SOUTHEASTERN NATURALIST2005 4(3):533–536

Unusual Offshore Occurrence of an American Alligator

RUTH M. ELSEY*

Abstract - An American Alligator (Alligator mississippiensis Daudin) was observedand photographed in the Gulf of Mexico on 4 May 2004, some 56 km south of MarshIsland, LA (approximately 63 km from the nearest point on mainland Louisiana).Alligators generally avoid saltwater and we are unaware of prior documentation of analligator occurring this distance offshore.

Introduction

The American Alligator (Alligator mississippiensis Daudin) occurs inwetlands of several southeastern states, and its range includes coastalmarshes adjacent to the Gulf of Mexico (Joanen and McNease 1987). InLouisiana, alligators prefer aquatic habitats of low salinity, and are morenumerous in freshwater lakes or bayous, or marshes categorized as interme-diate, or dominated by vegetation able to tolerate low salinity levels. Ingeneral, alligators become less common in brackish marshes and nesting israre in salt marshes (Elsey and Kinler 2004). Saltwater Crocodiles(Crocodylus porosus Schneider) have functional lingual salt glands that areessential to osmoregulation in salt water (Taplin and Grigg 1981). Thelingual glands in alligators are thought to be salivary rather than salt glands,due to low secretory rates of essentially isosmotic secretions (Taplin et al.1982); thus, alligators poorly tolerate hyper-saline conditions (Mazzotti andDunson 1984). The American Crocodile (Crocodylus acutus Cuvier) is theonly other crocodilian found principally in saline habitats (Taplin et al.1982), though four species (including the American Alligator, Crocodylusniloticus Laurenti, C. palustris Lesson, and C. johnstoni Krefft) occur occa-sionally in saline waters (Neill 1971, Taplin et al. 1982).

Observations and Discussion

On 4 May 2004, an alligator was observed by offshore oil companyemployees working on an oil platform and adjacent barge. The platform(Eugene Island - 133) is located at north 28º58.39' latitude and west91º51.00' longitude. These coordinates put the alligator far in the Gulf ofMexico, some 56 km south of Marsh Island. The nearest distance to main-land Louisiana from the alligator’s location was approximately 63 km fromPoint Au Fer to the east, or 74 km to Freshwater Bayou to the west (Fig. 1).The water depth at this location is approximately 23.62 m.

I interviewed two gentlemen who observed the alligator on site. Mr.Anthony Jackson, an operator for Chevron, USA, saw the alligator from the

*Louisiana Department of Wildlife and Fisheries, Rockefeller Wildlife Refuge, 5476Grand Chenier Highway, Grand Chenier, LA 70643; relsey@wlf.louisiana.gov.

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oil production platform. Mr. Johnny Migues, a construction supervisor forKellogg, Brown, and Root, was on a jack-up boat adjacent to the platformand photographed the alligator (Fig. 2). The following description is acomposite of the details provided by the two witnesses.

Both observers estimated the alligator to be at least 183 cm total length andpossibly closer to 213 cm in length. It approached the platform from the south/southeast sometime after 12:00 noon on 4 May 2004. It swam normally anddove intermittently. Both witnesses suggested the alligator circled the plat-form, possibly trying to find a surface upon which to rest. The alligator stayedin the vicinity of the platform and boat for several hours; Mr. Migues said thealligator was still swimming nearby when he left the platform area on the jack-up boat near dusk. Mr. Jackson (who works permanently at EI-133) said he hasnot seen the alligator subsequent to the afternoon of 4 May.

Mr. Migues stated that in 29 years of employment on offshore oil rigs, hehas never before seen an alligator offshore. Mr. Jackson has seven yearsexperience working offshore, and has only once previously seen an alligator inthe Gulf of Mexico. At the time he was on a platform approximately 16.09 kmoffshore. That alligator was swimming westward and never slowed or alteredits course. I asked several helicopter pilots who routinely fly oilfield crews tooffshore platforms if they had ever observed alligators in transit; none had,although they often fly at altitudes which would preclude direct observation.

Numerous physiological studies have illustrated that juvenile alligatorspoorly tolerate increasing water salinity (Lance et al. 2001, Lauren 1985,Morici 1996) which causes increased plasma corticosterone and decreasedgrowth rates.

However, we have seen numerous cases in which alligators traveled frommainland Louisiana (St. Mary, Terrebonne, and Vermilion Parishes) to MarshIsland, having traversed several km across Vermilion Bay (Campbell andKinler 2001, Elsey et al. 2001 ). The salinity in Vermilion Bay varies seasonallywith addition of flood waters from adjacent river systems (Vermilion andAtchafalaya Rivers) and ranges from essentially freshwater to approximately10–15 parts per thousand. It is unclear why such dispersal across hyper-saline

Figure 1. Map ofLouisiana showinglocation of alliga-tor sighted far inthe Gulf ofMexico. Note alli-gator was seen at apoint some 56 kmsouth of Marsh Is-land, and approxi-mately 63 km fromthe mainland atPoint Au Fer.

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waters occurs. We recently documented numerous cases of long-distancemovement in alligators, including a female alligator that moved some 90 kmfrom the initial capture site over a three year period (Elsey et al. 2004), althoughthis dispersal was via non-saline waterways and possibly over land.

We have also had numerous reports of “nuisance” alligators being caughtin the Gulf of Mexico, along the beach/shoreline in Holly Beach, RutherfordBeach, and Constance Beach in Cameron Parish in southwest Louisiana.These likely accessed the Gulf from adjacent brackish marshes or by travel-ing to the Gulf by man made ship channels (M. Savoie and E.C. Trahan,licensed Louisiana alligator trappers, pers. comm.). Many are in the 152–183 cm size class, but alligators as large as 274 cm have been caught at thesebeach sites (E.C. Trahan, pers. comm.).

The barnacles on the oilfield platform (Fig. 2) suggest the alligatorshown is in full strength seawater. The alligator appears to have a normalbody habitus and does not appear cachectic or anorexic (Fig. 2). Lance et al.(2001) suggested adult alligators can survive for some time in full strengthseawater, probably because their thicker skin (relative to hatchling/juvenilealligators) is relatively impermeable. To our knowledge this is the first

Figure 2. Photograph of alligator seen near oil field platform on 4 May 2004. Thelength of the alligator is unknown, but appears to be a relatively large adult. Photo-graph © by Mr. Johnny Migues.

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report of an alligator occurring so far offshore. Due to increasing concernsabout saltwater intrusion and habitat deterioration in coastal Louisiana,similar such observations warrant further study.

Acknowledgments

I thank Anthony Jackson and Johnny Migues for detailed information providedconcerning their observation, and Mr. Migues for use of the photograph in Figure 2. Iappreciate the assistance of Brandon and Mary Hebert in bringing the photograph to myattention, and Jeb T. Linscombe and Karen S. McCall for preparation of the manuscript.

Literature Cited

Campbell, L., and N. Kinler. 2001. 2000 Marsh Island Wildlife Refuge experimentalalligator harvest program. Unpublished report. 38 pp.

Elsey, R.M., L. McNease, and T. Joanen. 2001. Louisiana's alligator ranching pro-gram: A review and analysis of releases of captive-raised juveniles. Pp. 426-41,In G. Grigg, F. Seebacher, and C. E. Franklin (Eds.). Crocodilian Biology andEvolution. Surrey Beatty and Sons, Chipping Norton, Australia.

Elsey, R.M., and N. Kinler. 2004. Louisiana’s alligator program: Adapting manage-ment as populations recover and risk of unsustainable use decreases. Pp. 92–101,In Crocodiles. Proceedings of the 17th Working Meeting of the Crocodile Special-ist Group. IUCN-The World Conservation Union, Gland, Switzerland, andCambridge, UK.

Elsey, R.M., V. Lance, and P.L. Trosclair III. 2004. (Abstract). Evidence for long-distance migration by wild American Alligators. Pg. 70, In Crocodiles. Proceed-ings of the 17th Working Meeting of the Crocodile Specialist Group. IUCN-TheWorld Conservation Union, Gland, Switzerland, and Cambridge, UK.

Joanen, T., and L. McNease. 1987. The management of alligators in Louisiana, USA.Pp. 33–42, In G.J.W. Webb, S.C. Manolis, and P.J. Whitehead (Eds.). WildlifeManagement: Crocodiles and Alligators. Surrey Beatty and Sons Pty. Limited,Chipping Norton, Australia.

Lance, V.A., L.A. Morici, and R.M. Elsey. 2001. Physiology and endocrinology ofstress in crocodilians. Pp. 327–40, In G. Grigg, F. Seebacher, and C.E. Franklin(Eds). Crocodilian Biology and Evolution. Surrey Beatty and Sons, ChippingNorton, Australia.

Lauren, D.J. 1985. The effect of chronic saline exposure on the electrolyte balance,nitrogen metabolism, and corticosterone titer in the American Alligator, Alliga-tor mississippiensis. Comparative Biochemistry and Physiology 81A:217–23.

Mazzotti, F.J., and W.A. Dunson. 1984. Adaptations of Crocodylus acutus andAlligator for life in saline water. Comparative Biochemistry and Physiology.79A:641–646.

Morici, L.A. 1996. Endocrine and physiological response to osmotic stress in theAmerican Alligator, Alligator mississippiensis. M.Sc. Thesis. Department ofBiology, University of San Diego. San Diego, CA. 145 pp.

Neill, W.T. 1971. The last of the ruling reptiles: Alligators, crocodiles, and their kin.Columbia University Press, New York, NY. 486 pp.

Taplin, L.E., and G.C. Grigg. 1981. Salt glands in the tongue of the EstuarineCrocodile, Crocodylus porosus. Science 212:1045–1047.

Taplin, L.E., G.C. Grigg, P. Harlow, T.M. Ellis, and W.A. Dunson. 1982. Lingualsalt glands in Crocodylus acutus and C. johnstoni and their absence from Alliga-tor mississippiensis and Caiman crocodilus. Journal of Comparative Physiology149:43–47.