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Marine Turtle Newsletter 48:1-6, © 1990

Marine Turtle Newsletter-Online

Metal and PCB Concentrations in the "Harlech" Leatherback

John Davenport, John Wrench, Jim McEvoy and Victor Camacho-Ibar
School of Ocean Sciences, University College of North Wales, Marine Science Laboratories, Menai Bridge, Gwynedd LL59 5EY, United Kingdom

The leatherback turtle, Dermochelys coriacea (L.), is the largest and most pelagic of living turtles. Although it nests on exposed tropical beaches, the species forages widely in temperate waters, mainly upon medusae and siphonophores (Brongersma, 1969; Den Hartog and Van Nierop, 1984), and is a regular summer/autumn visitor to coastal waters around Japan, Peru, Newfoundland, Norway, the United Kingdom, Ireland and even Iceland (e.g., Nishimura, 1964; Bleakney, 1965). In temperate latitudes it tends to be associated with swarms of jellyfish such as Rhizostoma or Cyanea. Specialized medusivory makes it almost unique amongst air breathing vertebrates and places the species at the top of a poorly studied food chain.

The leatherback has other unusual features. The species is an exceptional deep diver (Eckert et al., 1986, 1989) and, unlike other living reptiles, possesses counter-current heat exchangers (Greer et al., 1973) together with extensive subcutaneous blubber which confers buoyancy and probably contributes to the facultative endothermy of the species (Pritchard, 1969; Mrosovsky and Pritchard, 1971; Frair et al., 1972; Mrosovsky, 1980). The leatherback is almost certainly very long lived (other sea turtle species may require > 30 years to reach sexual maturity: e.g., Limpus and Walter, 1980; Balazs, 1982), so the species would appear to be an ideal indicator of the degree of contamination of the oceanic food web by accumulating substances such as heavy metals and polychlorinated biphenyls (PCBs). However, the species is 'Endangered' (Groombridge, 1982) so killing specimens for analysis would be quite unacceptable. The present study arose from an unusual opportunity to collect fresh tissue samples from a large leatherback killed off the coast of the United Kingdom in 1988.

The "Harlech turtle" was a male, curved carapace length 159 cm (Table 1), that died after becoming entangled in whelk fishing lines four miles off Porthmadog, Gwynedd, Wales, on the afternoon of 22 September 1988 (Morgan, 1989). Fishermen cut the animal free and subsequently it washed ashore dead (drowned) on Harlech beach where it was found on 23 September. The water temperature in the Irish Sea at this time was about 12°C, the air temperature around 15°C. The turtle was transferred to a freezer store (-10°C) in Cardiff about 36 hours after death and was held there until dissected. The short interval between death and freezing, plus the low ambient temperatures, meant that tissue samples were in unusually good condition. Adipose tissue samples were collected subcutaneously from the carapace and plastron of the animal. Samples of liver and pectoral muscle were also removed. Metal analysis is now complete (Table 2) and total PCB concentrations in the blubber have been determined at about 1.2 µg g lipid-1. PCB fingerprinting is in train; early indications are that pesticides (e.g., dieldrin) are present, albeit at extremely low levels.

Table 1. Dimensions of an adult male leatherback turtle stranded on the coast of Wales, U. K., in September 1988 (from Morgan, 1989).

Dimension

Measure

Curved carapace (median) length 1

159 cm2

Total (nose to tail) dorsal curved length

291 cm

Total (nose to tail) ventral curved length

259 cm

Dorsal span (flipper tip to flipper tip)

277 cm

Ventral span (flipper tip to flipper tip)

254 cm2

Weight

916 kg

1 measured along the top of (as opposed to alongside) the median ridge
2 corrected from values reported in Eckert and Luginbuhl (1988)

Table 2. Trace metal concentrations (mg metal Kg dry wt-1) in tissues of an adult male leatherback turtle stranded on the coast of Wales, U. K., in September 1988.

Metal

Liver

Tissue Pectoral Muscle

Blubber

Hg

0.39±0.04

0.12±0.06

0.11±0.02

Cd

0.22±0.02

0.06±0.01

<0.01

Cu

0.15±0.04

0.26±0.05

0.06±0.02

Ni

2.13±0.16

1.62±0.21

0.07±0.02

Pb

0.12±0.02

0.31±0.03

0.04±0.03

Se

1.41±0.02

3.61±0.48

<0.05

As

0.58±0.11

0.21±0.07

1.28±0.18

Zn

2.62±0.15

1.89±0.10

0.08±0.01

For several of the heavy metals (Hg, Cd, Zn, Ni) the liver appears to contain the highest concentrations; this observation is in line with the trend in other marine animals (Bryan, 1984). None of the values reported here could be regarded as elevated above the "normal" background levels seen in other organisms, indeed most appear to be below values reported in the literature (see Bryan, 1984, for review). This is particularly true of cadmium, where the concentration of the metal in the liver of mammals and birds is usually two orders of magnitude above that reported here (Bryan, op. cit). In most cases, the subcutaneous blubber of the leatherback contained low levels of metals (particularly so in the case of Cd and Se). However, arsenic was more concentrated in the blubber than in liver or muscle. This observation is consistent with previous reports that arsenic may associate with polar lipids in organisms at lower trophic levels (probably phytoplankton in the case of Dermochelys), and that this may subsequently be transferred to organisms at higher trophic levels as "arsenolipid" complexes (Wrench and Addison, 1981).

Very few studies of metal concentrations/effects have been carried out upon sea turtles (and none on Dermochelys). Witkowski and Frazier (1982) reported much higher levels of Cu, Zn and Pb (8.6-9.1, 575-955, 41.5-97.2 mg kg dry ash wt-1, respectively) from the limb bones of cheloniid turtles (species unspecified), but comparisons are difficult because their data were derived from ashed material. Stoneburner et al. (1980) measured heavy metal levels in the eggs of loggerhead turtles (Caretta caretta) to confirm the existence of demes within the western Atlantic population. Comparisons with their work are difficult, because it is not clear whether their data were wet- or dry-weight specific (though judging from the description of the analytical procedure, probably the former). Amongst the metal investigated in Dermochelys they found higher levels of Zn, Pb, Hg and Cu in loggerhead eggs (levels of Zn were particularly high) than reported here for leatherback tissues. Concentrations of Cd and Ni were similar to those of leatherback tissues. More recently, Gramentz (1988) has demonstrated that Mediterranean loggerheads caught accidentally by Maltese fishermen may eat pieces of shiny metal (presumably from the seabed), but this observation is of little relevance to leatherbacks which feed pelagically.

PCB concentrations have rarely been measured in reptiles and we are aware of only one study in a chelonian species, and that was upon sedentary snapping turtles (Chelydra serpentina) from a grossly polluted freshwater ecosystem (the animals had extremely high PCB levels of <3,600 µg g-1 in their fat bodies; Olafsson et al., 1983). Unlike Chelydra, Dermochelys is extremely mobile and is the most widely distributed of living reptiles (Pritchard and Trebbau, 1984). In essence it is a continuously browsing species, so its tissue metal and PCB levels should represent an integration and biomagnification of concentrations in gelatinous plankton living in a great area of ocean. Structural and physiological features of leatherback turtles suggest that depuration of metals and PCBs would be extremely slow, thus reinforcing the concept of integration; the species is air breathing, and presumably shares the substantially impermeable integument and a water-conserving renal system of other marine reptiles (Dunson, 1984). The blubber of a male turtle is liable to be less subject to turnover than that of females (which may mobilize lipid to fuel their egg clutches), making it a rather better biological indicator of environmental contamination.

The total PCB concentration in leatherback blubber (ca. 1.2 µg g lipid-1) is 1-3 orders of magnitude higher than the lowest levels reported from fish taken from the open north Atlantic (e.g., Harvey et al., 1974), but is similar to the lowest concentrations reported from marine mammals (oceanic cetacean species. Subramanian et al. (1987) reported levels of 5.7-17.8 µg g blubber-1 from Dall's porpoises of the north Pacific (noting that even these low levels were sufficient to depress testosterone production, though no clear evidence of effects on reproductive success was available). The majority of coast marine mammals (particularly seals) and birds exhibit PCB levels 1-3 orders of magnitude greater than did this leatherback. Reijnders (1980) measured levels from 87-1447 µg g lipid-1 in adult harbour seals which were over 20 years old, while Helander et al. (1982) reported damaging levels of 800-900 µg g lipid-1 from eggs of white-tailed sea eagles (though levels in adult birds were no higher than 240 µg g wet wt-1 according to Bagge, 1975).

In conclusion, the metal and PCB concentrations recorded from the Harlech leatherback reveal no evidence of significant chemical contamination, beyond the predictable finding of trace concentrations of PCBs, which now seem to be detectable in virtually all organisms, particularly top predators. Hopefully the results reported here will function as a baseline for future analyses of leatherback tissues.

The authors wish to thank The Vincent Wildlife Trust for providing funds to support this study. They also thank Mr. Peter Morgan of the National Museum of Wales (Cardiff) for inviting them to collect samples from the Harlech leatherback.

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