My employer told me that he only has to pay me $8 per day while I am out of work. How can this be true?

What your employer is talking about is called maintenance. Maintenance is an amount of money sufficient to pay the reasonable cost of food and lodging while a seaman recovers from his illness or injuries. The courts have held that a seaman is entitled to his actual cost of living expenses not a arbitrary amount determined by your employer. However, if there is in place a collectively bargained-for rate of maintenance, as negotiated by the employer and the seafarer's labor union, the CBA rate will be enforced.