Overexploitation Flashcards
What is overexploitation?
harvesting a renewable resource faster than it can be produced
What percentage of threatened or near-threatened species on IUCN Redlist are being overexploited and what for?
72% (6.241)
For commerce, recreation or subsistence
What did humans implicate the extinction of in pre history?
most megafauna
can rapidly drive superabundant species to extinction e.g. passenger pigeon
Why have rates of overexploitation been increasing?
- high human population
- increased demand
- advanced technologies for harvesting
When populations stop growing?
when they reach carrying capacity (K)
Maximum Sustainable Yield Model
- in absence of overexploitation, population growth = highest at K/2
- The MSY depends on r (rate of population growth) and K (carrying capacity)
- these vary depending on characteristics of species concerned (reproductive rate etc)
What happens when fixed harvest (quotas) are set too high?
population driven to extinction
What happens when quota = MSY (Maximum Sustainable Yield Model)
harvesting will be sustainable if initial population level is above MSY, but lead to declines if population dips below MSY
Where are quota levels safer for harvesting?
low - only lead to decline if population goes below N1
What is required for a low harvesting quota?
accurate estimates of population size, K and r -> very challenging
What are proportional harvests?
dependent on population size
more sensible
all equilibria = stable, including MSY (which still occurs at K/2)
very difficult to implement as require constant, accurate population monitoring
Why are MSY modes oversimplistic?
- r and K may vary e.g. depending on population age structure and environmental variation
- more accurate models exist - hard to get accurate data to parameterise them
- challenging to implement - especially when moving across boundaries
- illegal harvesting and other sources of mortality must be taken into account
Types of overexploitation
Commercial
Subsistence
Recreational
What is commercial overexploitation?
unsustainable harvesting driven by a legal or illegal market
e.g. fishing - about 33% (possibly up to 66%) are overharvested
What can commercial overexploitation lead to?
huge population crashes and collapse of the industry
some populations are managed very well
What was the population crash of the Newfoundland Cod? (Commercial overexploitation)
- population crashed by 99%
Why does overfishing not always lead to extinction? (Commercial overexploitation)
due to high reproductive rates of many marine fish, but population may not bounce back after harvesting stopped
What can help fish sustainably? (Commercial overexploitation)
quotas but have problem
e.g. what about non-target species and excess catch?
What percentage of harvest in fishing is put back into the sea? (Commercial overexploitation)
between 25% and 75% of harvest in fishing operations is dumped back into the sea (dead or dying)
What solutions exist for fish harvest of non-target species and excess catch? (Commercial overexploitation)
e.g. improvement to fishing equipment
public awareness campaigns - help people choose their sources of seafood more wisely e.g. see the good fish guide
What is whaling? (Commercial overexploitation)
Hunting of whales
1986 - International Whaling Commission (IWC) banned commercial whaling to allow stocks to recover
What happens when larger species targeted, experiences a crash? (Commercial overexploitation)
then smaller species are targeted
Example of species that have recovered well (Commercial overexploitation)
- e.g. humpback whales reduced from >100,000 to around 10,000 - a 90% reduction -> populations now at >60,000 and increasing
Example of a species that has recovered less well (Commercial overexploitation)
- e.g. blue whale previous population: 200,000-300,000 current population around 2000-5000 whales despite being protected since 1966
What is still low after population recovery? (Commercial overexploitation)
genetic diversity
Effect on pinnipeds (Commercial overexploitation)
- Many pinnipeds hunted to almost extinction in 18th and 19th centuries - fur and blubber
- population sizes of many of these species recovered
- Stoffel et al (2018) investigated current genetic diversity in 30 pinniped species
- 11 species show genetic signs of severe bottlenecks, with effective population sizes declining to <500 - sometimes <50
What species had a lower genetic diversity? (Commercial overexploitation)
- went through bottlenecks
- have small current population sizes
- breed on land (easily accessible by human hunters)
- Bottleneck size = not related to IUCN status, indicating population recovery in many cases (although 3 of 4 most bottlenecked species are currently endangered)
What are the main solution for commercial overexploitation?
Certification schemes
- e.g. marine Stewardship council, Forestry Stewardship Council
- can’t boost standards across industry, but aren’t perfect
- rely on consumer awareness and buy-in
International agreements
- e.g. CITES - 36,000 species protected - 183 parties in CITES
Appendix I = trade permitted only in exceptional circumstances, 3% of all species (e.g. African rhinoceros, threatened with extinction)
Appendix II = trade strictly controlled, 97% of all species (e.g. Orchidaceae, at risk of becoming threatened)
Appendix III = request for assistance in controlling trade of species protected in species country (e.g. Chilean toad)
Illegal shipments (Commercial overexploitation)
- commonly run by organised crime syndicates
- often seized at airports/ports
- 76% of seizures are of CITES Appendix 1 or 2 species
Trade networks (Commercial overexploitation)
- complex
- important progress made
- current global resources allocated to combatting transnational wildlife crimes are in tens of millions of US $ globally = a fraction of resources available to those committing crimes
What is subsistence overexploitation?
- many people rely on wild plants, animals and fungi - food resource
- 10,000 yrs ago, all food came from wild
- Now: <1B people rely on wild plants, <1/th protein comes from wildlife in 62 developing countries, and almost 20% protein intake comes from wild fish for <3B people
Why is some harvesting not sustainable? (Subsistence overexploitation)
due to increased human population sizes and advances in modern harvesting technologies
Why are some location particularly vulnerable to subsistence hunting? (Subsistence overexploitation)
- high human density
- new road/transport links enable access
- increasing commercial trade
- difficult to regulate, considerations must be made to people who rely on subsistence hunting for food
What is there a large threat of? (Subsistence overexploitation)
Zoonotic diseases
- areas where both reservoirs of pathogens and human contact with wild meat = high
- risks from major transport hubs
How much of global human population participates in recreational fishing? (Recreational overexploitation)
around 11%
What do recreational fishers target? And their effect? (Recreational overexploitation)
- largest, most fecund individuals, which has disproportional effects on population growth
- can lead to substantial population declines
Effect of re-stocking programmes (for fish)? (Recreational overexploitation)
- boost numbers
- can damage natural populations e.g. by hybridisation of non-native species/populations, invasive species
What is the impact of recreational fisheries in comparison to other threats? (Recreational overexploitation)
low impact
Effect of unsustainable hunting practices from the colonial era? (Recreational overexploitation)
huge declines in many ‘big game’ species
- e.g. hunting and habitat loss reduced Bengal Tiger populations in India from 40,000 to less than 1,800 in 100 years
What can harvesting at sustainable levels contribute to? (Recreational overexploitation)
local economy and retain cultural important traditions
can enable protection of land for conservation
What is the argument against harvesting at sustainable levels? (Recreational overexploitation)
(especially for crueller hunting techniques)
- conflict with wildlife tourism
- much of money raised doesn’t stay in local communities
e.g. of the US$200 million generated annually from trophy hunting in Africa, only 3% reaches local communities
Effect of management for specific target species and an example (Recreational overexploitation)
can damage ecosystems
e.g. grouse-shooting in UK
- around 8% of combined area in England and Scotland are managed for grouse-shooting
- regular burning to boost supply of young heather and remove trees and grass
- killing predators and mountain hares (some persecution is illegal)
- increases grouse numbers, at expense of many other (but not all) species
management could be worse - e.g. sika plantations and intensive grazing
management could be improved - restore ecosystem and support landowners and recreational hunters - need to get stake holders onboard
