Official Statistics

Bluefin Tuna Catch and Release Recreational Fishery (CRRF): Methodology

Published 19 March 2025

1. Background

In 2024, the UK opened an English Catch and Release Recreational Fishery (CRRF) for Blue Fin Tuna (BFT) for permitted vessels only. The fishery allows for permitted vessels to be used to ‘catch and release’ BFT by rod and line, for a defined period in English waters. The MMO is responsible for issuing permits, and permit numbers are proportionate to the amount of quota available to cover incidental BFT mortalities. Vessel owners and skippers are both liable for ensuring that legislative requirements are followed. Briefly, the legislation outlines how the fishery must be exclusively ‘catch and release’ and how all BFT CRRF trips must be reported to the MMO within 24 hours of return. (The Sea Fisheries (International Commission for the Conservation of Atlantic Tunas) (Amendment) (No. 2) Regulations 2024).

To receive and maintain their permit, vessel owners are obligated to submit data on their trips and associated catch, which the MMO collects for operational purposes including monitoring and managing the fishery throughout the season. The MMO is also required to submit data to the International Council for the Conservation of Atlantic Tuna (ICCAT) to fulfil the UK’s reporting obligations as a contracting party.

The 2024 official statistics release is reflective of the information received by the MMO from permit holders for the season’s fishery. The statistics release covers vessel numbers, vessel activity, vessel outcomes, gear usage, the number of trips, the number of BFT caught, the trip success rate, the catch per unit effort, the length of the BFT, the estimated weight of the BFT, the release status of the BFT, and the quota uptake from the fishery. 

2. Data Source

Data from the fishery is collected via a trip report questionnaire that must be provided by vessel owners or skippers within 24 hours of return. The questionnaires are self-submitted and are submitted via the Qualtrics platform.

Submissions consisted of vessel and owner details, locations (ICES Statistical Rectangles), gear used (at the trip level), bycatch information and several BFT related questions.

On the BFT, the submissions required the skipper / vessel owner to enter the total number of BFT caught per trip, as well as the straight fork length (inches), fight time (minutes), recovery time (5-minute groups i.e. 0-5min) and release status of each individual fish.

Permit holders were required to make submissions to the database regardless of whether trips were successful in terms of BFT capture.

2.1 Processing

Permit holder submissions are imported to an integrated development environment for processing. The permit holder submissions are merged to MMO vessel licencing information that identifies vessel categories (private or charter). The merge is conducted using a unique identifier combining vessel name and permit number.

The extracted data is cleaned to address issues associated with user input error on vessel names and permit numbers. Errors are identified by filtering to the list of correct IDs. Erroneous entries are then manually assigned to the correct ID allowing the correction to be applied.

To estimate weights from individual length measurements, the straight fork length is first converted from inches to cm before being converted to round weight (RWT). Note that lengths entered as <=3 inches, or that refer to meters, were treated as entries in meters and are converted accordingly.

The relationship applied for the conversion is:

RWT (kg) = alpha x (SFL(cm)^beta), where alpha = 3.51 x E ^-5 and beta = 2.8758

The applied SFL (cm) to RWT (kg) relationship is sourced from Table 2 of Rodriguez-Marin et al., 2016, as applicable for Eastern Atlantic BFT stocks and consistent with the approach used in the 2021 – 2023 English scientific Catch and Release Tagging (CHART) programme.

3. Disclosure Control

To avoid the disclosure of any personal data contained within permit holder submissions, the following steps were taken:

• All vessel and owner details are removed as they are considered personal data under the Data Protection Act 2018 (Data Protection Act 2018)

• The reported locations (ICES Statistical Rectangles) detailed in the submissions were removed to avoid disclosure of activity that could be linked to vessels in regions with few registered vessels.

• The dates of activities reported in the submissions were aggregated into weeks to avoid the disclosure of vessel activity on specific days. Note that from 3rd of August to 31st of December is 21 weeks and 4 days, and as such week 22 only consists of 4 days.

4. Revisions policy

The Marine Management Organisation policy is to revise or produce revised figures each year to ensure that users have access to the latest data available. There are several causes of the revisions made in this publication:

1. Receipt of additional data. Despite strict data reporting requirements, some data are not received or entered at the time of publication.

2. Revisions to data sources. Corrections are made to database entries throughout the year where these are thought to be incorrect. Verification was sought from permit holders for entries that were outside of the expected ranges on BFT sizes and the reported activity location.

3. Rectification of data processing errors. Where data are found to have been incorrectly processed for a previous publication, these errors are corrected as soon as possible.

Users should always refer to the latest figures published by the Marine Management Organisation. Previous editions of all publications are made available online on the Marine Management Organisation website should users wish to examine the effect of revisions in further detail.

The Marine Management Organisation adheres to the Department for the Environment, Food and Rural Affairs’ policy on revisions and errors. Further information can be found in the Statement on Revisions and Errors at: https://www.gov.uk/government/publications/defra-policy-statement-on-revisions-and-corrections

5. Coherence with other sources

• The statistics presented here are comparable to other catch and release fisheries for BFT in the UK and adjacent waters. Key texts include the English CHART programme reports (2021-2022) and ICCAT summaries (2021-2023).
  • Cefas CHART page: CatcH And Release Tag (CHART) Scientific Data Collection Programme for Atlantic Bluefin Tuna (BFT) - Cefas (Centre for Environment, Fisheries and Aquaculture Science)
  • ICCAT Report: https://www.iccat.int/Documents/CVSP/CV081_2024/n_5/CV08105161.pdf
• This recreational data set is distinct from the MMO’s published commercial fishery statistics in that it does not contain information on landings.

6. Glossary of Terms:

Catch per Unit Effort - Catch per Unit Effort (CPUE) is calculated as the number of BFT hookups to the number of trips. 

Charter Vessel - Charter vessels in the CRRF were vessels that took paying anglers out on trips targeting BFT.

Daisy Chain - Daisy chains are a rod and line fishing gear that tow a string of lures on a single line with the final lure containing a hook. 

Fight Time - The period between the fish taking the hook (hook up) and being brought alongside the vessel.

Hookup - A hookup is determined by when a Blue Fin Tuna takes the hook and is effectively caught by the fisher.

ICES Statistical Rectangles – International Council for the Exploration of the Sea’s Statistical Rectangles are a gridded, latitude-longitude based area notation system covering the north-east Atlantic region. Each rectangle is denoted by 1 degree of longitude by 0.5 degrees of latitude.

Private Vessel - Private vessels in the CRRF were vessels that were for private use and did not take paying anglers on trips.

Recovery Time - The time allowed for the fish to recover prior to being released from restraint and returned to the wild. Recovery time groups were “0-5 minutes”, “5-10 minutes”, “10-20 minutes” and “over 20 minutes”.

Release Status - The condition the fish was in at the point of release.

Spreader Bars - Spreader bars are a rod and line fishing gear that tows multiple lures in a row perpendicular to the line, with one of the lures containing a hook.

Straight Fork Length - Straight Fork Length (SFL) is the straight-line distance from the tip of the upper jaw to the fork of the tail. 

Success Rate - Trip success rate is calculated as the number of successful trips as a percentage of total trips. A trip is determined successful if a hookup occurred.