Dolphin watching is a relatively newly developed tourist activity. Although it is assumed to contribute to the conservation of marine ecosystems, its long-term adverse effects are still unknown. The present work aims to assess the impact of tour vessels on the behavior pattern of dusky dolphins displaying diurnal and cooperative feeding. We evaluated potential bias of commercial vessels to specific activities, short-term responses of dolphins to vessel approach, and longer-term effects of these changes, particularly on the activity budget and the time dolphins need to resume an activity. Several field experiments were carried out in which dolphins were approached by a research vessel or by commercial vessels. Group tracking was also made from a research vessel. Behavioral sequences were modeled by stochastic matrix models. Activity budget and time to return to an activity were obtained from matrix properties. Commercial trips found mostly feeding groups. Feeding showed the highest rate of change at the moment of vessel approach, and commercial vessels had an effect on the direction of change. Over the longer term, feeding and socializing time budgets decreased when commercial vessels were present. The time to return to feeding as well as the time it took for a group of dolphins to feed increased in the presence of commercial vessels. Dusky dolphins in South Atlantic waters feed during the day on patchily distributed prey. Our study demonstrates that boat presence negatively affects the longer-term feeding efficiency of dusky dolphins.

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This is the first study in Argentine waters on the abundance of the threatened Franciscana dolphin, Pontoporia blainvillei. During 2003–2004 we carried out 17 aerial surveys using line transect sampling methodology. We observed 101 Franciscanas in 71 sightings. In northern areas density was estimated at 0.106 individual/km2. Density was lower in southern areas (0.055/km2) and declined with depth beyond 30‐m isobaths (0.05/km2). A correction factor for submerged dolphins was applied to density and then extrapolated to the strip between the coastline and the 30‐m isobath. Abundance in the northern area was estimated at 8,279 (4,904–13,960) individuals, while in the southern area it was estimated at 5,896 (1,928–17,999) individuals. Considering an annual mortality of about 500–800 individuals, about 3.5%–5.6% of the stock may be removed each year by the fishery and over the 2% recommended by the International Whaling Commission (IWC) and may not be sustainable by the population. Higher densities in coastal areas make Franciscanas more vulnerable to coastal fishing camps, which increased mortality in recent years. A remarkable finding was that while density decreases to the south, values of catch per unit effort (CPUE) increases, indicating different catchability of dolphins between areas.

The rocky intertidal zone around the city of Mar del Plata (SW Atlantic, 38° S–57° W) is characterized by dense mussel beds of Brachidontes rodriguezii. This intertidal community develops on natural and artificial hard substrates, including abrasion platforms in sewage‐impacted areas. A monitoring program, designed to assess the effect of sewage discharge on intertidal macrobenthic communities, has been conducted since 1997. During the spring season of 2008, a new spionid polychaete (Boccardia proboscidea) was found near the sewage outfall, forming large biogenic reefs. This is the first report of biogenic reefs being built by a non reef‐forming spionid polychaete in areas organically impacted by sewage discharges. The aim of this work was to evaluate the spatial–temporal dynamics (% cover and density of B. proboscidea) of these reefs. These biogenic reefs covered almost the entire impacted site, reaching a density of 650,000 ind·m−2. This phenomenon is unique in that there is no other record available worldwide of any other biogenic polychaete reefs that could be sewage‐induced. The presence and stability of these biogenic reefs is discussed in relation to increased organic contamination as a structuring factor.

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The management scheme of Marine Protected Areas (MPAs) includes monitoring protocols but such activities are not always carried out. This is the case for Golfo San José, a MPA in northern Patagonia, Argentina. It was created in 1975 for the protection of the southern right whale (Eubalaena australis) breeding grounds. Other components of the system, such as dolphin populations have received little attention. This study is the first attempt to estimate sighting rates, group size and overall abundance of a bottlenose dolphin (Tursiops truncatus) population in Golfo San José and adjacent areas after 30 years. An analysis of the seasonal sighting rates indicates that bottlenose dolphins were present in the study area throughout the year but a decline in group size and abundance and major shift in distribution was detected when compared with previous published reports. The settlement of the MPA failed to secure the persistence of the bottlenose dolphin population within its boundaries. Possible explanations for the detected decline are addressed including increased natural mortality, human induced mortality and disturbance, resources depletion and environmental shift.