Sara Magalhães

High gene flow in oceanic bottlenose dolphins ( Tursiops truncatus ) of the North Atlantic

Despite the openness of the oceanic environment, limited dispersal and tight social structure often induce genetic structuring in marine organisms, even in large animals such as cetaceans. In the bottlenose dolphin, mitochondrial and nuclear DNA analyses have revealed the existence of genetic differentiation between pelagic (or offshore) and coastal (or nearshore) ecotypes in the western North Atlantic, as well as between coastal populations. Because previous studies concentrated on continental margins, we analysed the population structure of bottlenose dolphins in two of the most isolated archipelagos of the North Atlantic: the Azores and Madeira. We analysed 112 samples collected on live animals in the two archipelagos, and nine samples collected on stranded animals in Madeira and mainland Portugal. Genetic analyses consisted in molecular sexing, sequencing of part of the mitochondrial hyper-variable region, and screening of ten microsatellite loci. We predicted that: (1) there is at least one pelagic and one or more coastal populations in each archipelago; (2) populations are differentiated between and possibly within archipelagos. Contrary to these predictions, results indicated a lack of population structure in the study area. In addition, comparison with published sequences revealed that the samples from the Azores and Madeira were not significantly differentiated from samples of the pelagic population of the western North Atlantic. Thus, bottlenose dolphins occurring in the pelagic waters of the North Atlantic belong to a large oceanic population, which should be regarded as a single conservation unit. Unlike what is known for coastal populations, oceanic bottlenose dolphins are able to maintain high levels of gene flow.

Occurrence and distribution of cetaceans in the waters around the Azores (Portugal), Summer and Autumn 1999- 2000

Boat-based surveys were conducted during the summer and autumn months of 1999 and 2000 around the islands of the Archipelago of the Azores to determine occurrence, distribution, and relative abundance of cetaceans. A total of 222 cetacean schools, corresponding to 11 species, were sighted over the two years. Cetaceans were widely distributed in the area surveyed, but the central group of islands recorded the highest relative abundance of cetaceans and the greater species diversity. Within each group of islands, cetaceans were more abundant in the coastal area (to 9 km from shore) than in the oVshore area (9 to 28 km). Atlantic spotted dolphins (Stenella frontalis ), short-beaked common dolphins ( Delphinus delphis ), and bottlenose dolphins (Tursiops truncatus ) were the most frequently sighted species and were found in all the islands surveyed. Although there was considerable overlap in spatial distribution among these species, common dolphins and bottlenose dolphins occurred in coastal areas, while Atlantic spotted dolphins were more common in o Vshore and deeper waters.

Why do dolphins form mixed-species associations in the Azores ?

Mixed-species associations are temporary associations between individuals of different species that are often observed in birds, primates and cetaceans. They have been interpreted as a strategy to reduce predation risk, enhance foraging success and/or provide a social advantage. In the archipelago of the Azores, four species of dolphins are commonly involved in mixed-species associations: the common dolphin, Delphinus delphis, the bottlenose dolphin, Tursiops truncatus, the striped dolphin, Stenella coeruleoalba, and the spotted dolphin, Stenella frontalis. In order to understand the reasons why dolphins associate, we analysed field data collected since 1999 by research scientists and trained observers placed onboard fishing vessels. In total, 113 mixed-species groups were observed out of 5720 sightings. The temporal distribution, habitat (water depth, distance to the coast), behaviour (i.e. feeding, travelling, socializing), size and composition of mixed-species groups were compared with those of single-species groups. Results did not support the predation avoidance hypothesis and gave little support to the social advantage hypothesis. The foraging advantage hypothesis was the most convincing. However, the benefits of mixed-species associations appeared to depend on the species. Associations were likely to be opportunistic in the larger bottlenose dolphin, while there seemed to be some evolutionary constraints favouring associations in the rarer striped dolphin. Comparison with previous studies suggests that the formation of mixed-species groups depends on several environmental factors, and therefore may constitute an adaptive response.

Sex bias in biopsy samples collected from free-ranging dolphins

Biological samples of free-ranging dolphins are increasingly used to gain information on population structure and ecology. In small cetaceans, the gender of individuals usually cannot be determined at sea, and population sex ratio has to be inferred indirectly. We used molecular sexing to determine the gender of 340 biopsy samples of bottlenose dolphins, Tursiops truncatus, spotted dolphins, Stenella frontalis, and common dolphins, Delphinus delphis, collected around the Azores and Madeira. Sex ratio was globally skewed in favor of males, and differed between species and archipelagos. Skew was probably influenced by the selectivity of biopsy collectors and seasonal or year-round predominance of males in natural populations. Skew was also influenced by sampling duration and intensity. In the Azores, when several samples were successively collected within the same group, the proportion of female samples decreased as a function of sample order. This trend indicated a tendency for females to increasingly avoid the boat while samples were being collected. It showed that males and females reacted differently to the perturbation caused by the biopsy sampling process (i.e., sample collection and driving style).

Population genetics and social organization of the sperm whale (Physeter macrocephalus) in the Azores inferred by microsatellite analyses

In the northeast Atlantic Ocean, the archipelago of the Azores is frequented by female–offspring groups of sperm whales (Physeter macrocephalus L., 1758), as well as large males. The Azores apparently constitute both a feeding ground and a reproduction site. Little is known about the population and group structure of sperm whales in the area. We analysed 151 sloughed skin and biopsy samples collected from 2002 to 2004. Molecular analyses involved genetic tagging using 11 microsatellite loci and molecular sexing. Our objectives were to determine the population genetic structure, compare relatedness within and between social groups, infer kinship, and estimate the age of males at dispersal. Results suggest that individuals visiting the archipelago of the Azores belong to a single population. High genetic diversity and absence of inbreeding suggest that the population is recovering from whaling. Individuals sampled in close association are highly related, as well as those observed in the same area on the same day, suggesting that secondary social groups (i.e., the union of primary social units) are largely but not exclusively composed of relatives. Probable mother–offspring and full-sibling pairs were identified. Age of males at dispersal was estimated at 16.6 years, which was well above previous estimates for this species.

Using blubber biopsies to provide ecological information about bottlenose dolphins (Tursiops truncatus) around the Azores

Fatty acid profiles were used to investigate aspects of bottlenose dolphin populations around the Azores archipelago. Biopsy samples were obtained from 70 dolphins during the period 2002–2004. No statistically significant differences in profiles were found between different island groups, between sexes or between year of sampling. Thus no evidence was seen for island group fidelity, in contrast to bottlenose dolphins found around similar island groups such as the Hawaiian archipelago or the Bahamas. The findings are consistent with concurrent genetic and photo-identification studies on dolphins in the Azores.

Fatty acid characterization of lipid fractions from blubber biopsies of sperm whales Physeter macrocephalus located around the Azores

Fatty acid profiles of blubber have been shown previously to provide information on stock structure and sex differences. Generally the predominant blubber lipid of marine mammal species is triacylglycerol (fatty acids linked to glycerol) and previous studies have focused on this lipid class. But in some species such as the sperm whales the predominant lipid is wax esters (fatty acids linked to fatty alcohols) although triacylglycerols are also present. In this study the fatty acids and fatty alcohols of these lipid classes were characterized and the fatty acid profiles compared in order to assess their potential to provide qualitative ecological data. Biopsy samples were obtained from 40 whales found in seas around the Azores achipelago during the period 2002–2003. The samples contained about 10% lipid of which 70% was wax ester and 11% triacylglycerol. The fatty acids of the triacylglycerols and wax esters were respectively approximately 19% and 16% saturated, 74% and 80% monounsaturated and 5% and 3% polyunsaturated with the main contributors being 18:1n-9, 16:1n-7 and 16:0. The alcohols of the wax esters were mainly either saturated or monounsaturated with the main contributors being 18:1n-9 (40%) and 16:0 (22%). No statistically significant differences in profiles were found between different island groups, between sexes or between years of sampling. In future studies there would not appear to be any apparent benefits over total lipid in examining each of the fatty acid classes of sperm whale blubber separately.