A recent experiment has confirmed a long-held suspicion among biologists: the bonnethead shark is not a pure carnivore and enjoys eating seagrass. The bonnethead shark (Sphyma tiburo) is a unique species of shark in many ways. It is the only shark species that exhibits sexual dimorphism in its head shape, meaning that the shape of the head differs significantly between males and females. Additionally, this species has long been suspected of not being a pure meat-eater, with biologists noting that the bonnethead shark occasionally eats seagrass. An international team of biologists has now confirmed that seagrass plays an important role in the diet of these sharks, as reported in the journal Proceedings of the Royal Society B.
Previously, it was thought that the bonnethead shark accidentally ingested seagrass while hunting for crabs that hide in the seagrass. However, an experiment conducted by Samantha Leight and her team at the University of California has shown that this is not the case. The researchers fed bonnethead sharks a diet consisting of 90% seagrass and 10% squid for three weeks, with the seagrass marked with carbon isotopes. The results were surprising: the sharks were able to digest about half of the seagrass and even gained weight during this time. This suggests that the bonnethead shark is not just eating seagrass, but also gaining nutrients from it.
This discovery sheds new light on the ecological importance of these sharks. In the Gulf of Mexico and the Atlantic, where an estimated 4.9 million bonnethead sharks live, seagrass beds are an important habitat. The researchers suggest that these sharks may play an important role in the nutrient cycle of these ecosystems. This is the first shark species known to have an omnivorous strategy, according to Leight. The findings of this study have important implications for the conservation of these sharks and their habitats.
