Whales extinction

For many decades the whales have been killed. In   this graph we can see information availble since 1950 where number of blue whales killed  reached its peak and start to decreasese.While the number of blue whales decrease sudenly in 1950s , the number of  fin whales  increase in the 1950s,  reaching a peak in the 1960s and subsequently falling down abruptly.In this moment. the killing of sperm whales increase until middle of 1960s where like in the other cases after got its peak it dicreased and the killing of  new species started. the number Sei whales that reach its peak in late 60s. As you can see in the graph the killing of whales has been progressive starting from bigger whales  to smaller whales