Fisheries are meant to influence the ecosystem by removing sustainable quantities of fish as food for humans. The fishery is, however, not considered sustainable if it impairs the recruitment of the fish stocks. Single species management often focuses on measuring the status of the fishery in relation to benchmarks called biological reference points (BRPs). BRPs for single species management are usually defined in terms of fishing mortality rate (F) and total or spawning stock biomass (TSB or SSB) and in terms of target and limit reference points.
Limit BRPs suggest maximum levels of F and minimum levels of B that should not be exceeded. These BRPs are then compared to estimates of F and B from stock assessments to determine the state of the fishery and suggest management actions.
The limit reference point for fishing mortality, Flim, will eventually bring the spawning stock down to Blim, below which the recruitment will be impaired. Flim may hence be used as an indicator for not sustainable exploitation and negative influence on the stock and the ecosystem. This may, however, not be considered as sufficient protection. Smaller and younger adults resulting from high fishing pressure have a lower reproductive potential than adults of a wider range of sizes and ages. The harvest rate and fishing pattern should hence fit with these biological requirements.
Northeast Arctic cod, haddock and saithe
Figure 4.4.1 shows the annual fishing mortalities of the Northeast Arctic cod, haddock and saithe stocks relative to the critical exploitation level Flim. Since 1985 the exploitation rate has in some periods been critically high, especially for cod. This seems to have improved in recent years (because of the harvest control rule and better control and enforcement), and although the exploitation rate may have been too high to fully utilize the production potential in the stocks, it may be concluded that the exploitation of these three stocks since 2000 have been sustainable and has not influenced the ecosystem negatively by impairing the recruitment.
Golden redfish (Sebastes marinus) and Greenland halibut
For golden redfish and Greenland halibut no limit reference points have been suggested or adopted. ICES has, however, in earlier assessment working groups for several stocks estimated the exploitation rate Fmed which is the fishing mortality that balance the number of fish caught and the number of fish recruiting to the fishable stock. For the Greenland halibut stock Fmed was estimated to 0.14 y-1. It should be noted that the time series of Greenland halibut fishing mortalities are considered imprecise due to errors in former age readings. Experience from other Sebastes stocks, e.g, in the Pacific and in the Irminger Sea, suggests that annual harvest rates of such slow growing and long-lived species should not exceed 5% if the stock is recruiting normal. This corresponds to a fishing mortality of 0.05 y 1, and this level is shown as a reference for the maximum sustainable exploitation rate for golden redfish in Figure 4.4.2. At a time when this stock is not recruiting normal even an annual exploitation rate of 5% may be too high. It can thus be concluded that the current fishery of golden redfish is too intensive and may have a negative influence on the ecosystem and the stock itself. For Greenland halibut, after many years of overexploitation of the stock the current exploitation seems, with some reservations due to an imprecise assessment, to be sustainable and hence not influencing the ecosystem negatively.
Beaked redfish (Sebastes mentella)
There exist at present no analytical assessment or reference points for this stock. From scientific surveys in the Barents Sea and Svalbard areas (Spitsbergen archipelago), it is confirmed that the stock is historically low taking all age groups into consideration, and this situation is expected to remain for a considerable period irrespective of current management actions. A directed pelagic fishery for S. mentella in international waters (outside EEZ) of the Norwegian Sea has developed since 2004. In 2009 this fishery is limited by a total quota of 10 500 tonnes. Results from pelagic surveys conducted since 2007 indicate a significant mature biomass of beaked redfish in the Norwegian Sea, but the estimate is uncertain. Since the stock produced very few recruits from 1991 to 2005, the recruitment to the fishable and mature stock in the next 12-15 years will be low. ICES hence states that it is necessary to prevent the stock from declining further and to maintain measures to protect this stock from bycatch in other fisheries. ICES recommends that there should be no directed trawl fishery on Sebastes mentella in Subareas I and II in 2010. Some signs of improved recruitment in the Barents Sea and Svalbard areas are found. These recruits need protection and careful monitoring.
Larvae and juveniles of all groundfish species are important predators on zooplankton. It is hence important for a sound ecosystem that there are sufficient plankton eaters present to utilize the plankton production and convert this into production of fish, both as food for humans, but also as food for other fishes and sea mammals that depend on fish prey. It is therefore not sufficient to manage the fish stocks to the extent that the recruitment is not impaired as seen from a single species point of view, but rather to maximize the larvae production as a valuable food contribution to the ecosystem as a whole.
Capelin
The fishery for capelin is regulated by quotas set according to a harvest control rule enforced by the Norwegian-Russian Fishery Commission. The harvest control rule is considered by ICES to be in accordance with the precautionary approach to fisheries management. The fishery is restricted to the pre-spawning period and the exploitation level is regulated based on a model taking natural mortality including predation from cod into consideration.
Polar cod
In recent years the fishery has been at a very low level compared to stock level, implying a low exploitation level which will not influence the stock.
Other fish species
Information about the species composition in the Norwegian fisheries north of 67N is available from the Norwegian Reference fleet (NRF), i.e., 17 high-seas and 10 coastal fishing vessels contracted by the Institute of Marine Research. Table 4.4.1 shows the species composition in the trawl and longline catches by the NRF during autumn 2008. Such data are now routinely being collected from these vessels’ fishery every day. What impact the fishery may have on all these species and the ecosystem as a whole will be a subject for further research.
Information about the total species composition in the Russian bottom trawl fisheries in Barents Sea and adjacent waters is available from the 30 high-seas fishing vessels with sea-observer of PINRO (total 3063 day at sea in 2008), and which is considered representative for the whole fleet (Table 4.4.2). The data were collected all year round and in all fishing areas of the Russian bottom trawl fleet (Figure 4.4.3).
