When I circumnavigated in the 70's there was plenty of sea life out there; we caught fish every time we set a line
, everywhere except the Med. Flying fish on deck almost every morn in the Pacific and squid in the Indian Ocean (both make a great breakfast).
Birds, sharks, mantas, sunfish, whales and dolphin/porpoise; you name it, they were around, not every day, but often enough to keep life interesting. I remember acres and acres of fish, dolphin (playing) as far as the eye could see and whales all around us on many a sail.
I set sail from Newport, RI in Nov, 2010 and sailed to St. Thomas via Bermuda. 3 measly fish in 14 days sailing. Return from Puerto Rico to Charleston, SC; 1 tuna in 10 days. Left Newport (Oct, 2011) again for St.T again via Bermuda; 2 smallish dolphin ONLY.
SAME fishing lures, SAME fishing line
, SAME fishing technique; I could ALWAYS count on fish to eat when I sailed, up until about 1984 when I shifted to large motor yachts.
"Remember the middle of the oceans are deep, thousands of meters deep. In the tropics there's not much nutrient to feed fish, therefore larger species don't prey there."
I always thought that way when I began sailing the oceans, but it just wasn't true. Now there are very few flying fish and little else out there to see, until you get close to the islands and even there everyone complains "it's NOT like the old days".
I can no longer offer advice on "sure fire fishing behind a sail boat" It worked like a charm for ALL who tried it for over 20 years.
THEY HAVE KILLED MY OCEANS FOR THEIR ALMIGHTY BUCK!