Fisheries and Food Webs
What are the three main types of fishery in this syllabus?
Artisanal, recreational and commercial fisheries.
What do B, I, D and E represent in the BIDE model?
Births, immigration, deaths and emigration.
What does maximum sustainable yield aim to maximise?
The long-term catch that a stock can support without ongoing depletion under the model assumptions.
What is total allowable catch?
The total quantity permitted to be taken from a defined stock or fishery in a specified period.
What is aquaculture?
Farming aquatic organisms, with management or intervention in production.
What is bycatch?
Organisms caught unintentionally while fishing for target species.
A population starts at 500, with B=80, I=20, D=60 and E=10. What is the final population?
500 + 80 + 20 - 60 - 10 = 530 fish.
How does maximum economic yield differ from maximum sustainable yield?
MEY maximises economic profit after costs; MSY maximises sustainable catch quantity.
How does an individual quota relate to total allowable catch?
It allocates a share or quantity of the overall allowable catch to a fisher or operator.
Name two characteristics of a desirable aquaculture species.
Examples: fast growth, resilience, efficient feed conversion, suitable breeding and strong market demand.
How does biomagnification differ from bioaccumulation?
Bioaccumulation occurs within an organism over time; biomagnification is increasing contaminant concentration across trophic levels.
Use N = M x n / m for M=40, n=50 and m=10. What is the population estimate?
N = 40 x 50 / 10 = 200 fish.
Why is ecosystem-based fisheries management broader than single-species management?
It considers habitats, food-web relationships, non-target species and cumulative impacts as well as the target stock.
How can size limits and seasonal closures support stock recovery?
Size limits can protect immature fish; seasonal closures can protect spawning or other vulnerable stages.
How does a recirculating system differ from an open system?
It treats and reuses much of its water; an open system exchanges water with the surrounding environment.
Why can upwelling support productive fisheries?
It supplies nutrients to surface waters, increasing phytoplankton production and food-web energy.
What assumptions support a reliable Lincoln index estimate?
A closed population, retained marks, thorough mixing and similar capture probability for marked and unmarked individuals.
How can a marine reserve support fishing outside its boundaries?
Adults can spill over and larvae can disperse, replenishing neighbouring fishing grounds.
How can dynamic spatial zoning and electronic monitoring improve management?
Zones adjust to changing fish distributions or risks; electronic records help monitor catch, bycatch and compliance.
A farm uses 150 kg of feed for 100 kg of biomass gain. Calculate feed conversion ratio.
FCR = feed mass / biomass gain = 150/100 = 1.5. Lower ratios generally indicate more efficient feed use.
How can shifting baselines hide the long-term decline of a fishery?
Each generation treats an already-depleted condition as normal, underestimating historical abundance and ecosystem change.
If marked fish avoid capture, how is the Lincoln estimate likely biased?
Too few marked fish are recaptured, decreasing m and inflating the estimated population size.
Why should catch limits be cautious when population data are uncertain?
The precautionary principle supports limiting harm despite uncertainty; conservative limits reduce the risk of stock collapse.
Illustrative values: aquaculture earns $1.2 billion and wild catch $0.8 billion. What share of total production value is aquaculture, and why is value not biomass?
1.2/(1.2 + 0.8) x 100 = 60%. Value also depends on price, species and market conditions; it does not directly measure harvest mass.
Why can increasing stocking density beyond carrying capacity reduce production and harm the environment?
Oxygen, space and waste-treatment capacity become limiting, increasing stress, disease and mortality and potentially nutrient pollution.