1. Introduction

"Consider the case in which a target species and a by-catch species are equally susceptible to the fishing gear being used, but the by-catch species is present in lower initial biomass; if the target species is fished at its maximum sustainable yield, the by-catch species could be fished to extinction. [This is]..a particular problem with by-catch that has an aesthetic value such as marine mammals" (King 1999)

Incidental mortality in fishing gear is recognised as a major threat to marine mammals in many parts of the world (e.g. IWC 1994). In EU waters, previous studies on by-catch rates have shown that harbour porpoise (Phocoena phocoena) mortality in fishing gear is probably unsustainable (e.g. Lowry & Teilmann 1994). The International Whaling Commission (IWC) reported that incidental mortality of harbour porpoises exceeds sustainable levels in areas where adequate data on abundance and by-catch levels exist (IWC 1996). Other species reported to suffer an important by-catch mortality include the common dolphin (Delphinus delphis), e.g. in the Cantabrian Sea (N Spain, Nores et al. 1992), off Portugal (Sequeira & Ferreira 1994) and in the Celtic Sea (Kuiken et al. 1994; Kirkwood et al. 1997). Other marine mammal species suspected to be at risk include bottlenose dolphins (Tursiops truncatus), Risso’s dolphins (Grampus griseus), long-finned pilot whales (Globicephala melas), white-beaked dolphins (Lagenorynchus albirostris) and striped dolphins (Stenella coeruleoalba) (IWC, 1994). Knowledge of the effect of by-catches on other cetacean species is presently more patchy.

Small cetaceans in general and harbour porpoise, bottlenose dolphin and common dolphin in particular are identified in Community regulatory provisions as being threatened or vulnerable. Both harbour porpoise and bottlenose dolphin are listed in the EU "Habitats Directive"¹, while both species together with common dolphins and several other small cetacean species are cited in the Bern and Bonn Conventions².

The current state of knowledge about by-catch in the north Atlantic is variable. In the NW Atlantic, the mandates of the Marine Mammal Protection Act (MMPA) of 1972 and its subsequent amendments have ensured that population estimates and detailed knowledge of by-catch rates and their impact has been sought for ‘depleted’ stocks since 1990. In European waters the picture is less complete. This is largely a result of the fragmented system of project-based funding and the lack of an official body to oversee the problem in all the countries in the EU. The Common Fishery Policy (CFP) does not mention marine mammal by-catch and at the present time, much effort is being put into proposals for its reform in 2002.

A possible cause for concern is that separate proposals are being put together by groups representing different interests and these proposals may therefore prove to be mutually incompatible with those of other interested parties. For example, the Irish National Strategy Review Group on the Common Fisheries Policy, a group linking Irish government and fishing interests, has published a series of proposals for reform of the CFP. The only mention of marine mammals occurs in a short section on implementation of an action plan for biodiversity, in which there is a recommendation that "International Commission for the Exploration of the Sea (ICES) conduct a stock assessment of marine mammals and the effect they have on fisheries" (INSRGCFP, 2000).

Jefferson & Curry (1994) suggested that cetacean by-catch may be one of the "no technical solution problems" described by Garret Hardin (1968) in his famous essay "The Tragedy of the Commons". However along with some strategic efforts, a number of technical devices have been designed and tested in efforts to mitigate the cetacean by-catch problem. These efforts have met with varying degrees of success and while we believe that communication and education between scientists, managers and fishermen is the ultimate key to reducing the occurrence of by-catch, we feel that the technical advances are of great value and that Jefferson & Curry’s (1994) concern is unfounded.

Whilst remaining sympathetic to the problems inherent in trying to quantify and mitigate the by-catch problem, we aim to present here a positive and forthright review of the problem and the resources available at the present time to try to alleviate the problem. The present report reviews the main findings of the recent projects on cetacean mortality in European fisheries that the CEC (Commission of the European Community) has financed over the last decade as well as drawing material from published papers. We present a synthesis of the current state of knowledge about cetacean by-catch, including its occurrence, likely causes, and possible mitigation methods. We conclude with a series of practical recommendations and a proposal for a gear modification which we feel may further our progress toward reducing, if not solving, the problem of cetacean entanglement in fishing gear.

Department of Zoology tel: 44 (0) 1224 272459

University of Aberdeen fax: 44 (0) 1224 272396

Tillydrone Avenue, AB24 2TZ Aberdeen

Project leader: Dr. Graham J. Pierce e-mail:g.j.pierce@abdn.ac.uk

Other staff: Dr. M. Begoña Santos Vázquez e-mail:m.b.santos@abdn.ac.uk

Ms. Nicky Spencer e-mail:n.j.spencer@abdn.ac.uk

• To review available literature on cetacean by-catches, the fishing techniques concerned and methods for reducing by-catch

• To contact other scientists working in the field to ensure that all relevant grey literature is accessed

• To review criteria used for assessing the impact of by-catch

• To assess the likely impact of by-catches on cetaceans, focussing on species by-caught in European waters

The project was divided in two phases to take place over 10 months:

1. identifying and acquiring relevant literature

2. review, synthesis and writing

At the start of the project literature searches were carried out in the libraries of the University of Aberdeen and the Fisheries Research Services Marine Laboratory. This searches included books, journals and magazine articles and reports, theses, conference proceedings and presentations to institutions such as the IWC, the European Cetacean Society (ECS), the Society for Marine Mammalogy, the North Atlantic Marine Mammal Commission (NAMMCO), etc.

Literature searches were carried out, papers and books obtained and information has also been obtained through electronic discussion lists such as MARMAM and ECS-all. Literature searches were aimed to obtain information on the following points:

• cetacean species with high mortality in fishing gear

• fishing techniques and gears responsible for more deaths

• areas and periods with high by-catch rates

• criteria used for diagnosis of by-catch

• components (e.g. juveniles) of cetacean populations that are most prone to by-catch mortality

• criteria for assessing impact of by-catch on populations

• data on numbers of animals by-caught in different fisheries

• data on population sizes

• the impact of by-catch on cetacean populations

• suggested options for reducing by-catch

All references collected to date have been introduced in a bibliographic database (ENDNOTE) and it is planned to make them available in the project web page at the end of the project.

Letters providing a description of the project objectives and requesting information on research carried out in by-catch were sent to the co-ordinators of all projects and studies dealing with the subject financed by the EC between 1994 to 1999³. Letters were also sent to relevant scientists, organisations and government ministries.

Project staff attended three relevant conferences during the project period:

• 1^st Symposium on the Spanish Cetacean Society (SEC), Ceuta, Spain from the 24^th to the 27^th of February, 2000, "Hacia la Conservación de los Mamíferos y Tortugas Marinos en España [Towards the Conservation of Marine Mammals and Turtles in Spain]".

• 14^th Annual Conference of the European Cetacean Society with the theme of "Cetaceans in the Ecosystem: Defining Critical Habitat". Cork, Ireland, 2-5 April, 2000.

• 6^th Greenwich Forum Conference in the series "Re-thinking the Common Fisheries Policy – looking forward to 2002 with the theme "Subsidiarity: Fisheries Management & the CFP". Peterhead, Scotland, 7-8 September, 2000.

Attendance to these conferences gave us the opportunity to contact relevant researchers working in the field such as Dr. A.J. Read, Dr. C. Lockyer, N. Tregenza, Dr. P. Hammond, Dr. D. Goodson, Dr. S. Northridge, S. Berrow, etc. and attend talks on threats to marine mammals and the legislation in place to protect them in different countries. Leaflets with information on the project were distributed among participants of all events requesting information.

A web page has been set up to provide publicity for the project as well as to invite researchers and members of the public to provide information. The web page address is: http://www.abdn.ac.uk/~nhi104/seals/by-catch.htm