Send it out, if it's not too late!
SPECIAL ATTACKS: Surprise, rear claws 1-4/1-4
SPECIAL DEFENSES: Surprised only on a 1
Moat cats, able to breathe water or air with equal ease, often stay completely submerged, then spring up to attack intruders. Opponents suffer a penalty of -3 to their surprise rolls when this occurs.
It should be noted that moat cats are silent creatures. Like the newts that are used in their creation, they make no vocalizations, so no great cat’s growl or roar will alert prey to the moat cat’s existence. More often than not, intruders first become aware of the aquatic predator when it pounces up at them—and by then, its usually far too late.
Like true amphibians, moat cats cannot survive in salt water.
Sounds reasonable.
Added to Homebrews.
Added rake because of this:
"Surprise" usually involves a racial bonus on Hide and/or Move Silently checks, plus Improved Initiative as a bonus feat.
This usually equats to a racial bonus on Listen and Spot checks and/or Alertness as a bonus feat.
This further supports the Hide and/or Move Silently bonus.
And even further support for a decent Move Silently bonus.
Convert this ability to "saltwater sensitivity"?
Freshwater Sensitivity (Ex): A sahuagin fully immersed in fresh water must succeed on a DC 15 Fortitude save or become fatigued. Even on a success, it must repeat the save attempt every 10 minutes it remains immersed.
All the above was included in my assumption of "Stats as Leopard, plus".
Do we want to keep the Water Dependency at 1 hour per 2 points of Constitution like a sahuagin or make the period shorter? It says "they usually stray only a mile or so", so maybe they can't stay out of water that long? They'd only need a couple of hours in the dry to travel that far.
Ahh...gotcha.
Updated.
I'd recommend increasing the Move Silently bonus to +8, since they seem even more silent than leopards based on the emphasis in the text.
I'm fine with keeping it the same, or simply making it flat 2 hours. I have no strong feelings either way.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.