Urgent threats to the Gulf of California ecosystem from modern human activity obscure the fact that humans have interacted with native plants and animals for millennia. Archaeological and historical evidence suggests that indigenous peoples occupied both sides of the Gulf some 13 000 calendar years ago and that they eventually inhabited six major islands and visited most smaller ones. Biologists have increasingly realized that these peoples probably played a role in shaping island biotic communities extant today. How much of a role is unknown, but the best places to find evidence may be archaeological sites, which often contain remains of plants and animals directly used by prehistoric peoples. The opportunity to investigate the interaction between early humans and island biota may be lost because modern island visitors endanger sites. Many people, whether boaters, ecotourists, government officials, scientists or artefact collectors, enjoy picking up artefacts. Small surface sites, with exposed remains, can be completely denuded in minutes. Visitors to small islands can obliterate entire archaeological records, thereby creating the illusion of pristine islands. This problem is bound to worsen as Mexico implements Escalera Náutica, a chain of marinas specifically intended to multiply manyfold the boating population. The Mexican government's management plan for Gulf islands, published in 2000, recognizes only a general need to manage cultural resources. Specific mechanisms for protecting sites should be developed. These should educate visitors about the importance of the archaeological record and the destructiveness of collecting. They should also provide adequate enforcement of Mexico's existing antiquities laws. Conserving the archaeological resources may be the best way of preserving biological data essential to island biogeographers and ecologists.