Introduction
Populations of the southern right whale (SRW) Eubalaena australis (Desmoulins, 1822) are distributed between 18°S and 65°S (Bastida et al., Reference Bastida, Rodríguez, Secchi and Da Silva2007). In the South-western Atlantic, the major calving areas are located in Argentina (Península Valdés, 42°46′S 65°02′W) (PV) and Brazil (Santa Catarina, 27°35′S 48°28′W) (SC). These whales spend part of the year (the austral winter and spring) in northern inshore waters where they breed and then migrate to southern feeding grounds during the summer (Bastida & Lichtschein de Bastida, Reference Bastida and Lichtschein de Bastida1984; Payne et al., Reference Payne, Rowntree, Perkins and Cooke1990; Best, Reference Best2000; Rowntree et al., Reference Rowntree, Payne and Schell2001; Santos et al., Reference Santos, Siciliano, Pacheco de Souza and Almayer Pizzorno2001; Arias et al., Reference Arias, Romero, Svendsen, Curcio, Jarma, Coscarella, Dans, Crespo and González2015, Reference Arias, Coscarella, Svendsen, Romero, Curcio, Sueyro, Crespo and González2017).
SRWs were exploited along the South American Atlantic coast for many years. During the 18th and 19th centuries, commercial whaling caused a drastic decline in SRW populations, leading the species to the brink of extinction (Baker & Clapham, Reference Baker and Clapham2004). Historically, whalers were continuously distributed from Brazil down to southern Argentina including Tierra del Fuego, Malvinas-Falkland Islands and South Georgia Islands (Townsend, Reference Townsend1935; Richards, Reference Richards2009). Catches showed a sharp increase during the mid-1800s, with a slow decrease following international protection in 1935, and another increase as a result of illegal Soviet catches in the 1960s (Tormosov et al., Reference Tormosov, Mikhalev, Best, Zemsky, Sekiguchi and Brownell1998).
Towards the end of the 20th century, SRW populations in Argentina, Brazil, South Africa and Australia have shown signs of recovery, doubling over a period of 10–12 years (Bannister, Reference Bannister2001; Best et al., Reference Best, Brandão and Butterworth2001; Cooke et al., Reference Cooke, Rowntree and Payne2001; Crespo et al., Reference Crespo, Pedraza, Dans, Coscarella, Svendsen and Degrati2015; Groch, Reference Groch, Rossi-Santos and Finkl2018). Since the 1970s, the population that breeds in PV (Argentina) grew at a rate of 6.9% per year (Cooke et al., Reference Cooke, Rowntree and Payne2001; Crespo et al., Reference Crespo, Pedraza, Dans, Coscarella, Svendsen and Degrati2014), and between 1999 and 2015, although it also grew, it did so at lower rates (Crespo et al., Reference Crespo, Pedraza, Dans, Svendsen, Degrati and Coscarella2019).
The increase in SRW numbers observed during the 1980s was followed by a tendency to re-occupy historical areas along the South-west Atlantic coastline like SC in Brazil, the Uruguayan coast and different regions of the Patagonian coast (Santos et al., Reference Santos, Siciliano, Pacheco de Souza and Almayer Pizzorno2001; Iñíguez et al., Reference Iñíguez, Belgrano, Tomsin, de Haro, Gribaudo and Tossenberger2003; Piedra et al., Reference Piedra, Costa, Franco-Fraguas, Menafra, Rodriguez Gallego, Scarabino and Conde2006; Belgrano et al., Reference Belgrano, Iñíguez, Gibbons, García and Olavarría2008; Failla et al., Reference Failla, Vermeulen, Carabajal, Arruda, Godoy, Lapa, Mora, Urrutia, Balbiano and Cammareri2008; Vermeulen, Reference Vermeulen2013; Danilewicz et al., Reference Danilewicz, Moreno, Tavares and Sucunza2016).
The coast of Mar del Plata (MDP) is located between the two main reproductive areas of the species in the South-west Atlantic (SC and PV). It is important to follow the presence of this whale not only in its breeding and feeding grounds, but also along its journey. In the case of the coastal area of MDP, in the last decade there is a potential interest in whale-watching from land, both from tourists and local residents.
SRWs have been protected in Argentina's territorial waters since 1984, when they were declared a National Natural Monument (Law 23.094, 1984). The species is listed as of least concern (LC) in the IUCN Red List of Threatened Species (Cooke & Zerbini, Reference Cooke and Zerbini2018); nevertheless, in Argentina the species was listed as Vulnerable (VU) (Ojeda et al., Reference Ojeda, Chillo and Díaz2012).
Monitoring the presence and frequency of marine mammal species in coastal areas is a basic step in providing information for conservation and management and because of their value as educational and touristic resources. The purpose of the present study is to report the presence of SRWs on their journey off the coast of MDP, an intermediate area between the two main breeding grounds of the species, based on sighting records during the past half century. Our hypothesis is that SRWs use the study area as a passage zone on their migratory route and as a transit area to the southern feeding grounds at the end of the austral spring.
Materials and methods
Study area and sighting period
The fieldwork took place along the coasts of MDP (38°03′S 57°31′W) (Figure 1). The area consists of ~40 km of sandy beaches, quartzite rock outcrops and sedimentary rock cliffs that reach heights of up to 40 m. These topographic features allow a better observation of marine mammals from the shore, making it one of the best areas in Buenos Aires Province (BAP) for such activities.
Sighting points along Mar del Plata coast (MDP) during 1970–2016. The circles on the upper map indicate the closest breeding grounds: Santa Catarina (Brazil) (SC) and Península Valdés (Argentina) (PV).
Observations were carried out as part of a marine mammal-monitoring project. Weekly surveys were made every month throughout year during the study period (1966–2016), in different points of MDP, between Constitución and Chapadmalal (Figure 1).
Sightings were performed from land by one or two observers, with either the naked eye or using binoculars and a monocular Bushnell Stalker Zoom 10 × 30 mm. For sightings at very great distances, we used a Bushnell Sport View telescope zoom 20–60 × 60 mm Spotting Scope.
For each sighting, we recorded the following data: number of individuals, general behaviour, eventual presence of calves, and displacement direction of individuals (when the animals were swimming actively and followed a fixed course sustained over time). Associated with whale sightings we also recorded the presence of other marine mammal species and seabirds. When whales were at a distance less than 1000 m from the observer, we recorded behavioural information of the individuals as defined by Costa et al. (Reference Costa, Piedra, Franco and Paez2007). We collected data on SRW activity patterns via an ad libitum sampling mode. Permanence time in the area was estimated based on direct observation of the same number of animals, in the same site, during continuing hours or days, assuming that those animals were always the same ones.
In addition, as complementary information, during 2007–2017, marine mammal observers obtained records of SRWs along seven oceanographic campaigns (which were not designed for the assessment of marine mammal populations, but were opportunistic sightings) and two seismic surveys in the Argentine continental shelf off BAP.
Data analysis
We analysed the frequency of SRW coastal sightings, geographic distribution and pod size throughout the 1966–2016 period and along different months of the year. We defined the total number of whales per year as the sum of individuals recorded from land along the year.
Time series analysis techniques were applied to assess the trends of sightings during the study period. We used non-parametric regression techniques to test the trend and the seasonality of a time series. For this purpose, a seasonal decomposition of a time series Xt determining a Tt trend was used; seasonal component St from the difference Xt−Tt was calculated (Cleveland et al., Reference Cleveland, Cleveland, McRae and Terppening1990). For the analysis of mean stability and seasonality, the original time series was plotted to establish if a trend was observed in relation with time and if there was seasonality or periodicity.
All analyses were carried out using R 3.3.1 Software (R Development Core Team 2015).
Results
Abundance and seasonality
Between 1966 and 2016 we recorded 344 SRW coastal sightings (N = 718) in the MDP area. Although coastal sighting routines began in 1966, we recorded the first SRW in 1970 and there were no further sightings of the species until 1976. Since that year until now, SRW sightings have increased gradually, reaching a peak of 28 sightings (N = 63 whales) in 2016 (Figure 2).
Number of SRW sightings (white circle) and number of whales (black box) recorded per year along MDP coast during 1970–2016 period. The lines represent the trends of sighting and whales records.
SRW presence in MDP has a clear trend and seasonality, as observed through the analysis of non-parametric regression techniques (Figure 3). Although we recorded SRWs between April and November, sightings were more frequent between July and mid-October (86.2%). In the 1970s, a few sightings occurred between July and November, and the number of sightings was similar to the number of whales observed; in the 1980s, the sighting season had extended and occurred from May to December, with a maximum number of whales and whale sightings in September. In the 1990s, sightings were more frequent in August, while in the 2000s they were more frequent in October followed by August and September, the latter with more sightings and a higher number of whales. Finally, in the first years of the current decade (2010–2016), the sighting peak was in August, followed by September and October (Figure 4).
Seasonal decomposition of a time series Xt by determining a trend Tt and calculating a seasonal component St from the difference Xt−Tt for SRW sighting along MDP coast during 1970–2016.
Number of SRW sightings (white bars) and number of whales (black bars) recorded along MDP coast throughout the different months, during 1970–2016, expressed by decades. The decades of 1970 and 1980 were plotted together due to the low amount of data obtained.
During the first years of our study, sightings of SRWs in MDP consisted of solitary individuals passing through the area. As time went by, group size increased to 2–8 individuals. Along the period of study 41.2% of sightings corresponded to groups of 2 individuals, 35.4% were solitary specimens, while 23.4% were groups comprising between 3 and 8 individuals (Figure 5). The mean group size registered during the last decade was 2.8 ± 0.4 whales, with the largest group made up of 8 individuals recorded in 2013.
Comparison of SRW pod size observed: along the MDP coast during 1970–2016 period (black bars), Uruguay (sampling in 2001–2003; Costa et al., Reference Costa, Praderi, Piedra and Franco-Fraguas2005, Reference Costa, Piedra, Franco and Paez2007) (grey bars) and Torres, southern Brazil (sampling in 2002; Danilewicz et al., Reference Danilewicz, Moreno, Tavares and Sucunza2016) (white bars).
Whales observed in the study area were mainly adults. The first calves recorded in MDP date back to 1983. The presence of calves during the whole period of this study was an unusual event. In spite of the fact that there was an increase in number of calves in the area during the last decades, the relative number of calves/number of SRWs along the five decades of this study was consistently low, with calves representing 5% of the total number of specimens sighted in MDP (Figure 6).
Relationship of number of calves/total number of sightings on the coast of MDP during 1970–2016 period.
Finally, we found that there is a positive tendency between increase of SRW sightings in MDP and the number of mother-calf pairs observed in the closest breeding grounds of the South-west Atlantic: PV, Argentina and SC, Brazil (Figure 7).
Number of whales per year recorded along MDP coast during 1970–2016 period (grey bars). Number of mother–calf pairs observed in the breeding areas of Península Valdés (white dots) and Santa Catarina (black box). (Brazil: Groch et al., Reference Groch, Palazzo, Flores, Adler and Fabian2005; Seyboth et al., Reference Seyboth, Groch, Dalla Rosa, Reid, Flores and Secchi2016. Argentina: own records, period 1981–1990; Payne et al., Reference Payne, Rowntree, Perkins and Cooke1990; Crespo et al., Reference Crespo, Pedraza, Dans, Coscarella, Svendsen and Degrati2014, Reference Crespo, Pedraza, Dans, Coscarella, Svendsen and Degrati2015; Cooke et al., Reference Cooke, Rowntree and Sironi2015).
Route and permanence
The majority of whales recorded from land in MDP before mid-October were travelling north, but later in the year most whales headed south (χ2 = 15.589, df = 2, P < 0.005).
In complementary oceanographic expeditions we recorded 17 SRW sightings (N = 32) within the Argentine continental shelf off BAP, between July and December. Sightings occurred between July and September at depths of up to 50 m. In contrast, sightings made between October and December were of animals moving close to the continental slope (depth > 200 m) (Figure 8).
Records of southern right whale obtained during seven oceanographic campaigns and two seismic surveys in the Argentine continental shelf off Buenos Aires Province in different months of the 2007–2017 period. Black dots: sightings between July and September. Black box: sightings between October and January.
During the period of study, SRWs remained in MDP for an average period of 2 days (mean = 1.78 ± 1.43; max = 5 days). However, in the last 10 years, their permanence increased slightly (before 2005: mean = 1.46 ± 1.46; after 2005 mean = 2.21 ± 1.1). Of all sightings, 3.16% (N = 11) were recorded in the harbour area, probably because whales were looking for shelter or calm waters.
The most frequent behaviour recorded during the period of study was free movement (travelling) (57%), followed by socializing (31%) and resting (12%). Other behaviours were observed within the socializing category, but were not quantified (flippers/tail exhibitions and slaps, breaching, spy hopping, mother–calf contacts, etc.).
We recorded other marine species at close distance to SRWs. Of these, the most frequent was the kelp gull (Larus dominicanus), present in about 30% of whale sightings. Less frequent (less than 5%) was the brown-hooded gull (Larus maculipennis), the South American tern (Sterna hirundinacea), the great grebe (Podiceps major), the Magellanic penguin (Spheniscus magellanicus), the South American sea lion (Otaria flavescens), the South American fur seal (Arctocephalus australis), the bottlenose dolphin (Tursiops truncatus gephyreus) and the killer whale (Orcinus orca).
Discussion
To research the recovery of commercially overexploited species such as the SRW, it is essential to carry out studies both in space and time, not only in breeding areas, but also throughout their entire geographic range (Payne et al., Reference Payne, Rowntree, Perkins and Cooke1990; Cooke et al., Reference Cooke, Rowntree and Payne2001; Richards, Reference Richards2002; Costa et al., Reference Costa, Praderi, Piedra and Franco-Fraguas2005; Aguayo-Lobo et al., Reference Aguayo-Lobo, Acevedo, Brito, Olavarría, Moraga and Olave2008; Arias et al., Reference Arias, Romero, Svendsen, Curcio, Jarma, Coscarella, Dans, Crespo and González2015; Danilewicz et al., Reference Danilewicz, Moreno, Tavares and Sucunza2016). In this paper, we present a unique record of sightings of SRW in Argentina over a period of 50 years, and the first data obtained during the journey of these whales off the coast of BAP.
SRW sightings in MDP have increased gradually since 1970 to the present. Over the last decades, sighting records in different sites are indicative of the growth of the main South Atlantic breeding populations (Argentina, Brazil, South Africa and Australia), after severe depletion by commercial whaling (Townsend, Reference Townsend1935; Bannister, Reference Bannister2001; Best et al., Reference Best, Brandão and Butterworth2001; Cooke et al., Reference Cooke, Rowntree and Payne2001; Richards, Reference Richards2009; Crespo et al., Reference Crespo, Pedraza, Dans, Svendsen, Degrati and Coscarella2019). Moreover, during the last decade, SRW breeding pods and non-social active groups have been increasing in the Golfo San Matías (Northern Patagonia), as it is a suitable habitat for social and reproductive activities (Vermeulen et al., Reference Vermeulen, Cammareri and Holsbeek2012; Vermeulen, Reference Vermeulen2013; Arias et al., Reference Arias, Romero, Svendsen, Curcio, Jarma, Coscarella, Dans, Crespo and González2015; Reference Arias, Coscarella, Svendsen, Romero, Curcio, Sueyro, Crespo and González2017). This growth is further confirmed by an increase in the frequency and number of sightings off the coast of MDP, as well as in other areas of the species' range (Uruguay and Southern Brazil) registered over the last years (Santos et al., Reference Santos, Siciliano, Pacheco de Souza and Almayer Pizzorno2001; Costa et al., Reference Costa, Praderi, Piedra and Franco-Fraguas2005; Reference Costa, Piedra, Franco and Paez2007; Groch et al., Reference Groch, Palazzo, Flores, Adler and Fabian2005; Danilewicz et al., Reference Danilewicz, Moreno, Tavares and Sucunza2016).
We recorded SRWs in MDP from April to November, with peaks between July and mid-October. This pattern coincides with the period of the highest number of sightings recorded in Uruguay (Costa et al., Reference Costa, Praderi, Piedra and Franco-Fraguas2005) and Brazil, where the season is shorter (July–October), with a maximum in August–September (Groch et al., Reference Groch, Palazzo, Flores, Adler and Fabian2005; Danilewicz et al., Reference Danilewicz, Moreno, Tavares and Sucunza2016; Seyboth et al., Reference Seyboth, Groch, Dalla Rosa, Reid, Flores and Secchi2016; Groch, Reference Groch, Rossi-Santos and Finkl2018). In addition, the season's length is similar to the reproductive period observed in Patagonia, where the first whales arrive in early April to May, and leave from November until late December (Crespo et al., Reference Crespo, Pedraza, Dans, Coscarella, Svendsen and Degrati2014, Reference Crespo, Pedraza, Dans, Svendsen, Degrati and Coscarella2019), although the extension of seasonal presence varies from year to year (Greig et al., Reference Greig, Secchi, Zerbini and Rosa2001; Crespo et al., Reference Crespo, Pedraza, Dans, Svendsen, Degrati and Coscarella2019).
As MDP is located between the breeding grounds of SC (Brazil) and PV (Argentina), whales recorded at the beginning of the season off the MDP coast could be individuals travelling from their southern feeding areas to the breeding areas of southern Brazil. All the sighted whales showed a clear south-north swimming direction, using the MDP area as a displacement route. Nevertheless, satellite tracking of individuals marked in Golfo San Matías and Península Valdés shows variations in movement patterns of individuals making coastal and offshore migrations to feeding grounds after the breeding season. During the coastal migration, some individuals moved southwards and others moved northwards along the coast of the BAP in Argentina and Uruguay before undertaking their final movement to the southern feeding grounds (Zerbini et al., Reference Zerbini, Rosenbaum, Mendez, Sucunza, Andriolo, Harris, Claphan, Sironi, Uhart and Ajó2016, Reference Zerbini, Fernandez Ajos, Andriolo, Clapham, Crespo and Gonzalez2018).
The first SRW sightings off the coasts of MDP were solitary individuals. Currently the whales also appear in small pods, similar to what happens in Torres (Brazil) and Uruguay, where the most frequent sightings were pairs and solitary individuals (Figure 5) (Costa et al., Reference Costa, Piedra, Franco and Paez2007; Danilewicz et al., Reference Danilewicz, Moreno, Tavares and Sucunza2016). Pods of more than three individuals were less frequent in the three non-breeding grounds (MDP, Uruguay and Torres). On the other hand, the permanence time of SRWs off MDP is about two days, a shorter time span than that recorded off the Uruguayan coast (Costa et al., Reference Costa, Piedra, Franco and Paez2007).
SRWs observed around MDP showed free movement as the most frequent behaviour. A different behaviour was observed off the Uruguayan coast, where interaction between animals was dominant, indicating that this area is a socialization place, where in the last years courtship/mating behaviour had been registered (Costa et al., Reference Costa, Piedra, Franco and Paez2007). Furthermore, Costa et al. (Reference Costa, Piedra, Franco and Paez2007) suggest that the adjacent areas of the Uruguayan and Rio Grande do Sul (Brazil) coasts could be a single ‘mating ground’ south of the main reproductive area of Brazil (SC).
The differences recorded in whale behaviour between MDP and the Uruguayan coast could be a consequence of dissimilar environmental conditions. The sheltered waters of the Uruguayan coast as opposed to the stormy open sea of MDP, could probably be linked to the greater interaction between individuals in Uruguay, and the use of the area for courtship/mating (Costa et al., Reference Costa, Piedra, Franco and Paez2007). Likewise, the search for protected and calm waters is confirmed in our work by the frequent presence of whales observed inside the MDP harbour.
There is a clear increase in the number of females with calves from BAP to the south of Brazil (Figure 9) (Groch et al., Reference Groch, Palazzo, Flores, Adler and Fabian2005; Costa et al., Reference Costa, Piedra, Franco and Paez2007; Danilewicz et al., Reference Danilewicz, Moreno, Tavares and Sucunza2016). SWR adults were the most frequently observed individuals off the coast of MDP, with an absence of calves during the 1970–1979 period. In the following decades the presence of mother–calf pairs was low, lasted a short period of time and its percentage did not vary throughout the different studied decades. We believe that the few cases of mothers with calves off MDP during the first months of the season are cases of natural premature births during the migratory period to the breeding ground off SC (Brazil).
Percentage females with calves (white) and SRWs without calves (solitary and groups) (black), sighted along Mar del Plata (MDP; sampling 1970–2016), Uruguayan (UY; sampling in 2001–2003) and Brazilian coasts: Rio Grande do Sul State (RS; sampling in 2002), and the main aggregation area in Santa Catarina (SC; sampling in 2001–2003).
We observed different marine species associated with SRWs in MDP, like seabirds and other marine mammals, similar to situations observed in the South West Atlantic breeding areas (Sironi et al., Reference Sironi, Rowntree, Snowdon, Valenzuela and Marón2009; Marón et al., Reference Marón, Beltramino, Di Martino, Chirife, Seger, Uhart, Sironi and Rowntree2015). The most common seabirds recorded in MDP were juvenile kelp gulls (Larus dominicanus); however, we did not register individuals feeding on whale's skin and blubber, as is frequently the case in PV (Bastida et al., Reference Bastida, Rodríguez, Secchi and Da Silva2007; Sironi et al., Reference Sironi, Rowntree, Snowdon, Valenzuela and Marón2009; Fazio et al., Reference Fazio, Bertellotti and Villanueva2012). Among the marine mammals interacting with SRWs we noted non-aggressive killer whales (Orcinus orca) on a few occasions; in contrast, harassment or predatory behaviour by killer whales was reported in Brazil (Ott et al., Reference Ott, Sucunza, Wickert, Danilewicz and Tavares2017) and PV (Sironi et al., Reference Sironi, López, Bubas, Carribero, García, Harris, Intrieri, Iñiguez and Payne2008; Bastida et al., Reference Bastida, Rodríguez, Secchi and Da Silva2018).
Whale watching activities of SRWs are currently quite common. Globally, this activity has increased exponentially in recent decades (O'Connor et al., Reference O'Connor, Campbell, Cortez and Knowles2009). In Argentina, and particularly in PV, whale watching from boats is an important natural tourism resource for Chubut Province (Chalcobsky et al., Reference Chalcobsky, Crespo and Coscarella2017). The calm and sheltered waters of Golfo Nuevo and Golfo San José offer suitable environmental conditions for SRW reproductive activities during the extensive breeding season and are an appropriate area for regulated tourist activity (Bastida, Reference Bastida1987). In contrast, we consider that the MDP coast is not suitable for whale watching from boats and we do not recommend this activity for several reasons: the presence of SRWs is unpredictable and sightings are opportunistic; animals may just swim through the area or remain in these waters for only a few days. Furthermore, the open and stormy seas of the studied area are not suitable for whale watching from small boats due to the water turbulence and the lack of sheltered coastal areas. MDP has the advantage of high coastal cliffs that allow whale watching from the shore, making it a valuable educational and accessible resource for both residents and tourists.
Based on our results, we consider that during the last 50 years the MDP area has been used by SRWs fundamentally as a transit area to the breeding ground in Southern Brazil (SC) and to the southern feeding grounds after the southern breeding season at the end of the austral spring. The opportunistic sightings obtained during oceanographic campaigns and seismic surveys allowed us to conclude that SRWs off BAP are also migrating, both in a northerly and in a southerly direction, not only in the coastal zone but also in the continental shelf and on the edge of the continental slope.
The data presented in this study are the only available data of SRWs in the MDP area obtained during such a long period of time. This information has value for future monitoring of the species in the north of BAP and outside their breeding grounds, where most of the studies have concentrated. These results may help local authorities to regulate coastal fishing activities, shipping traffic, tourism and other coastal activities in the area and thereby contribute to the conservation of the species. This would also allow the Argentine Government, an active member of the Convention on Migratory Species (CMS), to report periodically on the conservation status and threats affecting the SRW on its migratory routes in Argentine waters.
Acknowledgements
The authors wish to express their thanks to Mr H. Bezzi of IBM for his assistance from 1970 to 1990 and to Mr C. Orellano of INIDEP for continuing this work. To pilot S. D'Amato Fitzgerald for the flights and to M.A. Scelzo for the photographs. To Prefectura Naval Argentina and Aviación Naval of the Armada Argentina for their collaboration. To the Puglisi brothers for providing their coastal fishing vessel. To Juan and Marta Palumbo of the Fundación Ecológica de Pinamar and J. Rebollo of the Fundación Mundo Marino, to Club Náutico Mar del Plata and the Mar del Plata Yacht Club for their assistance. We also want to thank Yacimientos Petroliferos Fiscales Engineers J. La Vecchia, M. L. Ayoroa and M. Gómez for their collaboration in our work and the free use of the exploratory campaign data. We thank M. Natal who helped with the statistical analysis, and to Lic. Rosenthal and Organismo Provincial para el Desarrollo Sostenible, who collaborated in the registers of stranded whales. To the different generations of young researchers who were or are part of the Grupo de Biología, Ecología y Conservación de Mamíferos Marinos (Universidad Nacional de Mar del Plata). Finally, we thank Mr Peter Miles, Natalia Teryda, Victoria Lichtschein and Viviana Quse for reviewing the manuscript.
Financial support
Financial support for this work was provided by Instituto de Biología Marina (IBM), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Instituto de Investigación y Desarrollo Pesquero (INIDEP) and Facultad de Ciencias Exactas y Naturales (UNMdP).
