Why is UVC Important?

Underwater visual census (UVC) helps scientists understand and protect ocean life by tracking fish populations over time [1]. With UVC, scientists can answer important questions like: Are there more or fewer fish than last year? Are some species disappearing? Could pollution, climate change, or overfishing be the cause? The ocean is changing quickly, and UVC helps scientists spot early warning signs and see how these changes affect marine life. A drop in fish numbers might mean something is wrong with the ecosystem (a place where living things depend on each other to survive). UVC gives scientists early clues, so people can act before it is too late. For example, if a species is disappearing, fishing rules might be changed to help it recover.

UVC also helps scientists learn about fish behavior. By watching fish in their natural habitats, scientists can study how they feed, interact, or defend their territory. This helps scientists understand how rising ocean temperatures or pollution might affect where fish live and when they migrate (move between different habitats during the year).

One of the best things about UVC is that it does not harm marine life. Unlike nets or traps, divers simply observe and record fish without disturbing their environment. UVC is low-cost, does not need fancy gear, and is eco-friendly, especially in marine protected areas where efforts are made to protect populations of marine animals.

How Do Scientists Conduct UVC?

In UVC, the diver can work for a scientist or even be the scientist themselves! Either way, the diver is trained to observe, identify, and count marine life. There are three main ways to do a UVC: stationary point counts, transects, and timed swims (Figure 1). In stationary point counts, a diver stays still and counts the number of animals they see in a set time period (5–10 min). This works great for species that do not move much, like urchins. Transects involve a diver swimming at a steady pace along a straight path or rectangle and usually take longer than stationary counts. Because transects cover more area, they are better for counting species that move around more and for surveying animals on the sea floor, like coral reef fish. For larger areas or deeper water, divers may use a tow transect, where they are tethered behind a boat and use a board to glide down and collect data. Sometimes divers also use cameras, though rough water can reduce visibility. Finally, in timed swims, which last only a few minutes, divers follow a changing path and record animals they find along the way.

Visual Search in the Wild

When a diver is underwater trying to spot an animal, their eyes and brain are doing something called visual search. This means looking carefully for something specific in a busy scene, like trying to find your friend in a crowded playground or a pencil in a messy backpack. Our brains help with visual search by using what we already know: like what something looks like or where it might be hiding. During search, we move our attention like a spotlight to places we are most likely to find the object we are looking for. Searching gets easier when things stand out or when we know what to look for and where to look.

Sometimes the targets we search for stand out because they have a bright color, a strange shape, or sudden movement. Targets can be very noticeable, or salient, so our eyes and attention automatically go to them, making them easier to find [2]. During UVC, this helps with spotting species that look different from their surroundings. For example, the longnose butterflyfish is easy to see because it is bright yellow and has a long, unusual nose. Moving animals are also easier to notice, since motion catches the eye. Octopuses, on the other hand, are usually hard to see because their color blends in with the coral and they often stay still. But if an octopus moves, that movement can help someone notice it—even if the color does not stand out. Some animals, like sea cucumbers or urchins, hardly move at all and blend into rocks. Others, like moray eels, hide in crevices so only a small part of their body is visible (Figure 2).

Knowing where to look for a species, not just what it looks like, can also help during UVC. If a scientist understands how a certain species behaves, this knowledge can guide them to the right places. For example, triggerfish often stay near the edge of a coral reef, so it makes sense to look more carefully around the edges instead of the middle. Sounds can help too. Parrotfish, for instance, make a loud crunching noise as they eat coral. Hearing that crunching sound is a clue that a parrotfish might be nearby, and divers can look around the coral to try to spot it.

Visual Search in UVC Can Be Challenging!

Searching for animals underwater is not easy. The ocean is full of visual challenges, like murky water, fast-moving fish, and crowded coral reefs. Some difficulties come from the environment, and others from how marine species behave. Even when visibility is good, the way human attention works can still make searching hard. One major challenge is called visual interference, which happens when the target animal looks similar to others nearby. When many fish have similar colors, shapes, or sizes, a diver’s attention can be pulled toward the wrong one. The brain must work harder to tell them apart, which slows search and increases the chance of missing the target. Another challenge occurs when searchers miss something that has a low chance of appearing (which is called the low prevalence effect). Divers may overlook rare or shy species simply because these animals do not show up often. Animals can be missed even when they are in front of the diver [3].

Paying attention underwater for a long time is hard. As a dive goes on, divers can get mentally tired, making it harder to focus. This can lead to missed details or slower times to find their targets, especially when keeping track of fast-moving or hidden animals. Paying attention to a target animal is harder when other marine life moves through the area, distracting the diver or blocking the view. Some animals slip in and out of sight, making it hard to remember which have already been counted. Shy fish may disappear into coral, while bold fish might swim back and forth, increasing the chance of being counted twice. All these distractions put a heavy load on attention. If a diver becomes tired or overwhelmed, keeping track of multiple targets accurately becomes much harder [4].

You may wonder if there are other ways to look for marine animals when searching becomes too difficult for humans. Scientists can also use baited remote underwater video, where cameras record animals that swim by, or drones that survey the water from above. They can even use environmental DNA, which detects animals by testing the water for tiny bits of their genetic material.

Protecting the Oceans With UVC

UVC is a great way to learn about ocean animals, but because it depends on human attention, mistakes can happen while spotting or counting fish. By learning about the challenges of visual search, scientists can find ways to make UVC even better. With practice, training, and clear steps to follow, they can collect more accurate data and help protect ocean life. When we understand what fish eat, where they live, and how they behave, we can figure out the best ways to keep them and their homes safe. The more we learn, the better we can care for our ocean and all the creatures that live in it.

Glossary

Ecosystem: ↑ A community of living things, like fish, corals, plants, and the environment around them. All these parts interact and depend on each other for food, shelter, and survival.

Migration: ↑ When animals move from one place to another during the year to find food, reproduce, or stay in safe habitats.

Visual Search: ↑ The mental task of looking for something.

Target: ↑ The object or animal a searcher is looking for during visual search.

Salient: ↑ When something stands out and grabs a searcher’s attention, like a bright color, unusual shape, or sudden movement.

Visual Interference: ↑ When objects or animals that are not a searcher’s target grab their attention and keep them from finding the target quickly, if at all.

Low Prevalence Effect: ↑ When a target is rare and does not show up very often, a searcher might not notice it.

Conflict of Interest

The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

AI Tool Statement

The author(s) declared that generative AI was not used in the creation of this manuscript.

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