POTENTIAL IMPACTS OF

C

U. S

National O

N

F ARTIFICIA

CONSERVA

Micha

. DEPARTM

Oceanic and

National Mar

Southeas

263 13th

St. Petersb

Jan

NOAA

AL REEF D

ATION IN FL

By 

ael C. Barnet

MENT OF C

d Atmospher

rine Fisherie

t Regional O

h

 Avenue So

burg, Florida

nuary 2017

A Technical 

d

DEVELOPM

LORIDA 

tte 

COMMERCE

ric Administ

es Service 

Office 

outh 

a 33701 

Memorandu

doi: 10.7289/V

MENT ON SE

E

tration 

um NMFS-S

5/TM-NMFS-S

EA TURTLE

ER-5 

ER-5

POT

Nat

U. S. DE

Penny Pr

NATION

Dr. Kathr

NATION

Eileen So

NOAA T

January 2

doi: 10.728

ENTIAL IM

tional Marin

EPARTMEN

ritzker, Secre

NAL OCEAN

ryn D. Sulliv

NAL MARIN

obeck, Assis

Technical Me

2017 

89/V5/TM-NM

MPACTS OF

C

ne Fisheries S

NT OF COM

etary 

NIC AND A

van, Admini

NE FISHER

stant Admini

emorandum 

MFS-SER-5

F ARTIFICIA

CONSERVA

Micha

Service, Sou

St. Petersb

MERCE 

ATMOSPHE

istrator

IES SERVIC

istrator for F

NMFS-SER

AL REEF D

ATION IN FL

ael C. Barnet

utheast Regio

burg, Florida

ERIC ADMIN

CE 

Fisheries 

R-5

DEVELOPM

LORIDA 

tte 

onal Office, 

a 33701 

NISTRATIO

MENT ON SE

263 13th Av

ON 

EA TURTLE

venue South
ii

NOTICE 

The National Marine Fisheries Service (NMFS) does not approve, recommend or endorse any 

proprietary product or material mentioned in this publication. No reference shall be made to 

NMFS or to this publication furnished by NMFS, in any advertising or sales promotion which 

would imply that NMFS approves, recommends, or endorses any proprietary product or 

proprietary material mentioned herein which has as its purpose any intent to cause directly or 

indirectly the advertised product to be used or purchased because of this NMFS publication. 

Recommended citation: 

Barnette, Michael C. 2017. Potential Impacts of Artificial Reef Development on Sea Turtle 

Conservation in Florida. NOAA Technical Memorandum NMFS-SER-5, 36 pp. 

Copies of this report may be obtained from: 

Michael C. Barnette 

National Marine Fisheries Service 

Southeast Regional Office 

263 13th Avenue South 

St. Petersburg, Florida 33701 

(727) 551-5794 

Michael.Barnette@noaa.gov 

Or online at: 

http://sero.nmfs.noaa.gov 

doi:10.7289/V5/TM-NMFS-SER-5
iii

TABLE OF CONTENTS 

TABLE OF CONTENTS ............................................................................................................... iii

LIST OF TABLES ......................................................................................................................... iv

LIST OF FIGURES ........................................................................................................................ v

ABSTRACT ................................................................................................................................... vi

ARTIFICIAL REEFS AND THEIR DEVELOPMENT IN FLORIDA ......................................... 1

SEA TURTLE UTILIZATION OF ARTIFICIAL REEFS ............................................................ 3

INCREASED PREDATION OF HATCHLINGS .......................................................................... 5

SEA TURTLE ENTRAPMENT IN ARTIFICIAL REEFS ........................................................... 7

SEA TURTLE ENTANGLEMENT IN ARTIFICIAL REEFS .................................................... 11

CONSERVATION IMPLICATIONS .......................................................................................... 19

MANAGEMENT RECOMMENDATIONS ................................................................................ 19

ACKNOWLEDGEMENTS .......................................................................................................... 21

REFERENCES ............................................................................................................................. 22
iv

LIST OF TABLES 

Table 1. Documented instances of sea turtle mortalities due to confirmed or suspected 

entrapment in artificial reef material or shipwrecks. ...................................................................... 7 

Table 2. Documented sea turtle entanglement or suspected entanglement issues on Florida 

artificial reefs and shipwrecks. An asterisk (*) indicates multiple observations of dead turtles at 

the same site—either at the same time or over time. .................................................................... 16

Table 3. Documented instances of sea turtle entanglement on natural bottom. .......................... 18
v

LIST OF FIGURES 

Figure 1. Map illustrating abundance of artificial reef material and shipwrecks off Florida, with 

over 7,000 sites in the author’s database. ....................................................................................... 2

Figure 2. Artificial reef site off Miami-Dade County, illustrating the density of materials in one 

discrete (~1.6 x 1.1 kilometer) area. ............................................................................................... 3

Figure 3. Loggerhead sea turtle resting under shipwreck material in approximately 30 m off St. 

Johns County. .................................................................................................................................. 4

Figure 4. Artificial reefs and shipwrecks off Tampa Bay, in relation to overlapping residence 

areas of individual adult female loggerhead sea turtles represented as counts of unique 

individuals within five kilometer hexagonal cells (from Hardy et al. 2014). ................................. 5

Figure 5. Map at left illustrating locations of documented sea turtle mortalities due to confirmed 

or suspected entrapment in artificial reef material or shipwrecks; at right, five mortalities 

associated with artificial reef modules off Escambia and Okaloosa Counties. The red symbols 

are the locations of artificial reef modules that present a high risk of sea turtle entrapment. ........ 7

Figure 6. Various artificial reef modules: at left, a modified fish haven with open top, while 

center and right are restricted top pyramid modules. ...................................................................... 8

Figure 7. Images of sea turtle skeletal remains under a fish haven module off Escambia County 

(Images courtesy of FWC Artificial Reef Program). ...................................................................... 9

Figure 8. Skeletal remains of a loggerhead sea turtle; note humerus bone still hanging in a loop 

of lost anchor line. ......................................................................................................................... 13

Figure 9. Loggerhead sea turtle entangled in an anchor line on World War II aircraft debris. 

Two weeks later there was no trace of the carcass or skeletal remains. ....................................... 14

Figure 10. Map illustrating locations of over 40 documented sea turtle mortalities due to 

confirmed or suspected entanglement in artificial reefs or shipwrecks. ....................................... 15

Figure 11. Images of two entangled sea turtles observed on the same day in 2006 on the 

“Pillsbury Wreck” off Manatee County. ....................................................................................... 17
vi

ABSTRACT 

Artificial reefs have been constructed and deployed worldwide to enhance marine habitat, 

primarily to increase socio-economic benefits stemming from associated fishing and diving 

activities, but also for habitat restoration and mitigation purposes. As a result, the majority of 

studies focused on artificial reefs to date have centered on measuring performance, with metrics 

such as species’ richness and abundance compared to natural reefs, or economic benefits to local 

users. While there may be demonstrable benefits to artificial reef development, there may also 

be unforeseen consequences. This study investigates the impacts Florida artificial reefs may 

have on sea turtle populations, such as increased predation stemming from altered predator 

complexes, mortality due to entrapment, and entanglement issues. Based on some of the 

associated effects artificial reef development may have on sea turtles, management 

recommendations to minimize potential impacts are offered for consideration. 
1

ARTIFICIAL REEFS AND THEIR DEVELOPMENT IN FLORIDA 

In its broadest sense, an artificial reef is any manmade structure that mimics the attributes of a 

natural reef. Florida Administrative Code Chapter 68E-9.002(2) defines an artificial reef as “one 

or more manufactured or natural objects intentionally placed on the bottom in predominantly 

marine waters to provide conditions believed to be favorable in sustaining, or enhancing the 

spawning, breeding, feeding, or growth to maturity of Florida’s managed reef associated fish 

species as well as to increase the productivity of other reef community resources which support 

fisheries. Included in this definition are artificial reefs developed with one or more of the 

following additional objectives: enhancement of fishing and diving opportunities, fisheries 

research, and fisheries conservation/preservation purposes.” The Florida artificial reef program 

is the largest and most active program in the United States. It is also unique in that it is not a 

singular program run by a state resource agency. Instead, artificial reef development in Florida 

occurs on the county level with funding and technical guidance provided by the Florida Fish and 

Wildlife Conservation Commission (FWC) Artificial Reef Program. 

The two primary goals of artificial reefs in coastal habitats have been to enhance the production 

of reef-associated species (i.e., macroalgae, invertebrates, and fishes) and to increase the 

convenience or efficiency of harvesting those species (Seaman et al. 1989; Seaman and Sprague 

1991; Pratt 1994, Carr and Hixon 1997). Shipwrecks in particular have long been noted to 

attract marine wildlife and provide exceptional fishing sites. In fact, several fishing piers in 

North Carolina were constructed over the sunken hulls of Civil War blockade runners in the 

1930s and 1940s to take advantage of the submerged structure and facilitate recreational fishing 

activities (Wilde-Ramsing and Angley 1985). lnterest in formal artificial reef development in the 

United States began in the 1950s and was primarily driven by recreational fishermen (Jørgensen 

2009). The scuttling of the 56 meter (m) long former yacht Mizpah in April 1968 off Palm 

Beach could be considered the start of official artificial reef development in Florida, though 

other vessels and materials were intentionally sunk years before, unpermitted and clandestinely. 

In subsequent years, artificial reef activities in Florida would significantly expand. 

As of October 2015, the various Florida county artificial reef programs have deployed more than 

627,497 tons of concrete material and 258,817 tons of limestone rock and rubble, as well as over 

18,769 prefabricated artificial reef modules and 513 vessels in coastal waters (FWC database 

2015). In addition, there have been several hundred small, “private reefs” deployed off 

Escambia, Okaloosa, and Bay Counties in the Florida Panhandle, as well as countless more 

unpermitted, covert deployments of various materials elsewhere off Florida, not to mention 

thousands of Florida shipwreck events that have transpired throughout history (Figure 1). In 

some permitted artificial reef areas, the amount of material can be quite dense (Figure 2). 
Figure 1

over 7,00

. Map illust

00 sites in th

rating abund

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ance of arti

atabase. 

2

ficial reef material and shipwrecks off Florida, with 
Figure 2

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shallow, nearshore waters just off the nesting beach due to an abundance of predators 

(Witherington and Salmon 1992, Gyuris 1994). Mortimer (1982) suggested that the intensity of 

predation in these nearshore waters may be influenced by the type of habitat hatchlings must 

cross. Generally, more structurally complex habitats are likely to have greater species diversity 

and abundance, including predatory species (e.g., barracuda, shark, jacks, snapper, etc.) than less 

complex habitats (Mortimer 1981, Tews et al. 2004, Cole 2012). Therefore, it has been 

postulated that nearshore artificial reefs sited directly off nesting beaches could increase 

hatchling predation due to the anticipated habitat enhancement of deployed reef material. 

Several studies have investigated sea turtle hatchling predation over various habitat types. 

Gyuris (1994) found significant mortality of green sea turtle hatchlings crossing reef habitat off 

Heron Island, Queensland, Australia. Predation rates varied among trials (combinations of tide, 

time of day, and moon phase) that used 1,740 tethered and 57 free-swimming hatchlings, ranging 

from 0% to 85% with a mean of 31% for tethered hatchlings and 93.6% for free-swimming 

turtles. Observations of the free-swimming hatchlings noted that many of the successful 

predation events were preceded by attacks from fish too small or weak to be successful. 

Conversely, numerous studies off Florida have found much lower predation rates on sea turtle 

hatchlings over a variety of habitats. Witherington and Salmon (1992) evaluated three sites off 

the central east coast of Florida that possessed different offshore habitat characteristics: 

saballerid reef 130-170 m offshore, occasional low-profile patch reefs, and uniform sand bottom. 

Although the sample sizes were small, observed predation rates were 13.6% for the saballerid 

reef sites, 6.3% for the patch reef sites, and 0% for the sand sites. Glenn (1996) reported 9% of 

hatchlings crossing patch reef were taken by predators, while only 4.5% of hatchlings were lost 

to predators crossing over sand bottom; interestingly, no predation was observed over submerged 

breakwaters. Likewise, Stewart and Wyneken (2004) examined predation rates of hatchlings 

crossing over sand, nearshore reef, and transitional areas of sand and rock. Resulting predation 

rates were 2.7% for transitional sites, 4.3% at sand sites, and 8.1% at reef sites. Although the 

differences in rates were not found to be significant, hatchling predation was greater at reef sites 

when compared to the sand and transitional sites. 

Evaluating predation over a larger area, Whelan and Wyneken (2007) investigated sites on both 

the east and west coasts of Florida. The study included a nesting beach on Hutchinson Island 

with a nearshore area consisting of sand and patches of sabellarid reefs, a beach at Boca Raton 

with sandy bottom and bands of nearshore reef, and a site at Naples characterized by a nearshore 

homogenous sand bottom. The authors documented a significant difference in total hatchling 

predation rates between the Boca Raton site (9%) with adjacent reef habitat and their Naples site 

(1%) that was composed entirely of sand; predation at Hutchinson Island with mixed benthic 

habitat was 3%. Specific to predator assemblages at the various sites, the authors documented 

tarpon (Megalops atlanticus), snappers (lutjanids), and jacks (carangids) at both their Boca Raton 

and Hutchinson Island sites, but only common snook (Centropomus undecimalis) at their Naples 

site. The lack of predator diversity can be directly attributed to the general paucity of significant 

nearshore bottom structure along large swaths of the Florida west coast. While there appears to 

be a direct correlation between predation rates and benthic habitat adjacent to nesting beaches, 

Whelan and Wyneken (2007) also offered other factors that could influence the results including 

water clarity, water depth, temporal differences in nesting and migratory predatory fish 

populations, photopollution, and hatchling orientation. 
Artificial

sand bott

goal of ar

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effects co

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As previo

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habitat. A

unable to

documen

Lum 200

sea turtle

Table 1. 

entrapme

SPECIE

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UNKNOWN 

LOGGERHE

UNKNOWN 

LOGGERHE

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LOGGERHE

HAWKSBILL

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Figure 5

or suspec

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2002 

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TRAPMENT

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MATERIAL 

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HAVEN MODULE 

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g locations o

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re waters con

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FICIAL RE

end a signifi

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COUN

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of documente

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icant amount

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due to confi

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ROE DECOM

MBIA SKEL

MBIA DECOM

MBIA SKEL

MBIA DECOM

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ed sea turtle 

pwrecks; at r

Okaloosa C

high risk of 

redominately

ndance—that

redation risk

urtle nesting 

s into consid

as discussed

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le to drowni

ergence has b

Poiner and H

us document

hing (Table 1

irmed or sus

DITION 

H DEAD 

PECIFIED LUKE

MPOSING 

LETAL 

MPOSING 

LETAL 

MPOSING 

H DEAD 

H DEAD 

mortalities d

right, five mo

Counties. Th

sea turtle en

y homogeno

t is the desir

k of hatchlin

beaches. Th

eration the i

d later in the

derwater rest

as sheltering

ing if they ar

been 

Harris 1996,

ted incidents

1, Figure 5).

spected 

SOURCE 

STSSN 

ENS AND SELBERG

AUTHOR 

FWC 

R. TURPIN 

PATTERSON 2010

PATTERSON 2010

STSSN 

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1989 Sea T

t. Lauderdal

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sses of a Wo

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no mention o

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hawksbill se

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vidence that t

king. 

ven with ope

ve (i.e, DC-3

t of a sea turt

door of the 

pe through th

001 when the

rld War II 

or of the wrec

he sea turtle 

drowning. I

ge and no lo

h artificial re

tions) that 

duced, in 

later in this 

based on a la

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of entanglem

, ~10 m long

aningful inte

0 STSSN rep

ea turtle foun

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the death of 

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tle in 

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ack 

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Figure 7

(Images c

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deployment 

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a turtle entra

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nattractive to

as compare

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e
10

Network database. Compounding these issues is the fact that evidence of a mortality event may 

not be easily recognized, particularly if skeletal remains are scattered and get sanded over. 

Lastly, artificial reef monitoring effort is generally low. In 2015, there were only 39 FWC and 

78 county, university, and non-governmental organization site monitoring surveys conducted on 

artificial reefs across Florida. This low effort makes detection of these mortality events 

extremely unlikely. Yet, some records of these events do exist and entrapment could present a 

significant source of mortality on adult sea turtles. Additional research, however, is needed to 

investigate this issue. 

As mentioned, there is a general paucity of published data on sea turtle interactions—specifically 

entrapment—with artificial reefs; however, Patterson (2010) does provide some insight into this 

issue while examining the ecological function of unreported artificial reef modules deployed off 

the Florida Panhandle in 2003. During 2009-2010, surveys were conducted quarterly on 27 total 

sites comprising three designs: nine sites with single pyramid modules 3.05 m in height; nine 

sites with two fish haven modules, each 1.83 m in height; and nine sites with two reef ball 

modules, each 1.45 m in height. The pyramid design had an open bottom and a closed top, while 

the fish haven had an open bottom and a small open top; these designs are considered high risk 

for sea turtle entrapment due to the likelihood an adult turtle would be unable to exit if it had 

gained access to the interior. In contrast, the reef balls, while having small openings in the sides 

and top to allow fish entry/exit, have closed bottoms to prevent sea turtle access to the interior. 

During the survey period, Patterson (2010) recorded 15 sea turtle observations, 10 of which were 

unique entries, and two sea turtle mortalities; repeated observations of dead, decomposing, or 

skeletal remains comprised six entries from two separate modules. Five of the unique sea turtle 

entries were identified as loggerheads, three as greens, and two were unknown species. Both sea 

turtle mortalities were associated with the pyramid design, yet one of the documented mortalities 

was already skeletal upon the module’s first survey in 2009. Because the turtle was already 

skeletal at the start of the survey year, even though the cause of death is suspect due to the 

turtle’s proximity to a single artificial reef module, it will be excluded when calculating a 

proposed mortality rate. Based on the total number of observations on all artificial reef modules 

during the period, assuming all mortalities were observed during that year, there was a 0.556% 

documented annual mortality rate (1 mortality / 45 total modules x 4 surveys per year). This 

includes the reef ball modules that present no risk to sea turtle mortality through entrapment. 

Therefore, to get a more accurate estimate of sea turtle mortality due to entrapment, I now 

exclude those modules (1 mortality / 27 total modules x 4 surveys per year), resulting in a 

0.926% mortality rate for the pyramid and fish haven modules. Patterson (2010) estimated 

annual mortality differently. Using data collected from 2004-2010, he documented 23 unique 

sea turtle observations from a total of 513 surveys, resulting in 4.5% of all surveys having turtles 

present. Extrapolating that out over the entire 5.5-year period with the two observed mortality 

incidents, he calculated a 0.015% (95% CI = 0.011-0.024%) annual mortality rate for all artificial 

reef modules combined (i.e., including the no-entrapment risk reef balls). It is worth noting that 

almost half (43.5%) of all unique sea turtle observations occurred in the last year of the study. 

This may be a result of the artificial reef sites “maturing” since their 2003 deployment, sea 

turtles increasingly utilizing the artificial reefs, changes in local sea turtle populations, or some 

other factor. Regardless, I believe the 0.926% mortality rate is more appropriate for calculating 

mortality associated with high-risk artificial reef modules. Therefore, based on the 2,924 total 
11

estimated high-risk modules permitted and deployed in Florida waters, I estimate 27 sea turtles 

may be entrapped and drowned per year as a result of these deployed artificial reef modules. As 

sea turtle populations change and modules deteriorate, this estimate may change over time. 

Furthermore, there is much uncertainty in this estimate, as the underlying data are based on a 

single study conducted in the Florida Panhandle. 

These documented issues have been presented to the U.S. Army Corps of Engineers, which 

issues permits to establish or enhance artificial reef sites, as well as to FWC and private artificial 

reef companies. FWC and the artificial reef companies have implemented new measures to 

address these concerns in Florida. Specifically, they have required new open-bottom pyramidstyle modules that have their tops removed to allow sea turtles to exit the module’s interior. 

While intentionally deployed material intended to enhance habitat and local ecosystems may 

have deleterious effects on threatened and endangered species, sea turtles have been documented 

to drown after becoming entrapped in natural habitat as well, such as in the numerous submerged 

sinkholes and caves off Florida. Both fresh dead and skeletal remains of sea turtles were 

documented in 2007-2009 at a cave aptly named Dead Turtle Cave in approximately 37 m of 

water off Pinellas County, and a dead turtle was also found inside Glory Hole, a submerged sink 

hole in approximately 22 m of water off Pasco County. In both instances, it was assumed the 

turtles entered the cave entrances and proceeded farther into the caves’ periphery, but were 

unable to exit either due to constrictions or absence of ambient light to indicate the point of 

egress (J. Culter, personal communication, March 17, 2016). 

Entrapment in artificial reefs, notably in certain prefabricated module designs, has been 

documented as a source of mortality for sea turtles in Florida waters. While the identified highrisk module designs are no longer used in Florida, they are used in other states and in other parts 

of the world. Furthermore, the 2,924 permitted high-risk modules previously deployed off 

Florida will likely maintain their structural integrity for several more decades. Sea turtles will 

continue to interact with these modules, and it is possible entrapment mortality events may occur 

well into the future at some level. The majority of these high-risk modules have been deployed 

off the Florida Panhandle (Figure 5). Thus, given some of the modules’ proximity to sea turtle 

nesting beaches, there may be additional cause for concern if female sea turtles utilize them 

during inter-nesting periods (Hart et al. 2013). 

SEA TURTLE ENTANGLEMENT IN ARTIFICIAL REEFS 

Artificial reefs attract fishermen—that is one of the primary goals of artificial reef development. 

In turn, fishing activities on artificial reefs and shipwrecks invariably attract monofilament and 

anchor lines that get fouled on the material. Over time or with significant fishing pressure, 

monofilament and other lines can accumulate significantly on these structures, which now 

present a threat to sea turtles utilizing artificial reefs and shipwrecks as resting habitat. Sea 

turtles wedging themselves under structure to rest may encounter lost monofilament or anchor 

lines, which could become wrapped around a flipper or neck. If the line is fouled securely into 

the artificial reef or shipwreck, an unfortunate sea turtle may become effectively anchored to the 

bottom, unable to surface and breathe, and ultimately drown. Carr (1987) noted that sea turtles 

are “peculiarly prone to...tangle themselves in lines and netting discarded by fishermen, and 
12

records of such mishaps have increased markedly in recent years.” Concern has been expressed 

that entanglement on artificial reefs and shipwrecks may be a source of mortality not previously 

recognized, particularly given that it is not well represented by available sea turtle stranding data 

(Foley et al. 2008). 

Monofilament line is a prevalent form of marine debris and pollution, and entanglement in 

marine debris is a global problem affecting at least 200 marine species (NOAA 2014); all seven 

species of sea turtle have been reported entangled in marine debris globally (SCBD 2012). 

Balazs (1985), in one of the first comprehensive reviews examining the issues of marine debris 

as it relates to sea turtles, compiled 60 total documented incidents worldwide. Out of those 

incidents, 53 were likely fishery-related and 17 of those were cited as either “fishing line” or 

“monofilament line.” For several cases, there was evidence that the turtles had become 

entangled in lost line snagged on the bottom. In contrast to this current study, only 38% of the 

entangled turtles in Balazs (1985) were dead or later died, though that is likely a significant 

artifact of the data availability from that study. 

Foley et al. (2008) noted that monofilament line was the most common form of pollution found 

associated with stranded sea turtles (i.e., dead, injured, sick, tumored, or otherwise abnormal and 

sometimes seemingly normal and out of the water, usually along the shoreline) in Florida; during 

the period 1980-2007, 852 stranded sea turtles were found to have been entangled in or to have 

ingested monofilament fishing line. And the number and percentage of stranded sea turtles 

entangled in monofilament line has increased over that time (Foley et al. 2008). Sea turtle 

entanglement on artificial reefs and shipwrecks is highly unlikely to be captured in sea turtle 

stranding records due to the turtle’s carcass effectively being anchored to the wreck and unable 

to wash ashore. Therefore, the significance and potential scale of this issue has eluded proper 

recognition and consideration. Furthermore, there are other circumstances that make observation 

of these interactions even more problematic. 

Irrefutable evidence that entanglement is the source of mortality depends in large part on 

availability of a carcass anchored to an artificial reef or shipwreck by monofilament or other line. 

Decomposition of the carcass can erase that evidence in relatively short order. Rate of 

decomposition in sea turtles varies by water temperature, predation, sea turtle size, exposure, and 

other factors. There is little information in regards to sea turtle decomposition rates, particularly 

fully immersed sea turtles. Five turtles entangled in Virginia pound net leaders were examined 

during 1984 and none of these turtles became disentangled by natural causes, but instead 

completely decomposed in situ within five weeks (Bellmund et al. 1987). In 2002 and 2003, 

NOAA Fisheries observers left three documented dead entangled sea turtles in Virginia pound 

net leaders to monitor decompositional status. Initially, these turtles were fresh dead to 

moderately decomposed. One of the turtles was gone when observed three days later, another 

fell out after nine days when its flipper tore away from its body, and another turtle was still in the 

pound net leader five days later but in a severely decomposed condition (NMFS 2004). Higgins 

et al. (2007) documented the varying rate of decay in freshly dead juvenile Kemp’s ridley sea 

turtles positioned in the Texas surf zone. They found that a juvenile sea turtle went from fresh 

dead (Code 1) to clean bones (Code 5) in 4 days in warm water (33-34°C water temperature), 

and 12 days to decompose similarly in colder water (14-21°C water temperature). It was also 

noted that the production of decompositional gasses, which results in the carcass becoming 
positively

versus fiv

19-24°C 

anchored

days of m

While it m

less so w

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become c

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Figure 8

of lost an

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mortality. 

may be easy

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13

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14

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turtles and a

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usia County i

5 m in lengt

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the short 

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adequately 

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researchers, 

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Duval, Escam

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Figure 1

confirme

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ilament line,

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ity of these w

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in Alabama)

over time. T

rs not interve

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 8 were due 

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ment in artif

15

natee, Martin

ure 10). Of t

to ropes or a

tries listed th

ted with ske

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ttributed to a

intentionally

ites were ass

s reported mu

documented 

moved the en

er 40 docume

ficial reefs or

n, Monroe, M

the reported 

anchor line, 

he entanglem

eletal sea turt

on identified 

f the records

a vessel lost 

y deployed a

sociated with

ultiple turtle

entanglemen

ntanglement

ented sea tur

r shipwrecks

Miami-Dade

sources of e

4 were asso

ment source 

tle remains i

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s, followed b

in 1872 (obs

as an artificia

h permitted 

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nt interaction

t, the turtles 

rtle mortaliti

s. 

, Palm Beac

entanglemen

ociated with t

as unspecifi

in proximity

pecies, 

by green and

servation ma

al reef in 200

artificial ree

, either from

ns occurred 

would likely

ies due to 

h, 

nt, 14 

trawl 

ied or 

y to 

d

ade 

07 

efs 

m the 

with 

y
16

SPECIES YEAR LOCATION COUNTY YEAR SUNK CAUSE CONDITION 

LOGGERHEAD ~1985-95 KATHY* MONROE UNKNOWN TRAWL NET; MONOFILAMENT LINE SKELETAL DEAD UNKNOWN ~1985-95 BELLATRIX* MONROE 1964 NOT SPECIFIED SKELETAL DEAD UNKNOWN ~1985-95 BIG RED* MONROE 1970 NOT SPECIFIED SKELETAL DEAD LOGGERHEAD 1989 “ARTIFICIAL REEF” MARTIN UNKNOWN MONOFILAMENT LINE FRESH DEAD LOGGERHEAD 1994 WRECK LEE UNKNOWN ROPES DECOMPOSING LOGGERHEAD 1996 AMAZONE MARTIN 1942 LONGLINE MONOFILAMENT LINE FRESH DEAD UNKNOWN; LOGGERHEAD 2000-08 JOSEPH M. CUDAHY* MONROE 1942 TRAWL NET SKELETAL DEAD LOGGERHEAD 2000 SHRIMP BOAT FRANKLIN UNKNOWN TRAWL NET FRESH DEAD LOGGERHEAD 2000 VICTOR PALM BEACH 1872 ROPE DECOMPOSING LOGGERHEAD 2002 HALSEY ST. LUCIE 1942 ANCHOR LINE; MONOFILAMENT LINE FRESH DEAD LOGGERHEAD ~2003 GWALIA HERNANDO 1925 TRAWL NET FRESH DEAD LOGGERHEAD ~2004 PECK BARGE MARTIN 1986 GILL NET DECOMPOSING UNKNOWN; LOGGERHEAD 2004-2007 D-9 CRANE BARGE* SARASOTA UNKNOWN MONOFILAMENT; NOT SPECIFIED SKELETAL DEAD; DECOMPOSING LOGGERHEAD 2005 LESLIE BREVARD 1942 MONOFILAMENT LINE FRESH DEAD GREEN; LOGGERHEAD 2006-2009 PILLSBURY* MANATEE UNKNOWN MONOFILAMENT LINE; UNKNOWN FRESH DEAD HAWKSBILL 2007 AMARYLLIS PALM BEACH 1968 MONOFILAMENT LINE ALIVE LOGGERHEAD; UNKNOWN 2006-15 BAYRONTO* LEE 1919 UNKNOWN SKELETAL DEAD LOGGERHEAD 2007 BAJA CALIFORNIA MONROE 1942 ANCHOR LINE SKELETAL DEAD LOGGERHEAD 2008 MARCO PASS BARGE COLLIER 1987 CAST NET FRESH DEAD LOGGERHEAD 2009 MEISNER CRANE HERNANDO 1982 ANCHOR LINE OR ROPE FRESH DEAD LOGGERHEAD 2009 MEISNER BOX HERNANDO 1982 UNKNOWN SKELETAL LOGGERHEAD 2009 SULPHUR BARGE HILLSBOROUGH UNKNOWN ANCHOR LINE ALIVE LOGGERHEAD 2010 WWII AIRCRAFT VOLUSIA 1944 ANCHOR LINE FRESH DEAD UNKNOWN ~2011 PASCO SITE 2 PASCO 1980s UNKNOWN DECOMPOSING LOGGERHEAD; UNKNOWN 2011 BARBARA ANN* BREVARD 1990 UNKNOWN SKELETAL DEAD HAWKSBILL 2011 BRAZILIAN DOCKS PALM BEACH 1994 MONOFILAMENT LINE FRESH DEAD UNKNOWN 2012 RONALD B. JOHNSON BROWARD 1988 UNKNOWN SKELETAL DEAD SUSPECTED GREEN 2012 CASA BLANCA DUVAL 1972 MONOFILAMENT LINE FRESH DEAD UNKNOWN ~2013 WEE-II BREVARD UNKNOWN UNKNOWN SKELETAL DEAD UNKNOWN ~2013 MOORE WRECK BREVARD 1980s UNKNOWN SKELETAL DEAD UNKNOWN ~2013 STINK BOX* BREVARD 1980s UNKNOWN SKELETAL DEAD LOGGERHEAD 2013 TENNECO TOWERS BROWARD 1985 MONOFILAMENT GILL NET SKELETAL DEAD LOGGERHEAD 2013 FIN BARGE MANATEE UNKNOWN UNKNOWN DECOMPOSING LOGGERHEAD 2013 SAN PABLO ESCAMBIA 1944 MONOFILAMENT LINE DECOMPOSING LOGGERHEAD 2013 ALLEN LIBERTY SHIP ALABAMA 1975 UNKNOWN DECOMPOSING UNKNOWN 2013 ANNA DUVAL 1986 UNKNOWN SKELETAL DEAD LOGGERHEAD 2014 COMMODORE VOLUSIA 1897 MONOFILAMENT LINE FRESH DEAD UNKNOWN 2014 KORIMU PALM BEACH 2007 UNKNOWN SKELETAL DEAD LOGGERHEAD 2015 BARGE DUVAL UNKNOWN MONOFILAMENT LINE FRESH DEAD LOGGERHEAD 2015 NARWAL MIAMI-DADE 1986 ANCHOR LINE FRESH DEAD 

Table 2. Documented sea turtle entanglement or suspected entanglement issues on Florida artificial reefs and shasterisk (*) indicates multiple observations of dead turtles at the same site—either at the same time or over time.
Based on

turtle ent

however,

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17

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not a system

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i-Dade Coun

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tles seem to p

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and report e

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vessel struct

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day in 2006 

9, it is possib

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ida—an area

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active artific

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r 2015). Yet

unties. There

ing habitat to

of the Florid

nofilament fr

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habitat; visibi

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e vessels hav

ture is found

ull/seabed 

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wimming, the

agged 

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18

low-relief material, particularly where numerous turtles have been observed over time, it is 

important to remember that collapse of all artificial reef materials, particularly vessels, is 

inevitable. Therefore, sea turtle entanglement on these sites may become a more significant 

issue as the sites mature and deteriorate in the future. 

Entanglement in lost or discarded monofilament line, ropes, or netting on an artificial reef or 

shipwreck is a form of ghost fishing, a significant issue that has been examined in other contexts 

(Laist 1996). But little has been done to date specific to artificial reefs. Matsuoka et al. (2005) 

noted that gill nets tangled around artificial reefs continued ghost fishing for a much greater 

extent of time compared to gill nets lost on flat bottom. In that study, they experimentally 

tangled a monofilament gill net on an artificial reef and it was found to still maintain ghost 

fishing mortality after three years, even though the netting was heavily fouled. This was further 

demonstrated when an apparently discarded gill net became fouled on the “Tenneco Towers” 

artificial reef site off Broward County in 2013. After becoming snared on the artificial reef 

structure, the netting continued to trap and kill marine life, including a loggerhead sea turtle. 

Given the complex habitat and vertical relief afforded by artificial reefs and shipwrecks, it is not 

uncommon for these sites to accumulate significant amounts of lost gear over time. 

As with the entrapment issues discussed earlier, there have been a few instances of sea turtles 

becoming entangled in monofilament on natural bottom as well (Table 3). The two entangled 

turtles noted as alive were anchored to the bottom by the gear and would likely have drowned if 

it were not for diver intervention. While entanglement issues can occur on natural bottom, it 

does not appear to be as significant a problem compared to more complex artificial habitat. 

Artificial reefs typically have more relief, are more discrete compared to larger ledge, reef, and 

hard bottom areas, and, based on the material (e.g., metal), can more easily part fishers’ lines. 

Furthermore, many artificial reefs are deployed and advertised to enhance fishing opportunities, 

thereby potentially attracting and accumulating more monofilament and anchor lines. These 

factors help explain the significant difference in observations of entangled sea turtle observations 

made on artificial reefs and shipwrecks versus natural bottom. 

Table 3. Documented instances of sea turtle entanglement on natural bottom. 

SPECIES YEAR SITE DESCRIPTION COUNTY CONDITION SOURCE 

LOGGERHEAD 1978 WARSAW HOLE - LEDGE BAY FRESH DEAD BALAZS 1985 

HAWKSBILL 2008 LYNN’S REEF PALM BEACH FRESH DEAD M. TRUST 

HAWKSBILL 2009 JUNO LEDGE PALM BEACH ALIVE L. WOODS 

GREEN 2011 BOYNTON REEF PALM BEACH ALIVE REEF RESCUE WEBSITE 

Given the lack of regular monitoring on the thousands of artificial reef and shipwreck sites 

across Florida, it is not possible to quantify the number of sea turtle mortalities that could be 

occurring every year. Given the available information presented here, entanglement on artificial 

reefs and shipwrecks may well be a significant source of previously unreported mortality. 

Insight gleaned from other information sources also lends credence to this theory. An ongoing 

goliath grouper research project off the central west coast of Florida has conducted 441 surveys 

on artificial and natural habitat from 2007-2015. During the course of those surveys, seven 

incidents of sea turtle mortality confirmed or suspected to be a result of entanglement were 

documented; six were on artificial reefs or shipwrecks (A. Collins, personal communication, 

April 29, 2016). While not directly germane to the issue of artificial reefs, Bjorndal and Bolten 
19

(1995) examined the prevalence of entanglement in sea turtles. In studying a pelagic loggerhead 

population in the Azores, they concluded that over 6% of 800 turtles dip-netted during tuna 

fishing operations in that area were entangled in debris. Similarly, they received more than 

1,500 sea turtle observations throughout the world, in which 5% of those reports noted negative 

impacts by marine debris. 

Even with low anticipated mortality rates, given the thousands of artificial reef and shipwreck 

sites off Florida that are constantly “fishing” due to the accumulation of monofilament and other 

entangled lines, it is likely these sites account for significant numbers of sea turtle mortalities 

every year. As these materials have effective lifespans well over 100 years, it is clear this is a 

sea turtle conservation issue that perhaps deserves more research attention. On a global 

perspective, the cumulative impact on sea turtle populations is certainly of consequence. 

CONSERVATION IMPLICATIONS 

Given the number of observed sea turtle mortalities associated with artificial reefs, this issue may 

be a significant source of mortality previously unreported. It is unclear just how significant the 

level of mortality may be, either on an individual site, regionally, or globally. Given analysis of 

other activities, such as U.S. Army Corps of Engineers (USACE) dredging activities, artificial 

reef associated mortality is almost certainly not trivial. For example, in 2015 all USACE 

dredging projects from Texas through North Carolina, which have significant required 

monitoring oversight, documented only 12 lethal sea turtle takes. Regardless, as Balazs (1985) 

noted, “Considered separately, each of these lesser known impacts may not necessarily cause 

high rates of mortality or morbidity. However, their combined effect over an extended period 

could very well be a significant retardant to the recovery of certain populations. It is, therefore, 

imperative that each adverse element be adequately examined and understood.” 

It would appear from the compiled reports (Table 1), that loggerhead sea turtles may be 

especially vulnerable to the deleterious side effects of artificial reefs and shipwrecks, which may 

be associated with the species’ habitat preferences. At this time, there is insufficient information 

to quantify or further refine these mortality threats. It is conceivable that entrapment and 

entanglement of adult loggerhead sea turtles in artificial reefs could negatively impact local 

populations, particularly if there are regional differences in the effects that could selectively 

impact females from smaller nesting populations (e.g., Florida Panhandle) or recovery units (e.g., 

Northern Gulf of Mexico Recovery Unit). Further investigation is definitely warranted. 

MANAGEMENT RECOMMENDATIONS 

The following recommendations are based on the above analyses and offered for consideration in 

future artificial reef planning. They are focused solely at reducing potential sea turtle mortality 

associated with artificial reef development and do not factor in other concerns, such as enhancing 

marine habitat or maximizing socio-economic benefits from use of artificial reefs. 
20

MINIMIZING EFFECTS OF HATCHLING PREDATION 

Hatchling sea turtles exhibit a “frenzy” period of swimming once in the water, whereupon they 

swim almost constantly in an offshore direction. For loggerhead sea turtles, this behavior likely 

serves to quickly extricate the hatchling from shallow coastal waters where predators may be 

more abundant (Wyneken and Salmon 1992) and disperse them into offshore waters that 

constitute their juvenile epipelagic habitat. Using the maximum documented swimming speed of 

0.36 m/sec for hatchling loggerheads during their frenzy period (Salmon and Wyneken 1987; 

Witherington 1991) and based on an observed reduction of predation after 15 minutes of 

swimming from the beach (Glenn 1996, Wyneken and Salmon 1997, Wyneken et al. 2000, 

Stewart and Wyneken 2004), it is anticipated that initial hatchling predation rates, on average, 

should be reduced approximately 324 m off the nesting beach. Therefore, for any nearshore area 

that predominantly consists of sand and is directly offshore an identified nesting beach, at a 

minimum artificial reef development should be precluded within a 324 m buffer zone extending 

from the beach to avoid potential issues with increased predation of sea turtle hatchlings. 

Because artificial reef development is not expected to dramatically alter the predator complex in 

nearshore areas directly off nesting beaches that already have hard bottom or reef habitat in the 

immediate vicinity, a buffer would not be necessary in those areas. 

MINIMIZING ENTRAPMENT 

Prefabricated modules such as open-bottom, closed-top pyramids can allow sea turtles to gain 

access to the interior and potentially drown. These modules should not be utilized due to this 

documented risk. Instead, solid or closed-bottom modules should be the standard parameters for 

prefabricated modules. Modified designs, such as open-top fish haven modules could also be 

considered as low risk, if the opening in the top is sufficient to allow an adult sea turtle to escape. 

For triangular modules, that opening should be a minimum of 4 feet on each side. Due to the 

lack of documented or anticipated interactions between artificial reef modules and leatherback 

sea turtles, this study employs a conservative opening size based on the maximum observed 

carapace width for loggerhead sea turtles (K. Hart, personal communication, May 9, 2016). It is 

also important that these modified modules not retain any lifting point lines that may restrict the 

module’s opening at the top. Materials such as rock, rubble, and some secondary-use concrete 

materials also could be considered for preferential use due to an anticipated absence of 

entrapment hazards. 

MINIMIZING ENTANGLEMENT 

Managers should consider the type and location of material that is deployed for artificial reef 

purposes. For example, use of vessels or metal structure in areas devoid of other habitat may 

initially introduce an oasis for marine life. Over time, however, the introduction and 

accumulation of monofilament and other lines presents a threat to sea turtles that could result in 

entanglement and drowning. Therefore, other materials such as rock and rubble, or low-profile 

artificial reef modules like reef balls, may result in a reduced likelihood of lost fishing gear, 

which, in turn, may reduce the likelihood of sea turtle entanglement. Even secondary-use 

concrete materials such as storm-water structures, highway barriers, and bridge material absent 

of any exposed rebar may present a lower risk to sea turtles compared to vessels. In 2014, an 
21

entangled sea turtle was noted on a historic shipwreck (i.e., foundered in 1897) site off Volusia 

County that had been expanded to include an abundance of concrete culverts immediately 

adjacent to the wreck. Little to no monofilament line was noted on the culverts, yet snagged 

tackle on the scant remains of the Commodore was sufficient to result in the drowning of a small 

loggerhead sea turtle. While vessels provide abundant and complex habitat, present a large 

target for fishermen to locate, and are generally more attractive for recreational divers, they 

typically accumulate significant amounts of fouled monofilament line and ultimately will 

deteriorate, which is expected to increase the entanglement risk to sea turtles. Therefore, the use 

of vessels as artificial reefs should be carefully considered, particularly if the proposed site is 

adjacent to nesting beaches or is located in proximity to identified sea turtle critical habitat. 

Perhaps a more practical action that can reduce sea turtle entanglement risk is to require periodic 

artificial reef cleanup activities to remove monofilament and other lines entangled on artificial 

reef structure. As discussed earlier in this analysis, all it takes is one line to result in sea turtle 

mortality due to entanglement. Therefore, while reef cleanup activities would not totally 

eliminate the entanglement risk presented by lost line, it may help reduce the risk presented to 

sea turtles. Obviously, these activities would largely be restricted to recreational diving depths 

(i.e., ≤ 40 m). Therefore, managers may also want to reconsider deploying artificial reef material 

in deeper waters where sea turtles occur, but where monofilament line could significantly 

accumulate unabated. 

REPORTING 

Observations of dead sea turtles by recreational divers have not typically been reported, perhaps 

due to a lack of knowledge of where to submit such information. In some instances, it was 

reported that calls were made to the U.S. Coast Guard, FWC law enforcement, or county 

officials, all of whom (depending on the person or office that was contacted) were perhaps not 

the ideal principal contact or responder. Furthermore, those calls or information were not 

forwarded so that the information could be captured by the STSSN. Outreach similar to what 

has been conducted for incidentally captured sea turtles on fishing piers or for public sawfish 

sightings could be pursued. In addition, several dive agencies have environmental branches that 

could be utilized to help educate divers. 

While working on this study, it also became clear that dissemination of information could be 

improved. In some instances, county programs—while submitting the information to the 

STSSN—may not share the reports with the FWC Artificial Reef Program. In other instances, 

individuals pursuing another field of research had documented artificial reef related sea turtle 

mortalities that were not submitted to the STSSN or other entities. In large part, serendipity was 

responsible for learning about their observations. It is hoped that further discussion, 

examination, and analysis of this issue will help improve data reporting and accessibility. 

ACKNOWLEDGMENTS 

This study was significantly enhanced by the input of numerous individuals who shared their 

observations and/or data, including the following individuals in alphabetical order: Bryan Clark, 

Angela Collins, Jim Culter, Don Demaria, Kerry Dillon, Bradley Ennis, Allen Foley, Didier 
22

Follain-Grisell, Tony Hancock, Robert Hardy, Kristen Hart, Chris Johnson, Steve Johnson, Jim 

Joseph, Joe Kistel, Dan MacMahon, Jeff Marinko, Keith Mille, Robert Turpin, Larry Woods, and 

Ritchie Zacker. 

This manuscript was also improved thanks to the reviews of Alex Chester, Kristen Hart, Keith 

Mille, Brian Stacy, and Andy Strelcheck. 

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