Raymond F. Sis1; DVM, PhD; Andre M. Landry2, PhD
1Veterinary Anatomy/Public Health, College of Veterinary Medicine, Texas A&M University, College Station, TX; 2Institute of Marine Life Sciences, Texas A&M University-Galveston, Galveston, TX
An enhanced concern for the integrity of the coastal environment in the Gulf of Mexico has generated interest in the phenomenon of beach strandings as it relates to such highly visible species as marine turtles. Increased documentation of strandings (Laist, 1987; Toufexis, 1988; Plotkin, 1989) has led to questions of why Dead Sea turtles show up on Texas beaches and whether these mortalities are related to human activities such as shrimping, entanglement, ingestion of non-biodegradable debris and exposure to industrial wastes. Texas is the site of two major industries -- shrimp and oil -- whose operations are perceived in conflict with sea turtles. Texas annually leads all Gulf States in total number of stranded sea turtles. The strandings for Texas and southwest Louisiana reported to the southeast region of the Sea Turtle Stranding and Salvage Network (STSSN) were 525 in 1986; 220 in 1987; 186 in 1988; 191 in 1989; and 334 in 1990. The critically endangered Kemp's Ridley (Lepidochelys kempi) and the threatened loggerhead (Caretta caretta) have accounted for nearly 80% of these strandings since 1986.
There has been much controversy surrounding the claim that the majority of sea turtle strandings is caused by shrimping (Magnuson et al., 1990; Caillouet et al., 1991) because of the difficulty in determining cause of death (Plotkin, 1989). It is well documented that many other human activities besides shrimping adversely affect sea turtles (Wolke and George, 1981; Crouse, 1984; Klima et al., 1988; Stanley et al., 1988; Amos, 1989; Plotkin and Amos, 1989; Whistler, 1989; Shaver, 1990; Magnuson et al., 1990; Duronslet et al., 1991). Data generated by STSSN surveys and necropsies conducted at Texas A&M University (TAMU) have provided some trends relevant to describing sea turtle mortalities. Necropsies of stranded carcasses provide important clues as to the possible cause of death or allow an elimination process to rule out certain causes. For example, external signs of entanglement in marine debris or the presence of large foreign objects in the throat (e.g., fish hook and line) and gastrointestinal tract (e.g., large pieces of plastic) can be used to rule out shrimping as the cause of death. Stomach contents have been used to infer shrimping as the cause of death when composed of certain by-catch species or scavenger organisms (that feed on by-catch species) that otherwise would not enter the diet of sea turtles. Food habit analyses, in addition to producing useful information on natural dietary preferences, have shown that over 33% of the stomachs examined to date contained manmade debris in the form of plastics, rubber, wood, etc. (Plotkin and Amos, 1989).
Large numbers (200 to 500 each year) of endangered and threatened sea turtles are found dead on Texas and southwest Louisiana beaches. Texas annually leads all Gulf States in total number of stranded sea turtles, and is the site of two major industries -- shrimp and oil -- whose operations are perceived in conflict with sea turtles. This increased documentation of strandings has generated interest in the phenomenon of beach strandings and creates a need for the assessment of non-shrimping mortality of sea turtles. This assessment, utilizing a valuable resource of stranded sea turtles, is needed to determine the extent that human-related activities cause sea turtle mortality, such as entanglement, ingestion of non-biodegradable debris, and exposure to industrial wastes.
The research recently completed at TAMU assessed the possible cause(s) of mortality in beached sea turtles through necropsy and toxicological analysis. One of the specific objectives was to characterize post-mortem changes, important in estimating the time of death of a stranded sea turtle.
All stranded sea turtles recovered during NMFS STSSN beach surveys along the southwestern Louisiana (Cameron Parish) and Texas coasts (seven counties) were candidates for necropsy analysis. Data obtained from a given necropsy depended largely on the degree of decomposition of the carcass. In most cases, only gross information and presence of non-biodegradable material could be gathered, while in a few fresher specimens, histological examinations were conducted.
A field study of postmortem changes utilizing freshwater adult red-eared slider (Pseudemys scripta elegans) turtles was undertaken to determine an estimated time of death. After euthanasia with T-61, dead turtles were tagged and outfitted for retrieval from East Lagoon in Galveston at designated times for necropsy. Nine groups, of 4 dead turtles each, were placed in small mesh wire cages which were 0.9 m in diameter and 1.2 m tall. The cages were completely enclosed and of fine mesh to keep out crabs. The water temperature ranged from 20 - 31.5°C, and the pH ranged from 7.8 - 8.1. The salinity ranged from 16 - 22 ppt. Necropsies were conducted at 0 (control), 4, 8, 16, 32, 48 hours and 3, 4, 5, and 6 days. There were four replicates for each time interval. The 0 hour group did not need a cage. Baseline postmortem changes were developed, and data (i.e., when does a dead turtle sink, when does it surface and float) were recorded.
All turtles, except two, sank to the bottom when placed in the water after euthanasia. Sixteen turtles were necropsied at 0, 4, 8, and 16 hours before they surfaced to float. Six surfaced at 16 hours, three at 20 hours, and all the rest (14) surfaced by 30 hours.
The condition of the carcasses and internal organs was excellent at 0 hours and did not show any gross changes at 4 hours postmortem. At 8 hours post mortem, 2 animals in group 3 began to show gross tissue changes and gas began to fill the bladder and air sacs. The liver was the first organ to show gross color changes and focal necrosis. From 16 to 32 hours, the body cavities filled with gas, the cloaca protruded, and the carcasses floated to the surface. After 3 days, the bloat disappeared and the limbs became flaccid. The internal organs became soft and then liquified. The head and forelimbs fell off and the internal organs began to disappear. After 4 days, the hind limbs began to fall off. Most internal organs were gone or unrecognizable. After 5 days, all organs and limbs were gone, the shell and carapace began to soften, and the carapace began to separate from the plastron.
Over 400 microscopic slides were processed and evaluated from the postmortem study. Histologically, the liver was the first organ to begin to show autolytic change at the 4 hr examination period. The autolysis began in the remaining tissues examined, in the following order: heart (4 hrs); lung, brain, kidney, and muscle (8 hrs); stomach, small intestine, and bladder (16 hrs); spleen, and connective tissue (between 16 and 32 hours).
Few sea turtle carcasses, because of severe post-mortem decomposition, are compatible with a thorough necropsy analysis and, therefore, most dead stranded sea turtles yield few clues as to the cause of death.
Post-mortem studies provided very important findings using a surrogate species (red-eared slider). These findings indicate that turtles float to the surface as quickly as 16 to 32 hours and then begin to decompose very rapidly thereafter. Due to our findings that a turtle sinks to the bottom of the ocean after death and postmortem autolysis begins (at 8 - 16 hours postmortem) before it surfaces (16 - 32 hours post mortem) and appears on the beach, stranded fresh-dead turtles are rare. This decomposition hinders a histopathologic diagnosis. It takes a fresh dead turtle to make a more definitive diagnosis. It is important to take advantage of the rare fresh-dead strandings from which we can gain valuable knowledge. Also, these freshwater turtle results must be verified using sea turtle carcasses that become available from deaths of turtles held in captivity, deformed turtles which are sacrificed for scientific purposes or from accidental deaths.
References
1.Amos, A.F. 1989. Trash, debris and human activities: potential hazards at sea and obstacles to Kemp's Ridley sea turtle nesting, p. 42. In: Caillouet, C.W., Jr. and
2.A.M. Landry, Jr. (Editors), Proceedings of the First International Symposium on Kemp's Ridley Sea Turtle Biology, Conservation and Management, Texas A&M University, Sea Grant College Program, TAMU-SG-89-105, vi plus 260 p. (abstract only).
3.Caillouet, C.W. Jr., M.J. Duronslet, A.M. Landry, Jr., D.B. Revera, D.J. Shaver, `.M. Stanley, R.W. Heinley and E.K. Stabenau. 1991. Sea turtle strandings and shrimp fishing effort in the northwestern Gulf of Mexico, 1986-1989. Fishery Bulletin, U.S. 89(4):712-718.
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5.Duronslet, M.J., D.B. Revera and K.M. Stanley. 1991. Man-made marine debris and sea turtle strandings on beaches of the upper Texas and southwestern Louisiana coasts, June 1987 through September 1989. NOAA Technical Memorandum NMFS-SEFC279, 47 p.
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7.Laist, D.W. 1987. Marine Pollution Bulletin 18:319-326.
8.Magnuson, J. J. , K. A. Bj orndal, W. D. DuPaul, G. L. Graham, D. W. Owens, C. H. Peterson, P.C.H. Pritchard, J.I. Richardson, G.E. Saul and C.W. West. 1990. Decline of the sea turtles: causes and prevention. Committee on Sea Turtle Conservation, Board of Environmental Studies and Toxicology, Board of Biology, Commission on Life Sciences, National Research Council, National Academy Press, Washington, D.C., 190 P.
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10.Shaver, D.J. 1990. Hypothermic stunning of sea turtles in Texas, p. 25-27.
11.In: Eckert, K.L. and S.A. Eckert (Editors), Marine Turtle Newsletter No. 48, 32 p. Stanley, K.M., E.K. Stabenau and A.M. Landry. 1988. Debris ingestion by sea turtles along the Texas coast, p. 119-121. In: Schroeder, B.A. (Compiler), Proceedings of the Eighth Annual Workshop on Sea Turtle Conservation and Biology, NOAA Technical Memorandum NMFS-SEFC-214, 136 p.
12.Toufexis, A. 1988. The Dirty Seas. Time. August 1:44-50.
13.Whistler, R.G. 1989. Kemp's ridley sea turtle strandings along the Texas coast, 19831985, p. 43-50. In: Caillouet, C.W., Jr. and A.M. Landry, Jr. (Editors), Proceedings of the First International Symposium on Kemp's Ridley Sea Turtle Biology, Conservation and Management, Texas A&M University, Sea Grant College Program, TAMU-SG-89-105, vi plus 260 p.
14.Wolke, R.E. and A. George. 1981. Sea turtle necropsy manual. NOAA Technical Memorandum NMFS-SEFC-24, v plus 29 p.
