Although the oceans of the world seem immutable, no area is unaffected by human influence. In fact, 41% of the oceans have been seriously degraded by multiple human factors; to name a few: overfishing; fishing commercially a mile below the surface of the water with high-tech gear; pollution; commercial shipping; military sonar; offshore oil exploration, extraction, and the inevitable spills. Less than 4% of the oceans can be classified as areas of very low anthropogenic impact, and they are mainly near the poles.1
During the nineteenth century, commercial sealers hunted Antarctic fur seals to near extinction. What’s more that slaughter was followed in the twentieth century by the widespread killing of krill-eating baleen whales, which enabled the tiny crustaceans to proliferate essentially unchecked, until there is today a surplus of krill in the Southern Ocean.2 Clearly, the overexploitation of the Antarctic waters has left its mark, even if that human signature is faint by today’s standards.
As we humans attack marine life, we alter how the oceans relate to climate change.3 Consider, for example, that overexploiting of the large, predatory marine fishes, such as sharks and tuna, allows the populations of smaller, plankton-feeding fishes to proliferate:
Sharks, billfish, cod, tuna and other fish-eating fish—the sea’s equivalents to lions on the Serengeti—dominated the marine world as recently as four decades ago. They culled sick, lame and old animals and kept populations of marine herbivores in check, preventing marine analogs of antelopes from overgrazing their environment. . . . [Moreover,] physical and chemical changes, driven by Earth’s warming climate, threaten to diminish the maximum size that any species–predator or prey–can attain.4
In fact, immense numbers of sharks are slaughtered annually for their fins—not their meat, just their fins. Fleets catch the sharks, virtually any species, . Why? Because, fins can command $200 a pound in Asian markets, whereas their flesh yields no more than one percent as much revenue per pound. While outlawed in U.S. waters, “shark finning” is not regulated on the high seas or in territorial waters most nations’ of most nations, and so is carried out with impunity. Consequently, an estimated 26 to 73 million sharks are captured annually—and mutilated solely for their fins. In fact, a black market for the capture and sale of products from threatened and endangered species of sharks exists also.
Shark finning helps feed a growing appetite throughout Asia for the popular shark-fin soup—the main ingredient of which is the cartilage that, after hours of simmering, takes on the appearance and texture of cellophane noodles. A single bowl of shark-fin soup can cost $100 in a high-end Hong Kong restaurant.5
Today, large, predatory fish exist at one-third of their 1910 abundance, in part because global harvests during the mid-20th century totaled about 17 and a half million tons per year, almost exclusively along the continental shelves and coasts,6 where fishing fleets were increasingly employed to satisfy the continually growing demand for the top predators. However, these fleets included bottom trawling and bottom dredging—two of the most disruptive and widespread human-induced physical disturbances to seabed communities worldwide.
This type of fishing is especially problematic in areas where the interval between events of dredging or trawling is shorter than the time it takes for the ecosystem to recover. Extensive areas can be trawled from 100% to 700% or more per year; such a large amount of trawling affects the cycling of nutrients.
The frequency and extent to which nitrogen and silica in the bottom sediment are re-suspended in the water column by trawling and dredging has important implications for regional nutrient budgets. Trawling may also produce changes in the successional organization of soft-sediment infaunal communities. (An infaunal community is composed of aquatic animals that live in the substrate of a body of water, especially in the soft bottom of an ocean.) This type of bottom fishing can decrease habitat complexity and biodiversity, as well as enhance the abundance of opportunistic species and certain prey important in the diet of some commercially important fishes.
Bottom trawling and the use of other mobile fishing gear on the seabed are, in a manner of speaking, similar to clear-cutting a forest, which is recognized as a major threat to biological diversity and economic sustainability. Structures in benthic communities, while generally much smaller than those in forests, are just as critical to structural complexity and thus to biodiversity. Nevertheless, mobile fishing gear can have large and long-lasting effects on benthic communities, including the young stages of commercially important fishes, although some species benefit when structural complexity is reduced.
Use of mobile fishing gear crushes, buries, and exposes marine animals and structures on and in the substratum, thereby sharply reducing structural diversity. Its severity is roughly comparable to other disturbances that alter biogeochemical cycles. Recovery is often slow because recruitment is patchy and maturation can take years, decades, or even longer for some structure-forming species, such as corals.
Recent technological advances (such as rockhopper gear, global positioning systems, and fish finders) have all but eliminated natural havens safe from trawling. The frequency of yearly trawling on the continental shelf is orders of magnitude higher than the frequency of other severe seabed disturbances. In fact, trawling covers an area equivalent to perhaps half the world’s continental shelf each year, or 150 times the land area that is clear-cut on an annual basis.
In addition, fishing gear, which is used over large regions of continental shelves worldwide, can reduce habitat complexity by smoothing the micro-topography of the bottom, removing pebble-cobble substrate with emergent epifauna, and eliminating species that produce structures, such as burrows. (Epifauna are animals that live on the surface of sediments or soils.) The effects of mobile-fishing gear on biodiversity are most severe in areas least affected by natural disturbance, particularly on the outer continental shelf and slope, where damage from storm waves is negligible and biological processes, including growth, tend to be slow.7
By the 1980s, intensive fishing exploded in the open ocean through the use of more efficient gear, such as trawlers or helicopter-guided purse seines, which can mine the water of almost all fish within their reach. For example, when the tuna fishery adopted purse-seine nets, it gave rise to the three primary methods of purse seining for tuna in use today: School fishing, Dolphin fishing, and Log fishing (whole, drifting trees).
School fishing: In “school fishing,” tunas are detected from signs on the water’s surface that are visible from a vessel or helicopter. These signs include a school feeding or swimming rapidly close to the top, which disturbs the surface. A school may also have its presence betrayed by a flock of birds, or the fish may be seen jumping.
Types of schools are differentiated by the details of their behavior as they’re detected. A “breezer,” for example, is a school that affects the water’s surface in a manner similar to a breeze. A “boiler,” on the other hand, makes the water look like it’s actually boiling.
Although fishers call this type of fishing “school fishing” or “fishing on schools,” the terminology is misleading because schools are the target of several modes of fishing. So school fishing can be understood to by any kind of fishing that’s not associated either with floating objects, such as driftwood, or with dolphins.
Dolphin fishing: “Dolphin fishing” takes advantage of the association of large yellowfin tunas with herds of dolphins. By detecting the easily-visible, surface-swimming dolphins, chasing them, and maneuvering them into the net, fishers capture the tunas because they’re so closely associated with the dolphins that a school stays with the dolphins throughout the chase and encirclement.
Once caught, the tunas are retained while the dolphins are supposedly released. The problem with this kind of fishing arises because not all dolphins are released, and since dolphins are air-breathing mammals, those retained in the nets die by drowning.
Log fishing: In “log fishing,” a fisher searches for floating objects, such as large driftwood, under which a school of tunas is gathered. A net is then set around the object and the fish are thus captured. (To learn more about the role of driftwood in the world’s oceans, see From the Forest To the Sea: The Ecology of Wood In Streams, Rivers, Estuaries, and Oceans.8)
Japanese and American fishers have long known about such aggregations around large driftwood and (with a success rate well over four to one in favor of netting schools of tunas worth thousands of dollars) routinely seek large floating driftwood. In fact, the importance of this knowledge cannot be overstated if one understands how the purse-seine tuna fishery evolved in the western and central tropical Pacific from almost nothing in the mid-1970s to the world’s largest in both total catches and numbers of boats deployed within a decade or so after discovering that schools of tuna associate with such things as large, drifting wood.9
By the 1990s, the total global harvest had climbed to roughly 80 million tons per year,10 increasingly shifting the fish biomass (the collective weight of all the marine fishes) to smaller and smaller fish. To wit, predatory fish eat smaller prey fish, which in turn feed on still smaller fish, which in turn feed on still tinier fish that feed on plankton—phytoplankton (tiny floating plants) and zooplankton (tiny floating animals that eat the tiny floating plants). Plankton, the lowest rung of the marine food web, derives much of its nutrition from organic matter that wells up from the ocean’s cold depths.
Meanwhile, the fish biomass is shifting to smaller and smaller fishes, such as anchovies to blennies, that will over-populated the oceans and thus over-graze the phytoplankton, dramatically altering the marine ecosystem worldwide. At some point, their numbers become large enough to dramatically reduce the amount of phytoplankton and thus the ocean’s ability to absorb atmospheric carbon dioxide; in turn, these changes affect global warming.11
That said, curbs on fishing, such species as big-eye tuna and yellowfin tuna, until their populations are larger than those required to maintain a sustainable yield could, within biological limits, lead to maximum profits from fisheries.12 But then, warming oceans affect the major wind patterns, which affect the direction of ocean currents, which is shifting dead zones in the oceans, causing them to grow,13 which in turn affect the distribution of ocean fishes, as well as the global climate.
According to Alex Rogers, a professor of conservation biology at the University of Oxford, UK: “The speed of change, particularly related to climate change, is so great there simply isn’t time for marine life to adapt to these new conditions. When we’ve seen mass extinctions in the past they’ve been associated with large disturbances in the carbon system of the oceans. That’s what we’re bringing about through our own actions today.” An example of what Rogers is talking about is the fact that 50% of the sharks in the Mediterranean region are under the threat of extinction.14
Although the tradeoff of human activities in the ocean may at times cancel each other out, many are negatively synergistic, which means the cumulative effects are compounding. By that I mean the resilience of many marine ecosystem has already been so eroded, their increased vulnerability to climate change will decrease their capacity to recover through biophysical adaptation. For example, self-reinforcing feedback loops embodied in overfishing affects the overgrazing of the phytoplankton by small fishes, which increased the carbon dioxide in the water, which in turn increased oceanic acidification, which in turn causes the corals to bleach, and could lead to the virtual extinction of the most diverse marine ecosystems in the world’s oceans.15 (For a broader view of our human impact on the world, see Earth in Our Care: Ecology, Economy, and Sustainability.16 )
The challenge for humanity is that whatever happens in the oceans of the world affects virtually all of the global feedback loops because the oceans are not only the ultimate source of the world’s fresh water but also a primary arbitrator of the global climate. And, we humans continue to be the responsible party. In other words, we humans—through our intellectual/economic unconsciousness and subsequent destructive, self-centered behavior—are the authors of our own troubles, as well as those we increasingly bequeath to all generations, present and future!
If you doubt this statement, consider the August 7, 2012, story from ABC News:
An Alaska-based Coast Guard cutter is on the other side of the Pacific Ocean near Japan pursuing a vessel suspected of illegal high seas driftnet fishing.
Coast Guard Admiral Robert J. Papp, Jr. noted the ongoing case Monday as he testified at a Senate subcommittee hearing in Kodiak.
Papp says the 378-foot cutter Rush was nearly to Japan and escorting the stateless vessel.
Papp says the vessel has been boarded and 40 tons of fish was found on board. He says the crew had fished with an illegal 8-mile driftnet.
The nets have been banned internationally since 1992.17
Oceans in Crisis:
1. Benjamin S. Halpern, Shaun Walbridge, Kimberly A. Selkoe, and others. A Global Map of Human Impact on Marine Ecosystems. Science 319 (2008): 948–952.
2. Steven D. Emslie and William P. Patterson. Abrupt Recent Shift in 13C and 15N Values in Adélie Penguin Eggshell in Antarctica. Proceedings of the National Academy of Sciences 104 (2007): 11666–11669.
3. Phillip S. Levin, Elizabeth E. Holmes, Kevin R. Piner, and Chris J. Harvey. Shifts in a Pacific Ocean Fish Assemblage: The Potential Influence of Exploitation. Conservation Biology 20 (2006): 1181–1190.
4.Janet Raloff. Big Fishing Yields Small Fish: Researchers Map Predator Loss And Predict Unstable Oceans. Science News, 179 (number 8, 2011):28-29.
5. The discussion of shark finning is based on: (1) Shelley C. Clarke, Murdoch K McAllister, E.J. Milner-Gulland, and others. Global Estimates of Shark Catches Using Trade Records From Commercial Markets. Ecology Letters, 9 (2006): 1115–1126; (2) Janet Raloff. New Estimates of the Shark-Fin Trade; (3) Jaymi Heimbuch. Alarming Scale of Global Shark Fin Trade Revealed in New Photos; (4) Nadia Draske. Lopped Off. Science News, 180 (number 9, 2011):26-29; and (5) Boris Worm, E.B. Barbier, N. Beaumont, and others. Impacts of biodiversity loss on ocean ecosystem services. Science, 314 (2006):787–790.
7. The preceding three paragraphs are based on: (1) Jonna Engel and Rikk Kvitek. Effects of Otter Trawling on a Benthic Community in Monterey Bay National Marine Sanctuary. Conservation Biology, 12 (1998): 1204–1214; (2) Peter J. Auster. A Conceptual Model of the Impacts of Fishing Gear on the Integrity of Fish Habitats. Conservation Biology, 12 (1998): 1198–1203; (3) Cynthia H. Pilskaln, James H. Churchill, and Lawrence M. Mayer. Resuspension of Sediment by Bottom Trawling in the Gulf of Maine and Potential Geochemical Consequences. Conservation Biology, 12 (1998): 1223–1229; and (4) Les Watling and Elliott A. Norse. Disturbance of the Seabed by Mobile Fishing Gear: A Comparison to Forest Clearcutting. Conservation Biology, 12 (1998): 1180–1197.
8. Chris Maser and James R. Sedell. From the Forest To the Sea: The Ecology of Wood In Streams, Rivers, Estuaries, and Oceans St. Lucie Press, Delray Beach, FL. 1994. 200 pp.
9. (1) Ziro Suzuki. General description on tuna biology related to fishing activities on floating objects by Japanese purse seine boats in the western and central Pacific. Paper given at the Inter-American Tropical Tuna Commission, La Jolla, CA. 1992. 9 pp. and (2) Janet Raloff. Big Fishing Yields Small Fish: Researchers Map Predator Loss And Predict Unstable Oceans. op. cit.
10. Janet Raloff. Big Fishing Yields Small Fish: Researchers Map Predator Loss And Predict Unstable Oceans. op. cit.
11. (1) Ransom A. Myers and Boris Worm. Extinction, Survival or Recovery of Large Predatory Fishes. Philosophical Transactions of the Royal Society of London: Biological Sciences, 360 (2005): 13–20; (2) Peter Ward and Ransom A. Myers. Shifts in Open-Ocean Fish Communities Coinciding with the Commencement of Commercial Fishing. Ecology, 86 (2005): 835–847; and (3) Kenneth T. Frank, Brian Petrie, Jae S. Choi, and William C. Leggett. Trophic Cascades in a Formerly Cod-Dominated Ecosystem. Science, 308 (2005): 1621–1623.
12. (1) Benjamin S. Halpern, Karl Cottenie, and Bernardo R. Broitman. Strong Top-Down Control in Southern California Kelp Forest Ecosystems. Science, 312 (2006): 1230–1232; (2) Chris L. J. Frid, S. Hansson, S. A. Rijnsdorp, and S. A. Steingrimsson. Changing Levels of Predation on Benthos as a Result of Exploitation of Fish Populations. Ambio, 28 (1999): 578–582; (3) Chris L. J. Frid, Odette A. L. Paramor, and Catherine L. Scott. Ecosystem-based Management of Fisheries: Is Science Limiting? Journal of Marine Science, 63 (2006): 1567–1572; (4) Shelley C. Clarke, Jennifer E. Magnussen, Debra L. Abercrombie, and others. Identification of Shark Species Composition and Proportion in the Hong Kong Shark Fin Market Based on Molecular Genetics and Trade Records. Conservation Biology, 20 (2006): 201–211; and (5) R. Q. Grafton, T. Kompas, and R. W. Hilborn. Economics of Overexploitation Revisited. Science, 318 (2007): 1601.
13. (1) D. Pauly and V. Christensen. Primary Production Required to Sustain Global Fisheries. Nature, 374 (1995): 255–257; (2) John A. Barth, Bruce A. Menge, Jane Lubchenco, and others. Delayed Upwelling Alters Nearshore Coastal Ocean Ecosystems in the Northern California Current. Proceedings of the National Academy of Sciences, 104 (2007): 3719–3724; (3) F. Chan, J. A. Barth, J. Lubchenco, and others. Emergence of Anoxia in the California Current Large Marine Ecosystem. Science, 319 (2008): 920; and (4) Ryan R. Rykaczewski and David M. Checkley Jr. Influence of Ocean Winds on the Pelagic Ecosystem in Upwelling Regions. Proceedings of the National Academy of Sciences, 105 (2008): 1965–1970.
14. Christina Caron. Impending Disaster: Marine Species Face Mass Extinction, Experts Say. (June 22, 2011)
15. (1) Georgi M. Daskalov, Alexander N. Grishin, Sergei Rodionov, and Vesselina Mihneva. Trophic Cascades Triggered by Overfishing Reveal Possible Mechanisms of Ecosystem Regime Shifts. Proceedings of the National Academy of Sciences, 104 (2007):10518–10523 and (2) Alex D. Rogers and Dan. D’a Laffoley. International Earth System Expert Workshop On Ocean Stresses And Impacts. Summary Report. IPSO Oxford, 18 Pp. 2011.
16. Chris Maser. Earth in Our Care: Ecology, Economy and Sustainability. Rutgers University Press, New Brunswick, NJ. 2009. 304 pp.
17. Dan Joling. US Cutter in Pacific Pursues Fish Piracy Case. (August 7, 2012).
Text © by Chris Maser 2012. All rights reserved.