Ch. 5 Anthropogenic Extinction in Marine Ecosystems

Marine Extinction Crisis

Introduction:

This chapter challenges common myths about the ocean's resilience and highlights the pervasive and destructive impacts of human activities, particularly fishing, habitat destruction, and pollution.

Main Themes:

The Myth of Inexhaustibility and the Reality of Marine Extinctions:

• Challenging Assumptions: The traditional view of the ocean as vast and inexhaustible, with marine species considered "extinction-proof" due to their wide ranges, large populations, and high reproductive rates, is being proven false.

• Scale of Extinction: Marine extinctions occur on a massive scale, often locally but cumulatively, representing a global loss pattern. The long timescales involved and poor monitoring have obscured the full extent of the problem.

• Anthropogenic Extinction: While marine extinction started later than on land, technological advancements are accelerating the decimation of species and habitat destruction across all ecosystems.

  • "Many marine species may be particularly vulnerable to extinction because of a number of factors: long age at maturity, low reproductive rate, adaptation to an environment with little disturbance, and targeting by industries encouraged their destruction."

Limited Knowledge of Marine Biodiversity:

• Terrestrial Bias: Our understanding of marine biodiversity is significantly less comprehensive than that of terrestrial environments, largely due to our terrestrial nature.

• Difficulties in Tracking: Many extinctions go unnoticed, especially for less-studied taxa and deep-sea species, highlighting the challenge of counting, tracking, and discriminating among marine species.

  • "Even for the few areas that are regularly surveyed, such as the shelf areas of the North Atlantic, near extinctions of large, distinctive, and formerly common species can occur without anyone’s knowledge."

Vulnerability of Diverse Marine Species:

• Slow-Growing, Long-Lived Species: Many marine species, especially those long-lived and slow-growing, are extremely susceptible to habitat disturbance.

• Highly Fecund Species Are Not Immune: The idea that high fecundity protects species from extinction is a dangerous myth. Species such as the totoaba and Chinese bahaba have been severely decimated despite being highly reproductive.

  • "Both the totoaba (Totoaba macdonaldi) and the Chinese bahaba (Bahaba taipingensis), members of the highly fecund Sciaenid family (drums or croakers) have been decimated to less than 1 percent of their past recorded catches within one human lifetime of science’s awareness of them"

• Genetic Diversity and Endemism: Populations previously thought to be widely distributed can be genetically distinct in different areas, especially around islands and seamounts, making them particularly vulnerable to localized threats.

The Impact of Fishing:

• Industrialized Fishing: Industrial fishing fleets, using bottom trawling and other destructive methods, rapidly expand into deeper and more remote areas, causing widespread population declines.

  • "Declines in populations have occurred worldwide, even in the most remote and “pristine” parts of the ocean"

• Overfishing despite Management: Fishing can drive species to extinction, even under existing management regimes, with populations struggling to recover, if at all.

• Bycatch: Bycatch, especially of large marine animals such as turtles and sharks, is a significant, often overlooked, extinction driver.

  • "The leatherback turtle (Dermochelys coriacea), the largest turtle on the planet, is now dangerously close to extinction in the Pacific...linked to the introduction of new gillnet swordfish fisheries...that capture an unknown, but likely significant, number."

• Shifting Baselines: As fisheries deplete valuable species, they shift to smaller, less valuable species lower on the food chain, and move to deeper waters, impacting previously undisturbed habitats.

• The "Millions of Eggs" Myth: The erroneous idea that high fecundity prevents overexploitation is still prevalent in fisheries management, which is refuted by data.

  • "Perhaps the most pernicious myth sustaining current fishing practices is the “millions of eggs” hypothesis, which presumes that the high fecundity of many fishes and marine invertebrates protects them from extinction."

• Small-Scale Fishing Impacts: Even small-scale, artisanal fishing can cause severe changes in community structure and lead to extinctions, particularly with destructive practices like dynamite and cyanide fishing.

• Illegal Fishing: Illegal fishing is widespread and undermines even the most cautious management plans.

  • "Legally or illegally, fishing of endangered and/or “protected” marine species usually continues in all countries, although it is difficult to detect through official channels."

Habitat Loss and Degradation:

• Destructive Fishing: Bottom trawling and dredging destroy three-dimensional habitat complexity, reducing biomass, species richness, and diversity. These methods also destroy structurally complex species that are habitats for other creatures.

• Pollution: Pollution, especially the bioaccumulation of toxins in food webs, threatens the survival of top predators. Eutrophication also leads to habitat loss.

  • "Pollutants come in many forms, and the oceans are often the ultimate repository of these wastes."

• Climate Change: Ocean acidification and increased water temperatures from climate change are severely impacting coral reefs and other marine ecosystems.

  • "Increased water temperatures and acidification of the oceans caused by the increase in carbon dioxide in the atmosphere could severely affect the persistence of many calcifying marine organisms, such as corals."

• Loss of Biogenic Habitats: The loss of critical habitats like coral reefs, kelp forests, mangroves, and seagrass beds has staggering implications for extinctions due to their role in supporting a multitude of species.

Introduced Species:

• Competition and Predation: Introduced species can decimate local species through competition and predation.

  • "...introductions of species into areas where the introduced species have few or no natural predators can lead to the decimation of local species through predation or competitive exclusion..."

• Hybridization: Introduced species can hybridize with wild populations, spreading maladaptive genes.

Policy and Management Failures:

• Economic Unsustainability: Current fishery management practices are not only causing extinctions but are also economically unsound, as greater economic rent could be obtained with reduced effort.

  • "On a purely economic level, virtually all analyses of fishing conclude that greater economic rent could be obtained with reduced effort"

• Need for Ecosystem-Based Management: Current management approaches focus on target species rather than the entire ecosystem. Management must address the most sensitive species and the ecosystem effects of fishing.

  • "Preventing extinctions requires management for the most sensitive species taken and for the ecosystem effects of fishing, rather than merely the effects on the target species."

• Destructive Fishing is the Most Severe Threat: Bottom trawling and dredging are considered the most ecologically severe practices and cause much more damage than even high levels of bycatch.

• Lack of Selective Fishing: Many current practices are not selective, resulting in high bycatch and impacts on non-target species.

• Lack of Species-Level Data: Catch records that do not distinguish to the species level mask the disappearance of more vulnerable species.

  • "For example, until recently, catches of skates were not distinguished to the species level in the catch records in North America and Europe. Because of this practice, the disappearance of large, slow-maturing species was masked by increases in other skate species"

• Insufficient Marine Reserves: Many marine reserves are too small and too localized to protect a wide range of species.

  • "Although reserves of all sizes appear to foster population increases, large reserves more likely encompass more species, particularly rare species, at more stages in their life history, and are more likely to have substantial positive effects on ecosystem health and population recovery."

• Failure to Reduce Overall Fishing Effort: Simply redirecting fishing effort to other locations instead of reducing it can have as bad, or worse, impact.

Key Recommendations:

• Full Ban on Bottom Trawling and Dredging: In areas not yet trawled, and those that are likely to be sensitive.

  • "We join others in recommending a full ban on trawling and dredging in all areas that have not yet been trawled, and all areas that are likely to be sensitive to these types of gear..."

• Selective Fishing: Prioritize fishing methods that minimize habitat damage and bycatch.

• Ecosystem-Based Management: Management should focus on the most sensitive species and address the broader ecosystem impacts of fishing.

• Large Marine Reserves: Establish large, well-managed marine reserves near key habitats to ensure the persistence of biodiversity.

• Reduce Overall Fishing Effort: Redirecting fishing is not enough, it must be reduced.

• Accurate Data Collection: Improve the accuracy of catch records by distinguishing at the species level.

• Urgent Action on Climate Change: Implement energy policies that foster energy conservation and alternative energy production.

Conclusion:

The chapter underscores the urgency of the marine extinction crisis, driven by a combination of human activities, particularly destructive fishing. Countering this crisis requires a fundamental shift in our approach to marine resource management, prioritizing conservation, habitat protection, and sustainable practices. Without immediate action, we risk losing significant marine biodiversity with profound consequences for the entire planet. The authors conclude that by changing current fishing practices and reducing bycatch, we would both reduce extinctions and lead to economic benefits.