Seasonal occurrence of male Antillean manatees (Trichechus ...

Aquatic Mammals 2003 293 342ndash354

Seasonal occurrence of male Antillean manatees (Trichechus manatusmanatus) on the Belize Barrier Reef

Caryn Self-Sullivan12 Gregory W Smith3 Jane M Packard12 andKatherine S LaCommare23

1Texas AampM University Department of Wildlife amp Fisheries Sciences Mail Stop 2258 College StationTexas 77843ndash2258 USA

2Sirenian International Inc 200 Stonewall Drive Fredericksburg Virginia 22401ndash2110 USA3PO Box 142 San Pedro Town Belize Central America

4University of Massachusetts-Boston Department of Biology Boston Massachusetts 02125 USA

Abstract

A fragment of manatee habitat that crosses theborder of Belize and Mexico includes both activitycentres and travel routes linking rivers lagoonsseagrass beds and mangrove islands near ChetumalBay Little is known about how geophysicalfeatures like coral reefs may in uence manateemovements within and between habitat fragmentslike this In this inductive study (1995ndash2001) wedocumented the seasonal occurrence of Antilleanmanatees at breaks in the northern Belize BarrierReef Survey locations were at (1) Bacalar ChicoNational Park and Marine Reserve on AmbergrisCaye (Basil Jones Cut) and (2) breaks in the reef70 km south near the Drowned Cayes (GallowsReef) The probability of sighting at least onemanatee on a 20-min point scan survey was 40(n=382) Sighting probability was signi cantlyhigher during the summer season (MayndashAugust)compared to winter months (DecemberndashMarch)Group size ranged from one to ve manateespeaking earlier (May) at the northern than southernsite (August) Seventeen identi able individualsaccounted for 87 of the sightings at Basil JonesCut with re-sightings within and between yearsOne individual from Basil Jones Cut was re-sightedat Gallows Reef Of the manatees for which sex wasdetermined 100 were males No calves weresighted To better understand manatee activitycentres and travel routes we identi ed potentialhypotheses relating seasonal in uences stopoversites for travelling males and habitat connectivityTo protect this highly vulnerable species we recom-mend inclusion of the Belize Barrier Reef as animportant component of manatee habitat withinthe coastal zone of Belize

Key words Antillean manatee Trichechus manatusmanatus Caribbean Belize habitat connectivity

stopover sites coastal zone management BelizeBarrier Reef fragmented populations seasonalhabitat use

Introduction

A sub-species of the West Indian manatee theAntillean manatee (Trichechus manatus manatus)occurs in rivers and coastal marine systems of atleast 19 countries in the Wider Caribbean Regionincluding the Greater Antilles Mexico CentralAmerica and South America (CEPUNEP 1995Lefebvre et al 2001) It is listed by the IUCN(Hilton-Taylor 2001) as vulnerable in continuingdecline with severely fragmented populations (VUA1cd C2a) and has been identi ed as one of thelsquopriority protected species of regional concernrsquo(CEPUNEP 1995 pp 1)

One population of this focal species spans theborder of Belize and Mexico a diverse habitatincluding Chetumal Bay and the northern BelizeBarrier Reef Lagoon System (Fig 1) With arelatively short coastline extending from the Gulfof Honduras in the south to Chetumal Bay inthe north Belize reports the largest number ofAntillean manatees in the Caribbean region(OrsquoShea amp Salisbury 1991) The contiguousChetumal Bay is one of the most important areasfor manatees in Mexico (Morales et al 2000) andNorthern Belize (Auil 1998) Primary habitat con-sists of rivers coastal lagoons and bays and man-grove islands between the Belize Barrier Reef andthe mainland (Bengtson amp Magor 1979 OrsquoShea ampSalisbury 1991 Gibson 1995 Auil 1998 Morales-Vela et al 2000) OVshore atoll systems such asTurneVe Atoll are considered secondary habitat formanatees (Gibson 1995 Auil 1998 Morales-Velaet al 2000)

2003 EAAM

Figure 1 Northern Belize Barrier Reef Lagoon System and Southern Chetumal Bay showing surveylocations and the 100-fathom line (100 fathoms=183 m map modi ed from Purdy et al 1975)

343Manatees on the Belize Barrier Reef

As identi ed by Packard amp Wetterqvist (1986)in Florida the components of manatee habitatsystems include activity centres travel routesresources for expansion (potential feeding areas forrecovering populations) essential areas (necessaryto survive seasonal extremes) and the supportingecosystem For the purpose of the present study wefocused on the former two We de ned activitycentres as areas where manatees were frequentlyobserved using resources such as vegetation andfreshwater in all seasons For Belize previousstudies (Gibson 1995 Lefebvre et al 2001) indi-cated activity centres were located in silty sub-strates at 1ndash3 m depth Activity centres could haveattracted both residents and travellers (Reid et al1991 Koelsch 1997) We de ned travel routes asconnections between activity centres used by indi-vidual manatees for daily seasonal or migratorymovements (Sanderson 1966) We were interestedin whether geophysical characteristics such as a reefcould have been used as landmarks by travelingmanatees

Traditional knowledge in local communities indi-cated manatees were often sighted on the BelizeBarrier Reef in the summer However the reef hadnot been included in descriptions of manatee habi-tat in Belize possibly due to a bias from researchdone in Florida where reefs were not present inareas where manatees had been studied Only onesection of Belize Barrier Reef was included innational standardized surveys ie in the northwhere it lies within several 100 m of AmbergrisCaye and has been classi ed as the caye habitattype (Auil 1998) As recommended by Weeks ampPackard (1997) we listened to local residents andchose to document in a systematic manner thepatterns of manatee occurrence that they perceivedUsing an inductive approach we examined whetherthe seasonal trend was robust and explored thereasons that this component of the habitat systemwould be most attractive to manatees in thesummer

In this paper we describe the seasonal occurrenceof predominately male manatees at two locationsalong the Belize Barrier Reef (1) Basil Jones Cutwhich was isolated by Ambergris Caye from amanatee activity centre in Chetumal Bay and (2)Gallows Reef which was adjacent to a manateeactivity centre in the Belize Barrier Reef lagoonsystem (the Drowned Cayes) and exposed to fre-quent boat traYc The study was initiated at BasilJones Cut and extended to Gallows Reef Ifmanatee presence on the reef was in uenced byaccess to warm or fresh water during the winter weexpected to nd manatees at Gallows Reef whenthey were not at Basil Jones Similarly if thepredominance of males was in uenced by isolationfrom an activity centre we expected to nd female

manatees and calves at Gallows Reef when theywere not at Basil Jones

Materials and Methods

Study siteThe Belize Barrier Reef extends from the Mexicanborder where it is only a few meters from the coastto the Gulf of Honduras where it is 50 km oVshore(Purdy et al 1975) It forms an important geo-physical barrier between the shallow coastal lagoonsystem and the deep Caribbean Sea The BelizeBarrier Reef an extensive fringing and barrierreef developed along an escarpment that abruptlyterminates the 250 km-long Belize continental shelfthe sea oor plunges to over 183 m (100 fathoms)just beyond the reef crest (Fig 1)

In this tropical area of the Caribbean seasons areless de ned by temperature and more by rainfallThe average air temperature ranges from 24 C inNovemberndashJanuary to 27 C in MayndashSeptember(Purdy et al 1975) The dry season extends fromFebruary through May the rainy season extendsfrom June through November (corresponding tothe peak probability of hurricanes in JulyndashOctober)December and January are referred to as the tran-sition season (Auil 1998) Average annual rainfallincreases in a north to south direction with 124 cmnear Chetumal Bay 178 cm at Belize City and380 cm near the Gulf of Honduras (Purdy et al1975)

The two sampling locations are approximately70 km apart (Fig 1) These locations diVer substan-tially in both geophysical characteristics and humanactivity as described in more detail below Thenorthern location Basil Jones is relatively far fromboat traYc centres and manatee resources (abun-dant seagrass beds freshwater deep channels)Both locations could provide shelter from surfsurge with areas suitable for resting and socializingwith other manatees Compared to Gallows Reefseagrass beds appear sparser near Basil Jones

Northern locationBasil Jones Cut (Fig 2a) is a few hundredmetres east of Ambergris Caye (18 5 38 N87 52 12 W) Inside the Bacalar Chico NationalPark and Marine Reserve this cut is one of severaldozen small breaks in a 50 km continuous sectionof Belize Barrier Reef that hugs the windward shore(Purdy et al 1975) Basil Jones Cut (gt3 m) is usedby powerboats travelling to a shrimp hatcheryabout a dozen local residents and a few shermenor tour operators The reef lagoon is narrow(lt500 m) and shallow (0ndash2 m) with seagrass rootedin hard calcareous sediments Travel inside thelagoon appears to be hindered by a maze of backreef coral patches and shallow water Ambergris

344 C Self-Sullivan et al

Figure 2 Aerial photographs of (a) the northern survey location at Basil Jones Cut (manatees wereobserved resting in the deep water channel ie the darker water in the photo) and (b) the southernsurvey location east of the Drowned Cayes (Gallows Reef is located along the right margin ofphotograph mainland Belize is approximately 15 km to the west) Photographs by Jimmie C Smith

(a)

(b)


Caye is a solid landmass that blocks manatee travelfrom Belize Barrier Reef to Chetumal Bay a corecentre of manatee activity (Morales-Vela et al2000) Manatees at Basil Jones Cut could travel toactivity centres via two routes (Fig 1) (1) about7 km north via Bacalar Chico a secluded narrowcanal that connects Chetumal Bay to the CaribbeanSea along the border between Belize and Mexico or(2) about 30 km south around the southern tip ofAmbergris Caye where San Pedro Town is located(a highly developed tourist destination)

Southern locationGallows Reef (Fig 2b) is a section of Belize BarrierReef with two breaks North Gallows Cut(17 30 32 N 88 3 4 W) and South Gallows Cut(17 27 25 N 88 2 17 W) This central section ofthe Belize Barrier Reef is discontinuous with largebreaks in the reef crest which provide many con-nections between deep water and the Belize BarrierReef lagoon Gallows Reef is about 2 km east of theDrowned Cayes (Fig 1) an area of man-grove islands and associated seagrass beds used bymanatees in both winter and summer (Auil 1998Sullivan et al 1999 LaCommare et al 2001)About 15 km due east of Belize City this string ofislands provides potential navigational lsquosteppingstonesrsquo from the reef to the Belize River a long-term manatee activity centre identi ed frommodern aerial survey data (Auil 1998) and pre-historic archaeological data (McKillop 1984)Throughout this shallow coastal zone boat traYc isfrequent including shing boats tugboats pullingsugar barges recreational boats tour boats andwater taxis English Channel a deep-water shippingroute into the major port at Belize City is used bycargo ships tankers and cruise ships Cruise shipsand sugar ships which are too large for the porthave berths within the barrier reef lagoon Smallfast boats transport tourists in all directions fromthe cruise ships and Belize City including well-travelled routes through the cuts at Gallows Reefto TurneVe Atoll Tugboats tow barges of sugarfrom points north to temporary sites within theDrowned Cayes and then to the sugar ship

Sampling methodsBased on year-round eVort at Basil Jones Cutseasonal periods representing winter (Decemberthrough March) and summer (June throughAugust) were chosen for eYcient allocation ofsampling eVort at Gallows Reef At Basil JonesCut opportunistic observations of manatees by alocal resident (the second author) began prior to1995 and extended beyond 1997 (Smith 2000) A2-year period (April 1995ndashMarch 1997) of consist-ent eVort was selected for the purpose of the presentanalysis (Fig 3) Preliminary studies indicated that

manatees were not present in December-Februaryhence more eVort was allocated to summermonths To determine whether manatees from BasilJones Cut were re-sighted further south surveyswere extended to Gallows Reef during a study ofthe Drowned Cayes by the primary author (Sullivanet al 1999) Sampling eVort was limited to winter(DecemberndashMarch) and summer (JunendashAugust) atGallows Reef (1999ndash2001)

Observation and recording procedures weresimilar at both locations following a protocol thatminimized disturbance by in-water observers(Smith 2000) Each sample consisted of a 20-mincontinuous scan (Lehner 1996) around a xedsurvey point One to two snorkellers continuouslyscanned 360 around the survey point while oat-ing at the waterrsquos surface All samples were col-lected between 0800 and 1600 h local time Only onesample was taken at each survey point on any givenday at Gallows Reef no more than two samples(one in the morning about 1000 h and one in theafternoon about 1600 h) were taken at the surveypoint at Basil Jones Cut

To determine sighting probability any manateeobserved during the scan was recorded as alsquosightingrsquo If a manatee approached after the end ofthe scan it was not recorded as a sighting althoughit could have been photographed if feasiblelsquoGroup sizersquo was recorded as the total number ofindividual manatees present in a scan In otherwords the number of sightings within a 20-min scanwas limited (0 1) group size was unlimited (0 1 23 N) Group sizes greater than 1 were recordedonly if more than one manatee was observedsimultaneously or if sequential observationswere ofuniquely marked individuals Sketches and photo-graphs were used to record individual identities atBasil Jones Cut photographs and video tapes wereused to record individual identities at GallowsReef When visibility was too poor for positiveidenti cation of an individual it was recorded as anlsquounknownrsquo

Behaviours (resting feeding socializing millingand travelling) body size (calf adult) and gender(male female) were recorded when possibleDe nitions of behavioural activities were (a) whenlsquorestingrsquo the manatee was stationary either in con-tact with the sea oor or at mid-water occasionallyrising in the vertical direction for breaths but withno horizontal movement no rooting or chewingand no reaction to observer (b) when lsquofeedingrsquo themanatee was rooting or chewing in a seagrass bedor had seagrass parts trailing from itrsquos mouth whenit rose above the bottom (c) when lsquosocializingrsquo onemanatee touched or followed another (d) whenlsquomillingrsquo the direction of movement changed bothvertically and horizontally with no consistent orien-tation to other manatees to food or in any one


direction and (e) when lsquotravellingrsquo the manatee wasmoving horizontally in one consistent directioneither towards or away from the survey point

To aid in interpretation of results at GallowsReef additional data were collected regarding thecontext of samples As a check on visibility biasassistants on a boat (anchored at the survey point)recorded surface behaviours of manatees relative tothe in-water observer(s) Environmental measure-ments collected immediately following the sampleincluded (1) sea-surface water temperature using athermometer (analogue or digital) (2) sea-surfacesalinity using a refractometer and (3) verticalvisibility using an eight-inch Secchi disk In noinstance was a manatee sighted by above-waterassistants that was not also sighted by the in-waterobserver(s)

The analyses were designed to account for diVer-ences in sampling eVort at Basil Jones (n=336) andGallows Reef (n=45) Independent variables wereseason (winter summer) at Gallows Reef andmonth (January through December) at Basil JonesDependent variables at both locations included (a)group size (b) frequency of surveys with manateespresent or absent Environmental measures of sea

surface temperature salinity and visibility werealso analysed at Gallows Reef Non-parametricstatistical tests of continuous variables includedthe MannndashWhitney U and the KruskalndashWallis(Lehner 1996) Contingencies were tested using theFisherrsquos exact test and the FreemanndashTukey deviate(Bishop et al 1975)

Results

Manatees were documented at both locations onthe Belize Barrier Reef during the summer monthsbut not during the winter months On 40 of allsurveys at least one manatee was sighted Asfollows analyses were speci c to each location

Basil Jones CutAt least one manatee was sighted on 42 of the 336surveys at Basil Jones Cut (Fig 3) and mean groupsize varied signi cantly among survey months(KruskalndashWallis H=119 df=6 Plt00001) Groupsize ranged from 1 to 5 with a distinctive peak inMay (Fig 4) Only single manatees were observedduring most sightings (64) and groups larger thanthree manatees were infrequent (5) Manatees

Figure 3 Individual manatee sightings at Basil Jones (April 1995ndashMarch 1997) Black boxes indicate the manatee wassighted at least once during the month seasonal code indicates dry (white) rainy (dark grey) and transitional (light grey)months Monthly probability of sighting (ST) is de ned as the number of surveys that manatees were present dividedby the total number of surveys for each month Note BJ14 (an unmarked male) is included with unknowns in this gure


were present at Basil Jones during the rainy season(June through November) and absent fromDecember through March (Fig 3) They returnedat the end of the dry season (AprilMay)

Manatees stayed in the calm deep water of thechannel inside the reef crest The primary activitywas resting with occasional socializing During onesighting two manatees were observed with seagrasstrailing from their mouths During another sight-ing two manatees were observed rooting in an areaof sparse seagrass approximately 20 m east of theresting area On one occasion a bull shark wasobserved with the manatees with no interactionTravel into the shallower areas of the lagoon systemwas rare Trends in direction of travel by manateesoutside the reef crest could not be determined

For 87 of the manatees sighted identity wasdetermined (Fig 3) Seventeen individual manateeshad unique markings and were documented bysketches most were photographed at least onceFifteen of these individuals were observed to bemales No calves or females were sighted the sex ofonly two identi able individuals was undeterminedThe sex of unknowns (13 of the sightings forwhich individual identity could not be determined)was undetermined in most cases

Group composition was uid with no detectablelong-term associations among individuals (Fig 3)Two males (BJ01 and BJ08) were re-sighted in eachof 3 years sampled All seven males that were rstidenti ed in 1995 were re-sighted the next year Tenindividuals eight males and two undeterminedwere newly identi ed in 1996 The pattern ofre-sightings within each year was variable someindividuals were present only one month eachseason others departed and returned after a break

of 1ndash3 months One individual lsquoWhite Patchrsquo (BJ01)came and went regularly (1994ndash1997) being sighted17 times over seven consecutive months in 1996The most frequently sighted individual (BJ03) waspresent in 41 surveys between April and August1996 however he was not re-sighted again untilJune of 1998

Gallows ReefAt least one manatee was sighted on 27 of the 45surveys at Gallows Reef (Fig 5) Presence diVeredsigni cantly between seasons (Fisherrsquos exactphi=0492 df=1 P=0001) Manatees were absenton 100 of surveys during the winter season(FreemanndashTukey deviate z= 3494) and presentduring 44 of the surveys in the summer season(FreemanndashTukey deviate z=1611) Group sizeranged from one to three with the larger groupsoccurring only in late July and August lsquoWhitePatchrsquo (BJ01) who was frequently re-sighted at BasilJones was re-sighted at Gallows Reef in 1999Sex was determined to be male for 10 of the 17manatees observed during all sightings No calvesor females were sighted although the sex of sevenmanatees was undetermined

In general manatees approached the in-waterobserver paused momentarily and then retreatedbeyond visible range remaining within view ofassistants in the boat On several occasions thesame manatee approached the in-water observerand retreated multiple times during a 20-min scanOn two occasions more than one identi ablemanatee approached the in-water observer bothsimultaneously and sequentially Only once did asecond individual approach the in-water observerafter the end of the scan The primary activitywas milling with occasional socializing Rarelymanatees were observed with seagrass trailing fromtheir mouths however they were not observedrooting into the substrate for rhizomes

Figure 4 At Basil Jones group size varied signi cantly bymonth (1995ndash1997) Horizontal bars indicate means andcircles indicate the range of values

Figure 5 At Gallows Reef manatees were absent on all18 winter surveys and present on 12 of 27 summersurveys


Season signi cantly aVected mean sea surfacetemperature (MannndashWhitney U=33 n=18 27Plt0001) and salinity (MannndashWhitney U=84n=18 27 P=0008) but not visibility (MannndashWhitney U=241 n=1827 P=097) Mean seasurface temperature was higher in summer(297ampSD 07 C) than winter (276ampSD 12 C)Mean salinity was higher in the hot summer rainyseason (366ampSD 08 ppt) than during the coolerwinter dry season (357ampSD 09 ppt)

Discussion

These site speci c studies at Basil Jones Cut andGallows Reef showed that manatees use breaks inthe reef at least 9 months of the year Frequentmanatee sightings during the summer indicate thatthe reef should be included in the delineation ofprimary coastal habitat for manatees

Contrary to our expectations based on move-ments in Florida manatees did not appear to bemoving from the northern survey location to thesouthern location in the winter They were absentfrom both locations on the Belize Barrier Reefduring winter samples However we documentedthat north-south travel on the reef was possiblebecause one individual that was re-sighted fre-quently in the north was re-sighted 3 years later atthe southern survey location

Based on a model of potential east-west move-ments between the Drowned Cayes activity centrewhere females and calves were frequently sightedduring the same study period (Self-Sullivanunpub-lished data) and the reef we expected to seefemales at Gallows Reef Observations of onlymales at both locations were inconsistent with thisexpectation However our sampling eVort andtechniques may have been inadequate to detectfemale presence

Consistent with an inductive approach wecaution against interpretation of these results in amanner broader than the speci c locations monthsand years of this study To generalize from thespeci c to the broad we have identi ed alternativehypotheses related to the function of reefs as travelroutes and breaks in reefs as stopover points duringtravel as described in more detail below Multiplefactors are likely to in uence manatee use of thereef and we encourage further research as to whysome individuals stayed longer than others atbreaks in the reef On a larger scale both seasonalresidency and travel routes would have importantimplications for expanding populations and geneticexchange between demes in fragmented habitats

We hypothesized that variation in seasonal dis-tribution andor movement along the Belize BarrierReef could be related to (a) seasonal changesin water temperature salinity depth and surge or

(b) sex-speci c diVerences in reproductive activityMost likely these factors are not independentrather are correlated as discussed below

Seasonal use of activity centres relative to physicalfactorsOur observations are not consistent with thehypothesis that southern breaks in the reef serve asessential areas important for winter survival ofnorthern residents Areas de ned as essential withinnorthcentral Florida habitat include warm watereZuents (gt20 C) such as natural springs andhuman-made attractions such as the warm-watereZuents of power plants (Packard amp Wetterqvist1986) However the concept of an essential area isopen to critique based on more recent studiesof individual manatee movements using satellitetelemetry Individual manatees from the Floridapopulation vary widely in seasonal movements(Deutsch et al 2000) Some travel long distancesalong the east coast of the USA others travel shortdistances within Florida or between Florida andGeorgia and still others appear to be year-roundresidents remaining in one activity centre Sincesome southern-most ranges overlap with othernorthern-most ranges of Florida manatees (T mlatirostris) factors other than ambient watertemperature appear to interact in determiningseasonal movements Perhaps lsquoseasonal activitycentrersquo would be a better term for residentmanatees

We hypothesize that access to freshwater is moreof a directive factor than temperature in in uencingseasonal manatee use of the reef in the Belizecoastal zone Alternatively individual manateemovements may be determined by a complex inter-action of many factors experienced during a life-time including learning processes in uencing howtravel routes are stored and retrieved from memoryOur reasoning is as follows

Even though manatee presenceabsence on thereef was associated with water temperature thesame variation in seasonal water temperature wasfound in the adjacent Drowned Cayes wheremanatees were observed year-round during thesame sampling period (Sullivan et al 1999LaCommare et al 2001) Water temperature in thestudy area ranged between 25 C in the winterand 31 C in the summer well above the incipientlethal level (as de ned by Fry 1947) of coldtolerance for manatees (20 C cf Irvine 1983)Temperature may have been correlated withanother undetermined directive factor or gradient

An alternative hypothesis might be that manateesmove further from estuaries during the summerrainy season when freshwater plumes from riversare more likely to penetrate further into the coastalzone meaning that manatees are more likely to be


at the reef in the summer Annual salinity range atGallows Reef was 345ndash380 ppt Osmoregulationexperiments on Florida manatees indicate that (1)they are good osmoregulators in both fresh (0permil)and marine (34permil) environments (Ortiz et al 1998)and (2) although they drink large amounts offreshwater when available they do not drinkmarine water but possibly oxidize fat to meet theirwater needs when restricted to eating seagrass in themarine environment (Ortiz et al 1999) Manateesare considered to be dependent on freshwater inFlorida (Hartman 1979) and periodic access tofreshwater is thought to be important to manateesin Belize (Gibson 1995) However it is not knownwhether nor how often manatees might move fromthe oVshore activity centres to mainland sources offreshwater in Belize Although this distance is allwell within 1-dayrsquos travel range manatees withinthe Drowned Cayes area are often sighted withdozens of salt-water barnacles covering their bodies(Self-Sullivan unpublished data) an indicationof long periods of time spent in the marineenvironment (Husar 1997)

Alternatively underwater springs near our studylocations may dry up or become unpalatable duringwinter One manatee sighted three times at BasilJones in January and February 2001 was near aspring adjacent to the channel (G Smith unpub-lished data) Whether the manatee was drinkingfrom the underwater spring could not be deter-mined the water was sulphurous as determined bysmell and colour Since we documented highersurface salinity in the summer compared to thewinter at Gallows Reef we do not believe thatrainfall provides a lens of fresh surface water at thereef Possibly the higher salinity was related toevaporation during summer months

Another hypothesis might be that the breaks inthe reef could serve as a stopover site for manateestravelling in search of fresh water in an eastndashwestdirection to and from oVshore atolls Gallows Reefis midway between the Belize River (a freshwater source) and TurneVe Atoll located furtheroVshore Manatees have been opportunisticallysighted at TurneVe Atoll a large complex man-grove island-seagrass-coral reef system similar tothe Drowned Cayes (Auil 1998 Barbara Bilgrepers comm)

Seasonal distribution also might be related towinter storms from the northwest Cold air massesfrom North America frequently aVect both tem-perature and wind strength during October throughJanuary (Purdy et al 1975) lsquoNorthersrsquo as the localpeople call these events may lower the sea surfaceby as much as 08 m These events have a greatereVect than spring tides (05 m) on water depth inshallow northern lagoons If manatees move awayfrom shallow areas inside the reef then absence

would be more likely after storm events in thewinter

Alternatively manatees may have learned thatthe reef provides shelter from high surf during thesummer hurricane season For example threemanatees were at Gallows Reef 2 days afterTropical Storm Chantal hit the coast of Belize in2001 (Self-Sullivan unpublished data) This is thelargest group sighted at Gallows Reef If manateesthat move into the protected lagoon system senseprotection from strong currents created by stormsurge breaks in the reef might serve as stopoversites for individuals moving back out to the atolls orcontinuing their north-south travel outside thereef For obvious logistical reasons such move-ments during hurricanes would be better studied bysatellite telemetry than boat-based surveys

Clearly there are several physical factors that arecorrelated with seasonal changes in the habitat usedby manatees in Belize To tease out the relativeimportance of these factors we would recommenda combination of regional studies of individualmanatee movements using satellite telemetry as wellas simultaneous site-speci c studies at breaks in thereef This type of approach would also provide abetter understanding of how external environ-mental conditions interact with physiological statesas outlined below

Relation between travel and seasonal malereproductive activityNoting the distinctive absence of females at thebreaks in the reef that we studied a hypothesisemerged related to potential seasonal changes inreproductive activity of males The evidence thatmanatees show seasonal patterns in reproductivebehaviour is still ambiguous Early reports byHartman (1979) and Marsh et al (1978) found noevidence for strong seasonality in Sirenian repro-ductive behaviour However Best (1982) reportedseasonal breeding in the Amazonian manatee (Tinunguis) More recently seasonal spermatogenesishas been reported in both Florida manatees(Hernandez et al 1995) and dugongs (Dugongdugon) (Marsh 1995) Similarly seasonal variationin female reproductive hormones has been shown incaptive Florida manatees (Larkin 2000) Howeverseasonal reproductive activities were not tightlycoordinated within populations (Larkin 2000 Best1982 Marsh et al 1984 Marsh pers comm)

By tracking manatees using VHF radio andsatellite tags since 1997 Powell et al (2001) foundmore variation in male than female movementpatterns in coastal lagoons south of Belize City Forexample females and some males remained insidethe enclosed estuary year-round However a fewmales wandered outside the lagoon system northand south along the mainland coast of Belize one


male travelled at least as far as Belize City 33 kmnorth (Powell pers comm)

Based on published literature and our obser-vations of only males on the reef with seasonalpeaks and absences we hypothesized that malemanatees use the reef as a landmark during searchesfor oestrous females throughout the coastal lagoonsystem If there is a winter low in spermatogenesisthen movement rates might decline If there is apeak in both oestrous females and searching behav-iour of males in summer then male movement ratesmay increase Variations in seasonal reproductiveactivity within a population might explain thediVerence in sighting peaks between Basil Jones(MayndashJune) and Gallows Reef (JulyndashAugust)Alternatively sighting peaks could indicateclustered movements by males along the reef

To test these alternate hypotheses we wouldrecommend satellite-telemetry studies of both malesand females in activity centres adjacent to the reef(Drowned Cayes and Chetumal Bay) combinedwith simultaneous site-speci c studies of individu-ally identi able manatees Such studies couldanswer the critical question of the degree to whichthere is a seasonal peak in reproductive activityof manatees in Belize and the degree to whichmale manatees move along the reef during peakreproductive periods

Implications for expanding populations infragmented habitatBased on our sightings of lsquoWhite Patchrsquo (BJ01) atboth the northern (1994ndash1997) and southern (1999)sampling locations we hypothesized manateesmove along the reef in a north-south directionHowever we were not able to monitor both loca-tions simultaneously Extensive studies based onre-sightings of individually marked manatees havebeen successful in Florida (Reid et al 1991) andshould be continued in Belize Over the long-termthese studies can be combined with satellite-taggingstudies to determine variation in movement pat-terns during the lifetimes of individuals within apopulation (Beck amp Reid 1995 Reid et al 1995)By comparing records at TurneVe Atoll (Bilgreunpublished data) the Drowned Cayes GallowsReef (Smith 2000 Self-Sullivan unpublished data)and Basil Jones (Smith 2000) a more accuratemodel of what in uences manatee movements in thecentre of the speciesrsquo range may emerge for com-parison with what is known from the northernextreme of the range as studied in Florida

Long distance movements in uence gene owamong subpopulations as re ected in complex pat-terns of genetic variation among manatees in thegreater Caribbean area (Garcia-Rodriguez et al1998) Movements of individual Florida manateesalong the Atlantic coast of North America range

from 44 km to 2360 km (median=309 km) at ratesof 25 km to 87 km per day (Deutsch et al 2000) Incomparison the Belize Barrier Reef extends onlyabout 220 km with many breaks that could be usedas stopover sites or for ingress to manatee activitycentres such as Chetumal Bay Cayes oV BelizeCity Southern Lagoon the Gulf of Honduras andnumerous coastal rivers and bays (Auil 1998)Considering the long travel range of Floridamanatees Antillean manatees could move amongpopulation centres along the Yucatan Peninsulafrom Mexico through Belize to Guatemala andHonduras (Auil 1998) During population expan-sion following historical exploitation manateesfrom Belize may colonize unoccupied habitatbetween population centres in a wider region withpositive in uences on gene ow

The reef may also in uence connectivity withinthe Belize Barrier Reef lagoon system decreasingthe probability of inbreeding by increasing move-ments between southern areas and Chetumal BayThe deep water just east of the barrier reef oVers anunobstructed north-south travel corridor and thereef oVers a physical feature that could be used fornavigation Use of this travel route by manateescould be an alternative to movement through thecomplex labyrinth created by the mangrove-seagrass-coral lagoon system inside the barrier reefAn analogy might be a loop highway around ametropolitan maze of small roads

Consistent with knowledge of lsquobachelor malesrsquo inother marine mammals species we hypothesize thatthe turnover of individuals using stopover sites onthe reef could be related to turnover in male accessto breeding females In 2001 local tour guides andstaV at Bacalar Chico Reserve reported that theylsquoregularlyrsquo observed manatees in a side lagoonadjacent to Bacalar Chico and at another cut in thereef between Bacalar Chico and Basil Jones (Smithunpublished data) Another local tour guidereported that he observed a group of ve manateesinside the reef crest at GoVrsquos Caye (a sand caye onthe Belize Barrier Reef just south of Gallows Reef)in November 2001 (Self-Sullivan unpublisheddata) And a third tour guide reported seeing amanatee outside the reef crest at South Water Caye(a sand caye on the Belize Barrier Reef still furthersouth) in June 2002 (Self-Sullivan unpublisheddata) We recommend studies to determine if theseare young dispersing males prime males betweenperiods of breeding activity or old males unlikely tobreed again Answering these questions will provideinsight to how genetic heterogeneity may be main-tained in relatively isolated subpopulations ofmanatees

We recommend that the broader implications ofthis highly speci c study should be considered in thecontext of eVorts to design marine reserve systems


within the Caribbean The concept of lsquoconnectivityrsquowas used by Roberts (19971454) to draw attentionto how lsquolocal populations may depend on processesoccurring elsewherersquo Although Roberts referred topatterns of larval transport among coral reefs theconcept also should be applied to large-bodiedvulnerable species that use the lagoon systems pro-tected by reefs eg manatees We use the concept oflsquostopover sitesrsquo in a manner similar to its use instudies of migratory bird species For exampleHiguchi et al (1996) identi ed stopover sites wheremigratory cranes paused for less than 10 daysduring travel between breeding and non-breedinglocations Although Antillean manatees clearly arenot migratory as a species the concept of a stop-over site may be applied to a relatively shortinterruption of travel by individuals Protectingstopover sites within local lagoon systems could beas important for conserving genetic heterogeneityas protecting long-distance travel routes connectingfragmented populations on a regional scale

Conclusions

Developing eVective strategies for conservation ofmanatee habitat requires knowledge of activitycentres and movements among them We docu-mented manatee presence at breaks in the BelizeBarrier Reef with signi cantly more sightings inthe summer (rainy) season than in the winter(transitiondry) season Groups were small (averageof two manatees) some individuals were repeatedlysighted and others were not At least one individualmoved between the northern and southern breaksthat we monitored All of the manatees for whichsex was determined were male and no calveswere sighted However we are cautious aboutinterpretation of these data due to the inductivenature of this study We proposed several hypoth-eses related to physical (temperature salinitydepth storm surge) and physiological (thermo-regulation osmoregulation reproductive status)factors potentially aVecting manatee use of breaksin the reef To test these hypotheses we recommendsimultaneous studies of identi able manatees atseveral locations on the reef In addition satellite-tagging techniques would be appropriate for deter-mining the seasonality and extent of individualmanatee movements among activity centres andstopover sites along travel routes associated withgeophysical characteristics of the Belize BarrierReef Based on results of this study we proposethat reefs should be considered part of the networkof travel routes and stopover sites identi ed asimportant components maintaining connectivitywithin manatee habitat in Belize and between frag-mented populations of Antillean manatees in theCaribbean

Acknowledgments

This research project was reviewed by the BelizeNational Manatee Working Group Coastal ZoneManagement Authority and Institute and con-ducted under Scienti c Research Permits issued bythe Belize Forestry Department ConservationDivision Funding and in-kind support were pro-vided by The Oceanic Society of San Francisco TheLernerndashGray Marine Science Research Fund TheEarthwatch Institute Spanish Bay Resort TexasAampM University University of Massachusetts-Boston and the National Science FoundationGraduate Fellowship Program We are extremelygrateful to our Belizean eld assistants PachMunoz Landy Requena Jerry Requena andGilroy Robinson our Belizean student internsMaxine Monsanto Seleem Chan and CliftonWilliams our logistics interns Liz Johnstoneand Pam Quayle and our Oceanic Society andEarthwatch Institute volunteers for their assistancein data collection We thank Jimmie C Smith forproviding aerial photographs of our study areaOur gratitude is extended to Nicole Auil MiriamMarmontel and Leon David Olivera-Gomez forcomments on previous drafts of this manuscript

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Auil N (1998) Belize Manatee Recovery Plan UNDPGEF Coastal Zone Management Project BZE92G31BelizeUNEP Caribbean Environment ProgrammeKingston

Beck C A amp Reid J P (1995) An automated photo-identi cation catalog for studies of the life history ofthe Florida manatee In T J OrsquoShea B B Ackermanamp H F Percival (eds) Population Biology of the FloridaManatee pp 120ndash123 National Biological ServiceWashington DC

Bengtson J L amp Magor D (1979) A survey of manateesin Belize Journal of Mammalogy 60 230ndash232

Best R C (1982) Seasonal Breeding in the AmazonianManatee Trichechus inunguis (Mammalia Sirenia)Biotropica 14 76ndash78

Bishop Y M M Fienberg S E amp Holland P W(1975) Discrete Multivariate Analysis The MIT PressCambridge

CEPUNEP (1995) Regional Management Plan forthe West Indian Manatee Trichechus manatusCEP Technical Report No 35 UNEP CaribbeanEnvironment Programme Kingston

Deutsch C J Reid J P Bonde R K Easton D EKochman H I amp OrsquoShea T J (2000) Seasonalmovements migratory behavior and site delity ofWest Indian manatees along the Atlantic coast of theUnited States as determined by radio-telemetry FinalReport Research Work Order No 163 FloridaCooperative Fish and Wildlife Research UnitUS Geological Survey and University of FloridaGainesville

Fry F E J (1947) EVects of the environment on animalactivity University of Toronto Studies Biological Series


55 Ontario Fisheries Research Laboratory 68University of Toronto Press Toronto

Garcia-RodrieguezA I Bowen B W Domning D PMignucci-Giannoni A A Marmontel M Montoya-Ospina R A Morales-Vela B Rudin M BondeR K amp McGuire P M (1998) Phylogeography of theWest Indian manatee (Trichechus manatus) how manypopulations and how many taxa Molecular Ecology 71137ndash1149

Gibson J (1995) Managing Manatees in Belize MSThesis Department of Marine Sciences and CoastalManagement University of Newcastle upon Tyne

Hartman D S (1979) Ecology and Behavior ofthe Manatee (Trichechus manatus) in FloridaSpecial Publication No 5 The American Society ofMammalogists

Hernandez P Reynolds J E Marsh H amp MarmontelM (1995) Age and seasonality in spermatogenesis ofFlorida manatees In T J OrsquoShea B B Ackerman ampH F Percival (eds) Population Biology of the FloridaManatee pp 84ndash97 National Biological ServiceWashington DC

Higuchi H Ozaki K Fijita G Minton J Ueta MSoma M amp Mita N (1996) Satellite tracking ofWhite-naped crane migration and the importance of theKorean demilitarized zone Conservation Biology 10806ndash812

Hilton-Taylor C (compiler) (2001) 2000 IUCN Red Listof Threatened Species IUCN Gland Switzerland andCambridge UK

Husar S L (1977) The West Indian manatee (Trichechusmanatus) Wildlife Research Report 7 USDepartment of the Interior Fish and Wildlife ServiceWashington D C

Irvine A B (1983) Manatee metabolism and its in uenceon distribution in Florida Biological Conservation 25315ndash334

Koelsch J K (1997) The seasonal occurrence and ecol-ogy of Florida manatees (Trichechus manatuslatirostris) in coastal waters near Sarasota FloridaMasterrsquos Thesis Department of Biology University ofSouth Florida

LaCommare K S Sullivan C S amp Brault S (2001)Distribution and foraging ecology of Antilleanmanatees (Trichechus manatus) in the Drowned Caysarea of Belize Central America Abstracts 14thBiennial Conference on the Biology of MarineMammals November 29ndashDecember 3 2001Vancouver Canada

Larkin I L V (2000) Reproductive endocrinology of theFlorida manatee (Trichechus manatus latirostris)estrous cycles seasonal patterns and behavior PhDDissertation University of Florida

Lefebvre L W Marmontel M Reid J P RathbunG B amp Domning D P (2001) Status and biogeogra-phy of the West Indian manatee In Charles A Woodsamp Florence E Sergile (eds) Biogeography of the WestIndies Patterns and Perspectives pp 425ndash474 CRCPress New York

Lehner P N (1996) Handbook of Ethological Methods2nd edition Cambridge University Press

Marsh H (1995) The life history pattern of breeding andpopulation dynamics of the dugong In T J OrsquoShea

B B Ackerman amp H F Percival (eds) PopulationBiology of the Florida Manatee pp 75ndash83 NationalBiological Service Washington DC

Marsh H Heinsohn G E amp Glover T D (1984)Changes in the male reproductive organs of thedugong Dugong dugon (Sirenia Dugondidae) with ageand reproductive activity Australian Journal ofZoology 32 721ndash742

Marsh H Spain A V amp Heinsohn G E (1978)Minireview physiology of the dugong ComparativeBiochemisty and Physiology 61A 159ndash168

McKillop H I (1984) Prehistoric Maya Reliance onMarine Resources Analysis of a Midden from MohoCay Belize Journal of Field Archaeology 11 25ndash35

Morales-Vela B Olivera-Gomez D Reynolds J E ampRathbun G B (2000) Distribution and habitat use bymanatees (Trichechus manatus manatus) in Belize andChetumal Bay Mexico Biological Conservation 9567ndash75

Ortiz R M Worthy G A J amp Byers F M (1999)Estimation of water turnover rates of captive WestIndian manatees (Trichechus manatus) held in fresh andsalt water Journal of Experimental Biology 202 33ndash38

Ortiz R M Worthy G A J amp MacKenzie D S (1998)Osmoregulation in wild and captive West Indianmanatees (Trichechus manatus) Physiological Zoology71 449ndash457

OrsquoShea T J amp Salisbury C A (1991) Belize - a laststronghold for manatees in the Caribbean Oryx 25156ndash164

Packard J M amp Wetterqvist O F (1986) Evaluation ofmanatee habitat systems on the northwestern Floridacoast Coastal Zone Management Journal 14 279ndash310

Powell J A Bonde R Aguirre A A Koontz CGough M amp Auil N (2001) Biology and movementsof manatees in Southern Lagoon Belize Abstract inProceedings of the 14th Biennial Conference on theBiology of Marine Mammals Vancouver

Purdy E G Pusey W C III amp Wantland K F (1975)Continental shelf of Belize ndash regional shelf attributesIn K F Wantland amp W C Pusey III (eds) Studies inGeology No 2 Belize Shelf ndash Carbonate SedimentsClastic Sediments and Ecology and a paper on Petrologyand Diagenesis of Carbonate Eolianites of NortheasternYucatan Peninsula Mexico pp 1ndash52 The AmericanAssociation of Petroleum Geologists Tulsa

Reid J P Rathbun G B amp Wilcox J R (1991)Distribution patterns of individually identi ableWest Indian manatees (Trichechus manatus) in FloridaMarine Mammal Science 7 180ndash190

Reid J P Bonde R K amp OrsquoShea T J (1995)Reproduction and mortality of radio-tagged and recog-nizable manatees on the Atlantic Coast of Florida InT J OrsquoShea B B Ackerman amp H F Percival (eds)Population Biology of the Florida manatee pp 171ndash191National Biological Service Washington DC

Roberts C M (1997) Connectivity and management ofCaribbean coral reefs Science 278 1454ndash1457

Sanderson G C (1966) The study of mammalmovements ndash a review Journal of Wildlife Management30 215ndash235

Sullivan C S Packard J M amp Evans W E (1999)Spring distribution and behavior of Antillean manatees(Trichechus manatus manatus) in the Drowned Cayes


Belize Abstracts 13th Biennial Conference on theBiology of Marine Mammals November 28ndashDecember3 1999 Wailea Maui Hawaii

Smith G W (2000) Identi cation of Individual ManateeIn the Basil Jones Area of the Bacalar Chico MarineReserve and the Drowned Cays Area of Belize Annual

Report to the National Manatee Working GroupCoastal Zone Management Institute amp AuthorityBelize City

Weeks P amp Packard J M (1997) Acceptance ofscienti c management by natural resource dependentcommunities Conservation Biology 11 236ndash245


Figure 1 Northern Belize Barrier Reef Lagoon System and Southern Chetumal Bay showing surveylocations and the 100-fathom line (100 fathoms=183 m map modi ed from Purdy et al 1975)













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