6 Habitat Utilization and Migration in Juvenile Sea Turtles

John A . Musick and Colin 1 . Limpus

CONTENT

6.1 Introduction ................................................................................................... 137 6.2 Methods ........................................................................................................ 139 6.3 Early Juvenile Nursery Habitats ................................................................... 140

6.3.1 Loggerhead . Caretfa curella ............................................................. 140 6.3.2 Kemp's Ridley. Lepidm'helys kempi ................................................. 142 6.3.3 Olive Ridley. Lepidoc~helys olivaceu ................................................ 144 6.3.4 Flatback Turtle . Norator depressus ................................................. 144 6.3.5 Green Turtle . f helonia mydas ......................................................... 144 6.3.6 Hawksbill. Erefnwchelys tmbri~~ata .................................................. 145

................................................ 6.3.7 Leatherback. Dermot.he1y.s coriaceu 145 6.4 Later Juvenile Developmental Habitats ........................................................ 146

6.4.1 Loggerhead ........................................................................................ 146 6.4.2 Kemp's Ridley .................................................................................. 148 6.4.3 Olive Ridley ...................................................................................... 150 6.4.4 Flatback Turtle .................................................................................. 150 6.4.5 Green Turtle ...................................................................................... 150 6.4.6 Hawksbill .......................................................................................... 152 6.4.7 Leatherback ....................................................................................... 152

6.5 Conclusions ................................................................................................... 153 Acknowledgment ................................................................................................... 154 References .............................................................................................................. 155

6.1 INTRODUCTION

Sea turtles are basically creatures that spend their entire lives in marine or estuarine habitats . Their only remaining reptilian ties to terrestrial habitats are for nesting and restricted cases of basking . Consequently . physiological. anatomical. and behavioral adaptations have evolved largely in response to selection in the aquatic environment.

and sea turtles share many common elements with liirger tislics and cetaceans in their habitat utilization and migrations. A generalized habitat model may he con- structed for sea turtles based on ontogenetic stages (Figure 6.1):

I. Early juvenile nursery habitat (usually pelagic and oceanic). 2. Later juvenile developmental habitat (usually demersal and neritic). 3. Adult foraging habitat. 4. Adult inter-nesting andfor breeding habitat.

.

Internesting j Denatant Migration

P I - ", contranatant

Migration

Denatant Migration

- -- Juvenile Nursery Habitat , ! (Usually -- Pelagic 8, Oceania , -

I

Juvenile Developmental Habitat -- ernersal & Neritic)

FIGURE 6.1 Conceptual model of ontogenetic habitat stages in sea tunics.

All sea turtles move immediately to the sea after hatching, usually after dark, and swim actively offshore. Most then undertake a mostly passive, denatant {sensu Jones)' migration drifting pelagically in oceanic gyre systems. Subsequently, after a period of years, these now larger and older juveniles actively recruit to demersal neritic dcvelopmentai habitats in the tropical and temperate zones. Demersal juve- niles in some temperate zone populations make seasonal migrations to foraging areas at higher latitudes in summer and lower latitudes in winter (see below) while those in tropical areas are more localized in their movements, When approaching maturity, pubescent turtles move into adult foraging habitats. In some populations adult habitats are geographically distinct from juvenile developmental habitats;24 in others they may overlap or co in~ ide .~ .~ Upon maturity as the nesting season approaches adults make a contranatant migration toward the nesting beaches. Most mating occurs

at poorly defined courtship areas that are clone KÃ the nesting beaches relitlive lo the distant foraging areas. Afler mating the females move to their respcclivc nesting beaches.'-* Courtship areas may be directly HIT the nesting beaches,* or remote from the beaches,'" depending on the population. During the nesting season, females usually become resident in the internesting habitat in the vicinity of the nesting beach." The focus of the present paper is habitat utilization and migration of juvenile sea turtles and nursery and developmental habitats.

6.2 METHODS

Although some authors have attempted to define objective size catagories of sea turtles by ontogenetic stages,^ terminology for juvenile life history stages has been varied and often imprecise. The words hatchling and neonate have been widely used and clearly refer to animals that have quite recently hatched. The term post-hatchling obviously refers to individuals that are larger and older than a hatchling, but the size (or age) at which a hatchling becomes a post-hatchling varies by author and is ill defined. Even less well defined is the size or age when a post-hatchling becomes a juvenile or an "immature" or a "yearling", and when this stage becomes the subadult stage. Many authors have used the term subadult to refer to all juvenile turtles that have recruited to demersal, neritic habitats. This term i s a misnomer for animals that may not mature for 15 to 45 years. Critical ontogenetic habitat shifts such as that from the pelagic nursery to the demersal developmental habitats occur in different species or even populations at different ages and sizes. For instance, Erefmof'helys imhricufu and Lepidochelys kempi usually make this shift at a smaller size (and younger age) than Che/oiiiu mydas. which in turn makes this shift at a smaller size (and younger age), than does Curetta carcrto (see below). Even within C . raretta, western North Atlantic populations make the shift from the juvenile pelagic habitat to demersal habitat at a smaller size (and younger age) than do western South Pacific populations (see below). The adult stage would seem to be easily defined (i.e.. minimum size of nesting females and clearly mature males with large dimorphic tails); however, large numbers of Chehmiu ntyilas. Cciretru curetta, and E. imhricata that are larger than the minimum breeding size of the nesting females recorded on the beaches are still sexually immature and hence incapable of breeding."'." Sexually immature turtles that are within the size of breeding turtles also occur with L. kern@ and Dei-morhels.'i c a r i a ~ e a . ' ~ The average female commences to breed at a size only slightly smaller than the average size of the entire nesting p~pulation.'~ Conse- quently, the size and age range for transition from the juvenile to the adult stage is usually broad within most populations. In order to avoid further confusion concem- ing ontogenetic stages, we have restricted our use to the terms hatchling (or neonate), juvenile, and adult. Hatchlings refer to sea turtles that have quite recently hatched and are still on the nesting beach or at sea only until they commence to feed (i.e., while they are dependent on the internalized yolk sac).Ih The at-sea period for the hatchling is short (days). so that size is still essentially similar to that at hatching. Juveniles include turtles that have commenced feeding. but have not attained sexual maturity. The term adult will be used to describe all turtles that have attained adult

6.3 EARLY JUVENILE NURSERY HABITATS

NY. or southern New 1-t1mlund'"" Others are c u ~ ~ l o d hy t l i c (lull' S t r e m and North Atlantic gyre into the eastern AtlanticM~14 (see review in M.~rque/-)." The fate of these pelagic juveniles expatriated from the Gulf11I' Mexico has been conjectural, some authors suggesting that they are lost to the breeding p o p ~ l a t i o n . ~ ~ ~ ~ ~ Conversely, there is no reason to assume that Kemp's ridleys do not have navigational abilities equal to those of loggerheads and, therefore, probably are able to find their way back to the Gulf of Mexico. Mounting evidence on the behavior of demersal juveniles in neritic developmental habitats strongly supports the latter hypothesis (see below). In addition. MeylanSb reported that from 1980 to 1985, 29% of stranded ridleys (mostly juveniles) were reported from the Atlantic coast of the U.S.; the remainder from the Gulf of Mexico. If such a large proportion of the population regularly uses Atlantic coast developmental habitats, it is likely that they can return to the Gulf of Mexico to breed.

Neonate olive ridleys emerge from the nest at night and rapidly crawl across the beach to enter the Nothing is known of the early juvenile nursery area, although it most probably is pelagic and oceanic. Even the adults of some populations appear to use pelagic, oceanic feeding areas when not breeding or n e ~ t i n g . ~ ~ ~ ~ Pitman"' reported that 26 of 247 olive ridleys sighted at sea by shipboard observers in the eastern Pacific were associated with floating Sar,~a.c.cum. Unfortunately, he did not note the size of these animals.

6.3.4 FLATBACK TURTLE, NATA~OR DEPRESSUS

Flatback turtles emerge from the nest and rapidly enter the sea at night.6' Evidently they lack an oceanic stagea-" and use neritic nursery areas while still feeding near the top of the water column. Hatchling flatbacks are larger (5.7 to 6.2 cm scl) than most other cheloniidsM and thus may have higher survivorship in the neritic habitat.

6.3.5 GREEN TURTLE, CHELONIA MYDAS

Hatchling green turtles enter the sea and continue to swim actively offshore for at least 24 h.b.5-6' Thereafter, the hatchlings apparently rest at night, but continue to swim actively offshore during the day.37^'-" 14drrz2 documented several pelagic. oceanic records of Chelonia neonates or post-hatchlings (520 cm scl) both in the Atlantic and Pacificw Many of these were in the vicinity of Saqa.csum drift line^."^ However, the occurrence of juvenile Chelonia in or near .Sarp.e.e~~m might be for- tuitous because both the animals and the weed could be brought together passively in convergence zones." The strong counter-coloration of neonate green sea turtles suggest? they are open-water animals, and experiments in the lab~ratory~'-~%howed that hatchling Chelonia avoided floating weed and spent a greater amount of time swimming in open water than did Cureflu or Ereimwhe1.v.s. Carr and Meylan'" have speculated on the most probable routes of transport for early juvenile Cheloniu hatched at Tortuguero. Costa Rim, based on major ocednographic circulation patterns in the Caribbean. Withams provided a model for the transport of neonate green

tunics from the casi coast of Florida in the Gulf Stream, around the North Atlantic ! Basin in the North Atlantic gyre. with return to the Caribbean and Florida in the

North Equatorial Current (the same model presented for loggerheads above) (Figure 0.2). He also provided tagging records of yearling green turtles released in Florida and recovered in the Azores and Madeira. Oceanic records of juvenile Chelonia are not as common as those for Caretfa. In addition, the recruitment of Chefonia to neritic developmental habitats in general occurs at smaller sizes ( ~ 3 0 to 40 cm c ~ l ) ' ~ ~ " - ' ~ than those for Carelio (£5 to 70 cm C C I ) . " ~ Therefore. Chelonia must spend a shorter time in the oceanic nursery and recruits to demersal developmental habitats at a younger age than does Caretto, or it has a much slower pelagic growth rate.

6.3.6 HAWKSBILL, ERETMOCHEWS IMBRICATA

Upon hatching, neonate hawksbill behavior is much like that reported for other sea turtles with emergence at night and immediate movement to the ~ e a . 7 ~ CarrZ2 provided several pelagic records of early juvenile hawksbills (5 to 21 cm scl) many of which were found in association with Sorga.csum. Other recent records have been provided by Redfoot et al,,'b Limpus et and Parker." Unfortunately, other than the one original record Parker provided ( ~ 2 3 cm ccl), most of the others he cited were based on beach strandinas. and many of the animals might have been neritic and demersal prior to death. At least one of his records17 was based on a benthic hawksbill captured in clam tongs inside Chesapeake Bay. In the laboratory, neonate hawksbills were attracted to floating weed and used it for cover where they remained motionless for long peri0ds.2'~~ Apyarently at least some hatchlings may remain on reefs close to their natal be ache^.'^.^" However, Boulonn' reported that juvenile hawksbills recruit to the demersal coral reef habitat in the Virgin Islands at 20 to 25 cm (scl). This range complements the largest verified pelagic records (21 cm scl, 23 cm ccl) noted above, Thus hawksbills in the Atlantic recruit 10 the neritic developmental habitat at a smaller size than either the loggerhead or green turtle, probably at an age of 1 to 3 years. Age and growth have not been determined in pelagic hawksbills, and this tentative age estimate is based on growth rates in demersal juvenile hawksbills?' and pelagic juvenile loggerheads^ and juvenile Kemp's ridleys.4' In the Indo-Pacific region hawksbills recruit to inhabit coral reefs at a larger size (usually >35 cm [eel])' and presumably at a greater age.

Hatchling leatherbacks move immediately to the sea and swim actively offsh~re."~ Leatherbacks are pelagic even as adults, and it is not surprising that neonates are more active than other species of sea turtles, swimming offshore both day and night for at least six d after entering the sea!' The fate of pelagic juvenile leatherbacks after leaving the nesting beach is one of the grcat mysteries of sea turtle biology. Other than neonates. there are vety few records of leatherbacks <110 cm c ~ I . 4 ' ~ ~ ~ ' ~ If Zug and Parham'snn age estimates are correct, and leatherbacks grow rapidly, then juveniles virtually disappear for four years. Lutcavage and Lutzuq noted that small

0.4 LATER IUVENILE DEVELOPMENTAL HABITATS

Length (em)

I m a l e

0 n 1-0 .w 40 50 AO 7n KII w inn u n u n

loggerheads he tracked from Virginia wintered in two hasically distinct areas: one group went down the coast, stayed inshore (hesitating during warm spells at various major inlets), and wintered inshore off southern Georgia and Florida (one traveled as far as the Florida Keys). The other group followed the same inshore route south of Cape Hatteras to about Cape Lookout, NC, then moved offshore to winter on reefs along the shelf edge on the western side of the Gulf Stream. One might hypothesize that the group wintering off North Carolina was derived from Geor- giaJSouth Carolina rookeries, and those that wintered off Florida were from Florida rookeries. Only further genetic research will tell.

Juvenile loggerheads of about the same size distribution (50 to 80 cm scl) are common during the summer in estuaries as far south as Mosquito and Indian Lagoons, F l ~ r i d a ~ ~ - ' ~ ~ and in the Gulf of M e x i ~ o . ~ ~ ^ - ~ " ~ In South Carolina and Georgia they exhibit seasonal emigration from estuaries into the ocean in the autumn, with immigration occurring in the spring.'un In Mosquito Lagoon, Florida, juvenile Caretta occur year-round, but are captured in smallest numbers during February and March (the time of lowest water temperature)."" The reason for this may be because the turtles emigrate out into the ocean, or rather they may be inactive, actually brumating in the mud during this period. Juvenile loggerheads commonly brumate in winter by digging head first into the mud in the Canaveral Ship Channel (in the ocean not far from Mosquito Lagoon).""'-"0 We have never observed any evidence of brumation in Virginia, nor have Epperly el al.Iu3 in North Carolina where winter water temperatures fall below the lethal lower limit for loggerheads (5 to 6.5°C)."'~1' Henwood'" noted that juvenile loggerheads reached their peak abundance in winter in Canaveral Ship Channel, and that some turtles tagged there in winter were recaptured to the north in summer. In contrast, to the well-defined seasonal foraging migrations exhibited by juvenile loggerheads along the Atlantic coast of the U.S., both large 0 7 0 c m ccl) juvenile and adult Careiia were resident all year in the coral reefs of the southern Great Barrier Reef and in Moreton Bay, Australia in the southwestern P a ~ i f i c . ~ - " ~ The most southerly of these sites, Moreton Bay, has an annual water temperature range of 16 to 28'C. much more moderate than those found in estuarine and coastal waters north of Florida in the U.S. After recruitment into the eastern Australian demersal habitats, these juvenile loggerheads show strong forage site fidelity to relatively small areas, mostly remaining within a few square kilometers for the next 8 to 20 years of growth to sexual m a t ~ r i t y . ~ ~ - ~ " ~ ' ~ ~ Adult loggerheads, after completing their first breeding migration to distant nesting beaches, return with high fidelity to the same juvenile foraging areas in which each had completed its juvenile life."' They also retum to the same foraging sites fol- lowing subsequent breeding migrations.'" It is strongly indicated that individual loggerheads in the southwestern Pacific occupy very localized home ranges for the decades that span their later juvenile and entire adult lives.

Initial recruitment of juveniles from pelagic oceanic to demersal neritic habitats takes place at a size of 20 to 25 cm (scl) in the northern Gulf of Mexico and in New England and New York waters." Contrary to the assumption of Carrl%d Carr et

al.,>' the juveniles curricil hy the Gulf Stream into the Atlantic probably make an active rather than a passive migration west from the edge of the continental shelf to i n d suitable shallow developmental habitats such as Long Island Sound. Although Gulf Stream gyres may impinge upon the edge of the continental shelf, they rarely cross the shelf to near coastal habitats."' In the Gulf of Mexico, shallow coastal

I habitats serve as foraging areas for Kemp's ridley throughout the year, although there is evidence for seasonal offshore movements in response to low water temper- atures in inter.^"'^ Occurrence of L. kempi in shallow water off northwest Florida is seasonal, with no turtles captured in the coldest winter months."' In New York and New England, juveniles must emigrate coastally to the south or face cold stunning and death in the inter.^^^^'^'^^

Chesapeake Bay serves as an important developmental habitat for juvenile L. k ~ m p i . ~ - ~ - ' ^ The summer population size has been estimated to be 21 1 to 1083 (a minimum estimate) with a mean size of about 40 cm ( c c I ) ' ~ ~ (Figure 6.6). Juvenile L. kempi preferred shallower summer habitats in Long Island Sound (<8 m)'20~'2z and Chesapeake Bay (<5 m)" than were used by juvenile loggerhead^,^' and often foraged in submerged aquatic grass beds for Callineites sapidus and other crabs? The seasonal migration pattern is similar to that of the loggerhead, with immigration in May and June and emigration from September to November. Of 57 Kemp's ridleys tagged in Chesapeake Bay, 2 were recaptured there in subsequent summers.43 Thus, site fidelity is possible for summer foraging locations. Upon leaving Chesapeake Bay in autumn, juvenile L. kempi migrate down the coast, passing Cape Hatteras in December and January. These larger juveniles are joined there by juveniles of the same size from the North Carolina sounds and smaller juveniles from New York and New England to form one of the densest concentrations of Kemp's ridleys outside the Gulf of Mexico.'"2."" Keinath'" used satellite transmitters lo track three juvenile Kemp's ridleys released in Virginia in October. They followed the same inshore route noted for loggerheads above, and two individuals migrated as far as Florida

I by mid-January. (The transmitter failed on the third turtle in November when the animal was approaching Cape Fear, NC). Henwood and ogre^^'^^ noted that juvenile Kemp's ridleys reached their maximum abundance off Cape Canaveral, FL in Jan-

I uary to March, and that their tagging data suggested a northward movement in

! summer and a southward movement in the winter. These data complement and support the pattern of seasonal migration noted to the north.

Ogren" reported that the entire northern coast of the Gulf of Mexico from Port Aransas, TX to Cedar Key, FL served as demersal developmental habitat for juvenile Kemp's ridleys. Areas where significant concentrations of juvenile ridleys occurred included: the Sabine Pass area of Texas; Caillou Bay, Terrabonne Parish. LA; and Big Gulley east of Mobile Bay. AL. The smallest juveniles (20 to 25 cm scl) were found in two areas: one off western Louisiana and eastern Texas. and the other off northwest Florida."-'24 Most juvenile L. kempi in the latter area were captured at depths £6. m, and all ridleys <25 cm (scl) were from <I m. Juvenile Kemp's ridleys, then, recruit to shallow estuarine and coastal habitats in the western Gulf of Mexico and off New England and New York in summer. In winter they migrate south andlor offshore to avoid cold temperatures, but may remain resident in some areas of the

Juvenile prceii t u r ~ l c s reenlit in clerncrs:il (lt~vcloprncni:i l h;ihit.its ;it nhciit W to -Id on wl> o r lars'ef ' ' I " " (I'ILIIIW 6 .7 ) . I n the vvcstem Atl:intic the summer clcvelop- nient:il 1inhit:n cncompassrs estti:irinr w:nlSrs ;is t:ir 110rll1 :is l,onc Ishirul Soiimi. Clies:ipc;ike Ray. ;ind the Uor t l i C:irolin:i Scuntls soiit l i t l ~ r o i i i ' h ~ i i i ~ tl ie tropics. Green tunics north ot florid:^ must migr;itc smith i n :iiitiinin o r (Â¥ic the risk ( i f ' c-old slunninr,.l 1 ' 1 1 1 ' 1 I-*> Giisenian :ind F<lirli:irt"" noted t l i ; i i the sni;ilk'st ]ii\'i.-nilc y t - e n

i i in lcs f26.S in 45.3 cn i scl) t o ;ippe:ir in !hi* (lenirrs;il iirvelopn1ent;il l~:ihii;ii oi-i it if c:ist co:isi o f Flori(l;i t ~ c i i r r e d on s:ilwll:irid polycli:ieie r rc ls . :\nil 111;~ ;is j t~ \~c t i i l cs

0 10 20 30 40 50 60 70 80 90 1 0 0 1 1

CURVED CARAPACE LENGTH (crn)

Ix'ciinir l;irucr 12S.S 10 <if>.S cm scl) the! moved into the Iii(li:in River 1- hods to lor;iyc. I I c i i v . m ~ l ;iinl Ouren' ; i l so 1101ci.l th:it i i i \ e i i i l r f lreen 1

(';iii:ivcr;il \ w r e ~ m : i l l c r tti:in those i n thc M o s i l ~ i i t o l~iwiiii cslii:ir\'.''" Q y t - n ' ' s i ~ ~ ~ o ~ s t e ~ l tIi;it tlic<c sni; i l l ~-o; is t ; i l prwii 111rl1'\ n i i r l i t tx' i n ~ ~ i e n t : i l st;tt7cs pr ior to tlir s l i i i t t o Iierhivory ;init r c c n ~ i t m ~ n t to \ I t r ~ - t l i n ~ ; i s t i i r i ~ s . Vrndoi'n::~ mil Flirli:irtl"' shewed t l i ; i t i i i ~ t i i l c r i* l .~i i i tct I l o (lie Mos t l l~ i to L : i rn (~n (F111riil;i 1 t.-'ni:irintb ( I t - ~ ~ - l o p i i ~ c n t : ~ I 40 cm scl ;iii(l 11i;it soti ir irulivi(lii:ils lw:iiiiis rCsitlrnt. sliowinc l'(ir;i?i V;inv t i in Ic \ r ~ m ; i i n r t l i n the l - : i ~ n n i i ~i .~; i r-roi i i i ( l unt i l the! appro: 'tii.-v ;ilso notcil thiii tlir c;it~.Ii r:ite\ c l l i i \~t- i i i lc Cln'lo~ii(i i t ere hichc-'t 1mt tl i; it tlii.. winter tk.cliilc inii!hl he (IIIC i n p:irt 10 turtlt* in; ict i \ i t \ Severe ~Â¥nl i l -s t i inn in cv~- i i ts in t i n t e r i n 1*11" ;nul 1*l1S stunveil ill: were s t i l l common i n ilk- l.:i~:ooii. Felvcr 1-I :11.~" reponcd ('ln81uni the m u d ~ I ~ r i i n i ~ i t c i i n ttinti.*r i n tlic tiiill' 01' C';ififonii;i. Vienilonc li ivenilC rro.-n tunics in \ losi l i i i to l-:ii!oon \4;inilt'r~.O :is l;ir :is 5 11

when illc \v:itcr was a w l c r i l 1 ro I X ( ' I hut t~<i:iblishc<l h u m r r:ine! kn i u l i t - ~ i tr i i ipt .~: i t~ircs were ;ihovi* 25 ('. H]ornil;il ;in11 R111to1i" ' rrr e m l ~ ~ i i c n t s were import;int t le\~clopii ie~it; i l h:ibit:its lor i i ivci i i le srri B:ih;ini:is. Tl i i - i r t; ic?n~' stiiilies sl-umcd th;tt i i i im i r r ; i~ ion o c c u n - ~ ~ l 11

the R:ili;i~ii:is. C o l i ~ ~ i i l ~ i ; ~ . C'nh:). I lorni i i~-. : in R e p i i l ~ l ~ c . I l:i it i. \ic:irii~ii

;it Crccn lurllt". ( I lo burrow 111

;I"' notcil it1.11

i Ill krn ;I ~ l :n

:s nf 1.2 10 I . I x i r tn l th:it litl:il .-n tnrlk-s i n llir I oilier :irr:i\ I . P:in:ini:i. ;in11

cAlthni!;li lc:itlwrh;icks :irr pclayic. ihcy recruit sc;ison:illy t r le111pcr:ite ;incl hcirc;il co;ist:il Ii;ihit:its lo fccil on conccnrr:ilions o f j ~ ~ l l y l i s l i . " "' ' 11 ' I n the uzsteni Atlantic. ,iiivciiilib t)~,niii~rhrl\-\ ;ippe;ir i n ihrsc 1i;ihitats ;it ;ihout 110 10 120 cn i (eel) , liasc(f o n strandinu (l:~;i"' "" ( It if l ire (>.St. I f we :iccrpi the sire :it m:~tnr i ty 0 ~ : i s c t l on the n c s t i n ~ o p t i l ; i l i o n in St. C ' r o i ~ ) :is 137 cm (eel) ( t l i t * s ire o t tlie sn i : i l l ~ *s t i i e s i i n ~ fcm:i lo o r ;is 157 cn i i cc l t. dhe ;ipprnvim;ite ;ivcr:ice we of' ncst ind' l -m:i les 1.'"

then ;I ~ihs l : in t i : i l perc~'nt:iye o f Ic~ithcrh:icks str;in<linc :ilrni; tlic L1.S. e:ist const mifit hi' l;irccs ,iiivcnilC\. ACri:il surveys h:tve slinwn l:ir?!c ininih<.Ts o f le:itlierh;icks ofT i l ic ~iortli':isr ~o:I'-! 11) F lor i i l :~ i n Fchni:iry.':' son i l i~ -m V i rc in i :~ i n l;irP April." ' ;md the Gulf of f1:iinc i n sunlmer.'" 1-e:itlicrh:n;k str:inclin~'s from IOXO to I 'm I i n Florid:\ occurrcil most ly t ~ t n e e n October :inti April."" Siulit inus of lc:fllicrb:icks nfT M;is<;n.-hnsctts pe:lk i n Angis t . w i th n n live sir l i t incs tx'fnre Stme o r ;iSter Octohrr. '" AltIioiii!h scver:il t : i~g inc ;ind [rackin? ctmlies h:ivr hern tlone on ;i(lnlt fennles th;il show lon~!-dist:ii~-t.. oceanic ~ni,cr;ition 10 h i ~ h c r - I : i t i ~ i ~ ( k co;ist:il feeding h:ihit;ns. virtu:illy rio work o f this k ind h;is been (fonc on juveniles. I'alinlino et :it. " pointe(i ont th:n Iratl i~~rh:n.-ks were incni i i l e~itlotltcnns, hut tIi;it the l i ipt l siirl';ice ;ire;i-lo-

Length (cm)

f>..'Ã CONCLUSIONS

A comp;irison o f the o n t ~ ~ c n ~ t i c p:ittcrns o f Ii:ihit;il u t i l i ~ : i l i on ;itul niipr:ili the s e w n species of se;i mules Ie;ids to the I ' (~l louini ; hypotheses: n:itiir:i w i l l 1':ivor those nesting loc;iticns wi th the hipliest ~ i r v i \ , o r ~ l i i p i lur iny the m r l y juvenile st:ipe when p w h t i n n i s lii$iivst. ( l iven ;ill se;i turtles nest i suhtr11pic:il. o r \v;inn tcmpcnili- l;itinnk's. thr must inlporti int iletcrmin:int t'n:;~'ll \<~" . i \ ions proh;Èbl is stin,ivor\hip ol' h;nchlini"i und mll j w c n niirst-n, h;ihit:its.

I n %I t~ i r t l cs ;is i n lislies. (he i i i ~ n ~ h e r s ;in11 i l iverMt\ d potcnli;il prei resultinp 11111n;llity r;ites .ire inversel\' ~ ~ r o p ~ > r l i n n : i l in Ili' s i /c 01' the i t i t , ;~~I\.:II~I;I~~ o f pcl;ific. oceanic nurseries i s ihe low 1Ic11sily o f p rc~ l : i t~ l r y se:i hircls (here ilict;uecl h\ l o w primary pro(11i~~ti1111,'"' I : ' ~Pr0 (1uc t i vc -up !~~ ;lrc e \~ .~p t j i l ns . ) R;1sec1 o n pre~hi tor 11101itli s i x :ilcnt?. few potenti;il iivi

predators. except sharks."' :ire capable o f c n q i l t i ~ i ~ li:iril-bodied cpipc (such :i\ sc;i 111nles1 >-TI) id <(I c~ll i n ili:inietrr. \l;irinc 1.-rocoililes. ~ ~ 1 1 1 '

IK' sicnitic;inl p r c h t o r s o f most s i ~ e r:lnyLms of n~:trine mnles. ;ire !arcel! t o lropic:il inshore n1;irpins of' m r i n c tunlib for:iqinp hi i l i i t : i ts. \,1;1rine

l l i nc ;in-:I-. inn o r 11\11

1:1s?ic p r r \ I1 ran ;itio

n rcs t rk t i - i l m ; in i~ i i : i l ~~

appear to be rarely predators of marine turtles. lluwkshills ititcl Keinp's ridleys recruit ACKNOWLEDGMENT from pelagic. oceanic nurseries to neritic. demersul developmental habitats at about

20 to 25 cm (scl): green turtles do so at about 30 cm. In order to avoid predation virginia Institute of Marine Sciences contribution 2026. from sharks and large teleosts. the smallest demersal recruits tend to use structured habitats such as reefs that provide cover (hawkshills and green turtles) or very

shallow habitats where larger predators cannot go (Kemp's ridleys). Juvenile log- REFERENCES gerheads stay in the pelagic. oceanic nursery much longer and to a much larger size.

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