Harvesting species Flashcards
Definition
Harvesting species – taking species and/or their products from their environment to obtain a useful substance often for financial gain
*does not always involve killing e.g. honey
Sustainable harvesting essential to:
-conserve ecosystem services
-managing threatened species and ecosystems
-ensuring food security e.g. fishing quotas and tribes reliant on bush meat
-ensuring access to resources e.g. medicines
-ensuring job security for those employed in the harvesting industry
(and avoid overharvesting)
In the past unsustainable harvesting was not understood
e.g. T J Huxley said man could have no impact from his harvesting action leading to overharvest of birds for plumage and ferns for collections in the victorian era.
The target species and wider ecosystem are impacted by harvesting
see diagrams
Over harvest can disrupt a wide range of processes e.g. Antarctic krill exploitation results in wide ranging population decline of krill predators e.g penguins – longer foraging trips, lower adult mass and overall reduced populations. Bycatch species were affected and boom/bust fishing methods reduced genetic variation in krill resulting in reduced fitness
e.g. hunting of frugivorous primates and toucans reduces the distribution of fruit tree species in neotropical regions
e.g. Newfoundland and Norwegian unsustainable herring fishing resulted in population crash
Modelling populations for sustainable harvesting
Measuring population sizes and how they change
-visual census
-quadrats – sessile or slow moving species
-mark, release, recapture
-environmental DNA (eDNA)
-active acoustic measurements to produce an echogram
-Passive acoustic measurements: leaving a recorder out to capture sounds
Logistic growth model
population increases rapidly then plateaus at carrying capacity due to increased competition for food etc.
see notes for equation
Maximum sustainable yield (MSY) introduced by Mona Schafer
- Largest theoretical yield that can be harvested without affecting population size
- Equilibrium reached when dn/dt = 0
- Population growth rate is low at each population extreme
- MSY highest when population = k/2
(see notes for equations)
limitations
- MSY can vary contrary to logistic models
e.g. herring should only be harvested according to threshhold harvest
- Msy also doesn’t account for the age e.g. fish should not be harvested before they have bred however older females often more fertile and produce higher quality eggs
^ Controlled harvest practice e.g. moose hunting only in autumn and age/sex of harvested individuals determined
controls for this
Another limitation:MSY may overestimate of population size or growth rates
- harvesting quotas may be set too high leading to overexploitation
-Hard to get an accurate stock estimate and account for illegal harvest
Additionally - A certain level of variation may be necessary to maintain a population. Some subpopulations have lower productivity below the standard MSY.
Maximum economic yield
- Largest theoretical sustainable profit
- Models yield at different efforts over time
- Again yield lower at each extreme
- Slightly lower than MSY
What can we do to ensure sustainable harvesting?
1) Set quotas
2) Establish councils/committees/commissions
3) Create protected areas
4) Limit effort
5) Ban damaging practices and equipment
Fishing Quotas
- Implementation began late1970s
- Scientists recommend numbers for the TAC that will achieve MSY or MEY
- Reconsidered yearly
- Problems with overestimating populations
- Highly political
TAC =Total allowable catch - set yearly for each species by weight or number
Successful implementation of quota example: Atlantic blue fin tuna 15 year recovery plan
unsuccessful implementation of quota example: collapse of newfoundland cod fisheries
northwest atlantic cod fishing – abundance and growth rate was over estimated due to the efficiency of the fishing methods meaning that large hauls continued until close to extinction – 90% reduction in spawning. Moritorium ban was put in place to allow recovery.
Establishing Councils, Committees and Commissions
- Trusted groups are needed to monitor activity and be responsible for harvest management
- They collect data, publish reports, hold meetings, make recommendations etc
- There is illegal activity that is hard to monitor and prevent
Creating Protected Areas - What are they for?
o Help rebuild healthy populations
o Maintain biodiversity
o Protect endangered species
o Protect specific habitats e.g. breeding grounds
o Allow more individuals to reach the age of sexual maturity
o Enhance ecosystem resilience
o Encourage tourism
o Ensure food securityT
o be effective they must: be large enough; be in strategic locations; have a clear management plan; preferably link up to create corridors
marine protected areas (MPA)
“Any area of intertidal or subtidal terrain, together with its overlying water and associated flora, fauna, historical and cultural features, which has been reserved by law or other effective means to protect part or all of the enclosed environment” (IUCN)
Measures that can be taken to limit fishing effortand habitat destruction:
* Reduce: number of licenses; boat and engine size; number of fishing boats
* Create seasons or permitted times of year when species may be harvested (‘closed areas’)
* Ban damaging practices and equipment
Mismanagement, underfunding and poaching are issues
Protected Areas on Land
'’A clearly defined geographical space, recognised, dedicated and managed, through legal or other effective means, to achieve the long-term conservation of nature with associated ecosystem services and cultural values’’ (IUCN)
* Eg National parks, wilderness areas, community conserved areas, nature reserves, conservancies
* There are 202,467 protected areas today, covering 14.7% of the world’s land, excluding Antarctica (IUCN)
* Size and connectivity between protected areasare crucial
Mismanagement, underfunding and poaching are issues
Land protected areas must be large and connected to allow genetic diversity of larger predators
Future implications
Climate change: e.g. krill population decline may be underestimated
Overexploitation
e.g. Logging in the Amazon:
* Huge decrease in biodiversity due to loss of tree canopy
* Habitat loss for animals also leads to an increase in the transmission of zoonotic diseases
* Further implications for global warming due to decrease in carbon sequestration provided by trees
