Sustainable yield in fisheries
Encyclopedia
The sustainable yield of natural capital
is the ecological yield
that can be extracted without reducing the base of capital itself, i.e. the surplus required to maintain ecosystem services
at the same or increasing level over time. This yield usually varies over time with the needs of the ecosystem
to maintain itself, e.g. a forest
that has recently suffered a blight
or flooding or fire
will require more of its own ecological yield to sustain and re-establish a mature forest. While doing so, the sustainable yield may be much less.
In fisheries, the basic natural capital, or virgin population, must decrease with extraction. At the same time productivity increases. Hence, sustainable yield would be within the range in which the natural capital together with its production are able to provide satisfactory yield. It may be very difficult to quantify sustainable yield, because every dynamic ecological conditions and other factors not related to harvesting induce changes and fluctuations in both, the natural capital and its productivity.
and economics
, maximum sustainable yield or MSY is, theoretically, the largest yield/catch that can be taken from a species' stock over an indefinite period. Under the assumption of logistic growth, the MSY will be exactly at half the carrying capacity
of a species, as this is the stage at when population growth is highest. The maximum sustainable yield is usually higher than the optimum sustainable yield
.
This logistic
model of growth is produced by a population introduced to a new habitat or with very poor numbers going through a lag phase of slow growth at first. Once it reaches a foothold population it will go through a rapid growth rate that will start to level off once the species approaches carrying capacity. The idea of maximum sustained yield is to decrease population density to the point of highest growth rate possible. This changes the number of the population, but the new number can be maintained indefinitely, ideally.
In most fisheries, the population has been decreased so significantly from their native populations, that the only way to increase production is to decrease production, and wait for populations to recover. Establishing limits is a perennial difficulty.
MSY is extensively used for fisheries management. Unlike Schaefer's logistic model, MSY in most modern fisheries models occurs at around 30% of the unexploited population size. This fraction differs among populations depending on the life history of the species and the age-specific selectivity of the fishing method.
Unfortunately errors in estimating the population dynamics of a species can lead to setting the maximum sustainable yield too high (or too low). An example of this was the New Zealand Orange roughy
fishery. Early quotas were based on an assumption that the orange roughy had a fairly short lifespan and bred relatively quickly. However, it was later discovered that the orange roughy lived a long time and had bred slowly (~30 years). By this stage stocks had been largely depleted.
and economics
, optimum sustainable yield is the level of effort (LOE
) that maximizes the difference between total revenue and total cost. Or, where marginal revenue equals marginal cost. This level of effort maximizes the economic profit, or rent, of the resource being utilized. It usually corresponds to an effort level lower than that of maximum sustainable yield.
In environmental science
, optimum sustainable yield is the largest economical yield of a renewable resource achievable over a long time period without decreasing the ability of the population or its environment to support the continuation of this level of yield.
Natural capital
Natural capital is the extension of the economic notion of capital to goods and services relating to the natural environment. Natural capital is thus the stock of natural ecosystems that yields a flow of valuable ecosystem goods or services into the future...
is the ecological yield
Ecological yield
Ecological yield is the harvestable population growth of an ecosystem. It is most commonly measured in forestry;sustainable forestry is defined as that which does not harvest more wood in a year than has grown in that year, within a given patch of forest....
that can be extracted without reducing the base of capital itself, i.e. the surplus required to maintain ecosystem services
Ecosystem services
Humankind benefits from a multitude of resources and processes that are supplied by natural ecosystems. Collectively, these benefits are known as ecosystem services and include products like clean drinking water and processes such as the decomposition of wastes...
at the same or increasing level over time. This yield usually varies over time with the needs of the ecosystem
Ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
to maintain itself, e.g. a forest
Forest
A forest, also referred to as a wood or the woods, is an area with a high density of trees. As with cities, depending where you are in the world, what is considered a forest may vary significantly in size and have various classification according to how and what of the forest is composed...
that has recently suffered a blight
Blight
Blight refers to a specific symptom affecting plants in response to infection by a pathogenic organism. It is simply a rapid and complete chlorosis, browning, then death of plant tissues such as leaves, branches, twigs, or floral organs. Accordingly, many diseases that primarily exhibit this...
or flooding or fire
Fire
Fire is the rapid oxidation of a material in the chemical process of combustion, releasing heat, light, and various reaction products. Slower oxidative processes like rusting or digestion are not included by this definition....
will require more of its own ecological yield to sustain and re-establish a mature forest. While doing so, the sustainable yield may be much less.
In fisheries, the basic natural capital, or virgin population, must decrease with extraction. At the same time productivity increases. Hence, sustainable yield would be within the range in which the natural capital together with its production are able to provide satisfactory yield. It may be very difficult to quantify sustainable yield, because every dynamic ecological conditions and other factors not related to harvesting induce changes and fluctuations in both, the natural capital and its productivity.
Maximum sustainable yield
In population ecologyPopulation ecology
Population ecology is a sub-field of ecology that deals with the dynamics of species populations and how these populations interact with the environment. It is the study of how the population sizes of species living together in groups change over time and space....
and economics
Economics
Economics is the social science that analyzes the production, distribution, and consumption of goods and services. The term economics comes from the Ancient Greek from + , hence "rules of the house"...
, maximum sustainable yield or MSY is, theoretically, the largest yield/catch that can be taken from a species' stock over an indefinite period. Under the assumption of logistic growth, the MSY will be exactly at half the carrying capacity
Carrying capacity
The carrying capacity of a biological species in an environment is the maximum population size of the species that the environment can sustain indefinitely, given the food, habitat, water and other necessities available in the environment...
of a species, as this is the stage at when population growth is highest. The maximum sustainable yield is usually higher than the optimum sustainable yield
Optimum sustainable yield
In population ecology and economics, optimum sustainable yield is the level of effort that maximizes the difference between total revenue and total cost. Or, where marginal revenue equals marginal cost. This level of effort maximizes the economic profit, or rent, of the resource being utilized...
.
This logistic
Logistic function
A logistic function or logistic curve is a common sigmoid curve, given its name in 1844 or 1845 by Pierre François Verhulst who studied it in relation to population growth. It can model the "S-shaped" curve of growth of some population P...
model of growth is produced by a population introduced to a new habitat or with very poor numbers going through a lag phase of slow growth at first. Once it reaches a foothold population it will go through a rapid growth rate that will start to level off once the species approaches carrying capacity. The idea of maximum sustained yield is to decrease population density to the point of highest growth rate possible. This changes the number of the population, but the new number can be maintained indefinitely, ideally.
In most fisheries, the population has been decreased so significantly from their native populations, that the only way to increase production is to decrease production, and wait for populations to recover. Establishing limits is a perennial difficulty.
MSY is extensively used for fisheries management. Unlike Schaefer's logistic model, MSY in most modern fisheries models occurs at around 30% of the unexploited population size. This fraction differs among populations depending on the life history of the species and the age-specific selectivity of the fishing method.
Unfortunately errors in estimating the population dynamics of a species can lead to setting the maximum sustainable yield too high (or too low). An example of this was the New Zealand Orange roughy
Orange roughy
The orange roughy, red roughy, or deep sea perch, Hoplostethus atlanticus, is a relatively large deep-sea fish belonging to the slimehead family . The Marine Conservation Society has categorized orange roughy as vulnerable to exploitation...
fishery. Early quotas were based on an assumption that the orange roughy had a fairly short lifespan and bred relatively quickly. However, it was later discovered that the orange roughy lived a long time and had bred slowly (~30 years). By this stage stocks had been largely depleted.
Optimum sustainable yield
In population ecologyPopulation ecology
Population ecology is a sub-field of ecology that deals with the dynamics of species populations and how these populations interact with the environment. It is the study of how the population sizes of species living together in groups change over time and space....
and economics
Economics
Economics is the social science that analyzes the production, distribution, and consumption of goods and services. The term economics comes from the Ancient Greek from + , hence "rules of the house"...
, optimum sustainable yield is the level of effort (LOE
Loe
Loe or LOE may refer to:People:*King Loe, semi-legendary king of Maui*Erlend Loe, Norwegian novelist*Kameron Loe, American baseball pitcherPlaces:*Loe, Estonia, a village in Estonia*The Loe, also known as Loe Pool, Cornwall, UK...
) that maximizes the difference between total revenue and total cost. Or, where marginal revenue equals marginal cost. This level of effort maximizes the economic profit, or rent, of the resource being utilized. It usually corresponds to an effort level lower than that of maximum sustainable yield.
In environmental science
Environmental science
Environmental science is an interdisciplinary academic field that integrates physical and biological sciences, to the study of the environment, and the solution of environmental problems...
, optimum sustainable yield is the largest economical yield of a renewable resource achievable over a long time period without decreasing the ability of the population or its environment to support the continuation of this level of yield.
Annual Sustainable Yield
Annual Sustainable Yield (ASY) is defined as biomass that can be harvested from a fish population each year without resulting in a decline. ASY is dynamic and is adjusted based on population levels and performance of previous years fisheries.See also
- Sustainable yieldSustainable yieldThe sustainable yield of natural capital is the ecological yield that can be extracted without reducing the base of capital itself, i.e. the surplus required to maintain ecosystem services at the same or increasing level over time. This yield usually varies over time with the needs of the...
- Sustainable fisheriesSustainable fisheriesSustainability in fisheries combines theoretical disciplines, such as the population dynamics of fisheries, with practical strategies, such as avoiding overfishing through techniques such as individual fishing quotas, curtailing destructive and illegal fishing practices by lobbying for appropriate...
- Population dynamics of fisheriesPopulation dynamics of fisheriesA fishery is an area with an associated fish or aquatic population which is harvested for its commercial or recreational value. Fisheries can be wild or farmed. Population dynamics describes the ways in which a given population grows and shrinks over time, as controlled by birth, death, and...