Polar bear attack

On the second photo expedition to Svalbard this past summer (27/8-3/9), we experienced a rare situation between a Polar bear and a Glaucous gull. A polar bear suddenly dove and swam a good 10-15 meters underwater before it attacked the surprised young gull. I have never seen anything like this on previous expeditions to Svalbard, and the fight was more interesting than I had expected. Usually a polar bear can easily kill a 100+ kg seal, and a gull weighting in at 1.5 kg should be an easy match! After the first bite to the back of the gull, the bear continued its attack in the water. The gull fought heroically, and with its bill managed several direct hits to the bear's eyes and nose. This made the bear back off and the gull escaped after 10 minutes. Why didn´t the the Polar bear kill the gull quickly? Perhaps this was a teenage bear, and maybe he just wanted to play with one of the birds.