An ecological niche is an organism's mode of life; it is the sub of its adaptations. (You could think about it as the organism's "profession".)
The English term 'ecological niche' means (ecology) the status of an organism within its environment and community (affecting its survival as a species)
Mainly, it's the top scavenger. It's also a predator in many of its forms (Great White, Hammerhead, etc)
The niche of a shark in an ecosystem is to prevent overcrowding in it's environment.