I'm a professional shark spotter. It took time to get confident at it – this is what I've learned.

• Naveron Lesch gave up working on traditional fishing boats to work as shark spotter in South Africa.
• He works six-hour shifts in summer and five-hour shifts in winter watching the ocean.

This as-told-to essay is based on a conversation with Naveron Lesch, a 35-year-old professional shark spotter in Cape Town, South Africa. It has been edited for length and clarity.

I come from the fishing community of Ocean View, on the Cape Peninsula, so I have a long connection to the sea. I grew up there and started off fishing with my uncles, diving for crayfish and abalone, when it was still legal.

When I was 23, I began working with my uncle on the trek nets, the traditional fishing boats that use large nets from the beach.

I was watching the water for shoals of fish. Now I'm watching for sharks.

I've always loved being out in nature, and when I worked with the trek fishermen, I was often up on the mountains that look out over the bay, watching the ocean for long hours.

The trek netting was fine, but the money wasn't good. As a fisherman, you get paid only when you catch fish. So when I saw that they were recruiting shark spotters for the summer season, I was quick to apply. I started in 2012, and here I am 10 years later.

The shark spotters operate on four beaches in Cape Town all through the year, and then we have another two beaches that we monitor on weekends, public holidays, and school holidays.

At each beach, we have spotters up on the mountainside with polarized sunglasses and binoculars who scan the water to monitor the movement of sharks and how close they are to people. If we sight a shark, we'll radio the spotter down on the beach and, if necessary, set off the shark siren to clear the water.

When I started out, we spent four months training with an experienced spotter. We would spend time up on the mountain learning how a Cape fur seal looked in the water, how a sunfish looked, how to tell a "bronzie" — a bronze whaler shark — from a great white shark.

Bronze whalers are very fast, with a round head, and have very flexible tail movement. The great whites are bulkier, have more of a pointed head, and have a very relaxed swimming style.

In the beginning, it's tricky to tell a shark from other animals or things in the water

Sometimes you can think pieces of sea kelp are sharks. Or if there's a seal swimming underwater, it can confuse you. Dolphins are easy, though, because they come to the surface regularly. We also see sunfish out there, and in the beginning, it's easy to think they're sharks. Sometimes we have cleared the beach thinking it's a shark, only to realize it's a sunfish.

There are 30 of us, all from the local communities, working in shifts every day of the year. In summer, we work 35 to 40 hours a week in six-hour shifts. In winter, when the daylight is shorter, we do five-hour shifts.

In summer, I start my shift at 7 a.m. I'll go up to the mountain for spotting and work until 1 p.m. Then another spotter will arrive to take over on the mountain. If it's my day for a double shift, I'll move down to the beach and relieve the beach spotter.

The spotter down on the beach is in charge of making sure the correct flag is flying and sounding the shark siren if needed.

It took me awhile to get confident

You're looking for sharks in the water while people are out there surfing and swimming and enjoying themselves. If I see a shark, I must decide whether to sound the siren and clear the water. So you have to know shark behavior and decide how close the shark is going to get to the people in the water.

It's a lot of responsibility. It's people's lives that we're looking out for.

We also have a whole system of flags to communicate with people about any sharks that have been spotted. A black flag means that the spotting conditions are not ideal; maybe it's an overcast day or the water isn't clear.

It doesn't mean we can't see sharks — most of our sightings happen while a black flag is up — but it means it's not perfect for spotting. A green flag means the visibility is good and the water surface is clear.

If we've spotted a shark, but it's left the area, we'll open the beach with a red flag flying. A red flag can also mean there's a high shark alert for another reason. Maybe there's a whale carcass in the area, which can attract sharks. We also fly a red flag if there are trek-net fishermen because the bronzies like to follow them.

The white flag means a shark has been spotted. When we put that up, a siren sounds and everybody must clear the water.

The most difficult part of this job is the weather

In the winter, it can get cold up on the mountain. And it can get boring if there's nothing to spot, but when there's something in the water, time moves faster.

That's why I love summer. It's when there's a lot of action. The southeasterly wind comes up and makes the water warmer. That brings in the small baitfish, which brings in the bigger fish and then the sharks. There's so much happening in summer that it can never get boring.

The biggest shark I've seen was at Muizenberg Beach about five years ago, when I had trainees spotting with me. It was easily 5 meters long.

People don't need to be afraid of sharks. They just need to be cautious when they use the water. They must be aware of the situation in the ocean when they decide to go in. We're here to help them with that.