NO! this is not a nit, that is a material difference. Risk and volatility are priced into a lot of seasonal work, especially commodities like fishing. You have yield concerns, market price concerns, fluctaution in consumable prices (fuel, bait, etc). That's not the case for teachers. That's a HUGE difference. The greater the volatility, the less predictable their income is. I'm surprised you don't see that.
And I'm not being argumentative - it seems you're being pedantic. Of course they don't all realize economic income of 75k per year, but when comparing their wages to people who work 12 months a year, annualizing their 9 month salary is a reasonable approximation. Just saying "No, they make 56k so they're paid less than everyone else" is nonsense. If the average annual salary of people with a college degree is $60/year and teachers are making $56k per year for 9 months work, they're clearly doing better than average.