MSY (Maximum Sustainable Yield)
Maximum sustainable yield (MSY) refers to the maximum catch that can be sustainably harvested from a certain fish stock (fish school) over the long term, assuming that environmental conditions such as seawater temperature and nutrients do not change.
Understanding MSY isIt is used in resource management around the world because it is essential for keeping fish populations (schools of fish) growing at their fastest rate while continuing to produce without depleting the resource.
The basis of this idea lies in the research of researchers such as Russell (1931), Hjort et al. (1933), and Graham (1935) in the 1930s. Later, in the 1950s, the "surplus-production model" emerged, which made it possible to calculate MSY numerically based on the logistic growth curve (a curve that represents the population growth of an organism), and this became widely used (Schaefer, 1954).
density dependence(Density dependence)and carrying capacity
When deciding on MSY, it is important to"Density dependence"と"Carrying capacity""Density dependence" means that the population growth rate (growth rate) is affected by the density (number of individuals) of the population. "Carrying capacity" means the number of individuals that can live in a given habitat, when considering the conditions for food, shelter, and breeding partners.The maximum population size that a species can sustain on averageIt is estimated statistically from data such as the current population, growth rate, and environmental changes.
As a population approaches carrying capacity, the growth rate approaches zero, meaning the environment can no longer support any more individuals and births and deaths are balanced.
Conversely, when the population is small, there is an abundance of food and shelter, and growth rates are at their highest.
Theoretical concept of MSY
When a fish stock is at its carrying capacity, there is no room for it to grow any further. If we reduce the population by fishing a little, there will be "space" in the environment and the population will start to grow again.
A population grows fastest when the abundance is half its carrying capacity.
If we continue to catch this increased amount, we can sustain maximum catches without depleting the resources (this is the theoretical MSY).
There are two main methods for estimating MSY. The first, the "surplus production model," is a relatively simple method that uses data such as catch volume and fishing effort to determine the optimal catch volume that neither increases nor decreases the resource.
Another "age structure model" calculates sustainable catches more precisely based on biological information such as fish growth, maturity, mortality, and the size of fish that are most likely to be caught.
Limitations of MSY
MSY assumes density dependence, but the real environment is constantly changing.
"Carrying capacity" also depends on factors such as seawater temperature and nutrients.Environmental ConditionsBecause it changes depending onThere is no fixed MSY for a single fish species.
In addition, the age and size of the fish caught vary depending on the type of fishing gear and mesh size, which affects the growth and reproductive capacity of the population and ultimately changes the MSY value.
Criticism of MSY and subsequent developments
In applying the MSY concept to actual fisheries management, several problems were identified.
In 1977, Peter Larkin wrote an "epitaph" to the concept of MSY, pointing out its shortcomings:
・MSY isposes excessive risk to resources
-Regional productivity differencesdoes not take into account
-Impact on ecosystems other than target fishIgnoring
-Costs and social impacts of fishingdoes not take into account
-political pressureEasily influenced by
Thus, while MSY is theoretically appealing, it has been criticized for not adequately reflecting the complexity of real-world marine ecosystems and societies.
Nevertheless, MSY remains an important concept.
Nevertheless, MSY is stillBasic concepts of fisheries resource managementIt is considered important as a
Because of its ease of sharing, it continues to be used as a "standard for assessing the health of resources" in fisheries around the world.MSY is also an important pillar of international fisheries management and treaty frameworks.Has become.
