C7: Healthy seas: fish and shellfish populations

Interim Interim

Short description

This indicator tracks the health of our seas using assessments of fish populations (here separated into demersal communities and pelagic communities). It consists of 2 metrics. The first metric looks at the size of the fish in a community (Typical Length) and the second looks at the composition of fish communities (Mean Maximum Length). Together these metrics tell us about the health and status of fish communities. A healthy fish community will be made up of species in the expected ratio of numbers of individuals, and with individual species showing the age classes and sizes consistent with a healthy population. Typical Length: a reduction in the proportion of larger, older, fish (as measured by Typical Length) of several species, suggests the top (predator) level of the food web is in poor condition. Mean Maximum Length: if the species that tend towards larger individuals are depleted and smaller-bodied species become more abundant (shown by a reduction in Mean Maximum Length), the species composition of the community can change, suggesting prolonged periods of pressure. When the community is dominated by slow growing species (as expected at low Maximum Mean Length), the size structure is limited in its ability to recover (reduced Typical Length).

This indicator is not available for reporting in a finalised form. Further development of this indicator is required to include trophic guild biomass and therefore improve community classification. An interim indicator is presented here with communities classified as demersal or pelagic. The assessments used for this interim indicator have been reported under the UK Marine Strategy Part One (2019). Data on fish populations, analytical methods and assessment are available.

Note

While the currently available data predate the 25 Year Environment Plan, they provide the most recently available assessment of fish and shellfish populations. They enable a better understanding of a baseline from which to measure progress towards the goals of the 25 Year Environment Plan when the indicator is next updated.

Trend description

a) Typical Length of demersal and pelagic fish communities

In the Channel, northern North Sea and the eastern Irish Sea, the health of the demersal fish community has improved since the 1990s, with an increasing contribution of species that attain a large size (Typical Length). In the central and southern North Sea and on the shelf edge to the west of Scotland, the balance of species within demersal communities, relative to the early 1980s, has shifted towards smaller bodied fish (low Typical Length) indicating this community is in poorer health. In the northern North Sea no change in the Typical Length in the pelagic fish community is evident. The Typical Length of pelagic fish generally shows no long-term change at the sub-regional level in the Celtic Seas.

b) Mean Maximum Length of demersal and pelagic fish communities

In the central and southern North Sea and on the shelf edge to the west of Scotland, the balance of species within demersal communities, relative to the early 1980s, has shifted towards smaller species (low Mean Maximum Length), indicating this community is in poorer health. There has been no long-term change in Mean Maximum Length of demersal fish communities in the northern North Sea. Within the southern and central North Sea, the Mean Maximum Length of pelagic fish communities is declining suggesting the proportion of large or slow growing species is declining. There is no long-term change in the Mean Maximum Length in the northern North Sea.

Sub-categories

Choose categories from the dropdowns below to see different breakdowns of the data. Some will not be available until a higher level is chosen.

This table provides metadata for the interim or final indicator presented above.

Indicator name

Healthy seas: fish and shellfish populations

Indicator reference

C7

Outcome Indicator Framework theme

Seas and Estuaries

Headline indicator status

Health of our seas

Relevant goal(s) in the 25 Year Environment Plan
  • Thriving plants and wildlife
Relevant target(s) in the 25 Year Environment Plan
  • Making sure populations of key species are sustainable with appropriate age structures
  • Reversing the loss of marine biodiversity and, where practicable, restoring it
  • Ensuring that all fish stocks are recovered to and maintained at levels that can produce their maximum sustainable yield
Position in the natural capital framework
  • Condition of assets - seas
Related reporting commitments
  • Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR)
  • UK Marine Strategy (Marine Strategy Regulations 2010)
  • International Council for Exploration of the Seas (ICES)
  • Convention on Biological Diversity Aichi Target 6
  • Relevant to Sustainable Development Goal 14
Geographic scope

UK (Celtic Seas and Greater North Sea)

Status of indicator development

Interim

Date last updated

11 June 2021