The Indian Ocean tsunami of 26 December 2004 caused catastrophic loss of human life and livelihood. Yet the impacts on coastal and marine wildlife in the region remain little known (Albrecht 2005). Sri Lanka, one of the countries hardest hit by the waves, has 5 species of sea turtle, all of which are threatened with extinction, that nest on its beaches. Hamann et al. (2006) reported damage to turtle nesting beaches around much of the Indian Ocean, especially in India, Thailand, and Sri Lanka. They noted that, given the scope of the beach damage, any unhatched clutches and adults on land at the time of the tsunami likely perished. However, to our knowledge no attempts have been made to ascertain whether these initial impacts have affected sea turtle populations in the medium-to-long term. Here we report that sea turtle populations in southern Sri Lanka appear not to have been substantively affected by the tsunami (Fig. 1). The number of adult females nesting on the beach of Bundala National Park remained relatively constant over the 4 years preceding the tsunami, and the mean number of nesting individuals per month in 2005 (posttsunami) was nearly the same as in the previous year (Figs. 2 and 3).

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Olive ridley (Lepidochelys oliveacea), hawksbill (Eretmochelys imbricata), loggerhead (Caretta caretta), leatherback (Dermochelys coriacea), and green (Chelonia mydas) sea turtles nest on the southern coast of Sri Lanka. All 5 species are listed as vulnerable, endangered, or critically endangered on the International Union for Conservation of Nature (IUCN) Red List (IUCN 2008) and are on Convention on International Trade in Endangered Species of Wild Fauna and Flora Appendix I. Major conservation concerns include nest predation and degradation of nesting beaches (Pritchard 1980; Nichols et al. 2000) and incidental bycatch of adults in fishing nets (Pandav et al. 1998; Chaloupka and Limpus 2001; Kapurusinghe and Cooray 2002).

Bundala National Park (Fig. 1) comprises 6216 ha along 17 km of beach in this area. Monitoring of nesting turtles has occurred here since 2002. Park rangers follow fresh turtle tracks and place cement rings around the nests to deter egg predation by monitor lizards, pigs, and feral dogs. The rings have holes to allow hatchlings to escape. Rangers attempt to identify turtle species by track size or sightings of the females themselves.

At Bundala, the number of adult females returning to nest (as measured by nesting emergence counts) remained essentially unchanged between 2002 and 2005 (Fig. 2), despite the tsunami at the end of 2004. Indeed, one female green turtle nested the day after the tsunami, and January 2005 saw a peak in nesting adult female numbers despite the extensive beach erosion documented by Hamann et al. (2006). Though there is substantial variation in nesting turtle numbers between months, no substantive changes in annual turtle numbers attributable to the tsunami are apparent (Fig. 2A). A caveat to this observation is that we show numbers for all 5 turtle species combined. It would theoretically be possible for either the tsunami or long-term deterministic factors to negatively affect 1 or 2 species while benefiting or not affecting the others. Thus the stable trend that we observe could actually be the net result of concurrent positive and negative trends in the separate species. We do not believe that this is the case. Four of the five species were relatively rare throughout the monitoring period. Leatherbacks accounted for only 0%–4.6% of the total observations per year, loggerheads 0%–8.7%, hawksbills 0%–11.3%, and greens 6.6%–13.2%. Olive ridleys accounted for 48.2%–57.9% of the observations (the other 19.0%–42.3% were unidentified). Trends from 2002 to 2005 are very similar for the 3 groups examined: olive ridleys, green turtles, and all five species combined (Fig. 2B).

Egg deposition rates, although not as effective a measure of population trends as return rates of adult females (above), provide an alternative metric of population performance. At least 9 government-approved hatcheries are located on the southern coast of Sri Lanka, in the Bundala National Park vicinity but outside of official protected areas. People from local villages dig up newly deposited turtle eggs and sell them to the hatcheries that incubate them and release the hatchlings. The villagers view this as an important source of income, and hatchery personnel believe that nearly all deposited eggs are collected and sold to the hatcheries (R. Corea, pers. obs.). We assessed egg collection rates as a surrogate for egg deposition; 4 of the hatcheries kept inconsistent purchase records, so we analyzed data from the other 5: Kanin, Dadly, Abrewe, Wander, and Amara. The hatcheries were closed for 2 months following the tsunami, but egg purchasing resumed in March 2005. Though a 4-year time series is too short to detect statistically significant declines in abundance, purchase records suggest the possibility of a decrease in egg deposition over the time period (see Fig. 3). The drop in egg collection from 2004 to 2005 could be attributable to several factors, including social (e.g., fewer people collecting eggs), deterministic (e.g., a general decline in adult female return to hatchery beaches), stochastic (e.g., the tsunami affecting egg abundance), or 2005 simply being a low nesting year for one or more turtle species. But even if the drop was in fact due to the tsunami, this will likely have little effect on the turtle populations. Sea turtle population dynamics are driven much more strongly by the vital rates of older stage classes than those of eggs and hatchlings (Crouse et al. 1987; Crowder et al. 1994). As noted above, the abundance of adult females on the beach of Bundala showed essentially no change following the tsunami.

The likely destruction of eggs and adults on the beach at the time of the tsunami (Hamann et al. 2006) could conceivably affect the population in the long term and be detected as a reduction in abundance of those cohorts. But the loss of however many adults that may have been on the beach did not noticeably lower female return rates in the following year (Fig. 2). The loss of egg clutches (either on the beach or laid shortly thereafter on eroded substrate) is unlikely to cause a noticeable reduction in adult abundance as that cohort matures, given the very low probability of hatchlings surviving to the reproductive stage (Crouse et al. 1987; Crowder et al. 1994).

In addition to eroding nesting beaches, the tsunami also destroyed some of the habitats in which adult sea turtles forage, such as coral reefs and sea grass beds (Hamann et al. 2006). The impacts of this habitat degradation on sea turtle population dynamics will be difficult to ascertain, likely manifesting as long-term reductions in fecundity or adult or juvenile survivorship. But the habitat damage may not have been “. . .severe enough to have had even a local impact on marine turtles” (Hamann et al. 2006: 2), and sea turtles are fairly resilient to some loss of foraging habitat (Limpus et al. 2005).

The impacts of the tsunami on sea turtle nesting beaches were quite severe (Hamann et al. 2006). However, return rates of adult nesting females were apparently not affected by this disruption, at least in the year following the tsunami. Most of the adults in the population were likely at sea when the tsunami hit, and impacts there were minimal. Egg collection rates were slightly lower in the year following the tsunami than in previous years, but there are several potential explanations for this. Moreover, given the low elasticity of the hatchling stage class (i.e., little ability, relative to other stages, to affect overall demography), it is unlikely that potential impacts on eggs and hatchlings would importantly affect population dynamics. The sea turtles of the Bundala vicinity represent only a fraction of those present in Sri Lanka and the Indian Ocean region. But the southern coast of Sri Lanka was one of the hardest hit areas by the tsunami. It is likely that if the turtle populations in the Bundala area were only lightly affected by the tsunami, those in other areas may have been impacted even less. The Indian Ocean tsunami was widespread and devastating. However, we suggest that the fate of sea turtles in the region is more likely to be determined by long-term human influences than by infrequent natural catastrophes.