The organization Oceana has put out a report entitled “Hungry Oceans: What Happens When the Prey Is Gone?” The report looks at the impacts of overfishing of prey species on top predators–effects that have often been ignored up to now.
Seabirds may go hungry as prey fish decline21 04 2009
While overfishing of large predatory fish (like shark and tuna) has long been recognized as a problem, smaller species like herring were thought to be immune to overfishing because of their large numbers and rapid reproductive rates. Now, however, fishermen are turning up ever smaller catches of these prey fish, and the predators that rely upon them are showing signs of nutritional stress, including decreased breeding success. Malnutrition can also lead to increased susceptibility to disease, and may drive seabirds to seek food from unnatural sources like fisheries discards. This places them at increased risk of fatal entanglement in fishing nets.
Compounding the problem, prey fish are highly sensitive to climate change induced changes in the oceans, and the long-term impacts of such alterations remain unknown.
Take a look at the full report yourself; it’s very well put together and is accessible to any non-scientist. The Oceana site is also worth a general look for its take on issues like off-shore drilling, fishing practices, and assorted other issues facing ocean health today.