e-Digest Statistics about: Coastal and marine waters
Fish stocks
The main factors affecting living natural resources of the sea are fishing activity and natural factors. Anthropogenic inputs to the sea have little impact because concentrations of contaminants in sea water are generally low. To prevent over-exploitation of fish stocks it is important to balance fishing activity against the natural ability of fish stocks to regenerate.
Table 20 gives information about fish stocks and the age of recruits, young fish in the year class which is entering the fishery, for selected species for seas around the UK. The stocks figures, which are total biomass estimates, and the age of recruits relates to areas or divisions defined by the International Council for the Exploration of the Sea (ICES). These estimates are produced by ICES based on mathematical models which use time series information on international catches and fishing activity and estimates of relative abundance from research vessel surveys. Most stocks are over-exploited and some stocks are at historically low levels. Trends vary from species to species and stocks can also fluctuate substantially over relatively short periods, depending on the variable success of breeding from year to year.
Table 23 and Table 24 show time series of data on the status of finfish stocks around the UK, as identified by ICES. The data are derived from annual ACFM (Advisory Committee on Fishery Management) reports from May and October ACFM meetings, and are categorized according to the ICES definition of the state of stock. Since 1998, the state of stocks has been defined by ICES using new biological reference points based on the precautionary approach. Consequently, a new series has been started that is not fully comparable to pre-1998 data.
In 2004 ICES ceased the use of the terms inside or outside Safe Biological Limits (SBL) as previously used in these data. The phrases have been changed as follows:
- "Outside SBL" is now "Suffering reduced reproductive capacity"
- "At or close to SBL" is now "At risk of suffering reduced reproductive capacity"
- "Within SBL" is now "Stock at full reproductive capacity and harvested sustainably"
- "Harvested outside SBL" is now "Stock at full reproductive capacity but harvested unsustainably"
Biomass estimates are also used to evaluate whether the spawning population of each stock is sustainable. This is the biomass of mature fish size below which there is an increased risk that the reproductive potential of the stock will be diminished. For some stocks for which there is no indication of reduced breeding success at the lowest spawning stock biomass observed, this level is taken as sustainable. In 2005 the percentage of fish stocks around the UK which ICES has categorised as being at full reproductive capacity and harvested sustainably was 35 per cent. This means that for 65 per cent of stocks spawning levels were insufficient to guarantee stock replenishment.
Table 21 shows trends in total international fish landings of the fish stocks shown in Table 20.
Concentrations of toxic substances in fish are monitored. Table 22 gives heavy metals concentrations in fish muscle, and concentrations of organochlorine pesticides and PCBs in fish liver for selected species in both the North Sea and the Irish Sea. The biological variability present in any fish population makes the identification of temporal trends difficult, but there are indications of a reduction in concentrations for a number of the contaminants studied over the period covered.
Sustainability of fish stocks around the UK: 1990-2004
Trends vary from species to species and stocks can fluctuate substantially over relatively short periods. Most stocks are over-exploited and some stocks are at historically low levels, especially North Sea cod. The North Sea herring population was seriously affected by over-fishing in the 1970s and the fishery was closed between 1978 and 1982, allowing stocks to recover. See Tables 27 and 30 below.
The spawning stock biomass estimates are those produced in 2005 by the International Council for the Exploration of the Sea (ICES) based on mathematical models that use time series information on international catches and fishing activity and estimates of relative abundance from research vessel surveys.
For North Sea Cod in 2005, no assessment was possible and so the SSB time series was taken from the 2004 ACFM report.
In 2004, 25 per cent of reported fish stocks around the UK were at full capacity and were being harvested sustainably. These stocks had spawning levels which were sufficient to allow a good probability of stock replenishment. See Table 28 below.
There was an increase in the reported proportion of fish stocks considered to be sustainable between 1990 and 2004, but these stocks have seen a decrease of 5 per percent between 2003 and 2004. Since 2001, around 30 per cent of fish stocks around the UK have been at full reproductive capacity and being harvested sustainably, up from 5 per cent in 1990. However, this means that around 70 per cent of UK fish stocks have suffered reduced reproductive capacity and have been harvested unsustainably since 2001. For many of these stocks the ICES scientific advice is that the fishing rate should be reduced substantially in order to permit the stocks to recover.
Further Information:
- Data Tables:
- 27 North Sea fish stocks and stocks of North East Atlantic mackerel (spawning biomass index) (Key Fact) XLS
- 28 Sustainability of fish stocks around the UK XLS
- 30 North Sea fish stocks and stocks of North East Atlantic mackerel (mackerel as index) (Key Fact) XLS
- 20 Spawning Stock Biomass and Recruitment of Stock over the period for which assessments are available, North Sea: 1964-2004 XLS
- 21 International Fish Landings: 1963-2004 XLS
- 22 Average concentrations of contaminants in fish, by species and by area: 1983-1996 XLS
- 23 Fish stocks exploited by UK vessels (Sustainability of fish species) XLS
- 24 Fish stocks exploited by UK vessels (Bpa assessments) XLS
- Internet Links:
- Centre for Environment, Fisheries & Aquaculture Science (CEFAS)
- International Council for the Exploration of the Sea (ICES)
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Page last modified: 8 December 2004
Page published: 8 December 2004