Steven Seagull's name in real life is Sully. He lives (to this day) in a seagull sanctuary in Australia. Two extra seagulls were used to portray Steven Seagull. According to producer Matti Leshem, she added "They were all good but not nearly as good as him. Peggy was the vocal one, the very squawky bird. Gaviota (which means seagull in Spanish), I think he's almost 30 [as Steven is estimated to be about 15 or 20 years old]. The most challenging thing about Sully as an actor is that seagulls are remarkably clean. They self clean a lot, so the blood on Sully, obviously fake blood, he kept wanting to clean it off, so we had to deal with that."
Blake Lively only had a stunt double for the surfing scenes as she couldn't surf professionally, "All I did was paddle" she recalled, her surfing stunt double was professional Australian Surfer 19 year old Isabella Nichols, she taught Blake how to paddle correctly, how to wax a board and put a leg rope on and fins in to make it look authentic.
Blake Lively was partly inspired by her husband Ryan Reynolds work in the similarly minimalist film Buried (2010), stating "that was one of the reasons why I wanted to take on this movie so much, because I know how tough that was for him and how rewarding it was."
Blake Lively was pregnant with her second child during filming.
Jaume Collet-Serra teamed up with the art department for the design of the shark. "I came to the conclusion that the shark had to be female", says the director. "Females are slightly bigger and have great scars from mating. Visually they're scarier, as they are more protective." Creating the shark generally took thousands of hours of research, so the film crew watched every Shark Week episode to get the idea of creating the shark he further added "she's a female shark, we know exactly how much she weighs. Every scar that she has has a story behind it. It's really an incredible job of artistry and research".