Every turtle season is special for a nesting turtle or a turtle biologist but this year there was definitely something different. Nesting reports received from most countries were negative, indicating suppressed or delayed nesting.
Turtle monitoring in South Africa started in 1963 with two conservation rangers moving up and down the beaches of KwaZulu-Natal scouting for sea turtles. They discovered that both loggerhead and leatherback turtles nest on these shores, and are impacted on by the local communities. Both species have received significant conservation attention since. Every season for the last 45 years an army of people has patrolled the beaches, protecting them, counting turtles and tagging them.
This attention has resulted in a noteworthy increase for both species over these four decades. What has been clear from this long-term data set is that there is generally a large inter-annual fluctuation in the number of turtles that nest between seasons. And 2008/9 season seems to be one of those anomalous years where below average numbers were reported.
Researchers from Nelson Mandela Metropolitan University, doing research on behalf of the South African government and conservation authorities, noticed initially that the leatherback numbers were lower than normal. Moreover, the loggerheads that were nesting at what is usually considered to be the peak season, were mostly remigrants, some of them tagged as early as 15 seasons prior. That was in mid-December 2008. After doing a comparison between the current season and that of the 2007/8 season - which was considered an average season - it became evident that nesting trends for both loggerhead and leatherback turtles were different in 2008/9 season.
Keeping in mind that South Africa has a modest rookery for both loggerhead and leatherback turtles, just short of 84 leatherback nests were seen for the season up until late December. The same area and period in 2007/8 season delivered 126 tracks. Similar results were reported for loggerhead turtles. This equates to about 20 - 30% drop in nesting for both species. While pondering these results, Dr Ronel Nel and her team got similar reports from other nations, especially along the West African Coast. Possible reasons that could explain this regional suppressed nesting effect is ENSO, which seems to be on the rise with the December 2008 prediction being the highest in ten years. Is it similar to the 1998 event which caused large scale coral bleaching?
One of the ongoing research projects in South Africa is the tagging of leatherback turtles with satellite transmitters. These animals are normally tagged during mid-January as these females are usually busy with their last nesting for the season and are ready to start their long-distance migrations. So, to optimize distance covered, and to reduce wear on the harnesses during nesting emergences they are tagged at the end of their nesting season. The compromise is that it is a little more work for the researchers to find suitable animals to tag since the numbers of nesting females usually drop quickly in January. However, this season the numbers started to “sky-rocket” only in January, with 10 – 12 animals recorded on some nights. Three leatherback females were tagged with SPOT tags, of which two of the three have nested since and are still hanging around the nesting area, likely to nest again.
Satellite information from the last season indicated that these females do not stay in the Indian Ocean. The three leatherback females tagged in the last season ended up in different ocean basins being good barometers of ocean “productivity”: one female ended in the Southern Oceans, swimming past Crozet Island and then swam back up the Mozambique channel, whereas the other two ended up in the Atlantic ocean, one offshore off Namibia and the other way off the Angolan coast, almost for a rendezvous between St Helena and Ascension Island.
Another research question that is currently being investigated is monitoring of the in situ incubation temperature. In the mid-‘80s a study investigated the incubation temperature as well as sex ratios that are being produced in the nests of the main rookery. A repeat study two decades later is being conducted with more sophisticated equipment. iButton temperature loggers are placed in the sand to monitor incubation temperature, which should provide some information on incubation conditions, hatching success and sex ratios being produced, and possibly see some effect of climate change.
Another significant attribute about the South African turtle rookery is that the turtles are shared with its neighbour. Mozambique has certainly increased its conservation efforts which include the recent signing of the IOSEA MoU and an expansion of its monitoring programme. The effect is that monitoring is now almost continuous across the two country borders for 60km on either side. To date in this season five turtles have nested on both sides of the border carrying two tags; one with a ZA and the other an MZ country coded tag.
Research planned for the 2009/10 season includes a comparison of the recovery potential of loggerhead and leatherback turtles in the Southern African rookery. This will include a comparison of genetics, life history, hatching success and population dynamics. On the results for the 2008/9 nesting season ... only once all the data has been received and processed will scientists know if the 2008/9 season was just a delayed season with comparable nesting numbers or if it was a suppressed season with declines equivalent to those reported in other countries.
Dr. Ronel Nel
Nelson Mandela Metropolitan University