Introduction

Recent groundbreaking research has unveiled surprising insights into the behavior of great hammerhead sharks, revealing a fascinating dichotomy between those that migrate vast distances and others that prefer the comforts of their familiar surroundings. Conducted around Andros Island in the renowned Bahamas shark sanctuary, scientists observed that while some of these majestic creatures embark on long journeys, others thrive in their local environments, possibly due to an abundance of resources.

The Plight of Great Hammerhead Sharks

Dr. Tristan Guttridge, the lead author of the study published in the Frontiers in Marine Science, emphasized the alarming plight of the great hammerhead population, which has plummeted by over 80% in the last three generations. Low genetic diversity and inbreeding further threaten their survival. Understanding their movement patterns is crucial for devising effective conservation strategies. “By identifying areas where sharks show residency, we can better protect them year-round from fishing pressures,” Dr. Guttridge stated.

The Mysteries of Migration

While great hammerheads are known to undertake impressive migrations spanning up to 3,000 kilometers, some individuals have been observed remaining in thriving areas such as Bimini, where they typically winter before seeking cooler waters in summer. However, much remains unknown about the ecological significance of other Bahamian islands like Andros, which boasts one of the largest fringing reefs globally and is revered for its pristine flat habitats.

Before this study commenced, data regarding great hammerhead behavior in the central Bahamas was alarmingly scarce. Questions regarding their diets and habitat use were largely unanswered. To address this knowledge gap, the research team captured and tagged 22 sharks between March 2020 and June 2024, with assistance from Discovery's Shark Week. By employing various techniques to minimize stress during capture, they successfully attached satellite trackers to seven individuals to monitor their movements.

The data collected included 78 shark encounters from opportunistic sightings, revealing that the majority of observations involved large juveniles and adults. Interestingly, half of these sightings occurred during the peak months of January to March, with significant activity also noted from June to July. Two separate observations suggested recent mating events, hinting at the area’s potential importance for reproduction. Notably, some sharks were spotted in the same locations multiple times over the years, indicating a tendency for site fidelity.

Feeding Habits of the Sharks

Further analysis revealed that the sharks predominantly favored the eastern waters off north and central Andros, with one particular 400 square kilometer area standing out as a long-term residence hotspot. Rich edge habitats near the reef drop-off were specifically highlighted for their abundant prey, suggesting a robust food supply plays a crucial role in the sharks' spatial behavior.

Isotope analysis from muscle biopsies indicated that about two-thirds of their diet consisted of barracuda and stingrays, with smaller species of sharks making up the remainder. Interestingly, individual dietary preferences varied, with one shark predominantly feeding on silky sharks. This availability of food, combined with access to cooler deep waters during sweltering summers, may explain why some hammerheads choose to settle in the Bahamas year-round, unlike their migratory counterparts near Bimini.

Questions and Considerations