Question 1
Primary producers supply energy to aquatic food webs.
Define phytoplankton.
[1]
Distinguish macrophytes from phytoplankton.
[1]
Explain how phytoplankton provide energy for a predatory fish.
[1]
Question 2
Figure 1 shows energy flow through part of a shallow freshwater food web. The figures beside selected arrows show annual energy transfer.
Identify two primary producers shown in Figure 1.
[2]
Calculate the percentage transfer of energy from herbivorous fish to predatory fish. Show your working.
[2]
Explain how a large reduction in submerged macrophytes could reduce the harvest of predatory fish by humans.
[2]
Question 3
In a coastal state, annual per-capita consumption of aquatic animals increased from in 1990 to in 2020.
Calculate the percentage increase in annual per-capita consumption between 1990 and 2020. Show your working.
[2]
Outline one reason, other than population growth, for increasing demand for aquatic foods.
[1]
Outline one way in which values or perspectives may influence an individual's consumption of aquatic foods.
[1]
Question 4
Figure 1 shows three fishing practices.
Identify the fishing practice shown in panel B.
[1]
Outline two reasons why the practice shown in panel A is unsustainable.
[2]
Outline one way in which the practice shown in panel C may reduce future fish yields.
[1]
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Question 5
Figure 2 shows the estimated relationship between annual yield and fishing effort for a fishery.
Identify the fishing effort associated with the maximum sustainable yield.
[1]
Calculate the difference between the maximum sustainable yield and the yield at the current operating point.
[1]
Explain why reducing fishing effort from the current operating point could increase the long-term yield.
[2]
Question 6
A marine heatwave causes coral bleaching in a tropical reef ecosystem. The reef is also exposed to decreasing seawater pH.
Explain how coral bleaching may reduce populations of reef fish.
[2]
Explain how decreasing seawater pH may affect organisms with calcium-carbonate shells.
[2]
Question 7
An open-net salmon farm is located in a sheltered coastal inlet. Fish are held at high stocking density and are supplied with manufactured feed.
Explain two environmental impacts that may result from this aquaculture system.
[2]
Explain how one management technique could reduce an impact identified in (a).
[2]
Question 8
Figure 2 shows changes associated with the collapse of a hypothetical industrial sardine fishery on the west coast of South America.
Changes in sardine landings, sea-surface temperature anomaly and fishery conditions, 1967–1976.
| Year | Sardine landings / million tonnes | Sea-surface temperature anomaly / | Fishery condition |
|---|---|---|---|
| 1967 | 6.8 | -0.2 | — |
| 1968 | 7.5 | -0.1 | — |
| 1969 | 8.6 | 0.0 | High industrial fishing effort |
| 1970 | 9.5 | 0.0 | High industrial fishing effort |
| 1971 | 10.2 | 0.1 | High industrial fishing effort |
| 1972 | 5.4 | 0.9 | High fishing effort; warm-water event begins |
| 1973 | 1.7 | 1.8 | Strong warm-water event |
| 1974 | 2.1 | 0.7 | — |
| 1975 | 2.5 | 0.3 | — |
| 1976 | 2.8 | 0.0 | — |
Calculate the percentage decrease in sardine landings between 1971 and 1973. Show your working.
[2]
Describe two features of the fishery data that indicate a collapse rather than a single poor fishing season.
[2]
Explain how fishing pressure and the warm-water event may have acted together to cause the collapse shown in Figure 2.
[3]
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Question 9
Figures 3(a) and 3(b) show a no-take marine protected area (MPA) and changes in catch per unit effort in nearby fishing grounds.
Identify the process represented by the movement of adult fish from the MPA into the adjacent fishing ground.
[1]
Calculate the percentage increase in catch per unit effort in the fishing ground adjacent to the MPA from year 0 to year 6. Show your working.
[2]
Explain two ways in which the MPA could have caused the change calculated in (b).
[2]
Using Figure 3(a), suggest two limitations of this MPA for conserving aquatic populations.
[2]
Question 10
Figure 3 compares conditions in a thermally stratified offshore water body and a coastal upwelling zone.
Explain why strong thermal stratification may limit primary productivity in the offshore surface layer.
[2]
Explain why primary productivity may be higher in the coastal upwelling zone.
[2]
Question 11
In a tag–release–recapture survey, researchers mark and release 120 fish. After the fish have mixed with the population, a second sample of 150 fish contains 30 marked individuals.
Calculate the estimated fish population. Show your working.
[2]
State one assumption required for this estimate to be valid.
[1]
Outline one limitation of using landing records to monitor harvest rates.
[1]
Question 12
A commercially valuable fish stock has declined severely. The government proposes a two-year fishing closure, but fishing businesses and coastal workers are concerned about loss of income.
Explain why the perspectives of the government and fishing businesses may differ.
[2]
Outline two measures that could help resolve the conflict while supporting stock recovery.
[2]
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Question 13
Figure 4 shows a coastal state that has sold fishing access within part of its exclusive economic zone to a foreign industrial fleet.
State one right held by the coastal state within its exclusive economic zone.
[1]
State the maximum distance of an exclusive economic zone from the coastal state's baseline.
[1]
Explain one equity issue that may arise when the state sells fishing access to the foreign fleet.
[2]
Question 14
Global demand for aquatic food has increased while some wild fisheries have experienced severe declines.
Global per-capita consumption of aquatic animals and world population, 1965–2020.
| Year | Aquatic animals consumed / kg per person per year | World population / billion |
|---|---|---|
| 1965 | 10.0 | 3.3 |
| 1980 | 12.2 | 4.4 |
| 2000 | 16.0 | 6.1 |
| 2020 | 20.2 | 7.8 |
Calculate the percentage increase in global per-capita consumption of aquatic animals between 1965 and 2020.
[2]
Describe the change in silver anchovy landings between 1968 and 1974.
[2]
Explain how human and environmental factors may have interacted to cause the collapse shown in Figure 2.
[4]
Evaluate the use of catch quotas based on maximum sustainable yield to prevent another collapse of this fishery.
[5]
Question 15
A coastal authority established the Kalo Reef marine protected area (MPA) in 2018. Fishing is prohibited in the central no-take zone, while regulated fishing is permitted outside its boundary.
Identify one feature shown in Figure 1 that could support reproduction of the target fish.
[1]
Calculate the percentage of the total bottom-trawl catch that consists of non-target fish.
[2]
Explain two ways in which the MPA may have contributed to the trends shown in Figure 3.
[4]
Suggest how replacing bottom trawls with baited traps could make harvesting outside the MPA more sustainable.
[2]
Evaluate the effectiveness of the Kalo Reef MPA as a strategy for maintaining sustainable fish yields.
[4]
Question 16
Scientists investigated the effects of decreasing seawater pH on empty shells of one mollusc species. Five similar shells were placed in each treatment for 30 days at . The pH was adjusted once at the start using dilute acid.
Identify the independent variable in the investigation.
[1]
Calculate the difference in mean percentage shell-mass loss between pH 8.1 and pH 7.3.
[2]
Explain how increasing atmospheric carbon dioxide can cause effects consistent with the pattern in Figure 1.
[3]
Evaluate the reliability and ecological relevance of this investigation.
[4]
Suggest how declining mollusc populations could affect an aquatic food web and human food production.
[3]
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Question 17
Table 1 compares two salmon aquaculture systems producing the same annual mass of fish.
Table 1. Comparison of salmon aquaculture systems producing the same annual output.
| Indicator | Open-net coastal farm | Land-based recirculating system |
|---|---|---|
| Annual salmon output / tonnes | 10 000 | 10 000 |
| Nitrogen released / tonnes per year | 86 | 9 |
| Antibiotic use / kg per year | 42 | 4 |
| Escaped salmon / fish per year | 12 400 | 0 |
| Electricity consumption / GWh per year | 18 | 74 |
| Direct employment / full-time jobs | 48 | 61 |
| Feed | Manufactured feed for carnivorous salmon | Manufactured feed for carnivorous salmon |
Calculate the percentage reduction in nitrogen released when the recirculating system is used instead of the open-net farm. Show your working.
[2]
Compare the environmental impacts of the two aquaculture systems using two indicators from Table 1.
[2]
Evaluate the use of the land-based recirculating system as a strategy for making salmon aquaculture more sustainable.
[3]
Question 18
Figure 4 compares vertical water profiles at a thermally stratified offshore site and a nearby coastal upwelling site during summer.
Vertical water-profile measurements at a stratified offshore site, with surface measurements at a nearby coastal upwelling site. The photic zone extends from 0 to 40 m.
| Depth / m | Light zone | Offshore temperature / | Offshore nitrate / | Offshore chlorophyll / | Coastal nitrate / | Coastal chlorophyll / |
|---|---|---|---|---|---|---|
| 0 | Photic | 24 | 0.3 | 1.2 | 4.9 | 5.4 |
| 20 | Photic | 23 | 0.4 | 1.8 | — | — |
| 60 | Below photic | 12 | 5.8 | 0.3 | — | — |
| 100 | Below photic | 9 | 8.2 | 0.1 | — | — |
Identify the depth interval containing the strongest thermocline at the offshore site.
[1]
Describe the relationship between nitrate concentration and chlorophyll concentration with increasing depth at the offshore site.
[2]
Explain why phytoplankton productivity is higher at the coastal upwelling site than in the surface water of the stratified offshore site.
[3]
Question 19
Figures 7(a) and 7(b) show the marine jurisdiction and fishing-access agreement of a fictional coastal state.
Figure 7(b): Fisheries-access agreement indicators for the fictional state's EEZ.
| Indicator | Group or period | Value | Unit |
|---|---|---|---|
| Annual EEZ catch | Local small-scale fleet | 36 | thousand tonnes per year |
| Annual EEZ catch | Licensed foreign industrial fleet | 144 | thousand tonnes per year |
| Annual EEZ catch | Total | 180 | thousand tonnes per year |
| Government access-fee revenue | After agreement | 24 | million currency units per year |
| Mean local retail fish price | Before agreement | 2.40 | currency units per kg |
| Mean local retail fish price | After agreement | 3.30 | currency units per kg |
| Local fishing employment | Before agreement | 6200 | workers |
| Local fishing employment | After agreement | 4700 | workers |
| Observer coverage of foreign trips | After agreement | of foreign fishing trips |
State the approximate maximum seaward distance from the baseline to the outer boundary of the state's exclusive economic zone, as indicated by the scale in Figure 7(a).
[1]
Calculate the percentage of the catch from the state's EEZ taken by the local small-scale fleet. Show your working.
[2]
Explain two reasons why the foreign-access agreement may be considered an equity and justice issue.
[2]
Suggest one measure that could make the agreement more equitable and one measure that could make it more environmentally sustainable.
[2]
Question 20
Outline how phytoplankton and macrophytes support aquatic food production.
[4]
Explain how destructive fishing practices can reduce the long-term productivity of an aquatic food production system.
[7]
Using named examples, evaluate the effectiveness of legislation and consumer behaviour in preventing the overexploitation of aquatic food resources.
[9]
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Question 21
A government sets a fishing quota equal to the estimated maximum sustainable yield. Recruitment is lower than predicted during the following breeding season.
Explain why harvesting at the estimated maximum sustainable yield may be risky in this situation.
[2]
Explain how positive feedback could cause a rapid decline in this fish stock.
[1]
Outline one precautionary management response.
[1]
Question 22
An indigenous coastal community proposes a tightly limited harvest of a marine mammal with cultural and treaty significance. Scientific monitoring indicates that the wider population is currently stable.
Explain one argument supporting the proposed harvest from an indigenous-rights perspective.
[1]
Explain one argument opposing the harvest from an animal-rights perspective.
[1]
Outline two conditions that a conservation-based management plan could apply to the harvest.
[2]
Question 23
Open-net salmon farming has expanded in the fictional Relonc Bay. The farms supply export markets and provide local employment.
Monitoring results at sites near and distant from salmon cages before operation and after three years.
| Indicator | Distance from cages / m | Before operation | After 3 years |
|---|---|---|---|
| Dissolved oxygen / mg | 50 | 8.0 | 6.0 |
| Sediment organic carbon / % | 50 | 2.1 | 6.8 |
| Seagrass cover / % | 50 | 72 | 38 |
| Dissolved oxygen / mg | 1500 | 8.1 | 7.9 |
| Sediment organic carbon / % | 1500 | 2.0 | 2.2 |
| Seagrass cover / % | 1500 | 70 | 68 |
Annual production and management characteristics of two salmon-farming systems in Relonc Bay.
| Characteristic | Open-net system | Land-based recirculating system |
|---|---|---|
| Annual salmon production / tonnes | 12 000 | 10 500 |
| Direct employment / jobs | 150 | 210 |
| Electricity use / GWh | 18 | 74 |
| Liquid waste discharged to bay / % | 95 | 8 |
| Recorded escapees / year | 420 | 5 |
Calculate the percentage decrease in dissolved oxygen at 50 m from the cages after three years.
[2]
Explain the relationship between organic waste from the farm and the dissolved-oxygen and seagrass changes near the cages.
[3]
Analyse two environmental impacts of open-net salmon farming other than organic enrichment.
[4]
Evaluate whether the proposed land-based recirculating system would make salmon production in Relonc Bay more sustainable.
[5]
Question 24
Oceanographic conditions were studied at three sites in the fictional Meru Sea during summer.
Surface conditions at three Meru Sea sites and a depth profile for Site C.
| Site | Depth / m | Temperature / C | Nitrate / mol L | Chlorophyll-a / g L | Annual PP / g C m yr | Water-column setting |
|---|---|---|---|---|---|---|
| A | 0 | Not sampled | 5.8 | 6.5 | 540 | Shallow, mixed; river-influenced |
| B | 0 | Not sampled | 7.2 | 8.1 | 710 | Coastal upwelling |
| C | 0 | 24 | 0.4 | 0.7 | 95 | Strongly stratified |
| C | 25 | 23 | 0.5 | Not sampled | Not applicable | Strongly stratified |
| C | 50 | 17 | 2.8 | Not sampled | Not applicable | Strongly stratified |
| C | 100 | 9 | 7.9 | Not sampled | Not applicable | Strongly stratified |
| C | 200 | 7 | 11.0 | Not sampled | Not applicable | Strongly stratified |
Identify the site with the greatest annual primary productivity.
[1]
Describe the relationship between surface nitrate concentration and annual primary productivity across the three sites.
[2]
Explain why strong thermal stratification limits surface productivity at Site C.
[4]
Analyse why productivity differs between Sites A and B despite both having nutrient-rich surface water.
[3]
Suggest how a prolonged weakening of coastal upwelling could affect aquatic food production near Site B.
[3]
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Question 25
Managers assessed the fictional blue hake stock using tag–release–recapture surveys, scientific trawl surveys and fishing-vessel records.
Tag–release–recapture survey information for blue hake, 2024.
| Item | Information |
|---|---|
| Initially captured, tagged and released () | 1200 blue hake |
| Time before second sample | 4 weeks |
| Fish in second sample () | 150 blue hake |
| Tagged fish recaptured () | 30 blue hake |
| Population estimator | |
| Assumption: tag retention | No tag loss |
| Assumption: catchability | Tagged and untagged fish have equal catchability |
| Assumption: distribution | Tagged fish mix fully with the stock |
| Assumption: population closure | Negligible migration, births and deaths during the four weeks |
Blue hake monitoring data and reported landing-record limitations, 2020–2025.
| Year | Scientific biomass / tonnes | Commercial CPUE / kg vessel h | Reported landings / tonnes | Landing-record information |
|---|---|---|---|---|
| 2020 | 84 | 19.0 | Not given | |
| 2021 | 79 | 18.5 | Not given | |
| 2022 | 71 | 17.6 | Not given | |
| 2023 | 62 | 16.4 | Not given | |
| 2024 | 54 | 15.1 | Not given | |
| 2025 | 47 | 13.8 | Not given | |
| 2020–2025 | Not given | Not given | 39–42 (aggregate range; no annual values) | Observers covered of trips; discarded bycatch was not included; some vessels did not transmit location data. |
Calculate the estimated blue hake population in the 2024 tag–release–recapture survey.
[2]
Explain how failure of two assumptions in Figure 1 could reduce the accuracy of the population estimate.
[4]
Analyse the evidence for a decline in the blue hake stock between 2020 and 2025.
[3]
Evaluate the use of landing records and vessel logbooks as the main method of monitoring harvest rates in this fishery.
[5]
Question 26
A fisheries agency used tag–release–recapture and harvest records to assess a coastal snapper stock.
Tag–release–recapture survey records for a coastal snapper stock.
| Survey record | Number of fish |
|---|---|
| First sample captured and tagged | 600 |
| Tagged fish released alive | 600 |
| Second sample captured after mixing | 500 |
| Tagged fish found in second sample | 75 |
| Survey note | 30 tags were later found to have detached before the second sample. Fishing season remained open between samples. Tagged fish were released from one site while the stock occupied a long coastline. |
Harvest-monitoring fact file for the coastal snapper stock, same year.
| Record or estimate | Value | Information recorded |
|---|---|---|
| Reported landings | 760 tonnes | Catch landed and reported at port |
| Observer estimate | 18% of total legal catch | Discarded bycatch and undersized target fish, by mass |
| Illegal landings | 90 tonnes | Independently estimated |
| Vessel logbooks | — | Gear, fishing location and effort |
| Port records | — | Landed catch only |
Using the uncorrected survey data, estimate the snapper population using , where is the number marked and released, is the size of the second sample and is the number of marked fish recaptured. Show your working.
[2]
Explain two reasons why the estimate calculated in (a) may be inaccurate.
[2]
Estimate the total mass removed from the stock, including discarded catch and estimated illegal landings. Show your working.
[2]
Suggest why managers should combine scientific stock surveys, observer data, vessel logbooks and port records rather than use reported landings alone.
[1]
Question 27
Figure 6 shows two modelled yield–effort curves for the same fish stock under average and poor recruitment conditions.
State the difference between the maximum sustainable yields under average and poor recruitment conditions.
[1]
Calculate the percentage by which the quota exceeds the maximum sustainable yield under poor recruitment conditions. Show your working.
[2]
Explain how maintaining the quota shown during poor recruitment could cause a rapid decline in the fish stock through positive feedback.
[3]
Suggest one precautionary management response supported by Figure 6.
[1]
Question 28
Outline the relationship between fishing effort, sustainable yield and maximum sustainable yield.
[4]
Explain how a well-designed and well-managed marine protected area may maintain sustainable fish yields within and beyond its boundary.
[7]
Using named examples, to what extent are marine protected areas more effective than catch quotas in maintaining sustainable aquatic food production?
[9]
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Question 29
Outline four reasons for the expansion of aquaculture.
[4]
Explain how management can reduce the environmental impacts of intensive aquaculture.
[7]
Using named examples, evaluate the claim that expanding aquaculture is a sustainable response to increasing global demand for aquatic foods.
[9]
Question 30
Explain why strong thermal stratification may limit primary productivity in a deep water body.
[4]
Analyse how upwelling and land-derived nutrient loading may have contrasting effects on aquatic food production.
[7]
Using named examples, examine how climate change may alter the productivity and reliability of aquatic food production systems.
[9]
Question 31
The management authority for the fictional striped mackerel fishery estimates maximum sustainable yield (MSY) using a population model.
Figure 2. Striped mackerel fishery monitoring, 2022–2025.
| Year | Estimated / thousand tonnes | Quota / thousand tonnes | Recorded catch / thousand tonnes | Juvenile recruitment index / relative units () | Monitoring observation |
|---|---|---|---|---|---|
| 2022 | 80 | 80 | 78 | 100 | Most fishing occurs at predictable spawning aggregations. |
| 2023 | 80 | 80 | 82 | 88 | Unusually warm period began, reducing plankton prey during 2023–2025. |
| 2024 | 72 | 76 | 79 | 69 | Unusually warm conditions continued. |
| 2025 | 65 | 70 | 73 | 51 | Recorded-catch estimates exclude illegal landings. |
State the fishing effort associated with the estimated MSY in Figure 1.
[1]
Calculate the percentage by which the recorded catch exceeded the estimated MSY in 2025.
[2]
Explain why increasing fishing effort beyond 40 thousand vessel-days causes sustainable yield to decline in Figure 1.
[3]
Analyse how positive feedback may be contributing to the changes shown in Figure 2.
[3]
Evaluate the authority's use of estimated MSY as the annual quota target.
[5]
Question 32
The coastal state of Nambara has sold fishing access within its exclusive economic zone (EEZ) to foreign industrial fleets. The same migratory tuna stock is also harvested on the adjacent high seas.
Tuna catch by fleet and mean fish consumption in Nambara's coastal villages.
| Year | Local small-scale tuna catch / thousand tonnes | Licensed foreign tuna catch / thousand tonnes | Mean fish consumption / kg person^-1 yr^-1 |
|---|---|---|---|
| 2018 | 68 | 42 | 31 |
| 2025 | 39 | 96 | 19 |
State the maximum distance from Nambara's baseline over which its EEZ extends.
[1]
Calculate the percentage change in the local small-scale fleet's tuna catch between 2018 and 2025.
[2]
Explain why management of the migratory tuna stock is more difficult on the high seas than within Nambara's EEZ.
[3]
Analyse the equity and justice issues associated with selling foreign fleets access to Nambara's EEZ.
[4]
Evaluate a cooperative management plan that would allow the tuna stock to recover while addressing stakeholder interests.
[5]
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Question 33
Outline how fishery-independent surveys and harvest records can be used together to assess a fish stock.
[4]
Explain why setting an annual quota equal to an estimated maximum sustainable yield may cause rapid stock decline.
[7]
Using named examples, evaluate the importance of stakeholder cooperation in enabling an overexploited fish stock to recover.
[9]
Question 34
Distinguish the governance of fisheries within an exclusive economic zone from governance on the high seas.
[4]
Explain why decisions about access to marine resources may create both conservation and environmental-justice conflicts.
[7]
Using named examples, to what extent should ecological sustainability take priority over economic, indigenous and animal-rights perspectives when governing the harvest of marine resources?
[9]
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