Answer:
Vasco da Gama started his voyage in Portugal journeyed around the Cape of Storms(later name the cape of Good Hope)to buy spices and valuable things almost none of the merchants want anything of his trade but he succeeded on his mission to find an eastward sea route to the Indies so the answer is C.
is this what you meant?
Answer: There is pollution in the east river
Explanation: If we think about it cant be a lack of food as it talks about having a large food source. Nor can it be climate change as that would result in a low yellow Perch population. it cant be they aren't able to catch the bird. So the only logical answer is a pollution that the birds are adapted to.