The patterns of habitat use by the franciscana dolphins (Pontoporia blainvillei) along its distribution are poorly known. This study investigates the patterns of habitat use with respect to depth for 181 individuals of different age, size, gender and reproductive condition off Rio Grande do Sul, southern Brazil. The results reveal that franciscanas are very homogeneously distributed according to depth. Individuals from all lengths utilize nearly the entire range of depths of the surveyed area. Larger or older animals do not use deeper waters than younger animals, indicating that body size and age are not limiting factors for franciscanas that occupy deeper or offshore waters. Gestation seems to not cause a change in the distribution of females. Although the sex-ratio of the overall data did not vary from 1:1 in different depth intervals, a small-scale comparison between the northern and southern coast demonstrated the existence of some kind of sexual segregation. Franciscana by-catch in Rio Grande do Sul is not sustainable and it is agreed that management procedures are needed. Nevertheless, the available data on species distribution do not allow the designing of a protected area in order to minimize the by-catches of a particular sex/reproductive class.

The humpback whale, Megaptera novaeangliae, is a highly migratory species distributed in all oceans of the world. It has been indicated that humpbacks do not normally feed while in their tropical breeding grounds or during migration. Here we document the first evidence of recent feeding in southern Brazil, a mid-latitude area in the western South Atlantic Ocean. On 4 April 2002, the carcass of a 7.27 m humpback whale incidentally caught in Rio Grande do Sul, southern Brazil, was collected. Investigation of the stomach contents revealed that the whale had ingested large amounts of the small shrimp Acetes americanus (Decapoda: Sergestidae), as well as planktonic larvae of unidentified species of Brachyura. Applying the average swimming speed recorded for this species on the western South Atlantic coast, and the mean time passage of the food through the digestive tract of another balaenopterid, we can estimate that the feeding area is some 20.7 nautical miles off the coast. This demonstrates that the productive waters of the southern and south-eastern Brazilian coast may occasionally be used by humpback whales as an opportunistic feeding zone, and adds the shrimp A. americanus as a new prey species for the humpback whale. There is evidence that other baleen whales may also sometimes feed in this region.

The franciscana dolphin has been considered the most threatened small cetacean in the south-western Atlantic Ocean due to gillnet by-catch. The estimation of the species' abundance has been recommended as the highest research priority. A line transect aerial survey to estimate franciscana abundance in Rio Grande do Sul, southern Brazil, was carried out in February 2004. The overall surveyed area comprised 13,341 km²and at least 20 transect lines. Abundance was estimated using distance sampling methods and assuming g(0) = 0.304. The corrected density is 0.51 franciscanas/km², resulting in an abundance estimation of 6839 franciscanas (CV = 32%; 95% CI = 3709–12,594) for the surveyed area in Rio Grande do Sul. To improve this estimate: (a) perception bias should be determined; (b) the parameters influencing availability bias should be identified and quantified; and (c) survey sample size should be increased. While the lack of data to correct for perception bias and group size underestimation in this aerial survey is likely to yield an underestimate of franciscana abundance, the use of surfacing and diving time data from boat and land-based surveys to correct for availability bias is likely to cause its overestimation. Alternative values of the g₀group-size estimates and rates of increase were incorporated in the analyses, creating 240 different estimates of annual increment for this franciscana population. Even in the most optimistic scenario, the annual increment of franciscanas is not sustainable with the current levels of by-catch in Rio Grande do Sul, and fishery management to reduce by-catch must be initiated promptly.

Age and length data of 291 franciscana dolphins (Pontoporia blainvillei) incidentally captured on the coast of Rio Grande do Sul State (RS), southern Brazil, were used to fit growth curves using Gompertz and Von Bertalanffy growth models. A small sample of franciscanas (N = 35) from Buenos Aires Province (BA), Argentina, were used to see if there are apparent growth differences between the populations. Male and female franciscana samples from both areas were primarily (78–85%) <4 years of age. The Von Bertalanffy growth model with a data set that excluded animals <1 year of age provided the best fit to data. Based on this model, dolphins from the RS population reached asymptotic length at 136.0 cm and 158.4 cm, for males and females, respectively. No remarkable differences were observed in the growth trajectories of males and females between the RS and BA populations.

The southern right whale (SRW), Eubalaena australis, was heavily depleted by the whaling in the Southern Hemisphere. In the southwestern Atlantic, studies on SRWs have been concentrated in two main breeding grounds: Península Valdés, Argentina (~42°′S) and Santa Catarina (SC) State, Brazil (~28°′S). To better understand the ecology of SRWs in the region located between these breeding grounds, shore-based surveys were carried out off Torres (29°19′S, 49°43′W), Rio Grande do Sul (RS). Whales were observed in the area between July and October with peaks in August and September. Group sizes were relatively small (x̅=1.6; range=1–3). Distribution in relation to distance from the coast varied from 0.5 to 8.9 km (median=1.9 km). Unlike in other areas, mother-calf pairs were not observed to occur in shallower waters more often than unaccompanied whales. Mother-calf pairs presented northbound movements to SC more frequently than unaccompanied whales. A comparison of the present data with those from Uruguay and SC revealed that SRWs of different gender/reproductive status may use distinctively the eastern coast of South America. Within these regions, the proportion of mother-calf pairs increases progressively as latitude decreases (from 8% in Uruguay to 58.5% in SC), while the proportion of unaccompanied SRWs presents an opposite trend. This study indicates that RS is an important area for reproduction of SRWs because the three phases (birth, nursing, and mating) proposed for a breeding ground occur there.