That's probably partly true as they are opportunistic predators, but the article -
USGS press release clearly links a shift in bald eagle diet to a decline in otter numbers:
The sea otter is a keystone species in near-shore coastal environments because of the pivotal role it plays in maintaining a healthy balance in kelp forests. By eating sea urchins – the biggest threat to kelp forests – sea otters controlled sea urchin numbers and kept the ecosystem in balance. This ensured these underwater plants could thrive and reach their maximum height of 250 feet.
Kelp forests provide habitat, shelter, and a buffer from waves and currents for numerous aquatic species. This marine environment also provided the bald eagle with a diet of marine fishes and sea otter pups.
Also note, and this is very interesting:
Although the diet of these bald eagles changed with the decline of sea otters, the scientists discovered that the birds actually produced more eggs and young, a fact that Anthony suggests may be a result of high caloric content in the eagles’ increasingly seabird-dominated diet.
So it may be that protections caused bald eagle populations to rise, then another effect down the chain caused them to shift their diet. When they did so along came increased reproductive success.
Good case you make there for managing fish stocks, as in not over-fishing or destroying fish habit.
