Marine + Terrestrial Case Studies

Define allochthonous inputs:

Inputs into a system originating from outside that system.

Define autochthonous inputs:

Inputs into a system originating from elsewhere in that system.

Define reciprocal prey subsidies:

At different times of year, aquatic systems rely on terrestrial inputs, and at others vice versa.

Describe fish recruitment:

• The growth of fish from egg to maturity

• This can vary year on year

Define year class strength:

A relative measure of how many fish make it to maturity.

How is a fish’s length related to its survival?

A longer fish can hold it’s position in a river at higher flows, increasing it’s survival chances.

Describe Lake Naivasha, in Kenya:

• 150km²

• Population >1m

• 1 of 2 freshwater lakes in the Rift Valley of Kenya

• Super important wetland site

• A key flower-growing region, making US$141m in 2016

How has Lake Naivasha been damaged?

• Lake level is ~4m lower than it should be

• Papyrus (normally a great pollutant filter) has been cut down

• Overfishing and invasive species introduction has decimated tilapia populations

Give some impacts on humans the damage has caused:

• Reduced fishing accessibility as lake gets smaller

• Reduced fishing revenue esp. tilapia

Describe the River Frome:

• Fed by chalk aquifers 

• Stable flow regime and temperature 

• Mineral rich 

• An SSSI between Dorchester and Wareham

Describe the challenges that Atlantic Salmon face:

• Declining populations

• In Scotland 72% of rivers are “poor” for salmon conservation

• Global warming

• Exploitation

• Barriers to migration

How does global warming affect salmon populations?

Warmer winter temperatures when the salmon spawn hatch can reduce abundance.

How does exploitation affect salmon populations?

• IUU fisheries overexploit marine populations (shown to be where the greatest population damage occurs)

• Open-pen fish farms can transmit sea lice to wild migrating salmon

How do barriers to migration affect salmon populations?

Dams and weirs can prevent salmon from travelling upstream, kill them, or seriously deplete their energy.

Give some examples of initiatives aimed at reducing salmon population damage:

• Following surveys in Scotland, 153 rivers have mandatory catch-and-release orders on them (2025)

• Louds Mill fish pass is 8.5m long (River Frome) and has increased the number of recorded in its first year

Give some issues that freshwater conservation faces:

• Multiple uses of freshwater makes conservation difficult 

• Degradation from human use e.g. hydropower 

• Management is often taxon specific – hard to measure success 

Describe how tagging can be used to monitor fish mortality:

• Juveniles are tagged

• Smolt emergence (to the sea) can give a total population estimate

• Returning fish can also be recorded

• Tiny PIT tags are used

Name the 6 UK deer species, including which two are native:

• Fallow 

• Roe 

• Red 

• Chinese water 

• Muntjac 

• Sika 

• Roe and red are native

What factors have increased the UK deer population?

• Warmer winters

• A lack of natural predators e.g. lynx or wolves

• Tree planting initiatives providing lots of food

• Some herds are 2000-strong!!

Give some social impacts of deer overpopulation:

• Agricultural damage through consumption and trampling

• Woodland damage through consumption and bark damage

• Faecal contamination

• Increase in car accidents (74,000 a year)

• Vectors for lyme disease

Why are fences not ideal for deer management?

• Expensive

• Reduce the mobility of other animals

• Can trap deer that try to jump them an cause inhumane injury

Why are chemical repellents not ideal for deer management?

• E.g. Trico, washed away in the rain

• Must be regularly reapplied to every tree

• Cost and labour intensive

Why are scaring devices not ideal for deer management?

• E.g. auditory clues

• The deer adapt quite quickly - then no longer effective

• Esp. fallow deer which are quite intelligent

Why are repellent tree choices not ideal for deer management?

• Affected by environmental suitability

• Also may not align with land use goals

Give some benefits of deer lethal control:

• More ethical

• More sustainable

• More healthy

Give some issues with deer lethal control:

• Negative public attitudes

• Stalking culture (stalkers are territorial leading to insufficient numbers and few young people go into the profession)

• Insufficient infrastructure for processing

Why is deer management difficult?

• Highly mobile deer mean a landscape-wide approach is necessary

• 31% of landowners say collaboration with neighbours is difficult

Define deer impact risk:

The cumulative annual deer activity experienced by an area of a woodland

Describe how iDeer can help landowners:

Allows landowners to predict the impacts of tree-cover changes and facilitate collaboration and target resources.