Florida Fish and Wildlife

Conservation Commission 

National Park Service

U.S. Department of the Interior

South Florida Natural Resources Center

Everglades and Dry Tortugas National Parks 

Prepared by the 

National Park Service and the 

Florida Fish and Wildlife Conservation Commission

2012

Implementing the

Dry Tortugas National Park

Research Natural Area Science Plan

The 5-Year Report
RESEARCH NATURAL AREA BOUNDARY

RESEARCH NATURAL AREA BOUNDARY 

Hospital Key

Loggerhead Key

Middle Key East Key

0 1 Kilometer

0 1 Statute Mile

0 1 Nautical Mile

North

PARK BOUNDARY

PARK BOUNDARY

NATURAL CULTURAL ZONE

T O R TUGA S NORTH

ECOLOGICAL RESERVE

F L O RIDA KEY S

N A T I ONAL MARIN E

SANCTUA R Y

REASEARCH NATURAL AREA

Pulaski Shoal

HISTORIC

ADAPTIVE

USE ZONE

D R Y T O R T UGAS 

NATIONAL PARK

RESEARCH NATURAL AREA BOUNDARY

HISTORIC

ADAPTIVE

USE ZONE

DETAIL

North
Implementing the

Dry Tortugas National Park

Research Natural Area Science Plan:

The 5-Year Report

 Prepared by the

 National Park Service

 and the

Florida Fish and Wildlife Conservation Commission

2012

South Florida Natural Resources Center

Everglades and Dry Tortugas National Parks

Homestead, Florida

National Park Service

U.S. Department of the Interior

Florida Fish and Wildlife Conservation Commission

Tallahassee, Florida

Cover photograph of mutton snapper by Jiangang Luo, UM RSMAS.

Cover background photograph by Brett Seymour, Submerged Resources Center, NPS.
ii
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 iii

EXECUTIVE SUMMARY

In 2007, the National Park Service (NPS) and the Florida Fish 

and Wildlife Conservation Commission (FWC) developed 

a science plan, Assessing the Conservation Efficacy of the Dry 

Tortugas National Park Research Natural Area, specifically 

to assess the effectiveness of a 46-mi2

 Research Natural Area 

(RNA). The Dry Tortugas National Park (DRTO) RNA is a 

no-take (all forms of fishing are prohibited), no-anchoring 

(strategically placed mooring buoys are provided) marine 

reserve that was implemented to protect shallow water habitats and reef fish species in conjunction with two nearby existing marine reserves, the Tortugas North Ecological Reserve 

(TNER) and the Tortugas South Ecological Reserve (TSER). 

This 5-year report summarizes the progress of science plan 

activities to date. Progress in implementing the science plan 

has been facilitated by cooperative relationships between 

federal and state agencies, academic scientists, and continuous coordination between the FWC and NPS. The results of 

monitoring programs and scientific studies presented here 

document existing baseline conditions and analyze how 

resources have responded thus far to the protection provided. 

The 5-year report is structured around the six focal topic 

areas described in the science plan. A summary of each project and an evaluation of RNA performance is provided here.

RNA Topic 1: Quantify changes in the 

abundance and size-structure of exploited 

species within the RNA relative to 

adjacent areas

Chapter 1: Status of reef fish resources of the Tortugas region 

based on fishery-independent visual and trap survey assessments – Jerald S. Ault et al.

From 1999 to 2011, fishery independent visual surveys were 

conducted to assess the status of the coral reef fish community, and evaluate spatial and temporal trends in species 

abundance metrics in the Tortugas region with particular 

emphasis on the RNA post-implementation. In both the 

TNER and DRTO, abundance, as measured by occupancy 

rates and density at survey sites, and sizes of red grouper, mutton snapper, yellowtail snapper, and hogfish at or above the 

legal size of capture have increased since the implementation 

of the RNA. In contrast, abundance and size of these species 

either remained the same or decreased in nearby areas of the 

Tortugas region that are open to fishing. Abundance of adult 

spawning-sized fish has increased within the RNA relative to 

other areas, as well. The protection afforded to these reef fish 

species by the RNA is likely an important component for the 

recovery of their populations. 

Chapter 2: Nursery function of seagrasses within the Dry Tortugas National Park Research Natural Area – Theodore Switzer 

et al.

Fishery independent trapping surveys designed to assess fish 

assemblages associated with seagrass, including juveniles, 

were conducted within DRTO, inside and outside the RNA. 

In general, white grunts and red grouper collected in seagrass 

beds were smaller than those observed at nearby reefs. Juvenile red and black groupers were most frequently collected in 

the shallow seagrass beds of the RNA. Seagrass beds within 

the RNA most likely function as an important nursery habitat for juveniles of exploited reef fish species of the Tortugas 

region. 

RNA Topic 2: Monitor the immigration and 

emigration of targeted species in the RNA

Chapter 3: Regional connectivity of fishes within the Tortugas 

region of Florida – Michael W. Feeley et al. 

A migratory corridor for adult mutton snapper between the 

RNA and offshore spawning habitat at Riley’s Hump (RH) 

was identified using acoustic telemetry. Mutton snapper were 

observed to make that migration as many as four times during each summer spawning season. A large mutton snapper 

aggregation and repeated spawning events were documented 

for the first time in Florida, 5 days after the full moon, along 

the south slope of RH. The RNA, complemented by the 

TNER and the TSER, provides critical protection of essential reef fish habitat and important fish spawning habitat. The 

results suggest that the RNA may provide important support 

to the mutton snapper spawning aggregation at RH.

Implementing the Dry Tortugas National Park Research Natural Area 

Science Plan: The 5-Year Report 2012

The RNA, complemented by the TNER and the TSER, provides 

critical protection of essential reef fish habitat and important fish 

spawning habitat for species such as mutton snapper. Photo by 

©Christopher Parsons, Photography by Chris Parsons.
iv

Chapter 4: Spillover of select reef fish species in and near the Dry 

Tortugas National Park Research Natural Area – Michael W. 

Feeley et al. 

Home range estimates of acoustically tagged snappers and 

groupers were utilized to evaluate spillover across the boundaries of the RNA. Spillover was detected for all the species 

that were acoustically tagged. Many home ranges of individual fish straddled the RNA boundary. Low rates of return 

of conventionally tagged fish limited the ability to evaluate 

spillover from this method. However, long-range movements 

were detected for one red grouper and two yellowtail snapper. The RNA is likely providing benefits to the surrounding 

region through spillover. 

Chapter 5: Use of Dry Tortugas National Park by threatened 

and endangered marine turtles – Kristen M. Hart et al. 

Satellite and acoustic tracking results for green turtles, hawksbills, and loggerheads have revealed patterns in the proportion of time that tagged turtles spend within various zones of 

the park, including the RNA. Green turtles primarily utilize 

the shallow areas in the northern portion of the park. Hawksbills were mostly observed near Garden Key and loggerheads 

were observed throughout DRTO. Our record of turtle captures, recaptures, and sightings over the last 4 years serves as 

a baseline database for understanding the size classes of each 

species present in the park, as well as species-specific habitats 

in DRTO waters.

RNA Topic 3: Monitor changes in species 

composition and catch rates of exploited 

species throughout the surrounding 

region

Chapter 6: Status of the development and implementation 

of a creel survey and vessel permit system at Dry Tortugas 

National Park – Tracy A. Ziegler et al.

National Park Service staff has been working with 

University of Miami fisheries scientists to develop an improved creel census for DRTO. The survey design is complete and creel survey data will be used to calculate catch 

per unit effort for exploited fisheries species, which can 

help provide an estimate of species abundance during a 

given time period. The vessel permit system is in place and 

will be used in concert with the creel surveys to help assess 

the effects of RNA implementation on recreational fishing 

areas surrounding the RNA.

RNA Topic 4: Evaluate the effects of 

RNA implementation on marine benthic 

biological communities

Chapter 7: Assessing the effects of diving activities on coral 

communities at designated dive sites within the Dry Tortugas 

National Park Research Natural Area – Rob Ruzicka et al.

The goal of this project is to determine if diver-related 

impacts will occur at RNA dive sites designated with mooring buoys. In 2009, permanent monitoring stations were 

established at four RNA dive sites and three equivalent reference sites that have little or no diving activity and do not 

have mooring buoys. Surveys conducted in 2009 and 2010 

established excellent baseline information prior to installation of the mooring buoys, which was completed in 2011. 

Post-installation surveys will be conducted to evaluate the 

extent of diver impacts.

Chapter 8: Baseline surveys to detect trophic changes in shallow hard-bottom communities induced by the Dry Tortugas 

National Park Research Natural Area – Ilsa B. Kuffner et al.

A study was initiated to examine the potential impacts of 

reduced abundance of exploited reef fish species on herbivores, macroalgae, and corals. Surveys were performed 

inside and outside of the RNA to characterize relationships between different trophic level organisms inhabiting the coral reef ecosystem. No significant differences in 

the abundance of herbivorous fish and urchins or in the 

abundance of exploited fish species in the shallow, lowrelief hard-bottom communities were observed inside vs. 

outside the RNA. Evaluating and understanding trophic 

changes that may occur related to the RNA will require a 

long-term research and monitoring effort. Future surveys 

will be necessary to determine if changes have occurred in 

The record of turtle captures, recaptures, and sightings over the 

last 4 years provides baseline data for understanding the size 

classes of each species present in the park, as well as speciesspecific habitats in DRTO waters. Photo by Matt Patterson, NPS.

Executive Summary
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 v

the proportions of major coral reef ecosystem components 

and to help determine if the implementation of the RNA 

results in balanced benthic communities at DRTO. 

Chapter 9: Eight years of coral reef community monitoring: 

Results from inside and outside the Dry Tortugas National 

Park Research Natural Area – Jeff Miller et al.

The National Park Service conducts annual monitoring 

designed to observe long-term status and trends of benthic 

communities, with particular attention focused toward 

monitoring change associated with the RNA. Decreases in 

coral cover were observed at Bird Key Reef from 2004 to 

2011 while coral cover at all other sites remained relatively 

constant through that time period. A benthic habitat map 

was developed that now identifies more than 10,000 ha of 

DRTO habitats previously unclassified, including areas of 

previously unclassified hard bottom. 

Chapter 10: Evaluation of submerged cultural resource conditions within Dry Tortugas National Park – Memory et al.

Many submerged cultural resources exist inside and outside the RNA. A survey in 2009 was conducted at 40 of 50 

submerged cultural resource sites and condition assessments were performed at each site. Baseline condition data 

have been collected and will be used for monitoring change 

in the condition of cultural resources within the RNA and 

other areas of DRTO. Because submerged cultural resources serve as substrate for benthic natural resources and associated fish and invertebrate communities, opportunities 

exist for collaborative studies between NPS natural and 

cultural resource divisions to determine benefits of RNA 

implementation.

RNA Topic 5: Assess reproductive potential 

of exploited species by evaluating egg 

production and larval dispersal

Chapter 11: Larval transport modeling to assess the reproductive potential of reef fish spawning in the Tortugas region – Jerald 

S. Ault et al. 

A south Florida marine ecosystems model was developed 

to simulate the larval drift of marine organisms. This model 

was used to assess the reproductive potential of exploited 

reef fish species by evaluating the expected physical transport and fate of fish eggs and larvae spawned in the Tortugas 

region to the adjacent waters of the south Florida coral reef 

ecosystem. Simulation results indicate that spawning in the 

Tortugas region is likely supplying newborn recruits to reef 

fish populations throughout southern Florida, including the 

Dry Tortugas and Florida Keys reef tract, coastal bays along 

the West Florida Shelf, and along the east coast of Florida 

north of Miami.

RNA Topic 6: Incorporate social sciences 

into the research and monitoring program

Chapter 12: A survey of visitor demographics, attitudes, 

perceptions, and experiences at Dry Tortugas National Park 

– David Loomis.

This project will survey park visitors who participate in 

recreational boating, fishing, SCUBA diving, snorkeling, 

and other activities within DRTO, with an emphasis on 

understanding the use of the RNA. This survey will help 

managers understand the behaviors and actions of park 

visitors that have significant impacts on resources and the 

success of the RNA. The survey results will provide basic 

demographic information on the respondents, the frequency and extent to which they engage in different types 

of recreational activities, and their perceptions of the RNA. 

Summary Evaluation of Dry Tortugas 

National Park Research Natural Area 

Performance

Upon completion of the DRTO RNA science plan in 2007, 

NPS and FWC science managers set as their primary goal 

finding the means to fund and otherwise support research 

projects focused on the immediate high-priority RNA performance topic areas, especially those related to changes in 

fish populations. Their efforts to address this goal resulted 

in the initiation or expansion of projects designed to survey adult fish populations, evaluate juvenile fish within the 

seagrass beds of the RNA, conduct acoustic tagging studies 

of fish movements, and model larval-transport. Taken together, the results of these studies suggest that the RNA has 

A survey in 2009 was conducted at 40 of 50 submerged cultural 

resource sites and condition assessments were performed at 

each site. Photo by Brett Seymour, Submerged Resources Center, 

NPS.
vi Executive Summary

played a substantive role in enhancing some exploited reef 

fish species populations in the region and, especially in the 

case of mutton snapper, has likely contributed to the recovery of the spawning aggregations located at Riley’s Hump. 

Specifically, extensive surveys of adult fish (Chapter 1, this 

volume) observed increases in the abundance of exploited 

species within the RNA. Studies that tracked acoustically 

tagged fish not only detected spillover, but identified a previously unknown migratory behavior of mutton snapper 

where they travelled to Riley’s Hump from within the RNA 

as many as 4 times during one spawning season (Chapters 

3 and 4, this volume). This research team also observed 

for the first time aggregations of actively spawning mutton 

snapper at Riley’s Hump. They conclude that protection of 

mutton snapper offered by the RNA has been important 

to the recovery of the aggregation. The larval transport 

models indicate that fish larvae from these spawning aggregations settle throughout south Florida, including the 

Dry Tortugas (Chapter 11, this volume). Finally, the surveys 

conducted within the seagrass beds of the RNA indicate 

that these beds likely serve as juvenile nursery grounds for 

many exploited fish species of the region (Chapter 2, this 

volume). Overall, protection offered by the RNA has added 

substantial benefits to the protection already provided by 

the preexisting reserves in the Tortugas region. These benefits have not only occurred within its borders, but extend 

beyond its borders via larval transport.

Because it was expected that any changes in the habitat structure or trophic cascades would be slow to occur 

and only detectable over a longer time-period than five 

years, the science managers’ main goal was to ensure that 

appropriate baseline studies were conducted for these performance topics. Baseline studies for assessing the impact 

of diving on benthic habitats (Chapter 7, this volume) and 

initial surveys to set the baseline for understanding future 

trophic changes (Chapter 8, this volume) were completed. 

A more accurate habitat map was developed that will support future research (Chapter 9, this volume). Finally, the 

stage has been set for future evaluation of the human dimension components of the science plan (Chapters 6 and 

12, this volume). The RNA and associated reserves should 

serve as an important focal point for future research designed to understand the role that no-take marine reserves 

can play in marine ecosystem management.

Surveys conducted within the seagrass beds of the RNA indicate that these beds likely serve as juvenile nursery grounds for many 

exploited fish species of the region. Photo by Naomi Blinick, USGS.
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 vii
viii

Gray snapper and a red grouper congregate near a large coral head. Photo by Naomi Blinick, USGS.
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 ix

TABLE OF CONTENTS

ACKNOWLEDGEMENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x

INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

TORTUGAS REGION MANAGED AREA OVERVIEW. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

STATUS OF DRTO RNA PERFORMANCE PLAN ACTIVITIES BY TOPIC

RNA Performance Topic 1: Quantify changes in the abundance and size-structure of exploited species within the 

RNA relative to adjacent areas

Chapter 1: Status of reef fish resources of the Tortugas region based on fishery-independent visual and 

trap survey assessments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Chapter 2: Nursery function of seagrasses within the Dry Tortugas National Park Research Natural Area. . . . . . . . . . . . . . . 14

RNA Performance Topic 2: Monitor the immigration and emigration of targeted species in the RNA

Chapter 3: Regional connectivity of fishes within the Tortugas region of Florida. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Chapter 4: Spillover of select reef fish species in and near the Dry Tortugas National Park Research Natural Area. . . . . . . . . 24

Chapter 5: Use of Dry Tortugas National Park by threatened and endangered marine turtles. . . . . . . . . . . . . . . . . . . . . . . . 28

RNA Performance Topic 3: Monitor changes in species composition and catch rates of exploited species 

throughout the surrounding region

Chapter 6: Status of the development and implementation of a creel survey and vessel permit system at 

 Dry Tortugas National Park. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

RNA Performance Topic 4: Evaluate the effects of RNA implementation on the marine benthic biological communities

Chapter 7: Assessing the effects of diving activities on coral communities at designated dive sites within the 

Dry Tortugas National Park Research Natural Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Chapter 8: Baseline surveys to detect trophic changes in shallow hard-bottom communities induced by the 

Dry Tortugas National Park Research Natural Area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Chapter 9: Eight years of coral reef community monitoring: Results from inside and outside the Dry Tortugas 

National Park Research Natural Area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Chapter 10: Evaluation of submerged cultural resource conditions within Dry Tortugas National Park. . . . . . . . . . . . . . . . . 52

RNA Performance Topic 5: Assess reproductive potential of exploited species by evaluating egg production and 

larval dispersal

Chapter 11: Larval transport modeling to assess the reproductive potential of reef fish spawning in the 

 Tortugas region. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

RNA Performance Topic 6: Incorporate social sciences into the research and monitoring program

Chapter 12: A survey of visitor demographics, attitudes, perceptions, and experiences at Dry Tortugas National Park . . . . . 62
x

Comments and Questions on the RNA Science Plan, 3-Year Report, and 5-Year Report:

Contact Tracy_Ziegler@nps.gov or John.Hunt@MyFWC.com

Report produced by Science Communications, Everglades National Park.

Alice Clarke, Managing Editor, with the editorial support of Ellen Hardy. Desktop design and publishing by Larry Perez. GIS support by Caryl 

Alarcón.

Please reference the RNA 5-Year Report as follows:

Ziegler, T. A. and Hunt, J., editors. 2012. Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 

2012. South Florida Natural Resources Center, Everglades and Dry Tortugas National Parks, Homestead, FL, and the Florida Fish and Wildlife 

Conservation Commission, Tallahassee, FL. 63 pp. 

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although 

this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted material contained within this report. Printed on 30% post-consumer waste paper with vegetable-based inks. Fiber sourced from responsibly managed forests.

Science activities in the Dry Tortugas National Park Research Natural Area are guided by the science plan prepared in 2007 by the 

National Park Service and the Florida Fish and Wildlife Conservation Commission. All reports are available online at:

http://www.nps.gov/ever/naturescience/technicalreports.htm

ACKNOWLEDGEMENTS

We thank the captains and the crew of the M/V Fort Jefferson, Clay “Blue” Douglass, Janie Douglass, and John Spade, for their 

exceptional support for a large number of projects within this report. We also thank Captain Frank and Melanie Wasson, along 

with all the crew members of the M/V Spree, for their excellent support of the annual reef visual census. We sincerely thank Kayla 

Nimmo and Tree Gottshall for their unwavering support and logistical assistance with all the scientific activities at the park. In 

addition we thank John Chelko, Sharon Hutkowski, Pat Moran, Dustin Parker, Kimberly Pepper, Elizabeth Ross, Brion Schaner, 

Allen Zamrock, and Christopher Ziegler for their support at Dry Tortugas National Park.

We thank David Hallac for his leadership in the development of the science plan and associated research at Dry Tortugas 

National Park.

Editors:

Tracy A. Ziegler, National Park Service, Everglades and Dry Tortugas National Parks 

John Hunt, Florida Fish and Wildlife Conservation Commission, Fish and Wildlife Research Institute
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 xi

ASMIS Archeological Sites Management Information 

System

ATRIS Along Track Reef Imaging System

CPUE Catch per unit effort

CREMP Coral Reef Model Evaluation and Monitoring 

Project

DRTO Dry Tortugas National Park

FKNMS Florida Keys National Marine Sanctuary

FSA Fish spawning aggregation

FWC Florida Fish and Wildlife Conservation 

Commission

FWRI Fish and Wildlife Research Institute

GIS Geographic information system

GPS Global Positioning System

HAU Historic Adaptive Use Zone

HYCOM Hybrid Miami Isopycnal Coordinate Ocean 

Model

KDE Kernel density estimate

LiDAR Light Detection and Ranging

MCP Minimum convex polygon

MML Mote Marine Laboratory

MPA Marine protected area

NCZ Natural Cultural Zone

NMFS National Marine Fisheries Service

NOAA National Oceanic and Atmospheric 

Administration

NPS National Park Service

NTMR No-take marine reserve

OMB Office of Management and Budget

PIT Passive integrated transponder

RH Riley’s Hump

RNA Research Natural Area

RSMAS Rosenstiel School of Marine and Atmospheric 

Sciences

SCL Straight carapace length

SFCN South Florida/Caribbean Network

SPZ Special Protection Zone (as in Nurse Shark SPZ 

or Coral SPZ)

SRC Submerged Resources Center

TBO The portion of Tortugas Bank south of the 

TNER and west of DRTO that is open to 

fishing

TNER Tortugas North Ecological Reserve

TSER Tortugas South Ecological Reserve

UM University of Miami

USGS U.S. Geological Survey

LIST OF ABBREVIATIONS
xii
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 1

In 2007, the National Park Service (NPS) and the Florida Fish 

and Wildlife Conservation Commission (FWC) established 

the 46-mi2

 Research Natural Area (RNA) of Dry Tortugas 

National Park (DRTO) and prepared a science plan specifically to assess the effectiveness of the RNA (SFNRC and 

FWC 2007). The science plan was developed using an open 

and transparent process that started with a meeting (February 12 and 13, 2007) to obtain recommendations from state 

and federal agency scientists. Participating agencies included: 

Florida Fish and Wildlife Conservation Commission (Division of Marine Fisheries Management and Fish and Wildlife 

Research Institute), National Park Service (DRTO, South 

Florida Caribbean Network, and Water Resources Division), 

National Oceanographic and Atmospheric Administration 

(Fisheries, National Marine Sanctuary Program, and National 

Ocean Service), and the U.S. Geological Survey. Using the recommendations gathered, the NPS and FWC produced a draft 

science plan and distributed it to agency scientists, academic 

scientists, and members of the public for a 30-day review 

period. A public meeting was then held to gather additional 

comments and input on the draft science plan (May 3, 2007). 

The meeting was well attended by agency and academic scientists, representatives of nongovernmental organizations, 

and concerned citizens. Their comments were addressed in 

the final science plan.

Fort Jefferson National Monument was established in 

1935 and reauthorized in 1992 as Dry Tortugas National Park. 

Congress established DRTO to “preserve and protect for the 

education, inspiration, and enjoyment of present and future 

generations nationally significant natural, historic, scenic, 

marine, and scientific values in south Florida.” The enabling 

legislation stipulated that the park be managed to protect, 

among other values, “a pristine subtropical marine ecosystem, 

including an intact coral reef community.” The RNA directly 

supports the mission of the park as the RNA was established 

to protect shallow water marine habitat, ensure species diversity, and enhance the productivity and sustainability of fish 

populations throughout the region. The marine regulations 

instituted within the boundaries of the RNA prohibit all forms 

of fishing and do not allow anchoring (a limited number of 

strategically located mooring buoys are provided). Together, 

the RNA and the adjacent Tortugas North Ecological Reserve 

and nearby Tortugas South Ecological Reserve of the Florida 

Keys National Marine Sanctuary will help to ensure the success of the marine ecosystems, and thereby contribute to a 

region-wide effort to strengthen resource protection.

Dry Tortugas National Park is managed for the protection of a pristine subtropical marine ecosystem—including an intact coral reef 

community—for the enjoyment of present and future generations. Photo by Brett Seymour, Submerged Resources Center, NPS.

INTRODUCTION
2

The intent of the RNA science plan was to develop longterm studies and monitoring to document existing baseline 

conditions and analyze how natural resources will respond 

to the protection provided. Consequently, the science plan 

identified six areas of RNA performance to be evaluated: 

1. Quantify changes in the abundance and size-structure of exploited species within the RNA relative to 

adjacent areas,

2. Monitor the immigration and emigration of targeted 

species in the RNA,

3. Monitor changes in species composition and catch 

rates of exploited species throughout the surrounding region,

4. Evaluate the effects of RNA implementation on 

marine benthic biological communities,

5. Assess reproductive potential of exploited species by 

evaluating egg production and larval dispersal, and

6. Incorporate social sciences into the research and 

monitoring program.

Because ecosystems take time to respond to management 

actions, the science plan included a variety of indicators 

designed to evaluate RNA performance both in short and long 

time frames. Natural variability in sea temperature, weather 

events such as hurricanes, and other factors can affect many of 

the indicators described in the science plan and thereby have 

the potential to complicate RNA assessment. The full benefit 

of the RNA to the Tortugas region will only be measurable in 

the long-term. In 2010, NPS and FWC scientists submitted a 

3-year report (Hallac and Hunt 2010) that described progress 

in the implementation of science projects and some preliminary results. This 5-year report provides the first evaluation of 

the performance of the RNA. Although the results presented 

in this report provide considerable useful information regarding RNA performance, many of the research projects presented in this report are ongoing, and monitoring continues. 

Future evaluations will have the capacity to provide a more 

expansive discussion of the performance of the RNA.

The NPS and FWC remain committed to working together 

to conduct research, education, and adaptive management of 

the Dry Tortugas ecosystem. This jointly developed 5-year 

report provides a summary of the research results on the 

six areas of RNA performance and meets the requirements 

(Article III, Sections B(3) and C(4)) of the Memorandum of 

Understanding established between the FWC and DRTO 

and finalized in February of 2007. The report is structured by 

performance topics as established in the science plan. Each 

chapter contains a summary of progress and results obtained 

thus far, plus an evaluation of those results relative to the 

stated goals of the RNA. 

Literature Cited

Hallac, D.E. and Hunt, J., editors. 2010. Implementing the Dry 

Tortugas National Park Research Natural Area Science 

Plan: The 3-year report. South Florida Natural Resources 

Center, Everglades and Dry Tortugas National Parks, 

Homestead, FL, and the Florida Fish and Wildlife Conservation Commission, Tallahassee, FL. 37 pp.

SFNRC and FWC. 2007. Assessing the conservation efficacy 

of the Dry Tortugas National Park Research Natural Area. 

South Florida Natural Resources Center, Everglades and 

Dry Tortugas National Parks, Homestead, FL, and the 

Florida Fish and Wildlife Conservation Commission, Tallahassee, FL. 47 pp.

The RNA protects shallow water marine habitat, ensures species diversity, and enhances the productivity and 

sustainability of fish populations throughout the region. Photo by Jiangang Luo, UM RSMAS.

Introduction
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 3

TORTUGAS REGION MANAGED AREA 

OVERVIEW

The scientific activities reported in this document were conducted within the different management areas of the Tortugas 

region. Each chapter examines a specific performance measure and presents the results relative to these management 

areas. In order to facilitate the understanding of the chapters, 

we present an overview and definition of each of these management zones and their associated levels of resource protection. All management zones and locations discussed in this 

section are referenced on the maps located on the front and 

back inside covers of this report.

Dry Tortugas National Park (DRTO), located approximately 70 miles to the west of Key West, includes 100 mi2 of 

marine waters and seven small islands, one of which contains 

Fort Jefferson, a national historic site. Marine-related activities 

allowed park-wide include boating, snorkeling, SCUBA diving, and wildlife viewing. Commercial fishing and spearfishing are prohibited throughout the park. DRTO is comprised 

of three management zones: the Research Natural Area, the 

Natural Cultural Zone, and the Historic Adaptive Use Area. 

The Research Natural Area (RNA) encompasses 46% of 

the park. It is located in the western portion of the park. Recreational fishing is prohibited within the RNA. Snorkeling and 

SCUBA diving are allowed; however, boaters are required to 

use mooring buoys, as anchoring is prohibited.

The Natural Cultural Zone (NCZ) encompasses approximately 50% of the park. It is located in the eastern and southern portions of DRTO. Recreational fishing is allowed in this 

area as well as in the Historic Adaptive Use Zone. Anchoring is 

allowed within the NCZ, except on known cultural resources 

and on corals. 

The Historic Adaptive Use Zone (HAU) encompasses 

approximately 3% of the park. Like the NCZ, recreational 

fishing and anchoring are allowed within the HAU. The HAU 

is the only zone where overnight anchoring is allowed. Garden 

Key Harbor Light is the center of the HAU. The HAU extends 

outward for a distance of 1 nautical mile to encompass surrounding waters, including those around Bush and Long 

Keys. Within the HAU are two areas of increased protection: 

the Nurse Shark Special Protection Zone (SPZ) and the Coral 

Special Protection Zone (SPZ). Located to the west and south 

of Bush and Long Keys, these areas are closed to the public. 

The Nurse Shark SPZ is a shark-mating site and contains a 

high number of pregnant females during mating season. The 

Coral SPZ is an area that contains a large portion of the park’s 

rare and threatened corals, including elkhorn coral (Acropora 

palmata), staghorn coral (Acropora cervicornis), and the 

elkhorn-staghorn hybrid (Acropora prolifera). 

The Florida Keys National Marine Sanctuary (FKNMS) 

surrounds the boundary of DRTO. Two ecological reserves, 

the Tortugas North Ecological Reserve (TNER) and the Tortugas South Ecological Reserve (TSER), together encompass 

nearly 160 mi2

. The TNER is contiguous to the park along the 

northwestern boundary of the RNA. The TSER is located 

approximately 7 miles to the southwest of DRTO and contains 

Riley’s Hump, a historically known fish spawning aggregation 

site. Fishing and anchoring are prohibited in the TNER and 

the TSER. SCUBA diving and snorkeling are allowed in the 

TNER at mooring buoy locations and with appropriate permits. SCUBA diving and snorkeling are prohibited within the 

TSER. The remaining area within the FKNMS and adjacent 

waters are open to fishing. Fishing regulations for these areas 

are governed by the Florida Fish and Wildlife Conservation 

Commission in state waters, and by the South Atlantic Fishery 

Management Council and the Gulf of Mexico Fishery Management Council outside state boundaries.

Snorkeling and SCUBA diving are allowed in the RNA; however, boaters are required to use mooring buoys, 

as anchoring is prohibited. Photo by Naomi Blinick, USGS volunteer/NPS.
4 RNA Performance Topic 1: Quantify changes in the abundance and size-structure of exploited species within the RNA relative to 

adjacent areas

Investigators

Jerald S. Ault1, Steven G. Smith1, Ted Switzer2, James A. 

Bohnsack3

, Matt Patterson4, Michael W. Feeley2,4, David B. 

McClellan3

, Benjamin I. Ruttenberg3,4, David Hallac4, Tracy A. 

Ziegler4

, and John Hunt2

1

University of Miami, Rosenstiel School of Marine and 

Atmospheric Science

2

Florida Fish and Wildlife Conservation Commission, Fish 

and Wildlife Research Institute

3

National Oceanic and Atmospheric Administration, Southeast Fisheries Science Center 

4

National Park Service

For further information contact: jault@rsmas.miami.edu

Project Description

The National Park Service established the Research Natural 

Area (RNA), a no-take marine reserve (NTMR), in the western half of Dry Tortugas National Park (DRTO) in 2007. The 

RNA was designed as a shallow-water complement to two relatively large marine reserves, the Tortugas North Ecological 

Reserve (TNER) and the Tortugas South Ecological Reserve 

(TSER), established in 2001 in the Florida Keys National 

Marine Sanctuary. The remainder of the park, the Natural 

Cultural Zone (NCZ), has been closed to commercial fishing, 

recreational spearfishing, and lobstering since the 1960s. This 

section of the park is, however, open to recreational hookand-line fishing. 

To better understand the effects of RNA implementation on 

the abundance and size structure of exploited species within 

the RNA relative to adjacent areas (Performance Topic 1), it is 

important to view DRTO and the Tortugas region relative to 

the larger Florida coral reef ecosystem and in relationship to 

the regional spatial management actions implemented during 

the past decade. The Florida coral reef ecosystem, stretching 

400 km southwest from Miami to the Dry Tortugas, supports 

multibillion-dollar tourism and fishing industries (Ault et al. 

2005a). Regional spawning in the Tortugas region provides 

the Florida Keys with recruits because of its relative isolaRNA Performance Topic 1 

Chapter 1: Status of reef fish resources of the Tortugas region based on 

fishery-independent visual and trap survey assessments 

Fishery-independent visual surveys were conducted during 1999–2011 throughout the Tortugas region to assess 

the resource status of the coral reef fish community, including hogfish and other exploited species. Photo by the 

South Florida/Caribbean Inventory and Monitoring Network, NPS.
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 5

tion and upstream location where the Loop Current merges 

into the Florida Current (Schmidt et al. 1999; Ault et al. 2006; 

Chapter 11, this volume). However, the sustainability of these 

fisheries resources is in question. The ecosystem’s lucrative 

multispecies snapper-grouper complex has been intensively 

fished since at least the late 1970s (Ault et al. 1998; 2005b; 

2009). The number of recreational vessels in Florida, an index 

of sportfishing fleet size, has risen in step with increases in 

the human population. From 1960 to 2010, Florida’s human 

population increased from 4,951,560 to 18,801,310. During 

this same period registered recreational vessels increased by 

697%, reaching 896,093 at present. The commercial fleet, in 

contrast, has remained stable during this period. 

Fishery-independent visual surveys were conducted during 1999–2011 throughout the Tortugas region to assess the 

resource status of the coral reef fish community, and specifically to evaluate spatial and temporal trends in species-specific abundance metrics (occurrence, density, abundance, and 

size composition, for example) before and after implementation of the TNER and RNA (Performance Topic 1). Sampling 

effort was concentrated inside DRTO and the adjacent Tortugas Bank to the west of the park (Fig. 1). Highly trained and 

experienced divers collected biological data following a standard, non-destructive, in-situ monitoring protocol in which 

a stationary diver records reef-fish data (number and sizes of 

each species) while centered in a randomly selected circular 

plot 15 m in diameter. The field research team was comprised 

of scientific personnel from the National Oceanic and Atmospheric Administration, the University of Miami, the National 

Park Service, and the State of Florida. The statistical field 

design partitioned Tortugas Bank and DRTO into strata based 

on reef habitat characteristics (complexity and patchiness of 

reef structures, and depth) and spatial management zones 

(Fig. 1 and map shown on inside cover). This habitat-based 

survey design was developed in 1999 and 2000, and has been 

shown to provide accurate and precise abundance metrics 

for reef fishes in the Tortugas region in a cost-effective manner (Ault et al. 2006; Smith et al. 2011). Tortugas region-wide 

surveys were conducted during 1999, 2000, 2004, 2006, 2008, 

and 2010, with sample sizes ranging from 327 to 704 stations. 

In addition, DRTO-specific surveys were conducted in 2002, 

2009, and 2011, with sample sizes ranging from 191 to 445 stations. 

A complementary fishery-independent survey using 

baited chevron traps was conducted from May 2008 to June 

2011 to evaluate potential changes in the relative abundance 

and size structure of exploited reef fishes within the RNA and 

NCZ. Sampling followed a seasonal (spring and fall) stratifiedrandom survey design within the southern portion of DRTO 

(south of 24o 40’ N). The survey design was based on the reef 

fish visual census, although reef habitats were aggregated into 

three reef strata: contiguous reef; spur-and-groove reef; and 

isolated reef. At each sampling station, four chevron traps 

were baited with Atlantic mackerel and deployed over sand 

bottom adjacent to targeted reef habitat. Traps were allowed 

to soak for a minimum of 90 minutes prior to retrieval. All 

trapping was conducted during daylight hours. Seasonal sampling effort ranged from 29 to 46 stations. In total, trapping 

Figure 1. Map of benthic habitats and management zones in the Tortugas region (redrawn 

from Ault et al. 2006). See map on inside front cover for management zone identification.

Seagrass

Medium Profile

Reef

Patchy Hard Bottom

in Sand

Pinnacle Reef

Reef

Terrace

Tortugas Bank

Dry Tortugas National Park

Rocky

Outcrops

Low-Relief

Hard Bottom

Low-Relief

Spur & Groove

High-Relief

Spur & Groove
6 RNA Performance Topic 1: Quantify changes in the abundance and size-structure of exploited species within the RNA relative to 

adjacent areas

Figure 2. Spatial distribution of exploited mutton snapper density (mean number of fish per sample unit, 177 m2

) for Tortugas region 

visual surveys conducted in (A) 2000 and (B) 2008, and corresponding average densities and occupancy rates for three areas (TNER, 

DRTO, and TBO). Each sample point represents the average of four diver visual point counts. White circles represent sample points 

where no mutton snapper were observed. Colored circles represent sample points where mutton snapper were present. Occupancy 

rates within DRTO (RNA and open-use zones) are provided for 2008. Note that though the RNA was not established in 2000, boundary 

lines are shown for reference in Panel A. 

TNER

Density = 0.04

Occupancy = 5.3%

TBO

Density = 0.19

Occupancy = 21.9%

DRTO

Density = 0.10

Occupancy = 10.7%

RNA

HAU

TNER

Density = 0.32

Occupancy = 42.6%

TBO

Density = 0.27

Occupancy = 29.0%

DRTO

Density = 0.26

Occupancy = 33.9%

RNA

HAU

Within DRTO Occupancy

RNA = 34.7%

Open-Use = 32.3%

A

B
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 7

surveys were conducted at 117 stations (468 chevron trap 

sets) within the RNA and 122 stations (488 chevron trap sets) 

within the NCZ. In the RNA, 3,968 fish representing 35 taxa 

were collected, whereas 4,130 fish representing 32 taxa were 

collected in the NCZ. In both areas, the three most abundant 

and frequently occurring taxa were yellowtail snapper, white 

grunt, and red grouper. Accordingly, we focused our trap data 

analyses on these three species.

Results

Reef-fish population metrics from fishery-independent surveys were assessed from three perspectives: (1) changes at 

the regional scale from 1999 to 2011, pre- and post-implementation of both the TNER and RNA; (2) changes within 

DRTO focusing on the 2006–2011 time period, pre- and postimplementation of the RNA; and, (3) analysis of the ecological role of DRTO in the ecosystem for providing habitat for 

both juveniles and adults.

Visual survey abundance metrics were evaluated for 

the region through time, beginning with the baseline preNTMR implementation surveys during 1999–2000, through 

implementation of the TNER (2001) and DRTO RNA (2007) 

management zones, and concluding in 2011. A principal 

abundance metric evaluated was animal density, the number 

of individuals per unit sample area (177 m2

, the area of a diver 

circular plot). Maps of spatial density are illustrated in Figure 

2 for mutton snapper in the exploited life stage (fish at and 

above the minimum legal size of capture). A second abundance metric evaluated was frequency of occurrence (the 

percentage of diver visual samples in which at least one individual of a given species was observed). This statistic provides 

a measure of the occupancy rate (the percentage of the coral 

reef habitat area that is occupied by a species). As shown for 

mutton snapper in Figure 2 , both density and occupancy rates 

increased in the open-use area of Tortugas Bank (TBO), the 

TNER, and DRTO between the pre-implementation baseline 

survey of 2000 and the 2008 survey, post-implementation of 

both the TNER and DRTO RNA.

Evaluation of changes in density during 1999–2011 is 

illustrated for exploited-phase hogfish in Figure 3A. Because 

hogfish density in 1999, prior to implementation of management zones, varied across the region, density that year was 

set as a baseline of zero. Standard statistical procedures were 

used (described in Ault et al. 2006) to test for differences in 

density within each zone for each post-baseline survey year 

and the baseline level. For hogfish, statistically significant 

densities (p<0.05) above the baseline were detected in DRTO 

in three of seven years (2002, 2008, and 2011), whereas densities below baseline levels were detected in the TBO in two 

of the seven years (2006 and 2010) and were never above 

baseline. No differences from baseline levels were detected 

at the TNER. Table 1 summarizes the change in density from 

the 1999 baseline for a suite of exploited and non-target reef 

fish species, as well as two formerly exploited species that 

have been protected by a fishery moratorium since 1994. In 

DRTO, the densities of the exploited stage of the 5 exploited 

species were never below the baseline, and 4 were above the 

baseline in 16 of 35 sampling occasions. In contrast, densities 

of these species below the 1999 baseline were detected only in 

the TBO. As expected, the pattern of density change for nontarget species fluctuated in a pattern unrelated to the management zones. The pattern of change was mixed for the two species under fishing moratoria. Densities above baseline were 

detected for goliath grouper in both the TNER and DRTO, 

whereas the density of Nassau grouper below the baseline was 

detected in DRTO during one survey. 

Comparisons of length composition among management 

areas and time periods from the visual survey are illustrated 

for black grouper in Figure 4. A general increase between 2000 

and 2008 in the proportion of fish at sizes at and above the 

legal minimum was observed in the TNER and particularly 

-100%

-50%

0%

50%

100%

150%

2002 2003 2004 2005 2006 2007 2008 2009 2010 2011

TBO TNER DRTO

Year

Relative Density, % Change from Baseline

0

1

2

3

4

5

2006 2007 2008 2009 2010 2011

DRTO NCZ

DRTO RNA

Density

(A) Hogsh

(B) Yellowtail Snapper

Year

Figure 3. (A) Visual survey estimates of relative mean density 

(± Standard Error (SE)) for the exploited life stage of hogfish, 

2002–2011, for three management areas. Density (number of 

fish per diver visual point count of area 177 m2) is expressed as 

percent change from 1999–2000 baseline levels (solid line). (B) 

Visual survey mean densities (± SE) for the exploited life stage 

of yellowtail snapper in Dry Tortugas National Park, 2006–2011.
8

TBO TNER DRTO

Family Species Increase Decrease

No 

Change Increase Decrease

No 

Change Increase Decrease

No 

Change

Exploited

Groupers Red grouper 0 3 1 0 0 4 0 0 7

Groupers

Black 

grouper

0 0 4 1 0 3 2 0 5

Snappers

Mutton 

snapper

1 0 3 2 0 2 7 0 0

Snappers

Yellowtail 

Snapper

0 0 4 0 0 4 4 0 3

Wrasses Hogfish 0 2 2 0 0 4 3 0 4

Overall 

Exploited

1 5 14 3 0 17 16 0 19

Non-Target

Damselfishes Bicolor 

damselfish 2 1 1 2 1 1 3 1 3

Damselfishes Threespot 

damselfish 1 0 3 0 4 0 1 3 3

Parrotfishes Princess 

parrotfish 2 0 2 0 2 2 2 1 4

Seabasses Harlequin 

bass

1 1 2 2 0 2 0 2 5

Surgeonfishes Ocean 

surgeon

0 0 4 1 0 3 0 1 6

Wrasses Puddingwife 0 0 4 0 0 4 1 2 4

Overall 

Non-target

6 2 16 5 7 12 7 10 25

Moratorium

Groupers

Goliath 

grouper

0 0 4 1 0 3 3 0 4

Groupers

Nassau 

grouper

0 0 4 0 0 4 0 1 6

Overall 

Moratorium

0 0 8 1 0 7 3 1 10

Table 1. Summary of 1999–2011 visual survey results for density for a suite of exploited and non-target reef fish species, and two other 

species under fishing moratoria. Baseline surveys were conducted during 1999–2000; four surveys were conducted post-baseline in the 

TBO and TNER zones, and seven surveys were conducted post-baseline in DRTO.

RNA Performance Topic 1: Quantify changes in the abundance and size-structure of exploited species within the RNA relative to 

adjacent areas
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 9

in DRTO. These changes are characteristic of a relaxation of 

fishing pressure (fishing mortality rate) during the time frame, 

during which more fish survived and grew to larger mature 

sizes. In contrast, very few exploited phase fish were observed 

in the TBO in both time periods. Similar time-space patterns of 

change in length composition were observed for red grouper, 

mutton snapper, and hogfish. We also used our survey data to 

estimate abundance for the exploited phase of black grouper 

within each management zone pre- and post-implementation. 

Abundance markedly increased within DRTO, decreased in 

the TBO, and remained constant in the TNER. Six hurricanes 

impacted the Tortugas region between the surveys of 2004 and 

2006, and many species, fishery and non-target alike, experienced declines in density and abundance during this period. 

Even though Figure 4 shows similar levels of exploited phase 

abundance for black grouper, in 2004 prior to the intense hurricane period, abundance of exploited phase black grouper in 

the TNER more than doubled over 1999–2000 baseline levels 

(Ault et al. 2006). 

Direct comparisons of densities between the RNA and 

the NCZ are presented for yellowtail snapper in Figure 3B. 

Increases in density relative to the 2006 pre-RNA baseline 

0.0

0.1

0.2

0.3

0.4

0.5

5 15 25 35 45 55 65 75 85 95 105 115 125

0.0

0.1

0.2

0.3

5 15 25 35 45 55 65 75 85 95 105 115 125

0.0

0.1

0.2

0.3

5 15 25 35 45 55 65 75 85 95 105 115 125

0.0

0.1

0.2

0.3

5 15 25 35 45 55 65 75 85 95 105 115 125

0.0

0.1

0.2

0.3

5 15 25 35 45 55 65 75 85 95 105 115 125

0.0

0.1

0.2

0.3

5 15 25 35 45 55 65 75 85 95 105 115 125

Relative Frequency

TBO

Exploited Abundance = 4,146

1999-2000 2008-2010

TNER

Exploited Abundance = 9,742

DRTO

Exploited Abundance = 34,642

TBO

Exploited Abundance = 616

TNER

Exploited Abundance = 10,071

DRTO

Exploited Abundance = 68,265

Length (cm)

Figure 4. Visual survey length compositions for black grouper among three management zones for two time periods: the pre-implementation baseline, 1999–2000, and post-implementation of the TNER and RNA, 2008–2010. Open bars are the pre-exploited life stage, 

shaded bars are exploited (fished) life stage animals; exploited abundance is noted on each panel.
10

were detected for yellowtail snapper during the post-RNA 

period 2008–2011, but the pattern was inconsistent: significant increases occurred in both the NCZ and RNA zones in 

2009, only in the open-use area in 2010, and only in the RNA 

in 2011. Similar inconsistent patterns of post-RNA density 

changes also were observed for hogfish, red grouper, and 

mutton snapper, with no changes detected in either zone for 

black grouper. Additionally, occupancy rates also were similar 

between the RNA and the NCZ for most species (for example 

mutton snapper, Fig. 2B). Similarly, no consistent differences 

in the relative abundance of red grouper, yellowtail snapper, 

or white grunt were evident between the NCZ and RNA 

zones in the trap survey. A comparison of size structure of 

red grouper, yellowtail snapper, and white grunt from the trap 

survey showed that the size of individuals was similar between 

the RNA and NCZ (Fig. 5). For both red grouper and yellowtail snapper, a substantial proportion of individuals collected 

were at and above the recreational legal-minimum size limit.

The Tortugas region-wide visual surveys also were analyzed to evaluate the ecological role of DRTO in providing 

habitat for juvenile and adult life stages of principal fishery 

species. While DRTO contains about 60% of the Tortugas survey area (live coral reef habitats, 0–33 m depth), the percentage of juvenile abundance in DRTO was similar to or greater 

than this percentage, ranging from 62 to 93% for the five species analyzed (Table 2A). The proportion of adult spawner 

abundance, which includes the exploited life stage, increased 

by 10% or more in DRTO during 1999–2000 and 2008–2010 

for four of five fishery species (Table 2B). Over this period, 

the total number of adult spawners in the region decreased 

by about 10% for red grouper and hogfish, increased by 60% 

for black grouper, and more than tripled for mutton snapper and yellowtail snapper. By 2008–2010, DRTO contained 

62–87% of adult spawners in the Tortugas region for four of 

the five species. The analysis of adult spawners was expanded 

to include the combined Dry Tortugas and Florida Keys survey areas (mapped live coral habitats, 0–33 m depth), which 

Figure 5. Length frequencies of red grouper, yellowtail snapper, and white grunt collected during the trap survey in the RNA and NCZ 

areas, 2008–2010. Dashed lines represent the recreational size limit for red grouper and yellowtail snapper; no size limit exists for white 

grunt.

RNA Performance Topic 1: Quantify changes in the abundance and size-structure of exploited species within the RNA relative to 

adjacent areas
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 11

were conducted concurrently over the 1999–2010 time period 

(Smith et al. 2011). Between 1999–2000 and 2008–2010, total 

spawner abundance increased for all five species, more than 

doubling in most cases (Table 2C). For the combined Florida 

Keys/Dry Tortugas regions, DRTO contained 22% of the total 

survey area yet harbored a disproportionately larger percentage of the adult spawners in 2008–2010 for four of the five 

fishery species, ranging from 32 to 52%.

Table 2. (A) Percentage of abundance (total numbers) of juveniles in three management zones in the Tortugas region for five principal 

reef fishery species; the percentage of reef habitat area is denoted for each zone. (B) Adult spawner abundance and percentages among 

management zones in the Tortugas region for two time periods, 1999–2000 and 2008–2010. (C) Adult abundance and percentages 

among management zones in the combined Florida Keys/Dry Tortugas reef ecosystem for two time periods.

(A) Tortugas region, Juveniles, 2008–2010

Percentage of Juveniles

Species Area =

TBO

16.5%

TNER

23.7%

DRTO

59.8%

Red Grouper 11.8 20.1 68.1

Black Grouper 2.3 4.7 93.0

Mutton Snapper 26.1 1.5 72.4

Yellowtail Snapper 10.3 28.1 61.6

Hogfish 3.8 12.7 83.6

(B) Tortugas region, Adults

Percentage of Adults

Species

Time 

Period

Spawner Abundance

(1000s) Area =

TBO

16.5%

TNER

23.7%

DRTO

59.8%

Red Grouper

1999–2000 468.1 20.5 28.4 51.1

2008–2010 423.6 6.6 31.5 61.9

Black 

Grouper

1999–2000 48.5 8.5 20.1 71.4

2008–2010 79.0 0.8 12.8 86.5

Mutton 

Snapper

1999–2000 177.5 26.8 12.5 60.7

2008–2010 616.9 21.4 22.7 55.9

Yellowtail 

Snapper

1999–2000 3,379.5 17.2 33.5 49.2

2008–2010 10,021.1 4.9 25.9 69.2

Hogfish

1999–2000 1,067.7 21.9 21.6 56.5

2008–2010 937.5 13.9 19.9 66.2

(C) Florida Keys and Dry Tortugas, Adults

Percentage of Adults

Species

Time 

Period

Spawner Abundance

(1000s) Area =

TBO

6.2%

TNER

8.9%

DRTO

22.4%

Keys Open-Use

58.9%

Keys NTMR

3.6%

Red Grouper

1999–2000 522.8 18.3 25.4 45.7 9.9 0.6

2008–2010 540.1 5.1 24.7 48.6 19.9 1.6

Black 

Grouper

1999–2000 68.5 6.1 14.2 50.6 16.0 13.2

2008–2010 130.5 0.5 7.7 52.3 34.9 4.6

Mutton 

Snapper

1999–2000 409.7 11.6 5.4 26.3 53.1 3.6

2008–2010 1,078.4 12.3 13.0 32.0 39.5 3.3

Yellowtail 

Snapper

1999–2000 7,707.5 7.6 14.7 21.6 38.9 17.3

2008–2010 14,982.7 3.2 17.3 46.3 28.5 4.6

Hogfish

1999–2000 2,758.3 8.5 8.3 21.9 59.0 2.3

2008–2010 4,314.1 3.0 4.3 14.4 74.8 3.4
12

Performance Measure Evaluation

The visual survey enabled evaluation of changes in reef fish 

populations in the Tortugas region during the 1999–2011 time 

period. Key management and environmental events occurring during these years were implementation of the TNER in 

2001, intense hurricanes in 2004–2005, and implementation 

of the RNA in 2007. A complementary trap survey provided 

additional information for evaluating changes in reef-fish 

population metrics between the NCZ and RNA zones during 

2008–2011.

For five principal fishery species (red and black grouper, 

mutton and yellowtail snapper, and hogfish), visual surveys 

showed an increase in the density and abundance of fish at 

and above the legal size of capture in both the TNER and 

DRTO between the baseline years 1999–2000 and 2010, postimplementation of the TNER and RNA. These increases 

in density were generally accompanied by increases in both 

the occupancy rate and the size of fishes in the exploited life 

stage. In contrast, density, occupancy rate, and sizes of these 

fishery species either remained the same or decreased in the 

TBO during the same time period. This same spatial pattern 

of change also was observed for goliath grouper, a species 

under a fishing moratorium in U.S. (Florida) waters since 

1994. Density and occupancy rates for a suite of non-target 

reef fishes showed a different spatial pattern of change during the 1999–2010 period, with fluctuations above and below 

baseline levels occurring in each management zone depending on the species.

Within DRTO, the visual survey detected some increases 

in density and occurrence for principal fishery species 

before (2006) and after (2008–2011) implementation of the 

RNA; however, these increases occurred in the NCZ and 

RNA zones with equal frequency. The focused trap study 

conducted during 2008–2011 also detected no consistent 

pattern of differences in relative abundance or size structure 

between the NCZ and RNA zones for three fishery species: 

red grouper, yellowtail snapper, and white grunt. Acoustic 

tagging studies of fish movement (Farmer and Ault 2011; 

Chapters 3 and 4, this volume) show that the principal fishery 

species move freely between the NCZ and RNA zones, both 

of which comprise a similar mix of reef habitat types (Fig. 1) 

and depths. Taken together, results from the visual and trap 

surveys and tagging studies indicate that there has been no 

dramatic displacement of fishing effort from the RNA to 

the NCZ post-implementation of the RNA. From a broader 

fishing perspective, more and larger reef fish are available for 

capture by recreational anglers in the NCZ at present (2011) 

compared to 1999 before implementation of the TNER and 

RNA.

RNA Performance Topic 1: Quantify changes in the abundance and size-structure of exploited species within the RNA relative to 

adjacent areas

Visual surveys showed an increase in the density and abundance of mutton snapper in both the TNER and DRTO between the baseline 

years 1999–2000 and 2010, post-implementation of the TNER and RNA. Photo by Douglas Morrison, NPS.
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 13

Visual surveys conducted concurrently in the Dry Tortugas and Florida Keys regions (Ault et al. 2006; Smith et al. 

2011) provide a unique perspective on the ecological role of 

DRTO in both the Tortugas region and in the larger Florida 

Keys/Dry Tortugas reef ecosystem. DRTO comprises 60% of 

the coral reef habitat in the Tortugas region, yet it harbors a 

disproportionately greater number (62–93%) of juveniles of 

principal fishery species in the region. This is likely attributed to the wider range of depths and reef habitats present 

in DRTO as compared to Tortugas Bank, as well as the presence of shallow seagrass habitats in DRTO, which are known 

nursery areas for juvenile reef fishes (Chapter 2, this volume). 

DRTO also contains a disproportionately greater number of 

adult spawners (>60% in most cases) of fishery species in the 

region, likely owing to the combination of favorable adult reef 

habitats in DRTO as well as the restrictions on fishing to recreational angling only. 

Viewed from the perspective of the southern Florida 

coral reef ecosystem, the role of DRTO with respect to reef 

fish spawning stock is even more striking. Although DRTO 

accounts for 22% of the total reef habitat area, it contains 

one-third to one-half of the adult spawners for four of the five 

principal species analyzed, and this proportion has generally 

increased from 1999 to 2010. These results, combined with 

studies of regional connectivity, oceanography, and larval 

transport (Chapters 3 and 11, this volume) strongly indicate 

that DRTO is perhaps the major source point providing production of newborn recruits to populations of principal reef 

fishery species in the Tortugas region, but also the Florida 

Keys and southeast Florida reef tract, and the West Florida 

shelf. Setting aside the RNA within DRTO as a place of refuge for juveniles and adults of principal reef fishery species 

to live, grow, and reproduce with minimal human impacts is 

thus beneficial for the future sustainability of these economically and ecologically important fishery resources in Florida, 

particularly in light of the ever-increasing human population, 

environmental changes, and accompanying increases in recreational boaters and anglers using the Florida coastal marine 

ecosystem.

Literature Cited

Ault, J.S., Bohnsack, J.A., and Meester, G.A. 1998. A retrospective (1979–1996) multispecies assessment of coral reef fish 

stocks in the Florida Keys. Fishery Bulletin 96:395–414.

Ault, J.S., Bohnsack, J.A., Smith, S.G., and Luo, J. 2005a. 

Towards sustainable multispecies fisheries in the Florida, 

USA, coral reef ecosystem. Bulletin of Marine Science

76:595–622.

Ault, J.S., Smith, S.G., and Bohnsack, J.A. 2005b. Evaluation of 

average length as an estimator of exploitation status for the 

Florida coral-reef fish community. ICES Journal of Marine 

Science 62:417–423.

Ault, J.S., Smith, S.G., Bohnsack, J.A., Luo, J., Harper, D.E., 

and McClellan, D.B. 2006. Building sustainable fisheries 

in Florida’s coral reef ecosystem: Positive signs in the Dry 

Tortugas. Bulletin of Marine Science 78:633–654.

Ault, J.S., Smith, S.G., and Tilmant, J.T. 2009. Are the coral reef 

finfish fisheries of south Florida sustainable? Proceedings 

11th International Coral Reef Symposium 11:989–993.

Farmer, N.A. and Ault, J.S. 2011. Grouper and snapper movements and habitat use in Dry Tortugas, Florida. Marine 

Ecology Progress Series 433:169–184.

Schmidt, T.W., Ault, J.S., and Bohnsack, J.A. 1999. Site characterization for the Dry Tortugas region: Fisheries and essential habitats. Florida Keys National Marine Sanctuary and 

National Park Service. NOAA Technical Memorandum 

NMFS–SEFSC–425.

Smith, S.G., Ault, J.S., Bohnsack, J.A., Harper, D.E., Luo, J., 

and McClellan, D.B. 2011. Multispecies survey design for 

assessing reef-fish stocks, spatially explicit management 

performance, and ecosystem condition. Fisheries Research 

109:25–41.
14 RNA Performance Topic 1: Quantify changes in the abundance and size-structure of exploited species within the RNA relative to 

adjacent areas

Investigators

Theodore S. Switzer, Brett Pittinger, and Sean F. Keenan

Florida Fish and Wildlife Conservation Commission, Fish and 

Wildlife Research Institute

For further information contact: Ted.Switzer@MyFWC.com

Project Description

The ecosystems of Dry Tortugas National Park (DRTO) are 

unique in terms of the variety and complexity of available 

habitat, including extensive seagrass beds in addition to a 

diverse range of coral reef habitats (Franklin et al. 2003). In an 

attempt to mitigate the effects of fishing and habitat loss in the 

park, a large (11,914 ha) Research Natural Area (RNA) was 

established in 2007, within which fishing and other potentially 

destructive activities were restricted or eliminated. Combined 

with the Tortugas North Ecological Reserve (TNER) and 

the Tortugas South Ecological Reserve (TSER), established 

outside the park in 2001 by the National Oceanic and Atmospheric Administration, the RNA brings the total protected 

area within the Tortugas region to 67,235 ha. Although all 

three areas protect a large quantity of coral reef habitat, the 

RNA is the first to offer direct protection to shallow seagrass 

beds. The nearest shallow seagrass beds to the Tortugas region 

are close to the Marquesas Keys, approximately 70 km away.

This chapter addresses the performance measure to 

quantify changes in the abundance and size-structure of 

exploited species within the RNA relative to adjacent areas 

(Performance Topic 1). Exploited fishes are generally thought 

to respond to the establishment of no-take marine reserves 

(NTMR) through increased abundances and expanded size 

structure through time, although the effects of NTMR on 

non-exploited species and juveniles of exploited species are 

RNA Performance Topic 1 

Chapter 2: Nursery function of seagrasses within the Dry Tortugas National 

Park Research Natural Area

Seagrass meadows are known to provide important nursery habitat and forage for a variety of reef species in the Dry Tortugas. 

Photo by Brett Seymour, Submerged Resources Center, NPS.
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 15

much less predictable. Species that exhibit an association with 

seagrasses during their life history should respond positively 

as the quality and quantity of seagrass habitat improves within 

the RNA (Lindholm et al. 2001; Rodwell et al. 2003). Nevertheless, these benefits may be offset to some degree through 

increased predation from exploited species that generally 

receive the greatest protection from the establishment of 

NTMR and are known to leave their coral reef habitat to forage in adjacent seagrass meadows (Robblee and Zieman 1984; 

Babcock et al. 1999). These potential ecosystem-level changes 

highlight the importance of considering both exploited and 

non-exploited species as well as critical habitat when assessing the effectiveness of NTMR, especially in terms of overall 

ecosystem function. 

Fishery-independent surveys were conducted in fall 2009, 

spring 2010, and fall 2010 (spring surveys were conducted 

during May/June, whereas fall surveys were conducted during 

August/September) using wire-mesh Antillean Z-traps. These 

surveys were designed to complement fishery-independent 

visual and trap surveys (Chapter 1, this volume) by (1) providing data on seagrass-associated fish assemblages, and (2) 

providing data on small-bodied fishes, including juveniles of 

several exploited taxa. Sampling followed a stratified-random 

survey design within the southern portion of DRTO (south of 

24° 40’ N). For each seasonal sampling event, sampling sites 

were randomly selected from identified seagrass and reef habitat strata, with effort equally partitioned between the RNA 

and adjacent Natural Cultural Zone (NCZ) including the 

Historic Adaptive Use Zone (HAU). At each sampling station, 

paired Z-traps, baited with cut Atlantic mackerel (Scomber 

scombrus), were deployed during daytime hours (beginning 1 

hr after sunrise and ending 1 hr before sunset) and allowed 

to soak for 90 min. All fishes collected were identified and 

enumerated, and as many as 40 individuals per trap were measured to the nearest mm standard length (SL) prior to release.

Results

A total of 72 seagrass and 100 reef stations were sampled 

during the three seasonal sampling events with two traps 

deployed per station (Table 1). Reef sampling stations were 

distributed throughout the sampling area and were divided 

between 46 stations within the RNA and 54 within the NCZ 

(Table 1; Fig. 1). Seagrass sampling stations were located in 

shallower, spatially distinct areas and were divided between 

37 stations within the RNA and 35 stations within the NCZ 

(Table 1; Fig. 1).

A total of 1,388 individuals representing 26 fish taxa were 

collected from 72 seagrass stations. Yellowtail snapper (Ocyurus chrysurus) (n=644), slippery dick (Halichoeres bivittatus) 

(n=472), and white grunt (Haemulon plumierii) (n=141) were 

the most abundant fishes collected over seagrass habitat. A 

total of 2,381 individuals representing 36 fish taxa were collected from 100 reef stations. Yellowtail snapper (n=1,064), 

tomtate (Haemulon aurolineatum) (n=497), slippery dick 

(n=272), and white grunt (n=235) were the most abundant 

fishes collected over reef habitat. Individuals of several managed reef fishes, including red grouper (Epinephelus morio), 

black grouper (Mycteroperca bonaci), graysby (Cephalopholis 

cruentata), and lane snapper (Lutjanus synagris) were collected at both seagrass and reef stations.

Examination of catch-per-unit-effort data (CPUE; individuals per soak-hour) indicated that differences between 

spatial zone (RNA vs. NCZ) and habitat (seagrass vs. reef) 

were minimal, although seasonal differences were evident 

(Fig. 2). CPUE was higher in fall 2009 than either spring 2010 

or fall 2010 for all zones and habitats; observed differences 

were primarily driven by the CPUE of yellowtail snapper, 

white grunt, and slippery dick.

Examination of habitat-specific length frequency plots 

indicated that, although differences in CPUE between habitats 

Habitat Strata

 Spatial Strata Fall 2009 Spring 2010 Fall 2010 Total

Seagrass

RNA 14 (28) 12 (24) 11 (22) 37 (74)

NCZ 12 (24) 10 (20) 13 (26) 35 (70)

Reef

RNA 4 (8) 19 (38) 23 (46) 46 (92)

NCZ 7 (14) 24 (48) 23 (46) 54 (108)

Table 1. Summary of total number of stations sampled with Antillean Z-traps during seasonal fishery-independent surveys of fishes 

associated with seagrass and reef habitats within the RNA and NCZ. Number in parentheses represents total number of trap sets.
16

were minimal, some size differences were evident (Fig. 3). For 

both white grunt and red grouper, smaller individuals were 

primarily found in seagrass habitat, with a potential ontogenetic shift toward reef habitat for older and larger individuals; 

individuals in the smallest size classes were mostly observed 

in seagrass habitats. No such shifts were evident for yellowtail 

snapper. Locations where all juvenile (≤200 mm SL) red grouper and black grouper were collected, including individuals 

collected during exploratory surveys, were plotted to explore 

spatial distributions (Fig. 4). Juveniles of both species were 

most frequently collected in the shallow seagrass beds of the 

RNA as well as in the seagrass beds of the HAU. In particular, 

approximately 50% of the juvenile red and black groupers 

were observed in the seagrass bed north of Loggerhead Key.

Performance Measure Evaluation

Surveys of non-exploited species and juveniles of exploited 

species have potential in assessing the ecosystem-level effects 

of the RNA because (1) increases in the abundance of juveniles of exploited species may be an early indicator of RNA 

success, and (2) declines in the abundance of non-exploited 

species may result from trophic cascades as populations 

of exploited reef fishes recover. On the basis of our results, 

we are unable to quantify changes in abundance associated 

through the establishment of the RNA. No marked differences were evident between the RNA and NCZ with respect 

to overall CPUE or the CPUE of abundant taxa. Although 

temporal differences were evident, observed declines from 

fall 2009 to spring 2010 were most likely attributable to an 

extreme cold snap in January 2010 rather than any effects of 

RNA establishment. 

Results from this study do, however, lend credence to 

the notion that seagrasses within the RNA may function as 

nursery habitat for juveniles of exploited reef fishes. For both 

white grunt and red grouper, smaller individuals were more 

often collected in association with seagrass habitat whereas 

larger individuals were most often collected near reef habitat. 

Similarly, juvenile (≤200 mm SL) red grouper and black grouper were most frequently collected in the shallow seagrass 

beds of the RNA as well as in the seagrass beds of the HAU. 

Although observed patterns indicate the potential that seagrass habitat is essential for post-settlement reef fishes, these 

results do not conclusively establish the nursery function of 

seagrass beds within DRTO. Accordingly, additional research 

is recommended to further explore this hypothesis.

Figure 2. Mean overall catch per unit effort of Antillean Z-traps 

during seasonal fishery-independent surveys of fishes associated 

with seagrass and reef habitats within the RNA and NCZ. The 

top panel represents comparisons between habitats (seagrass 

vs. reef) and zones (RNA vs. NCZ). The bottom panel represents 

comparisons for the three most abundant species.

RNA Performance Topic 1: Quantify changes in the abundance and size-structure of exploited species within the RNA relative to 

adjacent areas

Figure 1. Spatial distribution of overall sampling effort during 

seasonal fishery-independent surveys of fishes associated with 

seagrass and reef habitats within the DRTO RNA and NCZ. Each 

point represents an individual Antillean Z-trap.
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 17

Acknowledgements

We wish to thank the National Park Service personnel stationed at the Florida City office (D. Hallac and D. Morrison) 

for their invaluable assistance in helping design the study, and 

NPS personnel at Dry Tortugas National Park on Garden Key 

(D. Walton, P. Walton, T. Gottshall, and C. Douglass) for providing logistical support. Thanks to the captain and crew of 

the Yankee Freedom II for facilitating the transport of personnel and gear. Thanks to Fish and Wildlife Research Institute 

(FWRI) personnel (B. McMichael, J. Hunt, A. Acosta, and M. 

Feeley) for scientific insight, and to L. Torres for assistance 

in administering this grant. Last but not least, we acknowledge the numerous FWRI staff that put in countless hours 

collecting and processing data. Funding for this project was 

provided by the Florida Fish and Wildlife Conservation Commission’s Florida’s Wildlife Legacy Initiative and the U.S. Fish 

and Wildlife Service’s State Wildlife Grants program (project 

number 2007–0083–023).

Literature Cited

Babcock, R.C., Kelly, S., Shears, N.T., Walker, J.W., and Willis, 

T.J.. 1999. Changes in community structure in temperate 

marine reserves. Marine Ecology Progress Series 189:125–

134.

Franklin, E.C., Ault, J.S., Smith, S.G., Luo, J., Meester, G.A., 

Diaz, G.A., Chiappone, M., Swanson, D.W., Miller, S.L., 

and Bohnsack, J.A. 2003. Benthic habitat mapping in the 

Tortugas region, Florida. Marine Geodesy 26:19–34.

Lindholm, J.B., Auster, P.J., Ruth, M., and Kaufman, L. 2001. 

Modeling the effects of fishing and implications for the 

design of marine protected areas: Juvenile fish responses 

to variations in seafloor habitat. Conservation Biology

15:424–437.

Robblee, M.B. and Zieman, J.C. 1984. Diel variation in the 

fish fauna of a tropical seagrass feeding ground. Bulletin of 

Marine Science 34:335–345.

Rodwell, L.D., Barbier, E.B., Roberts, C.M., and McClanahan, 

T.R. 2003. The importance of habitat quality for marine 

reserve – fishery linkages. Canadian Journal of Fisheries 

and Aquatic Sciences 60:171–181. 

Figure 3. Size/frequency distribution of select fishes captured 

with Antillean Z-traps in seagrass and reef habitats. Values in 

parentheses represent total number of individuals collected 

in association with each habitat type. Smoothed curves were 

constructed using a two-parameter logarithmic function.

Figure 4. Locations where juvenile (≤200 mm SL) red grouper 

(Epinephelus morio) and black grouper (Mycteroperca bonaci) 

were collected with Antillean Z-traps. Graduated symbols represent the number of individuals per trap set, ranging from one 

(smallest symbol) to three (largest symbol). The black arrow 

points to the location of potential seagrass nursery habitat to 

the northeast of Loggerhead Key.
18 RNA Performance Topic 2: Monitor the immigration and emigration of targeted species in the RNA

Investigators

Michael W. Feeley1,2, Danielle Morley1, Alejandro Acosta1, 

Theodore S. Switzer1

, and Harold L. Pratt, Jr.3

1

Florida Fish and Wildlife Conservation Commission, Fish 

and Wildlife Research Institute

2

National Park Service, South Florida/Caribbean Inventory 

and Monitoring Network 

3

Mote Marine Laboratory, Tropical Research Laboratory

For further information contact: Michael_Feeley@nps.com

Project Description

With the establishment of the Dry Tortugas National Park 

(DRTO) no-take Research Natural Area (RNA), a series of 

performance measures were defined to assess the efficacy of 

the RNA in protecting marine habitat, conserving biodiversity, enhancing productivity and sustainability of exploited 

fish populations, and determining the effects of fishing on 

surrounding exploited areas. Consequently, field studies were 

undertaken to monitor the immigration and emigration of 

targeted fish species in the RNA (Performance Topic 2) and 

assess connectivity of fishes in the greater Tortugas region. An 

understanding of migration patterns and habitat requirements 

of fish species is critical to establishing an effective marine 

protected area (MPA) design (Sale et al. 2010), especially 

no-take marine reserves (NTMR). NTMRs can be effective 

in sustaining fish populations when spawning occurs within 

their boundaries or when strong connectivity exists between 

populations within NTMR boundaries and fish spawning 

aggregations (FSAs) located elsewhere.

The Tortugas region refers to 1,243 km2

 of ocean located 

approximately 112 km west of Key West and 225 km from 

mainland Florida, comprised of three carbonate banks and 

seven small islands. The carbonate banks are individually 

known as the Dry Tortugas, Tortugas Bank, and Riley’s Hump 

(RH) and collectively are considered highly productive coral 

reef habitat critical to the south Florida marine ecosystem 

(Ault et al. 2006). RH rises to 30 m depths at the intersection 

of the Gulf of Mexico and the Straits of Florida approximately 

20 km southwest of Garden Key, the location of historic Fort 

Jefferson. The established NTMRs and associated open-use 

areas of the Tortugas provide an excellent system in which to 

document habitat use, broad-scale movements of fishes, and 

connectivity across reserve boundaries. Acoustic telemetry 

methods were used to determine the temporal dynamics of 

fishes and to study spawning aggregations and demographic 

connectivity with emphasis on testing the hypothesis that 

adult reef fish emigrate from DRTO to spawn at an offshore 

FSA. 

An array of 64 underwater VEMCO (VR2) acoustic 

receivers provided partial coverage across approximately 755 

km2

 and was deployed by July 2008 in water 6–50 m deep (Fig. 

1). These receivers recorded the presence of fish tagged with 

coded transmitters as they swam within a detection range of 

up to 800 meters when conditions were ideal. A more typical 

effective range was 300 meters. From May 2008 through March 

2011, selected reef fish species were captured and acoustically 

tagged in DRTO and at RH, which is located within the Tortugas South Ecological Reserve (TSER). Fish were surgically 

implanted with VEMCO V16 coded transmitters on board 

a research platform or in situ to avoid barotrauma-induced 

mortality associated with capturing fish from relatively deep 

water (30–40 m). 

Within the context of how RNA habitat contributes to 

regional connectivity, results are presented on the annual 

spawning migratory movements of adult mutton snapper 

(Lutjanus analis) between the RNA and RH, which, according 

to Lindeman et al. (2000), protects the most valuable known 

snapper spawning habitat in south Florida. Preliminary observations suggested that the mutton snapper spawning aggregation had begun to reform on RH after years of intensive fishing 

pressure (Burton et al. 2005) (Table 1). Additionally, the movements of acoustically tagged nurse sharks (Ginglymostoma cirratum), lemon sharks (Negaprion brevirostris), and bull sharks 

(Carcharhinus leucas) are presented. Nurse sharks, a common 

resident of Florida waters and DRTO, have been recorded in 

the waters that are now within the Nurse Shark Special Protection Zone (SPZ) for reproductive activities for nearly 100 

years (Gudger 1912) (see map on inside front cover).

Results

Reef Fish

Fifty-five mutton snapper (45.7–89.7 cm) were acoustically 

tagged offshore at the RH FSA (n=28) and inshore within the 

RNA and recreational-fishing-only Natural Cultural Zone 

(NCZ) (n=27). Four of the 55 tagged mutton snapper were 

never detected on the receiver array and were removed from 

further analysis. Approximately 1.4 million mutton snapper 

tag detections were recorded by the array between May 2008 

and August 2011. Of those detections, approximately 1.3 million were in DRTO, 265 were in open fishing areas outside 

of DRTO, 45 were in the Tortugas North Ecological Reserve 

RNA Performance Topic 2 

Chapter 3: Regional connectivity of fishes within the Tortugas region of 

Florida
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 19

Date Number observed Moon phase

May 28–June 1, 1999 1 fish in 3 of the 11 dives Full moon May 301

July 31–August 3, 2000 1 fish in 5 of the 6 dives New moon July 301

July 17, 2001 10 3 days before new moon1

May 27, 2002 75–100 1 day after full moon1

June 15, 2003 75–100 1 day after full moon1

June 15, 2003 200+ 1 day after full moon1

July 4, 2004 300 2 days after full moon1

July 3, 2007 100+ 3 days after full moon2

June 12, 2009 (1415–1715 hrs) ~4,000 5 days after full moon3

Table 1. Observations of mutton snapper at Riley’s Hump.

1

Burton et al. 2005. 

2

Michael Burton, NOAA, pers. comm.

3

This study.

Figure 1. Location of VR2 receiver stations relative to bathymetry and management zones including the recreational fishing only 

Natural Cultural Zone (NCZ), no-take Research Natural Area (RNA), no-take Tortugas South Ecological Reserve (TSER), no-take Tortugas 

North Ecological Reserve (TNER), and open-use areas of the Florida Keys National Marine Sanctuary (FKNMS) and surrounding waters 

in the Tortugas study area, Florida. Mote Marine Laboratory (MML) receivers (yellow) are located in the Nurse Shark Special Protection 

Zone (SPZ).
20

(TNER), and the remaining detections were recorded at RH 

(33,460). Individual mutton snapper (n=51) were tracked an 

average (±standard deviation) of 315 (±338) days (d) with a 

range of 3–1,056 d.

Of the 51 tracked mutton snapper, we conclusively 

documented that 15 made seasonal migratory movements to 

spawning grounds on RH. These mutton snapper made migratory round trips of as many as four trips per fish per spawning 

season. Twelve of these mutton snapper were residential fish 

of the RNA or migrated through the RNA. The home ranges 

of these mutton snappers and the movement patterns of three 

selected individual fish are presented in Figure 2 to elucidate 

the migratory routes. We used the kernel density estimation 

(KDE) technique to determine “hotspots” of mutton snapper 

activity in the region. 

KDE is a method used to identify one or more areas of disproportionately heavy use (the colored regions on the map) 

within a home-range boundary. The colored regions within 

the black contour lines represent 95% of the detections of 

mutton snapper and within each contour, the probability of 

finding a fish increases as the coloration moves toward red. 

The light blue areas outside the contours represent other areas 

where detections occurred. These mutton snapper resided 

within the RNA most of the time, as indicated by the yellow to 

red areas of heavy use; and had hotspots of detections along 

the migratory route in the southern NCZ and at RH. The 

migratory routes are hand-drawn but when they pass near 

one of the stations, it means that a fish was detected at that 

station. For example, fish 2167 (69.2 cm total length, gender 

Figure 3. The daily frequency of mutton snapper transmitter 

detections from the south slope receiver in the Tortugas South 

Ecological Reserve on Riley’s Hump relative to the full moon 

phase. Circles indicate the time of the full moon.

Figure 2. Fixed kernel density estimate (KDE) and home range estimate (95% contour) for pooled 

DRTO adult mutton snapper (n=12) indicating connectivity between the Research Natural Area 

(RNA) and Riley’s Hump. All VR2 stations detecting tagged mutton snapper, the relative probability of finding a fish in a location (higher color intensity [blue to red] indicates higher probability), and migrations of three individual fish are shown.

RNA Performance Topic 2: Monitor the immigration and emigration of targeted species in the RNA
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 21

unknown; see red dashed line, Fig. 2) was initially tagged on 

May 30, 2008, within the RNA; it first moved offshore near the 

full moon on June 18, 2008, and returned to the RNA 11 days 

later. It next arrived at RH on May 6, 2009, and stayed until 

May 14 (8 days). It arrived back at the RNA on May 15, 1 day 

later. This fish then remained undetected until June 5 when it 

again began moving toward RH, arriving 2 days later. It stayed 

at RH for 6 days and returned to the RNA area 1 day later. 

This entire pattern was repeated one more time during the 

July full moon. The tag battery expired shortly thereafter and 

no more detections of this fish were possible. The other two 

mutton snapper made similar multiple spawning migrations. 

Daily transmitter detection frequency peaked at RH on the 

full moon during the spawning season (May through August) 

(Fig. 3). Mean residence time on the spawning grounds was 7 

(±3) d. The mean day of arrival relative to the full moon (+1±3 

d) varied significantly (p=0.002); however, the mean day of 

departure (+7±1 d; p=0.06) did not vary significantly over 

seven distinct spawning periods. 

Twenty-eight of the 55 tagged mutton snappers were 

initially tagged at RH. Some of these fish were among the 

residents in the RNA. However, mutton snapper tagged at 

RH also exhibited a much wider range of movement patterns. 

One RH-tagged mutton snapper traveled through the TNER 

and was ultimately detected in the northeastern area of the 

NCZ near Pulaski Shoal, a movement of 40 km in two days. 

Another mutton snapper (71.1 cm), initially tagged at RH during the June 2009 full moon, left RH shortly thereafter and 

was detected on the array in the open fishing area to the south 

of DRTO and east of RH. It returned to RH during the July 

2009 full moon and was again detected in the same area later 

that month. It was then no longer detected on the array but 

traveled eastward and was ultimately caught on December 5, 

2009, by an angler fishing near Rebecca Shoals approximately 

50 km east of RH. Finally, some of the RH-tagged fish left RH 

but were not detected within our array of acoustic receivers. 

A large mutton snapper aggregation (~4,000) and repeated 

spawning events were documented by divers on June 12, 2009, 

between 1415 and 1715 hrs, 5 d after the full moon, along the 

south slope of RH (35–50 m) (Table 1; Fig. 4). Additionally, 

groups of cubera snapper (Lutjanus cyanopterus), dog snapper (Lutjanus jocu), and permit (Trachinotus falcatus) were 

observed on the south slope of RH. Spawning coloration 

displays by blue runners (Caranx crysos), horse eye jacks 

(Caranx hippos), crevelle jacks (Caranx latus), and actively 

nesting ocean triggerfish (Canthidermis sufflamen) also were 

noted. 

Some mutton snapper demonstrated that they used certain geographic features to travel to and from the spawning 

aggregation site at RH. For example, six mutton snapper utiFigure 4. A subgroup of mutton snapper spirals upward just before a spawning event at Riley’s Hump during the fish 

spawning aggregation of July 2009. Photo by ©Christopher Parsons, Photography by Chris Parsons.
22

lized the reef edge margin south of Long Key, with the longest 

continuous reef edge movement recorded as 16.2 km. This 

movement involved passing through multiple management 

zones, including the Florida Keys National Marine Sanctuary 

(FKNMS) waters south of the RNA, through the RNA, and 

eastward of Long Key on the eastern bank of the NCZ. 

Sharks

The receiver array also recorded 190,828 acoustic tag detections from 31 nurse sharks tagged within DRTO. Additionally, 700 detections were recorded within our VR2 array for 

3 lemon sharks and 6 bull sharks tagged and released off 

Jupiter, Florida (Dr. Steven Kessel, pers. comm.). Adult male 

and female nurse sharks arrive in the Bush Key bight to mate 

during mid-June. Females typically reside for 3–4 weeks using 

the shallows within the Nurse Shark SPZ to take refuge from 

courting males (Pratt and Carrier 2001). Male nurse sharks 

visit frequently, patrolling Long and Bush Keys. Forty to 60 

pregnant females return to the same warm shallows to rest 

and gestate in September and October prior to giving birth. 

Three lemon sharks tagged off Jupiter, Florida, reached the 

Tortugas in late January to early February and all departed 

the area by the end of April. Six bull sharks tagged off Jupiter, 

Florida, also made migrations (500 km) to the Tortugas with 

detections recorded from late November to late May; two 

of these sharks were later detected by acoustic receivers 320 

km miles north in the Gulf of Mexico (Angela Collins, pers. 

comm.). Most bull sharks were only briefly detected (1 d), 

with most detections offshore, including four sharks at RH.

Performance Measure Evaluation

Our acoustic telemetry research on mutton snapper has definitively revealed the regional connectivity between the shallow 

waters of the RNA and the spawning aggregation site at RH. 

However, the RNA is not the only location from which mutton 

snapper migratory movements originate. Although some mutton snapper initially tagged at RH moved to the RNA, others 

moved to a different location within our array, and some have 

moved off RH and have gone undetected. However, we were 

able to document DRTO, especially RNA-resident, mutton 

snapper migrating multiple times over the spawning season to 

the aggregation site at RH. These results suggest that the RNA 

may be important to support the mutton snapper spawning 

aggregation at RH.

Repeated directional use of the high- and low-profile contiguous reef edge near and south of Long Key coinciding with 

the full moon, suggests that these features play an important 

role in spawning movements between the RNA and RH. The 

maximum documented distance along the Long Key route 

A courting male nurse shark (left) attempts to grasp the pectoral fin of a female on the Dry Tortugas shark mating 

grounds. The fin grasp is a necessary prelude to mating. Photo by Harold L. Pratt, Jr., Mote Marine Laboratory.

RNA Performance Topic 2: Monitor the immigration and emigration of targeted species in the RNA
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 23

was 16.2 km, after which the reef edge is less well defined 

south of the Dry Tortugas. The Long Key pathway includes 

movement across NTMR boundaries, including movements 

across RNA boundaries into the recreational fishing areas of 

the NCZ and the open-use areas of the FKNMS. Farmer and 

Ault (2011) report similar migration-related movement of a 

mutton snapper along the contiguous reef edge northwest of 

Loggerhead Key. 

The RNA provides year-round protection to a proportion 

of the population excluding the estimated time (1–2 d) it 

takes to migrate across the open-use area between NTMRs. 

Although this is a relatively short exposure, mutton snapper 

migration pathways have previously been targeted by commercial fishing leading to permanent collapse of the FSA 

(Craig 1966), emphasizing the importance of protecting both 

migration corridors and spawning sites (Graham et al. 2008). 

As knowledge of migratory pathways of the RNA residents to 

the spawning areas becomes better defined, consideration of 

appropriate management action along these corridors could 

be considered to further enhance the mutton snapper fishery. 

The migration of several shark species from as far as Jupiter, 

Florida, through the Tortugas NTMR network expands the 

connectivity of this area to both the east and west coasts of 

Florida (up to 500 km). Pratt and Carrier (2001) determined 

that DRTO is an important annual mating site for nurse sharks. 

Preliminary results show juveniles to be year-round residents 

of the RNA while adults make seasonal movements relative to 

their gender and reproductive condition. Male sharks wander 

thru the RNA and the TNER and a few have been detected 

in the middle and upper Florida Keys. Females may remain 

in the area until giving birth and then range for hundreds of 

kilometers, to return every two or three years to the Nurse 

Shark SPZ mating grounds. Future tag detections will help fill 

in gaps in our knowledge of their movements. The purpose 

of the long-range movements of bull sharks and lemon sharks 

to the Tortugas remains unknown (Dr. Steven Kessel, pers. 

comm.).

A large mutton snapper spawning aggregation at RH supports the hypothesis that this FSA has rebounded nearly 10 

years after the establishment of the TSER and provides direct 

evidence of the spawning of this species for the first time in 

Florida. The RNA, complemented by the Tortugas Ecological Reserves, provides critical protection of essential reef fish 

habitat and multispecies FSA habitat, and temporary refuge 

for transient fish species. The regional connectivity of fishes 

and protection of residential habitat within the RNA, combined with the relative increase in the number of mutton 

snapper at the RH FSA, can be linked to a suite of successful 

management actions including the establishment of the RNA. 

This research primarily focused on mutton snapper utilizing 

one known spawning site; however, other potential ecologically and economically important species also may use RH as 

an aggregation site (for example, black grouper (Mycteroperca 

bonaci)) and potentially other important regional spawning 

sites yet to be discovered. 

Acknowledgements

Dr. Steven Kessel, BBFS, Bimini, Bahamas; Dr. James Locascio, USF, St. Petersburg, Florida; Angela Collins, FWC/FWRI, 

St. Petersburg, Florida; Michael Burton, NOAA/NMFS, 

Beaufort, North Carolina; Lee Richter, NPS/SFCN, Palmetto 

Bay, Florida; and Paul Barbera and Ben Binder, FWC/FWRI, 

Marathon, Florida.

Literature Cited

Ault, J.S., Smith, S.G., Bohnsack, J.A., Luo, J., Harper, D.E., 

and McClellan, D.B. 2006. Building sustainable fisheries 

in Florida’s coral reef ecosystem: Positive signs in the Dry 

Tortugas. Bulletin of Marine Science 78:633–654.

Burton, M.L., Brennan, K.J., Munoz, R.C., and Parker, R.O., 

Jr. 2005. Preliminary evidence of increased spawning 

aggregations of mutton snapper (Lutjanus analis) at Riley’s 

Hump two years after establishment of the Tortugas South 

Ecological Reserve. Fishery Bulletin 103:404–410.

Craig, A.K. 1966. Geography of fishing in British Honduras 

and adjacent coastal waters. Louisiana State University 

Coastal Studies Laboratory, Baton Rouge, Louisiana.

Farmer, N.A. and Ault, J.S. 2011. Grouper and snapper movements and habitat use in Dry Tortugas, Florida. Marine 

Ecology Progress Series 433:169–184.

Graham, R.T., Carcamo, R., Rhodes, K.L., Roberts, C.M., and 

Requena, N. 2008. Historical and contemporary evidence 

of a mutton snapper (Lutjanus analis Cuvier, 1828) spawning aggregation fishery in decline. Coral Reefs 27:311–319.

Gudger, E.W. 1912. Summary of work done on the fishes 

of Tortugas. Carnegie Institute of Washington Yearbook

11:148–150. 

Lindeman, K.C., Pugliese, R., Waugh, G.T., and Ault, J.S. 2000. 

Development patterns within a multispecies reef fishery: 

Management applications for essential fish habitats and 

protected areas. Bulletin of Marine Science 66:929–956.

Pratt, H.L., Jr. and Carrier, J.C. 2001. A review of elasmobranch reproductive behavior with a case study on the 

nurse shark, Ginglymostoma cirratum. Environmental 

Biology of Fishes 60:157–188.

Sale P.F., Van Lavieren, H., Ablan Lagman, M.C., Atema, J., 

Butler, M., Fauvelot, C., Hogan, J.D., Jones, G.P., Lindeman, K.C., Paris, C.B., Steneck, R., and Stewart, H.L. 2010. 

Preserving Reef Connectivity: A Handbook for Marine 

Protected Area Managers. Connectivity Working Group, 

Coral Reef Targeted Research and Capacity Building for 

Management Program, United Nations University UNU–

INWEH.
24 RNA Performance Topic 2: Monitor the immigration and emigration of targeted species in the RNA

Investigators

Michael W. Feeley1,2, Danielle Morley1, Alejandro Acosta1, 

Theodore S. Switzer1

, Nicholas A. Farmer3,4, and Jerald S. Ault3

1

Florida Fish and Wildlife Conservation Commission, Fish 

and Wildlife Research Institute

2

National Park Service, South Florida/Caribbean Inventory 

and Monitoring Network 

3

University of Miami, Rosenstiel School of Marine and Atmospheric Science

4

National Oceanic and Atmospheric Administration, National 

Marine Fisheries Service, Southeast Regional Office

For further information contact: Michael_Feeley@nps.gov

Project Description

The no-take Research Natural Area (RNA) was implemented 

within Dry Tortugas National Park (DRTO) in 2007 to preserve marine biodiversity and fishery resources. The RNA is 

complemented by two no-take marine reserves (NTMRs): 

Tortugas North and South Ecological Reserves (TNER and 

TSER). Adjacent to the RNA is the Natural Cultural Zone 

(NCZ), where recreational hook-and-line fishing is permitted. 

Due to its upstream location relative to the Florida Current, 

the Tortugas region is recognized as a source of larval recruitment and is considered the most productive coral reef ecosystem in Florida (Ault et al. 2006). The Tortugas NTMRs were 

designed to provide critical refuge for the exploited phase of 

fish stocks, giving fishes the opportunity to reproduce and 

thereby stimulate regional recruitment. Additionally, NTMRs 

may contribute to increased fishery yield through direct spillover of fish moving across NTMR boundaries. In this chapter, 

we summarize information on direct spillover; Chapter 11 

summarizes information regarding regional recruitment. 

To monitor the immigration and emigration of selected 

reef fish species in the RNA (RNA Performance Topic 2), 

two VEMCO (VR2) hydroacoustic arrays were deployed in 

and around the RNA (Fig. 1). These arrays, one in the southeastern part of the RNA (managed by the Florida Fish and 

Wildlife Conservation Commission (FWC)) and one along 

the northwestern RNA boundary (managed by the University 

of Miami (UM)), were set-up in areas known to support a 

rich and diverse assemblage of exploited reef fishes. The FWC 

array of 64 receivers began operation in 2008 and currently 

encompasses approximately 755 km2

 throughout DRTO and 

surrounding waters. Thirty-one of those receivers were within 

DRTO, with 16 receivers located within the RNA. To examine 

the movement of adult fish from the RNA to fishing grounds 

(spillover), the FWC array was concentrated along high- and 

low-relief contiguous reef that traverses RNA boundaries. 

The FWC array was complemented by six receivers managed 

by Mote Marine Laboratory (MML). To address fine-scale 

movements, UM previously had deployed 25 receivers in 

two grid configurations (16 and 30 km2

) over a representative 

range of depths and complex coral reef habitats during 2006 

and 2007 (Farmer and Ault 2011).

Proximal to the acoustic arrays, selected snappers and 

groupers were captured by hook and line or fish traps for 

acoustic tagging from 2006 through 2011. After capture, the 

abdominal cavities of selected fish were surgically implanted 

with VEMCO V9 or V16 coded transmitters following aseptic 

techniques. Fish were held for a short recovery period (5–25 

min) and then released at their point of capture. Additionally, from May 2008 to May 2011, FWC conducted stratifiedrandom surveys with chevron traps and hook-and-line gear 

throughout the southern half (south of 24° 40’ N) of the NCZ 

and the RNA. As part of these surveys, individual fish were 

implanted with external dart tags prior to release. Recaptured 

individuals were then obtained through future sampling 

efforts or reported by recreational anglers. 

Based on acoustic telemetry and conventional tag returns, 

home range analysis was used to examine fish movements and 

evaluate spillover between the RNA and other areas of the 

Dry Tortugas. The results of this analysis will assist in evaluating the design and contribution of NTMRs to the sustainability of marine fisheries resources in the Tortugas.

Results

Acoustic tagging: Southeast RNA

FWC tagged 120 fish from May 2008 through July 2011 with 

approximately 2.2 million detections recorded during that 

time. Time-at-liberty (number of days between initial tagging 

and last detection) for FWC-tagged snappers and groupers 

ranged from 114 to 1,115 days (d) with a mean (± Standard 

Error (SE)) of 754 (±35) d for mutton snapper (Lutjanus analis) 

(n=51), 411 (±7) d for yellowtail snapper (Ocyurus chrysurus) 

(n=18), 452 (±47) d for black grouper (Mycteroperca bonaci) 

(n=27), 482 (±237) d for red grouper (Epinephelus morio) 

(n=4), 666 (±292) d for Nassau grouper (Epinephelus striatus) 

(n=3), and 415 (±0) d for goliath grouper (Epinephelus itajara) 

(n=2). Average home ranges for individuals observed on the 

FWC array (Table 1) were calculated using 95% kernel density 

estimates (KDE; Animal Movement Extension, ArcView 3.3; 

see results section of Chapter 3, this volume), examining only 

RNA Performance Topic 2 

Chapter 4: Spillover of select reef fish species in and near the Dry Tortugas 

National Park Research Natural Area
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 25

Figure 1. Detailed view of the study area within and near Dry Tortugas National Park showing the location of VR2 receiver stations 

relative to hard-bottom habitat and management zones (including the recreational fishing only Natural Cultural Zone (NCZ), the recreational fishing only Historic Adaptive Use Zone (HAU), and the no-take Research Natural Area (RNA)). See Figure 1 in Chapter 3 (this 

volume) for the entire study area. Fish acoustic-tagging locations are represented with each species corresponding to a different color.

Table 1. Home range estimates (± standard error) for tagged fish detected by the Florida Fish and Wildlife Conservation Commission 

(KDE analysis) and University of Miami (MCP analysis) receiver arrays.

Florida Fish and Wildlife Conservation Commission University of Miami

Species Number 

tagged

Total length 

(cm) 

KDE home 

range (km2) Species Number 

tagged

Total length 

(cm) 

MCP home 

range (km2)

Mutton 

snapper 23 46–90 30.9 ± 10.5 Mutton snapper 1 70 16.1

Yellowtail 

snapper 10 40–51 1.6 ± 0.9 Yellowtail snapper 5 48–55 4.2 ± 1.8

Black 

grouper 17 46–122 0.1 ± 0.04 Black grouper 2 57–75 1.4 ± 1.0

Red 

grouper 28 44–66 2.1 ± 0.4
26

fish that were tagged in and around the RNA with a detection 

period of 2 months or more.

Of the 23 mutton snapper FWC tagged in and around 

the RNA, 13 (57%) moved between the RNA boundary 

and other areas. The mean area of home range for these 13 

individuals was 54.2 (±16.0) km2

 with 15.0 (±4.6) km2 of that 

home range inside the RNA. For mutton snapper crossing the 

RNA boundary, 30.6 (±7.8)% of their home range was within 

the RNA. Five mutton snapper tagged within the RNA were 

never detected outside of its boundaries. Of the 10 yellowtail 

snappers tagged in and near the RNA, 4 (40%) moved across 

the RNA boundary. The mean home range for this subset of 

fish was 3.8 (±0.9) km2

 with 22.9 (±6.5)% of that home range 

encompassed within the RNA. Seven black grouper tagged in 

and near the RNA provided more than 2 months of detection 

data. Of those seven fish, three were tagged just outside of the 

RNA border but never crossed it. One individual was detected 

exclusively within the RNA. Two black grouper crossed the 

RNA boundary briefly, but with insufficient net movement to 

affect their home range estimate. The remaining black grouper 

was documented crossing the RNA boundary. The estimated 

home range for this fish was 0.42 km2

 with 36.1% of this home 

range within the RNA.

Examples of three fish that demonstrate spillover are 

presented in Figure 2. One mutton snapper moved southwest 

outside of the RNA and was detected on receivers throughout 

the region (Fig. 2A). The yellowtail snapper and black grouper 

spent a considerable amount of time (see the red portion of 

the KDE) within the Historic Adaptive Use Zone (HAU), the 

RNA, and the NCZ to the south of the RNA, demonstrating 

movement patterns across management zones (Figs. 2B and 

C).

Acoustic tagging: Northwestern RNA boundary

Between 2006 and 2008, nearly 2.5 million detections from 65 

acoustically tagged fish representing 11 species were recorded 

by the UM array. Time-at-liberty ranged from 2 to 280 d with 

a mean (± SE) of 135 (±31) d for black grouper (n=3), 92 d 

for gray snapper (Lutjanus griseus) (n=1), 86 (±58) d for mutton snapper (n=3), 111 (±2) d for red grouper (n=45), and 83 

(±9) d for yellowtail snapper (n=5). Average home range sizes 

along the northwestern RNA boundary were estimated by 

Minimum Convex Polygon (MCP; Animal Movement Extension, Arcview 3.3) analyses (Table 1, see Farmer and Ault 

(2011) for details).

Even though most of the UM receivers were within the 

RNA, some spillover was detected. In 2006, 2 of 31 (6%) red 

grouper were detected moving across the northwestern RNA 

boundary. In 2007, after reconfiguring the acoustic array to 

cover a larger area, 4 of 14 (29%) red grouper were detected 

moving across RNA boundaries into the TNER. No black 

grouper were detected moving across reserve boundaries in 

either year; however, this species was not well represented by 

the tagging study. In general, black grouper home ranges are 

relatively small (Table 1). One of 5 yellowtail snapper moved 

across the reserve boundary; this fish crossed the boundary 

62 times, but spent less than 2% of its total time in TNER. The 

1 tagged gray snapper was detected crossing the boundary 

10 times, spending 3.4% of its time in TNER. One of 2 mutton snapper was detected moving across reserve boundaries, 

but it did so 702 times, spending 9% of its time in TNER. No 

detections for this fish were recorded within the array during 

the full moons of June 1 and June 30, 2007. These observations are consistent with the behavior of tagged mutton snapper conducting spawning migrations to Riley’s Hump during 

the summer spawning season (Chapter 3, this volume).

Figure 2. Examples of kernel density estimate (KDE) home range estimates with VR2 stations and 95% volume contour of detections 

indicated for selected individual (A) mutton snapper, (B) yellowtail snapper, and (C) black grouper relative to management zones. All 

VR2 stations with a detection of the fish and the relative probabilities of detecting a fish within these areas are indicated by the color 

gradient. The higher the probability of finding a fish near a certain receiver, the closer to the red spectrum the color becomes.

RNA Performance Topic 2: Monitor the immigration and emigration of targeted species in the RNA
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 27

Conventional tagging

Conventional tagging was a third mechanism used to document spillover between the RNA and other areas. However, 

due to the relatively low level of fishing activity within the 

remote Dry Tortugas region, return rates were low and 

accordingly limited the usefulness of conventional tagging to 

evaluate spillover associated with the RNA. Although various 

species were tagged throughout the FWC chevron-trap and 

hook-and-line study, individuals of only four species were 

subsequently recaptured: yellowtail snapper, red grouper, gray 

snapper, and lane snapper (Lutjanus synagris). The majority 

of individuals were recaptured within the management area 

in which they were originally tagged. The FWC research team 

made most of these recaptures. Throughout the study, 2,202 

yellowtail snapper were tagged in the RNA, of which 6 were 

recaptured in the RNA, 1 was recaptured in the NCZ, and 1 

was recaptured more than 100 km to the east by an angler near 

Key West. For red grouper, 302 individuals were tagged in the 

RNA, with 13 recaptured in the RNA and 2 recaptured in 

the NCZ. No lane snapper or gray snapper tagged within the 

RNA were ever recaptured. Within the NCZ, 1,703 yellowtail 

snapper were tagged, of which 6 were recaptured within the 

NCZ and an additional 2 were recaptured as far as 18.5 km 

outside DRTO. For red grouper, 386 individuals were tagged 

and 23 individuals were subsequently recaptured in the NCZ. 

One hundred and fourteen lane snapper and 78 gray snapper 

were tagged within the NCZ, and 1 of each species was subsequently recaptured in the NCZ and none was recaptured in 

the RNA. For white grunt (Haemulon plumierii) (n=642), mutton snapper (n=71), and black grouper (n=23), no individuals 

tagged during this study were ever recaptured.

Performance Measure Evaluation

The results reported here provide a better understanding of 

the ecology of valuable reef fishes and the first estimates of 

snapper and grouper movements and home ranges for the 

Tortugas region. Red grouper and yellowtail moved moderate distances (700–900 m) along the northwestern boundary and conventional tag returns demonstrated red grouper 

movements (as far as 1 km) across RNA boundaries to and 

from the NCZ. Conventional tag returns and acoustic movements of yellowtail snapper along the contiguous reef south 

of Long Key, however, indicate longer-range routine movements (3–18 km), with one fish recaptured more than 100 

km east (Key West). Black grouper movements were generally spatially limited and infrequent; although one black 

grouper (TL=66.7 cm) migrated out of the HAU 1.5 yr after 

being tagged, and expanded its home range to the contiguous reef south of the RNA (Fig. 2C). Mutton snapper tended 

to have a central resident habitat and made short, frequent 

routine movements coupled with repeated long-range (≤32 

km) seasonal spawning migrations from the RNA to the 

TSER. Because of their sensitivity to outliers, MCP analyses 

generally resulted in less conservative home range estimates 

relative to KDE calculations. The relatively large mean home 

range reported for FWC-tagged mutton snapper was due to 

the greater spatial and temporal scale of the FWC array. This 

array was distributed across the RNA, NCZ, TSER, TNER, 

and FKNMS (Florida Keys National Marine Sanctuary) (see 

Fig. 1 in Chapter 3, this volume).

NTMRs can increase the abundance and size of exploited 

fish species, which can in turn increase fishery yield due to 

spillover and increased total reproductive output of protected 

fish (Watson et al. 2000; Bohnsack 2011). In the case of the 

RNA, movements across reserve boundaries for all acoustically tagged species demonstrate how the RNA can promote 

surrounding fisheries in the near-term through spillover into 

fishable areas. Additionally, the spawning migration movements of mutton snapper illustrate how the RNA can increase 

long-term fisheries yield by supporting increased spawning 

stock biomass and consequently greater larval dispersal to 

surrounding areas (Chapter 11, this volume). The direct and 

indirect applications of our results benefit fishery habitat 

management agencies, as well as commercial and recreational 

anglers. Our findings suggest that movements across the RNA 

boundary to areas where fishing is permitted occurred consistently. The combination of the protection offered by the 

RNA and consistent spillover will provide continuous fishing opportunities in nearby open fishing areas and may likely 

increase fishing yield in the Tortugas region through time.

Acknowledgements

Paul Barbera and Ben Binder, FWC/FWRI, Marathon Florida, 

and Lee Richter, NPS/SFCN, Palmetto Bay, Florida.

Literature Cited

Ault J.S., Smith, S.G., Bohnsack, J.A., Luo, J., Harper, D.E., 

and McClellan, D.B. 2006. Building sustainable fisheries 

in Florida’s coral reef ecosystem: Positive signs in the Dry 

Tortugas. Bulletin of Marine Science 78(3):633–654.

Bohnsack, J.A. 2011. Impacts of Florida coastal protected 

areas on recreational world records for spotted seatrout, 

red drum, black drum, and common snook. Bulletin of 

Marine Science 87(4):939–970. 

Farmer, N.A. and Ault, J.S. 2011. Grouper and snapper movements and habitat use in Dry Tortugas, Florida. Marine 

Ecology Progress Series 433: 169–184.

Watson R., Alder, J., and Walters, C. 2000. A dynamic massbalance model for marine protected areas. Fish and Fisheries 1(1):94–98.
28

Investigators

Kristen M. Hart1, Ikuko Fujisaki2, and Autumn R. Sartain1,3

1

U.S. Geological Survey, Southeast Ecological Center

2

University of Florida, Ft. Lauderdale Research and Education Center

3

Jacobs Technology

For further information contact: Kristen_Hart@usgs.gov

Project Description

Dry Tortugas National Park (DRTO) harbors several key benthic habitats that are important for marine turtles. Threatened 

loggerhead turtles (Caretta caretta) forage in hard-bottom 

areas on spiny lobsters and crabs; endangered hawksbill 

turtles (Eretmochelys imbricata) forage on reefs and consume 

sponges; and endangered green turtles (Chelonia mydas) 

graze on seagrasses and marine algae. The sandy beaches of 

DRTO provide suitable nesting habitat for all three species. 

The majority of nesting activity at DRTO consists of nest 

construction on East and Loggerhead Keys by loggerhead 

and green turtles. In order to monitor the immigration and 

emigration of targeted species in the Research Natural Area 

(RNA), we characterized the populations of the three sea 

turtle species in DRTO and quantified the proportion of time 

individuals spent in the RNA as compared to other areas of 

the park. We examined turtle data with respect to the RNA 

and DRTO boundaries.

We initiated our on-going turtle tagging and tracking project in 2008. To distribute capture effort within park boundaries, we captured nesting turtles on East and Loggerhead Keys, 

and captured turtles in the waters near Bush and Garden 

Keys, Northkey Harbor, and Pulaski Shoal. Our total area 

patrolled to catch turtles has expanded over time as determined by suitable turtle capture conditions, with more area 

being incorporated outside the RNA than inside the RNA. In 

addition to capture efforts, we recorded sightings of turtles as 

we patrolled the park by boat and marked the locations with 

a Global Positioning System (GPS) receiver. Sightings could 

include one or more turtles at a single location.

RNA Performance Topic 2: Monitor the immigration and emigration of targeted species in the RNA

RNA Performance Topic 2 

Chapter 5: Use of Dry Tortugas National Park by threatened and endangered 

marine turtles

USGS researcher K. Hart lifts a subadult hawksbill (Eretmochelys imbricata) captured by hand in the Dry Tortugas. The 

activity depicted was conducted pursuant to National Marine Fisheries Service Permit No. 13307–02. Photo by Kaare 

Iverson, USGS volunteer.
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 29

Turtles were captured by intercepting reproductive 

females on nesting beaches and catching turtles in the water 

with rodeo (diving from boat to snorkel-capture turtles), 

hand-capture, and dip-netting methods. We individually 

marked each turtle with internal passive integrated transponder (PIT) tags and external flipper tags. We took standard 

length, width, and mass measurements and obtained blood 

and tissue samples for genetic, isotopic, and dietary analyses. 

We attached acoustic and/or satellite-telemetry tags to a subset of turtles. 

Seven acoustic receivers were placed by the U.S. Geological Survey (USGS) in the northeastern region of the park; all 

but one of these were placed outside the RNA. These locations were chosen based on spatial gaps in the network of 

receivers deployed by the Florida Fish and Wildlife Conservation Commission (FWC) and Mote Marine Laboratory 

(MML) (see Chapter 4, this volume).We received data from 

the FWC/MML receiver array, which included more than 80 

receivers spread throughout the park in all management areas 

and outside the park to the southwest.

Using satellite and acoustic telemetry techniques, we 

determined daily locations and movement patterns for tagged 

turtles, calculated home ranges and core-use areas, and statistically summarized the extent of overlap of these areas 

with that of the RNA. We used the kernel density estimation 

technique (KDE) (Worton 1989; White and Garrott 1990) to 

determine “hotspots” of turtle activity in the park. KDE is a 

method used to identify one or more areas of disproportionately heavy use (core-use areas) within a home-range boundary, with appropriate weighting of outlying observations. We 

also compared the number of turtle-days within and outside 

the RNA using only days the turtles spent inside the park 

(DRTO turtle-days). We combined these data sets to determine residence times inside the park and locations of coreuse areas for all three species.

It is essential to understand the locations, movements, 

estimated population size, preferred habitats, and status (for 

example nesting, foraging, number of juveniles and adults, 

etc.) of marine turtles within DRTO to effectively manage 

activities that affect these imperiled species. Our capture and 

tagging results summarized here can inform decision-makers 

by providing key information on these population characteristics. Our spatial habitat-use information provides details on 

locations and areas within and outside the park that turtles 

select, regardless of capture site.

Results

Captures and Sightings

We captured and marked 145 individual marine turtles in 

DRTO, including 98 green turtles (67.6%), 41 loggerheads 

(28.3%), and 6 hawksbills (4.1%) (Fig. 1). Green turtles ranged 

in size from 22.7 to 109.0 cm straight carapace length (SCL), 

Figure 1. Size distribution of sea turtles captured (N=145) and sampled in DRTO, May 2008–October 2011.

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

0-10

11-2021-3031-4041-5051-6061-7071-8081-90

91-100

101-110

111-120

# Sea Turtles

Straight Carapace Length (SCL, tip), in cm

Hawskbill

Loggerhead

Green
30

loggerheads ranged in size from 62.5 to 111.6 cm SCL, and 

hawksbills ranged in size from 16.5 to 69.8 cm SCL (Fig. 1). We 

captured 41 turtles on nesting beaches (28.3%) and 104 turtles 

in the water (71.7%) (Fig. 2A). Due to successful recapture of 

turtles, we had 221 unique capture events between May 2008 

and October 2011, with 57.5% in the Historic Adaptive Use 

Zone (HAU), 34.8% in the Natural Cultural Zone (NCZ), and 

7.7% in the RNA.

We have logged 595 sightings, totaling 674 individual 

turtles in the water within the park (Fig. 2B); a sighting 

can include multiple turtles at a given point. We may have 

observed the same individual turtle multiple times. Most 

sightings were green turtles (81.7%), with fewer sightings of 

loggerheads (4.5%) and even fewer sightings of hawksbills 

(1.8%); a portion (11.9%) could not be identified to species, 

and were coded as “unknown” species. Of these 595 sightings, 529 were in the NCZ, 40 were in the HAU, and 26 were 

in the RNA.

Acoustic Tagging and Tracking

We outfitted 69 individual turtles with 70 acoustic tags (Vemco 

V16–4Ls); 1 juvenile green turtle was re-tagged upon recapture. Thirty-five (50.0%) of these 70 tags have been placed 

on green turtles, 32 (45.7%) on loggerheads, and 3 (4.3%) on 

hawksbills. We placed acoustic tags on juveniles, subadults, 

and adult male and female turtles.

On our 7 USGS receivers (Vemco VR2Ws), we logged 207 

unique animal/receiver combinations (the combined number 

of detections at each receiver from unique individuals) (Fig. 

3). Of these, 89 (43.0%) were unique turtle/receiver combinations, 105 (50.7%) were unique shark/receiver combinations, 

and 2 (1.0%) were unique fish/receiver combinations; an 

additional 11 (5.3%) were unique unknown species/receiver 

combinations. The total number of detections across all 7 

USGS receivers was 28,065 (Fig. 3). Of these, 24,195 (86.2%) 

were turtles, 3,824 (13.6%) were sharks, and 3 (<0.1%) were 

fish; an additional 43 (0.2%) detections were unknown. Of 

the 24,195 turtle detections, 3,714 (15.4%) were detections 

of green turtles and 20,481 (84.6%) were detections of loggerheads.

Cooperative data sharing among the USGS, FWC, and 

MML has occurred since the acoustic tracking project began 

in 2008. On the FWC receivers, there have been 14,475 detections of 51 acoustically tagged turtles (N=22 green turtles; 

N=28 loggerheads; N=2 hawksbills). Individual turtles were 

detected on an average of 4 different FWC receivers, and on as 

many as 17 different FWC receivers. There were an additional 

65,535 detections of 6 acoustically tagged turtles (N=3 green 

turtles; N=1 loggerhead; N=2 hawksbills) on 10 MML receivers. All of these were inside the HAU and five of six individuals had been detected on FWC receivers. Individual turtles 

were detected on an average of six and on as many as eight 

different MML receivers.

Overall, the total number of turtle detections in DRTO 

was 108,075. Across all areas of DRTO, we have 119 unique 

turtle/receiver combinations in the NCZ, 67 in the RNA, and 

58 in the HAU, indicating that turtles are being detected by 

receivers throughout the park. At least one loggerhead female 

that we tagged on Loggerhead Key has been detected by a 

receiver in another array near Tampa, Florida. 

RNA Performance Topic 2: Monitor the immigration and emigration of targeted species in the RNA

Figure 2. Location of all marine turtle captures (N=221) and sightings (N=595) in DRTO, October 2007–October 2011. Panel A: location of 

all turtle captures by species; panel B: location of turtle sightings by species (N=674 individuals).

Panel A Panel B
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 31

Satellite Tagging and Tracking

We satellite-tagged 51 marine turtles (N=34 nesting turtles, 

N=17 turtles captured in the water). These included 22 green 

turtles, 26 loggerheads, and 3 hawksbills. Of these 51 tagged 

turtles, 44 (86%) were females, and 7 (14%) were males. All 

individuals were either adults (N=44/51 or 86%) or subadults 

(N=7/51 or 14%); all subadults were females (N=4 green turtles; N=3 loggerheads). As of November 15, 2011, we documented a total of 11,414 turtle tracking days for the DRTO sea 

turtle project (http://www.seaturtle.org/tracking/?project_

id=402), with a range of 41 to 884 tracking days per individual. 

We determined “hotspots” of turtle activity using the 

KDE technique; locations of core-use areas (the 50% KDE) 

revealed that turtles used habitat both inside and outside the 

RNA, in the NCZ, and in the HAU (Figs. 4A, B, and C). Size of 

core-use areas differed by species and ranged from a minimum 

of 7.3 km2

 for green turtle males and subadults (Fig. 4B) to a 

maximum of 32.5 km2

 for loggerhead subadults (Fig. 4A). The 

size of core-use areas for green turtle nesters (20.0 km2

; Fig. 

4B) was remarkably similar to that of loggerhead nesters (20.1 

km2

; Fig. 4A). Finally, the size of the core-use area for hawksbills was 10.5 km2

 (Fig. 4C). All turtle species spent a mean 

28.2% (standard deviation (SD) 26.0) of their time within the 

RNA while in DRTO. Loggerheads spent the most time in the 

RNA (mean 32.2%, SD 29.6), hawksbills spent slightly less 

time in the RNA (mean 30.9%, SD 1.9), and greens spent even 

less time in the RNA (mean 24.0%, SD 23.7). 

Chi-square test results comparing number of DRTO 

turtle-days within and outside of the RNA revealed that only 

2 of 22 (9.0%) of the satellite-tagged green turtles spent a 

significant proportion of their time within the RNA while in 

DRTO. Sixteen of 22 (72.7%) spent a significant proportion 

of their time (p<0.05) outside the RNA. The remaining four 

green turtles (18.2%) spent approximately equal proportions 

of their time in both sections of the park. Only 1 of 26 (3.8%) 

loggerheads spent a significant proportion of its time in the 

RNA. In contrast, 15 of 26 (57.7%) loggerheads spent a significant proportion of their time outside the RNA and 10 of 26 

(38.5%) loggerheads extensively utilized the RNA and NCZ. 

Hawksbill turtles show a strong preference for the HAU.

Figure 3. Summary of acoustic detections at each of the seven USGS receivers. Pie charts represent the proportion of the total detections 

by taxa (number reported to the left of receivers) and the proportion of total individuals detected by taxa (number reported to the right 

of receivers) detected by each receiver, with overall totals per receiver below the pie charts.
32 RNA Performance Topic 2: Monitor the immigration and emigration of targeted species in the RNA

Figure 4. Core-use areas for satellite-tagged marine turtles tagged in Dry Tortugas National Park, May 2008–August 2011. Panel A: 

Core-use areas for two groups of loggerheads (N=26); Panel B: Core-use areas for two groups of green turtles (N=22); Panel C: Core-use 

areas for hawksbills (N=3). We grouped daily mean locations for each group of turtles (green turtle males and subadults; green turtle 

nesters, loggerhead subadults, loggerhead nesters, and hawksbills) for analysis using the kernel density estimation (KDE) technique. 

The hcv values (the bandwidth, in km, calculated using fixed-kernel least-squares cross validation) were as follows: green turtle males 

and subadults = 0.258; green turtle nesters = 0.364, hawksbills = 0.398; loggerhead nesters = 0.220, and loggerhead subadults = 0.804.

Panel B

Panel C

Panel A
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 33

Performance Measure Evaluation

The RNA represented a small proportion of the area utilized 

by the turtles in this study; this was demonstrated through 

both our acoustic and satellite-tracking results. The majority of our captures and sightings occurred outside the RNA 

(Fig. 2), primarily because of chosen locations of capture and 

tagging efforts. Capture efforts were not concentrated within 

the RNA, except on the Loggerhead Key nesting beach. Consequently, we are not yet able to definitively assess the suitability of the RNA for marine turtles; however, we highlight 

important turtle-use areas within the boundary of DRTO that 

are not designated as restricted-use areas. Results indicate 

that turtles captured outside the RNA rarely ventured into 

that area, and that, at least for most tagged turtles, the RNA is 

likely not preferred habitat. 

Acoustic and satellite telemetry allowed us to track turtles 

to assess their preferred foraging and nesting areas; we documented turtle movements away from capture locations and 

for long periods of time (as long as ~2.4 years). Across all areas 

of DRTO, we have 119 unique turtle/receiver combinations 

in the NCZ, 67 in the RNA, and 58 in the HAU, indicating 

that turtles are being detected by receivers throughout the 

park. Only 27% of acoustic detections for all tagged turtles 

have occurred inside the RNA, demonstrating that the majority of our tagged turtles are not spending time in the RNA. 

Satellite-telemetry results support these acoustic results, as 

the majority of our satellite-tagged turtles’ core-use areas also 

were outside the RNA. Further, the main core-use areas that 

were inside the RNA were in close proximity to Loggerhead 

Key, indicating that the primary useful habitat within the RNA 

is restricted to the area immediately around this nesting area. 

Across multiple tracking years, we have observed consistency in core-use areas (Hart et al. 2010), suggesting that the 

RNA will likely not become preferred core-use area for these 

tagged turtles in the future. However, additional tracking of 

DRTO turtles captured on nesting beaches and in the water 

will illuminate the longer-term spatial habitat-use patterns of 

DRTO marine turtles and will continue to provide insight into 

the effectiveness of the RNA for protecting threatened and 

endangered marine turtles and their requisite habitats. This 

will contribute toward the development of more effective 

decision-support tools to adaptively manage protected areas.

Acknowledgements

We thank B. Ackourey, J. Beauchamp, G. Blakemore, N. Blinick, A. Brame, J. Chelko, M. Cherkiss, R. Crespo , A. Crowder, 

M. Denton, C. Douglass, J. Douglass, T. Gottshall, K. Iverson, 

B. Jeffery , C. Kellogg, I. Kuffner, E. Larrivee, K. Ludwig, K. 

Nimmo, B. Reynolds, T. Selby, J. Spade, P. Thompson, W. 

Wright, D. Zawada, and T. Ziegler for assistance with field 

work and project logistics. We acknowledge the use of the 

Satellite Tracking and Analysis Tool (STAT; Coyne and Godley 2005) for organizing and filtering Argos location data. We 

thank K. Iverson of Kaare Iverson Photography.

Literature Cited

Coyne, M.S. and Godley, B.J. 2005. Satellite Tracking and 

Analysis Tool (STAT): An integrated system for archiving, 

analyzing and mapping animal tracking data. Marine Ecology Progress Series 301:1–7.

Hart, K.M., Zawada, D.G., Fujisaki, I., and Lidz, B.H. 2010. 

Inter-nesting habitat-use patterns of loggerhead sea turtles: Enhancing satellite tracking with benthic mapping. 

Aquatic Biology 11:77–90. 

White, G.C. and Garrott, R.A. 1990. Analysis of wildlife radiotracking data. Academic Press, New York, New York. 

Worton, B.J. 1989. Kernel methods for estimating the utilization distribution in home-range studies. Ecology 70:164–

168.

USGS researchers and volunteers waiting for epoxy to dry on 

a satellite- and acoustic-tagged loggerhead (Caretta caretta) 

female, Loggerhead Key, Dry Tortugas National Park. All marine 

turtle images taken in Florida were obtained with the approval 

of the U.S. Fish and Wildlife Service and the Florida Fish and 

Wildlife Conservation Commission (FWC MTP #11–176) under 

conditions not harmful to this or other turtles. Photo by Kaare 

Iverson, USGS volunteer.
34

Investigators

Tracy A. Ziegler1, Jerald S. Ault2, and Steven G. Smith2

1

National Park Service, Everglades and Dry Tortugas National 

Park

2

University of Miami, Rosenstiel School of Marine and Atmospheric Science

For further information contact: Tracy_Ziegler@nps.gov

Project Description

The Research Natural Area (RNA) at Dry Tortugas National 

Park (DRTO) was established in 2007 and serves as a no-take 

marine reserve (NTMR) that complements the Florida Keys 

National Marine Sanctuary ecological reserves. One outcome 

of protecting marine resources in these collective reserves 

may be to enhance fisheries in proximate areas, such as the 

adjacent Natural Cultural Zone (NCZ) of DRTO, which is 

open to recreational fishing. Fish tagging studies associated 

with the RNA have demonstrated that spillover of fish across 

the RNA boundary is occurring (Chapters 3 and 4, this volume). The system by which recreational anglers in DRTO 

are directly surveyed is being redesigned to provide a better 

estimate of potential fishery effects of the RNA and associated 

NTMRs in the region (Performance Topic 3).

To support monitoring of changes in species composition 

and catch rates of exploited species throughout the Tortugas 

region, National Park Service (NPS) staff members have been 

working with University of Miami (UM) fisheries scientists to 

develop an improved creel census for DRTO (Ault et al. 2011). 

Creel surveys estimate angler effort and harvest in areas within 

the park that are open to fishing. Once implemented, the data 

collected through the creel survey will be used to calculate 

reef fish catch per unit effort (CPUE), a fishery-dependent 

measure of fish abundance. We will be able to compare these 

data to the fishery-independent data from the reef visual census (Chapter 1, this volume) as they relate to the RNA. 

NPS staff will interview anglers that are fishing on Garden 

Key and anglers on anchored boats within the Garden Key 

anchorage. A typical survey will ask basic questions regarding 

how long the anglers were fishing, what species of fish were 

caught, and how many were kept or released. Additionally, 

fish length measurements will be taken by the survey clerk. 

Interviewees will be shown a map of the park and asked to 

identify by region where their fishing activity occurred. UM 

scientists have developed a new spatial map of fishing zones 

to incorporate the no-take RNA (Fig. 1). The new map divides 

DRTO into four fishing areas that are comparable to the fisheries independent surveys (Chapter 1, this volume).

RNA Performance Topic 3: Monitor changes in species composition and catch rates of exploited species throughout the surrounding 

region

RNA Performance Topic 3 

Chapter 6: Status of the development and implementation of a creel survey 

and vessel permit system at Dry Tortugas National Park

Commercial fishing vessels anchored in the harbor near Garden Key, Dry Tortugas National Park. NPS photo by Joy Brunk.
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 35

Creel survey data will be used to calculate CPUE for 

exploited fisheries species. An estimate of CPUE can help 

provide an estimate of species abundance during a given time 

period, whereas the estimate of exploited phase species length 

can provide a measure of fishing intensity. For example, DRTO 

staff collected creel surveys during 1981–1984 and 2000–2004. 

This historical data set was used to calculate CPUE for species 

of interest, as well as the average length in the exploited phase 

of fish species of interest. However, DRTO managers are 

missing information that is critical to understanding the status of the fishery. The park needs to obtain estimates of total 

effort (total number of hours fished) and total species catch in 

DRTO waters that are open to fishing. This new survey design 

will help gather that missing information. 

In order to estimate total fishing effort, we need to know 

how many vessels are engaged in fishing within the park. To 

address this issue, DRTO implemented a vessel permit system in 2011. This permit system will provide managers with 

consistent information about public use in the park including 

the number of vessels that are engaged in fishing. Anglers will 

soon be required to provide fishing activity and catch data as 

a component of this permit system. Once the creel survey is 

fully implemented within the park, the statistics from the vessel permit system will contribute to fishery dependent surveys. 

Another purpose of the DRTO vessel permit system is to 

protect resources, minimize human impacts, monitor visitor 

use, and increase awareness of the RNA. The permit system 

achieves this goal by providing reliable information to the 

public about the delicate resources within the park, the significance of the RNA, and appropriate regulations for RNA 

visitation. The permit system also enhances safe boating practices through a greater level of staff and visitor interaction. 

This, in turn, is expected to lead to a reduction in the number 

of violations and incidents within the park.

Law enforcement rangers are implementing the vessel permit system at DRTO. When visitors come to the park 

aboard a vessel, a ranger contacts the vessel via VHF radio, 

requesting that the visitors come to Garden Key to obtain a 

permit. The permit application identifies park users and the 

Figure 1. Map of the proposed new spatial fishing zones for the creel survey. (Bathymetry: lighter areas are shallower, darker 

areas are deeper.)

Zone E:

RNA

Zone B:

Northeast

Lagoon

Zone C:

Northeast

Outer Reef

Zone A:

Anchorage

Zone D:

Southwest
36

activities they intend to participate in during their visit. Every 

permit holder is given a packet of park brochures that specify 

park regulations and includes a map of the park and the RNA. 

The ranger explains the pertinent rules and regulations to the 

visitor during this contact. Permits apply to all recreational 

vessels, commercial vessels, and vessels operating under a 

Commercial Use Authorization. DRTO staff compiles all the 

information from permits into a database. Activity categories 

include fishing, snorkeling, SCUBA diving, camping, kayaking, visiting Loggerhead and Bush Keys, and mooring ball use 

within the RNA.

Results

DRTO staff issued a total of 3,082 boat permits in 2011. Of 

these, 2,479 were recreational vessel boat permits. Recreational sailboats were the most popular vessel to visit the park, 

followed by recreational motor vessels (Fig. 2). Permits were 

issued to kayaks independently of motor and sailing vessels. 

Staff also collected boat permits from 603 commercial and 

law enforcement vessels. Most visitors arriving by recreational 

vessel came to the park for sightseeing (Fig. 3). Fishing, snorkeling, and visiting Loggerhead Key were the next three most 

common visitor activities.

Performance Measure Evaluation

The creel survey for DRTO is still a work in progress. DRTO 

recently hired a fisheries biologist to assist with the implementation of the creel survey at the park. The new survey 

design developed by UM includes recommendations for a 

2-year study to optimize the creel survey specifically for the 

Tortugas region. This study will be the first step in helping to 

estimate total fishing effort in the park and, when combined 

with interview sampling, will allow park staff to estimate total 

catch for exploited fish species. These statistics are necessary 

to evaluate the performance measure of monitoring changes 

in species composition and catch rates of exploited species in 

the Tortugas region. 

Several recreational and commercial fisheries dependent 

monitoring programs exist for the Tortugas region. For example, the National Marine Fisheries Service (NMFS) has been 

collecting fishing activity from chartered “head boats” since 

1981 using a logbook system. These existing data sets could be 

used to evaluate the effects of RNA implementation on fisheries outside of DTRO. 

The DRTO vessel permit system is in its introductory 

phase of operation. The vessel permit system allows NPS staff 

to maintain statistics of visitor use. The information gathered from the vessel permit system will also allow managers 

to determine the carrying capacity of recreational dive and 

snorkel sites, including mooring ball use. DRTO staff members are currently working on an electronic version of the 

permit application that will be added to the DRTO website. 

Eventually, anglers in the park will be required to declare their 

intended fishing activity in order to obtain a permit. Anglers 

will then be required to return a completed angler survey 

to DRTO staff on Garden Key in person, by U.S. mail, or by 

internet. These survey data will then be used to calculate 

CPUE and record the size of reef fish. This survey method will 

be used in concert with the in-person creel interview surveys 

to help assess the effects of RNA implementation on recreational fishing areas surrounding the RNA.

Literature Cited

Ault, J.S., Smith, S.G., Zurcher, N., McClellan, D.B., Bohnsack, 

J.A., Luo, J., and Vaughan, N. 2011. Assessment of coral 

reef multispecies fishery resources and RNA performance 

in Dry Tortugas National Park, 1999–2010. National Park 

Service Final Report.

Recreational sailboats were the most popular vessel to visit the 

park, followed by recreational motor vessels. NPS photo.

RNA Performance Topic 3: Monitor changes in species composition and catch rates of exploited species throughout the surrounding 

region
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 37

0

50

100

150

200

250

300

350

400

450

500

Number of Visitors

Visitor Activity

Figure 3. Visitor activity from recreational vessel permits at DRTO in 2011. GK, Garden Key; LK, Loggerhead Key.

0

200

400

600

800

1000

1200

Commercial Recreational 

Motor

Recreational 

Kayak

Recreational 

Sailing

Law 

Enforcement

Other

Number of Vessels

Vessel Type

Figure 2. Number of vessels by type from permits at DRTO in 2011.
38

Investigators

Rob Ruzicka, Kate Lunz, Michael Colella, Vanessa Brinkhuis, 

Jim Kidney, Jennifer Morrison, and Kevin Macaulay

Florida Fish and Wildlife Conservation Commission, Fish 

and Wildlife Research Institute

For further information contact: rob.ruzicka@myfwc.com 

Project Description

Implementation of the Dry Tortugas National Park (DRTO) 

Research Natural Area (RNA) prohibited boat anchoring 

within RNA boundaries and established designated dive sites 

with mooring buoys for diving and snorkeling activities within 

the RNA. This is a potential concern for DRTO because concentrating diving activities at sites with mooring buoys can 

have adverse effects on coral reef communities. Multiple studies from around the world have found that intensive SCUBA 

diving activity can negatively impact coral reefs (Tratalos 

and Austin 2001; Zakai and Chadwick-Furman 2002). Recreational divers can unintentionally harm corals by kicking, 

abrading, or dusting them with sediment and this has led some 

coral reef managers to institute diver “carrying capacities” so 

that the incidence of diver-induced damage can be minimized 

(Luna et al. 2009). 

An RNA resource stewardship goal is to have no long-term 

effects of diving activities on corals (Performance Topic 4). 

The primary performance measures are damage to and loss 

of stony corals, including the federally listed Acroporid species. Secondary performance measures focus on damage to 

and loss of sponges, branching soft corals, and other benthic 

taxa (such as zoanthids). A fully replicated Before-After-Reference-Impact sampling design was established to compare 

changes in coral communities at RNA dive sites and equivalent 

reference sites with no or little diving activity. In 2009, permanent monitoring stations were installed at Texas Rock, Davis 

Rock, and The Maze (Fig. 1), all pinnacle reefs and RNA dive 

sites. Two pinnacle reefs, Mayer’s Peak and Temptation Rock, 

were selected as the reference sites. To monitor specifically for 

damage to Acropora cervicornis, another RNA dive site (OffRamp) and a reference site (Perfection) were selected at two 

shallow reefs where A. cervicornis is common. The location 

of all RNA dive sites with mooring buoys and those used for 

reference sites is shown in Figure 1. This project is part of a 

long-term benthic monitoring and assessment program conducted by the Coral Reef Evaluation and Monitoring Project 

RNA Performance Topic 4

Chapter 7: Assessing the effects of diving activities on coral communities at 

designated dive sites within the Dry Tortugas National Park 

Research Natural Area

RNA Performance Topic 4: Evaluate the effects of RNA implementation on the marine benthic biological communities

Figure 1. Location of RNA dive sites and equivalent reference sites.
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 39

(CREMP) via cooperative agreement between the Florida 

Fish and Wildlife Conservation Commission and the National 

Park Service.

It is often challenging to differentiate accurately between 

coral damage inflicted by divers as opposed to damage caused 

by other stressors (such as storms). As a result, a combined 

approach, using short-term measures of stress (such as 

bleaching and damage) and longer-term measures of population density and benthic cover, was used to assess benthic 

community change at the pinnacle reef RNA dive sites and 

reference sites. If impacts by divers were greater at the RNA 

dive sites than at the reference sites, it would be anticipated 

that the frequency of stress would be higher at the RNA dive 

sites and lead to larger declines in density and benthic cover.

Four stations were surveyed at each site. Benthic cover of 

stony corals, octocorals, sponges, and zoanthids was determined from image analysis acquired through video or still 

camera transects (Ruzicka et al. 2010). At each station, three 

22-m x 40-cm fixed location transects were filmed annually. 

Images were analyzed using a custom software package, Point 

Count ’99, and between 200 and 250 abutting images were 

overlaid with 15 random points per image, resulting in about 

3,000 points counted for each station. Coral density was estimated by recording all stony corals ≥4 cm in diameter or height 

at each 22-m x 2-m survey station by divers. To quantify coral 

stress, 10-m x 1-m belt-transects were conducted at each station. The maximum width; the presence of disease, bleaching, 

and damage; and the percentage of estimated tissue mortality 

were recorded for each stony coral colony ≥4 cm in diameter. 

An entirely different methodology was used at Off-Ramp and 

Perfection because the surveys were specifically designed to 

study the highly dynamic coral, A. cervicornis. Radial plots, 

7 m in diameter, were established in lieu of traditional 22-m 

x 2-m sampling stations used by CREMP. Within each radial 

plot, all A. cervicornis colonies were mapped and a subset 

tracked for estimates of disease and damage.

Results for benthic cover and stony coral density are 

reported here and were calculated by averaging the station 

values for the three RNA dive sites (N=12) and two reference 

sites (N=8). Baseline estimates of coral stress and damage 

were completed in 2009 and included in the DRTO RNA 

3-year report (Hallac and Hunt 2010). The radial plots to 

assess the condition of A. cervicornis were first established in 

2011. The radial plots will be surveyed a minimum of three 

times annually.

Results

Benthic cover data were collected in 2009 and 2010 and stony 

coral density data were collected in 2010 at the pinnacle reef 

RNA dive sites and reference sites. There were no significant 

differences in the cover of stony corals, octocorals, sponges, 

or zoanthids between years at the RNA dive sites or reference 

Figure 2. Percent cover (±SE) cover of stony corals, octocorals, sponges, and zoanthids at three RNA dive 

sites (Davis Rock, Texas Rock, The Maze) and two reference sites (Mayer’s Peak and Temptation Rock). No 

significant differences in benthic cover were detected for any taxonomic group between years. N=12 for 

RNA dive sites and N=8 for two reference sites.
40

sites (Fig. 2). The RNA dive sites had higher stony coral and 

sponge cover than the reference sites (Fig. 2). Octocoral and 

zoanthid cover was greater at the reference sites than at the 

RNA dive sites (Fig. 2). Overall stony coral density (number of 

corals per m2

) was higher at the RNA dive sites in comparison 

to the reference sites (Table 1). The density of foliose/plating, 

massive/encrusting, and solitary corals was higher for each 

category at the RNA dive sites than at reference sites (Table 

1). Only the density of branching coral species was greater at 

the reference sites compared to the RNA dive sites (Table 1).

Although the installation of mooring buoys was anticipated 

to occur in 2010, installation was not complete until 2011. As 

a result, the first assessment of diver impacts at the RNA dive 

sites has not yet occurred. However, the results from the 2009 

and 2010 surveys provide excellent baseline information on 

benthic community structure prior to any impacts associated 

with diving activities. Additionally, the delay in mooring buoy 

RNA Performance Topic 4: Evaluate the effects of RNA implementation on the marine benthic biological communities

RNA Dive Sites Reference Sites

Branching 0.179 ± 0.036 0.342 ± 0.080

Acropora cervicornis 0.002 ± 0.002 0.026 ± 0.017

Oculina diffusa 0.012 ± 0.006 0.031 ± 0.021

Eusimilia fastigiata 0.037 ± 0.011 0.016 ± 0.006

Mussa angulosa 0.012 ± 0.005 0.006 ± 0.004

Porites porites 0.116 ± 0.034 0.264 ± 0.084

Foliose/Plating 0.188 ± 0.039 0.154 ± 0.030

Agaricia agaricites (complex) 0.068 ± 0.016 0.077 ± 0.022

Agaricia fragilis 0.049 ± 0.017 0.029 ± 0.016

Agaricia lamarcki 0.005 ± 0.003 0.000 ± 0.000

Leptoseris cucullata 0.002 ± 0.002 0.000 ± 0.000

Mycetophyllia aliciae 0.044 ± 0.013 0.009 ± 0.004

Mycetophyllia ferox 0.011 ± 0.005 0.006 ± 0.004

Mycetophyllia lamarckiana 0.009 ± 0.004 0.034 ± 0.009

Massive/Encrusting 3.084 ± 0.259 2.409 ± 0.287

Montastraea annularis (complex) 0.367 ± 0.043 0.118 ± 0.025

Montastraea cavernosa 0.715 ± 0.087 0.250 ± 0.055

Colpophyllia natans 0.135 ± 0.023 0.061 ± 0.019

Dichocoenia stokesii 0.017 ± 0.006 0.058 ± 0.019

Diploria labyrinthiformis 0.009 ± 0.005 0.029 ± 0.008

Diploria strigosa 0.072 ± 0.015 0.097 ± 0.016

Madracis decactis 0.139 ± 0.046 0.052 ± 0.022

Madracis pharensis 0.002 ± 0.002 0.000 ± 0.000

Meandrina meandrites 0.040 ± 0.010 0.051 ± 0.011

Porites astreoides 0.615 ± 0.067 0.561 ± 0.064

Siderastrea radians 0.003 ± 0.002 0.007 ± 0.004

Siderastrea siderea 0.635 ± 0.073 0.702 ± 0.092

Solenastrea bournoni 0.002 ± 0.002 0.003 ± 0.003

Stephanocoenia michelinii 0.332 ± 0.047 0.392 ± 0.075

Manicina areolata 0.000 ± 0.000 0.025 ± 0.013

Isophyllia sinuosa 0.000 ± 0.000 0.004 ± 0.004

Solitary 0.006 ± 0.003 0.001 ± 0.001

Phyllangia americana 0.002 ± 0.002 0.000 ± 0.000

Scolymia cubensis 0.004 ± 0.002 0.001 ± 0.001

Total 3.456 ± 0.264 2.906 ± 0.276

Table 1. Stony coral density (number of corals per m2

) at three RNA dive sites (Davis Rock, Texas Rock, and The Maze) and two reference 

sites (Mayer’s Peak and Temptation Rock). N=12 for RNA dive sites and N=8 for reference sites. ± value is standard error.
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 41

installation allowed for a revision to the monitoring protocol 

used for assessing damage to A. cervicornis at the Off-Ramp 

and Perfection sites.

Performance Measure Evaluation

The surveys conducted in 2009 and 2010 provide an excellent baseline against which to evaluate the impacts that diving activities may have on coral communities at the RNA dive 

sites. Benthic cover estimates were consistent across years and 

stony coral density surveys encompassed a minimum of 150 

m2

 at each of the RNA dive and reference sites. The combination of these long-term measures coupled with previously 

reported estimates of coral stress will serve as reliable indicators to assess the long-term condition of coral communities 

at these sites and assist in determining if diver related impacts 

are the cause of any detectable differences between the RNA 

dive sites and reference sites. 

Identifying the diver carrying capacity at the RNA sites is 

critical if RNA resource stewardship goals are to be achieved. 

Estimating an acceptable diver capacity at intensively used 

dive sites can be difficult and previous attempts from reefs 

around the world have varied widely, ranging from 5,000 to 

50,000 divers per site per year (Luna et al. 2009). Many factors such as the biological and physical characteristics of the 

dive site, the presence of other anthropogenic stressors, the 

frequency of large-scale natural disturbances, and the education and competence of the divers all play a role in estimating 

diver carrying capacity. With installation of the mooring field 

completed, data on diver activity at the RNA sites can now be 

obtained through the DRTO vessel permit system (Chapter 

6, this volume). Most likely RNA dive sites will be visited by 

fewer than 6,000 divers per year, a level generally accepted 

as non-detrimental to coral reef communities (Hawkins et 

al. 1999). Conservative diver thresholds are typically applied 

to dive sites where branching corals are the most dominant 

constituent because branching corals are more vulnerable to 

diver-inflicted damage (Hawkins et al. 1999). At the RNA pinnacle reef dive sites, however, massive/encrusting stony corals 

and octocorals represent a large proportion of the reef community and this may increase the number of divers that can 

visit these sites without causing any discernible impacts.

Acknowledgements

All monitoring activities in 2009 and 2010 were jointly performed with DRTO under monitoring permits DRTO–2009–

SCI–0002 and DRTO–2010–SCI–0017. All activities were 

funded by cooperative agreement #H2117 08 3732, task 

agreement #J5299 08 9502, between the National Park Service and the Fish and Wildlife Research Institute (FWRI). We 

would like to thank multiple DRTO staff who made this work 

possible including Dr. Doug Morrison, Dr. Tracy Ziegler, and 

Kayla Nimmo. We also need to extend our sincere gratitude to 

FWRI employees Dr. Dave Palandro and Dave Eaken whose 

assistance was invaluable for completing the installation of 

the new survey stations at three RNA sites.

Literature Cited

Hallac, D.E. and Hunt, J., eds. 2010. Implementing the Dry 

Tortugas National Park Research Natural Area Science 

Plan: The 3-Year Report 2010. South Florida Natural 

Resources Center, Everglades and Dry Tortugas National 

Parks, Homestead, FL, and the Florida Fish and Wildlife 

Conservation Commission, Tallahassee, FL. 37 pp.

Hawkins, J.P., Roberts, C.M., Van’T Hof, T., De Meyer, K., 

Tratalos, J.A., and Aldam, C. 1999. Effects of Recreational 

Scuba Diving on Caribbean Coral and Fish Communities. 

Conservation Biology 13:888–897. 

Luna, B., Valle Pérez, C., and Sánchez-Lizaso, J.L. 2009. Benthic impacts of recreational divers in a Mediterranean 

Marine Protected Area. ICES Journal of Marine Science

66:517–523. 

Ruzicka R, Semon, K., Colella, M.A., Brinkhuis, V., Morrison, 

J., Macaulay, K., Kidney, J., Porter, J., Meyers, M., Christman, M., and Colee, J. 2010. Coral Reef Evaluation and 

Monitoring Project 2009 Final Report. Fish and Wildlife 

Research Institute/Florida Fish and Wildlife Conservation 

Commission, Saint Petersburg, FL, 110 pp. 

Tratalos, J.A. and Austin, T.J.. 2001. Impacts of recreational 

scuba diving on coral communities of the Caribbean island 

of Grand Cayman. Biological Conservation 102:67–75.

Zakai, D. and Chadwick-Furman, N.E., 2002. Impacts of 

intensive recreational diving on reef corals at Eilat, northern Red Sea. Biological Conservation 105:179–187.
42

Investigators

Ilsa B. Kuffner1, Valerie J. Paul2, Raphael Ritson-Williams2, 

T. Don Hickey1

, and Linda J. Walters3

1

U.S. Geological Survey 

2

Smithsonian Marine Station at Fort Pierce

3

University of Central Florida, Department of Biology

For further information contact: ikuffner@usgs.gov

Project Description

This chapter addresses the performance of the Dry Tortugas National Park (DRTO) Research Natural Area (RNA) in 

restoring coral reef ecological processes, including recovery 

of coral abundance and cover, coral recruitment, herbivory by 

fishes, and abundance of key species (Performance Topic 4). 

Like other reefs in the south Florida and Caribbean regions, 

Dry Tortugas communities have experienced significant 

degradation in the form of decreases in exploited species, 

reduced live coral, and increases in fleshy macroalgae. It 

remains to be determined to what extent humans are responsible for the decline in live coral coverage, as meteorological 

events are known to have contributed. Alexander Agassiz 

mapped the Dry Tortugas benthos in 1881, showing tens of 

hectares of Acropora palmata, but drilling has revealed that 

this species was not responsible for reef accretion in the Dry 

Tortugas (Shinn et al. 1977). In 1976, a comprehensive habitat 

map was created to examine change since the Agassiz map 

was prepared; the map showed that A. palmata had virtually 

disappeared and that Acropora cervicornis coverage was vast 

(Davis 1982). In January 1977, a severe cold front killed most 

of the A. cervicornis reefs. Populations have not recovered on 

patch reefs they once dominated in the early 1970s; in fact, 

a representative site showed steady decline due to bleaching 

and disease from 1999 to 2005 (Beaver et al. 2005). Regardless 

of what forces are responsible for the present state of reefs, 

there is some evidence that protecting reefs from any harvesting may help restore coral populations by restoring the balance among all trophic levels (Mumby et al. 2006).

The purpose of our study was to document the status of 

reef resources across multiple trophic groups in DRTO, both 

inside the RNA and in the adjacent Natural Cultural Zone 

(NCZ), with particular focus on the important reef process 

of herbivory. We investigated trophic cascades by examining 

the distribution and abundance of herbivores, the macroalgae 

they eat, and the stony corals that provide shelter for most 

reef organisms. Because of our focus on herbivory and trophic functioning, and because other monitoring programs 

(National Park Service, South Florida and Caribbean Network 

(SFCN); National Oceanic and Atmospheric Administration; 

and Florida Fish and Wildlife Conservation Commission, 

Fish and Wildlife Research Institute) have focused on habitat 

deeper than 6 m, we chose to focus our study on the shallow 

(<6 m) reef environment. We focused specifically on lowrelief, hard-bottom habitat (equivalent to remnant low profile 

and patch reef categories as categorized by SFCN, see Chapter 9, this volume) because it is the most abundant biological 

community habitat class within DRTO (Franklin et al. 2003). 

We randomly selected 18 sites for surveys conducted during October 2007, 9 within the RNA and 9 within the NCZ 

(Fig. 1). We conducted species-level surveys of macroalgae, 

scleractinian and gorgonian corals, herbivorous and game 

fishes, and sea urchins (Fig. 2), and also assessed substratum 

composition and quantified rugosity. Three 15-m transects 

were laid out radially from each Global Positioning System 

(GPS) location at bearings of 0°, 120°, and 240°. One reef fish 

visual census (7.5-m-radius cylinder with stationary observer) 

was conducted on each transect line (Bohnsack and Bannerot 1986; Brandt et al. 2009) with a downsized species list to 

reflect our objectives (for example, small benthic fishes were 

not included). The benthic community was assessed using 

n=4 quadrats (0.0625 m2

 with line demarking 25 equal boxes) 

per transect by visually estimating percent cover of taxa 

within the quadrat, and urchins and damselfish were counted 

in a 2-m-wide belt along each transect line. Rugosity was estimated by repeatedly draping a 1-m chain (3-cm link size) on 

the substratum underneath each transect line, giving the ratio 

between contoured and linear distance. Gorgonian and scleractinian diversity at each site was determined by recording 

all species observed throughout the approximately 1-hourlong dive in the proximity of the three transect lines (~700 m2 

area). The “game fish” category used here included grouper 

(Epinephelus, Mycteroperca, Cephalopholis) but excluded the 

small-bodied hamlets (Hypoplectrus), jacks (Caranx), snapper 

(Lutjanus and Ocyurus), and hogfish (Lachnolaimus maximus). Details on calculation of fish biomass are available in 

Kuffner et al. (2009).

RNA Performance Topic 4

Chapter 8: Baseline surveys to detect trophic changes in shallow hardbottom communities induced by the Dry Tortugas National Park 

Research Natural Area

RNA Performance Topic 4: Evaluate the effects of RNA implementation on the marine benthic biological communities
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 43

Results

Our surveys revealed that no variables measured were 

significantly different within the RNA vs. within the NCZ 

(Table 1; Kuffner et al. 2009). Game fish, particularly red 

grouper (Epinephelus morio), were abundant compared to 

sites of similar habitat in Virgin Islands National Park (data not 

shown). We counted a total of 19 E. morio during 54 censuses 

at the 18 sites throughout the park. Initial-phase hogfish 

(Lachnolaimus maximus), which are important predators of 

benthic invertebrates including sea urchins, were recorded at 

6 of the 18 sites. The long-spined urchin (Diadema antillarum) 

was present and fairly evenly distributed at all 18 sites. Mean 

densities ranged from 0.01 to 0.54 individuals m-2, with 11 of 

the 18 sites having densities above 0.10 individuals m-2. Mean 

percent of the substratum covered by macroalgae across all 

sites was 34% and dominated by brown algae (Dictyota spp.). 

D. antillarum density, scleractinian-coral species richness, 

scarid (parrotfish) abundance and biomass, and damselfish 

(Stegastes spp.) abundance were positively related to rugosity 

of the substratum. D. antillarum density also was positively 

related to percentage of the substratum composed of A. 

cervicornis rubble, and the amount of variance explained 

increased (adjusted R2

=0.49) when both the rugosity and 

rubble variables were included in a multiple linear regression 

model. Small (<1-m-diameter), live colonies of A. cervicornis

(Fig. 3) were noted at 12 of the 18 sites, evenly distributed 

across the RNA and the NCZ.

Performance Measure Evaluation

Can resource managers expect to reverse the decline in live 

coral coverage through the establishment and enforcement 

of the RNA? To have realistic expectations for the RNA’s efficacy with respect to benthic communities, it is necessary to 

take stock of initial conditions and to understand what forces 

drive coral population levels. Our data provide an important 

baseline that can be used to evaluate change with respect to 

the establishment of the RNA. A key element of our dataset 

is that no pre-existing differences exist among sites within the 

RNA vs. within the NCZ in any of the variables measured. 

Although there are too few ecological data to determine if 

the Caribbean-wide mortality of the key herbivore, Diadema 

antillarum, played a role in coral decline at this location since 

the early 1980s, the recent increases in this population could 

potentially enhance coral recruitment through the removal 

of Dictyota spp. and other algae from otherwise suitable 

substrata (Kuffner et al. 2006; Paul et al. 2011). Also, our data 

indicate that testing the hypothesis that A. cervicornis rubble 

acts as nursery habitat for D. antillarum would be worthwhile. 

We suggest the possibility of a positive feedback mechanism 

between these two recovering species.

No-take areas are considered an important tool in managing for reef resilience (Bellwood et al. 2004), and there is 

a growing body of evidence that no-take areas facilitate the 

recovery of key ecological processes like coral recruitment 

Figure 1. IKONOS satellite mosaic of Dry Tortugas National Park showing the location of 18 randomly 

selected sites where in-situ surveys were conducted during October 2007.
44

Table 1. Variables measured during in-situ surveys in Dry Tortugas National Park, October 16 – 20, 2007. Means, standard errors (SE), 

and p values of two-tailed two-sample t-tests are reported for variables comparing sites within the RNA and NCZ. The sites within the 

NCZ are still within the national park boundary where there are limited restrictions on resource use, including a ban on spear fishing. 

1 T-test assuming unequal variance using Satterthwait’s method as reported by Statistix© 9 software.

2 “Encrusting invertebrates” includes only Briareum asbestinum, Erythropodium caribaeorum, and Palythoa caribaeorum. 

Variable RNA (n=9) NCZ (n=9) T-test

Mean SE Mean SE P value

Rugosity 1.33 0.04 1.29 0.03 0.49

No. of coral species 14.1 0.9 12.2 1.0 0.19

No. of gorgonian taxa 13.3 1.0 14.9 0.8 0.23

Diadema antillarum (no. m-2) 0.18 0.05 0.16 0.06 0.79

Acanthurids (no. cylinder-1) 4.4 0.85 2.4 0.72 0.09

Acanthurid biomass (g cylinder-1) 151 34 143 85 10.93

Scarids (no. cylinder-1) 14.4 3.2 13.9 2.9 0.91

Scarid biomass (g cylinder-1) 418 105 283 152 0.48

Stegastes spp. (no. m-2) 0.66 0.04 0.7 0.13 10.74

Game fish (no. cylinder-1) 5.3 1.6 5.2 1.9 0.96

Crustose coralline algae (% cover) 33.9 4.7 24.8 2.9 0.12

Total calcified macroalgae (% cover) 9.0 1.1 9.0 0.44 11.00

Total fleshy macroalgae (% cover) 32.9 3.8 34.3 2.6 0.80

Halimeda tuna (% cover) 6.2 1.0 6.8 0.5 10.59

Dictyota spp. (% cover) 25.1 3.0 23.0 3.6 0.66

Encrusting invertebrates2 (% cover) 3.6 1.0 5.5 1.2 0.26

RNA Performance Topic 4: Evaluate the effects of RNA implementation on the marine benthic biological communities

Figure 3. The threatened staghorn coral (Acropora cervicornis)

on substrata mainly occupied by weedy brown algae in the 

genus Dictyota. Photo by Raphael Ritson-Williams, Smithsonian.

Figure 2. Valerie Paul conducting benthic community surveys 

in shallow, low-relief, hard-bottom habitat typical of the sites 

we surveyed in Dry Tortugas National Park. Photo by Raphael 

Ritson-Williams, Smithsonian.
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 45

and herbivory (Hughes et al. 2007). If enforcement of the new 

RNA management regime persists, DRTO presents a unique 

case study of no-take area efficacy with minimal underlying 

problems of land-based pollution present in the adjacent 

inhabited Florida Keys. Recent studies have shown that the 

calcification (growth) rate of at least one species of coral is 

30% faster in DRTO compared to three other sites throughout the Florida Keys (Kuffner, unpublished data). Nonetheless, it is important that realistic expectations are set for the 

RNA with regards to benthic community change. To achieve 

this, we need to appreciate regional and global-scale trends in 

coral mortality, as well as recognize the impacts of localized 

disturbances such as hurricanes and cold events. Changes in 

the resource illustrating the efficacy of the RNA in meeting 

the goal of restoring benthic communities are thus expected 

to be subtle and slow to occur.

Acknowledgements

Funding for this work was provided through a U.S. Geological Survey State Partnership Program award. We thank Gary 

Brewer (U.S. Geological Survey) for programmatic advice and 

continued support of our on-going work on coral/algal/herbivore interactions.

Literature Cited

Beaver, C., Brooke, S., Callahan, M., Wade, S., Johnson, D., 

Kupfner, S., and Kidney, J. 2005. Long-term monitoring 

of selected coral reef sites at the Dry Tortugas National 

Park. Fish and Wildlife Research Institute, St. Petersburg, 

Florida.

Bellwood, D.R., Hughes, T.P., Folke, C., and Nystrom, M. 

2004. Confronting the coral reef crisis. Nature 429:827–

833.

Bohnsack, J.A. and Bannerot, S.P. 1986. A stationary visual 

census technique for quantitatively assessing community 

structure of coral reef fishes. National Oceanic and Atmospheric Administration Technical Report 41.

Brandt, M.E., Zurcher, N., Acosta, A., Ault, J.S., Bohnsack, 

J.A., Feeley, M.W., Harper, D.E., Hunt, J.H., Kellison, T., 

McClellan, D.B., Patterson, M.E., and Smith, S.G. 2009. A 

cooperative multi-agency reef fish monitoring protocol for 

the Florida Keys coral reef ecosystem. Natural Resource 

Report NPS/SFCN/NRR–2009/150. National Park Service, Fort Collins, Colorado.

Davis, G.E. 1982. A century of natural change in coral distribution at the Dry Tortugas: A comparison of reef maps from 

1881 and 1976. Bulletin of Marine Science 32:608–623.

Franklin, E.C., Ault, J.S., Smith, S.G., Luo, J., Meester, G.A., 

Diaz, G.A., Chiappone, M., Swanson, D.W., Miller, S.L., 

and Bohnsack, J.A. 2003. Benthic habitat mapping in the 

Tortugas region, Florida. Marine Geodesy 26:19–34.

Hughes, T.P., Rodrigues, M.J., Bellwood, D.R., Ceccarelli, D., 

Hoegh-Guldberg, O., McCook, L.J., Moltschaniwskyj, N., 

Pratchett, M.S., Steneck, R.S., and Willis, B. 2007. Phase 

shifts, herbivory, and the resilience of coral reefs to climate 

change. Current Biology 17:360–365.

Kuffner, I.B., Paul, V.J., Ritson-Williams, R., Hickey, T.D., and 

Walters, L.J. 2009. Reef communities in the Dry Tortugas 

(Florida, USA): Baseline surveys for the new no-take area. 

Proceedings of the 11th International Coral Reef Symposium: 311–315.

Kuffner, I.B., Walters, L.J., Becerro, M.A., Paul, V.J., RitsonWilliams, R., and Beach, K.S. 2006. Inhibition of coral 

recruitment by macroalgae and cyanobacteria. Marine 

Ecology Progress Series 323:107–117.

Mumby, P.J., Dahlgren, C.P., Harborne, A.R., Kappel, C.V., 

Micheli, F., Brumbaugh, D.R., Holmes, K.E., Mendes, 

J.M., Broad, K., Sanchirico, J.N., Buch, K., Box, S., Stoffle, 

R.W., and Gill, A.B. 2006. Fishing, trophic cascades, and 

the process of grazing on coral reefs. Science 311:98–101.

Paul, V.J., Kuffner, I.B., Walters, L.J., Ritson-Williams, R., 

Beach, K.S., and Becerro, M.A. 2011. Chemically mediated interactions between macroalgae Dictyota spp. and 

multiple life-history stages of the coral Porites astreoides. 

Marine Ecology Progress Series 426:161–170.

Shinn, E.A., Hudson, J.H., Halley, R.B., and Lidz, B. 1977. Topographic control and accumulation rate of some Holocene 

coral reefs: South Florida and Dry Tortugas. Proceedings 

of the 3rd International Coral Reef Symposium 2:1–7.
46

Investigators

Jeff Miller, Rob Waara, Matt Patterson, Michael W. Feeley, 

Andrea Atkinson, Andy Davis, Andy Estep, and Lee Richter

National Park Service, South Florida/Caribbean Inventory 

and Monitoring Network

For further information contact: William_J_Miller@nps.gov

Project Description

The South Florida/Caribbean Network (SFCN) of the 

National Park Service (NPS) Inventory and Monitoring Program is monitoring coral reef communities within Dry Tortugas National Park (DRTO) to evaluate trends in cover of key 

benthic community indicators from selected coral reef sites 

both inside and outside the Research Natural Area (RNA). 

This monitoring addresses the need identified in Performance 

Topic 4 to evaluate the effects of RNA implementation on 

marine benthic biological communities.

We began monitoring during 2004 at Bird Key Reef (study 

site termed “Bird Key”; area = 19,765m2

), adding an adjacent 

site in 2005 (“Bird Key North”; 25,642m2

) (Fig. 1). The Bird 

Key Reef sites are situated within a 2-km long, high-relief spurand-groove habitat. These sites were selected for management 

interest in human activities in and around Fort Jefferson, and 

for comparison with historical monitoring results. Each site 

consists of 20 permanent, randomly selected 10-m transects 

that are monitored with a high-definition video camera. 

Percent cover by benthic groups/categories is quantified by 

visual identification of 10 random dots placed on 30–35 nonoverlapping video images (per transect). Benthic categories 

RNA Performance Topic 4

Chapter 9: Eight years of coral reef community monitoring: Results from 

inside and outside the Dry Tortugas National Park Research Natural Area

RNA Performance Topic 4: Evaluate the effects of RNA implementation on the marine benthic biological communities

Figure 1. The 2010 Dry Tortugas National Park benthic habitat map showing habitat classifications and location of 

coral monitoring sites at Bird Key (BK), Bird Key North (BKN), nine sites (labeled with “I” prefix) inside the Research 

Natural Area (RNA) and nine sites (labeled with “O” prefix) inside the Natural Cultural Zone (NCZ). Refer to Table 1 

for the habitat legend.

RNA

HAU

NCZ
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 47

include living coral by species, macroalgae, turf algae, crustose 

coralline algae, octocorals, and sponges. Additional field data 

are collected on coral disease, abundance of long-spined sea 

urchins (an important algal grazer), stony coral species diversity, rugosity, and reef-depth water temperature. The Bird Key 

sites straddle the Historic Adaptive Use Zone (HAU) boundary 

(see map on inside front cover), where 12 of the 40 combined 

transects fall within the RNA and 28 in the HAU, which may 

allow a future analysis of boundary effects. 

We expanded benthic monitoring in 2008 to include additional randomly selected sites that increased the spatial scale of 

benthic sampling in DRTO. More than 150 hard-bottom habitat sites were evaluated (2–20 m depth range), which led to 18 

sites (termed “extensive” sites; 9 inside the RNA and 9 inside 

the Natural Cultural Zone (NCZ)) that met the criteria of having >5% stony coral cover (see site locations in Fig. 1). Each site 

consists of four 10-m video transects and the same data are collected as described at the Bird Key sites. Monitoring of all sites 

by SFCN staff has continued annually.

In 2007, we entered into a cooperative agreement with the 

Florida Fish and Wildlife Conservation Commission (FWC) to 

produce a benthic habitat map for the coral reef ecosystems of 

DRTO. An initial benthic habitat map was completed in 2008 

by the contractor, Avineon, Inc. Acquisition of new higher 

resolution side scan sonar data and 2,054 field data points from 

multiple sources (SFCN, National Oceanic and Atmospheric 

Administration, and University of Miami) allowed SFCN to 

correct classification deficiencies in the 2008 map and improve 

the detail level of the line work to produce the 2010 DRTO benthic habitat map (Fig. 1, Table 1; Waara et al. 2011).

Map Classification Color RNA (ha) NCZ (ha) DRTO Total (ha)

Aggregate Patch Reefs 326.08 306.97 633.06

Continuous Submerged Rooted Vegetation (SRV) 1,242.18 1,025.6 2,267.78

Discontinuous SRV 672.16 783.9 1,456.06

High Relief Spur and Groove 21.54 134.06 155.59

Individual Patch Reefs 200.78 324.82 525.6

Land 23.18 16.19 39.37

Low Relief Spur and Groove 249.84 167.91 417.75

Patchy Coral or Rock in Unconsolidated Sediment 200.79 812.94 1,013.73

Pavement 170.85 36.61 207.46

Reef Rubble 47.3 80.85 128.15

Reef Terrace (high profile) 1,226.84 655.91 1,882.75

Remnant (low profile) 1,879.03 2,389.03 4,268.05

Unconsolidated Sediment 5,738.22 7,495.31 13,233.53

Table 1. The 2010 Dry Tortugas National Park benthic habitat map classifications with corresponding color scheme and the areas (in 

hectares) inside the Research Natural Area (RNA) and the Natural Cultural Zone (NCZ) along with the area totals for Dry Tortugas 

National Park.
48

Results

Bird Key Reef: Monitoring from 2004 through 2011 indicated 

a significant decrease in stony coral cover at the Bird Key site 

(13.2% to 10.6%; p<0.0001). This decrease primarily occurred 

from 2004 through 2007 and then appeared to stabilize. Bird 

Key North, initiated in 2005, did not show a significant overall 

trend (Fig. 2). Octocoral cover (such as sea fans, sea plumes, 

etc.) showed a significant 1-year decline at both Bird Key Reef 

sites from an average of 20.0% in 2005 to 8.9% cover in 2006 

(p<0.0001) followed by an increase through 2011. This trend 

is likely the result of four hurricanes passing over DRTO during the extremely active hurricane season of 2005. 

Extensive sites: Results of annual monitoring at the 18 

extensive sites showed that stony coral cover had no significant 

trends at these sites during 2008–11. Two sites located within 

the RNA in Loggerhead Forest (I05, I50), had exceptionally 

high stony coral cover (I05 : 4-year mean = 31.0% [Standard 

Error (SE)=0.5]; I50: 4-year mean = 20.1% [SE=1.3]). This 

finding is notable because in June and July of 2008, SFCN 

staff observed an outbreak of the coral disease white plague 

in DRTO, much of it located in the Loggerhead Forest area. 

This outbreak was investigated again in July 2008 by a team 

of coral disease specialists from the U.S. Coral Disease and 

Health Consortium and George Mason University. Loggerhead Forest sites (I05, I50) were resurveyed and tissue samples 

were collected (results pending) but by the time of the resurvey, the outbreak had subsided. Cover by macroalgae varied 

throughout the study and was inversely related to the turf 

algae category. Macroalgal cover was ephemeral; when present, cover of turf algae and other substrate categories (sand, 

for example) decreased as they were replaced or became covered by macroalgae.

Temperature: Analyses of reef-depth water temperature 

data indicated that benthic communities in DRTO were subject to large variations in water temperature, both seasonally 

and episodically. Daily average temperatures in the summer 

regularly exceeded the theoretical 30.5°C bleaching threshold; 

however, NPS staff stationed at the park did not report widespread coral bleaching, possibly indicating that the bleaching 

threshold at DRTO may be higher. Daily average temperatures 

during the winters of 2009, 2010, and 2011 fell below 19.5°C 

(Fig. 3), with 2009 and 2011 temperatures even lower than 

those experienced in DRTO during Florida’s deadly coldwater event in 2010 (Lirman et al. 2011). Cold-water events 

also were recorded in the summers of 2009, 2010 and 2011, 

when temperatures at several monitoring sites (primarily Loggerhead Forest) rapidly dropped 4–8°C in a matter of days, 

remaining well below temperatures recorded at other DRTO 

locations for days to weeks. Although these cold temperatures 

were above the 16°C minimum temperature stress threshold, 

they demonstrate that benthic communities are exposed to 

wide fluctuations in temperature, at times exceeding 10°C. 

Benthic Habitat Map: We conducted an accuracy assessment of the 2008 Avineon, Inc. DRTO benthic habitat map 

and found the overall classification accuracy to be acceptable 

(83.2%; lower 90% Confidence Interval (CI)=79.8%). However, upon closer evaluation, the soft-bottom habitat classifications displayed a relatively high level of accuracy (89.4%; 

lower 90% CI=85.2%), whereas the hard-bottom habitat classifications were below an acceptable level (75.2%; lower 90% 

CI=69.1%). All unknown areas (10,444 ha) in the 2008 map 

were identified, and the line work for the hard-bottom areas 

Figure 2. Trends in average percent cover of stony corals at coral monitoring sites grouped into Bird 

Key, Bird Key North, inside the Research Natural Area (RNA), and the Natural Cultural Zone (NCZ) strata.

RNA Performance Topic 4: Evaluate the effects of RNA implementation on the marine benthic biological communities
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 49

was fine-tuned in the 2010 DRTO benthic habitat map (Waara 

et al. 2011). The overall accuracy assessment of the redrawn 

2010 DRTO benthic habitat map was 89.7% (lower 90% 

CI=86.0%). The accuracy of hard-bottom habitats improved 

to 88.0% (lower 90% CI=83.4%). The 2010 map consists of 

13 mapping classes and 1,709 polygons totaling an area of 

26,229 ha. A map layer also was developed to identify areas 

that have a higher potential for fish and benthic biodiversity. 

In addition, a final bathymetry layer for the park was created 

by merging the 2004 Light Detection and Ranging (LiDAR) 

data and newly acquired side scan sonar bathymetry data. To 

facilitate visualization of underwater sites, a hyperlink tool 

was developed that displays photos and videos together with 

field data when a point is selected in ArcGIS.

Performance Measure Evaluation

The SFCN benthic monitoring program at DRTO was developed, in part, to address the need identified in RNA Performance Topic 4. The program will continue to be a useful tool 

to evaluate the effectiveness of the RNA in the years to come.

Bird Key Reef: Although trends observed at this site are not 

necessarily representative of park-wide DRTO trends, SFCN 

monitoring conducted at this site can be evaluated within a 

valuable historical context. In 1975, coral cover on this site, 

measured at 11 transects with a line transect method, ranged 

from 17.9% to 63.9% (mean: 42.3% [SE=4.3]; Jaap et al. 1989). 

Additionally, monitoring conducted by the FWC at 12 stations 

in DRTO (including 4 at Bird Key Reef) during 1999–2008 

reported a significant decrease in coral cover (p<0.001; 

Ruzicka et al. 2009). Thus, although methods differ, we are 

concerned that the current decrease in coral cover during 

2004–2011 may be part of a longer downward trend at Bird 

Key Reef. The observations of very large toppled coral boulders and distinct patches of coral mortality suggest that hurricanes and coral diseases are the likely causes of these dramatic declines in coral cover. Given this context, monitoring 

of benthic communities is important not only for determining 

effects of the RNA on this aspect of the ecosystem, but also for 

correctly interpreting results of other performance measures 

that could be tied to benthic community health, such as fish 

abundance and size structure (RNA Performance Topic 1).

Extensive Sites: The development of a DRTO GIS-based 

benthic habitat map has facilitated management-based sample 

designs in benthic monitoring. In 2008, we installed four benthic monitoring transects at nine randomly selected sites inside 

the RNA and NCZ with the purpose of tracking changes in 

the benthic community. Despite the white plague disease outbreak in June 2008, no appreciable coral loss was subsequently 

observed (Brandt et al. in review). Results of video monitoring 

during 2008–2011 showed no change in stony coral cover at 

the nine RNA sites (2011 mean cover: 7.5% [SE=3.3]) or the 

nine NCZ sites (2011 mean cover 3.8% [SE=1.0]). Although 

mean stony coral cover in the RNA appears higher than outside, this was driven by the exceptional coral cover at the two 

previously mentioned sites located within the high profile 

reef terrace in the northwestern part of the RNA (Loggerhead 

Forest). This area has relatively high coral species richness 

and high rugosity, and may contain the highest remaining living stony coral cover within DRTO. During the study period, 

stony coral species richness remained relatively constant at 

sites in the RNA and NCZ, with higher diversity at sites in the 

RNA, again primarily reflecting the high diversity of coral speFigure 3. Water temperature measured at coral monitoring sites in Dry Tortugas National Park, 2004–2011. 

Prior to the introduction of 18 extensive monitoring sites in 2008 (indicated by red circle), temperature was 

recorded only at Bird Key (blue) and Bird Key North (red). Cold-water stress threshold of 16°C and bleaching 

threshold of 30.5°C are shown.
50

cies in Loggerhead Forest. Cover by sponges, octocorals, macroalgae, and turf algae was not significantly different between 

the two management zones, with macroalgae being the most 

abundant benthic community group. 

Benthic Habitat Map: The greater accuracy and detail of the 

2010 DRTO benthic habitat map as well as the new bathymetry layer should facilitate both monitoring and management 

planning. As an example, the proportions of different habitats 

can be shown for the management zones. Soft-bottom habitats 

(such as unconsolidated sediment, continuous or discontinuous submerged rooted vegetation, or reef rubble) comprise 

65.8% of the area in the RNA and 71.7% in the NCZ. In both 

management zones, remnant reef (low profile) is the dominant hard-bottom component, followed by reef terrace (high 

profile). However, there is more than twice the amount of reef 

terrace inside the RNA than inside the NCZ. Patch reefs are 

common features in both strata, comprising 12.9% of the hard 

bottom in the RNA and 15.7% in the NCZ; while the area of 

individual and aggregate patch reefs are nearly equal in the 

NCZ (324.8 ha vs. 306.9 ha, respectively), there are fewer individual patch reefs in the RNA (200.8-ha vs. 326.1-ha aggregate 

patch). Spur-and-groove reefs are moderately abundant hardbottom features in DRTO. In the RNA, the majority are low 

relief (249.8 ha low relief vs. 21.5 ha high relief); distribution is 

more equal in the NCZ (167.9 ha low vs. 134.1 ha high).

The additional habitat delineated in the 2010 map includes 

areas with potential for high coral cover, diversity, and rugosity, primarily in the northeastern and southwestern sections 

of DRTO (for example, low- and high-relief spur and groove, 

and reef terrace). We are currently considering revising our 

extensive-site study design to include these areas in the survey domain. Monitoring for status and trends in the benthic 

community, specifically coral cover, requires a well-designed 

monitoring program. Declines in coral cover can occur rapidly (such as from hurricane effects or disease outbreaks) or 

be prolonged (for example, from climate change). Given the 

very slow rate of coral growth, quantifying increases in coral 

cover takes many years if not decades. We are structuring our 

monitoring program to capture declines and increases in coral 

cover and growth.

Monitoring of coral cover and other benthic communities is important not only for determining effects of the RNA on the ecosystem, 

but also for correctly interpreting results of other performance measures that could be tied to benthic community health, such as fish 

abundance and size structure. Photo by the South Florida/Caribbean Inventory and Monitoring Network, NPS.

RNA Performance Topic 4: Evaluate the effects of RNA implementation on the marine benthic biological communities
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 51

Literature Cited

Brandt, M.E., Ruttenberg, B.I., Waara, R., Miller, J., Witcher, 

B., Estep, A.J., and Patterson, M.. In review. Dynamics 

of an acute coral disease outbreak associated with the 

macroalgae Dictyota spp. in Dry Tortugas National Park, 

Florida, U.S.A. Bulletin of Marine Science.

Jaap, W.C., Lyons, W.G., Dustan, P., and Halas, J.C. 1989. Stony 

coral (Scleractinia and Milleporina) community structure 

at Bird Key Reef, Ft. Jefferson National Monument, Dry 

Tortugas, Florida. Florida Marine Research Publication. 

No. 46. Florida Marine Research Institute, St. Petersburg, 

Florida.

Lirman, D., Schopmeyer, S., Manzello, D., Gramer, L.J., Precht, W.F., Muller-Karger, F., Banks, K., Barnes, B., Bartels, 

E., Bourque, A., Byrne, J., Donahue, S., Duquesnel, J., 

Fisher, L., Gilliam, D., Hendee, J., Johnson, M., Maxwell, 

K., McDevitt, E., Monty, J., Rueda, D., Ruzicka, R., and 

Thanner, S. 2011. Severe 2010 cold-water event caused 

unprecedented mortality to corals of the Florida reef 

tract and reversed previous survivorship patterns. Public 

Library of Science One 6(8):1–10. 

Ruzicka, R., Semon, K., Colella, M., Brinkluis, V., Kidney, J., 

Morrison, J., Macaulay, K., Porter, J., Meyers, M., Christman, M., and Colee, J. 2009. Coral Reef Evaluation and 

Monitoring Project: 2009 Annual Report. Florida Fish 

and Wildlife Conservation Commission Fish and Wildlife 

Research Institute, Funded by US EPA and NOAA, USEPA 

Grant award X7–97468002–8, 110 pages.

Waara, R.J., Patterson, J.M., Atkinson, A.J., and Estep, A.J. 

2011. Development and policy applications of the 2010 

benthic habitat map for DRTO. Natural Resource Technical Report NPS/SFCN/NRTR–2011/474. NPS, Fort Collins, Colorado.
52

Investigators

Melissa Memory1, David L. Conlin2, Andres Diaz2, and Paul 

O’Dell1

1

National Park Service, Dry Tortugas National Park 

2

National Park Service, Submerged Resources Center 

For further information contact: Melissa_Memory@nps.gov

Project Description

The National Park Service (NPS), including staff from 

Dry Tortugas National Park (DRTO) and the Submerged 

Resources Center (SRC), with additional assistance and support from Biscayne National Park staff, conducted condition 

assessments on the known submerged archeological sites 

throughout DRTO from July 2009 to July 2011. 

Goals of the project were to reconcile the existing archeological site database with accurate site location information 

and current conditions, and to develop a monitoring plan 

to prioritize future assessment work in the park. Condition 

assessments were completed of all known sites that had been 

recorded over decades but were not monitored. This project 

has provided a baseline from which sites within the Research 

Natural Area (RNA), established inside the park in 2007, can 

be compared to sites outside of the RNA to evaluate the effectiveness of the management strategy for the protection of submerged cultural resources. As a part of the ongoing fieldwork, 

a supplemental goal is the discovery of previously unknown 

sites. 

The condition assessment information collected is tracked 

in the Archeological Sites Management Information System (ASMIS) database, which is an NPS-wide repository of 

archeological data. Use of this standardized database to collect a consistent basic dataset across researchers and research 

designs allows for monitoring of basic site data as well as longterm condition trends within the park and in comparison to 

RNA Performance Topic 4: Evaluate the effects of RNA implementation on the marine benthic biological communities

RNA Performance Topic 4 

Chapter 10: Evaluation of submerged cultural resource conditions within 

Dry Tortugas National Park 

Figure 1. Hard corals and seafans grow on a drum of wire rope from a shipwreck on Pulaski Reef on the northeastern side of 

the park. Photo by Brett Seymour, Submerged Resources Center, NPS.
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 53

Figure 2. National Park Service diver John Spade records information about a cultural resource near Garden Key, Dry Tortugas 

National Park. Photo by Brett Seymour, Submerged Resources Center, NPS.

other units of the national park system. Because submerged 

cultural resources often provide good substrate for thriving 

benthic communities, protection of cultural resources in the 

park also serves to enhance natural resources (Fig. 1).

The methodology of a condition assessment of a submerged archeological site consists of a review of known information about the site, including initial site documentation, 

photographs, maps, and previous condition assessments, 

and includes visiting the site and noting any difference since 

the last visit (Fig. 2). If new discoveries have been made or if 

significant change has occurred, new measurements are taken 

and added to the site map. Qualitative data, such as observed 

impacts or threats, also are interpreted and documented. 

Together, these observations are expressed as a condition designation of good/fair/poor/destroyed/not relocated/unknown 

in the ASMIS database (National Park Service 2007). All 

known sites at DRTO have been determined to be in good or 

fair condition. As defined by ASMIS, a good site is defined as:

“The site, at the first condition assessment or during the 

time interval since its last condition assessment, shows no 

evidence of noticeable deterioration by natural forces and/

or human activities. The site is considered currently stable 

and its present archaeological values are not threatened. 

No adjustments to the currently prescribed site treatments 

are required in the near future to maintain the site’s present condition.”

A fair designation is:

“The site, at the first condition assessment or during the 

time interval since its last condition assessment, shows 

evidence of deterioration by natural forces and/or human 

activities. If the identified impacts continue without the 

appropriate corrective treatment, the site will degrade to 

a poor condition and the site’s data potential for historical 

or scientific research will be lowered.”

According to NPS policy, sites that have been designated 

in fair condition require that corrective action take place to 

either stabilize or improve the condition of the site. Treatment of a site found in fair condition may include increased 

monitoring, archeological data recovery, site closure, or other 

management action. Monitoring may include regular site visitations by trained archeologists or increased law enforcement 

patrols in the area. Archeological data recovery would include 

the creation or update of a site plan, and/or intensive still and 

video imaging, or recovery of sensitive artifacts. 

Results

The SRC spent a substantial amount of time during the early 

1990s locating, mapping, and interpreting DRTO submerged 

cultural resources. This work resulted in site maps for 11 shipwreck sites and hundreds of individual photographs and vid-
54 RNA Performance Topic 4: Evaluate the effects of RNA implementation on the marine benthic biological communities

eo images (Murphy 1993). An additional site was mapped 

in July of 2010. Together these site documentations serve as 

strong baseline data to track changes to submerged cultural 

resources in subsequent years. 

Along with the work that was conducted from 2009 

through 2011, a supplemental goal was met in the development of the capability of park staff to conduct condition assessments of submerged archeological sites. In 2011, seven 

submerged archeological sites were assessed by park staff. Six 

of the sites assessed were determined to be in good condition. One site, the Cement Barrel Site, was assessed to be in 

fair condition. 

The Cement Barrel Site, located on South Loggerhead 

Reef, has maintained a fair condition since its assessment in 

July of 2009, despite its continuous impact by dynamic natural 

forces. Further monitoring of the site, as well as the completion of an updated site map from information collected during 

the 2009 field season, will aid researchers in the understanding of the forces that are affecting this site. 

When conducting ongoing condition assessments, remote 

sensing targets identified from survey efforts in the early 1990s 

by the SRC were investigated when time allowed. The investigation of these targets resulted in the addition of 15 previously unrecorded sites. With condition assessments completed in 

2011, the NPS will now develop a monitoring and management plan in 2012.

Performance Measure Evaluation

This chapter documents the classification of submerged 

archeological site condition assessments as a performance 

measure for Performance Topic 4, to evaluate the effects of 

RNA implementation on marine benthic biological communities. Cultural resources of DRTO support important 

natural resources. Whether intentional or inadvertent, human 

disturbance to submerged cultural resources threatens both 

the integrity of the historic resource and the marine benthic 

biological communities that they support. The first 5 years of 

the RNA at DRTO revealed that of the 50 submerged cultural 

resources surveyed in the park, both inside and outside of the 

RNA, 49 of them were determined to be in good condition, 

and 1 in fair condition. This consistent baseline will provide 

an outstanding opportunity to compare long-term effects of 

the RNA through monitoring these resources.

The buoyed Windjammer site on South Loggerhead Key is 

a prime example of a site that should be studied to determine 

the effects of RNA implementation. On August 21, 2011, the 

site was assessed and it was documented that the ship’s structure continues to serve as substrate for coral, which appears to 

be growing well. Such observations present the opportunity 

for collaborative studies with biologists to study the health 

and size of coral communities associated with submerged 

cultural resources. An example of a suitable control site is the 

East Key Construction Wreck. This site is outside the RNA, is 

visited, and has not been buoyed. The site is also marked on 

marine charts and park literature, revealing its location and 

attracting visitation. 

In addition, submerged cultural resources in DRTO are 

desirable habitat for invasive lionfish (Pterois volitans). Collaborative studies regarding impacts of lionfish on cultural 

resources, as well as the potential impacts of lionfish eradication activities on cultural resources, also are recommended.

Ideally, performance goals for cultural resources should 

have their own topic in the RNA Science Plan. This topic 

should be developed by the NPS in collaboration with the 

Florida Bureau of Archeological Research, Florida Department of State.

Literature Cited

Murphy, L.E., editor. 1993. Dry Tortugas National Park: 

Submerged Cultural Resources Assessment. Submerged 

Resources Center Professional Report No. 13. National 

Park Service, Santa Fe, New Mexico.

National Park Service. 2007. Data Dictionary: Archeological 

Information Management System 3.01. Department of the 

Interior, Washington, DC.
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 55

NPS archeologist Andres Diaz inspects the propeller of the Bird Key Wreck, Dry Tortugas National Park. Photo by Brett 

Seymour, Submerged Resources Center, NPS.
56 RNA Performance Topic 5: Assess reproductive potential of exploited species by evaluating egg production and larval dispersal

Investigators

Jerald S. Ault1, Jiangang Luo1, Steven G. Smith1, and David B. 

McClellan2

1

University of Miami, Rosenstiel School of Marine and Atmospheric Science

2

National Oceanic and Atmospheric Administration, Southeast Fisheries Science Center

For further information contact: jault@rsmas.miami.edu

Project Description

The goal of this study was to assess the reproductive potential of exploited reef fish species by evaluating the expected 

physical transport and fate of fish eggs and larvae spawned 

in the Tortugas region to the adjacent waters of the south 

Florida coral reef ecosystem (Performance Topic 5). Species 

in the snapper-grouper complex utilize a mosaic of crossshelf habitats and oceanographic features over their life spans 

(Lindeman et al. 2000; Ault et al. 2005). Most adults spawn on 

the barrier reefs, where they sometimes form large spawning 

aggregations (Domeier and Colin 1997). Eggs and developing 

larvae are transported from spawning sites along the barrier 

reef tract by a combination of water currents and unique 

animal behaviors. Eventually they settle as young juveniles 

in a variety of in-shore benthic habitats (Lee et al. 1994; Ault 

et al. 1999). Some of the most important nursery habitats are 

located in near-shore areas (Lindeman et al. 2000; Ault et al. 

2001). The Tortugas region, in particular, contains numerous 

known spawning aggregation sites for reef fishes (Schmidt 

et al. 1999; Chapter 4, this volume). The Dry Tortugas also is 

where the Loop Current in the southeastern Gulf of Mexico 

merges with the Florida Current and then flows parallel to 

the barrier reef through the Straits of Florida toward Miami. 

These factors indicate that the Tortugas region may be an 

important source of newborn fish that replenish reef fish 

populations in the Florida Keys.

This project was designed to complement concurrent 

intensive field studies in the Tortugas region: (1) fishery-independent surveys providing abundance metrics of reef fishes, 

including juveniles and spawning adults (Chapters 1 and 2, 

this volume); and (2) acoustic tagging providing information 

on adult fish movements and spawning migrations (Chapters 3 and 4, this volume). Our research utilized a physical 

oceanographic model known as the Hybrid Miami Isopycnal 

Coordinate Ocean Model (HYCOM) and high-performance 

computational resources, along with detailed demographic 

information on spawning and larval life history characteristics 

of key snapper and grouper reef fish species. We developed 

a computer interface to link the HYCOM model (Kourafalou et al. 2009) with a particle flux model to simulate larval 

transport. The model domain was the northern Caribbean 

Sea, Gulf of Mexico, and southeastern United States with a 

grid spacing of 4 km. The model utilized meteorological and 

oceanographic data that allowed “real time” simulations of 

transport. HYCOM model year 2008 was used for the simulations. Biological information, including the timing and duration of spawning and larval phase duration, was compiled for 

principal snapper and grouper species. 

A factorial experimental design for the simulation analyses 

was developed for three principal factors. The first factor was 

Spawning Season, defined as either winter (February 1 release 

date) or summer (July 15 release date). The second factor was 

Spawning Location, which was either Riley’s Hump (located 

inside Tortugas South Ecological Reserve) or Sherwood Forest (located inside Tortugas North Ecological Reserve). The 

third factor was the Depth Layer (m), which we defined as 

either 0 m (surface), 10 m, 20 m, or 30 m deep. The timing of 

egg and larval release corresponded to the general spawning 

seasons for groupers (winter) and snappers (summer). The 

two spawning locations were chosen on the basis of numerous field observations of spawning aggregations of various 

reef-associated and coastal pelagic species, including mutton 

snapper (Riley’s Hump; Chapter 3, this volume) and permit 

(Sherwood Forest; Ault et al. 2006 and Fig. 1). Depth layers 

represent the range of conditions for the buoyancy of larval 

particles: positively buoyant (surface, 0 m depth), neutrally 

buoyant at the substrate depth of the spawning location (30 

m), and neutrally buoyant at two intermediate spawning 

depths (10 m and 20 m). 

A separate simulation experiment was conducted for each 

combination of season, location, and depth. Each experiment 

entailed continuous tracking in time and space of thousands 

of passive larval particles for 30 days, approximating the larval 

duration of snappers and groupers. The principal metric was 

the percentage of released particles that could have potentially settled in a coastal environment on the ith day from the 

start of the simulation. Results are provided for days from start 

i=10, 15, 20, 25, and 30. Particles located in environments with 

substrate depths shallower than 50 m on the ith day were considered to be successful with respect to potential settlement.

RNA Performance Topic 5

Chapter 11: Larval Transport Modeling to Assess the Reproductive Potential 

of Reef Fish Spawning in the Tortugas Region
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 57

Figure 1. Spawning aggregations of permit (Trachinotus falcatus) observed during fishery-independent visual surveys in the 

Dry Tortugas (west Tortugas Bank) in (A) June 2010 (photo by J. Luo, UM RSMAS) and (B) June 2004 (photo by D. Bryan, UM 

RSMAS). In (B), note the dark patches behind the dorsal fins that are only present during spawning for this species.

A

B
58

Results

Lagrangian simulation results of larval drift patterns by 

season, location, and depth are summarized in Table 1. The 

highest percent settlement generally occurred for particles 

spawned at the surface depth layer irrespective of season and 

location. Relatively higher settlement also occurred for particles spawned at the substrate depth layer of 30 m for most 

seasons and locations, with the lowest percent settlement for 

particles spawned at depth layers of 10 m and 20 m. A general 

seasonal trend in settlement success also was observed, with 

winter having higher overall percent settlement compared to 

summer, irrespective of spawning location.

Spatial patterns of larval drift were evaluated with respect 

to three general areas presented in Figure 2. Area 1 is defined 

as southern Florida, including the Florida Keys and greater 

Tortugas region; Area 2 is the West Florida Shelf; and Area 3 is 

the east coast of Florida and the South Atlantic Bight (Fig. 2). 

The location of larval particles (day 25 at depth layer 0 m) for 

two spawning locations and two seasons is shown in Figure 

3. Our results suggest that larval spatial distribution patterns 

may be dependent on the spawning season (Table 1). During 

winter, successful settlement was concentrated in south Florida (Area 1) and the east coast of Florida (Area 3), with very 

little settlement occurring on the West Florida Shelf (Area 

2). In contrast, during summer, settlement was concentrated 

in south Florida and the West Florida Shelf, with very little 

settlement occurring along the east coast of Florida.

Performance Measure Evaluation

We developed a general south Florida marine ecosystems 

model that can be used to simulate the larval drift of any 

marine organism for any start time and period of duration. 

Our simulation results indicate that spawning in the Tortugas region is likely supplying newborn recruits to reef fish 

populations throughout southern Florida, including the Dry 

Tortugas and Florida Keys reef tract, coastal bays along the 

West Florida Shelf, and along the east coast of Florida north 

of Miami. Our results also suggest that the potential success of 

larval settlement and the ensuing spatial distribution may be 

dependent upon the spawning season.

While the Tortugas region is a known spawning area 

for reef fishes (Schmidt et al. 1999), it also appears to be an 

important spawning area for other economically important 

coastal marine species. The permit (Trachinotus falcatus) is a 

prized gamefish most often associated with inshore shallowwater sport fisheries for bonefish and tarpon, some of the 

most economically important species in Florida (Ault 2008). 

Large aggregations of permit (hundreds to thousands of 

fishes; Fig. 1A) possessing “spawning marks” (Fig. 1B; Graham and Castellanos 2005) have been encountered during 

each visual survey conducted on Tortugas Bank since 2004 

(Ault et al. 2006; Smith et al. 2011; Chapter 1, this volume). 

These surveys occurred during the spring-summer spawning 

season for permit in Florida (Crabtree et al. 2002). Early juvenile permit have been captured in netting studies in shallow, 

inshore habitats ranging from Charlotte Harbor on the west 

coast of Florida, through the Florida Keys in the south, to the 

coastal areas north of Miami (Adams et al. 2006; Snodgrass 

and Harndon 2009). This corresponds very well to the spatial 

distribution of larval settlement predicted by the simulation 

model for the summer spawning months (Fig. 3). 

Our analyses of reproductive potential via larval transport 

modeling, combined with results from fishery-independent 

surveys (Chapters 1 and 2, this volume) and tagging studies (Chapters 3 and 4, this volume), shed some light on the 

ecological importance of DRTO and the Tortugas region in 

sustaining the productivity of coral reef and coastal marine 

fisheries in southern Florida. DRTO harbors from one-third 

to one-half of the adult spawners of principal snapper-grouper species in the south Florida coral reef ecosystem (Chapter 

1, this volume), and provides a home base for migrations to 

and from spawning aggregation sites such as Riley’s Hump 

(Chapter 3, this volume). Eggs spawned at these locations 

have a wide geographic distribution in terms of potential larval settlement (Fig. 3). The relatively small geographic area of 

DRTO appears to contain some of the most valuable marine 

habitat in the southern Florida ecosystem. The area provides 

newborn recruits to populations of principal coral reef and 

coastal marine fishery species in the Tortugas region (Chapter 

2, this volume), the Florida Keys reef tract, the West Florida 

shelf, and along the east coast of Florida north of Miami.

Figure 2. Three general areas denoting the spatial distribution 

of passive larval particles: Area 1 (southern Florida), Area 2 

(West Florida Shelf), and Area 3 (east coast of Florida and South 

Atlantic Bight).

RNA Performance Topic 5: Assess reproductive potential of exploited species by evaluating egg production and larval dispersal

AREA 1

AREA 2 AREA 3
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 59

Percent Potential Settlement

Spawning Location Spawning 

Date Depth (m) Days from start

Overall Area 1 Area 2 Area 3

Riley's Hump Feb 1 0 10 93.9 53.6 0.0 40.3

Riley's Hump Feb 1 0 15 90.5 48.9 0.0 41.6

Riley's Hump Feb 1 0 20 91.5 47.5 0.0 44.0

Riley's Hump Feb 1 0 25 90.8 46.5 0.0 44.3

Riley's Hump Feb 1 0 30 92.3 46.0 0.0 46.3

Riley's Hump Feb 1 30 10 24.6 19.1 0.0 5.5

Riley's Hump Feb 1 30 15 35.1 19.2 0.0 15.9

Riley's Hump Feb 1 30 20 30.4 19.2 0.0 11.2

Riley's Hump Feb 1 30 25 37.7 19.2 0.0 18.5

Riley's Hump Feb 1 30 30 46.7 19.2 0.0 27.5

Riley's Hump Jul 15 0 10 21.5 21.5 0.0 0.0

Riley's Hump Jul 15 0 15 26.9 25.2 1.7 0.0

Riley's Hump Jul 15 0 20 33.0 30.4 2.6 0.0

Riley's Hump Jul 15 0 25 41.3 28.8 10.6 1.9

Riley's Hump Jul 15 0 30 42.3 35.0 3.2 4.1

Riley's Hump Jul 15 30 10 26.5 26.5 0.0 0.0

Riley's Hump Jul 15 30 15 29.0 28.6 0.0 0.4

Riley's Hump Jul 15 30 20 35.1 32.7 0.1 2.3

Riley's Hump Jul 15 30 25 40.3 34.1 0.7 5.5

Riley's Hump Jul 15 30 30 44.1 34.8 0.9 8.4

Sherwood Forest Feb 1 0 10 88.8 88.8 0.0 0.0

Sherwood Forest Feb 1 0 15 88.9 88.0 0.0 0.9

Sherwood Forest Feb 1 0 20 80.0 75.5 0.0 4.5

Sherwood Forest Feb 1 0 25 83.2 72.4 0.0 10.8

Sherwood Forest Feb 1 0 30 80.8 71.3 0.0 9.5

Sherwood Forest Feb 1 30 10 60.6 60.6 0.0 0.0

Sherwood Forest Feb 1 30 15 64.5 63.0 0.0 1.5

Sherwood Forest Feb 1 30 20 65.7 63.8 0.0 1.9

Sherwood Forest Feb 1 30 25 72.8 63.9 0.0 8.9

Sherwood Forest Feb 1 30 30 79.5 63.9 0.0 15.6

Sherwood Forest Jul 15 0 10 27.6 27.5 0.1 0.0

Sherwood Forest Jul 15 0 15 38.0 25.0 13.0 0.0

Sherwood Forest Jul 15 0 20 43.4 27.6 15.8 0.0

Sherwood Forest Jul 15 0 25 54.5 29.9 23.2 1.4

Sherwood Forest Jul 15 0 30 55.0 36.1 16.5 2.4

Sherwood Forest Jul 15 30 10 34.0 34.0 0.0 0.0

Sherwood Forest Jul 15 30 15 35.2 35.2 0.0 0.0

Sherwood Forest Jul 15 30 20 37.6 37.5 0.1 0.0

Sherwood Forest Jul 15 30 25 42.6 39.9 0.5 2.2

Sherwood Forest Jul 15 30 30 49.1 40.0 1.5 7.6

Table 1. Percent potential settlement of passive larval particles at simulation day 10, 15, 20, 25, and 30 by spawning location, date, and 

depth. Areas are described in Figure 2.
60

Figure 3. Spatial distribution of larval particles (red) at 25 days after spawning at the surface depth layer simulated with 

HYCOM model current vectors (model year 2008) for two spawning seasons and locations.

RNA Performance Topic 5: Assess reproductive potential of exploited species by evaluating egg production and larval dispersal
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 61

Literature Cited

Adams, A.J., Wolfe, R.K., Kellison, G.T., and Victor, B.C. 2006. 

Patterns of juvenile habitat use and seasonality by permit, Trachinotus falcatus. Environmental Biology of Fishes 

75:209–217.

Ault, J.S., ed. 2008. Biology and management of the world tarpon and bonefish fisheries. CRC Press/Taylor and Francis 

Group, Boca Raton, Florida.

Ault, J.S., Bohnsack, J.A., Smith, S.G., Luo, J. 2005. Towards 

sustainable multispecies fisheries in the Florida, USA, coral 

reef ecosystem. Bulletin of Marine Science 76:595–622.

Ault, J.S., Diaz, G.A., Smith, S.G., Luo, J., and Serafy, J.E. 

1999. An efficient sampling survey design to estimate pink 

shrimp population abundance in Biscayne Bay, Florida. 

North American Journal of Fisheries Management 19:696–

712.

Ault, J.S., Smith, S.G., Bohnsack, J.A., Luo, J., Harper, D.E., 

and McClellan, D.B. 2006. Building sustainable fisheries in 

the Florida coral reef ecosystem: Positive signs in the Dry 

Tortugas. Bulletin of Marine Science 78:633–654.

Ault, J.S., Smith, S.G., Meester, G.A., Luo, J., and Bohnsack, 

J.A. 2001. Site characterization for Biscayne National Park: 

Assessment of fisheries and habitats. NOAA Technical 

Memorandum NMFS–SEFSC–468.

Crabtree, R.E., Hood, P.B., and Snodgrass, D. 2002. Age, 

growth, and reproduction of permit (Trachinotus falcatus). 

Fishery Bulletin 100:26–34.

Domeier, M.L. and Colin, P.L. 1997. Tropical reef fish spawning aggregations: Defined and reviewed. Bulletin of Marine 

Science 60:698–726.

Graham, R.T. and Castellanos, D.W. 2005. Courtship and 

spawning behaviors of Carangid species in Belize. Fishery 

Bulletin 103:426–432.

Kourafalou V.H., Peng, G., Kang., H., Hogan, P.J., Smedstad, 

O.M., and Weisberg, R.H. 2009. Evaluation of Global 

Ocean Data Assimilation Experiment products on south 

Florida nested simulations with the Hybrid Coordinate 

Ocean Model. Ocean Dynamics 59:47–66.

Lee, T.N., Clarke, M.E., Williams, E., Szmant, A.F., and Berger, 

T. 1994. Evolution of the Tortugas Gyre and its influence 

on recruitment in the Florida Keys. Bulletin of Marine Science 54:621–646.

Lindeman, K.C., Pugliese, R., Waugh, G.T., and Ault, J.S. 2000. 

Developmental pathways within a multispecies reef fishery: Management applications for essential fish habitats 

and protected areas. Bulletin of Marine Science 66:929–956.

Schmidt, T.W., Ault, J.S. and Bohnsack, J.A. 1999. Site characterization for the Dry Tortugas region: Fisheries and essential habitats. Report to the Florida Keys National Marine 

Sanctuary and National Park Service. Homestead, Florida.

Smith, S.G., Ault, J.S., Bohnsack, J.A., Harper, D.E., Luo, J., 

and McClellan, D.B. 2011. Multispecies survey design for 

assessing reef fish stocks, spatially explicit management 

performance, and ecosystem condition. Fisheries Research

109:25–41.

Snodgrass, D. and Harndon, C.W. 2009. Composition of fish 

species on ocean-side beach habitats in the Florida Keys. 

Florida Scientist 72:153–170.
62

RNA Performance Topic 6 

Chapter 12: A survey of visitor demographics, attitudes, perceptions, and 

experiences at Dry Tortugas National Park

Investigators

David K. Loomis

East Carolina University, Institute for Coastal Science and 

Policy 

For further information contact: loomisd@ecu.edu

Project Description

This project will survey visitor demographics, attitudes, 

perceptions, and experiences of park resources among visitors who enjoy recreational boating, fishing, SCUBA diving, 

snorkeling, and other activities within Dry Tortugas National 

Park (DRTO), with emphasis on understanding the use of 

the Research Natural Area (RNA) (Performance Topic 6). 

In addition, surveys will include a geospatial assessment of 

geographic locations of these uses. The RNA science plan 

identifies the need to understand the behaviors and actions of 

park visitors, which have significant impacts on resources and 

the success of the RNA. Better understanding of the human 

dimension will greatly inform adaptive management efforts 

by the National Park Service (NPS) and the Florida Fish and 

Wildlife Conservation Commission (FWC) to evaluate the 

RNA and other park management zones. By characterizing 

visitors’ ecological knowledge and perceptions, NPS and 

FWC will improve education and outreach messages, encourage compliance with fishing and anchoring regulations, and 

enable visitors to protect the resources they enjoy. The survey 

questions will help elucidate heavily utilized areas within the 

park as well as highlight possible areas of user-group conflicts. 

Finally, NPS also seeks to measure visitor satisfaction and 

enjoyment after RNA implementation. The project is funded 

by the NPS service-wide recreational fee program and coordinated by the NPS Ocean and Coastal Resources Branch of the 

Natural Resource Program Center and DRTO.

Survey data will be collected through visitor contact, plus 

mail and electronic surveys. Separate surveys will be administered to visitors arriving either by commercial ferry or by private boat. Visitors will be contacted on-site and those agreeing 

to participate will complete a brief on-site contact sheet. The 

main survey questionnaire will be sent to these identified 

individuals within one month of being contacted and will be 

completed either by mail or electronically.

Results

East Carolina University and NPS collaborated to develop the 

quantitative survey questionnaires and methodology. Development of the two survey questionnaires has been completed. 

Separate survey questionnaires were designed for ferry passengers and for private boat operators. Prior research drawn 

from a wide array of social science literature, and discussions 

with park management, informed the design and format of 

specific questions. 

Regulations under the Paperwork Reduction Act require 

review by the Office of Management and Budget (OMB) on 

social science surveys as well as two opportunities for public 

notice and comment. The initial public notice was published 

in the Federal Register on May 6, 2009, with only one comment received during the 60-day comment period. The investigator working with NPS staff then submitted justifications 

and copies of the survey questionnaires as required by OMB. 

The Department of the Interior and OMB must review these 

materials before publication of the second and final 30-day 

opportunity for public notice and comment in the Federal 

Register and final approval. This process was recently completed and the final justifications and survey questionnaires 

have been submitted to OMB. Upon approval, the questionnaires will be ready for distribution at the park.

Performance Measure Evaluation

Each survey instrument is unique because of differences 

in opportunities for visitors arriving by ferry at Garden Key 

and arriving on private boats with greater access to marine 

resources. Each has an identical set of core questions followed by questions specific to primary recreational activity 

and location. The survey questionnaires will provide basic 

demographic information on the respondents; the frequency 

and extent to which respondents engage in different types of 

recreational activities; respondent experience level as anglers, 

divers, or in other activities; respondent perceptions of the 

RNA; respondent views on the ecological health of resources 

and the relative impacts of environmental stressors and recreational activities; respondents’ preferred sources of information; and factors such as ecological health and visitor crowding that diminish respondent enjoyment. 

Data collection will begin during the spring of 2012 and 

continue through November 2012. Our team will have a final 

report completed by October 2013.

RNA Performance Topic 6: Incorporate social sciences into the research and monitoring program
Implementing the Dry Tortugas National Park Research Natural Area Science Plan: The 5-Year Report 2012 63

This project will survey demographics, attitudes, perceptions, and experiences of park resources among visitors who enjoy recreational boating, fishing, SCUBA diving, snorkeling, and other activities within Dry Tortugas 

National Park, with emphasis on understanding the use of the Research Natural Area. Photo by Brett Seymour, 

Submerged Resources Center, NPS.

DRY TORTUGAS 

NATIONAL PARK

Naples 

Miami

Key West

Area of Detail

RESEARCH

NATURAL

AREA

FLORIDA KEYS NATIONAL 

MARINE SANCTUARY

TORTUGAS NORTH 

ECOLOGICAL RESERVE

TORTUGAS SOUTH 

ECOLOGICAL RESERVE

TORTUGAS BANK

OPEN USE AREA

North
South Florida Natural Resources Center

Everglades and Dry Tortugas National Parks

950 N. Krome Ave, 3rd Floor 

Homestead, FL 33030-4443

www.nps.gov/ever/naturescience/sfnrc.htm

www.MyFWC.com