Fishing Capacity and Environmental Conditions Drive Short Term Patterns of Fishing Effort and Catch in Ghana's Artisanal Marine Fishery

In the coastal waters of Ghana, a vast network of small wooden canoes forms the backbone of the nation's food supply and economy. These boats, operated by local crews, do not hunt massive whales or deep-sea giants; instead, they target schools of small, fast-moving fish like sardinellas and anchovies, often called the "people's fish." For decades, scientists and managers have tried to understand how much fish is being caught and whether the population is healthy. To do this, they have traditionally relied on a simple calculation: they count the total time boats spend at sea and divide the total weight of the catch by that time. This metric, known as catch per unit of effort, assumes that if a boat stays out longer, it will catch more fish, and that the amount of fish caught per hour is a reliable sign of how many fish are swimming in the ocean. However, this assumption works best when fish are spread out evenly. In reality, these small fish travel in dense, shifting clouds called shoals. Finding a shoal is a matter of luck and skill, not just time. If a boat finds a massive school, it might fill its hold in an hour; if it misses, it might return empty after a full day. This disconnect between time spent and fish caught makes it difficult to know if the fishery is sustainable or if the boats are simply getting better at finding the few fish that remain.

A team of researchers from Ghana's Kwame Nkrumah University of Science and Technology set out to look beyond the yearly averages and examine the daily reality of these fishermen. They wanted to know what actually drives the catch on any given day: is it simply the number of hours the boat is in the water, or are other factors more important? To find out, they gathered detailed records from 316 fishers across 16 different landing beaches along the coast. Over two specific periods in 2025, they tracked 2,203 individual fishing trips, recording exactly how long each trip lasted, how many people were on board, what kind of net was used, and how much fish was landed. They also matched these daily records with environmental data, such as water temperature, wave height, and the amount of plant life in the water, to see if the ocean's condition played a role.

The results revealed a story that challenges the standard way of measuring fishing pressure. The researchers found that the length of time a boat spent at sea was a very poor predictor of how much fish it would bring back. In fact, once they accounted for who was fishing, what gear they used, and how many people were on the crew, the number of hours at sea had almost no connection to the catch. A boat that stayed out for ten hours was not guaranteed to catch more than a boat that returned after five. Instead, the most consistent factor was the size of the crew. Larger crews, which usually meant larger boats and bigger nets, consistently brought in more fish. The type of gear mattered immensely as well; boats using beach seines, which are dragged along the shore, caught significantly more fish per trip than those using other types of nets. The identity of the fisher themselves was also a massive factor, accounting for the majority of the differences in trip duration that could not be explained by gear or location. This suggests that the skill, experience, and specific habits of the skipper and their team are far more influential than the clock.

The study also showed that the ocean's daily mood plays a critical role. The amount of fish caught was not a straight line but followed a complex curve based on environmental conditions. For instance, the height of the waves mattered; catch rates were low when the sea was too calm, peaked when the waves were moderate, and dropped again when the water became too rough. Similarly, the temperature of the sea surface and the amount of rain falling on the coast influenced the catch in non-linear ways. The researchers noted that these environmental factors interacted with the fishing capacity of the boat. A large boat with a big crew could take advantage of good conditions to land a massive haul, while a smaller boat might struggle even if the conditions were perfect. The data also highlighted that the fishery is highly variable from day to day. On some days, a few boats would return with enormous loads, while most returned with very little, creating a "heavy-tailed" pattern where a few lucky trips dominate the total catch.

These findings have significant implications for how the fishery is managed. For years, policies in Ghana have focused on limiting the number of hours boats can fish or closing the fishery during specific seasons, operating on the idea that time at sea is the main driver of overfishing. However, this study suggests that time is a misleading measure. Because the catch is driven more by the size of the boat, the number of crew members, and the type of net, simply counting hours does not accurately reflect the pressure on the fish stocks. A boat with a large crew and powerful gear can exert much more fishing power in a short time than a small boat with a few people. The researchers argue that management strategies should look at the physical capacity of the fishing units—the size of the canoes, the length of the nets, and the size of the crews—rather than just the duration of the trip. They also caution that using catch rates as a sign of fish abundance can be dangerous. Because fishers are so good at finding the remaining shoals, they can continue to catch high amounts of fish even as the overall population declines, creating a false sense of security. By understanding that the daily catch is a complex mix of human skill, boat capacity, and environmental luck, managers can design better rules to protect the "people's fish" and ensure the fishery remains viable for the thousands of Ghanaians who depend on it.