recurring large-scale conch concentrations exist along the western shelf. Recurring large-scale conch concentrations exist along the western shelf. These may be classified by habitats and depthsThese may be classified by habitats and depths More pronounced conc’s in the SW shelf due to expansive seagrass habitatMore 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 Current patterns, habitat type, and the attraction of conspecifics are likely playing a role in the recruitment of individuals to these areas. role in the recruitment of individuals to these areas.

Juveniles are settling/recruiting into both shallow seagrass and deeper algal sand Juveniles are settling/recruiting into both shallow seagrass and deeper algal sand habitats, but higher proportions and densities are found within seagrasses.habitats, but higher proportions and densities are found within seagrasses.

Adults and older conch are somewhat more restricted in location along the shelf and Adults and older conch are somewhat more restricted in location along the shelf and lower in number.lower in number.

ConclusionsConclusions

GIS mapping of surveys permits high understanding of large scale habitat GIS mapping of surveys permits high understanding of large scale habitat connectivity in queen conch.connectivity in queen conch.

Distinct regions and their concentrations may be identified to aid in future Distinct regions and their concentrations may be identified to aid in future management, and to complement stock abundance montioringmanagement, and to complement stock abundance montioring

It would appear that the seasonal closures were effective in allowing for population increase, but still It would appear that the seasonal closures were effective in allowing for population increase, but still a long way to go.a long way to go.

Alee Effect at <48 conch/ha, where reproduction ceasesAlee Effect at <48 conch/ha, where reproduction ceases

Future Applications:Future Applications: Essential Fish HabitatEssential Fish Habitat Population DynamicsPopulation Dynamics Comparison to fishermen dataComparison to fishermen data Ecosystem based managementEcosystem based management Biological and Management applicationsBiological and Management applications Seasonal survey periodicity and stratificationSeasonal survey periodicity and stratification Future studiesFuture studies

ConclusionsConclusions

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