Estimating discard survival

Latest Cooperative Research Report, No. 351, provides a state-of-the-art review of the current best practice for methods to estimate discard survival.
Published: 20 September 2021

​​​​​“Discards are the portion of a catch of fish which is not retained on board during commercial fishing operations and is returned to the sea”  

On 1 January 2014, the European Union introduced a phased discard ban or “Landing Obligation” for regulated species, as part of Common Fisheries Policy (CFP). Since January 2019, the Landing Obligation has been fully in force. 

In 2021, in the post-Landing Obligation world, it may appear that a report on discard survival has little relevance. However, the Landing Obligation policy includes a high survival exemption (HSE) for “species for which scientific evidence demonstrates high survival rates, taking into account the characteristics of the gear, of the fishing practices and of the ecosystem” (Article 14, paragraph 4b). The HSE generated considerable interest from stakeholders, who wished to demonstrate that their particular fisheries did in fact have a suitably high survival rate for discarded unwanted catch. 

Research aimed at determining whether aquatic organisms survive after being caught and subsequently released has been conducted over many decades. However, in 2014, there had been no comprehensive assessment of all the scientific methods and approaches that can be employed to estimate the survival of discarded fish and other aquatic animals. To that end, the Workshop on Methods for Estimating Discard Survival (WKMEDS) was established in January 2014, to provide guidance on best practice for methods to quantify the survival of discarded, unwanted catch. WKMEDS published its first preliminary guidance​ on best practice for survival estimation methods in April 2014. 

This preliminary guidance provided the framework for WKMEDS to develop and apply these methods over the following years and to gather evidence in support of applications for HSEs. The publication of CRR 351 ICES Guidelines on Methods for Estimating Discard Survival is the culmination of the collective research, providing a state-of-the-art review of the current best practice for methods to estimate discard survival.


There are three main approaches for conducting discard survival assessments presented in CRR 351. 

Discard subjects should be assessed on their vitality (e.g. activity, reflex responses, and injuries) to quantify “at-vessel” or “immediate” mortality levels. The vitality score can then be combined with either captive observations and/or tagging, to be used as a proxy for survival likelihood. 

Captive observations are carried out on subjects that have gone through the catch and sort process and then held in captivity for a sufficiently long period to determine their fate. Tagging involves release to monitor behaviour/physiological status, determining both post-release fate and survival estimates from the number of returned tags.

The group recommends that survival assessments should: 

  • be representative of the discarded catch and practices in commercial fishing, ideally at a metier scale;  

  • utilise one or more of three methods: vitality assessment, captive observation and/or tagging observation;  

  • clearly define the state of death for the species of interest, preferably using multiple criteria pertinent to the chosen method; 

  • avoid biasing results through observation induced mortality, and wherever possible demonstrate this using appropriate controls;  

  • monitor the subject animals at a frequency and over a sufficient period to describe any delayed mortality attributable to the catch-and-discarding process;  

  • incorporate careful design and analysis to ensure that the results are scientifically valid, while optimizing the use of resources and subject animals; and 

  • where practical, integrate two or more of the methods to increase the scope of the investigation, as well as improve the accuracy, precision, and applicability of discard survival estimates. ​

CRR 351 ICES Guidelines on Methods for Estimating Discard Survival, edited by Michael Breen and Tom Catchpole can be viewed and downloaded in ICES library​.​​

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Estimating discard survival

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