No abstract

Sperm whales (Physeter macrocephalus) are sexually dimorphic in several respects, including size, latitudinal distribution, and social structure. Females are known to have complex social structures, including long-term bonds, but the social structures of sexually mature or maturing males have received much less attention. Using data from aggregations of males off Norway, Nova Scotia, New Zealand, and the Galápagos Islands, we examined aggregation size, residence times within aggregations, clustering at the surface, and long-term bonds. Results were generally consistent among study areas. The aggregations found in each area contained around 10-30 males at any time, and were usually a few tens of kilometres across. Mean residence times within aggregations ranged from a few days to a few weeks. Close clustering at the surface was rare, but present at each site. There was no evidence for preferred companionship between individuals at any temporal scale in any of the study areas. The rarity of clustering and the apparent lack of long-term relationships amongst male sperm whales contrast strongly with results of studies on females, suggesting that both close spatial proximity at the surface and permanent bonds between individuals may be a consequence of the need for care of the young.Résumé : Les cachalots (Physeter macrocephalus) présentent un important dimorphisme sexuel, notamment en taille, en distribution latitudinale et en organisation sociale. Les femelles ont une organisation sociale très complexe qui inclut des associations à long terme entre individus, alors que l'organisation sociale des mâles adultes, ou subadultes, reste encore largement inconnue. En utilisant des données provenant de regroupements de mâles au large de la Norvège, de la Nouvelle Écosse, de la Nouvelle Zélande et des Îles Galápagos, nous avons examiné la taille des regroupements, la durée du séjour à l'intérieur de ces regroupement, la manière dont les individus se rassemblent à la surface et les associations à long terme entre individus. Les résultats étaient cohérants d'une région à l'autre. En général, les regroupements avaient quelques dizaines de kilomètres de diamètre et contennaient environ 10-30 mâles. La durée moyenne du séjour à l'intérieur de chacun de ces regroupements allait de quelques jours à quelques semaines. Les individus formaient rarement des groupes compacts de deux ou plusieurs individus séparés par moins de 100 m, mais de tels groupes ont été observés en surface dans chaque région. Rien dans nos données, dans aucune région, ni à aucune des échelles temporelles étudiées, ne laissait croire que certains individus puissent s'associer plus souvent avec tel mâle qu'avec tel autre. Le fait que les individus se regroupaient rarement à la surface et l'absence d'associations à long terme entre mâles présentent un contraste remarquable avec les résultats obtenus chez les femelles. Cela suggère que la proximité spatiale à la surface ainsi que les associations permanentes entre individus servent principalement à assure...

Sperm whale (Physeter macrocephalus) photoidentification data spanning 12 years of study around the Galápagos Islands were examined to investigate the size, variability, and stability of social units. Adult females and immature whales of both sexes have two types of associates: "constant companions," which are members of an individual's "stable" social unit, and "casual acquaintances," which are temporarily associating members of different units. We analysed long-term association patterns and calculated that individuals have a mean of 11.3 constant companions. Estimated social unit size ranged from 3 to 24 individuals. Evidence of splitting and merging of units and of transfer of individuals between units is presented. The estimated overall frequency of these unit-membership changes is 6.3% per individual per year. These forms of unit dynamics are rare in species with male dispersal and matrilineally related social groups, and cannot be easily explained in this species. There is considerable variation in unit size (perhaps caused by demographic processes), suggesting that the benefits of remaining in a social unit usually outweigh selection for some optimal unit size. However, the occurrence of merging and transfers suggests that the ecological or social cost/benefit of leaving one's matrilineal unit may sometimes outweigh the cost/benefit of staying.

Little is known about the movements of male sperm whales, Physeter macrocephalus, in the North Atlantic. Recoveries of traditional harpoons and tags during commercial whaling indicated movements from Nova Scotia to Spain and from the Azores to Iceland and Spain. We compared collections of photo-identification images from different areas using the North Atlantic and Mediterranean Sperm Whale Catalogue and the Eurphlukes Phlex/Match programs. The largest collections of identified males (number of individuals, start and end date for data collection shown in parentheses) are for the Azores ). There were six matches between Andenes and Tromsø ( 25 nm), with three of these re-sighted in multiple years and three photo-identification matches from the Azores to Norway ( 2400 nm). In all cases individuals first photographed in the Azores (in 1993, 1999 and 2003) were matched to images collected later in Tromsø (in 2007 and. In 1997 a photo-identification image from Andenes matched a male stranded on the west coast of Ireland. No matches were made to images in smaller collections from Iceland, Nova Scotia, Greenland, Dominica, Guadeloupe, Gulf of Mexico and the Mediterranean. These findings show the value of data collected from whale watching vessels and the importance of collaboration between groups to allow investigation on an ocean basin scale. It is hoped that with the coordinated collection of more images from around the Atlantic, further insight might be gained into the movements of these widely ranging animals.

Count cryptic species in biodiversity tally The race to describe and archive the planet's dwindling biodiversity (see K.-D. B. Dijkstra Nature 533, 172-174; 2016) becomes even more urgent with the realization that the task's scale may be an order of magnitude greater than estimated. Dijkstra notes that we have so far named only about 1.2 million of Earth's estimated 8.7 million or so eukaryotic species. Such estimates are based largely on counts of invertebrate 'species' that are visually distinguishable ('morphospecies'). However, genetic analysis has revealed that many supposedly uniform morphospecies are complexes of multiple, reproductively isolated lineages, each of which constitutes a separate but cryptic species (D. Bickford et al. Trends Ecol. Evol. 22, 148-155; 2007). These discoveries boost the biodiversity of even the largest vertebrates, such as elephants. The effect is greater in small vertebrates (such as lizards and frogs) and in invertebrates, which are often complexes of ten or even more species (P. M. Oliver et al. BMC Evol. Biol. 10, 386; 2010). The quoted estimate of the number of (morpho)species on Earth could therefore be just 10% of the true species number.