4.3.1.3.1 — Marine Mammals: Whales and Dolphins

Baleen whales
Most of the great whales (baleen whales: Mystacoceti) migrate between calving and feeding grounds. A variety of factors determine the suitability of calving grounds, while high nutrient productivity seems to be the main factor for the selection of feeding grounds. Baleen whales (Mystacoceti) migrate into highly productive, summertime polar regions, to feed on plankton. They return to warm, but unproductive tropical regions to give birth, and for lactation. Minimisation of thermal energy loss for calves seems to be among the decisive factors for these movements (Kshatriya & Blake 1988).

Pictures (Figure A2.20), maps and more detailed species accounts are given for the humpback whale (Megaptera novaeangliae: Figure A2.21), the bowhead whale (Balaena mysticetus: Figure A2.22), the blue whale (Balaenoptera musculus: Figure A2.23), and the northern and southern right whales (Eubalaena glacialis and E. australis: Figure A2.24). All these species are listed in CMS Appendix I., the right whales as subspecies of Baleana glacialis. Clapham et al. (1999) review recent genetic evidence indicating that full species status is appropriate. For all mentioned species, different populations exhibit distinct migration patterns. Satellite tracking, genetic studies, monitoring of acoustic behaviour and photo-identification of individuals has helped to reveal these patterns more clearly (see references within Figures A2.21-A2.24). This requires differentiated threat assessment, and the recent IUCN Red List (Hilton-Taylor 2000) documents considerable differences for the conservation status of distinct stocks. One of the most extreme examples can be observed among the right whales (Figure A2.24): All southern populations (Eubaleana australis) are recovering and are classified as "Lower Risk/Conservation Dependent," while the Pacific and Atlantic stocks of the northern species (Eubalaena glacialis) are "Endangered" (Hilton-Taylor 2000). In addition, Clapham et al. (1999) differentiate between the western and the eastern North Atlantic stock, with the latter consisting of only tens of individuals, and no present activity in former breeding grounds off the North African coast. This could mean that there are no individuals left who know these breeding grounds, and that recovery is now impossible because of an interruption in cultural transmission of behaviour patterns. This example illustrates that even learning and culture must be understood for an efficient conservation of migratory species. It seems that we are loosing an important species for the biodiversity of the north-eastern Atlantic: the northern right whale (Eubalaena glacialis), in spite of its protection against whaling. A similar situation is observed for the bowhead whale (Balaena mysticetus), where the critically endangered Barents Sea stock has been reduced to only tens of individuals (Figure A2.22, Clapham et al. 1999).

The sad story of the near extinction of great whales by commercial whaling is well known and documented whales previously populated the seas in numbers unimaginable today (see Figure A2.21). Historical population numbers can be reconstructed easily from well-documented statistics reaching back to the 16^th century, and from the trade statistics of whale products such as oil, spermaceti (wax for candles) and baleen plates (Bloch et al. 1996, Gregr et al. 2000). Whaling has been regulated by the International Whaling Commission (IWC) since 1946. The IWC adopted a resolution calling for an indefinite moratorium on commercial whaling, which became effective in 1986. As a result, many stocks are recovering slowly (Zeh et al. 1995, Smith et al. 1999). According to a Revised Management Procedure adopted in 1994, the IWC will allow the reintroduction of commercial whaling if stocks increase to 54% of pre-exploitation levels. The recent assembly of the IWC (London 2001) rejected (with a slim majority) the proposal to resume hunting of minke whales (Balaenoptera acutorostrata), because it has been unable to design an acceptable observer system. There are some additional problems regarding compliance with the moratorium: due to its voluntary nature, any member country can file a protest, and then need not abide by it, as in the case of Norway hunting minke whales in the North Atlantic. In addition, whaling for "scientific research" is allowed, if it satisfies IWC criteria. The respective Norwegian and Japanese research programmes have been criticised severely; the complex debate is reviewed by Gillespie (2000). The homepage of the IWC summarises the current research programmes (http://ourworld.compuserve.com/homepages/iwcoffice/iwc.htm). Results are published annually within the "Report of the International Whaling Commission" (for example, see Notarbartolo-di-sciara 1998). The multilingual Japanese whale portal site provides access to news about IWC (http://www.e-kujira.or.jp/world.html), and a link to The Institute of Cetacean Research (I.C.R.), a unique organisation in Japan specialising in the biological and social sciences related to whales (http://www.whalesci.org/research.html). In addition, the website http://www.iwc.org provides interesting news about whale conservation and research.

Even without whaling, there are numerous threats slowing down recovery of some species. These include ship collisions and entanglement in fishing gear (Eubalaena spp. seem to be particularly sensitive, for references see Figure A2.24), environmental pollution and environmental change. Though difficult to measure, global warming and increased UV-B radiation could have considerable effects on plankton availability, and thereby affect the recovery prospects of already weakened populations (Burns 2000). It is speculated that the recent decline in grey whales migrating along the North American coast must be attributed to reduced food availability, caused by unknown environmental changes.

Underwater noise from military operations and seismic explorations alters behaviour and might affect acoustic communication. Microscopic lesions in the auditory structures of whales stranded after explosions indicate that noise pollution may also affect orientation behaviour (Frantzis 1998).

The CMS included 5 baleen taxa in its Appendix I since 1979, mainly as a reinforcement of the measures of the IWC. Both the Sei whale (Balenoptera borealis) and the common rorqual (better finwhale) (Balaenoptera physalus) have been classified as "Endangered" by the IUCN Red List 2000 (Hilton-Taylor 2000). Their unfavourable conservation status in conjunction with their pronounced poleward migrations would therefore justify CMS listing.

Small whales
Economic interest and a worldwide conservation movement are fuelling research on large baleen whales. In contrast, we know much less about the migration and conservation status of the toothed whales (Odontoceti), which are often summarised as "small cetaceans". There are about 70 species, consisting of all cetaceans other than the baleen whales and the sperm whale (Physeter macrocephalus: Physeteridae). They prey on fishes or even marine mammals. Their dependence on plankton is thus only indirect, and consequently their migration patterns are entirely different than those of the great whales. Migratory patterns are less well studied, and probably less predictable than in the great whales. There is an urgent need for research for a considerable number of dolphins listed as "Data Deficient" by the Red List 2000 (Table 4.5). The CMS secretariat initiated an extensive review of small cetaceans. This report confirmed that the knowledge on small cetaceans is extremely inhomogeneous: For some species, there are hundreds of references (e.g. beluga or white whale; Delphinapterus leucas), allowing detailed population estimates for well-identified stocks (Culik 2001, p. 69), while other species are still enigmatic, like the gingko-toothed whale Mesoplodon gingkodens, which is only known from 15 stranding records. It is evident that nothing can be said about the migratory behaviour of such poorly known species. With respect to their conservation status, it must be assumed that threats affecting related species are also damaging the rarer species, at least in a general way.

Major threats identified by Culik (2001) include catch, bycatch, overfishing, noise pollution, habitat degradation (including dams) and mass stranding. The SCANS project evaluated distribution and abundance of the harbour or common porpoise (Phocoena phocoena) in the North Sea (see Figure A2.19), and summarises the current knowledge about bycatch of this protected species (Table 4.6). The species most affected is the harbour porpoise (Phocoena phocoena), and the fishing gear most responsible is the bottom-set gillnet. Porpoise populations are believed to be able to increase in numbers by no more than 4% a year. This low reproductive potential means that porpoise populations are particularly vulnerable to bycatch. Formerly, in early spring, the animals were seen migrating between Danish waters and the Baltic sea, but this phenomenon virtually ceased during 1940-1950, probably due to overhunting (Culik 2001, p. 240).

18 species of small cetaceans are listed in CMS Appendix II, and two special agreements are dedicated to their protection: ACCOBAMS (Figure A2.18), for the Black Sea, Mediterranean Sea and Contiguous Atlantic Area, and ASCOBANS (Figure A2.19) for the Baltic and North Sea. In addition, all cetaceans in EU waters are listed by the Commission Directive on the Conservation of Natural Habitats and of Wild Fauna and Flora (Council Directive 92/43/EEC, 21 May 1992, Annex IV: strict protection). The harbour porpoise (Phocoena phocoena) and the bottlenose dolphin (Tursiops truncatus) are listed in Annex II as species whose conservation requires the designation of Special Areas of Conservation.

Several species of river-dolphins migrate within rivers and coastal areas, such as Pontoporia sp.
(Figure A2.25), the Amazon river dolphin (Inia geoffrensis) or the Ganges river dolphin (Platanista gangetica). They suffer particularly from dam construction and pollution of riverine habitats, and some of the necessary conservation measures are similar to those needed for migratory fishes (see below).

Both the Vaquita (Phocoena sinus) and the Yangtse river-dolphin (Lipotes vexillifer) are "Critically Endangered", but their movements are restricted to one range state. Therefore, conservation efforts are the national responsibility of the United States and China, respectively.

This document should be quoted as part of the publication "Riede, K. (2001): The Global Register of Migratory Species ­ Database, GIS Maps and Threat Analysis. Münster (Landwirtschaftsverlag), 400 pp." + CD

 by Klaus Riede