Conservation

Key Definitions

2.1 Decline

  • Reduction in abundance.

  • Can be local or across entire range.

  • May be rapid or gradual.

2.2 Extirpation

  • Local extinction.

  • Species disappears from a specific area but persists elsewhere.

2.3 Extinction

  • Species no longer exists anywhere.

  • Natural process over geological time, but current rates are unprecedented.

3. Natural vs Current Extinction Rates

3.1 Background extinction rate

  • Fossil record suggests ~1–2 species per year globally.

  • Equivalent to ~9% of species per million years.

  • Over 500+ million years, five major mass extinction events occurred.

3.2 Mass extinction events

  • Five major events in the last 500 Myr.

  • The Permian extinction: ~75% of marine species lost.

  • Others less severe but still catastrophic.

3.3 Modern extinction rates

  • Faster than any time in recorded human history.

  • Faster than many mass extinction events.

  • Driven by a single species: Homo sapiens.

4. IUCN Red List – Global Conservation Status

4.1 What it is

  • Most comprehensive global inventory of threatened species.

  • Uses standardised criteria across taxa.

4.2 Current numbers (updated in lecture)

  • ~94,500 animal species assessed.

  • Categories: Least Concern → Near Threatened → Vulnerable → Endangered → Critically Endangered → Extinct in the Wild → Extinct.

  • Also includes Data Deficient species.

4.3 Fish representation

  • ~29,000 teleost + other bony fishes assessed.

  • ~⅔ are Least Concern.

  • ~14% are in threatened categories (Vulnerable, Endangered, Critically Endangered).

  • ~11% of teleosts are threatened (2026 update).

  • ~12% of extinct species on the Red List are fish.

4.4 Limitations

  • Many fish species recently discovered → insufficient data.

  • Marine species especially difficult to assess due to vast ranges.

5. Extinction Rates in Marine Fishes

5.1 Geological patterns

  • Heinecke et al. review: extinction rates of marine genera over 500 Myr.

  • Calculated using 7‑million‑year intervals.

  • Major extinction peaks correspond to known mass extinction events.

5.2 Last 65 million years

  • Bony fishes show ~3% extinction rate over this period.

5.3 Last 400 years (modern era)

  • Known extinctions increasing.

  • Many more local extirpations than global extinctions.

  • Marine extinctions under‑reported because:

    • Hard to survey entire ocean

    • Must prove species is absent everywhere

    • Many species cryptic or deep‑sea

5.4 Updated 2026 interpretation

  • ~11% of teleosts are threatened.

  • True extinction numbers likely higher.

6. Freshwater Fish Extinction Rates

Freshwater fishes are far more vulnerable than marine fishes.

6.1 Why freshwater species are more at risk

  • Restricted ranges (rivers, lakes, ponds)

  • Cannot escape stressors

  • Strongly affected by local human activity

  • Easier to detect extinctions → better data

6.2 North America as a case study

  • Best‑studied freshwater fauna globally.

  • Extinction rates increasing each decade since 1880.

  • ~5–10 species extinct per decade.

  • Cumulative extinctions rising sharply.

6.3 Global underestimation

  • IUCN lists ~90 extinct fish species.

  • True number likely >400 based on North American patterns.

  • Underestimates due to:

    • Poor sampling in Africa, South America, SE Asia

    • Rapid discovery of new species

    • Lack of long‑term monitoring

    • Unrecorded extinctions (e.g., Lake Victoria cichlids)

7. Main Drivers of Decline and Barriers to Recovery

7.1 Habitat Loss & Modification (major driver)

Affects both marine and freshwater fishes.

Marine examples

  • Bottom trawling

  • Dredging

  • Removal of 3D structure (reefs, kelp, seagrass)

  • Loss of essential fish habitat (EFH)

Freshwater examples

  • Channelisation

  • Dredging

  • Removal of woody debris

  • Bank stabilisation

  • Straightening rivers

  • Increased flow rates → unsuitable for many species

  • Loss of spawning grounds

7.2 Introduced Species

  • Predation

  • Competition

  • Hybridisation

  • Disease introduction

  • Particularly severe in freshwater systems

7.3 Overfishing

  • Less important for freshwater (except large rivers/lakes)

  • Major driver in marine systems

  • Removes top predators → trophic cascades

7.4 Pollution

  • Nutrient loading

  • Pesticides, herbicides

  • Industrial waste

  • Plastics

  • Heavy metals

7.5 Climate Change

  • Temperature shifts

  • Ocean acidification

  • Altered flow regimes

  • Extreme weather events

  • Range shifts and mismatches

8. Habitat Loss in Detail

8.1 Essential Fish Habitat (EFH)

Provides:

  • Refuge from predators

  • Refuge from fast flow (freshwater)

  • Attachment sites for eggs

  • Habitat for prey species

  • Nursery areas

Loss of EFH → immediate declines in abundance and diversity.

8.2 Marine habitat degradation

  • Trawling flattens seabed, removes structure

  • Dredging increases turbidity

  • Sedimentation smothers benthic communities

8.3 Freshwater habitat degradation

  • Woody debris removal eliminates shelter

  • Channelisation increases flow → fish washed downstream

  • Straightening rivers reduces habitat heterogeneity

  • Bank stabilisation removes riparian vegetation

  • Loss of spawning grounds

9. Watershed (Catchment) Effects

Human activities on land strongly influence aquatic ecosystems.

9.1 Key impacts

  • Deforestation → erosion → siltation

  • Agriculture → fertilisers, pesticides → eutrophication

  • Overgrazing → bank collapse, sediment input

  • Urbanisation → runoff, pollutants

  • Water abstraction → reduced flow, habitat shrinkage

9.2 Importance of riparian vegetation

  • Stabilises banks

  • Provides shade (reduces heat & UV exposure)

  • Supplies terrestrial food inputs

  • Reduces erosion

  • Maintains water quality

Loss of riparian vegetation → major declines in freshwater fish diversity.

9.3 Downstream effects

  • Sediment and nutrients flow into coastal seas

  • Example: Amazon sediment plume

  • Example: Gulf of Mexico “dead zone”

    • Hypoxic bottom waters

    • Up to 8,000 mi² (size of Wales)

    • Caused by nutrient runoff → microbial blooms → oxygen depletion

10. Dams and Their Impacts

Dams cause both construction-phase and operational impacts.

10.1 Construction impacts

  • Flooding of land

  • Deforestation

  • Increased siltation

  • Habitat loss

  • Displacement of communities (human & ecological)

10.2 Operational impacts

  • Altered flow regimes

  • Disrupted hydrology

  • Blocked migration routes

  • Changed nutrient flows

  • Reduced productivity downstream

  • Example: Aswan Dam (Nile)

    • Reduced nutrient input to Mediterranean

    • Decline in coastal fisheries

10.3 Ecological consequences

  • Fragmentation of river systems

  • Loss of migratory species (e.g., salmon, sturgeon)

  • Altered temperature regimes

  • Sediment trapping → downstream erosion

  • Reduced spawning habitat

11. Summary

  • Extinction is natural, but current rates are unprecedented.

  • Teleosts: ~11% threatened; true extinction numbers likely underestimated.

  • Freshwater fishes are at highest risk due to restricted ranges and intense human impacts.

  • Marine extinctions harder to detect but still significant.

  • Major drivers: habitat loss, introduced species, pollution, overfishing, climate change.

  • Habitat degradation (especially EFH loss) is the most widespread threat.

  • Watershed effects and dams have profound impacts on both freshwater and marine ecosystems.

  • Conservation must address:

    • Habitat protection

    • Catchment management

    • Pollution control

    • Sustainable fishing

    • Invasive species management