TAGGING WHALE SHARKS IN INDONESIA: CONCLUSION

Written by Mark Erdmann on conservation.org
November 25, 2011

Mark Erdmann has been participating in an expedition tagging whale sharks in Indonesia’s Cenderawasih Bay.

Heading into our last dive of the trip in Cenderawasih Bay National Park, it’s been a great trip, albeit too short! The interactions with the whale sharks (Rhincodon typus) and the successful tagging of five individuals (one female, one large male, and three adolescent males) were undoubtedly the highlights of the trip. But beyond this, we’ve also managed to do some important science.

Throughout the trip, I’ve been collecting and downloading temperature loggers that we have installed at various sites throughout the bay since 2005; these loggers record temperature every 15 minutes and provide a very interesting picture of the natural variation in the bay. Last March, colleagues from WWF-Indonesia reported significant coral bleaching in Cenderawasih, apparently a result of abnormally high temperatures.

Over the course of our trip, we’ve been taking notes on which reefs recovered the best from this bleaching, and which suffered significant coral mortality. This information is very important to the long-term adaptive management of the park’s reefs, as we certainly can expect more warming and bleaching in the future. The data I’ve downloaded from the temperature loggers have provided a high resolution look at what temperatures the corals in the bay experienced earlier this year.

We can see that beginning in about January 2011, water temperatures in the bay rose significantly and frequently reached 31 degrees Celsius, which is about 1.5 degrees warmer than normal for the bay and a potentially lethal stress for the corals there. This pattern continued until June, when temperatures finally dropped dramatically and returned to their normal average of about 29.5 degrees. Overall I’m pleased to note that most of the reefs seem to have recovered, though we did note a few reefs where up to 40 percent of the corals had bleached and died. Nonetheless, there were already signs of recovery even on these reefs, with numerous baby corals beginning to grow on top of the bleached dead coral skeletons.

In other news, we’ve also been fortunate to photograph and collect what are likely two new species of reef fish — both dottybacks, a family of small and generally shy species that many divers overlook. Both of these fish are closely related to previously known species (Pseudochromis marshallensis and Pseudochromis litus), but have some significantly different color patterns than those known species and likely will turn out to be new. I’m currently corresponding with world experts on these species — Dr. Anthony Gill from the Australian Museum and Dr. Gerald Allen from the Western Australian Museum — and hope to have confirmation on whether these are definitely new species within the next week.

We also took genetic samples of these two species to be analyzed by our colleagues at the Indonesian Biodiversity Research Center in Bali, which should provide yet more evidence. In the past, we’ve uncovered close to 20 new species from Cenderawasih Bay that showed a unique color pattern different from the closest known relatives from other areas of Indonesia, so I would expect we will likely find the same thing with these two dottyback fish species.

Overall it’s been a rewarding trip, and we are all eagerly looking forward to the day six months from now when the five satellite tags pop off of their respective whale sharks, float to the surface, and beam the data they’re now collecting to the nearest Argos satellite. It’s hard to predict what unexpected trends we may find, but at the very least we hope to better understand if Cenderawasih’s whale sharks are truly remaining resident in the bay or if they are actually moving about the Bird’s Head Seascape or even beyond. We’ll be sure to update you on what we find.

Dr. Mark Erdmann is the senior advisor to CI-Indonesia’s marine program.
PHOTO CREDIT © CI/Photo by Mark Erdmann