Download8 Use of Living Marine Resources

Too many fish stocks are still outside safe biological limits

The status of around 130 commercial fish stocks in the OSPAR area is assessed annually by ICES as a basis for advice to fisheries authorities on the management of fishing. The approach used is to assess individual fish stocks in terms of spawning stock biomass (SSB), representing the total weight of fish in the stock able to spawn, and fishing mortality (F), representing the fishing pressure on the stock. An analysis of 37 stocks covered by ICES in the OSPAR area for which there was an agreed assessment in 2008 showed that around 45% of these stocks had a significantly higher level of SSB in 2007 compared with 1997, while around 60% of stocks had a significantly lower fishing mortality Figure 8.4. This analysis shows that the key stock parameters have been moving in the right direction for many stocks suggesting that recent efforts in fisheries management are having the desired effect of pushing exploitation rates downwards. However, a number of the fish stocks considered by this analysis remain beyond safe biological limits according to the ICES precautionary approach.

Within the fisheries management framework the use of SSB and F is guided by defined reference points. These provide an expression of the status of the stock. For SSB, these reference points include a limit reference point (B_lim) below which reproductive capacity is considered to be impaired and there is a probability of stock collapse, and a precautionary limit reference point (B_pa) which, traditionally, has been the reference point below which stocks are described as being outside safe biological limits. Since 2004, stocks with an SSB below B_pa but greater than B_lim have been described as being at risk of suffering reduced reproductive capacity. Reference points for fishing mortality (F_lim and F_pa) define whether harvest rates are sustainable; when the fishing mortality of a stock is greater than F_lim the stock is being harvested unsustainably. If SSB is kept above the agreed precautionary limit (B_pa) it is likely that the point at which there is a serious stock collapse will never be reached. The safest way to achieve this is to keep fishing mortality below the levels that would in the long term result in SSB below the agreed precautionary limit. Over the period 2003 to 2009 the number of stocks assessed by ICES as being outside safe biological limits (i.e. below the precautionary limit B_pa) varied from 23 to 28 while 8 to 11 stocks were assessed as being within safe biological limits Figure 8.5. In 2006, around 20% of fish taken from EU-managed waters was taken from stocks outside safe biological limits.

Improved management of stocks depends on developments in science and data quality

A key limitation in ICES stock assessments is that reference points have been defined only for stocks for which sufficient data are available. Some 48 to 56 stocks were designated as being of unknown status between 2003 and 2009 due to poor data Figure 8.5. Reforms under the EU Common Fisheries Policy have allowed the systems for providing fisheries management advice to become more transparent, to involve stakeholders, and to take into account ecosystem aspects. These are positive developments, but place increasing demands on the fisheries science for information and improved accuracy. ICES advice on these topics is generally followed when setting the TACs for the following year. For many stocks advice is based on weaker scientific evidence and historic catch figures, which give some indication of how the stock develops.

Status of stocks and assessment capacities varies between Regions

In the North Sea, OSPAR has established an Ecological Quality Objective (EcoQO) on commercial fish stocks based on the reference points for SSB. These have been defined for 15 stocks accounting for roughly 20% of total landings in the Region.

For other Regions, the availability of reference points varies Table 8.2. In Region I, a large proportion of landings are from stocks with defined reference points and only two stocks were not at safe levels in 2009 according to ICES. For Regions III and IV, reference points have been defined for relatively few stocks and other criteria are used to assess a large proportion of the stocks. For example, the stocks of whiting to the west of Scotland and in the Irish Sea are considered to be depleted on the basis of historic catch and landing information. Likewise no assessments of the herring stock to the west of Ireland and in the Celtic Sea have been made in relation to the reference points since 2003, but ICES has recommended either that a rebuilding plan is put in place or that there is no fishing. In 2009, a management plan was put in place for Celtic Sea herring. Some of the recovery plans in these Regions have started to show a positive effect, for example, the status of the northern stock of hake has improved in Regions III and IV, but the poor status of cod in Regions II and III is a continuing concern.

Most deep-sea stocks in Region V are data poor and analytical assessments cannot be undertaken. Many deep-sea species are particularly sensitive to exploitation as they are slow-growing and slow to reproduce. Some species aggregate around specific features, such as seamounts, which make them vulnerable to exploitation. OSPAR has included the orange roughy in its list of threatened and/or declining species. There is strong evidence that some deep-sea fish have been depleted around the continental slope in Region V. Current ICES advice for a number of deep-sea stocks emphasises their continued vulnerability. For example, ICES advised that there should be no direct fishing for blue ling during 2009 and 2010, while fisheries for greater forkbeard, blackscabbard fish and greater silver smelt should not be allowed to expand unless it can be shown that it is sustainable. Long-line fisheries appear to have depleted populations of giant redfish on seamounts of the northern Mid-Atlantic Ridge.

Several commercially important pelagic stocks straddle more than one Region. These include blue whiting, mackerel, herring and northern bluefin tuna. Of most concern is the status of northern bluefin tuna in the East Atlantic and the Mediterranean, for which, based on 2008 estimates, SSB has declined by 70% since 1950 with the bulk of this decline having occurred in the past ten years. In 2006, fishing mortality was estimated to be more than three times the level the stock could sustain. It is estimated that catches have been reduced to a level within the TAC set for 2008 following intense verification within EU waters in the Mediterranean. ICCAT has adopted TACs for the period 2009–2011 which continuously decrease, but substantial further reductions are needed to move towards sustainable levels. The distribution of mackerel has changed dramatically in recent years with a northward and westward movement of both immature and mature fish corresponding to changes in sea surface temperature. This presents challenges for allocation of quotas and supporting science.

Some improvements in demersal fish community structure

The structure of fish communities has been affected by fishing, with size composition altered and certain species no longer being found in some areas because mortality rates were unsustainable (e.g. common skate in Region II). Several characteristics of the fish community can be used to indicate its general health, for example, abundance/biomass/productivity, size composition, species richness, species evenness, and average life-history traits (such as age or length at maturity, growth rate or ultimate body length). OSPAR has set an EcoQO to indicate the general health of the demersal fish community in Region II based upon its size composition. An assessment of bottom trawl data for this QSR shows that – although size composition in the North Sea has not yet reached the level of the EcoQO – measurements of the other characteristics suggest that overall the general health of the demersal fish community in the North Sea has improved since 2000.

In Region III, nearly all aspects of the demersal fish community have improved over the past decade, particularly in the north, to the extent that the community is now in a similar state to that observed when data were first available in the early 1980s. The size composition and the abundance/biomass/productivity of the community are, however, still of concern. In the pelagic community in Region III, there has been an increase in smaller pelagic fish as a result of fishing pressure on their predators.

In Region IV, bottom trawl data were only available for the French continental shelf. Most aspects of the fish community are in a poorer state than in the mid-1980s. There have been improvements in life-history trait composition and species richness over the past decade, but little change in other indicators.

In Region V, bottom trawl data were only available for the Rockall Bank Plateau area. Species diversity and the size composition of the demersal fish community have improved over the past decade, while the abundance/biomass/productivity has changed little.

Over the past decade the size composition, species richness and species evenness aspects of the demersal fish community have all improved in Regions II, III and V, while only species richness has improved in Region IV. There has been little change in the abundance/biomass/productivity aspects, while Regions III and IV showed an improvement in life-history trait composition. Currently four of the five aspects are generally on parity with the situation prevailing when data in each Region were first available; the exception being the size composition of the community. Here the assessment indicates that, despite recent improvements, a full recovery to earlier conditions has yet to be achieved.

Physical disturbance has increased in some areas and reduced in others

Heavy towed demersal fishing gears (e.g. beam trawls, otter trawls, scallop dredges) cause considerable physical damage to seabed habitats and communities. They are a major source of disturbance on the continental shelf to habitats such as horse mussel beds, sea-pen and burrowing megafauna communities and Sabellaria spinulosa reefs. Considerable damage has been caused to cold-water corals and seamounts in deep waters with an estimated 30% to 50% of cold-water coral areas impacted in the Norwegian Sea. On the shelf in Region II, beam trawling is reported to have reduced benthic biomass by 56% and benthic production by 21% compared to an unfished situation Figure 8.6. Set nets and longlines also affect fragile ecosystems that can take many decades to recover. Some of the remaining fragile habitats have been protected by closing fishing grounds. Although shallower, coarser and higher energy sediments in general recover faster than deeper water muds, trawling on sandbanks has also caused long-term changes.

The area disturbed by fisheries has increased in some Regions. This is the case for the Great Mud Bank (Grande Vasière) in the Bay of Biscay (Region IV). In the North Sea (Region II), although there has been a decline in overall hours fished, fishing effort has moved to areas that were previously lightly fished due to closures elsewhere. Nephrops trawling has increased by 65% in some areas. Displacement and changes in the distribution of fishing effort can have significant impacts due to local variations in the sensitivity of seabed habitats to disturbance. This has to be accounted for if large declines in previously heavily fished areas are offset by even slight increases in previously unfished or lightly fished areas.

Fishing activity affects the food web

Changes in fishing activity, discards and fish community structure affect the food web and in turn populations of predators and scavengers. These relationships are complex and often linked to other factors. In Region I, there is a close link in the population dynamics of cod, herring and capelin in the Barents Sea and hence overfishing of one species can have a strong effect on the food web. Currently the management of these stocks is well balanced. The increase in smaller pelagic fish in Region III, as a result of fishing pressure on their predators, has been linked to a decline in abundance of Calanus zooplankton. Climate factors are also implicated with an overall decline in zooplankton abundance of 70% in the North-East Atlantic since the 1960s.

In the northern North Sea, there is evidence that the regime shift in the composition and breeding cycle of Calanus zooplankton in the 1980s (C. finmarchicus progressively replaced by C. helgolandicus) has depressed the productivity of lesser sandeel. The breeding success of black-legged kittiwake in the northern part of Region II appears to be linked to variation in local sandeel abundance, and is susceptible to being depressed as a result of industrial fishing activities.

The distribution of seabirds at sea is influenced considerably by the supply of discards that are used as food for some scavenging species. In Region IV, a strong link has been shown between the demersal fishing fleet in the Gulf of Cadiz and the Cantabrian Sea and the distribution of scavenging seabirds.

There are indications that fishing has affected the genetic evolution of a number of fish species in the OSPAR area, particularly with regard to the onset of sexual maturation (cod in the North-East Arctic and cod, haddock and plaice in the North Sea), but there is no overall assessment of the effect on all exploited stocks.

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