Present stage of the salmon experiment

Though grilse weighing from 31bs. to 71bs. have during the last four years been taken in the Derwent, how is it that no mature salmon, that is, fish weighing from 151bs. to 301bs., have been captured? This is a question frequently asked both here and in the neighbouring colonies, but it will be necessary before attempting to answer it to refer to what is known of the early life history of the salmon in Europe and Tasmania.