Roca Partida pokes out of the ocean like a decayed tooth. This volcanic remnant is only about 100 yards long and 110 feet high, but the fish love it. It used to be a hot spot for the commercial tuna fleet. We arrived before dawn on Feb. 19, and didn’t waste any time. Under the watchful eye of a Mexican Navy patrol boat, we fished from large schools of tuna, and noticed large schools of silky sharks -- humans aren’t the only ones who know about this hot spot. We tagged 257 yellowfin and 27 wahoo with plastic dart tags, and put two archival tags in yellowfin and 12 in skipjack. We left Roca Partida at 2 p.m. and set a course for our next stop, Clarion Island.