are there any mammals, whales, dolphins and sharks in the SL ocean that do not belong to a resident

[hallebarde]

...but to the Linden lab, as buildings exist with such a status?

(Here I am again, but try not to post too often, honest.)

[Syo Emerald]

Short answer: No.

The oceans in SL are empty.

[Rolig Loon]

Quite a few.  If you wander around in the Mainland ocean regions of SL, you will find that a lot of them have fish, sea monsters, and other interesting aquatic things in them.  Visit the Somagalags region at http://maps.secondlife.com/secondlife/Somagalags/191/51/16 or the waters offshore from Meauxle Bureaux at http://maps.secondlife.com/secondlife/Fernandes/82/72/8 to see what the Linden Department of Public Works (LDPW) does to decorate public areas.  None of those objects are owned by SL residents.

ETA: Clarification -- Many of those objects will show a creator or owner with the name "Linden" or "Mole", all of whom are Lindens or Linden contractors in LDPW.