EL cCrocodylus rnoreletii.

by Steven G. PlattClemson University, South Carolina

Morelet's Crocodile, Crocodylusmoreletii, was described in j'851 by Augusteand Andre Dumeril, based on specimenscollected in the Peten region of Guatemalaby the explorer-naturalist P. M. A. Morclet.Owing to confusion over Morelet's localitydata it was later suggested that the animalsoriginated in Cuba, and that C. moreletiiwas therefore synonymous with the Cu-ban Crocodile, C. rhombifer. This confusionpersisted until 1'924, when Karl SchmiMofthe Chic<lgu Museum of Natural History

collected additional material from the vi-cinity of present-day Belize City, and re-solved the question. But even todily thisreptile remains reliltively unstudied.

Morelet's Crocod ile is found through-out the Atlantic lowland of Mexico, Belize,eastern Guatemala, and (possibly) extremenortheastern Honduras. In Mexico, thespe-cies has been reported in northernTamaulipas, within 100 miles of the inter-national border, and at one time it mayhave been found ·as far north as the lower

Rio (;rande Valley, Within this ran;;fMorelet's j ildapted tf' 3 wide variety ofhabitats including lakes, swamps, rivers,marshes, and even man-made livestockponds and roadside ditches. In coastalmangrove swamps, it may occursympatri-cally with the American Crocodile, C.acutus. However,optimum habitatappearsto be heavily vegetated freshwilter lagoonsand marshes.

At one time Morelet's Crocodile wasabundant. Early writers tell of numerousspecimens in ditches along major roads, aswell as the banks of jungle rivers beinglined with basking animals. Even allowingfor the exaggeration of tra'vellers' tales, it isevident that these reptiles were commonlyencountered.

Populations have since been greatlyreduced,and the species is included on the1990 IUCN Red Ust as Endan&cred. The

rnajoi f:ictO:·~ ,'\.J l.rib· ClI( •..• ;11:,·';eciJ~.are habitat destructio,l and overhuntll1~.The belly skin lacks ostcoderms and h<lssmall scutes--qualities highly desirable tothe leather industry. During the 1950s ano1960s populations we:e heavily exploited.Crocs were hunted at night, located by thered glow of their eyes in the beam of aheadlight, and shot or harpooned at clost'range. Harpooning was the preferredmethod of the professional hide hunters asfew animals were lost. A. Starker Leopold,in his book Wildlife of Mexico, tells howgroups of Americans operating from large'ships systematically hunted the coas't,,1

•swamps, decimated populations, and then.moved on. Elsewhere, IiIgarteros, (alligatorhunters) harvested populations to near ex-tinction; incredible numbers of crocodileswere killed. A professional hunterin Beliz(>related how, in a single night, he killed

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over 40 crocodiles. The only thing regulat-ing his kill was the number of animals hecould skin before the carcasses began tospoil in the tropical heat.

By 1980, populations in all but themost inaccessible swamps had been se-verely impacted. Morelet'sCrocodileisnowlegally protected in all countries where it isfound, and is afforded protection underAppendix I of the Convention on Interna-tional Trade in Endangered Species(C.I.T.E.S.). Commercial trade in Appen-dix iwildlife is prohibited, with the excep-tion of captive-bred animals. A low levelofpoaching continues. l..>utpopulations haveincreased in many areas. Today largepopu-lations are found in LakeCatemacoand theSian Kaan Biosphere Reserve of Mexico,Lake Peten in Guatemala, and in somewetbnds of northern Belize, most notablythe New River and it's watershed.

Morelet's is not large by crocodilianstandards, being similar in size to theAmerican Alligator (A. mississippiensis).Most adults range from six to nine feet in

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length. Large males may reach 13 feet, whilefemales are generally smaller and reachsexual maturity at about five feet. Themaxi-mum size reported was a 13.6-foot speci-mencapturcd in Lake Catemaco, Veracruz,Mexico.

Only recently have studies begun tounravel the life history of this hithertopoorly known species. An elaborate court-ship takes place in the late dry sea"on(March to May) and nesting commen.:cswith thcon:-ctofthera'ny :,easo in mid-l'~late June. Females appear to be terntonaland nests arc usually widely spacL>d.

Nest site selection is one of the JeLlstunderstc 'xl Llspeets of crocod ilian biology.Unlike the American Alligdtorand Saltwa-ter Crocodile (c. porosus) which readilynest on mats of floating. vegetation,Morelet's shun such sites, and seem torequire a solid substrate, elevated abov,ethe normal water level, with adequatecover. Manyofthenestsexamined in Belizewere constructed on small islands. Such asite confers an obvious advantage in the

protection afforded from nest predators,C. moreletii is the only mound-nesting

sJX"Ciesof crocodile in the New World. Thefemale constructs the structure over a pe-riod of two to four days, raking vegetation,soil, and other debris i"to a large pile whichmay measure up to two feet high and ayard across. Humidity within this moundapproaches 100%. A clutch of 10 to 50 eggsis deposited within thenc"t.Generallyoldertemale::. lay arger clutches,In captivity re-m,) .~~.nt,,,t dr';l~<\lly, but it's unknown if"similar cycle occ r;;"'in the wile!.

Fertility ot croc-exlile eggs is L1etermined by noting the presenccor absenccolan opaque band on the shel! This bandbegins forming shortly after laying, whel.the embryo attaches to the shell tllcmbran,';albumen is dehydrated, and water is trans-ferred to the yolk. The dehydration of theLllbumen results in the formation of a tell-tale stripe which expands from the mid-point of the egg as embryo developmentproceeds. The numberof fertile eggs within

• a clutch varies widely, from zero to almost

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CrocodileslackXand Ychromosomes,and the sex of hatchlings is determined bythe incubation temperature. Extremely highor low temperatures result in the produc-tion of females, while males are producedat moderate temperatures. Optimum nesttemperature in most. species is 89.6°F ±1.5°F. Under natural incubation regimes,nest temperatures usually fall within the86.8° to 91.4°F range, which probably re-sults in a mixture of males and femalesbeing p~oduced. Nest temperatures mayincrease one or two degrees during thefinal stages of incubation as a result ofmetabolic heat produced by the develop-ing embryo. In addition to determiningsex, the temperature of the nest has beenfound to influence a wide range of post-hatching attributes, most notably growthrates and survival.

During the incubation period, femalesremain close to the nest site, actively de-fending it from predators. Nest dcfense by

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the males has not been observed in thewild, although one in Belize routinely en-gages in this practice, and responds to ta pe-recorded vocalizations of hatchlings.

Nesting success, defined as the num-berof nests which produce hatchlings, var-ies from year to year. In Belize, only aboutone-third are successful. The principalcauses of failure are flooding and preda-tion. Heavy rains, a common occurrenceduring the wet season, often raise waterlevels drastically in a period of severalhours, flooding crocod ile nests. Those eggssubmerged for 12 to 24 hours suffer nearlycomplete mortality. Predators such as rac-coons, and to a lesser extent Gray Foxesand Coatimundis, also take a heavy toll.

Incubation time varies somewhat de-pendingon temperature, b\lt most clutcheshatch in 75 to 85 days. Upon escape fromthe egg, the young begin to vocalize, whichstimulates the remaining hatchlings to·alsoemerge, and the female responds by dig-ging open the nest. Using her forelegs, she

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tears at the nest mound, gently scoops upthe hatchlings in her mouth, and carriesthem to the water. Eggs which fail to hatchare consumed. If the female is unable toreturn to the nest and open it, the hatchlingswill most likely perish.

Most activity among both the adultsand neonates takes place at night. The day-light hours are spent in bank dens, or lyingon the bottom, surfacing occasionally tobreathe. Animals may emerge at any timeof the day to bask, but do so primarily inthe early-morning hours before the tropicalsun becomes too intense. Foraging beginsat dusk and continues throughout the night.

Young crocodiles search for food inthe heavily vegetated shallows, rarely ven-turing into open water. This microhabitatoffers escape cover and an abundance ofprey. Adults forage in these areas and indeeper, more open water.

Morelet's Crocodiles are opportunis-tic feeders and consume a diverse assem-blage of prey. Stomach contents of juve-niles and subadultsarereadily obtained by

stomach pumping, a method easy to em-ploy in the field and harmless to the ani-mals. Based on results of such studies ithad been found that young animals feedprimarily on invertebrates such as insects,spiders, crayfish, and snails. Surprisinglyfew fish or frogs are taken by these smallersize classes. Subadults, while still consum-ing a considerable amount of invertebrateprey, also feed heavily on turtles, basilisklizards, various surface swimming fish,birds, and rodents. Due to the difficulty ofcapturing large crocodiles, the food habitsof ad ults are not well known. Observers inMexico have chronicled a long list of preyitems including crabs, toads; iguanas,turtles, various wading birds and water-fowl, opossums, dogs, and even goats. Thestomachsoftwodead females thatdrownedin fishing nets were found to contain largenumbers of Apple Snails, and it has beensuggested that these may proVide a sourceof calcium for egg formation.

Necrophagy, the scavenging of de-composing prey, is occasionally observed

in Morelet's Crocodile. Large specimenshave been observed to sequester prey un-derwater,-returning later and consuming itin an advanced state of decomposition. InBelize, crocodiles fed on cattle which be-came mired in the soft lake margin anddied.Crocodiles located the carcasseswithin 24 hour." probably by smell, andaggregated in the immediate vicinity. De-spite the bloated condition of the carcasses,the crocod iles were unable to gain access tothe interior of the dead cow until blackvultures ripped open the thin abdominalwall. A dominance hierarchy was evident,with smaller crocodiles yielding as largerones moved in to feed. Each carcass wastypically consumed within 48 hours.

Man-eating by Morelet's Crocodiledoes not occur with any regularity, al-though several cases have been docu-mented. Predation on dogs, particularlyhunting dogs pursuing deer throughswamps, is reputed to frequently occur.Crocs have also been known to remove fishand turtles from nets set by fishermen.

C,mnibalism has been documentedamong captive Morelet's, but not in thewild. Cannibalism among most crocodil-'ians seems to be a density-dependentmechanism of population regulation. Whenpopulations reach carrying capacity thelarge, dominant males begin to feed onsmaller animals. It is unlikely that anypopu-lations of Morelet's Crocodile have reachedpopulation levels great enough for canni-balism to become manifest. Excess animalsprobably just disperse into unoccupiedhabitats.

Morelet's Crocodile reproducesreadily in captivity. Several commercialfarming ventures have l?een launched inMexico, but to date none has been eco-nomically successful. These programs ha v£>been hailed as a possible source of allimal-for reintrod ction into the wild in theevpntpopulations become severely depleted utextirpated. However, given adequate habi-tat and protection from poaching, reintro-duction will not become necessary and the.future of the species looks promising. -JP<

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