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Assessment and reduction of the by-catch of small cetaceans


a. Develop methodologies for assessing the magnitude of marine mammal bycatch in selected EU fisheries.
b. Develop a framework for assessing the ecological importance of this by-catch, and collect relevant data.
C. Investigate the way in which the risk of by-catch varies in relation to gear type, environmental factors and season.
d. Develop a framework for assessing the relative costs and benefits of gear modifications and area closures for reducing by-catch, and the socio-economic impacts of such measures.
State of progress

Progress in year 1 of the project was slow because of delays in appointing new staff, illness of key staff members, and difficulties in establishing the independent observer scheme in some fisheries. Permission to extend the project by an additional 12 months was sought from the Commission and this was granted.

Estimates of by-catch rates are now available for all the target fisheries although it has only been possible to estimate total by-catch for the Swedish gillnet fishery in the Kattegat/Skagerrak Genetic analysis of material from by-caught and stranded animals has been used to identify at least two distinct populations of harbour porpoises in the North Sea, and to demonstrate differences between these populations and those in the Baltic and Kattegat/Skagerrak. Additional information on population structure from an analysis of contaminant levels, variation in tooth structure, and the composition of fatty acids in blubber supports this division.

There have been only one or two dedicated surveys of cetacean abundance in the areas used by the fisheries which are being studied in this project. In order to assess the ecological impact of the levels of by-catch estimated in this project information on a more detailed spatial and temporal scale is required. Studies are now underway to obtain this information from observations of cetaceans which have been collected opportunistically on surveys directed at other marine species. Studies of the movements of harbour porpoises using satellite-linked telemetry have been conducted.

Participants in the BY-CARE project have made a major contribution to discussions about the ecological consequences of the reported
by-catches of porpoises in the Scientific Committee of the International Whaling Commission and ' in the Advisory Committee of the Agreement on the Conservation of Small Cetaceans of the Baltic and North Seas. A model framework for evaluating these impacts has been developed and will be implemented in year 3.

Trials of acoustic alarms, to deter porpoises from becoming entangled in nets, have been conducted successfully in the Danish bottom set gillnet fishery-

Preliminary work has begun on developing a model framework to evaluate the effects of changes in fisheries practice on cetacean populations
and the catches and profitability of relevant fisheries.

IV. Achievements

A standardised methodology for monitoring by-catch of small cetaceans using independent observers has been developed and used to estimate by-catch rates in all of the target fisheries. These results have been used to estimate total by-catch in the Swedish bottom-set gillnet fishery in the Kattegat/Skagerrak.

Satellite-linked telemetry has been used to follow the movements of a harbour porpoise for 42 days.

Trials of acoustic alarms have indicated that use of these devices can result in a significant reduction in the by-catch rate for harbour porpoises in bottom-set gillnets.

V. Future actions

Independent observers will continue to monitor by-catch rates in the English and Danish gillnet fisheries and in the Irish drift net fishery. Samples from by-caught and stranded animals will continue to be analysed to determine the nature of the by-catch and to investigate population structure.

Estimates of total by-catch for each fishery, and estimates of cetacean abundance at appropriate spatial and temporal scales will be made,

A model framework for investigating the effects of by-catches on population status (particularly for the harbour porpoise in the North Sea) will be implemented. The relationship between by-catch rates and operational factors will be investigated.

The model framework for analysing the socio-economic implications of various management options designed to reduce by-catch will be developed.
Description of work

The effectiveness of a range of techniques for determining by-catch rates has been evaluated. A standardized technique, using independent observers placed on participating fishing vessels, has been agreed and used to estimate by-catch rates in English, Danish and Swedish bottom-set gillnet fisheries in the North Sea and Kattegat/Skagerrak, and in the Irish drift net fishery for tuna. The ecological importance of these by-catches is being evaluated first by estimating the additional mortality on individual cetacean populations caused by the by-catches, and then by evaluating the likely consequences of this for the status of each species.

The relationship between by-catch rates and various operational features of each fishery is being investigated. Trials of various modifications to gear, especially the use of acoustic alarms, have been carried out in the Danish gillnet fishery in the North Sea. A set of computer programs which can be used to establish a framework for evaluating the implications of various management actions is being assembled.

Funding Scheme

CSC - Cost-sharing contracts


Natural Environment Research Council
High Cross, Madingley Road
KY16 8LB St Andrews, Fife
United Kingdom

Participants (4)

Danish Institute of Fisheries Research
Charlottenlund Castle
2920 Charlottenlund
Stockholms Universitet
Svante Arrheniusvaeg 14-16, Frescati
106 91 Stockholm
Lee Maltings Prospect Row
University of Warwick
United Kingdom
Gibbet Hill Road
CV4 7AL Coventry