Fish Stock Assessment

Image of a boat fishing
 

The Marine Institute's Fisheries Ecosystems Advisory Services (FEAS) assess many of the key commercial fish and shellfish stocks around Ireland.

The overall aim of fisheries science is to provide information to managers on the state and life history of the stocks. This information feeds into the decision making process. Fisheries science, economic, social and political considerations all have an impact on the final management decision.

What is a stock?

A "stock" is a population of a species living in a defined geographical area with similar biological parameters (e.g. growth, size at maturity, fecundity etc.) and a shared mortality rate.

The aim of stock assessment

Stock assessment involves using mathematical and statistical models to examine the retrospective development of the stock and to make quantitative predictions to address the following fisheries management questions:

1) What is the current state of the stock?
2) What has happened to the stock in the past?
3) What will happen to the stock in the future under alternative management choices? 

Stock assessment framework

Ireland shares the Total Allowable Catches (TACs) for many stocks we exploit with our European Union partners. Due to this international dimension, many stocks need to be assessed in an international forum

Fisheries Ecosystems Advisory Services staff actively participate in around 20 international meetings associated with the stock assessment and advisory process on an annual basis, as well as carrying out assessments on many stocks in the inshore sector and non-TAC stocks that are of particular importance to Ireland. 

Stock assessment methods

FEAS employ a wide variety of recognised assessment models and statistical methods to assess the stocks of fish around Ireland.

These methods can be classified in groups:
1) Simple Holistic Methods
2) Complex Analytical Methods 

If we know about the stock size (biomass) and biology of the fish stock, we can estimate how many fish can be safely removed from the stock in order to ensure a sustainable resource.

Data requirements for stock assessment

Fisheries Ecosystems Advisory Services (FEAS) staff sample landings of marine fish and shellfish around the coasts of Ireland. In addition, the Fisheries Assessment Technicians sample discards and landings at sea on commercial vessels. Since January 2002 these sampling programmes have been enshrined in EC legislation, initially through EC Regulation 1543/2000 and now through EC Regulation 199/2008, concerning the establishment of a community framework for the collection, management and use of data in the fisheries sector and support for scientific advice regarding the Common Fisheries Policy. 

Sampling programmes provide information on the age structure. Fish are 'aged' to give an indication of the health of the stock. A broad range of ages signifies a healthy stock; a lack of young fish could mean poor spawning in a particular year; a lack of older fish may signify overfishing. 

Surveys provide important fisheries-independent data on structure, catch-per-unit-effort (CPUE), distribution, recruitment and biology of fished stocks.

Equally important are data on landings and catch per unit effort (CPUE) from the commercial fleet. FEAS work in close cooperation with the Department of Agriculture, Food & the Marine DAFM to analyse catch and effort data from the EC Logbooks. 

Industry and stock assessment

As fisheries develop, it is essential to involve the industry in the stock assessment process. These assessments may identify sustainable fisheries development opportunities.

In fully and over-exploited fisheries, stock assessment will help managers and industry by defining the risk associated with various management choices. Computer-based simulations can quantify the long-term gains from rebuilding stocks as well as the short-term costs required to rebuild.

A summary of the most recent stock assessments together with fisheries management advice from the Irish perspective are presented each year in the FEAS Stock Book.

In this section:

Total Allowable Catches (TACs)
Working with Industry
Data Collection
Ecosystems
Biologically Sensitive Area