Monitoring changes in exploitation pattern for a data deficient species with decreased quota: northern North Sea ling


Ling is an economically important species for the Scottish whitefish fleet, but there has been a lack of data collection and research into the species. As such there is a lack of information to allow scientific assessment of the stock and it is therefore classed as a data deficient species. This project is the first dedicated study where information relating to ling biology, population dynamics and its fishery by the Scottish fleet in the northern North Sea was collected.

The work programme comprised three main parts:

  1. A review of existing information on ling biology and fisheries
  2. Implementation of a tallybook scheme to gather data on geographical distribution of fishing effort, and of catch and discard rates
  3. Implementation of an observer programme onboard fishing vessels and an enhanced fish market sampling programme to collect biological data from ling catches.

The main findings of the project are:

  1. The review of information shows that Norway dominates the ling fisheries in the NE Atlantic; Scotland takes 90% of the UK ling catch and mostly from the northern North Sea (IVa). Within IVa highest catches are from the shelf edge to the west of Shetland and areas around the N and NE of Shetland and in IVa there is a strong seasonal cycle with highest catches in late spring. Existing information on ling biology was sparse and many of the basic parameters unknown for ling in the northern North Sea.
  2. The tallybook data confirmed highest catches being concentrated around the north of Shetland and peaking during April – June. The seasonal discarding of large quantities of ling by some vessels due to quota restrictions was also confirmed and quantified.
  3. Observer data confirmed and quantified discarding rates during observed trips. Biological findings include the following: ling catches of mainly 50-90 cm (4-6 year old) fish; a spawning season mainly between April and July; a sex ratio strongly biased towards males, particularly during the spawning season; 71 cm female and 62 cm male lengths at 50% maturity and similar growth rates between males and females.

Start Date and Duration

The project began in September 2010 and ran until 31st August 2011.


The project was funded under Scottish Science/ Industry Partnership (SISP).

Deliverables/Outputs  - download the final report

Monitoring changes in exploitation patterns for a data deficient species with decreased quota: northern North Sea ling (pdf)