Twice as many fishing vessels now, but it’s harder to catch fish

How many ships and boats ply the world’s oceans for seafood today? Researchers have a new estimate: where there were about 1.7 million boats harvesting fish in 1950, the number more than doubled to 3.7 million fishing vessels in 2015.

More fishing vessels have become motorized as well. While only 20 percent of the global fishing fleet was powered by motors in 1950, this number rose to 68 percent in 2015, albeit most are equipped with small engines of less than 50 kilowatts. The ballooning fishing fleet is, however, catching less seafood for the same effort, the researchers report in a new study published in the Proceedings of the National Academy of Sciences.

“It is the most thorough and detailed attempt to estimate the trend in fishing power and effort around the world,” Ray Hilborn, a marine biologist and fisheries scientist at the University of Washington, U.S., told Mongabay. Hilborn was not involved in the study, but he edited the paper.

International organizations like the United Nations’ Food and Agriculture Organization (FAO) have previously come up with numbers of global fishing vessels. But these data have gaps in them, making comparisons or predictions difficult, the researchers say. So a team led by Yannick Rousseau, a graduate student at the University of Tasmania, decided to recalculate the numbers from scratch.

Rousseau and his colleagues collated fishing fleet data from several sources, including national and international databases, government records, and scientific papers and reports. They then separately analyzed the data for powered and unpowered small-scale fishing boats, or artisanal boats, and larger, commercial, or industrial vessels, which can venture further out to sea.

“The artisanal and industrial fleets are often aggregated, and that is an issue as they are not at all managed the same way. So considering them as one homogenous block would lead to great uncertainties,” Rousseau told Mongabay.

Overall, there was an increase in number of fishing boats and ships globally since 1950, and a corresponding decline in catch per unit effort, or CPUE. The latter measures the amount of fish being caught over the same effort — over a single day’s effort, for example — and is often considered to be an indicator of how fish populations are doing.

But zoom into the data and you see different geographic patterns emerge.

The fishing fleet in Asia has dramatically increased over the past decades, for example, while fleet sizes in North America and Western Europe experienced slight reductions. Similarly, the motor power of fleets in Europe, North America and Australia more than doubled between 1950 and 1980, followed by a dramatic reduction in the 2010s. On the other hand, the total engine power of the Asian fleets has drastically increased since 1950.

Between 2000 and 2015, Europe and North America saw some increase in catch per unit effort, suggesting fish stocks may have stabilized, possibly due to effective fisheries management. Yet during the same time period, there was a sharp decline in CPUE in Southeast Asia, the Indian subcontinent and Latin America, indicating that “their fisheries expanded at a much faster rate than fish stocks could support,” Rousseau said.

The lesson, Hilborn said, “is that yes fishing effort can be reduced, and it has been done in some of the world. It needs to be done in most of the places where it has not been reduced.”

There were variations among artisanal and industrial fishing vessels as well. Until the 1980s, both artisanal and industrial fleets showed similar trends of increasing engine power. But over the past three decades, where the growth of motorized industrial fleets has slowed, the combined engine power of all powered artisanal boats is now equal to that of the industrial. Most of the smaller boats dominating the global fishing fleet in number are powered by engines of less than 50 kilowatts, however, and make up only a small part of the total engine power. By contrast, the large, powered industrial vessels represent less than 5 percent of the fleet, but account for a third of the total engine power.

“What is considered artisanal today is more ‘powerful’ than what was considered artisanal 50 years ago although it is highly variable by region,” Rousseau said. “So the number of vessels in each sector keeps on increasing — except in richest countries, where they have undergone fleet reductions — but as the average engine power is increasing too, that leads to boats capable of going further and longer at sea, more efficiently, higher powered gears and increased pressure on the oceans.”

The researchers note that there are “vastly varying definitions of artisanal fishing globally,” which could bring “a certain level of uncertainty and overlap” to their findings.

Despite the growth in powered artisanal boats, the impacts they have on fish stocks could be very different from that of large trawlers, Ratana Chuenpagdee, a professor at Memorial University of Newfoundland, Canada, told Science news. The impacts, she says, will also depend on the type of fishing gear the fishing vessels use, as well as politics.

Rousseau said the trend toward increased motorization of the global fishing fleet is likely to continue, which means the average engine power will also keep on growing. “If countries do not reduce the number of vessels, the oceans might not be able to sustain more efficient vessels,” he said. “It is important to note, however, that developed countries have started fleet reduction schemes, which mean that they do take the science into account and realise that it is possible to manage fisheries sustainably.”

Banner image of fish being sold in Indonesia by Rhett A. Butler/Mongabay.

Citation:

Rousseau, Y., Watson, R. A., Blanchard, J. L., & Fulton, E. A. (2019). Evolution of global marine fishing fleets and the response of fished resources. Proceedings of the National Academy of Sciences, 201820344. doi:10.1073/pnas.1820344116