The current challenge is to practically and effectively implement the principles advocated in these agreements. Diverse ecosystems are considered to be more resilient and have a greater ability to withstand changes in the environment, such as ecosystem shifts and climate change. For example, the abundance of northern shrimp and crab stocks in the North East Atlantic may be a result to some degree of the overfishing of their predator, Atlantic cod (in addition to potential changes in oceanic conditions). For example, large sharks (which are slow maturing, long living species) play a role as a key predator in the ecosystem.