Fishing mortality in the Barents Sea
The Barents Sea is an important area for the fisheries and large quantities of important fish like northeast arctic cod, northeast arctic haddock, deep-sea redfish, Greenland halibut and shrimps are caught. Capelin is fished when conditions allow for sustainable quota. Today, the Barents Sea stocks are sustainably managed.
What is being monitored?
Cite these dataInstitute of Marine Research (2020). 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||0.22||0.219||0.082||-0.033||-0.086||-0.166||-0.022||-0.023||-0.084||-0.291||-0.424||-0.471||-0.466||-0.475||-0.5||-0.471||-0.441||-0.418||-0.402||-0.34|
|Deep sea redfish||Institute of Marine Research||-0.059||-0.064||-0.067||-0.058||-0.072||-0.077||-0.074||-0.071||-0.04||-0.056||-0.065||-0.068||-0.066||-0.065||-0.066||-0.068||-0.056||-0.046||-0.034||-0.041|
|Northeast arctic haddock||Institute of Marine Research||-0.302||-0.298||-0.399||-0.404||-0.428||-0.36||-0.349||-0.329||-0.377||-0.409||-0.474||-0.507||-0.526||-0.536||-0.561||-0.604||-0.601||-0.569||-0.514||-0.379|
Fishing mortality as a consequence of the fisheries is one of several mortality factors for fish. The instantaneous total mortality rate (Z) is calculated on the basis of a clearly defined formula where the mortality for a year class of fish for one year is determined on the basis of the number of fish at the start of the year and the number of fish at the start of the following year. Total mortality concerns all the mortality in the stock and is therefore a measure of how many fish disappear from a given year class in the course of the year. It can be divided into human-induced mortality (F) due to fishing and natural mortality (M) due to 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 year classes from 5 to 10 years inclusive, termed F5–10, is often used. However, it is not easy to select some year classes rather than others because the mortality varies with the age and size of the fish. Young fish have the highest mortality, even though they are not fished to a significant 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 fishing effort. A doubling of F is almost a doubling of the fishing effort.
The following factors are used in the measurements: the limit reference point for spawning stock biomass (Blim), the precautionary reference point for spawning stock biomass (Bpa) and Btarget, the level of the spawning stock you are aiming for/trying to attain, the limit reference point for fishing mortality (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 limit reference point for fishing mortality 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 mortality. For instance, quotas are 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 with different methods, 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.
The stocks included in this indicator are mainly managed by management plans. Harvesting rules defines how the fishing mortality should be reduced when the size of the spawning stock drops below a certain level.
Status and trend
Fishing mortality is a measure of the proportion of fish stocks that are fished. If fishing mortality is estimated to be less than the precautionary level (Fpa), we say that the stock is harvested sustainably. If it is higher than the precautionary level, but lower than the International Council (ICES) has defined as critical fish mortality level (Flim), there is a risk that the stock is not harvested sustainably. Then there is an increased chance that the spawning stock could drop below the precautionary level.
The figure below shows fishing mortality for cod, haddock and rosefish in the Barents Sea. The situation is good for all these stocks, as harvesting has been sustainable for many years.
The size of the fishing mortality is included in the assessments made when fishing quotas and harvest rules are determined. If a fish stock has poor development, smaller quotas are set. In some cases extended time and area limited bans are set on fishing.
The state and development is satisfactory for most commercial fish stocks in the Barents Sea. The capelin stock is an exception, and has declined sharply from 2013 to 2016.The capelin fishing was stopped from 2016. Despite for an improvement in the contitions, it is still discouraged to harvest capelin, also in 2019.The capelin stock is still below the level where capelin fisheries are not expected to have an effect as reduced food availability for cod and other fish.
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 bigger than from fishing.
An evaluation of alternative harvesting rules for cod, haddock and capelin was commissioned by the Norwegian-Russian Fisheries Commission in 2015, and was presented by the International Council for Exploration of the Sea (ICES) in March 2016. The Norwegian-Russian Fisheries Commission chose to continue with the existing harvesting rules for haddock and capelin. For cod, the rule was changed so that the fishing mortality now increases when the spawning stock is high, and maximum change in quota from year to year has increased from 10 percent to 20 percent.
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, presupposes 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 unsound 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 that which ICES has defined as the action limit for sustainability (Flim), there is a risk that the stock cannot be sustainably harvested. There is then a greater likelihood that the fishing mortality is at a level which will take 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 said to be not harvested sustainably.
Places and areas
Relations to other monitoring
- Monitoring programme
- International environmental agreements
- Voluntary international cooperation
- Related monitoring