"marine snow" and other detritus from surface to bottom. The phenomenon has been termed the "whale pump". The Gulf of Maine study also found that the view of whales and other marine mammals as competitors for fishing, advocated by some nations, is incorrect as whales play a vital role in maintaining the productivity of phytoplankton and consequently the fish. Culling marine mammal populations threatens the nutrient supply and the productivity of fishing grounds. In addition, the feces of krill-eating whales is rich in iron. The release of iron from whale feces encourages the growth of phytoplankton in the sea, which not only benefits the marine food chain, but also sequesters carbon for long periods of time. When phytoplankton, which is not consumed in its lifetime, perishes, it descends through the euphotic zone and settles down into the depths of sea. Phytoplankton sequesters an estimated 2 billion tons of carbon dioxide into the ocean each year, causing the ocean to become a sink of carbon dioxide which holds an estimated 90% of all sequestered carbon. The Southern Ocean is amongst the largest ranges for phytoplankton and has the characteristic of being nutrient-rich in terms of phosphate, nitrate and silicate, while it is iron-deficient at the same time. Increases of nutrient iron results in blooming of phytoplankton. Whale feces is up to 10 million times richer in iron than the surrounding sea water and plays a vital role in providing the iron required for maintaining phytoplankton biomass on the earth. The iron defecation of just the 12,000 strong sperm whale population in the Southern Ocean results in the sequestration of 200,000 tonnes of atmospheric carbon per year. A study of the Southern Ocean found that whales not only recycled iron concentrations vital for phytoplankton, but also formed, along with krill, a major source of sequestered iron in the ocean, up to 24% of the iron held in the surface waters of Southern Ocean. Whales formed part of a positive feedback loop and if whale populations are allowed to recover in the Southern Ocean, greater productivity of phytoplankton will result as larger amounts of iron are recycled through the system. Accordingly, whales are referred to as "marine ecosystem engineers". A study conducted in the Fernando de Noronha Archipelago of the southwest Atlantic Ocean, revealed the feces and vomit of Spinner dolphins (Stenella longirostris) formed part of the diet of twelve species of reef