with Andrej Gajić

National Geographic Explorer and marine biologist Andrej Gajić studies a shark's jaw.

Before you read

Our Changing Planet

Life Science

As you read, think about
how this scientist uses observations and collects evidence in order
to understand a problem.

07/07/2024 05:25:42

Andrej Gajić usually dives alone. At night. In shallow, murky water. He dives in this setting because that’s where and when he’ll find sharks. And Gajić needs to find sharks.

Gajić is more than just a diver. He’s a National Geographic Explorer and a marine biologist. His goal is to understand the effects of pollution on sharks and skates and rays (flat fish closely related to sharks). To do this he needs to work both in a lab and in the water.

Difficult Dive

Many of Gajić’s dives take place at Neum Bay on the Adriatic Sea. It’s a hotspot for sharks, rays, and skates. It’s also a good place to observe these nocturnal creatures.

The bottom of Neum Bay is only about 30 meters (98 feet) below the surface. The water here is thick with sediment and colonies of plankton—small organisms that float in the sea. Gajic can’t see his hands in front of his face. He lets his eyes adjust. Then, he can make out some shapes.

His video camera carries a powerful light. He switches it on. Then he sees them. Smoothhound sharks swim in circles near the seabed. He knows he must avoid sudden movements.

Gajic examines an unborn smoothound shark, searching for signs of deformities.

A lesser spotted dogfish rests on the seabed.

Be watchful! That’s Gajić’s advice. Most of the marine animals Gajić encounters have no interest in people. They are not likely to attack. But his presence must
not cause stress to the animals. He pays close attention to the body language of the sharks. Is he seeing any sudden movements toward him? No. The sharks appear curious but not threatened by him.

As they swim around him, he looks closely at their jaws and teeth. He studies their gills, skin, and muscles. He’s looking for any signs of disease.

Gajić spends close to an hour in this silent world. To his eye, the sharks appear healthy. But to truly know, he needs to look much deeper.

Sharks in the Adriatic

There are 33 species of sharks in the Adriatic Sea. Catsharks, dogfish, and smoothhounds are the most abundant. These sharks are fairly small and like to stay near the ocean floor.

In the open water, Gajić’s team has encountered elegant blue sharks, as well as lightning-quick mako sharks. Makos may have bursts of speed up to 18.8 meters a second (68 kilometers or 42 miles an hour).

The thresher shark has a tail fin that grows up to 3 meters (almost 10 feet). It stuns its prey with its tail.

Europe

Bosnia-Herzegovina

Adriatic
Sea

Mediterranean
Sea

Neum Bay

Malta

07/07/2024 03:04:25

Shark Sightings

In deeper water, Gajić has come upon rough sharks and lanternsharks. He doesn’t need his camera light to see lanternsharks. They glow! The light comes from many small organs called photophores, which dot their bellies and sides.

Gajić’s interactions with rays and skates are a little less tricky than with sharks.

He’s able to get closer to rays, including stingrays, eagle rays, and leopard whiprays, as he studies them.

For Gajić, it is a dream come true to be among these animals. He grew up in the country of Yugoslavia and never lived near the ocean. Yet, he was fascinated by the sea and what lived in it. Especially sharks. He was inspired by National Geographic magazine. He vowed that he would one day swim with sharks.

researching unborn smoothhound sharks

Gajić examines a deep-water rough shark in the lab.

Dangerous Waters

As much as he loves sharks, Gajić knows that they are in trouble in the Adriatic. Pollution is causing illnesses in many marine animals. Plastics, pesticides, and waste poison the sea. Though Neum is a popular vacation spot, much of its sewage flows into the sea. This becomes hazardous.

Outwardly, a marine animal might seem healthy. To know for certain, however, Gajić must put on his white lab coat. In
the lab, he must examine shark organs and tissue. Only then can he see what’s really happening.

Under the Microscope

Gajić rarely collects samples from live sharks. Instead, a tissue sample is taken from an already-dead shark. These come in the form of bycatch—when a shark is accidentally caught in a fisher’s net and killed. When a shark is killed by mistake, local fishers give the sharks to Gajić.

In the lab, each specimen is given a full x‑ray and a scan so Gajić can see inside the animal. Tissue samples are taken. From these samples, Gajić can learn a lot.

In one shark, he found the disease hepatitis. That’s a disease of the liver. It might be caused by high amounts
of heavy metals in the water. In other sharks, he found disease in both kidney and brain tissue. Pollution made these sharks sick.

This sevengill shark was bycatch off the coast of Malta in the Mediterranean Sea.

07/07/2024 04:13:45

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