Possible Clues:

• Great swimmer taking part in decider or qualifier
• Tail of diver or another bird, not one that's a big swimmer
• Blue or fin whale, eg
• A baleen whale of streamlined appearance with pleated skin on the underside
• Streamlined type of baleen whale
• Sea creature of some power or quality
• Spain plays no part in silly quarrel about oxygen for whale
• Whale getting thinner finally, or the same topless?
• Large baleen whale
• Baleen whale