SCENE: Sampling Techniques

Kick sampling

A method of sampling aquatic invertebrates by disturbing the substrate, common when looking at benthic ones like harpactoid copepods

Kick sample structure

Net bag protected by outer frame from stone abrasion, different mesh sizes/bag lengths available, handle either wood or aluminium to float in water

How does kick sampling work?

Dislodges invertebrates from substrate, stream flow collects them in net, sample emptied into sorting tray and taken to lab for ID

How are kick samples standardised?

By timing each effort

What is iNaturalist?

Online citizen science platform for recording biodiversity, IDs confirmed by community consensus and AI recognition for common species

Stream sampling measurements

Depth at centre of measured sections, width of section, water flow speed at 60% depth and at the bottom, substrate type, macroinvertebrates found through kick sampling

Surber sampling

Freshwater invertebrate sampling technique involving collecting samples with a net using the river flow

Zooplankton, phytoplankton sampling techniques

Horizontal tow nets and vertical hauls, bottle traps at varying depths

Fish abundance and structure sampling techniques

Depletion electrofishing - abundance and size structure of fish, habitat assessment - measuring area of habitat sampled to estimate density

Water column physiochemical properties sampling

Electronic probe to measure temperature, dissolved O2 concentrations and light availability

Benthic macroinvertebrate sampling techniques

(Eckman) grabs

Last stage of all sampling techniques

Laboratory identification using dichotomous keys, and statistical analysis

What is the purpose of using carbonated water in plankton sampling?

To displace oxygen and sedate plankton, making them easier to observe or collect

Why is oxygen removal important in zooplankton sampling?

Because it puts the organisms to sleep, reducing movement and stress during collection

What kind of water is used to put zooplankton to sleep?

Carbonated water, because it contains no oxygen

Which group of zooplankton is commonly found using kick samples?

Harpactoid copepods

Lab process for zooplankton samples

Agitate bottles for mixing, measure volume of sample, pipette 5ml onto microscope slide, count zooplankton from each taxon, measure length of each one

Lab process for phytoplankton samples

Agitate bottles for mixing, pipette onto microscope slide, identify phytoplankton from different taxa (too small to count on standard microscope)

Zooplankton taxa identified

Cladocera, cyclopoid and calanoid copepods

Why is fish population estimation important?

Fish are sensitive to environmental changes and serve as key indicators for ecosystem health and human impacts like windfarms.

What is one reason fish are used to study environmental impacts?

They are vulnerable to environmental changes and can reflect ecosystem-level effects.

What is another term for fish populations in fisheries science?

Stocks

What complicates estimating fish populations?

Fish mobility, habitat complexity, species behavior, and seasonality make accurate estimation difficult.

Why is intraspecific competition more intense than interspecific competition?

Individuals of the same species compete for identical resources.

Why is knowledge of age structure important?

Fish grow indeterminately, and size can help estimate age, aiding population modeling.

What is mortality rate used for in fish population studies?

To calculate maximum sustainable yield without depleting the population.

What is electrofishing and how does it work?

A method that stuns fish using electricity, making them easy to net; settings can be adjusted for different fish types.

What are the pros and cons of electrofishing?

Pros: effective in shallow water; Cons: less effective in low conductivity water, selective for larger species, may harm fish.

What affects the success of electrofishing?

Water conductivity and fish species—e.g., lampreys don't stun well.

What is CPUE (Catch Per Unit Effort)?

A relative measure of fish abundance based on catch per standard effort (e.g., time/fishing volume).

What is a limitation of CPUE?

Assumes linear relationship between catch and abundance; may mislead if gear efficiency improves.

What are gill nets and how are they used?

Nets that catch fish by entanglement; fish size determines capture due to mesh selectivity.

What are pros and cons of gill nets?

Pros: Simple, passive collection; Cons: Lethal, size-biased, can't sample live fish for some studies.

What are fyke nets?

Funnel-shaped nets that trap live fish; useful for non-lethal sampling.

What are the limitations of fyke nets?

Eels may prey on other fish in the trap before counting; active fish may escape.

How does hook-and-line sampling work?

Uses baited hooks to catch fish; selective based on hook size and species behavior.

What are limitations of hook-and-line sampling?

Not all species take bait; highly selective and non-representative of the whole community.

What is seine netting?

Dragging a net through shallow water to enclose and capture fish.

What are the pros and cons of seine nets?

Pros: Good in littoral zones; Cons: Not usable in deep water, labor-intensive, species like carp may escape.

What is a trawl survey?

A net is pulled by a boat, with otter boards keeping it open; area and speed are known, so it's quantitative.

Where is trawling mostly used?

In marine environments.

What are pros and cons of trawling?

Pros: Quantitative; Cons: Energy-intensive, not suitable for all habitats.

What is a drop-down net?

A plankton-style net with a set depth; good for vertical sampling.

What is a strength of drop-down nets?

You know the volume sampled, making them a good quantitative method.

What is acoustic telemetry?

Uses sound waves to track tagged fish; species can be inferred from size and movement patterns.

What is the advantage of acoustic telemetry?

Good for high-conservation fish; non-invasive and informative over time.

What is sub-bottom profiling used for?

Detecting structures under the sediment—not direct population estimation.

What is the use of ROVs (Remotely Operated Vehicles)?

Underwater drones used for visual surveys, especially in restricted dive zones.

What is a downside of ROV-based surveys?

Some fish may return to the bait repeatedly, skewing counts; mostly Nmax is used (max seen at once).

What is PIT tagging?

Inserting microchips into fish to identify individuals in mark-recapture studies.

What are some alternative marking methods?

Physical tags, tattoos, branding, otolith (ear bone) clipping—though these may not ID individuals.

What assumption does mark-recapture rely on?

That the population is closed, which is rarely true in open systems.

How is population size estimated in mark-recapture?

N = (T × C) / R, where T = tagged, C = total catch, R = recaptures

Why might fish sampling be dangerous?

Techniques like electrofishing at night carry risks.

Why is statistical analysis important in population estimates?

Basic formulas give fixed numbers without confidence intervals; stats help validate results.

What is a legal restriction on fish surveys in the UK?

Scientific diving requires a specific license.

What is an ethical advantage of video and acoustic surveys?

Non-invasive and typically don't require formal ethics approval.

Why are bigger fish more often caught?

Gear tends to be size-selective, making larger individuals more susceptible.

What is the purpose of macrophyte sampling?

To assess aquatic plant diversity, abundance, and relate it to environmental conditions for monitoring lake health.

What tools are commonly used in macrophyte sampling?

Grapnels and Ekman grabs.

When is a grapnel used?

To retrieve plant material from shallow or moderately deep waters to estimate diversity and abundance.

What is a limitation of grapnels?

Plants can fall off during retrieval, making biomass estimation difficult.

When is an Ekman grab used?

To collect sediment and associated macrophytes for biomass measurement.

What is measured along a transect?

Plant presence/absence, depth, and substrate type at regular depth intervals.

Why is consistency in transect intervals important?

It ensures repeatable and comparable data collection across sites.

What should be recorded even when no plants are found?

Depth and substrate type, to characterise habitat conditions.

What role does visual observation play in shallow water?

It can help detect plant presence without needing tools.

Why is the littoral zone important in sampling?

It's where light penetration allows most macrophyte growth.

What did macrophyte sampling reveal about exposed sites?

They were dominated by low-growing Littorella uniflora due to frequent disturbance.

What adaptation allows Littorella to dominate exposed areas?

Dense roots for anchoring and fast reproduction via stolons.

Why is Littorella less abundant in deeper or sheltered waters?

It is outcompeted by larger, more productive species like Elodea.

What was found in deeper

more sheltered zones?, Higher species richness and abundance of taller, bushier plants like Elodea nuttallii.

What is punctuated succession?

A pattern where exposure limits succession nearshore, while diversity increases in deeper, sheltered pockets.

How does zonation appear in the sampling results?

A clear transition from Littorella-dominated nearshore to diverse communities deeper out.

What causes the shift in dominant species with depth?

Reduced disturbance and increased light attenuation allow different species to thrive.

Why are intermediately disturbed sites the most diverse?

They balance stress and competition, allowing coexistence of more species.

What does high biomass in sheltered sites indicate?

Greater productivity due to dominance of large species like water lilies.

What does low biomass in disturbed areas suggest?

Fewer or smaller plants dominate, with more bare substrate.

What does a high plant trophic score suggest?

Elevated nutrient levels and possible eutrophication.

What trend was observed in trophic scores across Loch Lomond?

A north-to-south gradient with increasing nutrient pressure.

How can historical data complement current sampling?

It shows trends in species shifts and eutrophication over time.

What major shift was observed over time in Loch Lomond?

Replacement of Elodea canadensis by the more invasive Elodea nuttallii.

How does invasive species presence relate to sampling data?

Their dominance in sheltered areas indicates competitive advantage under enriched conditions.

Why are macrophytes effective indicators of ecological change?

They respond predictably to light, nutrients, disturbance, and remain stationary in the environment.

What is the primary application of macrophyte sampling?

To assess ecological status and monitor the health of freshwater ecosystems.

Why are macrophytes used in biomonitoring?

Because they are sensitive to environmental changes and remain fixed in place, providing long-term indicators of lake conditions.

What makes macrophytes reliable indicators?

Their distribution reflects long-term nutrient levels, disturbance, and light availability.

What does macrophyte sampling help detect?

Eutrophication, habitat disturbance, invasive species spread, and shifts in biodiversity.

How does macrophyte data support restoration?

By identifying sites below "good ecological status" and guiding targeted conservation efforts.

What EU directive guides the use of macrophytes in monitoring?

The Water Framework Directive (WFD), which requires consistent ecological status assessment.

How is macrophyte data used under the WFD?

It contributes to the Ecological Quality Ratio (EQR), comparing current conditions to reference baselines.

What is the goal of macrophyte-based assessment under the WFD?

To attain and maintain "good ecological status" across all member states' water bodies.

Why is macrophyte sampling increasingly important?

It complements invertebrate and algal assessments, offering a broader view of ecosystem health.

How do macrophytes respond to physical habitat conditions?

Their presence and life forms reflect substrate type, water depth, flow, and exposure.

How does SEPA use macrophyte data?

SEPA collects, analyzes, and uses it to classify water bodies and inform environmental objectives.

What practical skills are gained from macrophyte sampling?

Plant identification, habitat classification, data collection, and interpretation of ecological status.

How does trophic scoring apply in macrophyte studies?

It estimates nutrient enrichment by analyzing which plant species are present.

What is one advantage of using macrophytes over algae or inverts?

Macrophytes are less mobile and integrate long-term environmental conditions.

What does a holistic approach to water quality assessment include?

Multiple biological quality elements like macrophytes, algae, and invertebrates for a full picture.

What are some alternative macrophyte sampling techniques besides grapnels?

Other techniques include using an Ekman grab for biomass and sediment sampling, visual observation in shallow waters, and transect profiling with consistent depth intervals to measure species presence and depth distribution.