Description: We report on the investigation of a mass stranding of 68 short-beaked common dolphins (Delphinus delphis) that occurred in Golfo Nuevo, Península Valdés, Argentina in March 2018. Twenty-one of the stranded dolphins were returned alive to the sea, while 47 animals died. Dead dolphins included all ages, with more males than females (29 males and 18 females). The cause of death investigation reported here is restricted to 15 adult individuals and one fetus on which a full set of diagnostics was prioritized due to limited funding. Our results demonstrate that the death of 16 dolphins assessed in this study was not due to obvious human effects (e.g. bycatch) or underlying pathologies, as all animals were in good body condition and had no external evidence of injuries. Infections by Morbillivirus, Influenza A virus, Sarcocystis spp., Toxoplasma gondii, or Neospora caninum, as well domoic acid (DA) toxicity were ruled out as ethiologies in this event. Notably, results on exposure to paralytic shelfish toxins (PSP) were the only investigated cause of death found positive. This is the first documentation of exposure to PSP toxins in short-beaked common dolphins from the Argentine Sea. At present our results are insufficient to assess whether PSP toxin exposure played a role in the death of the stranded dolphins. Notwithstanding, the full documentation and investigation of the most commonly reported pathogens and toxins involved in cetacean mass strandings allowed us to clear the most relevant health differentials and suggests areas for future study. Additional potential hypothesis related to factors known or speculated to cause cetacean mass strandings are currently being explored within the ecological context at the time of the event.

Description: Information on the incidental mortality of dusky and common dolphins in mid-water trawl fisheries along the Argentine shelf was obtainedfor the 1990s. The Argentine anchovy is believed to be an under-exploited resource and is usually taken in purse seine fisheries. However,on the few occasions when it was the target species of large mid-water trawlers, anchovy-eating dolphins were incidentally caught. A fewincidents accounted for relatively high numbers of dolphins but in most of the cases the information obtained was insufficient for detailedanalysis. For three cases, however, sufficient information was obtained to estimate mortality rates. Nevertheless, interpretation of these ratesis difficult for a number of reasons. FV Mar Salvajecaught around 60 common dolphins (Delphinus delphis) in only a few days and in onetow 20 dolphins were caught. Biological information on 18 common dolphins (12 males and 6 females) was obtained and ages ranged from5-10 for females and 2-18 for males.

Description: Food habits of the South American sea lion (Otaria flavescens) off Patagonia were studied by means of stomach content analysis. The samples were collected during 1982–1987 and 1990–1998 in northern and central Patagonia. The samples (n=59) came from individuals found dead on beaches and from animals recovered in incidental catches of the fishery. Forty-one prey species (including fishes, cephalopods, crustaceans, gastropods, polychetes, sponges, and tunicates) were identified; most important were Argentine hake (Merluccius hubbsi), red octopus (Enteroctopus megalocyathus), Argentine shortfin squid (Illex argentinus), “raneya” (Raneya brasiliensis), Patagonian squid (Loligo gahi), and Argentine anchovy (Engraulis anchoita). Differences in diet were found between sexes but not between geographical area of sampling, period of sampling, or source of samples. Females fed mostly on benthic species, whereas males fed mostly on demersal-pelagic species. The difference in diet between sexes was associated with different feeding grounds or different home ranges and could be produced by different constraints in the feeding behavior of each sex. These different constraints and restrictions could lead females to feed in more coastal and shallower waters than those waters where males feed. Some of the important prey were commercial species (Argentine hake, Argentine shortfin squid, Patagonian squid) consumed at both commercial and noncommercial sizes by sea lions. The presence of gastroliths was independent of the presence of stomach parasites; however, gastrolith weight was positively correlated with individual sea lion’s length, indicating that gastroliths could be involved in buoyancy control. In summary, these stomach content analyses indicate that South American sea lions feed primarily on demersal and benthic species and, in general terms, use resources according to their environmental availability.