I had a similar experience sailing south from Newport twice and north to Charleston from PR
in 2010 and 2011.
These are waters I have sailed at least 40 times on deliveries, north and south (US to/from the Caribbean) between 1979 and 1992, catching fish almost daily.
2010 south; 2 dolphin both under 16 pounds.
2010 north; 1 bluefin tuna 16 pounds.
2011 south; 2 dolphin both under 12 pounds.
Average trip between 1979 and 1992; 6 or 7 dolphin to 35 pounds plus several tuna up to 30 pounds.
This is the same exact fishing line and same exact lures I used for 25 years, hooking fish whenever we put it in the water.
Also interesting to note; very few flying fish, dolphins, other sea life or birds on all three trips, certainly much, much less than before, even in the Gulfstream.