Some vessels off America’s coast are now fishing 800 kilometers further north than they did some 20 years ago, as warming waters push fish polewards. These extraordinary shifts were revealed in a new study that’s among the first to show how climate change influences not only the location of marine species, but also the behaviour of the fishing communities who depend on them.
Looking at the period from 1996 to 2014, the study examined fleets of both large and small vessels that fished off America’s east coast, a region where rapid ocean warming is taking place. It found that large fishing vessels have moved four kilometers north every year since 1996, on average, but some have shifted as far up as 21 kilometers per year to catch northward-moving fish. The researchers even found that certain vessels which had started out fishing off the coast of North Carolina in 1996 were routinely catching their fish from the coast of New Jersey–800 kilometers north–by 2014.
These changes seemed to be heavily determined by how diverse a fleet’s catch was. Larger vessels which caught only one or two species were among those who had to fish the furthest north, to follow the trail of their target species. On the other hand, several smaller vessel fleets with lower catch diversity simply disappeared over time from the fishing records the researchers analysed–presumably because, unlike sturdier large boats, they were unable to travel long distances north to salvage their trade.
In fact, changes in the location of fish seem to be at least partly responsible for a considerable crash in the number of fishing fleets over time: roughly half of the small vessel fleets, and a quarter of the large vessel fleets surveyed, ultimately disappeared during the 18-year study period.
But the more successful fleets–large and small–had one thing in common: they caught a greater variety of fish species. These vessels survived for longer, and also tended to stay closer to their original fishing grounds instead of being forced to venture north. This suggests that catching more types of fish makes fleets more flexible, which insulates them from the effects that warming seas may have on their catch.
This doesn’t mean that warming water is the only factor influencing fishing patterns. The researchers found that fishing quotas and changing regulations over this period also had a role to play in where vessels roamed. The changing career aspirations of young people who wish to find jobs other than fishing was another possible factor that contributed to the decline of fishing fleets, they report.
And yet they still think that environmental changes dominate: in particular the researchers note that the greatest northwards shifts occurred in vessels that relied on just two species–summer flounders and Atlantic croaker–which are known to be undergoing a dramatic poleward migration.
To make these findings, they grouped individual vessels in the study area into ‘community fleets’, according to their location, type of fishing gear used, and vessel size. Then they pored over fisheries data from vessel logbooks, recorded from 1996 to 2014. Using this information there were able to track changes in the different community fleets over time, and to identify the main drivers of change across the entire dataset.
This study suggests that if fishers want to secure their future on America’s east coast, then increasing the diversity of catch and being able to travel further are both key.
But that’s just one region. Globally, fisheries provide protein for half the world’s population and a livelihood for more than 60 million people. Understanding more about how global fishing communities are keeping up with their catch will have a huge bearing on how we feed ourselves in the future–and how we do so sustainably.