Winning money from a competition is either going to show up as a prize or gambling on the "Other Income Line on Form 1040. It will be taxable income no matter the name.
If it is considered hobby income, the taxable entry point will still be on Other Income, 1040 but you may take expenses up to the amount of income on Schedule A Itemized Deductions subject to 2% of AGI floor.
Since you are not self-employed as a professional fisherman (unless you are), you can't deduct expenses all your expenses to have a potential loss. I am assuming the income was in Box 3 of the 1099-Misc. There are rules that have to be met in order to consider yourself self-employed.
