What is the subject of "putting"

Evolution works to maximize the number of descendants that an animal leaves behind. Where the risk of death from fishing increases as an animal grows, evolution favors those that grow slowly, mature younger and smaller, and reproduce earlier. This is exactly what we now see in the wild. Cod in Canada’s Gulf of St. Lawrence begin to reproduce at around four today; forty years ago they had to wait until six or seven to reach maturity. Sole in the North Sea mature at half the body weight they did in 1950. Surely these adaptations are good news for species hard-pressed by excessive fishing? Not exactly. Young fish produce many fewer eggs than large-bodied animals, and many industrial fisheries are now so intensive that few animals survive more than a couple of years beyond the age of maturity. Together this means there are fewer eggs and larvae to secure future generations. In some cases the amount of young produced today is a hundred or even a thousand times less than in the past, putting the survival of species, and the fisheries dependent on them, at grave risk.

1. What is the subject of the underlined "putting"? I think its subject is the whole sentence before putting. Am I right?

2. Can I change the "putting" into which is putting?