We assessed the level of genetic variability and population structure of the common bottlenose dolphin (Tursiops truncatus) in the tropical and subtropical portions of the southwestern Atlantic Ocean and compared the results with previous morphological findings. We analyzed 109 samples of common bottlenose dolphins that were sequenced for control region mtDNA and genotyped for seven polymorphic microsatellite loci. The results suggested that the species in this region can be separated in two major biological units, northern and southern, with an area of parapatry at southern Brazil. The northern unit seems to occur in a wide range of depths, including

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Two minke whale species are recognized, the Antarctic minke (Balaenoptera bonaerensis) and the cosmopolitan common minke (Balaenoptera acutorostrata) whales. The latter is divided into three subspecies: North Pacific (NP) B. a. scammoni, North Atlantic (NA) B. a. acutorostrata, and the Southern Hemisphere 'dwarf' minke whales B. a. unnamed subsp. Genetic variation of two populations of dwarf common minke whales from the Western South Atlantic (WSA) and Western South Pacific (WSP) was assessed through analysis of mitochondrial DNA (mtDNA) control region sequences (313 bp) and microsatellite DNA (msDNA) (11 loci). For comparative purposes, the mtDNA analysis involved samples of Antarctic minke whales, NP, and NA common minke whales. The msDNA analysis included individuals from the WSA, WSP, and NP. There was no shared mtDNA haplotype among common minke whales, and the mtDNA haplotype phylogeny analyses placed WSA in a different cluster from WSP and closer or within the NA clade. The WSA population exhibited the lowest estimates of diversity for both markers. The estimate of Nei's net nucleotide substitution (d A ) between WSA and WSP (0.027) was larger than between WSA and NA (0.014) whales. Significant msDNA differences (based on F ST and D SW ) were found among NP, WSA and WSP, and the pattern of differentiation was similar to that of the mtDNA. Results suggested that the taxonomical status of common minke whales in the Southern Hemisphere should be revised and that regardless of their taxonomical status, dwarf common minke whales from WSA and WSP are unique populations that require separate management for conservation.

A little‐studied common bottlenose dolphin (Tursiops truncatus) population inhabits the offshore waters surrounding Saint Paul's Rocks, a Brazilian marine protected area in the equatorial Atlantic Ocean. Five field expeditions (May 2011–May 2013) were conducted to characterize the habitat use, population size, and site fidelity of this population. Three different survey methods were employed: line‐transect surveys, land‐based surveys, and photo‐identification surveys. A population size of 23 individuals (19–28, CI 95%), which were present on most sampling days (>90% of surveys), was estimated. The maximum resighting interval of photo‐identified animals was 9 yr and 3 mo for five distinct individuals, based on data from nonsystematic efforts that have been ongoing since 2004. The dolphins exhibited strong site fidelity, as the minimum convex polygon (MCP, 95%) method revealed that they restricted their movements to a 0.5 km2 area across seasons and a 0.99 km2 area across years (95% kernel). The dolphins preferred shallow waters close to the archipelago (<1.2 km from the islands), especially on the eastern and southeastern sides, where oceanographic models have revealed persistent upwelling that may result from underwater currents and where food may be more predictably available.

Marine mammals and humans are apex predators and both may compete for fish in ecosystems under continuous fishing pressure. We assessed the degree of trophic overlap between prey species found in the diet of 5 marine mammals (39 specimens of sea lion Otaria flavescens, 61 fur seals Arctocephalus australis, 76 franciscana dolphins Pontoporia blainvillei, 25 bottlenose dolphins Tursiops truncatus and 28 Lahille’s bottlenose dolphins T. gephyreus) and the catches of the 6 main commercial fishing gears used in southern Brazil (coastal gillnets, oceanic gillnets, purse seine, demersal pair trawling, bottom [single] trawl and double-rig trawling) between 1993 and 2016. An adjusted general overlap index indicated an overall moderate to high overlap. Specific overlap analysis showed that O. flavescens and T. truncatus presented high trophic relationships with fisheries, followed by T. gephyreus. Smaller interactions were observed for A. australis and P. blainvillei, even though they also exploit commercial fishing resources. Coastal gillnet and pair bottom trawling are the fisheries that most target the fish species favoured by O. flavescens, T. gephyreus and T. truncatus. The information presented in this study on trophic interactions may assist decision making for both fishery management and conservation measures for these apex predators. Commercial fishing activities are a major threat to marine mammals both regionally and globally. Current levels of fishing or its intensification may lead to dramatic changes in the coastal marine food web, including additional threats to coastal marine mammal populations in southern Brazil.