Genetic isolation and morphological divergence of Black Sea bottlenose dolphins

The Black Sea is a semi-enclosed body of water that differs from the adjacent Mediterranean Sea in terms of its biodiversity, oceanographical and ecological characteristics. There is growing international concern about pollution in the Black Sea and other anthropogenic threats to its fauna. The bottlenose dolphin (Tursiops truncatus) is one of three species of cetaceans living in the Azov-Black Sea basin. Despite considerable research on bottlenose dolphins elsewhere, the extent of human impacts on the Black Sea populations is unknown. Previous attempts to award special conservation status to Black Sea cetaceans have failed specifically because policy makers have viewed their ecological and evolutionary uniqueness as equivocal. This study assessed divergence between Black Sea, Mediterranean Sea and Atlantic Ocean bottlenose dolphins for 26 cranial measurements (n = 75 adult bottlenose dolphin skulls) and mitochondrial DNA (n = 99 individuals). Black Sea bottlenose dolphins are smaller than those in the Mediterranean, and possess a uniquely shaped skull. As in a previous study, we found the Black Sea population to be genetically distinct, with relatively low levels of mtDNA diversity. Population genetic models suggest that Black Sea bottlenose dolphins have so little gene flow with the Mediterranean due to historical isolation that they should be managed separately.

Biological Background on Bottlenose Dolphins (Tursiops spp.) in the 'Live-Capture' Trade and Specifically on the Indo-Pacific Bottlenose Dolphin, T. Aduncus

The most significant cetacean trade items until commercial whaling all but ceased in the 1990s (aside from scientific exchanges of tissues etc.) were meat and blubber from baleen whales for human consumption. Since then, live dolphins and 'small' whales for display (and to some extent for research, military use, and 'therapy') have become the most significant cetacean 'products' in international trade. Trade in live cetaceans is presently dominated by bottlenose dolphins (Tursiops spp.), beluga whales (Debhinapterns leucas) and to a lesser extent killer whales (Orcinus orca) (Fisher and Reeves 2005). In the past, most of the dolphins in trade were common bottlenose dolphins (Tursiops truncatus) originating in the United States, Mexico and the Black Sea, but since the 1980s the United States has essentially stopped its capture-for-export activities and in 2001Mexico implemented a moratorium on live-captures. The source countries for dolphins in trade are now geographically diverse, but Cuba and Japan are currently major source nations for common bottlenose dolphins. Russia is the only current source for belugas. Russia and Japan have become the main potential sources for killer whales since Iceland ceased exporting them in the 1980s or early 1990s.

The Gonads of the South American Dolphins, Inia geoffrensis, Pontoporia blainvillei, and Sotalia fluviatilis

The appearances of the gonads are described in males and females of 18 Inia geoffrensis, 11 Pontoporia blainvillei, and eight Sotalia fluviatilis from South America. Males of I. geoffrensis become sexually active at a length of about 228 centimeters, females at 175 to 180 centimeters. Length at birth is 76 to 80 centimeters; parturition occurs from about July to September in the upper Amazon. Males of P. blainvillei are still sexually immature at a length of 128.5 centimeters, females become sexually active at a length of 137 centimeters. Off Uruguay, pregnant females have fetuses 6 centimeters in length in February and 61 centimeters in October. Males of S. fluviatilis are sexually active at a length of 148 centimeters, females at 140 centimeters. Gonad weights and details of corpora lutea and albicantia are given. Corpora albicantia appear to persist as in other cetaceans. The ovaries of I. geoffrensis are relatively bulky with the corpora enclosed in the ovarian substance and not pedunculated as in P. blainvillei and S. fluviatilis in which the right ovary is poorly developed.

Taxonomy of the Common Dolphins of the Eastern Pacific Ocean

Delphinus bairdii Dall is a species of dolphin distinct from D. delphis Linnaeus, with which it has usually been synonymized. D. bairdii has a longer rostrum relative to the zygomatic width of the skull; the ratio of these measurements falls at 1.55 or above for bairdii and 1.53 and below for delphis. In the eastern Pacific Ocean, D. bairdii is found in the Gulf of California and along the west coast of Baja California, Mexico; D. delphis is presently found in the waters off California. Until approximately the beginning of the present century, bairdii occurred farther north in the eastern Pacific Ocean, at least to the Monterey Bay area of California. Restriction of bairdii to more southerly waters, probably as an indirect result of a change in water temperature, may have permitted delphis to move into inshore Californian waters. The Pacific population of D. delphis has a somewhat shorter rostrum than the Atlantic population, and is perhaps subspecifically different. A thorough analysis of the entire genus Delphinus is needed before the relationship of all the populations can be understood and names properly applied.

Evolution of river dolphins

The world's river dolphins (Inia, Pontoporia, Lipotes and Platanista) are among the least known and most endangered of all cetaceans. The four extant genera inhabit geographically disjunct river systems and exhibit highly modified morphologies, leading many cetologists to regard river dolphins as an unnatural group. Numerous arrangements have been proposed for their phylogenetic relationships to one another and to other odontocete cetaceans. These alternative views strongly affect the biogeographical and evolu- tionary implications raised by the important, although limited, fossil record of river dolphins. We present a hypothesis of river dolphin relationships based on phylogenetic analysis of three mitochondrial genes for 29 cetacean species, concluding that the four genera represent three separate, ancient branches in odontocete evolution. Our molecular phylogeny corresponds well with the first fossil appearances of the primary lineages of modern odontocetes. Integrating relevant events in Tertiary palaeoceanography, we develop a scenario for river dolphin evolution during the globally high sea levels of the Middle Miocene. We suggest that ancestors of the four extant river dolphin lineages colonized the shallow epicontinental seas that inundated the Amazon, Parana, Yangtze and Indo-Gangetic river basins, subsequently remaining in these extensive waterways during their transition to freshwater with the Late Neogene trend of sea-level lowering.

Book Review of Cetacean Societies: Field Studies Of Whales And Dolphins Edited by I. Mann, R. C. Connor, P. L. Tyack & H. Whitehead

Studying the sociobiology and behavioral ecology of cetaceans is particularly challenging due in large part to the aquatic environment in which they live. Nevertheless, many of the obstacles traditionally associated with data gathering on tree-ranging whales, dolphins and porpoises are rapidly being overcome, and are now far less formidable. During the past several decades, marine mammal scientists equipped with innovative research methods and new technologies have taken field-based behavioral studies to a new level of sophistication. In some cases, as is true for bottlenose dolphins, killer whales, sperm whales and humpback whales, modern research paradigms in the marine environment are comparable to present-day studies of terrestrial mammal social systems. Cetacean Society stands testament to the relatively recent advances in marine mammal science, and to those scientists, past and present, whose diligence has been instrumental in shaping the discipline.