The main purpose of this work is to present evidence of sea turtles by-catch increase in northern Peru during the 1997-1998 El Niño Southern Oscillation (ENSO) process. The study area is located off Lambayeque, between 6°20′S and 7°10′S, and from the coastline up to 35 nm offshore. The gill-net artisanal fishery was analyzed and described, since this was the fishing gear which most interact with sea turtles, the boat characteristics were evaluated as well. Sea turtle captures and species identification were registered from January 1996 until December 1998. The catch per unit effort (CPUE) was analyzed. Data was correlated with sea surface temperature (SST). A total of 265 fishing operations were analyzed, from which a total of 383 sea turtles were captured: being 80.4% olive ridleys (Lepidochelys olivacea); 19.3% green turtles (Chelonia mydas) and 0.2% hawksbill turtles (Eretmochelys imbricata). A positive significant correlation with a 99% confidence interval was found between sea turtle captures and SST (Pearson; r = 0.787; σ = 0.000; N = 36). We recommend strengthening collaboration between public and private organizations, to implement appropriate management measures for the conservation of sea turtles, especially during an ENSO event.