Fishing mortality in the Barents Sea
The Barents Sea is an important fishing area. Every year large quantities of primarily cod, haddock, capelin as well as some shrimp, Greenland halibut and deep-sea redfish are caught.
What is being monitored?
Cite these dataInstitute of Marine Research (2021). Fishing mortality in the Barents Sea. Environmental monitoring of Svalbard and Jan Mayen (MOSJ). URL: http://www.mosj.no/en/influence/fishery-freshwater-fishing/fishing-mortality-barents-sea.html
|Northeast arctic cod||Institute of Marine Research||0.2202||0.22||0.0832||-0.0328||-0.0849||-0.164||-0.0202||-0.0201||-0.081||-0.2875||-0.4212||-0.468||-0.463||-0.4717||-0.4974||-0.4693||-0.4414||-0.4216||-0.4103||-0.3534||-0.3185|
|Deep sea redfish||Institute of Marine Research||-0.062||-0.067||-0.071||-0.061||-0.076||-0.081||-0.078||-0.075||-0.042||-0.059||-0.068||-0.071||-0.069||-0.068||-0.07||-0.071||-0.058||-0.048||-0.035||-0.042||-0.034|
|Northeast arctic haddock||Institute of Marine Research||-0.31||-0.304||-0.402||-0.405||-0.429||-0.363||-0.353||-0.334||-0.381||-0.415||-0.479||-0.511||-0.529||-0.538||-0.564||-0.606||-0.602||-0.569||-0.515||-0.387||-0.392|
Fishing mortality due to fisheries is one of several mortality factors for fish. The instantaneous total mortality rate (Z) is calculated from a clearly defined formula, where the mortality rate for a year class of fish one year is determined by the number of fish at the start of the year and the number of fish at the start of the following year. Total mortality is all the mortality in the stock and is therefore a measure of how many fish disappear from a given year class during the year.Total mortality can be divided into two:
1. Mortality (F) as a result of fishing
2. Natural mortality (M) as a result of predation, disease etc.
Fishing mortality for a species is thus a complicated measure for several year classes. For example, in the case of cod, an average of the annual classes from 5 to 10 years, designated as F5–10, is often used. However, it is not easy to select certain year classes over others as fishing mortality varies with age and size of fish. Young fish have the highest mortality rates, although they are not fished to any great extent and can thus have low fishing mortality, but high natural mortality.
The fishing mortality (F) is usually between 0 and 1, and is proportional to the catch effort. A doubling of F is almost a doubling of the catch effort.
The following factors are included in the measurements: Critical spawning stock level (Blim), the precautionary reference point for spawning stock biomass (Bpa) and B-target, the spawning stock level one are aiming for/ trying to achieve. Critical fishing mortality level (Flim), the precautionary reference point for fishing mortality (Fpa) and fishing mortality consistent with achieving Maximum Sustainable Yield (FMSY). “About the monitoring” gives more information on these terms.
Flim is the upper limit for F to ensure sustainable fisheries. When advice is offered, the F value is usually given as FMSY. If there is negative development in both the stock and recruitment, and the fishing mortality remains below the reference value over time, measures are taken to protect the stock and reduce the fishing mortality. For instance, quotas will be regulated.
The monitoring is not certified, but the methods used are quality assured and to a large degree coordinated between Norway and Russia. Data are collected in several contexts, and data from the commercial fishery origins both from fishery reports and statistics from the Directorate of fisheries.
The indicator applies only to fishing mortality for cod, haddock and deep sea redfish in the management plan area of the Barents Sea.
Reference level and action level
The stocks are managed mainly in accordance with agreed management plans, which include a harvesting regulation defining how fishing mortality must be reduced when the spawning stock biomass falls below a certain level.
To ensure sustainable fisheries, a critical limit for fishing mortality for many fish stocks (Flim) has been set. In recent years, however, the fishing mortality that is expected to produce the maximum sustainable yield of fisheries (Fmsy) has become governing when the International Council of the Sea (ICES) provide countries advice on sizes of fishing quotas. The indicator is based on the actual deviation in estimated fishing mortality (F) related to the recommended Flim.
Deviations between the calculated actual fishing mortality for the species, and critical fish mortality level (Flim) recommended by ICES, is calculated with 95% uncertainty, but not presented here. For some species the precautionary value Fpa is recommended. This is used in variance calculation when Flim is not given.
Status and trend
Throughout history, fisheries have had a clear impact on commercial stocks with following impacts on the ecosystems. Fishing mortality is a measure of the proportion of fish stocks that are fished. The extent of fishing mortality is included in the assessments made when determining fishing quotas and harvesting rules. The data is gathered from calculations by the International Council for the Exploration of the Sea (ICES).
The fishing mortality is affected by the amount of fish landed by the fisheries and is thus related to the harvest rate. If the fishing mortality is calculated to be below the precautionary value (Fpa), the stock is harvested sustainably
Fish mortality is an important part of the quota agreements. In the case where a fish stock undergo low development rate, the fisheries will receive smaller quotas and it may also lead to extended time- and area restrictions for the fisheries.
The capelin stock is an exception and has greatly declined from 2013 to 2016. The capelin fishing was stopped from 2016 and has still not opened in 2020. The capelin's short life span and the fact that it is a one-time-spawner makes the calculation method for fish mortality not suitable for this species.
The stocks of cod and capelin are managed in context, taking account of the cod grazing on capelin and the capelin's importance as food for cod. Capelin fishing has also been stopped several times previously (1987-1990, 1994-1998, 2003-2007). Impact on capelin stocks from cod, herring and other species are believed to be greater than from fishing.
About the monitoring
- Blim = Limit reference point for spawning stock biomass
- Bpa = Precautionary reference point for spawning stock biomass
- Flim = Limit reference point for fishing mortality
- Fpa = Precautionary reference point for fishing mortality
- Fmp = Fishing mortality reference point as defined in management plans
- FMSY = Fishing mortality consistent with achieving maximum sustainable yield
- F = Instantaneous rate of fishing mortality
- Z = Total mortality
- M = Natural mortality
A spawning stock which is calculated to be at a level that most likely will give good recruitment has good reproductive ability (the spawning stock is above Bpa). Good recruitment presupposes that environmental factors which influence fry survival are favourable.
When the level of the spawning stock is calculated to be such that there is increasing likelihood of it giving reduced recruitment, the stock is at risk of having reduced reproductive ability (the spawning stock is below Bpa, but above Blim). This, in turn, assumes that environmental factors are favourable for recruitment. Should the spawning stock be calculated to be at a level which in all probability will result in poor recruitment irrespective of environmental conditions, the stock is said to have an diminishing reproductive ability (the spawning stock is below Blim).
Fishing mortality is connected with the degree of harvesting. If the fishing mortality is calculated to be below the precautionary level (Fpa), the stock is said to be harvested sustainably. If the fishing mortality is calculated to be above the precautionary level (Fpa), but below what ICES has defined as the action limit for sustainability (Flim), there is a risk that the stock cannot be sustainably harvested. Then there is a greater likelihood that the fishing mortality is at a level which will lead the stock biomass below the precautionary level (Bpa). If the fishing mortality is calculated to be above the action limit for sustainability (Flim), the stock is not harvested sustainably.
Places and areas
Relations to other monitoring
- Monitoring programme
- International environmental agreements
- Voluntary international cooperation
- Related monitoring