Possible Clues:

• Swimmer's half-heartedly feeble balance
• Sea creature (reported close behind by the 10 to the 9!)
• Victim of a drift net
• Sea beast
• Dolphin-like beast
• Mammal seen in river? Get up to catch its second appearance
• Sea creature's elegance beneath river, right?
• Petty officer read Grace Leviathan perhaps
• Mammal meat — there's a kilo out on balance
• Marine mammal having power, initially, or composure