Safe assessments for the Eastern Tropical Pacific’s pregnant silky sharks
Silky sharks are widely overfished, the second most traded shark species in the largest dried-fin markets and among the most captured sharks by local fisheries on Mexico’s Pacific coast. Revillagigedo National Park is North America’s largest fully protected marine protected area and hosts large concentrations of silky sharks. There is evidence of connectivity between Revillagigedo and coastal regions of the Mexican Pacific, but the drivers of these movements aren’t clear. Pregnant female silky sharks may be pupping on the shelf edge and in offshore habitats. Irene is using shark-safe hormone analysis and ultrasonography to improve our understanding of the drivers behind regional movements.
Irene Casanova
I was born in Alicante, a city in Spain on the Mediterranean coast, and the ocean has always been a presence in my life. My grandfather and father taught my brothers and me to love the sea at an early age and we would dive from a small boat called Javiral, a fusion of our names. But I was the only one who decided to dedicate my life to the marine environment.
Ten years ago, I moved to Mexico to work as a dive master on the country’s Caribbean coast. That is where I first encountered bull...
Non-Lethal Assessment of Pregnancy in Silky Sharks from the Eastern Tropical Pacific
The primary objective of this project is to develop non-lethal methods to detect pregnancy in sharks by combining ultrasound imaging and steroid hormone analysis.
The silky shark is one of the most frequently caught shark species worldwide, yet little is known about its endocrinology and its use of habitat when breeding. By developing non-lethal research methods such as ultrasound imaging and hormone analysis, this project will fill critical knowledge gaps, provide tools that can be applied to other studies and expand our understanding of the movements and preferences of pregnant female sharks.
The silky shark is a highly migratory species with a global tropical distribution and it occurs in both oceanic and coastal–pelagic habitats. It is an opportunistic predator, strongly associated with skipjack and yellowfin tuna, which are target species of longline and purse-seine tuna fisheries in the tropics. This association has made the silky shark one of the shark species most frequently caught as incidental bycatch worldwide, with 727 tons reported in 2024 from the Eastern Tropical Pacific. In addition, silkies rank as the second most traded shark species in the world’s largest dried-fin markets and also as one of the species most caught by local fisheries along Mexico’s Pacific coast.
This fishing pressure, combined with the silky shark’s biological traits, makes the species susceptible to overfishing and has resulted in declining population trends. Revillagigedo National Park, located in the Mexican Pacific, is North America’s largest fully protected marine protected area. Hosting large concentrations of silkies, it is central to this project. Studies of silky shark movements have provided evidence of connectivity between Revillagigedo and coastal regions of the Mexican Pacific. However, this shark’s use of the archipelago and the reasons for its movements to the continental coast remain unclear. It has been suggested that pregnant females use shelf-edge and offshore habitats as parturition areas. Our main motivation is to find out more about the silky shark’s reproductive biology by using non-lethal methods, such as hormone analysis and ultrasound imaging. This approach will generate baseline data for silky sharks, improve our understanding of the drivers behind regional movements, provide transferable tools for similar studies, and inform the conservation of exploited populations.
- To examine the reproductive parameters and endocrinology of female silky sharks in the Revillagigedo Archipelago.
- To assess pregnancy in silky sharks using non-lethal methods.
- To evaluate the role of the Revillagigedo Archipelago in the reproductive cycle of silky sharks.