Location and exploration of natural reefs on Georgia's continental shelf

LOCATION AND EXPLORATION OF NATURAL REEFS ON GEORGIA'S CONTINENTAL SHELF1/
By C. Duane Harris
GEORGIA DEPARTMENT OF NATURAL RESOURCES COASTAL RESOURCES PROGRAM BRUNSWICK, GEORGIA

May 1978

I

l/This work was supported in part by funds from the

"I

Federal Aid in Fish Restoration Act, Dinge11-Johnson

Project F-31, Georgia
...--. ~--

FINAL REPORT

State: Georgia

Project Number: F-3l

Project Type: Research

Project Title: Marine Reef Investigations

Study Title: Location and Exploration of Natural Reefs

Period Covered: July 1, 1973 - June 30, 1977

Study Objectives:

To locate and explore natural reefs for possible use by

sport fishermen.

ABSTRACT

Thirty-one live bottom areas were located offshore along Georgia's Continental Shelf during this study. Ground truth investigations were made of six of these areas by project personnel and all were found inhabited by ichthyofaunal assemblages such as snapper, grouper, and porgies which are important to offshore recreational fishermen.
Geographic locations of the remaining 25 locations were provided by recreational and commercial fishermen, U. S. government agencies, and the University of Georgia. These areas were not subject to ground truth exploration by project personnel, but remotely sensed information (in addition to the geographic locations) suggest they also are inhabited by fishes of interest to recreational anglers.

1

BACKGROUND
The Continental Shelf of the Atlantic Coast of the United States encompasses areas from the shore to the 183 m (100 fm) depth curve .. In the South Atlantic Bight -- that part of the Western Atlantic Ocean bounded on the north by Cape Hatteras, North Carolina, and on the south by Cape Canaveral, Florida (Figure 1) -- the width of the Continental Shelf varies from about 22 km (12 nautical miles) to about 148 km (80 M).
Struhsaker (1969) described the Continental Shelf offshore of the Southeastern United States as being characterized by five general
.habitat types: Coastal, open-shelf, live-bottom, shelf-edge, and
lower-shelf. A brief summary of Struhsaker's description (1969) of these five habitat types follows and a schematic drawing is depicted in Figure 2.
Coastal habitat extends from the estuaries out to a depth of about 15 or 18 m (8 or 10 fm), and is primarily composed of a smooth, sandy mud bottom. Bottom water temperatures, influenced by estuarine drainage, generally vary more than the other habitat types, and range from 100 to 29 0 C (500 to 85 0 F). Coastal habitat is inhabited by commercially important species of shrimp, crabs, and sciaenid fishes.
Open-shelf habitat begins along the rather arbitrary line where coastal habitat ends, generally about 18 m (10 fm) and proceeds offshore to about 46 to 64 m (25 to 35 fm). This area is characterized by a smooth sandy bottom. Bottom water temperatures do not fluctuate as greatly as those of coastal habitat because of the influence of
2

N.
s, C. \
\
\

N, C,
,
."..-:.:.>. ;.:.,,/.
,.
,. / /
" ,/
,/
/"
/ / / /
I I

Cape Hatteras r"
I"
r I
, ,,-
"",,-
/
"
SOlffH
ATLANTIC BIGHT

"
DAYTONA '..
29 BEACH .

,
I
I \
\
Canaveral

FLA.

ATLANTIC OCEAN

Figure 1. The South Atlantic Bight (Cape Hatteras to Cape Canaveral) of the Western Atlantic Ocean.
3



\ LIVE-BOTTOM HABITAT

(small areas of broken relief within the open-shelf habitat. A rich sessile

~

) invertebrate fauna)

CHOAASBTITAALT /

'\

(smooth, sandy-mud bottom out to

OPEN-SHELF HABITAT

--~)l

8 - 10 fathoms)

(smooth sand bottom from

.+>-

10 to 25-30 fathoms) SHELF-EDGE HABITAT
(smooth to highly broken bottom in

J>" . .

about 30 to 60 fathoms. Sediments

variable)

LOloJER-SHELF HABITAT

_

(smooth mud bottom from about 60 to at least 100 fathoms)

Figure 2. A schematic section of the Continental Shelf off Southeastern United States showing the five general habitat types (From: Struhsaker, 1969, Figure 9, p. 271)

warmer oceanic waters associated with the Gulf Stream. Bottom water temperatures generally range from 110 to 27 0 C (52 0 to 800 F). The
most abundant fishes inhabiting this area include: scup, Stenotomus chrysops (Linnaeus); orange filefish, AZuterus schoepfi (Walbaum); sea robins, family Triglidae; inshore lizardfish, Synodus foetens (Linnaeus); and sand perch, DipZectrum formosum (Linnaeus); but are
of little commercial importance. Live-bottom habitat (synonymous with natural reefs in this study's
objectives) are areas of broken relief (rock outcroppings) scattered irregularly over the shelf which are encrusted by sessile invertebrates such as sponges, sea fans, anemones, etc. Bottom water temperatures on the live bottom areas are similar to those of the open-shelf habitat. Live-bottoms are inhabited by a rich assoication of tropical and subtropical fishes which are important to both the recreational and commercial fishing industries. Although the majority of live-bottom areas occur at depths greater than 27 m (15 fm), numerous "scatterings" of these areas are found from 16 to 26 m (9 to 14 fm). Live-bottoms closer to shore along the 18 m (10 fm) curve are inhabited by fishes of a more subtropical nature, such as
black sea bass, Centropristis striata (Linnaeus), and scup; while
live-bottoms farther offshore, in deeper water, harbor fishes more
tropical in nature such as snapper, Lutjanus sp. and RhombopZites aurorubens (Cuvier); grouper, EpinepheZus sp. and MYcteroperca sp.;
and porgies, family Sparidae.
5

Shelf-edge habitat occupies a more-or-less continuous zone along the entire edge of the Continental Shelf. The shelf-edge extends from depths of about 46 m (25 fm) to about 110 m (60 fm), and is characterized by extremely diverse bottom types ranging from smooth mud to rocky areas of great relief with heavy encrustaceans of coral, sponge and other tropical invertebrates. Since the Gulf Stream generally follows the contour of the shelf-edge on its course northward, the bottom water temperatures in this area fluctuate less than the habitat areas closer to shore and range from about 130 to 260 C (55 0 to 780 F). Fishes of the shelf-edge are TIlostly tropical in nature and consist of snapper; grouper; porgies; wrasses, family Labridae; damselfishes, family Pomacentridae; and parrotfishes, family Scaridae.
Lower-shelf habitat is probably the most strikingly different of the various Continental Shelf habitat types. Geologically it is part of the upper Continental Slope, and depths range from 110 to 183 m (60 to 100 fm). Bottom water temperatures on the lower-shelf range from 110 to 140 C (510 to 57 0 F). Fishes inhabiting the lower-shelf are of a more cold water, higher latitude type such as the hakes,
Upophycis sp.; flatfishes, families Bothidae and Pleuronectidae; butterfish, family Stromateidae; and John Dory, Zenopsis oceZZata
(Stcrpr). Off the Georgia coast, the Continental Shelf is about 148 km
(80 nautical miles) wide. Numerous live-bottom areas are known to occur within this area. Some of these areas (Brunswick and Savannah snapper banks) which occur about 74 km (40 M) offshore, have supported commercial fishing for snapper, grouper, and other
6

fishes for many years. The extent of some of these areas and their fishery resources may be well known by the commercial fishermen who earn their livings from these resources, but only one of these areas has received more than simply a cursory investigation by scientists. This area, the Sapelo Live Bottom (Gray's Reef) is located 31 km (17 M) east of Sapelo Island and is marked with Georgia Department of Natural Resources buoy. Because it is relatively close to shore and well marked, Gray's Reef is a popular offshore recreational fishing area and scientists have conducted detailed studies of this reef's geology' and fishery resources (Hunt, 1974; Harris, Unpubl. manu.). These studies have shown that abundant populations of a large number of fishes valued by marine offshore recreational anglers, occur at the Sapelo Live Bottom. Hunt (1974) suggested that other live-bottom areas similar to the Sapelo Live Bottom probably exist along the same depth contour. The present study was initiated to determine the geographic location and extent of live-bottom areas, and the magnitude of their potential use by recreational anglers.
PROCEDURES Live-bottom areas offshore along the Georgia coast were located by: (1) obtaining and reviewing information on known hard or livebottom locations along Georgia's Continental Shelf from the National Marine Fisheries Service, U. S. Bureau of Land Management, University of Georgia, and commercial and recreational fishermen; and (2) conducting remotely sensed bottom surveys using depth recorders, underwater
7

closed circuit television, dredges (to differentiate live-bottom), and various positioning systems (including LORAN A and C), to determine precise geographic locations of live-bottom.
Ground truth exploration and resource evaluation of live-bottom areas was accomplished by direct observation using SCUBA, experimental hook and line sampling, evaluation of dredge samples, fish trapping, and closed circuit underwater television.
RESULTS Thirty-one live bottom areas were ~ocated and evaluated during this study. The geographic location, water depth, physical description ~nd evaluation of the fisheries resources inhabiting these 31 areas are given in Table 1. A chart of the geographic locations of these areas is presented in Figure 3.
ANALYSIS Stations 6, 7, 8, la, 12, and 23 were subjected to ground truth explorations and their fishery resources evaluated during the study. Of these areas, station 12 (Sapelo Live Bottom) has been investigated previously, and is currently being utilized extensively by recreational anglers. Station 23, located adjacent to artificial reef J, was investigated for the first time during this study. It was found to be similar to the Sapelo Live Bottom in structure, and harbors ichthyofauna of a similar nature. This live-bottom area (artificial reef J, station 23, Figure 3) is about 50 m east and south of buoy J, and is currently being utilized by recreational anglers in conjunction with reef J.
8

Tabla 1,

Oaoarapllie location, daptll, and phy.ieal de.cription and/or raaource avaluation for the 31 live bottom areas located offshore along Georgia'a Continental Shelf
during this study (NHFS - National Karine Fisheries Service; DNR - Georaia Department of Natural Resources; NDA - no data available)

Latitude/ Lonsit ude

LORAN A

LORAN C

Water depth (meters)

Source of Information

1

30' 43.2' N. 80 56.7' W.

3Ll-3680 3H6-4222

13523/ 70921

20

NMFS

2

30 39.1' N. 80 32.2' W.

3Ll-3655 3H6-4172

13536/ 71061

35

NMFS

3

30 38.0' N. 3Ll-3647

13534/

38

80' 25.2' W. 3H6-4l55

71101

,

4

30' 45.7' N. 3Ll-3730 13591/

31

80' 39.4' W. 3H6-4195

71017

5

30' 43.0' N. 3Ll-3722

13643/

55

80 06.2' W. 3H6-4113

71204

NMFS NMFS
NKFS

6

30 54.7' N. 3Ll-3840 13702/

37

DNR

80' 35.0' W. 3H6-4l98

710ll

7

30' 50.4' N. 3Ll-38l0 13734/

47

80' 04.5' W. 3H6-4118

71220

I

30' 57.8' N. 3Ll-3820 13732/

26

80' 37.0' W. 386-4200

71030

30 58.3' N. 3Ll-3907

13803/

38

80 11.6' W. 386-4149

71173

30' 59.2' N. 80' 04.5' W.

3Ll-3922 386-4132

31' 04.8' N. 80 24.2' W.

3Ll-3972 386-4190

31 22' N. 80 55' W.

3Ll-4260 386-4262

13836/ 71212
13850/ 71105
13982/ 70922

42 22-26
20

DNR
DNR
NMFS
DNR
NMFS
DNR

31 18.7' N. 80' 32.8' W.

3Ll-4130 386-4228

13974/ 71047

29-33

NMFS

31' 16.5' N. 80' 21.8' W.

3Ll-4l20 386-4203

13980/ 71110

37

NMFS

* See Fiaure 3 for location

Physical Description and/or Resource Evaluation

Underwater television and dredae tow rev.alad liva

bottom with <1 a relief. Sponge, aea pana, aeattared

dead coral, starfish, acallopa, aea urchina, aea fana,

lizard fish and scad observed.

'

Underwater televiaion reveal ad firm aand bottom with patches of broken shell. Fauna observed includad Busycon ap., Astropecten sp., aponae, acallopa, aea urchins, sea pens, sand dollsrs snd razorfiah.

Dredge tow revealed hard bottom with numerou. molluake, aea pens, aea urchina, Loligo ap., aea cucuabar, .lip per lobater, ocellated flounder amana other
Dredge tow revealed hard bottom with numaroua .peciaa of molluska, nudibranch., aand perch, haka, Btropua sp., Loligo sp., aea pena, .nd ocellated floundar among others,
Underw.ter television revaaled rock of >1 raliaf and live bottom of <1 relief. Snapper boat vaa oba.rvad nearby.
SCUBA investigation revealed extenaiva liva bottoa although very little relief (no ledgea). Obaarvad jewfiah (136 kg), red anapper (9 kg), aaa (14 ka), vermilion anapper, black aea ba.. , biaaye, aabarjack, and large sponges (1 a tall).
Experimental hook and line aamplina producad kina mackerel and wahoo. Fathometera indicated hard. rough bottoa.
Fathometer indicated rough, hard botto.. Hook end line sampling produced red anapper. varmilion'anappar, grouper (scamp. gag), amberjack, kina ..ckaral.
Underwater television revealed algal flat a coapriaed of sea fans, sponge, aea pena, starfiah, and unidentified fishes. Tersed very aparsa liva bottom.
800k and line sampling produced king mackerel by trolling. Fathometer revealed many bottoa fiahaa. Commercial fiahermen report aood catchea of aDapper and grouper.
Dredge tow ravelaed numerous molluaka. cru.taceena, echinoderms, coelenteratea, and a faw fiahe
Extensive live bottom coverina approxiaatlay 12.9 ~ of ocean floor. Abundant epifauna inc Iud ina apona.a, sea fans, soft and hard coral t mollusks, cruataceans, and fishes such as black aea baaa, porgi.a, rad anapp.r, gsg, amberjack, barracuda. Atlantic apad.fiah. aha.pahead, etc.
Dredge tow revealed numerou8 mollusks, cruat.ena t echinoderms, longhorn bryozoan, and fiahee aoch aa aea bass, ocellated flounder, and Etropua sp,
Dredge tow revealed hard bottom with nuaarou. molluak., crustscesns, bryozoans, echiooderaa, and fi.haa (haka. sand perch).

9

Table 1 (continued).

Geographic location, depth, and physical description and/or resourcel evaluation for the 31 live bottom areas ~ocated offshore a10na GeOrat.'1 Continental Shelf during this Itudy (NHFS - National Harine Filhartel
Service; DNa - Georgia Department of Natural Reaourcel; NDA - DO data available)

ltation *
luaber

Latitude/ Lon itude

IS

31" 14.9' N.

80" 10.3' W.

16

31" 13.7' N.

80" 07.S' W.

17

31" 13.2' N.

79" 53.2' W.

18

31" 20.2' N.

80" 06.2' W.

LORAN A 3Ll-4112 3H6-4172
3Ll-4095 3H6-4161
3Ll-4092 3H6-4114
3Ll-4175 3H6-4167

19

31" 18.1' N. 3Ll-4150

80" 01.8' W. 3H6-4152

20

31" 17.8' N. 3Ll-4155

79" S3.5' W. 3H6-4125

21

31" 28.0' N. 3Ll-4259

80" 21.S' W. 3H6-4219

22

31" 31.4' N. 3Ll-4335

, 80" 19.7' W. 3H6-4235

23

31" 36.3' N. 3Ll-4301

80" 48.0' W. 3H6-4270

24

31" 35.4' N. 3Ll-4344

80" 20.8' W. 3H6-4228

2S

31" 34.8' M. 3Ll-4342

80" 17.1' W. 3H6-4220

26

31" 31. S' N. 3Ll-4325

79" SO.5' W. 3H6-413S

27

31" 39.1' N. 3Ll-44l0

80" 03.2' W. 3H6-4l90

28

31" 42.S' M. 3Ll-4435

80" lS.S' W. 3H6-4236

29

31" 44.2' M. 3Ll-4462

80" 14.2' W. 3H6-4229

30

31" S2.9' N. 3Ll-4579

80" 01.5' W. 3H6-4210

31

31" 58.6' N. 3Ll-4657

79" 54.6' W. 3H6-U98

* See 'iaure 3 for locstion

LORAN C 13990/ 71180
13989/ 71192
1402S/ 71277
14066/ 71209

Water <Iepth meters
44
44
53
44

14056/ 71234
14080/ 71279
14111/ 71110
14155/ 71120

46 46 NDA 27-31

14119/

22

70945

14192/

NDA

71112

14198/

33

71137

14265/

MDA

71300

14292/

40

71222

14271/

33

71125

14313/

MDA

71152

14448/

MDA

71230

14530/

NDA

71265

Source of Information
NMFS
NMFS
Commercial fisherman NMFS
NMFS
Recreational fisherman
Recreational fisherman
Commercial fisherman
DNR
Commerical fisherman
Commerical fisherman University
of Georsia NMFS
NMFS
University of Georgia Commercial
fishermen University of Georgis

Ph sical Descri tion and or aelourcl Ivaluati D Dredge tow revealed numeroue mollulka, cruataceaDl, and fishee Isaociated with very Iplrle livl bottoa.
Dredge tow revealed hard bottom vith Icallopl, nudibranchl, ao11usks, hake, aand plrcb, aaoDa othan. aed ~napper and large rock ledge reported,
Underwater television revealed algal f1atl with acattered ahel1, achinoderas, sponae. lei panl, and unidentified fishes.
Dredge tow reves1ed hard bottom with aalociatad species of fishes snd crultaceana.
North to South trending ridae
Live bottom and fish reported
Two North-South trending ridgee occurriDI approx1aat.1y 9.3 km apart and 14.8 km lana.
SCUBA investigstion revealed patchea of liva bottOm with interfinger1ing ridgea and trougha aimi1er in phylical structure to the Sapelo Live Bottom. Th.ee patchaa appeer to the east and south of the buoy aarkina thl location of Artificiel aeef J. The rida'l srI heavllY encrusted with aessile benthoa. Fiah.. ob.erved included black aea b.as, sas. rad anapper, poraiel, asberjack, end Atlantic apadefiah.
Live bottom and fish reported
Live bottom and fish reported
Live bottom with snapper and arouplr
Dredge tow revealed hard bottom, produced SOl aponge, molluaks, crultaceane, oceilited flounder and aea robina.
Dredge tow produced 501 sponge with cruetaceane, mollusks, nudibrancha, flounder, li&ardfilh. Etropul sp., comprisins the remainder of the catch.
Good ledge
Live bottom snd fish reported
Live bottom but very few fish taken witb ro11ar trawl

10

.14400

~

/ -

,L
.~

.-8

,//

14200

.'8

~

,//

./

GEORGIA COAST

o h-......

-- -------~--- _: ~~OTIC~L ~JLES

o

So

10

"

!\

I-' I-'

J~'.l~~

.,~.s,~~ \1
"~~"'~-I''"'--'

Jekyt

bl3nd

,

.~

~

~.

--~-7~

-------- --~14~ r~

~

~

~~
\

i

a. ./ .r- \ .:

~\\ \

:!:"

~

,;X

~'
A

- 13800
..",.. I

~@
~~

~
~ _\.-8
-~-~--

....:'
l:' I
~: ~ ....
~.
..,~'::
...'~:
.,

~

:/
/

1]600
<D ~

/
i

"

,!!) ~

\
\
\
---
---

Figure 3. Locations of natural reefs (indicated by black triangle) on the Georgia Continental Shelf in relation to artificial reefs (black circle) and the Georgia coastline [circled numerals = Station No. in Table 1]

Stations 6, 7, 8, and 10 were also found to harbor ichthyofaunal resources of interest to offshore recreational anglers. These areas
(6, 7, 8, and 10, Figure 3) are, however, located farther offshore
than most Georgia anglers are able to reach safely in average size (22 ft.) offshore sportfishing boats. Larger boats, capable of utilizing these areas safely, are usually equipped with depth recorders,
LORAN, etc., that enable their operators to locate these areas without
the aid of buoys. Since project personnel did not explore and evaluate all areas
located during the study, some of the evaluations given in Table 1 are from persons knowledgeable about specific areas. In most instances, these evaluations do not provide information necessary to determine the area's potential for offshore recreational angling. However, based on our knowledge and evaluations of similar areas, it is likely that most of these areas are inhabited by fishes of interest to recreational anglers.
RECOMMENDATIONS 1. All previously identified live-bottom areas located and reported
herein, but not explored by Georgia Department of Natural Resources personnel during this study, should be explored and evaluated as soon as possible. 2. Fishery resource evaluations should be more quantitative in nature. When Possible, evaluation methodology should consist of direct observation of the area using SCUBA, submersibles, or underwater television, as well as hook and line sampling, trawling, trapping, etc.
12

3. The results of these evaluations should be made available to the offshore angling public; however, it is not recommended that the Georgia Department of Natural Resources place and maintain buoys at any of these locations at the present time because of the time and equipment necessary to do so. It is recommended that efforts be made to encourage the U. S. Coast Guard to buoy at least two locations (one offshore of Brunswick, and one offshore of Savannah) to be determined by the Georgia Department of Natural Resources based on further studies, as soon as possible.
4. It is recommended that the Georgia Department of Natural Resources encourage offshore anglers to utilize areas reported herein and report the results of their efforts to this agency.
13

LITERATURE CITED
Hunt, J. L. Jr. 1974. The geology and origin of Gray's Reef, Geor3ia Continental Shelf. Ms. Master's Thesis. University of Georgia, Athens, Georgia.
Struhsaker, P. 1969. Demersal fish resources: composition, distribution, and commercial potential of the continental shelf stocks of the Southeastern United States. Fish. Ind. Res. 4 (7): 261-300.

C. Duane Harris Research Unit Manager Coastal Fisheries Section

Date: '2~ 14"(} /C/7f

Approved bY:~~! K' /1/1a.l!.{J'd-'-
Robert K. Mahood Chief - Coastal Fisheries Section
CB1(i(~k~ Approved by: _ _ -~~""':"'-l..L-~4-"-':::"'-L:;.......J.:....-=~=Dr. Robert j. Reimold Director - Coastal Resources Program

1 I.