The Net Effect? - Whale and Dolphin Conservation Society

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6 The Net Effect? A WDCS report for Greenpeace Introduction 1.1 Bycatch worldwide The term bycatch refers to the unintended mortality of non-target species in fisheries. The phenomenon is common and widespread, affecting an extremely wide range of species from marine mammals, sea birds and turtles to sharks and numerous other nontarget fish species. The scale of this mortality is such that bycatch may affect the structure and function of marine systems at the population, community and ecosystem levels (Crowder & Murawski 1998). Indeed, bycatch is widely recognised as one of the most serious environmental impacts of modern commercial fisheries (Alverson et al. 1994; Dayton et al. 1995). It has been estimated that 23% of the global fisheries catch is thrown back into the sea – dead and wasted. This figure includes nontarget species as well as target species that cannot be landed because they are, for instance, over quota or undersized. This figure translates to some 20 million tonnes of marine life being discarded every year (Horsten & Kirkegaard 2002). Long-lived and slow-reproducing species such as sharks, turtles and marine mammals are likely to be most vulnerable to the depletion of populations through fisheries bycatch (Read 2000). In the case of harbour porpoises, it has been agreed internationally that an annual loss of even 1% of a population should be a cause for concern that merits investigation as a matter of priority (Bjørge & Donovan 1995). Indeed there are cases, such as that of the vaquita, a small porpoise found only in the Gulf of California, Mexico, where bycatch is driving a species to extinction (D’Agrosa et al. 2000). A recent study of estimated marine mammal bycatches in fisheries in the United States in the 1990s, extrapolated to figures for fishing effort worldwide, concluded that global bycatch of cetaceans (all whales, dolphins and porpoises) is likely to exceed 300,000 animals each year (Read et al. 2003). In addition to the large bycatches that are known and documented in some areas, the authors note that, with mortality levels on this scale, it is likely that important conservation problems exist that have not yet been identified and that bycatch is likely to be an important factor influencing the dynamics of many marine mammal populations. Cetaceans get caught in a very wide variety of fishing gear including active towed gears such as trawls and seines, hooks and lines, passive gillnets and driftnets and even the lines of pots and creels. The significance of these different gears for cetacean bycatch varies in different areas according to the fisheries present, the distribution of cetacean species and the vulnerability of populations. However, on a global scale, the vast majority of cetacean bycatches are thought to occur in gillnet fisheries (Read et al. 2003). There is a great deal that is still unknown about cetacean bycatch in fisheries, with regard to both the scale and impact of the interactions involved, and the magnitude and composition of the fishing fleets in many parts of the world (Read et al. 2003). Even in fisheries where the bycatch of cetaceans has been quantified, there is still a dearth of information on the nature and causes of the interactions, such as is required in order to identify effective mitigation measures or alternative fishing methods (e.g. ICES 2002). There is now a range of technical and management measures that have been, or are being, developed to reduce cetacean bycatch levels, some of which are being applied with some success. However, it is recognised that it is seldom possible to generalise from one bycatch problem to another, and that most interactions will require a solution that reflects the particular species and fishery involved (Read 2000). Moreover, it is widely considered that effective bycatch reduction requires the establishment of an
appropriate management framework to ensure that conservation objectives are identified and that appropriate action is taken to meet these (Read 2000, CEC 2002b). 1.2 Cetacean bycatch in the north-east Atlantic Bycatch in fisheries has been acknowledged to be a major threat to the conservation of cetaceans in the north-east Atlantic region by bodies ranging from national governments to the European Commission (e.g. DEFRA 2003; ASCOBANS 2000a; CEC 2003a). It is a problem that has been known about and documented in the region for at least 20 years (e.g. Andersen & Clausen 1983; Northridge 1984), but it is only relatively recently that governments and international bodies have started to take action to investigate the problem and initiate research into its mitigation. There are still only a few examples of measures that have been actively introduced to reduce the bycatch of cetaceans in the north-east Atlantic region. Cetacean bycatch in the north-east Atlantic, as elsewhere, affects mainly small cetaceans – i.e. dolphins, porpoises and the smaller toothed whales. Species caught in the region are primarily the harbour porpoise, common dolphin, striped dolphin, Atlantic white-sided dolphin, white-beaked dolphin, bottlenose dolphin and long-finned pilot whale (e.g. CEC 2002a). However, other larger cetaceans, such as the minke whale, are also among the victims of fisheries bycatch in the region (e.g. ASCOBANS 2003a). Chapter 2 below examines the main species affected by bycatch in more detail. The various species have different distributions, behaviour patterns and prey preferences, which result in different levels of interaction with the various types of fishery. In general, and as would be expected, the harbour porpoise, which tends to be distributed in the shallower waters on the continental shelf and which often feeds at or near the seabed, suffers the greatest mortality in bottom-set gillnet and tangle net fisheries. The more oceanic species such as common, striped and Atlantic white-sided dolphins are caught most frequently in pelagic (i.e. midwater) trawls and pelagic driftnets. However, some species, including the common dolphin, are known to be bycaught in a number of different types of fishing gear, even within the same sea area, which is likely to compound the impact on the affected populations (e.g. Tregenza & Collet 1998). Attention and concern during the 1980s and early 1990s focused mainly on the issues of dolphin bycatch in pelagic driftnets and harbour porpoise bycatch in bottom-set gillnets. A series of studies revealed bycatch levels exceeding what is considered sustainable in a number of fisheries using these gears. During and since the 1990s, however, increasing concern has arisen about the level of bycatch in the pelagic trawl fisheries that operate in the north-east Atlantic. The main fisheries implicated in cetacean bycatch are examined in Chapter 3. Although we know which fisheries are responsible for some of the bycatch in the north-east Atlantic and have, in some cases, an indication of the scale of the problem, there remain major deficiencies in the available information. These include lack of information on: bycatch rates in many fisheries, fisheries data (including effort data, location and methods used) and cetacean populations (including abundance, distribution and population structures). As a result, it remains impossible in many cases of bycatch to ascertain properly the scale of the problem and its significance in conservation terms, or to suggest appropriate mitigation measures. A number of international bodies have attempted to establish what level of cetacean bycatch could be considered ‘sustainable’ in conservation terms. For example, the Scientific Committee of the International The Net Effect? A WDCS report for Greenpeace 7
Page 1 and 2: The Net Effect? A review of cetacea
Page 3 and 4: Executive Summary The incidental ca
Page 5: Contents 1. Introduction 6 1.1 Byca
Page 9 and 10: ered by other countries such as the
Page 11 and 12: in the late 1990s (Jauniaux et al.
Page 13 and 14: It has also been calculated that in
Page 15 and 16: the animals were positively identif
Page 17 and 18: men interviewed in this study, duri
Page 19 and 20: Distribution of the Atlantic white-
Page 21 and 22: Bottlenose dolphins are also common
Page 23 and 24: 3. Fisheries associated with Bycatc
Page 25 and 26: Figure 1. Schematic representation
Page 27 and 28: prises 70 full-time pelagic pair bo
Page 29 and 30: (1.5%) and white-beaked dolphin (1.
Page 31 and 32: from October to February, with a pe
Page 33 and 34: y the (full-time) Galician fleet is
Page 35 and 36: catches in the cod, sole, skate and
Page 37 and 38: hibits the use of driftnets longer
Page 39 and 40: 4. Measures to reduce Bycatch 4.1 W
Page 41 and 42: Table 3. Comparison of catches betw
Page 43 and 44: fishery and the Californian driftne
Page 45 and 46: The system is triggered manually fr
Page 47 and 48: the report of this work does not in
Page 49 and 50: 5. Bycatch regulation 5.1 Regulatio
Page 51 and 52: 5.2 Existing obligations within the
Page 53 and 54: Irish and North Seas (ASCOBANS 2003
Page 55 and 56: 3: Annex I specifies the fishing ge
Page 57 and 58:
subjected to bycatch rates that far
Page 59 and 60:
to investigate any potential exclus
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Acknowledgements We would sincerely
Page 63 and 64:
Appendix 2 Breakdown of the French
Page 65 and 66:
References Aguilar, A. 1997. Invent
Page 67 and 68:
CEC 2002d. Proposal for a Council R
Page 69 and 70:
Hiby, L., Lovell, P. 1996. Baltic/N
Page 71 and 72:
Northridge, S.P., Di Natale, A., Ki
Page 73 and 74:
Commission, June 2000. SC/52/SM26.
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