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South Africa's strange turtle season

Source: Dr. Ronel Nel, Nelson Mandela Metropolitan University

Photos:


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.‎
 

Loggerhead turtle nestingResearchers 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?‎
 

Tagging Leatherback turtle with satellite tracking

Leatherback turtle nesting


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. ‎


 Satellite tracking map captured on 22nd February 2009  c/o Google Map


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

   
 
   
 
   
 
   
 
   
 
   
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