Visitors to Mandalay Bay this Halloween season are being alerted to multiple sightings of semi-aquatic predatory carnivores lurking about. They’re not on the loose, but they can be found in Shark Reef Aquarium’s jungle and can chomp down with a powerful bite. The four female Johnston’s Crocodiles are housed in an environment where a thick layer of clear acrylic keeps them separated from humans and protects them from the ghosts and goblins who stop by Oct. 26-28 for Hallow-Reef, the latest edition of the annual Halloween spooky scene that the aquarium presents every year.

The four Australian freshwater crocodiles, all sisters, replace a golden saltwater crocodile that had outgrown Shark Reef and was transferred to an alligator farm in Florida. “One thing that Shark Reef is always trying to do is bring in animals that are unique and different into our collection. We’re always looking for that,” says general curator Jack Jewell, who largely oversees acquisitions and moving animals to other locations. “The Johnston Crocodiles came up as something on our radar that was appropriate for our enclosure, that allows us to exhibit a number of crocodilians at once.”

Jewell says it’s not typical to see multiple “crocodilians” in one exhibit, and that there are very few Johnston Crocodiles anywhere in the U.S. Adding them to the more than 2,000 residents of Shark Reef’s living animal collection, representing at least 100 species, is a coup for the curator’s team. The “freshies,” on loan from the San Diego Zoo, are 14 years old and 4 feet in length. At 30-35 pounds, they are not capable of consuming trick-or-treaters in one sitting. They are not hiding in the touch pool among the rays and guitarfish. They are not waiting in shadowy tunnels of Hallow-Reef, waiting to attack unsuspecting prey as macabre music plays in the background.

Or are they? The optimal way to find out is to show up on Friday, Oct. 26, when costumed kids 12 and under receive complimentary aquarium admission and treats, then discounted admission on Saturday and Sunday. The American Red Cross will be on site Friday to accept blood donations in observance of Community Day, and donors receive complimentary Hallow-Reef admission as well as free parking. Entry to Hallow-Reef is included in regular admission to Shark Reef Aquarium and Polar Journey this weekend through Shark Reef’s 8 p.m. Sunday closing time.

The crocodile siblings can be found near the beginning of the path through the Shark Reef, in the jungle environment where a Komodo Dragon, a Burmese Python and piranha can be encountered. Hammerheads are among the 15 shark species that can be sighted through the first windows into the underwater world guests see through, and the touch pool allows people to lean over and gingerly feel a ray or horseshoe crab. The Johnston Crocodiles are relatively active animals, says Jewell, and are much more visible than the golden saltwater crocodile was. “They spend a lot of time on basking on land, which really increases their visibility.”