Yesterday’s Oceans – Too vast to spoil
For most of human history, people considered the oceans so vast and their resources so plentiful that it was impossible to spoil them. Guided by this mindset, humans have been unsustainably using Earth’s oceans over many generations. This has resulted in changes that, from a 21st century perspective, are almost impossible to comprehend. In the absence of information and an historical perspective, all of us underestimate the scale of these changes. Here are just a few examples to demonstrate this point. See Resources for references to the literature cited below.
Mediterranean Sea
- In Greek and Roman times, the Mediterranean Sea was a beautiful and productive marine ecosystem teeming with life that provided a rapidly growing population with a diverse and plentiful source of food. The Mediterranean Sea is now one of the most altered bodies of ocean on the planet as a result of centuries of overfishing and pollution, habitat loss, the introduction of alien species, and climate change. Virtually all traditional marine food species in the Mediterranean have been reduced to less than 50 per cent of their original abundance, a third are now exceedingly rare, and many are functionally extinct. The once abundant Mediterranean monk seal now numbers less than 700 individuals. (Lotze et al., 2011; Mladenov, 2020).
Mosaic with fish, Pompeii, 1st Century B.C., http://commons.wikimedia.org/wiki/File:Mozaiek-uit-woonhuis-Pompei.jpg 
One of the first pictures of the monk seal colony found by Eugenio Morales Agacino on Ras Nouadhibou, Western Sahara (December 26, 1945). https://commons.wikimedia.org/wiki/File:Colonia_de_focas_monje_de_Cabo_Blanco_(1945).jpg
North Atlantic Ocean
- Marine life in European seas was once unbelievably plentiful. Fish abundance is now just one-tenth of what it was in 1900. Compared to when European fish stocks were unexploited, European seas now probably contain less than 5 per cent of the total mass of fish that once swam there. (Roberts, 2007).
European fish market circa 1621. Artists Frans Snyders (1579 – 1657) and Anthonis van Dyck (1599 1641). https://commons.wikimedia.org/wiki/File:Frans_Snyders_and_Anthonis_van_Dyck_-_Fish_market_(Tribute_Money%3F).jpg - It has been calculated that in the early 1500s 7 million tonnes of cod consisting of several billion fish congregated on the Grand Banks and east coast of Canada. When a moratorium on cod fishing was introduced in 1992, only about 22,000 tonnes were left, or 0.3 per cent of the original population. Their average size has also decreased greatly— from about 1 to 0.3 metres, a three-fold decrease. (Jackson et al., 2001; Rose, 2004; Roberts, 2007).
A haul of codfish. https://commons.wikimedia.org/wiki/File:Labrador-_its_discovery,_exploration,_and_development_(1910)_(14780343804).jpg - The Great Auk, a flightless diving bird, was found in the millions all along the coasts of the North Atlantic Ocean. It is now extinct as a result of hunting, with the last recorded breeding pair killed in June 1844 on Eldey Island, Iceland. (Thomas et al., 2019)
Great Auks by John Gerrard Keulemans and commissioned by the 19th century ornithological writer H.E. Dresser. https://commons.wikimedia.org/wiki/File:Great_auk_with_juvenile.jpg
Chesapeake Bay
- Over 600,000 tonnes per year of oysters could be harvested from Chesapeake Bay, USA in the late 19th century. Landings are now about 12,000 tonnes per year. In pre-colonial times oysters filtered the entire volume of Chesapeake Bay in about 3.3 days, removing phytoplankton and dead particulate matter and purifying the seawater; by 1988 this had increased to 325 days. (Jackson et al., 2001; NOAA. Oyster reefs. Ecological Importance (Online) Available from: http://habitat.noaa.gov/restorationtechniques/public/habitat.cfm?HabitatID=2&HabitatTopicID=11 (Accessed 3 May 2020)
Dredging for oysters, Chesapeake Bay, ca. 1901. https://commons.wikimedia.org/wiki/File:STARBOARD_DREDGE_BASKET_BEING_HAULED_WITH_OYSTERS_-_KATHRYN-Two-sail_Bateau_%22Skipjack%22,_Dogwood_Harbor,_Chesapeake_Bay,_Tilghman,_Talbot_County,_MD_HAER_MD,21-TILG.V,1-11.tif
Caribbean Sea
- In pre-Columbian times there were more than 90 million adult green turtles living in the Caribbean Sea grazing large expanses of healthy seagrass meadows. Green turtles now number about 300,000 in the Caribbean, or 0.33 per cent of their historic numbers, because of hunting and habitat loss. (McClenachan et al., 2006).
Shipping green turtles around 1895, Key West, Florida from Robert N. Dennis collection of stereoscopic views. https://commons.wikimedia.org/wiki/File:Shipping_green_turtle,_Key_West,_Fla,_from_Robert_N._Dennis_collection_of_stereoscopic_views.png - Caribbean Monk seals once numbered in the hundreds of thousands. They were hunted extensively for their oil to lubricate sugar plantation machinery. Their numbers were severely depleted by the 1840s and they were extinct by 1952. (McClenachan and Cooper, 2008).
Captive Caribbean monk seal, Monachus tropicalis, of unknown sex at the New York Aquarium in ca. 1910. Specimen originally captured from either Arrecife´s Tria´ngulos (Campeche) or Arrecife Alacra´n (Yucatan) in Mexico (Townsend 1909).
https://en.wikipedia.org/wiki/Caribbean_monk_seal#/ - In 1956 the average size of fish caught by sport fishers in Key West, Florida was about 20 kilograms. In 2007 this was just over 2 kilograms. Landings in 1956 were dominated by large groupers and other large predatory fish with an average length of just under 2 metres. In 2007 landings consisted of small snappers with an average length of 34 centimetres. (McClenachan, 2009).
Key West trophy fish, 1956. A catch of large goliath groupers. (Photo credit: Monroe County Public Library) 
Key West trophy fish, 2007. A catch of small snappers and a small shark. (Photo credit: Loren McClenachan). - Less than 50 years ago live coral coverage was about 73 per cent on reefs in Jamaica. As a result of disease, overfishing, pollution and climate change, live coral coverage is now only about 4 per cent. (Jackson et al., 2001).
Florida Keys Coral – https://commons.wikimedia.org/wiki/File:Caribbean_Porites.JPG - Puerto Rico lost almost 90 per cent of its mangrove forests between 1930 and 1985 due to land use change; the southern part of India lost about 96 per cent of its mangroves between 1911 and 1989. Between 1980 and present the area of mangrove forests declined globally from about 20 million hectares to 8 million. (Romañach et al., 2018; Mladenov, 2020).
Mangrove Forest, India – https://commons.wikimedia.org/wiki/File:Mangroves_park_pappinisseri5.JPG
Eastern Australia
- Looking back 100 years, dugongs numbered more than a million in Eastern Australia. They now number about 14,000, a 74-fold decrease. (Jackson et al., 2001).
Dugong near Marsa Alam, Egypt – https://commons.wikimedia.org/wiki/File:Dugong_Marsa_Alam.jpg
High Seas
- Whales at one time were so numerous they helped regulate the Earth’s climate by fertilizing the surface waters of the oceans with their faecal plumes and helping to vertically mix the oceans during their dives, thus allowing more nutrients to reach surface waters. Between 1900 and 1999 about 2.9 million large whales were killed, the largest hunt in human history in terms of biomass. Southern Ocean blue whales alone were reduced to less than 1 per cent of their pre-whaling numbers. Try to imagine our oceans with 100 times more blue whales in them! (Pershing et al., 2010; Rocha et al., 2015; Stone, 2019; Chami et al., 2019).
Blue whale (Credit: NOAA Fisheries/Marjorie Foster, under permit #17355) – https://apps-nefsc.fisheries.noaa.gov/rcb/photogallery/blue-whales.html
An Unsustainable Mindset
These few examples illustrate the folly of the human mindset that the oceans are “too vast to spoil”. It has allowed unsustainable use of our oceans which have now been fundamentally transformed, first by overfishing and hunting, and then by habitat loss, pollution, the spread of harmful alien species, and, most recently, the release of climate-changing greenhouse gases causing ocean warming and acidification.
