Tiger Shark and Albatross Fledgling Interactions

Quantifying predation rates and their impacts

Every summer, tiger sharks (Galeocerdo cuvier) arrive at island seabird nesting sites to hunt albatross chicks as they fledge from shallow water. Although this phenomenon is widespread and well known, all available evidence is anecdotal and unquantified. This study involves visual and drone observations of tiger shark predation on two species of albatross chicks, Laysan (Phoebastria immutabilis) and black-footed (Phoebastria nigripes) at Kure Atoll in the Hawaiian chain. The aim of the study is to quantify the tiger shark/albatross interactions with respect to tiger shark arrival and departure times; tiger shark hunting habits (time of day; weather conditions; ambush vs pursuit); and tiger shark predation success rates. These data will serve as a baseline for answering broader questions surrounding tiger shark depletion.

Tiger sharks are listed as near threatened by the IUCN (Ferreira & Simpfendorfer, 2019). The IUCN expects their population to continue to decline for the next three generations (2018 – 2086) due to exploitation. Past research and models suggest that a decline in shark populations would have a negative impact on fish populations (Polovina, 1984, and Stevens et al., 2000). In fact, with an assumed tiger shark population of zero, one model showed an immediate increase in seabird populations, followed by tuna and jack populations plummeting and not recovering during the 100-year simulation. These results emphasize the important role tiger sharks play in balancing the ecosystem.

Specific aim of the project:

• Determine how successful tiger sharks are at preying on albatross spp. fledglings

• Quantify the proportion of albatross fledglings that are predated on by tiger sharks

• Explore the impact of greater albatross fledglings spp. survival