Recent studies show human fishing fleets are out-competing seabirds for fish, leading to steep population declines and degraded marine ecosystems.
Almost two decades ago, a study by Jeremy Jackson from Scripps Institution of Oceanography, with international colleagues, concluded that “extinction caused by overfishing precedes all other pervasive human disturbance to coastal ecosystems, including pollution … and climate change.”
Five years later, in 2006, research by Boris Worm from Dalhousie University in Canada, and others, documented an “accelerating loss” of biodiversity in marine ecosystems as “recovery potential, stability, and water quality decreased exponentially.”
In 2016, an international team led by David Grémillet at the Centre d’Ecologie Fonctionnelle et Evolutive in Montpellier, France, published a paper in Marine Biology, presenting evidence that over-fishing was “starving seabirds” along the southwest coast of Africa. They studied Cape gannets, large diving seabirds that compete with purse-seiners for small pelagic fish. They found that 80–95 % of the birds’ feeding dives were unsuccessful, and that both adult health and chick growth rates had declined significantly.
Concerned by these results, the Grémillet team reviewed forty years of global seabird monitoring and catch statistics for all fisheries targeting seabird prey. Their study, published in Current Biology last year, found that the global catch of seabird prey fish had increased by 10% during that period, while global seabird food consumption had decreased by 19%. They concluded that global fishing “constrains a vanishing seabird community.”
Seabirds are among the most devastated and threatened species of wild animals in the world. Furthermore, since seabirds perform critical food-web functions, their decline contributes to the destabilization of marine ecosystems worldwide.
According to a 2015 bird population trend study by Michelle Paleczny and colleagues at the University of British Columbia, in Canada, seabirds suffered a “70% community-level population decline between 1950 and 2010.” The largest declines appear among species that feed on deep-sea fish, severely reduced by industrial fishing fleets.
The famous and beloved albatross, closely related to the gannet and booby, provides a good example. Albatross have the longest wingspan on Earth, up to four metres. They live for decades, and one female Laysan albatross, banded in 1954, is still alive. Albatross rely on remote island breeding grounds and dive for squid, fish, and krill. These magnificent birds, however, have suffered substantial declines.
A 2017 study by Deborah Pardo and colleagues with the British Antarctic Survey Ecosystems Programme found that three major groups — the Wandering, Black-browed, and Grey-headed albatrosses — had declined by 40–60% in 35 years. Of the 22 known species, all appear on the International Union for Conservation of Nature (IUCN) Red List, 17 “Threatened with extinction.”
In the 19th century, albatross colonies were harvested for the fashion industry feather trade, leading to the near-extinction of some species. In 1909, over 300,000 albatrosses were killed on Midway and Laysan Islands alone. Thousands of albatross are killed colliding with tall military air traffic towers on Midway. Invasive species carried on ships — rats, mice, and cats — attack breeding colonies, taking chicks and eggs. Albatross chicks require five to nine months to fledge, and remain extremely vulnerable during that time.
Meanwhile, plastic flotsam kills over a million seabirds per year. Global heating, ocean acidification, oil spills, and toxic chemical pollution also contribute to seabird decline.
Albatross are particularly vulnerable to longline hooks and and trawling nets. Thousands of birds get snared in “ghost nets,” virtually invisible nylon netting lost from ships, drifting throughout the oceans. We now know from the Grémillet, Paleczny and other studies, that seabirds are disappearing due to a lack of food, as industrial-scale fishing fleets over-harvest prey fish species.
The 2018 Grémillet research found that the prey species had been significantly depleted in 48% of all seabird marine habitats, particularly in the Southern Ocean, Asian shelves, Mediterranean Sea, Norwegian Sea, and along the Californian coast.
“Seabirds are particularly good indicators of the health of marine ecosystems,” says Michelle Paleczny in her seabird population study. “When we see this magnitude of seabird decline, we can see there is something wrong with marine ecosystems.” Furthermore, the loss of seabirds becomes a system feedback that “causes a variety of impacts in coastal and marine ecosystems.” Seabirds, for example, transport nutrients in their waste from the deep sea, back to the coastal ecosystems in which they breed, helping to fertilize entire food webs.
State of the Oceans
Over-fishing is only one of many human impacts on the oceans, along with plastic, oil, and chemical pollution. Perhaps the most pervasive human impact comes from our carbon dioxide emissions.
Since the 1970s, the world’s oceans have absorbed over 30% of the carbon dioxide from the burning of oil, coal, and gas. When water (H2O) reacts chemically with carbon dioxide (CO2), the process leaves an abundance of positive hydrogen ions (H+), the criterion of acidity, measured on the pH scale. Since the beginning of the industrial revolution in the 18th century, the average ocean pH has dropped from approximately 8.25 to less than 8.1, representing a 30% increase in acidity. The pH acid/base scale, like the Richter scale for measuring earthquakes, is logarithmic, so drop of only 0.1 pH units represents a 25% increase in acidity. If human society continues to burn petroleum as a primary energy source, the world’s seawater pH could drop to 7.7 by 2100, creating an ocean more acidic than any seen since the Miocene heating, around 14 million years ago, long before hominids emerged in Africa, and when global temperatures had reached about 3°C warmer than today.
Acidification has already limited coral growth, and contributes to the decline of coral beds, which serve as nurseries for thousands of marine species, and which effects the entire ocean food web. Increased acidity corrodes coral skeletons, slows growth, and can prevent coral larvae from maturing into adulthood.
Acidic water inhibits shell formation among clams, oysters, mussels, urchins and starfish, contributing to the decline of some species. The shells of tiny forminifera zooplankton begin to dissolve in the more acid sea water. A study by Sven Uthicke and others at the Australian Institute of Marine Science has predicted that tropical foraminifera — and entire class of amoeboid protists critical to the marine food web — will be extinct by the end of the century. Researchers have observed that the shells of pteropods, free-swimming sea snails, are already dissolving in the more acidic water of the Southern Oceans.
Ocean acidification also changes the pH of some fishes’ blood, a chemical reaction called acidosis. A small pH change can make a large difference in health and survival. In humans, a blood pH drop of 0.2 can cause seizures and even death.
Ocean dead zones, along populated coast lines, are primarily caused by fertilizer runoff and fossil-fuel use. Algal blooms, augmented by the nutrient increase, create hypoxic, oxygen-depleted waters that kill other marine life. According to the 2017 “World Scientists’ Warning to Humanity,” these coastal dead zones have increased by 75% since the 1960s, with more than 600 coastal ecosystems affected.
That report also warns of unsustainable marine fisheries that have exceeded the maximum sustainable yield, are in steady decline, and “on the verge of collapse.” Global marine fisheries catches peaked in 1996 and have been declining ever since despite expanded industrial fishing fleets with improved technologies. As a result, fishing fleets have turned to previously non-commercial species, which include the smaller prey of seabirds.
Jellyfish, which have more resistance to pH changes are already beginning to dominate some marine ecosystems, disrupting the food web by competing with fish for declining zooplankton, thereby effecting the prey of seabirds.
As we should know well enough by now: when human activity touches anything within a complex ecosystem, those actions necessarily affect the entire web of life that binds that ecosystem together.
The picture emerging from these studies has inspired interest in marine reserves and protected areas. For seabird populations to recover, this political work needs to expand.
In 2017, Chile stopped the massive Dominga open-pit copper and iron mining project near Coquimbo, to safeguard the Humboldt Penguin Marine Reserve, located off the coast. The reserve supports the rare Humboldt penguin, blue whales, humpback and sperm whales, bottlenose dolphins, sea turtles, sea lions, albatross, and many species of fish.
In 2011, Belize permanently banned trawling in all its waters, the third nation to do so, partially to protect the Belize Barrier Reef System. Venezuela and Palau have also banned trawling completely. Large areas in the US, Indonesia, Philippines and other Pacific islands are closed to trawling. Under president Obama, the US banned bottom trawling in a 23,000 square mile area off the Southeast Atlantic coast and reinstated a ban on offshore drilling in the eastern Gulf of Mexico and the Atlantic coast. Morocco and Turkey recently banned illegal drift-net fishing.
In 2004, 13 countries ratified the Agreement on the Conservation of Albatrosses and Petrels, to reduce bycatch and remove invasive species from nesting islands.
However, 2016 paper by Avigdor Abelson in BioScience, concludes that “current practices are insufficient to reverse ecosystem declines.” The Ableson study shows that restoration ecology must become an integral part of marine conservation efforts. The Worm research showed that active restoration of marine biodiversity could increase ocean productivity fourfold. There remains an urgent need for increased international seabird and marine conservation effort internationally.
Resources and Links:
“Persisting Worldwide Seabird-Fishery Competition Despite Seabird Community Decline,” David Grémillet et al., Current Biology, v. 28, # 24, Dec. 17, 2018
“Historical overfishing and the recent collapse of coastal ecosystems,” Jackson, J.B., et al., Science 293, 629–637, pdf, 2001.
“Impacts of biodiversity loss on ocean ecosystem services,” Worm, B., et al. Science 314, 787–790. pdf , 2006.
“Starving seabirds: unprofitable foraging and its fitness consequences in Cape gannets competing with fisheries in the Benguela upwelling ecosystem,” David Grémillet, et al.; Marine Biology, 2016.
“Population Trend of the World’s Monitored Seabirds, 1950-2010,” Paleczny M, Hammill E, Karpouzi V, Pauly D, PLoS ONE 10(6): e0129342, 2015
“State of World Fisheries and Aquaculture,” US Food and Agriculture Organization, 2018 pdf.
“Ecosystem consequences of bird declines; Sekercioglu CH, Daily GC, Ehrlich PR; PNAS, 101(52):18042–7. pmid:15601765, 2004.
“The food consumption of the world’s seabirds,” Brooke Mde. L., The Royal Society Biology Letters,271:S246–S8, pmid:15252997, PubMed/NCBI, 2004.
“A Global Map of Human Impact on Marine Ecosystems,” Benjamin S. Halpern, Science, pdf, 2008.
“Adverse Effect of Ocean Acidification on Marine Organisms,” Alessandra Gallo, Elisabetta Tosti; Journal of Marine Science, 2016
“Ocean Acidification,” Smithsonian, 2018
“Ocean acidification to hit levels not seen in 14 million years,” Julia Short, Cardiff University, Phys Org, 2018.
“High risk of extinction of benthic foraminifera in this century due to ocean acidification,” Uthicke, P. Momigliano & K. E. Fabricius, Nature, 2013.
Plastic garbage patches, NOAA Marine Debris project, revised 2019.
“Oceans in shocking decline,” Richard Black, BBC, 2011
World Scientists’ Warning to Humanity: A Second Notice, William J. Ripple, et al. with 15,364 scientist signatories from 184 countries, BioScience, 2017.
“The biomass distribution on Earth,” Yinon M. Bar-On, et al., Weizmann Institute of Science, Rehovot, Israel; PNAS: May 21, 2018, , National Academy of Sciences, US, Article #17-11842:
Improving Ocean Management through the Use of Ecological Principles and Integrated Ecosystem Assessments, Melissa M. et al. BioScience, 2013.
“Upgrading Marine Ecosystem Restoration Using Ecological‐Social Concepts,” Avigdor Abelson, et al., BioScience, 2016
“Chile Stops Billion-Dollar Mining Project To Protect Humboldt Penguins,” IFL Science, 2017.
Trawling Banned In Belize, Ambergris, 2010