From Revenue Canada:
If you lease computers, cellular telephones, fax machines, and other equipment, you can deduct the percentage of the lease costs that reasonably relates to earning your fishing income. You can also deduct the percentage of air-time expenses for a cellular telephone that reasonably relates to earning your fishing income.If you buy a computer, cellular telephone, fax machine, or other such equipment, you cannot deduct the cost. You can deduct CCA and interest you paid on money you borrowed to buy this equipment that reasonably relates to earning your fishing income.
That's the Fishing Activities tax information page. It's the same in the Business and Professional guidelines, but that's only available in PDF. (Somewhere in there. ;)
And if it's an Apple yer after:
Tax advantages ("Fair Market Value Lease") The monthly lease payments may be fully deductible as an expense. Consult your financial or tax advisor.
Yup yup yup. Just waiting for CoreDuo MacBook Pros. Thanks Steven for pointing it out! You'd mentioned it before, but now I get it. ;p