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Fisheries management

The management of fish stocks is more effective if it is based on true biological stocks rather than arbitrary defined stocks and there could be severe effects of lumping together populations that have separate population genetics and population dynamics when managing species. Disregarding a complex population structure could for example mask a steady decline in estimates of spawning stuck biomass


Here you can find a step-by-step guide to successful genetic management of fisheries.

Step 1: Which species are you interested in?

Step 2: Does your species show a genetic structure? Click Species to find out.

Step 3: On what scale should management be based? See the table below.

Step 4. Do you have mixed stock fisheries? See definition below.

Step 5. Is there a risk of fishery induced selection? If you answer yes to the qusetions below there is a risk for negative evolutionary effects.

    a) Is the fishing not random, i.e you use size selective gear?

    b) Is a large proportion of the population fished each year?


 

In the following table we describe the concerns and recommendations related to management of species with different type of genetic structuring.

Type of structure Genetic concerns Other conserns Recommendation
No differentiation
No immediate risks
Demographic effects
Evolutionary effects
Global management is most effective, like for eel. 
Continuous change
Risk of local extinction
Risk of loss of local adapation
Demographic effects
Evolutionary effects
Regional management - stakeholders within the region need to collaborate.
Mixed stock fishing needs to be identified.
Discrete populations
Risk of local extinction
Risk of loss of local adapation
Demographic effects
Evolutionary effects
Local management - stakeholders within the local need to collaborate. To identify propal scale use the species maps.
Mixed stock fishing needs to be identified.
No information
Risk of local extinction
Risk of loss of local adapation
Demographic effects
Evolutionary effects
Monitoring is needed.

 

Demographic effects:  High fishing pressure could, apart from a declining population,   result in changed age and size structure of the population which could make it less productive. For example, for many species the big, old, females are especially important for production of young and if the age and size structure have changed due to fishing such that big and old fishes are lacking in the population the recruitment will be negatively affected.

Evolutionary effects: If the fishing is selective, for example targeting large individuals, and there is a heritable variation in life-history parameters such as growth and size/age at maturity in the population at hand, a selective fishery could result in genetic changes of these. For several species it has been shown that selective fishing on larger individuals have resulted in lowered size and age at maturity which also has led to a lower total production of the population. These genetic changes can be very hard to undo even if the selective fishing stops.

Local extinction: If the population is in some way structured, subjected to high fishing pressure and management is applied on a large scale there is always a risk that a local population will go extinct, despite that the population as a whole is not threatened. Depending on the degree of structure in the population it will take shorter or longer time for recolonisation to happen. If the structure are very high, i.e. populations are distinct, and migration between local population is very limited it is possible that the extinct local  population will never be replaced.

Local adaptation: The environment in the Baltic Sea are highly variable between different parts of the Sea and populations have during centuries adapted to local conditions.  The most prominent environmental factor for fish in the Baltic Sea is salinity which varies from saltwater condition in the Kattegat to almost freshwater conditions in the innermost parts of Gulf of Bothnia and Gulf of Finland. Local adaptation to different salinity conditions have for example been shown for cod, flounder and turbot. If a local population with a unique local adaptation is lost it will take a very long time to replace that population since even if migration between populations occur neighbouring populations are not adapted to the local conditions.

Mixed stock fishing: Mixed stock fishing occurs when genetically different populations that are either discrete or belongs to different parts of a continues change mix during parts of the year and fishing takes place during the time of mixing. This is a common problem when fishing is made on feeding aggreations that consists of several different populations. An example of this problem is the fishing on salmon from different rivers when they mix at sea.

 

CONTRIBUTORS
Teija Aho and Ann-Britt Florin, Swedish University of Agricultural Science, Sweden


Responsible editor: Teija Aho, Swedish University of Agricultural Science, Sweden 
You are welcome to contribute to the development of this section. Please add a comment or visit the Forum. 


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