Mapping nearly a century and a half of global marine fishing / by Francisco Blaha

Fisheries has such a myriad of present issues and one is dealing with “every day trees” that never have the time of “looking at the forest”. Furthermore, fisheries data collection seems to be incomplete even today, that one wonder how can you say anything past a decade of activities. Yet I enjoy reading this paper by Reg Watson & Alex Tidd. Not only because I like my mate Alex Tidd, besides being a top data guy at fleet dynamics. He is a fellow biologist that appreciates good Dub, and this (at least in my book) means a lot.

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As usual when I like a paper I quote the abstract, and some of the key parts I like… yet nothing repleace reading the original.

Understanding global fisheries patterns contributes significantly to their management. By combining harmonized unmapped data sources with maps from satellite tracking data, regional tuna management organisations, the ranges of fished taxa, the access of fleets and the logistics of associated fishing gears the expansion and intensification of marine fisheries for nearly a century and half (1869–2015) is illustrated. 

Estimates of industrial, non-industrial reported, illegal/unreported (IUU) and discards reveal changes in country dominance, catch composition and fishing gear use. Catch of industrial and non-industrial marine fishing by year, fishing country, taxa and gear by 30-min spatial cell broken to reported, IUU and discards is available. Results show a historical increase in bottom trawl with corresponding reduction in the landings from seines. Though diverse, global landings are now dominated by demersal and small pelagic species.

Mapping industrial marine catch since 1869
Though the global geographic scope of industrial fishing was undoubtedly limited before the 1900s, the reporting was similarly poor. Records available include just three fishing countries: Canada, the USA and Japan (Fig. 2a above). Reported landings, even when adjusted for likely underreporting and discarding were much lower than the current intensity of fishing (note units for Fig. 2a and b are in kg whereas for Fig. 2c and d they are in tonnes).

By the early 1900s more countries were collecting national fisheries landings statistics (Fig. 2b) and ICES has a historical time series of landings in the European seas which still continues from that time. Most fisheries were coastal in nature and the majority of fishing vessels had a limited endurance because of a range of factors including the challenges of preserving the catch. There were exceptions such as the very long voyages for cod which was readily accepted salted.

Just before and since the 2nd world war (Fig. 2c) there was a vast expansion of global fishing fleets. Fishing intensified inshore but, moreover, fleets now pursued large pelagics like tuna species across entire oceans. Fishing deeper allowed fishing down the continental slope and to distant seamounts, however, some of these deeper stocks were not as productive as initially thought. It was then feasible to fish in polar regions but it soon became accepted that while some species such as krill appeared to have great potential, others were long-lived species requiring careful management. Many regional and international management agencies began during this period as fleets travelled increasingly greater distances, and deals were struck for access to the declared exclusive economic zones of 200-nautical miles that most countries claimed. During this time many poorer countries reduced their commercial fishing and allowed the access of foreign fleets but it was not always to their advantage to do so.

By 2000 (Fig. 2d), fisheries had generally intensified, particularly in the Asian region but also in many other locations. While management in some areas limited expansion, there was little control in other places as levels of effective fisheries management varied greatly. The increased use of waters along the African north-west and west coast by initially European fleets (sometimes involving reflagging) was compounded by fleets from Asia. Catches did not increase despite the additional fishing intensity and the increasing area of the oceans fished. A greater portion of the finite marine ecosystem primary productivity was directed to harvested seafoods than ever before Substantial increases to fish and seafood consumption was increasingly supported by expansions to marine and freshwater aquaculture, although feed for these farms often came from marine stocks – forage fishes. While important to farming fish these species, often small pelagics, have important roles in marine food webs and support marine mammals and seabirds.

In Fig. 2c and d it is clear that the inclusion of additional spatial information from tuna RFMOs and from the AIS satellite data more recently has allowed relative hot-spots of fishing on the high seas to be highlighted more precisely than previous attempts. Increases to spatial precision will have special significance to investigations of the interaction of fisheries and sensitive habitats and/or wildlife. Because fisheries can consume the same species as marine predators it is important to be able to make use of all spatial detail available as the energetics of foraging by some species are not nearly as generous as fossil fuels allow fishing fleets.

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Fishing gears associated with global catch
Although the association of fishing gear to reported landings could not be extrapolated back in time beyond the 1950s there had already been substantial changes in fishing practices since the 1880s. Sails and oars were replaced with steam and eventually diesel propulsion. Ice allowed longer trips and, with the introduction of freezers, vessel endurance and range greatly expanded. Vessels were faster and more powerful, and capable of facing the winds and waves of all seasons.

Fishing at night became possible and, for some trawled species, finally allowed fishing to occur when predator-wary species like prawns were active and available. Trawling gears evolved to cover large areas of the bottom and drive small fish shoals into the nets. Sonar and radar guided vessels and fishing gear for safety and effectiveness. Available data only allows a brief glimpse into the important and complex development of fishing.

Association of fishing gear with catch shows that the relative use of fishing gears has changed since 1950 (Fig. 4b above). Proportionately, the most obvious change is the increase in bottom trawling while the use of seine fishing gear appears to have declined. Midwater trawling which requires guidance by newer technologies such as sophisticated sonar arrangements has also increased. This does suggest that although our use of energy to fish has been high for decades it may have continued to increase. Nevertheless, at least some fishing operations compare favorably with the energy expenditure required in land based food production systems. Bottom trawling has additional implications to marine habitats as it has high levels of non-targeted catch and is well known to often damage or even remove important substrates and sessile organisms.

Fishing has coevolved with humans and has been vital to our survival since prehistoric times. Our technologies have adapted and allowed fishing in all but the most extreme environments. Mapping global marine catch is very important for a variety of reasons, not least because the push to increase wild fish capture often appears to conflict directly with the accepted need to maintain marine ecosystems at their most diverse, resilient and productive causing much division in the marine science community. Perhaps best tackled at a smaller scale (national or less) it is nevertheless valuable to get an all-inclusive overview if possible, and to see how things have changed over time.

The challenges are great in inshore waters; however, they now increasingly extend to high seas areas and to greater depths. Indeed, of necessity, more and more fishing and marine conservation interests have become partners of mutual concern as marine resources are pursued by mining, petroleum and other industries. Who would have imagined that the petroleum industry's widely used seismic survey methods could kill the zooplankton vital to marine ecosystems ?

Though some estimate that our living marine resources such as mesopelagics may be huge, understanding marine food webs remains vital, including through detailed mapping, to avoid overestimating what can be safely removed. Man will have to know much more before it can be deemed safe to sequester greenhouse gases into the ocean depths. With climate change comes new challenges. The distribution and productivity of stocks currently supplying seafood and income to many of the world's populations will likely change. In all likelihood, there will be interest in adjusting ocean acidity and sequestering greenhouse gases in the oceans. These activities will have international, and as yet, poorly understood impacts on marine systems and the services mankind currently depends on.

Continued development and use of all technologies is required to maintain productive and diverse marine environments to safeguard the future food security that the sea can provide. The increasingly sophisticated data processing of AIS inputs is rapidly increasing their contribution to monitoring global fishing. Future surveillance will include greater use of satellite technology such as NOAA's Visible Infrared Imaging Radiometer Suite (VIIRS) to add ‘night vision’ to the sophisticated repurposed data coming from other vessel signals such as AIS. Unique QR codes for valuable fish products, combined with block chain technologies will strengthen traceability and help combat illegal fishing. These technologies and more will also be vital if marine protected areas are used to protect offshore areas where patrols are costly or ineffective. Managing conflicting uses will be very challenging in remote areas because marine resources will only become more valuable.

Humans have had a long association with marine resources, indeed, they may have ensured our very survival in the past but our use of marine resources through fishing has changed remarkably since the 1800s. Much can be learnt from looking at historical patterns of fishing, and they can help make decisions vital to maintaining the marine resources and their environments that mankind all depends on - now and in an uncertain future.

The dataset used to create all these figures and maps are available to the public here.