This is Scientific American's 60-second Science, I'm JasonGoldman.
The image of a dorsal fin cutting through the sea surface is iconic. But scientists studying the stomach contents of young great white sharks off the coast of Australia were in for a surprise when they learned that the predators seem to spend a lot of time patrolling the seafloor.
"They have a predominantly fish-based diet, which is not unexpected for juvenile white sharks. The most important prey species we identified was eastern Australian salmon."
University of Sydney graduate student Richard Grainger. He and his team sorted through the stomach contents of more than 50 juvenile white sharks that died after being entangled in shark exclusion nets meant to protect swimmers.
"The overall unexpected finding was just the diversity and importance of bottom-dwelling fishes. Things like stargazers—which bury themselves in the sand, they're quite strange-looking fish—and flathead but also stingrays."
People actually did not have a good idea of the particulars of great white shark diets. As Grainger points out, the sharks enjoy protections throughout the world. So most researchers estimated their diets through the chemical markers that they can ethically access by taking small skin samples. These measurements indicate at what level of the food chain the predator is feeding but not the actual critters that make up their meals.
"There's quite a lot of evidence that lots of different animals, so even carnivores, omnivores, herbivores self-select different prey or food based on a particular balance of nutrients."
Grainger hopes that by further understanding what juvenile white sharks like to eat, he can begin to piece together how and why they make their predatory choices. The study was published in the journal Frontiers in Marine Science.
"Understanding and predicting when sharks might be more abundant in certain areas would be an ultimate end goal."
Avoiding or mitigating human-shark conflicts means understanding the sharks' nutritional goals. And if researchers can anticipate where and when sharks are likely to spend their time hunting, they can better protect humans from getting bitten—and sharks from getting killed.
Thanks for listening for Scientific American's 60-second Science. I'm Jason Goldman.
背鳍划破海面是种标志性画面 。但是，研究澳大利亚沿海年轻大白鲨胃内容物的科学家，在发现这种食肉动物似乎花大量时间在海底巡游时，还是大吃了一惊 。
“它们的食物以鱼类为主，这对幼年大白鲨来说不足为奇 。我们此前识别出的最重要猎物种类是东澳大利亚三文鱼 。”
悉尼大学研究生理查德·格兰杰说到 。他和团队将50多只幼年大白鲨的胃内容物进行了分类，这些大白鲨因被用来保护游泳者的防鲨网缠住而死亡 。
“全部出乎意料的发现是，底栖鱼类的多样性和重要性 。比如将自已埋进沙子的胆星科鱼，它们的外表非常奇怪，还有鲬科鱼和黄貂鱼 。”
人们其实并不太了解大白鲨饮食的特殊性 。正如格兰杰所指出，大白鲨享受着世界各地的保护 。因此，大多数研究人员通过化学标志物来估计大白鲨的饮食，这些化学标志物可以从小块皮肤样本上道德地获取 。这些测量结果显示的是这种食肉动物在食物链的哪个层次进食，而不是其饮食由哪些实际生物组成 。
格兰杰希望，通过进一步了解幼年大白鲨喜欢的食物，他可以开始拼凑出它们做出捕食选择的方式和原因 。这项研究发表在《海洋科学前沿》期刊上 。
避免或缓解人类与鲨鱼的冲突，意味着了解鲨鱼的营养目标 。如果研究人员能够预测鲨鱼可能在何时何地捕食，他们就能更好地保护人类不被咬伤，同时保护鲨鱼不被杀死 。
谢谢大家收听科学美国人——60秒科学 。我是杰森·古德曼 。
1. be in for 肯定会经历；注定遭受；
You might be in for a shock at the sheer hard work involved.
2. sort through 整理；分类；
Their specific task is to sort through the reams of information and try to determine what it may mean.
3. make up 组成；构成；
Women make up 56% of the student numbers.
4. piece together 拼凑出（真相）；
In the following days, Francis was able to piece together what had happened