Geneticist Nathan Sands and his daughter Nicole are hired by the U.S. Navy to create a new weapon; they create an intelligent shark that has the tentacles of an octopus, dubbed S-11, controlling the creature using electromagnetic pulses with a device attached to its head. During one of the test missions, S-11 discards the device before traveling to Mexican waters to find food. Sands and his daughter are then assigned to catch S-11 and travel down to Mexico, where they meet up with fishermen Andy Flynn and Santos, who work for Sands to help capture S-11. Andy, Nicole and Santos track S-11 on Andy's boat as Sands and his men follow in a yacht behind them. Several sightings occur as S-11 kills tourists and locals in the area. Fisherman Pez sends a photo of the creature to a news station, and news reporter Stacy Everheart and her cameraman Bones arrive to find the creature, enlisting Pez's help in the process. Stacy researches Sands and deduces that S-11 is a biological experiment. She, Bones and Pez record it killing a few people on a beach before heading into the ocean on Pez's boat to capture more evidence. Andy and a group of his diver friends go into a cave to find S-11, although the creature attacks them, killing everybody except Andy. He, Nicole and Santos then encounter Stacy, Bones and Pez, although Pez is killed by S-11 before it runs off. Andy, Nicole and Santos pursue it, resulting in Santos being killed. An enraged Andy radios Sands and tells him he's going to kill S-11 despite his orders. Andy and Nicole track S-11 to the mainland, where it kills a few people before Sands and his men arrive and hold Andy hostage. Nicole reprimands her father for wishing to further the experiments, although S-11 arrives and kills Sands's men before Sands himself is killed saving Nicole. Andy and Nicole encounter Stacy and Bones again, who drive them to a resort which S-11 is attacking. Nicole creates a plan to shoot S-11 with a device that will allow her to blow up a computer chip in its brain using her computer. The group arrives at the resort and Bones soon quits as Stacy attempts to put his life in danger to record S-11. However, S-11 then kills them both. Andy manages to shoot S-11 with the device, and Nicole hacks into the chip before overloading it, causing it to explode and kill S-11. Andy and Nicole reunite, and walk off to safety.
On Rotten Tomatoes, Sharktopus has a 57% approval rating, based on reviews from 7 critics. Kevin Carr of 7M Pictures described it as "cinematic junk food" and gave it 3.5 out of 5. Annalee Newitz of io9 wrote "Sharktopus represents both your guilt, and the assuaging of it, all in one tasty morsel" and called it the Inception of giant monster movies.
A similarly themed movie, Piranhaconda, was released in 2012. Two official sequels called Sharktopus vs. Pteracuda, which was released on August 2, 2014, and Sharktopus vs. Whalewolf, which premiered on July 19, 2015 during Sharknado Week on the SyFy Channel.
