Summary 1.The status of small cetaceans in the North Sea and adjacent waters has been of concern for many years. Shipboard and aerial line transect surveys were conducted to provide accurate and precise estimates of abundance as a basis for conservation strategy in European waters. 2. The survey, known as SCANS (Small Cetacean Abundance in the North Sea), was conducted in summer 1994 and designed to generate precise and unbiased abundance estimates. Thus the intensity of survey was high, and data collection and analysis methods allowed for the probability of detection of animals on the transect line being less than unity and, for shipboard surveys, also allowed for animal movement in response to the survey platform. 3. Shipboard transects covered 20 000 km in an area of 890 000 km 2 . Aerial transects covered 7000 km in an area of 150 000 km 2 . 4. Three species dominated the data. Harbour porpoise Phocoena phocoena were encountered throughout the survey area except in the Channel and the southern North Sea. Whitebeaked dolphin Lagenorhynchus albirostris and minke whale Balaenoptera acutorostrata were found mainly in the north-western North Sea. 5. Phocoena phocoena abundance for the entire survey area was estimated as 341 366 [coefficient of variation (CV) = 0·14; 95% confidence interval (CI) = 260 000-449 000]. The estimated number of B. acutorostrata was 8445 (CV = 0·24; 95% CI 5000-13 500). The estimate for L. albirostris based on confirmed sightings of this species was 7856 (CV = 0·30; 95% CI = 4000 -13 000). When Atlantic whitesided dolphin Lagenorhynchus acutus and Lagenorhynchus spp. sightings were included, this estimate increased to 11 760 (CV = 0·26; 95% CI 5900-18 500). 6. Shortbeaked common dolphin Delphinus delphis were found almost exclusively in the Celtic Sea. Abundance was estimated as 75 450 (CV = 0·67; 95% CI = 23 000 -149 000). 7. Current assessments and recommendations by international fora concerning the impact on P. phocoena of bycatch in gillnet fisheries in the North Sea and adjacent waters are based on these estimates.

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1. Mixed species groups have long been noted in birds, but they also occur among different species of mammals ranging from closely related species to species from different orders. Mixed species groups of mammals occur in many different habitats, e.g. ungulates on the savannah, primates in various types of forests and cetaceans in the oceans. Mixed species groups are very different in their duration, frequency, predominant activity and structure depending on the species interacting and the habitat they occur in. 2. Functional explanations for mixed species groups usually fall within two categories: foraging advantages and predator avoidance. However, there could also be other social and reproductive advantages of mixed species groups that could contribute to their formation and stability. The advantages do not have to be equally distributed between the participating species and can also vary according to season and the presence of predators. 3. It is important that all investigators of mixed species groups take their studies one step further after the naturalistic description and test the function and benefits of mixed species groups in order to give more strength to their conclusions. In this paper we review and discuss the function of mixed species groups in mammals and suggest an approach on how to investigate the function of such groups.

Capture-recapture methods are frequently employed to estimate abundance of cetaceans using photographic techniques and a variety of statistical models. However, there are many unresolved issues regarding the selection and manipulation of images that can potentially impose bias on resulting estimates. To examine the potential impact of these issues we circulated a test data set of dorsal fin images from bottlenose dolphins to several independent research groups. Photo-identification methods were generally similar, but the selection, scoring, and matching of images varied greatly amongst groups. Based on these results we make the following recommendations. Researchers should: (1) determine the degree of marking, or level of distinctiveness, and use images of sufficient quality to recognize animals of that level of distinctiveness;(2) ensure that markings are sufficiently distinct to eliminate the potential for "twins" to occur; (3) stratify data sets by distinctiveness and generate a series of abundance estimates to investigate the influence of including animals of varying degrees of markings; and (4) strive to examine and incorporate variability among analysts into capture-recapture estimation. In this paper we summarize these potential sources of bias and provide recommendations for best practices for using natural markings in a capture-recapture framework.

We examined population substructure of bottlenose dolphins (Tursiops sp). in Shark Bay, Western Australia, using 10 highly polymorphic microsatellite loci, and mitochondrial DNA (mtDNA). For microsatellite analysis, 302 different animals were sampled from seven localities throughout the bay. Analysis of genetic differentiation between sampling localities showed a significant correlation between the number of migrants (Nm) calculated from FST, RST and private alleles, and distance between localities–a pattern of isolation‐by‐distance. For mtDNA, 220 individuals from all seven localities were sequenced for a 351 base pair fragment of the control region, resulting in eight haplotypes, with two distinct clusters of haplotypes. Values of FST and (φ)ST for mtDNA yielded statistically significant differences, mostly between localities that were not adjacent to each other, suggesting female gene flow over a scale larger than the sampled localities. We also observed a significant correlation between the number of female migrants calculated from FST and φST and the distance of sampling localities. Our results indicate that dispersal in female dolphins in Shark Bay is more restricted than that of males.

The short-term effects of tourist boats on the behaviour of Indo-Pacific bottlenose dolphins Tursiops aduncus were investigated off the south coast of Zanzibar, Tanzania, by comparing dolphin group behaviour in the presence (impact) and absence (control) of tourist boats. Groupfollows were conducted from a carefully maneuvered (non-invasive) independent research vessel and behavioural data on group activity were collected using scan sampling methods. By using a timediscrete Markov chain model, the transition probabilities of passing/changing from one behavioural state to another were calculated and compared between impact and control situations. The data were further used to construct behavioural budgets. In the presence of tourist boats, dolphins were less likely to stay in a resting or socialising activity but were more likely to start travelling or foraging, as inferred from the Markov chain model. The behavioral budgets showed that foraging, resting and socialising all decreased as an effect of tourist boat presence, while travelling increased. The behavioural responses are likely to have energetic implications, mainly by increasing physical demands.Further, the results demonstrate that the current level of tourism intensity off the south coast of Zanzibar affects the dolphins' cumulative behavioural budget. Regulations on dolphin tourism are therefore urgently needed to minimise potential long-term negative effects on the dolphins.

The conservation status of small cetaceans has significantly worsened since the 1980s, when the baiji was the only species of small cetacean listed as Endangered by IUCN. Now the baiji is almost certainly extinct and 13 other species, subspecies, or populations (hereafter units-to-conserve or units) of small cetaceans are listed as Critically Endangered (CR) on the IUCN Red List. Bycatch is the main threat to 11 of the CR units. Entanglement in gillnets contributed to the extinction of the baiji and is responsible for the imminent extinction of the vaquita. Unfortunately, there is no simple technical solution to the problem of bycatch of small cetaceans. If the 8 CR units with 100 or fewer remaining individuals are to be saved, conservation zones must be established where gillnets are eliminated and bans on their use are strictly enforced. Recent experience with the vaquita in Mexico demonstrates that enforcement of such conservation zones can be very difficult. Ineffective enforcement is also a problem for at least 4 of the other CR units. Time is very short and, unless major efforts are made now to address the bycatch problem, the prospects for CR small cetaceans and other at-risk aquatic megafauna are grim. The ultimate long-term solution to the bycatch problem is the development of efficient, inexpensive, alternative fishing gear that can replace gillnets without jeopardizing the livelihoods of fishermen. Good fishery governance and the direct involvement of fishing communities are also essential to the successful conservation of most threatened populations of small cetaceans.

J. 8. BF.KGC;KT:N, P. 1997: Sponge carving by dolphins (Delphinidae, Turrip sp.): a foraging speciabzation involving tool use? F,thology 103, 4.54465. AbstractDuring long-term research on bottlenose dolphins (Tursiops sp.) in Shark Bay, K'estern Australia, sevcral individuals were observed carrying sponges, lici,inodic!pum mesemterinum, on their rostra. Over multiple years, five regularly sighted individuals were usually carrying sponges when encountered (67-100 "%I of encounters). Four additional regularly sighted individuals were observed with sponges lust one timr each. All fix e individuals that routinely carried sponges were female. Two of the anomalous, one-timc carriers were female, one was likely female, and one was male. Most observations of sponge carrying occurred within a restricted .ires, a relati~ deep water channel (8-10 m deep). Surface observations of sponge carrying, including focal animal observations, revealed a stereotyped surfacing and diving pattern, and occasional indications of prey consumption. Three hypotheses are considered regarding the function of sponge carrying: 1. dolphins wcrc playing with the s p t q e s ; 2. the sponges contain some compound of use to the dolphins (e.g. for medicinal purposes); and 3. the sponges were used as a tool to aid in foraging. The foraging tool hypothesis is hest supported, but thc exact manner in which sponges are used remains to be discovered. Sponge carrying is a beharioural specia'iTation, probably involving foraging, and regularly engaged in by onl! a small proportion of female dolphins in Shark BaJ-.