Complex sentence: They are generally considered to be less adapted to aquatic lifestyle, breeding on land and hauling out more frequently than true seals; however, they can attain higher bursts of speed and greater maneuverability in the water.
Split into simpler sentences: They are generally considered to be less adapted to aquatic lifestyle, since they breed primarily on land and haul out more frequently than true seals. However, they can attain higher bursts of speed and greater maneuverability in the water.