Ayumi Kuramae Izioka

Abstract

Since its introduction in the Western Atlantic more than 30 years ago, the lionsh (Pterois volitans/miles complex) has spread throughout the Gulf of Mexico and the Caribbean having massive and unprecedented ecological impacts. This invasion is among the most studied marine sh invasions but very little is still really known about the population dynamics of the species and the factors ultimately governing its abundance. We here document a large population crash for the lionsh following its rapid increase in abundance on the Saba Bank following its appearance in 2010. In doing so we document the third case of apparent local population boom-bust event for the Greater Caribbean, and the rst for the Eastern Caribbean. We also document gradual increases in the mean size of lionsh of the Saba Bank that coincided with the increase and subsequent decline in lionsh abundance. Contrary to the previously documented epizootic disease outbreak associated with the population crash observed in the Gulf of Mexico we were unable to nd any signs of the occurrence of epizootic disease. We suggest that the population crash on the Saba Bank might have been due to non-local causes, such as reduced reproductive output in distant larval source populations. Boom-bust dynamics are often witnessed in biological invasions and have critical implications for both understanding and managing invasive species. While the underlying cause for the boom-bust event we document remains unknown, our work helps improve our understanding of this most serious biological invasion.

Hi everyone. My name is Ayumi Kuramae Izioka and I work as the as the science coordinator and daily operations manager of the Saba Bank Management Unit (SBMU), on Saba in the Dutch Caribbean.

Saba Bank- Dutch Caribbean. © DCNA/Eseld Imms

The Saba Bank National Park is a large, submerged atoll just 3 nautical miles south of the island of Saba. With a surface area of over 2600km2, it is classified as the 3rd largest of its kind in the world. Such a large area has many different habitats which in turn attracts many different species from the region. With so many different life and biodiversity, it has been classified as biodiverse hotspot in the Caribbean region and recently, it is a marine mammal and shark sanctuary named “Yarari”.

Many different shark species are seen on the Saba Bank, ranging from pelagic species like the Silky sharks to benthic species like the nurse sharks. These sharks are most often seen by fishermen, but also by the park officers who maintain the national park. One of the larger shark species that is commonly seen on the Saba Bank, is the tiger shark.

© Daniel Norwood

Tiger sharks are apex predators, meaning that they are on top of the food chain and maintain a healthy balance of the ecosystem. These sharks are transboundary species, meaning that they cross many different waters as they cruise along our ocean, connecting many countries.

In the previous expeditions done on the Saba Bank, most of the tiger sharks captured were females that were big and old enough to start reproduction. But what are these particular sized females doing here on the Saba Bank? Do they hold the clue to the future generation of tiger sharks, right here on the Saba Bank? If they are already pregnant and ready to give birth, why is the Saba Bank so interesting to them? Or where do these sharks move once they are pregnant?

With this expedition, including the new technology of ultrasound for sharks, we hope to answer a few of these questions. So far we have had very successful days of tagging sharks and we can’t wait to show you more about the tiger sharks. We have been investigated 56 sharks- 39 reef sharks, 1 nurse sharks and 16 tiger sharks.

Keep following us on DCNA’s website,  Facebook (Dutch Caribbean Nature Alliance), Instagram (dcnanature) for updates about the Pregnant Tiger Shark Expedition!

This article was included in the Special Edition BioNews: Tiger Shark Expedition