In the case of edible fishes such as cod and tuna a major threat is overfishing. Where overfishing persists, it eventually causes the collapse of the fish population (known as a "stock") because the population cannot breed fast enough to replace the individuals removed by fishing. One well-studied example of the collapse of a fishery is the Pacific sardine Sadinops sagax caerulues fishery off the coast of California. From a peak in 1937 of 790,000 tonnes the amount of fish landed steadily declined to a mere 24,000 tonnes in 1968, at which point the fishery stopped as no longer economically viable. Such commercial extinction does not mean that the fish itself goes extinct, merely that it can no longer sustain a profitable fishery. The main tension between fisheries science and the fishing industry is the need to balance conservation with preserving the livelihoods of fishermen. In places such as Scotland, Newfoundland, and Alaska the fishing industry is a major employer, so governments have a vested interest in finding a balance between conserving fish stocks while maintaining an economic level of commercial fishing. On the other hand, scientists and conservations push for increasingly stringent protection for fish stocks, warning that many stocks could be wiped out within fifty years.