and Freshwater Research, it was determined that the resuspended sediment created anaerobic turbid conditions, which was capable of killing scallop larvae that use the ocean floor as a habitat as they mature. Furthermore, the same study also revealed that for filter feeders, despite there being more particulate matter in the water after a trawl, the protein per unit weight of sediment decreased meaning they have to filter much more water for the same nutritional value. A 2021 study estimated annual carbon emissions from bottom trawling at almost 1.5 billion tonnes (about 3% of the world total) and recommended that more marine protected areas be established. As a result of these processes, a vast array of species are threatened around the world. In particular, trawling can directly kill coral reefs by breaking them up and burying them in sediments. In addition, trawling can kill corals indirectly by wounding coral tissue, leaving the reefs vulnerable to infection. The net effect of fishing practices on global coral reef populations is suggested by many scientists to be alarmingly high. Published research has shown that benthic trawling destroys the cold-water coral Lophelia pertusa, an important habitat for many deep-sea organisms. Midwater (pelagic) trawling is a much "cleaner" method of fishing, in that the catch usually consists of just one species and does not physically damage the sea bottom. However, environmental groups have raised concerns that this fishing practice may be responsible for significant volumes of by-catch, particularly cetaceans (dolphins, porpoises, and whales). Studies on population and trawling The population of Alaska's Bristol Bay red king crab experienced an abrupt collapse during a three-year time span after 1980. During the 1970s the Bristol Bay red king crab fishery represented Alaska's most valuable single-species fishery until 1980, then in 1982 the catch had dropped to zero and was an incredible example of a population crash. The cause of this crash was controversial with U.S. and Alaskan crab managers and modelers, with some stating the phenomena was a natural occurrence due to Pacific decadal oscillation, a shifting the location of warm and cold waters at an irregular pattern, while other marine biologists questioned the involvement of the new trawling fishery targeting Yellowfin sole in the area. Subsequently, a study was conducted by C. Braxton Dew and Robert A. McConnaughey in 2005 using data from the yearly Bristol Bay bottom-trawl survey conducted by the National Marine Fisheries Service and