By the spring of 1917, so much of Canada's workforce had entered the armed forces that industry and agriculture were severely short of labour. As a result, all able-bodied internees were paroled from the internment camps to work in factories, railway camps and mines. Parole conditions included travel restrictions and required parolees to carry identity cards and report regularly to local authorities. Those assigned to railway labour in northern Ontario experienced conditions as hard as in the camps. Some 1,300 prisoners were paroled from Kapuskasing that spring. Approximately 60 men remained in camp for health or security reasons. They were soon joined by 400 prisoners of war transferred from the Fort Henry internment station. To hold these more dangerous inmates, high barbed-wire fences were erected around the camp and a stricter regime was instituted. Soon the camp's population again rose to over 1,200 prisoners. The majority now were German prisoners of war, mostly sailors and merchant seamen taken from German ships in the Caribbean.
Why was Fredrich Gerull considered "dangerous"? Most likely he was just a merchant seaman like Grandpa who got caught in the wrong place at the wrong time.
Update: Fredrich was most likely in the German military and was captured and interred on behalf of England in Canada.