Lucas Milmann

The ecology and distribution of most baleen whales are poorly known in Brazilian waters, despite the history of whaling and the recent increase in the research effort. Although stranding data presents some caveats, it is useful to understand patterns of distribution and occurrence and to detect population trends. In this scenario, data from 25 years of a monitoring marine mammal stranding program were used to evaluate the composition and spatial-temporal patterns of Balaenoptera whales in southern Brazil. A stretch of 270 km on the coast of Rio Grande do Sul State (from 29°20’S to 31°21’S) was surveyed year-round between 1993 and 2018. Whales were identified, measured and sex determined whenever possible. Molecular identification through mtDNA analysis was obtained for 22 individuals and confirmed field identification in 17 cases. Forty-eight whales of four species were recorded: common minke whale B. acutorostrata n = 27, Antarctic minke whale B. bonaerensis n = 1, Bryde’s whale B. brydei n = 13, fin whale B. physalus n = 1. In addition, six whales were not identified at species level due to advanced decomposition. The larger number of strandings of common minke and Bryde’s whales may be related to their greater abundance and/or more coastal distribution. Both species were recorded year-round, but strandings of common minke and Bryde’s whales occurred mostly during winter/spring (77.77%) and spring/summer (66.66%), respectively. Although Bryde’s whales appear to remain in southern Brazilian waters during the entire year, the results suggest the existence of seasonal inshore-offshore movements. Moreover, the greater number of strandings of juveniles of common minke whales compared to adults (ratio 1.86:1) and their occurrence in different seasons suggest that some immature individuals may not leave this region, as previously pointed out by other studies. This long-term survey brings new evidence of the importance of this region in the Southwestern Atlantic Ocean for some Balaenoptera species.

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.

The stomach content of a male, immature dwarf minke whale (Balaenoptera acutorostrata subsp.) stranded in September of 2008 in southern Brazil revealed a large consumption of the Argentine shortfin squid (Illex argentinus), probably in multiple feeding events. Stable isotopes signals from kidney and liver samples of the whale are consistent with values for this squid species, and prey size indicates consumption over spawning aggregations near the continental slope off southern Brazil. The present record adds a new prey species for dwarf minke whale and reinforces the hypothesis that some baleen whales could feed in middle latitudes of the Brazilian coast.

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.