Study Finds Staggering Decline in Marine Fishery Biomass

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When a study claiming that marine fisheries were going to be completely depleted by 2048 first appeared 14 years ago, the idea still seemed to be in the domain of apocalyptic sci-fi. 

However, the new 2020 research confirms that we are, unfortunately, rushing towards the foreseen scenario.

The unique study by researchers from the University of British Columbia, the GEOMAR Helmholtz Centre for Ocean Research Kiel, and the University of Western Australia, is the first global long-term fishery biomass trends evaluation

Popular market seafood like the Common Octopus (Octopus vulgaris) are facing rapid decline.  Photo: Caroline Rogers, NPS, public domain.
Popular market seafood like the Common Octopus (Octopus vulgaris) are facing rapid decline. Photo: Caroline Rogers, NPS, 2001, public domain.

The team assessed biomass of over 1320 fish and invertebrate populations of 483 species, inhabiting the 232 coastal marine ecoregions around the world. The focus was specifically on species known to be exploited by fisheries.

The trends were derived using the Bayesian CMSY stock assessment method, applied to the global fisheries 1950–2014 catch database for every maritime fishing country. The database was reconstructed by the Sea Around Us, a research initiative at The University of British Columbia, to improve current issues in fish catchment statistics. 

The study’s results are clear and worrying – there is a significant decline in average fishery biomass in all observed regions, across all oceans and climate zones. The paper underlines “systemic wide-spread overfishing of the world’s coastal and continental shelf water.” The claim is consistent with the finding that fishery catch peaked in the 1990s, and have been declining ever since.

Map: The global system of Marine Ecoregions (ME in dark blue, Spalding et al., 2007) overlaid over climatic zones of the world (Anonymous, 1991). Graphs: Relative changes in population biomass of analyzed populations over time expressed as a percentage of the average biomass at the start of the time series (1950–1954), grouped by climatic zone and ocean basin. Figure: Palomares et al., 2020, CC BY 4.0
Map: The global system of Marine Ecoregions (ME in dark blue, Spalding et al., 2007) overlaid over climatic zones of the world (Anonymous, 1991). Graphs: Relative changes in population biomass of analyzed populations over time expressed as a percentage of the average biomass at the start of the time series (1950–1954), grouped by climatic zone and ocean basin. Figure: Palomares et al., 2020, CC BY 4.0

In marine ecoregions that have questionable catch statistics, the results show smaller declines than in reality (most likely), meaning that the results are not exaggerated. While that certainly lends to a positive conclusion about the methodology, it leaves a bleak impression that fisheries’ true condition is even worse.

The mechanism behind the plummeting numbers is simple: seafood is being caught at rates that exceed its capacity to replenish. Consequently, the fishers are catching fewer animals over time, despite fishing longer and harder.

Of all the analyzed populations, 82 percent are below the levels that produce maximum sustainable yields. Out of these, 87 percent are in the “very bad” category, with biomass levels of less than 20% of the biomass needed for maximal sustainable fishery catches. 

Orange roughy (Hoplostethus atlanticus).  Photo: NOAA OKEANOS EXPLORER Program, Gulf of Mexico 2014 Expedition, public domain.
Orange roughy (Hoplostethus atlanticus). Photo: NOAA OKEANOS EXPLORER Program, Gulf of Mexico 2014 Expedition, public domain.

Even fish market favorites with presumably-abundant populations – the orange roughy (Hoplostethus atlanticus), queen conch (Lobatus gigas), and common octopus (Octopus vulgaris) are facing rapid decline.

Interestingly, this contrasts the findings from several years ago that cephalopod populations – octopuses included – were experiencing a boom. It seems that even their high reproductive rates can’t compete with the rate of overfishing.

The greatest declines were found in the southern temperate and polar Indian Ocean and the southern polar Atlantic. Since 1950, fishery populations there has shrunk by over 50 percent.

One of the rare regions that are bucking the trend, having higher fishery biomass than in the 1950s, in the northern Pacific – specifically the polar-boreal zone. In polar and subpolar zones, the population biomass increased by an impressive 800 percent. In the temperate zone, the increase is more modest but still substantial – around 150 percent.

The authors suggest that the positive impact on fish populations occurred due to environmental changes in the region, in combination with sensible fisheries management.

However, although they have something to teach us about the value of good management, the improvements in few locations remain an almost incidental exception in a concerning big picture.

That notion is confirmed by Daniel Pauly, the principal investigator at Sea Around Us, and co-author of the study.

Despite the exceptions, our findings support previous suggestions of systematic and widespread overfishing of the coastal and continental shelf waters in much of the world over the last 60-plus years,” 

Pauly goes on to explain that we need improvements in fisheries management and that such measures shouldn’t be driven only by clear total allowable annual catch limits, but also by securing “well-enforced and sizable no-take marine protected areas” that would allow stocks to rebuild.

What is Fishery Biomass?

At the beginning of the paper, the authors explain the term ‘fishery biomass’. They define it as is “the biomass of fish populations, defined as the weight (whole-body, wet weight) of the in-water part of a fishable population, i.e., that part of a population (also called ‘stock’) that is exposed to fishing gears.”

Detailed and scientifically significant data on fishery biomass assessments are typically only available for a limited number of species in the waters of economically developed regions. They are generally lacking for developing countries, even when it comes to their most exploited species. The aim of the Sea Around Us team was to fill in the gaps by using specially designed computer-intensive stock assessment.

Resources

The Study

Palomares, M.D.L., et al. 2020. Fishery biomass trends of exploited fish populations in marine ecoregions, climatic zones and ocean basins. Estuarine, Coastal and Shelf Science. Vol 243, https://doi.org/10.1016/j.ecss.2020.106896

Articles

Leotaud, V. R. (2020, July 27). Popular seafood species in sharp decline around the world. UBC News. https://news.ubc.ca/2020/07/21/popular-seafood-species-in-sharp-decline-around-the-world/

Monahan, P. (2016, May 23). World octopus and squid populations are booming. Science | AAAS. https://www.sciencemag.org/news/2016/05/world-octopus-and-squid-populations-are-booming

Roach, J. (2006, November 2). Seafood may be gone by 2048, study says. National Geographic. https://www.nationalgeographic.com/animals/2006/11/seafood-biodiversity/

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