Deep dropping at night is just as productive...and not as hot, temperature-wise.
Caught rosies all over Hollywood Hills when I tried it in '99. Good to eat but spiny and small.
Contrary to popular belief, you don't necessarily need a light to catch fish. We've been doing it for over twenty years and only started using lights the last 6 or 7 (LP's or those clear white ones). You'll still catch without them but not as quickly.
Don't know about mercury levels.