Conservation Flashcards
Anthropocene extinction
Losing species, much of this directly related to overgrown over consumptive human population
Most extinctions occur in ____
isolated freshwater water systems (95.9%) as marine fishes are less vulnerable due to large populations connected populations (but many are now commercially extinct e.g., Northern cod)
- Worldwide, considering areas with uncatalogued species, estimates suggest 20 - 35% (~3000+) freshwater vs. 5% (~1000) marine fishes have gone extinct since 1900
Major causes of fish extinction
habitat change and species introductions
Recent fish extinctions
Since 2011, 52 more fish extinctions worldwide and 12 just in North America
Freshwater extinction susceptibility (6)
- Increasing probability of extinction where freshwater fishes are typically in closer contact with human activities than are marine ones
- Many freshwater fish are endemics, adapted to unique habitats occurring nowhere else in the world
- Isolated streams, rivers, and lakes can be destroyed by
- Pollution
- Introduced species for aquaculture
- habitat alterations
General causes of fish biodiversity loss (8)
- Bottom type modification
- Channelization
- Damming
- Watershed perturbations
- Introduced species
- Pollution
- Exploitation
- Climate change
Bottom type modification
- Activities disrupting or removing bottom structure disrupts essential fish species habitat
Dredging carves deep trenches to keep shipping channels open
Trawling, mining and anchoring
Reduce essential habitat for key fish species and can cause important shifts in species interactions
* Removing structure
Channelisation or bank stabilisation
Straightens river with smooth sides Reduces floodplain flooding Increased land use in floodplain Decouples land from water resources
Reduces cleaning potential of floodplain
Increases flow and erosion
Water levels must be maintained
Increases leeching and waste runoff in channel and eventually elsewhere
Decreases fish diversity, and changes assemblages favouring high disturbance species
Dams
Provide hydroelectric power water storage and increased water for agricultural and domestic use
* Cause generally poor water management, high erosion and silt accumulation which must be removed
* Tropical countries, increased standing water conduit for pathogens
* Alters hydrology and changes fish assemblages just as bottom type modification in rivers can
Fish ladders
used to help with damning, good but fish need to find the ladders
Watershed perturbations
Changes in landscape use within watersheds has impact on aquatic species (logging, agriculture expansion, mining)
can change water chemistry, flow and temperature regimes, habitat types within aquatic systems
Introduced species
(nonindigenous, invasive, alien)
can be accidental or intentional
Homogenisation
Introduced species are often an added stressor to an already stressed systems
* With greater disturbance specialised endemics lose essential habitat and are displaced by native generalists
* At local scale, system shows overall diversity increase, but as endemics disappear, diversity drops
* Addition of alien species may also initially increase diversity, but the long-term impacts are unpredictable
introduced species are common additions, they can make very different systems become increasingly_____
homogenous
Predator release hypothesis
In their native range, the species have natural predators, competitors, parasites and environmental tolerances that keep them in check
- In their introduced environments predators, and other controls are substantially reduced allowing species to increase almost uncontrollably
How do Species introductions lead to the reductions of native species populations
- Directly through predation on adults, young, or eggs
Nile Perch - Indirectly by being a superior competitor, by hybridization, or the transmission of other non- native parasites and pathogens into local populations
Predation example, Nile perch
In lake Victoria;
Nile Perch introduced in 1960s convert useless (small bony) cichlids to large fish biomass
Nile perch wiped out most haplochomines and other endemic species, turning to cannibalism as main food source
- Algae eaters went extinct and increasing agriculture in area caused increasingly turbid waters and low CO2
- Converted a complex food-web and intricately niche packed system into a simplified community, with reduced fish biodiversity in less than 30 years
Competition example, Arctic cod
Arctic cod is a Keystone planktivore in most Arctic marine food webs
* Increasing evidence show that Capelin, a north Atlantic species are moving north and show high niche overlap with Arctic cod in Southern Beaufort Sea
* Fear is that warming Arctic causing will cause competitive exclusion of Arctic cod as Capelin invading
Pollution – Contaminants
Human produced substances (1000s) with toxic elements
Direct toxicity to fish by interfering with developmental pathways
Have indirect impacts through food chains (eutrophication or bioaccumulation) inhibiting survival and reproduction
Enter aquatic systems attached to sediments, dissolved in water or in the air
Agricultural pollution
Pesticides, herbicides and fertilizers – responsible for extermination of many fishes in isolated habitats world-wide
- Increases in fertilizer/nutrients loads also increase algal blooms which decrease CO2 when blooms die and decompose
Endocrine disruptors
Chemicals interfering with growth and development at low concentrations
* Can act early during sex determination but also later in the development of gonads and germline cells
- Documented impacts include:
- Abnormal gonad morphology
- Reduced rate of sperm/egg production - Reduced quality of gametes
- Failure to mature
- Chemical pollutants often act in concert or with other factors to exacerbate fish population declines
Commercial exploitation
Most of the world’s commercial fisheries either collapsed or overexploited
Fish continue to be major source of protein and
essential fatty acids (FA) to human population
- So, fishing will continue but with fewer sustainable resources available
Natural vs Human predation
Natural predation
- Focused on young, most abundant cohorts
- sick/dying individuals
- Easy meal
Weeding out less fit individuals sustainable
Human predation
- Indiscriminate
– targeting entire local aggregates (populations)
- Healthy/larger individuals
- Often targeting those of prime
reproductive age (e.g., salmon)
Decimation of populations not sustainable
Overfishing – example
- Overfishing is the removal of species at rate it cannot replenish, resulting in species becoming depleted or underpopulated in given area over time
- Purse seine fishery for Pacific Sardine began in late 1800s, and became the largest marine fishery off California by 1925
- 175,000 t canned and waste reduced for feed
Reduced fish value became greater than actual fish, leading to floating reduction plants operating outside legal zones of catch restrictions - Catches increased to 790,000 t in 1937, with a mean of 600,000 t/year for 10 years
- Estimated yields, however, were at 250,000 t/year max
- Pattern repeated in many exploited species; Atlantic herring, Northern Cod, Anchoveta in Peru, Mexican Totoaba etc,…
