Fisheries collapse

Main contributors: Garry Peterson, Juan Carlos Rocha

Other contributors: Henrik Österblom, Reinette (Oonsie) Biggs

Last update: 2014-10-14

Summary

A fishery collapses when the structure of the marine community (i.e. its species composition) changes radically, trapping the fishery into a regime in which high-valued commercial species cannot recover. These dynamics are often characterized by cascading effects across multiple trophic levels in marine food webs. Both top-down and bottom-up drivers contribute to the collapse of commercial fisheries. Overfishing is the main top-down driver, and is associated with indirect drivers that maintain fishing effort despite variation on fisheries demand, such as number of fishing boats in a fleet and fishing quotas that are insensitive to stock variation, as well as indirect drivers which increase fishing effort, such as demand from new markets, new possibilities to export fish, and technology improvements. The chief bottom-up drivers of collapse are drivers that influence the productivity of the base of marine food web. These include both anthropogenic and natural climate change that can shift the intensity and frequency of upwelling of cool nutrient rich water. Other factors, such as diseases spread, changes in ocean circulation, winds and temperature variation can act as synergistic factors contributing to collapses. The collapse of a commercial fishery can have substantial economic and social impacts.

Categorical attributes

Impacts

Ecosystem type:’

  • Marine & coastal
  • Freshwater lakes & rivers

Key ecosystem processes:

  • Primary production
  • Nutrient cycling

Biodiversity:

  • Biodiversity

Provisioning services:

  • Fisheries

Regulating services:

  • Pest & disease regulation

Cultural services:

  • Recreation
  • Aesthetic values
  • Knowledge and educational values

Human well-being:

  • Food and nutrition
  • Livelihoods and economic activity
  • Cultural
  • Aesthetic and recreational values
  • Cultural identity

Links to other regime shifts:

  • Bivalves Collapse
  • Hypoxia
  • Marine food webs
  • Marine eutrophication
  • Freshwater eutrophication

Drivers

Key drivers:

  • Harvest and resource consumption
  • External inputs (e.g. fertilizers
  • pest control
  • irrigation)
  • Adoption of new technology (e.g. new fishing nets)
  • Species introduction or removal
  • Disease
  • Global climate change

Land use:

  • Fisheries

Key attributes

Spatial scale:

  • Local/landscape (e.g. lake
  • catchment
  • community)
  • National (country)
  • Sub-continental (e.g. southern Africa
  • Amazon basin)

Time scale:

  • Years
  • Decades

Reversibility:

  • Irreversible (on 100 year time scale)
  • Hysteretic (difficult to reverse)

Evidence:

  • Models
  • Paleo-observation
  • Contemporary observations
  • Experiments

Confidence: existence of the regime shift

  • Contested – Reasonable evidence both for and against the existence of RS

Confidence: mechanisms underlying the regime shift

  • Contested – Multiple proposed mechanisms, reasonable evidence both for and against different mechanisms

Detail information

Alternative regimes

During the 20th century global fisheries greatly expanded in terms of effort and range. This expansion resulted in the overfishing of many fish stocks, and in some cases triggered fisheries collapses, for example the collapse of the highly productive Newfoundland cod fishery (Worm et al. 2009). While overfishing can severely deplete fish stocks, it will not necessarily trigger a fisheries collapse. A collapse occurs when once fishery pressure has been removed, stocks fail to rebuild (Hutchings 2000, Kirby et al. 2009), suggesting that the system has become locked into an alternate regime. In this case, alternate regimes are usefully conceptualized as alternative food web structures:

High abundance of a commercial fish species.

In this regime a valuable fish species is common and the fishery is highly productive. The main ecosystem services associated with high abundance of commercial fish are the production of food in first place, employment for both artisanal and industrial fishermen; followed by pest and disease regulation by healthy food webs, recreational values as recreational fishing, knowledge and educational values, as well as maintenance of biodiversity.

Low abundance of the commercial fish species.

This regime is characterized by a substantially reduced abundance of the valuable fish species. In cases where the valuable fish species performs key ecological functions, it can lead to trophic cascades that lead to an overabundance of planktivorous fish or primary producers such as seagrass, macroalgae, sponge or phytoplankton (Jackson et al. 2001). With low fish abundance, food production is the most immediate ecosystem services affected. While industrial fishermen often can move and harvest new areas or new species, artisanal fishermen often can lose their livelihoods and traditions.  

Drivers and causes of the regime shift

There are two key direct drivers of fisheries collapse: overfishing as a top-down disturbance, and the change in nutrients input as a bottom-up disturbance.

Overfishing reduce the population size of commercial fish species, reduce their ability to perform their functional role in the ecosystem, can destabilize their population dynamics (Anderson et al. 2008), and ultimately could change the structure of the food web. Nutrient inputs, on the other hand, affect fisheries by increasing the abundance of lower trophic levels e.g. phytoplankton and zooplanktivores such as jellyfish (Daskalov et al. 2007). Such changes in food web configuration can reduce the energy transfer to fish and hence reduce fishing productivity. These drivers can reduce the resilience of a regime making it more vulnerable to other types of regime shift, such as climate driven food web reorganization [see: Climate & Marine Food Webs]. The indirect drivers that explain overfishing and changes in nutrient input interact in synergistic ways, making their identification a challenging process (Ocean Studies Board 2006, Kirby et al. 2009).

Indirect drivers of overfishing include oversupply of fishing boats, inflexible fishing quotas, demand for fish, the development of new fishing technologies, the facilitation of trade (market connectivity), governance failures such as the failure of regulation to halt illegal fishing, and market failures such as subsidies or perverse incentives. Nutrient enrichment of marine ecosystems is also indirectly driven by runoff of fertilizer nutrients from agriculture and sewage from urban areas (Diaz and Rosenberg 2008).

Impacts on ecosystem services and human well-being

Shift from high to low abundance of commercial fish species

Since 1950 the world marine fisheries catch has expanded almost fivefold, and is currently about 80 million tonnes of fish. According to FAO, about 30% of fish stocks are overexploited, 60% are fully exploited and about 10 % are not fully exploited (FAO 2012). Global marine fish catches have plateaued and are not expected to increase. Local fisheries decline has been estimated to have affected the employment of roughly 14 million fishermen, 12 million of which correspond to artisanal fisheries (Pauly et al. 2006). There is not clear assessment of the number of stocks that have collapsed but FAO suggests about 5% of fish stocks are depleted (FAO 2012). Some collapsed stocks have remained at under 10% of their previous sizes even after decades of fishing closure (Ainley and Blight 2009). Food production, primary productivity, pest regulation, and cultural services are the ecosystem services most affected by the collapse of fisheries.  

Shift from low to high abundance of commercial fish species

An abundant fish population regime will likely better maintain marine biodiversity and will be more resilience to climate variation and climate change. Society will benefit of high abundance regime in terms of high primary productivity that translate in more food, jobs and livelihoods in small coastal communities. It will also better regulate marine hypoxia.

Management options

A review of marine fisheries in the Millennium Ecosystem Assessment offer a synthetic set of managerial options for addressing fisheries collapse(Pauly et al. 2006).

Options for enhancing resilience

There are two types of strategies for enhancing resilience. The first is to stop doing things that are eroding resilience, while the second is to being activities that build resilience. There are a number of fishing practices that could be eliminated because they damage the resilience of fisheries. For example, fishing practices that destroy habitat such as bottom trawling should be avoided. Developing alternative technologies and reduction of fishing effort are suggested. Bycatch, the killing but not consuming of unwanted fish, can also have substantial impacts and can be reduced. Indirectly, fisheries subsidies and inflexible quotas can drive fishing effort to high levels that erode the resilience of a fishery.

Options for reducing resilience of unwanted regime to encourage restoration or transformation

Direct resilience building strategies include the establishment of Marine protected areas (MPAs) (Takashina and Mougi 2014). These areas can play an important role by providing refugia for fish and increasing ecologically diversity. Research suggests that they need to cover ecologically significant areas, including different habitats, ensuring connectivity among them. However their remains controversy over the extent to which MPAs shift fishing pressure to less protected sites.

Indirect resilience building efforts include efficient regulation and policing of fishing can reduce illegal fishing, while comprehensive fisheries policies at the international and national level can also build resilience if they result in fisheries policies that reinforce one another. Indirect resilience building strategies include improving the ability of fishers to exit fisheries.

Good management of fishing pressure has been able to restore fisheries stocks. For example, in the US fishing closures and implementation of management measures for bottom fishing have enabled the restoration of George Bank haddock, Atlantic scallops, George Bank yellowtail flounder, Atlantic stripped bass, Atlantic Arcadian redfish, Pacific chub mackerel, and Pacific sardine. However, there is no clear strategy that works across many ecosystems or nations (Beddington et al. 2007).

Regime shift Analysis

Feedback mechanisms

High abundance of a commercial fish species.

Food web regulation mechanisms: trophic cascades / trophic triangles (local, contested): When a valuable fish population becomes substantially reduced, it may be replaced by a competitor species that performs the same ecological role. Thus, their functional role is not lost. High biodiversity increase resilience of the food web to disturbance such as fishing or climate oscillations. Fundamental mechanisms are not contested, their strength, variability and persistence is what varies and is contested.

Low abundance of the commercial fish species

Food web regulation mechanisms: trophic cascades / trophic triangles (local, contested): When a valuable fish population becomes substantially reduced, it may be replaced by a competitor species that performs the same ecological role. However, if it is not replaced substantial changes in the food web may occur. If the commercial fish species is a fish predator, a drastic decrease in its abundance can lead to an explosion in the fish species that form its prey.

Trophic triangles occur when prey species feed on the juveniles of their predators - e.g., sprat and cod in the Baltic Sea (Moellmann et al. 2009). A dramatic increase in the prey population can therefore lead to increased predation on juvenile predators. If the system becomes locked in this regime, it may be very difficult for the predator population to recover even if fishing pressure is removed, because few juvenile reach maturity. This in turn means that the prey population remains large because the adult predator population is too small to substantially impact on the prey population. In this case, the feedback loop is due to predation in a trophic triangle.

A second mechanism related to food web dynamics emerges from competitive interactions which can lock-in a dominant species. When food web structure is modified by top-down or bottom-up forces, species can shift their dietary preferences in order to adapt to new conditions. In such a situation a new species can become a dominant species, and even once fishing effort is reduced it will continue to dominate. In this case a positive feedback loop is due to density dependent competitive interactions. Historic competitors or new competitors can be locked in at low numbers because competition has become too strong to allow population growth. For both mechanisms, nutrient input, climate and fishing are drivers that might can causes a food web to shift from one dominant competitor to another (Scheffer et al. 2008).

Allee effect (local, contested): The Allee effect refers to a situation where a decrease in the breeding population (mature individuals) leads to a reduced population growth rate. This effect is often termed depensation in fisheries. Depensation can result from the reduced likelihood of finding a mate when populations become low, or because lower population numbers reduce the per fish effectiveness of predator avoidance strategies such as schooling (Liermann and Hilborn 1997). When the population falls to a level at which population growth rates are lowered it can remain stuck in a lower population density even when fishing pressure is removed (Carpenter 2003). Low population levels due to the Allee effect may trigger or promote other trophic changes, discussed above, that can reinforce the low abundance regime.

Drivers

Shift from high to low abundance of commercial fish species

Important shocks (eg droughts, floods) that contribute to the regime shift include:

Climate anomalies such as extremes of the ENSO - PDA - NAO - HCE can push marine food webs from one regime to another (Regional, well supported): Although the underlying mechanism are not fully understood, climate dynamics often vary over decadal periods and this variation is thought to influence the structure of food webs and their inherent dynamics. Such is the case of ENSO (El Niño / La Niña Southern Oscillation), PDO (Pacific Decadal Oscillation), NAO (North Atlantic Oscillation), and HCE (Humboldt current ecosystem) (Moellmann et al. 2008, Takasuka et al. 2008, Alheit 2009, Jiao 2009, Moellmann et al. 2009)

The main external direct drivers that contribute to the shift are:

Fishing pressure (Local to regional, well-established): Overfishing is the most common cause of fisheries collapse. Drivers of overfishing are related: unresponsive quotas, overcapitalization of boats, demand from new markets, global export of fish, subsidies for fishing, and technology improvements. Overfishing of international waters is also exacerbated by the tragedy of the commons, a dynamic where fishermen have strong incentives to fish more favoring their personal gains over the common good (Berkes et al. 2006).

Nutrients inputs (Local to regional, well-established): Nutrients inputs can come from nutrient leakage from agriculture or urbanization. Over enriched water typically lead to the dominance of lower trophic levels and other symptoms of marine eutrophication (e.g. lower light penetration due to turbidity, algae blooms) that potentially impact fish stocks (Jackson et al. 2001, Bakun et al. 2010).

The main external indirect drivers that contribute to the shift are:

Fishing fleet (Local to regional, well-established): – The difficulty of boats exiting a fishery, means that often fishing occurs at higher effort levels than are sustainable.

Inflexible quotas (Local to regional, well-established): – quotas that are not lowered in response to declines in fish populations can lead to too many fish being caught to sustain the population.

Technology (Local to regional, well-established): In the same way, technological developments substantially increase catch per unit effort, hence accelerating stocks depletion. Such is the case of storage technologies as refrigerators, geo positioning systems (GPS), sonars, telecommunications, and more efficient engines.

Tragedy of the commons (Local to regional, well-established): many fisheries are common pool resources (CPR), making it very difficult to control who uses the resource, and very difficult to transfer the right to do so, creating a social dilemma called the Tragedy of the commons (Berkes et al. 2006). The tragedy of the commons can be exacerbated by regulatory capture: Dominant groups can shape the way a fishery works by controlling the regulation of their industry. Such regulatory capture, removes the independence of regulation for social benefits and switches it to benefit specific groups which can exacerbate the tragedy of the commons (Fisherman’s problem).

Loss of local knowledge (Local, contested): in small scale fisheries the loss of traditional ecological knowledge can causes fisheries regulation and monitoring to become less effective because of loss of ability to interpret fisheries resilience (Berkes 2008).

Demand for food (Local to regional, well-established): Food demand is thought to drive fishing pressure. As market mechanism and trade facilitate the commerce of fish, more fishing effort is encouraged and stocks are depleted faster, having less time to recover (Berkes et al. 2006). Demand for food is further strengthened by the increasing preferences for sea food since the willingness to pay for it spreads over markets and increases fishing pressure.

Trade facilities (Global, well-established): Trade accelerates the flow of fish and money spatially, masking the effect of local depletion by importing resources from somewhere (Clarke 2004, Lenzen et al. 2012).

Urbanization (Local to regional, well-established): The development of coastal areas have lead to nutrients leaking increase, generating coastal eutrophication and sometimes dead zones (hypoxia)(Diaz and Rosenberg 2008). Such nutrient related phenomena can interact with upwellings related nutrient inputs and change the food web energy and carbon flow. [see Hypoxia]

Global warming (Global, contested): Another set of mechanisms that may reinforce a low abundance regime of a valuable fish species are climate ocean interactions which influence marine food webs through bottom-up effects. Global warming increase sea surface temperature (SST) and may lead to more frequent ENSO events. An increasing frequency and intensity of warm events accentuates the density contrast in the water column, inhibiting nutrient exchange through vertical mixing, and thereby reducing the productivity of marine food webs. Roughly half the biosphere’s net primary production is synthesized by phytoplankton in the oceans. These microscopic plants daily fix more than a hundred million tons of carbon dioxide, which in turn supports marine food webs that consume the total phytoplankton biomass every two to six days. Hence, inhibited mixing due to an increase in SST may substantially reduce fishery productivity by directly affecting net oceanic primary production. This phenomena has already been observed in the South American Pacific coast through satellite measurements of chlorophyll production during warm events (Bakun et al. 2010).

Global warming may play a fundamental role in destabilizing primary productivity in marine food webs (Kirby et al. 2009, Bakun et al. 2010). Such dynamics have been reported in regime shifts in kelp forests, coral reefs and estuaries. [see Coral transitions, kelp transitions]

Slow internal system changes that contribute to the regime shift include:

Population structure (Local, well-established): At the population level, the demographic structure of the population is a slow process of change that can trigger mechanism as the Allee effect (Hutchings and Reynolds 2004). By demographic structure one refers to the distribution of class size (eggs, larvae, juveniles, adults and elders) which can trap the stock in low productive regime when altered (e.g. too many elders or too many juveniles).

Trophic level diversity - functional groups (Regional, well-established): Functional groups are species that perform the same functions in the ecosystem (e.g. herbivores). High diversity in a functional group make its response behaviour to fishing effort slow and delayed (Jackson et al. 2001).

Upwellings (Regional, well-established): Upwellings bring cool nutrient rich water to the surface, altering the structure of marine food webs. Upwellings are always present in the sea and follow seasonal dynamics. Climate variation impacts the strength and dynamics of upwelling. The strength and frequency of upwelling produces shaping new climate dynamics due to higher sea surface temperature, rain anomalies or ENSO-like events (Behrenfeld et al. 2006, Bakun et al. 2010).

Summary of Drivers # Driver (Name) Type (Direct, Indirect, Internal, Shock) Scale (local, regional, global) Uncertainty (speculative, proposed, well-established) 1 ENSO Shock regional well-established 2 nutrients input direct local well-established 3 fishing effort direct local well-established 4 quota inflexibility indirect regional speculative 5 fishing boats indirect local/regional speculative 6 demand of food indirect regional well-established 7 technology indirect local/regional well-established 8 tragedy of the commons indirect local / regional well-established 9 subsidies indirect local/regional well-established 10 perverse incentives indirect local/regional well-established 11 trade facilites indirect global well-established 12 urbanization indirect local/regional well-established 13 global warming indirect global speculative Summary of Ecosystem Service impacts on different User Groups References (if available) Provisioning Services Freshwater Food Crops Feed, Fuel and Fibre Crops Livestock Fisheries Wild Food & Products Timber Woodfuel Hydropower Regulating Services Air Quality Regulation Climate Regulation Water Purification Soil Erosion Regulation Pest & Disease Regulation Pollination Protection against Natural Hazards Cultural Services Recreation Aesthetic Values Cognitive & Educational Spiritual & Inspirational

Citation

Acknowledge this review as:

Garry Peterson, Juan Carlos Rocha, Henrik Österblom, Reinette (Oonsie) Biggs. Fisheries collapse. In: Regime Shift Database, www.regimeshifts.org. Last revised: 2014-10-14

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This work is licensed under CC BY-NC-SA 4.0. It is an initiative lead by the Stockholm Resilience Centre. The website was developed by Juan Rocha and build with Rmarkdown.