Authorities on opposite coasts are stepping up patrols and closing some swimming areas after a series of shark encounters in the run-up to the July 4 holiday. On Long Island, Nassau County Executive Bruce Blakeman ordered additional drones, helicopters and marine patrols at Jones Beach after a 20-year-old woman suffered minor foot lacerations when a juvenile sand tiger shark bit her while she was waist-deep in the surf last Wednesday. County and state park police said they will keep lifeguards on high alert and coordinate with aviation units throughout the summer. In California, fishermen off La Jolla filmed a 16- to 18-foot great white shark over the weekend, drawing crowds and prompting warnings from San Diego officials. Farther north, Seacliff State Beach was closed after a separate shark sighting, and beaches in Aptos were shut down when a great white bumped a swimmer taking part in a Junior Lifeguard program. Marine biologists say cleaner coastal waters and abundant bait fish are drawing sharks closer to shore, increasing the likelihood of encounters. Officials in both states are urging beachgoers to avoid swimming near schools of fish, stay in groups and remain close to shore, especially at dawn or dusk.