Based on the photos, it looks likely the prime breeding area on the island is still disturbed by the presence of anglers as there is no buffer area between the core area and the fishing zone. It is called the edge effect.
If the number of birds on the island drops continually, the authority concerned should review and strengthen the practice, e.g. designating the island as no-go area during the breeding season.
There are plenty of islets in HK for fishing but just few for terns to breed. Who should get the priority? anglers or terns or even the photographers?
Captain
