Sharks in Fijian rivers

One of the main goals of the Bull Shark Tagging Programme has been to locate the nursery grounds of the bull sharks encountered at the Shark Reef Marine Reserve in Fiji. From visual observations made over the years it became obvious that the sharks leave Shark Reef in September/October each year and start returning back to the site in December. Interestingly, female bull sharks that are clearly pregnant before they leave return non-pregnant and we also see quite a few females with fresh mating scars when they turn up in December/January at the site. So we are confident that reproduction takes place when they cannot be encountered in the Shark Reef Marine Reserve. Which also means that we should try to find their nursery grounds and movement corridors that link the protected area with habitats where they reproduce. In order to achieve this, I have been pop-up satellite tagging adult bull sharks at Shark Reef just before they leave the site in September. Unfortunately, there’s a lot of issues with externally attached pop-up satellite tags and this approach most likely will not tell us where the Fijian nursery grounds are.

A more promising approach to locate shark nursery grounds in Fiji is using local people’s knowledge. Back in 2004 I interviewed a local fisherman living in a village situated on Fiji’s largest river and he told me that he catches sharks in the river in November and December each year. He did not know what species this could be but described his catch as "sharks with a rounded snout and being greyish/brownish in colour". Most of the sharks he catches are small but he also mentioned that he catches large individuals. When he cuts them open he sometimes finds baby sharks! Pregnant females in Fijian rivers! Well, this was certainly something we wanted to know more about. This summer, we set out to collect more information about the occurrence of sharks in Fijian rivers. We visited a good number of villages situated along the major rivers on Viti Levu and Vanua Levu (the two main Fijian islands) and interviewed the locals. What they told us is way more than what we expected. All interviewees confirmed that they regularly see and catch sharks in the rivers as far up as 30 km inland! Closer to the river mouths they reported to catch small hammerhead sharks and unknown species further up river. We also learned a lot about how they use and regard sharks. All very interesting and exciting! There will definitely be future posts here that report the results from these visits. Stay tuned!