batteries are likely dead. with no evidence in hand, searchers for flight 370 are considering their next moves. >> we may not have all of the clues, and we may have overlooked something. >> reporter: australian officials say they will scale back the air search soon. >> the chances of any floating material being recovered have greatly diminished. >> reporter: under sea recovery efforts may expand, if necessary, experts say, extending parts of the search area. >> i think that will involve retracing that initial arc of the suspected flight path, and that will require some broad-scale sonar tools. >> reporter: sonar even more powerful than the bluefin-21 that can dive deeper and create even wider images of the ocean's bottom. it's still the best tool searchers have at their disposal. >> until we actually locate some debris with sonar, there's no point in bringing in