Wayne Perryman, a senior whale researcher with the Southwest Fisheries Science Center in La Jolla, leads an aerial photo team"We want to sample early in the migration, sample at the peak and sample at the tail end of migration," said Perry.That means from early January to early February, the team riding in a twin otter aircraft can capture beautiful images that provide valuable ways to measure how the whales are doing.Dave Weller is part of the whale research team and said the photos allow them to take measurements to check for things such as pregnancy and whether the population is well-fed."What we're looking for is that trend over time to make sure nothing has changed over the past decade," said Weller.Researchers said the trend is that the gray whales are thriving and are roughly 20,000 strong. That is one possible reason why some -- such as the juvenile gray whale spotted in Mission Bay recently -- have ventured close. However, Weller said there may be a simpler reason."They're curious," said Weller. "Gray whales are curious so they explore bays and other areas."Scientists said they have been seeing more calves born during the migration, which starts around the Arctic Seas and extends all the way down to the calving areas off the coast of Baja California, Mexico. Nearly 900 calves were counted last year.Perryman said while they take to the air for their research, it is the whales that actually make their job easier. He said it is because their swim near the area lets scientists do more in-depth studies at a relatively low cost.The research team said from about mid-April to June, the gray whales will start to head back up north to start the cycle all over again.