Mako Sharks (Deep Blue Sea)

"All right, people. These sharks are thinking hard and clear. So here's the riddle: What does an 8,000-pound Mako shark with a brain the size of a flathead V-8 engine and no natural predators think about?"

- Russell giving his riddle commenting about the sharks' true purpose

"That's the answer to the riddle. Because that's what an 8,000-pound Mako thinks about..... about freedom...... about the deep blue sea."

- Carter answering Franklin's riddle commenting about the sharks' true purpose

The three Mako sharks are the main antagonists of the 1999 science fiction horror film, Deep Blue Sea. They were genetically engineered to harvest protein complex for a cure for Alzheimer's, but later on, they are shown to be more smarter and dangerous than spoken.

History
They were genetically engineered by Dr. Susan McCallister of the Aquatica facility to produce protein complex from their brains that will serve as a cure to reactivate human brain cells. According to one of the researchers named Janice Higgins, the team used a hormonal enhancer to increase the sharks' brain 5 times the normal size. However, it turns out that Susan herself used gene therapy to increase the brain mass, which is considered a violation of a code of ethics called the Harvard Genetics Compact. As a side effect, the sharks become more smarter and dangerous than ever. This also allows the sharks to develop an ability to swim backwards (something which a normal shark can't do) and developing a taste of their own kind, such as the time when the crew released a tiger shark into the test sharks' pen, and the test sharks instantly devoured the tiger shark.

In the beginning of the film, one of the Mako sharks escaped captivity and attacked a boat full of teenagers, but fortunately, expert shark wrangler Carter Blake (one of the members of the team and the hero of the film) arrives to the rescue and brings the shark back to its pen. This incident puts Aquatica's finances at risk, so Chimera Pharmaceuticals (the facility's main sponsor) sends in their board president Russell Franklin to investigate the facility. When the day of the test is about to begin, Susan had Carter to round up the largest shark into the lab. After having it sedated and put to sleeping, Susan extracts the protein complex from its brain and applied 2 CCs of it onto a sample of inactive brain neurons of an Alzheimer's patient. The result was a complete success as the cells start to reactivate and maintain membrane integrity in 6.5 seconds. However, things get out of hand when Dr. Jim Whitlock ends up having his arm chopped off by the big shark. Carter then attempts to shoot the shark with a shotgun, but Susan releases it back into its pen, much to Carter's anger.

The crew then calls in a paramedics helicopter to evacuate Jim for medical attention, but a strong hurricane made it too difficult for the pilots to reel the stretcher, causing it to fall into the pen waters. One of the sharks then grab the stretcher and pull the cable, causing the helicopter to crash into the facility's tower, killing both pilots and the tower operator Brenda Kerns. This also caused a complete system shutdown in the entire facility. The sharks then uses the stretcher to ram against a underwater window, and Jim dies succumbing to asphyxiation just as the facility slowly starts to flood. The sharks also proved to be strong enough to break down steel doors with a single hit, which is considered unusual. At that point, Susan is forced to confess her illegal experiments on the sharks, causing the other members to be very furious at her for this.

As time goes by, many of the members end up being attacked by the sharks one by one. Franklin was the first one to be devoured as he was giving a motivational speech to the team at the submarine deck. The second was Janice, who ended up being devoured while trying to catch up with the team climbing through the flooding maintenance ladder. This third was Tom Scoggins, who ended up being devoured while trying to help Carter activating some controls to drain the water from a stairwell leading to the surface. The only survivors left are Susan, Carter, and the ship's cook Sherman 'Preacher' Dudley.

Preacher managed to kill the first shark by throwing his lighter at the kitchen's heating oven to blow it up after it ate his pet parrot. Susan managed to kill the second shark by electrocuting it with a power cable, at the cost of destroying her remaining research in the process. As Susan, Carter, and Preacher finally head up to the surface, Preacher ends up being attacked and dragged on the leg by the third and final shark (presumably the big one), but he manages to swim to safety by stabbing the shark's eye with his crucifix, forcing it to let him go.

After tending to Preacher's injured leg, Susan and Carter learn of a horrible realization: the sharks have been herding the team into flooding the facility so that they could escape through the plain steel fences at the surface into the open deep blue sea. Realizing now that the big shark is too dangerous to be set free into the wild, Susan decides that she and Carter would have to kill it.

Carter devises a plan to kill the big shark: he would fire a harpoon filled with dynamite powder at the shark, and that Susan would have to connect the trailing wire to a car battery that will send in a electric current to blow it up. However, the big shark is too far away and too deep for Carter to make a clear shot. In a last-minute effort to get the shark's attention, Susan cuts her hands and dived into the water, causing the big shark to smell her blood. Having attracted the shark's attention, Susan then tries to climb out, but the ladder breaks, and despite Carter's attempt to save her, the giant shark devours Susan whole, much to Carter's distraught. Despite Susan's death, her effort was enough for Carter to get the shark at firing range, allowing Preacher to fire the harpoon at the shark's dorsal fin, though it pierced Carter's leg in the process. As the giant shark finally attempts to swim out to the open sea, Carter frees himself from the harpoon and Preacher connects the trailing wire to the battery, blowing the giant shark to bits and avenging the deaths of Susan and the rest of the team, much to both Carter and Preacher's relief.

With the sharks now gone for good, Carter and Preacher reunite in the wreckage of the facility as they await for an incoming boat en-route on the horizon.