Abstract
Since the 1980s, the distribution range of the southern right whale (Eubalaena australis) in Argentina was mostly located in the winter calving grounds around Península Valdés. After the international moratorium that forbade the commercial hunting, southern right whales have shown signs of recovery during the last few decades. Nowadays, it is thought that the species is experiencing a density-dependent process while expanding its distribution range in Patagonia. From 2007 to 2016, data on right whale distribution, group composition and relative abundance were collected in Golfo San Matías, Patagonia through aerial surveys. Generalized linear models with a negative binomial error distribution were used to determine the population trend of right whales in this area. In addition, the group composition and the relative abundance of right whales among the northern Patagonian gulfs were compared. Finally, a literature review was conducted to assess the historical presence of right whales in Golfo San Matías, revealing the presence of right whales in Golfo San Matías during and after the commercial exploitation. During aerial surveys (2007–2016), right whales were observed from August to October in the area, with a peak in late August-early September. Our results suggested a geographic distribution change with a regular use of the northwest coast of the gulf in recent years and a positive trend in the population growth rate inside Golfo San Matías. This area was dominated by unaccompanied whales (solitary individuals and breeding groups) as opposed to Península Valdés where the dominant group type was the mother calf pairs. Therefore, Golfo San Matías appears to be important for socializing and mating but not as a nursery ground. In addition, the density of whales was four times greater in the gulfs of Península Valdés. Our findings contribute to a better understanding of the recovery of this species in Patagonia, Argentina and should be considered for the management measures for right whales in this region.
Highlights
During the eighteenth and nineteenth centuries commercial whaling caused a drastic decrease in the number of southern right whales (SRW) Eubalaena australis bringing them to the brink of extinction [1] with only 200–300 individuals left by 1920 [1,2]
The Beaufort was recorded in each of the 5 km coast segments mentioned above, and the median was estimated as a proxy for the conditions in each flight. The objective of this model building was to test if there is an effect of the year on the number of whales recorded in the coastal aerial surveys; we only considered the subset of models that included the explanatory variable Year plus the null model
The second expedition was made by the Captain Benjamin Morrell, who in his passage through the port of Rıo Negro (Fig 1, mouth of Rio Negro river), in the north coast of Golfo San Matıas (GSM), on 9/21/1822 commented “. . .our vessel being the first from the United States that ever entered to this river. (. . .) Rio Negro had been of very little note; but it is much frequented, especially by whalers, who touch here for refreshments” remarking the presence of whaling ships in the area
Summary
During the eighteenth and nineteenth centuries commercial whaling caused a drastic decrease in the number of southern right whales (SRW) Eubalaena australis bringing them to the brink of extinction [1] with only 200–300 individuals left by 1920 [1,2]. Areas with suitable environmental conditions around these wintering grounds could be colonised by the species This hypothesis is supported by more frequent sightings of SRW in recent years in Rio Grande do Sul in Brazil [9], Uruguay [15, 16] and Golfo San Matıas (GSM) in Argentina [17,18,19]. In the latter, the presence of whales has become so frequent that whale watching has taken place since 2012 [18]
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