3 ranks each in Listen, Spot, and Swim?
Eh? Silkies have enough skill points for 8 skills at 9 ranks!
I'd look for inspiration in the Nixie and the Nymph:
Nixie: Bluff +8, Craft (any one) +5, Escape Artist +6, Handle Animal +8, Hide +7*, Listen +8, Perform (sing) +7, Search +3, Sense Motive +5, Spot +8, Swim +6
Nymph: Concentration +10, Diplomacy +6, Escape Artist +12, Handle Animal +13, Heal +12, Hide +12, Listen +12, Move Silently +12, Ride +5, Sense Motive +12, Spot +12, Swim +8, Use Rope +3 (+5 with bindings)
Both have Swim at their racial default, so I'd give the Silkie the same.
Since Silkie are all sorcerers they need Concentration and Spellcraft at a minimum, and I'd add Knowledge (arcane) and Use Magic Device since the "Land Below Waves" seems quite advanced technomagically.
Handle Animal, Listen and Spot seem appropriate.
That leaves one more skill (assuming they're all maxed-out). As they are very charming fellows I'd go for Diplomacy.
Skills: Concentration 9, Diplomacy 9, Knowledge (arcane) 9, Handle Animal 9, Listen 9, Spellcraft 9, Spot 9, Swim 0, Use Magic Device 9