The Collaborative International Dictionary
Sea beast \Sea" beast`\ (Zo["o]l.) Any large marine mammal, as a seal, walrus, or cetacean.
Wikipedia
Sea Beast, also known as Troglodyte, is a Canadian-American 2008 Horror/ Syfy Channel movie starring Miriam McDonald, Daniel Wisler, Brandon Jay McLaren and Corin Nemec. It was released to DVD on June 30, 2009. It is the 16th film of the Maneater Series. It is probably a reference to the Deep Ones.
Usage examples of "sea beast".
The ribs of the schooner curled up from the keelson like the skeleton of some sleek sea beast cast ashore, embraced by the cradle that held them in place while the frame was spiked and treenailed together.
Theo watched her fade into the dark where the Sea Beast was pulsing with dim spots of green and blue.
Or it could have been the perfect darkness outside that fostered an impression of incredible depth, even greater than when our poor little Wuphon's Dream fell into the maw of this giant metal sea beast.