Peter B. Best

The phylogeography of dusky dolphins (Lagenorhynchus obscurus): a critical examination of network methods and rooting procedures

We investigated the phylogeography and evolutionary history of dusky dolphins (Lagenorhynchus obscurus) using DNA sequences of the full mitochondrial cytochrome b gene in 124 individuals from the putative stocks off Peru, Argentina and Southwest Africa. While genetic differentiation within oceans is surprisingly low, there is no evidence for recent female gene flow between Atlantic and Pacific waters. Highest genetic variability in terms of sequence divergence and number of haplotypes is found in the Atlantic. Our analyses also indicate that the eastern South Pacific dusky dolphins stock should be considered a separate management unit. Given the high level of mortality experienced by the Peruvian dusky dolphin in local fishery activities, these findings have important implications for an objective management of the species. Furthermore, we analysed our mitochondrial sequence data with several widely used network estimation and rooting methods. The resulting intraspecific gene genealogies and rooting inferences exhibited substantial differences, underlying the limitations of some algorithms. Given that scientific hypotheses and management decisions depend strongly on inferred tree or network topologies, there is a clear need for a systematic comparative analysis of available methods. Finally, the present study indicates that (i) the dusky and the Pacific white‐sided dolphins are sister species and (ii) not only the Westwind Drift hypothesis but also other models of dispersion are compatible with the current geographical distribution of dusky dolphins.

World-wide genetic differentiation of Eubalaena: Questioning the number of right whale species

Few studies have examined systematic relationships of right whales (Eubalaena spp.) since the original species descriptions, even though they are one of the most endangered large whales. Little morphological evidence exists to support the current species designations for Eubalaena glacialis in the northern hemisphere and E. australis in the southern hemisphere. Differences in migratory behaviour or antitropical distribution between right whales in each hemisphere are considered a barrier to gene flow and maintain the current species distinctions and geographical populations. However, these distinctions between populations have remained controversial and no study has included an analysis of all right whales from the three major ocean basins. To address issues of genetic differentiation and relationships among right whales, we have compiled a database of mitochondrial DNA control region sequences from right whales representing populations in all three ocean basins that consist of: western North Atlantic E. glacialis, multiple geographically distributed populations of E. australis and the first molecular analysis of historical and recent samples of E. glacialis from the western and eastern North Pacific Ocean. Diagnostic characters, as well as phylogenetic and phylogeographic analyses, support the possibility that three distinct maternal lineages exist in right whales, with North Pacific E. glacialis being more closely related to E. australis than to North Atlantic E. glacialis. Our genetic results provide unequivocal character support for the two usually recognized species and a third distinct genetic lineage in the North Pacific under the Phylogenetic Species Concept, as well as levels of genetic diversity among right whales world‐wide.

Soviet catches of southern right whales Eubalaena australis, 1951–1971. Biological data and conservation implications

Between 1951/1952 and 1970/1971, a total of at least 3368 southern right whales Eubalaena australis were taken by Soviet whaling expeditions in the Southern Hemisphere, despite the species being internationally protected since 1935. These catches and the associated biological data (presented here for the first time) represent a unique source of information on the distribution, movements, size composition, reproduction and feeding of southern right whales during summer months. Revelation of these previously unreported catches also has implications for the assessment of the current status of right whale stocks. Incorporation of the Soviet catches into population assessments generally leads to higher estimates of the size of the population at protection, but the relative increase in this size depends on the intrinsic rate of increase in the population.

Population structure of humpback whales from their breeding grounds in the South Atlantic and Indian oceans

Although humpback whales are among the best-studied of the large whales, population boundaries in the Southern Hemisphere (SH) have remained largely untested. We assess population structure of SH humpback whales using 1,527 samples collected from whales at fourteen sampling sites within the Southwestern and Southeastern Atlantic, the Southwestern Indian Ocean, and Northern Indian Ocean (Breeding Stocks A, B, C and X, respectively). Evaluation of mtDNA population structure and migration rates was carried out under different statistical frameworks. Using all genetic evidence, the results suggest significant degrees of population structure between all ocean basins, with the Southwestern and Northern Indian Ocean most differentiated from each other. Effective migration rates were highest between the Southeastern Atlantic and the Southwestern Indian Ocean, followed by rates within the Southeastern Atlantic, and the lowest between the Southwestern and Northern Indian Ocean. At finer scales, very low gene flow was detected between the two neighbouring sub-regions in the Southeastern Atlantic, compared to high gene flow for whales within the Southwestern Indian Ocean. Our genetic results support the current management designations proposed by the International Whaling Commission of Breeding Stocks A, B, C, and X as four strongly structured populations. The population structure patterns found in this study are likely to have been influenced by a combination of long-term maternally directed fidelity of migratory destinations, along with other ecological and oceanographic features in the region.

Comparative analysis of the diets of smaller odontocete cetaceans along the coast of southern Africa

The diets of 20 species of smaller Odontoceti were investigated. The material was collected along the southern African coast between 1966 and 1990 and included 158 strandings, 29 animals killed incidentally and 49 animals caught under permit. In total, 57 species in 34 families of fish and 89 species in 24 families of cephalopods were identified from remains in the 236 stomachs investigated. Most Odontoceti fed on commercially unexploited cephalopods and fish, or on fish below commercially utilized sizes. However, the average sizes of anchovy and pilchard eaten by Delphinus delphis and Lagenorhynchus obscurus were larger than the sizes most frequently taken commercially. The species composition of the prey items reflected the onshore-offshore distribution (and possibly the foraging depths) of different Odontoceti. Tursiops truncatus and Cephalorhynchus heavisidii were closest to shore and D. delphis and L. obscurus over the continental shelf. The rest were distributed around the shelf-edge and just off th...

The distribution of small odontocete cetaceans off the coasts of South Africa and Namibia

A total of 2 077 records of approximately 49 000 small cetaceans, including dedicated and incidental sightings and specimens, was analysed to define distribution patterns of the 28 species found within southern African waters. Distribution analyses reveal distinct component patterns, including cosmopolitan (found in all waters) and pelagic cosmopolitan (found in all pelagic waters) components, tropical, subtropical and warm temperate components of the Agulhas Current system, an Agulhas Bank component, a South and East Coast inshore component, and West Coast neritic and pelagic components. While the offshore distribution appears to be determined by water depth, possibly through distribution of the principal prey, longshore distribution appears to be determined by water temperature. The high diversity of small cetacean species found within the relatively small study region results from the wide range of zoogeographic components present. These components arise from the wide range of water temperature resulti...

Evidence for male dispersal along the coasts but no migration in pelagic waters in dusky dolphins (Lagenorhynchus obscurus)

Using nine nuclear species‐specific microsatellite loci and two mitochondrial gene fragments (cytochrome b and control region), we investigated the processes that have shaped the geographical distribution of genetic diversity exhibited by contemporary dusky dolphin (Lagenorhynchus obscurus) populations. A total of 221 individuals from four locations (Peru, Argentina, southern Africa, and New Zealand) were assayed, covering most of the species’ distribution range. Although our analyses identify a general demographic decline in the Peruvian dusky dolphin stock (recently affected by high natural and human‐induced mortality levels), comparison between the different molecular markers hint at an ancient bottleneck that predates recent El Niño oscillations and human exploitation. Moreover, we find evidence of a difference in dispersal behaviour of dusky dolphins along the South American coast and across the Atlantic. While data in Peruvian and Argentine waters are best explained by male‐specific gene flow between these two populations, our analyses suggest that dusky dolphins from Argentina and southern Africa recently separated from an ancestral Atlantic population and, since then, diverged without considerable gene flow. The inclusion of a few New Zealand samples further confirms the low levels of genetic differentiation among most dusky dolphin populations. Only the Peruvian dusky dolphin stock is highly differentiated, especially at mitochondrial loci, suggesting that major fluctuations in its population size have led to an increased rate of genetic drift.

Killer Whale Nuclear Genome and mtDNA Reveal Widespread Population Bottleneck during the Last Glacial Maximum

Ecosystem function and resilience is determined by the interactions and independent contributions of individual species. Apex predators play a disproportionately determinant role through their influence and dependence on the dynamics of prey species. Their demographic fluctuations are thus likely to reflect changes in their respective ecological communities and habitat. Here, we investigate the historical population dynamics of the killer whale based on draft nuclear genome data for the Northern Hemisphere and mtDNA data worldwide. We infer a relatively stable population size throughout most of the Pleistocene, followed by an order of magnitude decline and bottleneck during the Weichselian glacial period. Global mtDNA data indicate that while most populations declined, at least one population retained diversity in a stable, productive ecosystem off southern Africa. We conclude that environmental changes during the last glacial period promoted the decline of a top ocean predator, that these events contributed to the pattern of diversity among extant populations, and that the relatively high diversity of a population currently in productive, stable habitat off South Africa suggests a role for ocean productivity in the widespread decline.

Composition and possible function of social groupings of southern right whales in South African waters

We collected behavioural data and skin samples for molecular sex determination from 327 right whales (Eubalaena australis) in the coastal waters of South Africa between July and October, 1995 and 1996, as well as from 147 cows with calves-of-the-year between August and October 1996, September and November 1997. Data on group size, composition and behaviour were also available for 85 sightings of right whales south of 40degreesS. Although right whales are considered to be relatively non-social, only 23.3% of animals (apart from cow-calf pairs) encountered in South African waters were alone (N = 649), compared to 84.6% of animals seen south of 40degreesS in summer (N = 94). Of the pairs other than cows with calves encountered off South Africa, 31.0% (N = 58) were believed to be composed of cows with last-years calves (=yearlings): 93.3% (N = 15) of these yearlings were female, suggesting a possible mechanism for female philopatry. The incidence of these mother-yearling pairs dropped sharply after early August, indicating the abrupt weaning of some calves at an age of approximately one year. Most other animals were observed either in surface-active groups (SAGs) that indulged in apparent courtship behaviour, or in non-surface-active groups (non-SAGs). SAGs tended to be larger on average than non-SAGs (4.45 animals, N = 33, range 2-10, versus 2.57 animals, N = 108, range 2-5, respectively), and males predominated, while females predominated in non-SAGs. The number of animals participating per SAG increased through the season, whereas the size of non-SAGs remained constant. Given that most conceptions in southern right whales are estimated to occur in a 118-day period around mid-July, the observed increase in group size through late August and September may be due to declining availability of receptive females. Focal animals in SAGs proved to be predominantly female (83.3%, N = 24) and non-focal animals predominantly male (85.2%, N = 61): a few groups observed late in the winter season had a male rather than female focal animal. Sighting histories of the focal females revealed that none was seen with a calf in the 17 years that preceded the surveys, but four had been seen as calves, 2-5 (average 3.75) years previously. Six females were photographed with calves from 2 to 5 years after being the focal animal in a SAG, which is consistent with the observation that most focal females in SAGs were young, pre-pubertal animals, and therefore being the focal animal did not normally result in conception. It is still unclear where (and when) conceptions occur in southern right whales, but it is hypothesised that the focal females are practising a mating strategy in which the chances of conceiving with a larger male will be maximised. As neonatal survival is partly related to size, the female will in this way protect her substantial investment in time and energy represented by the calf.

RANGE AND MOVEMENTS OF FEMALE HEAVISIDE'S DOLPHINS (CEPHALORHYNCHUS HEAVISIDII), AS DETERMINED BY SATELLITE-LINKED TELEMETRY

Abstract Heavisides dolphin (Cephalorhynchus heavisidii) is a coastal delphinid with a limited inshore distribution off the west coast of southern Africa. Knowledge of its habitat usage is an essential precursor to assessing its potential vulnerability to fisheries interactions. Six Heavisides dolphins (1 male and 5 females) were fitted with satellite-linked transmitters in 2004, and tracked for up to 54 days. The 5 tags fitted to female dolphins transmitted continuously, allowing for analysis of movements at a fine temporal scale. Four dolphins showed an initial avoidance of the capture site by moving over a wider area in the first 2–5 days posttagging than later in the deployment period. All dolphins had used their full home ranges (determined as 100% minimum convex polygons) 5–20 days before tag failure, suggesting measured home ranges were stable at this temporal scale. Home-range estimates using local convex hulls ranged from 301.9 to 1,027.6 km2 (90% isopleths) and 875.9 to 1,989.6 km2 using the 100% isopleths and scaled positively with body size but varied in shape, usage, and number of core-use areas. Although the distance from shore and depth at which individual dolphins moved varied greatly, all dolphins showed a strong onshore–offshore diurnal movement pattern, generally being closest inshore between 0600 h and noon, and farthest offshore between 1500 h and 0500 h. This pattern is assumed to be related to the movements of their principal prey, juvenile shallow-water hake (Merluccius capensis), which migrate into the upper water column at night. Movements inshore may be associated with rest, socializing, and predator avoidance.