Marine mammal stranding events are used as an important tool for understanding cetacean biology worldwide. Nonetheless, there are vast gaps of knowledge to be filled in for a wide range of species. Reputable information is required regarding species from large baleen whales to sperm and beaked whales, as well as pelagic dolphins. This paper describes new cetacean records from north and north-eastern Brazil, which are both the least surveyed areas regarding aquatic mammals. Regular beach surveys were conducted to recover cetacean carcasses along the coast of Pará beginning November 2005. At the coasts of the Maranhão and Piauí states, the surveys were conducted between 2003 and 2013. From 2003 to 2014, 34 strandings of cetaceans were registered. The study provides four additional species records’ in the area based on strandings (Balaenoptera borealis, Balaenoptera physalus, Peponocephala electra, and Pseudorca crassidens). A mass stranding of Guiana dolphins (Sotalia guianensis, N = 12), the most common species for the region, was reported for the first time. The records presented herein are of special concern, since they expand the knowledge on cetaceans from the Brazilian coast. In addition, this study conducted an analysis to verify the similarity between cetacean compositions described for north and north-eastern Brazil and the southern Caribbean region. The results showed a high similarity between these regions, proving the connection with the Caribbean cetacean fauna.

Amazon, Balaenopteridae , beach survey, cluster analysis, Delphinidae , marine mammals distribution, Physeteridae , South America

The Amazon Coastal Zone (ACZ), between 4°N and 4°S, presents a singular environment, characterized by the immense discharge of the Amazon River. ACZ is an unique aquatic ecosystem where the largest continuum of mangrove belt of the world is found (Souza-Filho et al. 2005). These characteristics combined with the recent coral reef ecosystem discovered in the mouth of the Amazon (Moura et al. 2016) make this region a top priority for conservation among Brazilian coastal environments. In this vast coastal area cetacean records have been documented only in the last decade. The north and north-eastern Brazil have been one of the least surveyed areas regarding aquatic mammals. Only one report made a compilation of cetacean records from this area (Siciliano et al. 2008) bringing the number of recorded species to 22, including large whales and dolphins. This study is an effort to increase this information after abovementioned study. Stranding events is one of the best ways to access data on biology and ecology of marine mammals (Norman et al. 2004, Evans et al. 2005, Pyenson 2010, Santos et al. 2010, Peltier et al. 2012, Covelo et al. 2015).

The cetacean fauna of Brazil has been subject to an extensive number of groups dedicated to conservation and research issues since the 1980’s. Because of this, a considerable amount of new information on cetacean distribution, biology and ecology has arisen (e.g. Pinedo et al. 2001; Zerbini et al. 2004). In 2005, with the establishment of the ‘Grupo de Estudos de Mamíferos Aquáticos da Amazônia (GEMAM)’ at the Museu Paraense Emílio Goeldi, the first systematic studies on aquatic mammals were initiated in the region.

Nevertheless, there are vast gaps of knowledge to be filled in for a wide range of species. From large baleen whales to sperm and beaked whales, as well as pelagic dolphins, reputable information is required. This is due, in part, to the lack of inventories over large areas of the Brazilian coast.

Studies on the occurrence of cetaceans around the world are made using different methodologies such as: strandings, historical records, opportunistic sightings, and dedicated surveys (Maldini et al. 2005, Lucena 2006, Toledo and Langguth 2009, Ramos et al. 2010, Authier et al. 2014, Prado et al. 2016). In other words, cetacean composition in a specific area could be assessed through strandings when other sources of information are not available (Maldini et al. 2005, Byrd et al. 2014, Jung et al. 2015). In this sense, Pyenson (2010) validated that cetacean death assemblages is a faithful method to document taxonomic richness and relative abundance of living cetaceans.

The main goals of this report are to: (1) present a variety of new cetacean records along the northern Brazilian coast, (2) increase baseline information on cetacean occurrence over 11 years (2003–2014); and (3) compare the cetacean composition in distinct areas along the north and north-eastern Brazilian coasts with southern Caribbean region, investigating the similarity between these sectors. The results of this study could open a promising new window for understanding the cetacean community structure in this vast stretch of coast.

Stranding data are an important source to understanding the biology and ecology of marine mammals (Geraci and Lounsbury 1993, Moura and Siciliano 2012, Covelo et al. 2015). Indeed, the records presented herein are of particular importance, as they clarify the composition and richness of the cetacean community in a vast stretch of the Brazilian coast. Current data, with the addition of four species to the previous list (Siciliano et al. 2008), expanded this number to 26 aquatic mammal species. This study is in accordance to (Pyenson 2010) which suggests that stranding records at extensive latitude gradients (>1000 km) and for long time periods, provide an useful and faithfully method to understand richness and cetacean community in a particular area than the sighting surveys (e.g. line-transect method). Maldini et al. (2005) analyzing the composition of cetaceans of the Hawaiian Islands suggested that the stranding data reflects the species composition found in living animals surveys and defends the usefulness use of stranding data as an important source of information in the absence of other data. Marine mammalogists assumed that stranding events could be affected by oceanographic features such as bottom topography, tides, currents, winds and seasonal patterns (Norman et al. 2004). Carcasses can be moved by currents and winds along the coast and the oceanographic differences observed in this vast area of the north and north-eastern Brazilian coast should be considered important factors on stranding distributions. This coastline is singular and considered a continuous belt of mangroves with approximately 7591km² (Souza-Filho 2005) which complicates access and, consequently the rescue and reports of stranded marine mammals. The macrotidal characteristic observed in the Marajó Bay and Eastern Pará sectors is another factor that should explain the low frequency of strandings especially of small and medium-sized cetaceans. The dynamic of macrotidal regime may in a few hours carry the carcass of a small cetacean without it could be seen in these vast uninhabited areas.

The spatial distribution of species in the three sectors (MB, EP and MA/PI coastline) provides relevant information on their occurrence through stranding notifications. Small pelagic and neritic-pelagic cetaceans have been recorded in higher numbers along the EP and MA/PI sectors. In contrast, the MB area and adjacent coastline are influenced by the Amazon and Pará/Tocantins Rivers discharges, thus presumably limiting the occurrence and subsequent stranding of pelagic species. It should be considered that areas of difficult access and sparsely populated in the Amazon coastal zone, as the eastern Pará and the western Maranhão states, could represent potential circumstances for the low stranding notifications in these sectors. Although the systematic monitoring effort was lower at Maranhão/Piauí coastline, this area resulted to be singular due to the exclusive cetacean records of pelagic and neritic-pelagic species (e.g. Lagenodelphis hosei, Peponocephala electra). Despite the surveys were more dedicated in the MB sector, the frequency of uncommon strandings (e.g. oceanic species) were lower. However, single strandings of Sotalia guianensis, Inia geoffrensis and I. araguaiaensis in MB are not included in this report as they are commonplace and will be analyzed separately.

Earlier records of balaenopterids on the Amazon coastal zone were performed by Siciliano et al. (2008) and Silva et al. (2013). Previous revised information on stranding and sighting records of baleen whales along the Brazilian coast post-1997 (Siciliano et al. 2011) emphasizes the relevance of the current records. They are the very first evidence of the Fin and Sei whales occurrence along the northern Brazilian coast. The stranding intervals in each case could be informative of their movements and migration periods. The Sei whale was stranded in September 2008, during the peak migration period of southward migration (August–October) (sensu Best and Lockyer 2002). In accordance to these authors, the Viseu specimen (MPEG 39691), TL = 10.32 m in length, is acceptable as the size of immature females caught off South Africa (range 10.7–13.7 m). The Fin whale stranding demands a more complex interpretation, since the specimen became stranded in January, by the time most large whales have already reached Antarctic and sub-Antarctic waters. Siciliano et al. (2011) reported on a Fin whale sighted in January 2004 off the Santos Basin. Our present record poses an intriguing question, whether this whale was of a southern hemisphere origin or truly representative of a northern hemisphere stock.

The newborn Bryde’s whale recorded in Praia da Água Boa (MB) on 15 September 2012 is a remarkable record, since very limited information exists on the pregnancy and time of birth of this tropical balaenopterid and, in Brazil, information on the calving season is almost non-existent (Santos et al. 2010). Moura and Siciliano (2012) report on two newborns stranded only a few months apart in south-eastern Brazil (August and September). Our record was in September, agreeing with these authors’ previous observations and, thus, suggesting the same period of the year as a calving season for Bryde’s whales off the northern Brazilian coast. Records of Humpback whales herein expands significantly the presence of the species westwards the north-eastern Brazilian coast. Pretto et al. (2009) reported the first occurrence of M. novaeangliae for eastern coast of Pará at Praia de Fora, Quatipuru municipality.

In relation to odontocetes, four additional Sperm whales records are included from the Pará state and Maranhão/Piauí coastlines. One of them is of a very young specimen (TL = 4.22 m) stranded at east coast of the Marajó Island. This record strongly suggests the existence of calving off in the northern Brazilian coast. Sperm whales are a regular component of cetaceans found stranded on the north-eastern coast of Brazil. For example, Meirelles et al. (2009) provided 26 records for the Ceará state alone over the period from 1993 to 2005. The sample includes specimens of all sizes, from a 3.53 m newborn to a 18.10 m bull male. It was assumed that the strandings took part mostly in spring, summer, and winter months, influenced by strong north-western winds, when carcasses have more chance of coming ashore. Magalhães et al. (2008) have contributed with two records of Sperm whales for the Maranhão coastline, during their short-term surveys from 2004 to 2006. Other records for the north-eastern coast include a newborn stranded near of Baía do Capim (1°76'S, 44°83'W), Maranhão coast (S3 File), and four other specimens reported by Tosi et al. (2006). In a broader perspective, it is highly recommended to conduct future surveys in order to estimate Sperm whale density and abundance off the north and north-eastern Brazilian coasts. The structure of this Sperm whale population in relation to more southerly aggregations in Brazil deserves further studies and agreed with literature which report that females and immature males inhabit lower latitudes in subtropical and tropical oceans (Whitehead 2009).

Blackfish records were represented by the False killer whale, Melon-headed whale, Short-finned pilot whale, and Risso’s dolphin recovered in distinct areas. These specimens improve the knowledge on blackfish occurrence off the northern Brazilian coast. The False killer listed in this study is noteworthy; this is the first record of this species in the region. The specimen (MPEG 42132) had marks of human interaction; the peduncle was cut-off and most of the teeth were removed. This strongly suggests interactions with the pelagic fishery activity. Such marks were also observed in a rough-toothed dolphin stranded in eastern Pará (MPEG 42131) and on a pantropical spotted dolphin found on Piauí (MPEG 42085), suggesting that this kind of negative interaction may be more common than previously thought. Luksenburg (2014a) has informed on injuries found in live small cetaceans off Aruba, in the southern Caribbean. The author reported that of the 18 False killer whales individuals presenting injuries, six (33.3%) showed wounds that were probably caused by human activities. Two of these injuries were most likely caused by fishing gear and two others were most likely the result of a propeller hit. Further investigation on the impact of such fishing operations off northern and north-eastern Brazil on False killer whales and other smaller pelagic delphinids is highly needed.

The records of Bottlenose, Rough-toothed, and Common dolphins indicate their regular presence in neritic waters off northern Brazil, where then are referred by the fishermen as ‘tuninas’. The Common dolphin specimen recorded at Praia da Pedra do Sal is certainly of special interest as so little is known of this population inhabiting the north-eastern coast (see Tavares et al. 2010 for more details).

The evidence of consumption of a fresh Fraser’s dolphin denotes further investigation on the use of marine bushmeat along small fishing communities of north-eastern Brazil. Tosi et al. (2008) have reported a similar episode involving Fraser’s dolphin consumption in the coast of Maranhão. Even if these represent fortuity events, dolphin and whale meat consumption should be more deeply investigated in such villages in future surveys.

Regarding coastal species, a mass stranding of Guiana dolphins was reported for the first time, based on an incident recorded in Salinópolis (EP), on January 2013. The coastline of Pará possesses certain unique features, such as very strong tides that cause accelerated movement of the sand banks and tidal channels. It seems plausible to believe in a natural condition characterized by this muddy beach and fast lowering tide acting as a trap. Although Guiana dolphins are familiar with flat waters and tide dynamism, the particular location of the Praia da Corvina could have acted as a natural trap. Nonetheless, the singularity of this event is worth mentioning and adds a new feature to the natural behavior of Guiana dolphins.

The cetacean fauna off the north and north-eastern Brazilian coast is much richer and diverse that previously thought, including both residents of tropical oligotrophic waters and highly-migrating baleen whales. Species associated to productive environments are also included, such as Bryde’s whales and the Common dolphin. As pointed out by the present survey, the connection with the southern Caribbean cetacean fauna seems plausible and deserves further investigation. This is particularly relevant for understanding the affinity of north Brazilian Bryde’s whale and Common dolphin populations with the adjacent Venezuela regional aggregations of these species (Galindo 2007). There is a lack of information on countries of Wider Caribbean Region as Guyana, Suriname, and French Guiana, however, surveys developed at Guiana’s coastal province supply important records on cetacean composition (Manocci et al 2013, Boer 2015). Such a relationship is highly expected and could potentially connect the north Brazilian cetacean fauna with that from the southern Caribbean.

Strandings of uncommon cetacean species and a live beached Sperm whale are recorded for the first time along the north coast of Brazil. Balaenopterids records (Balaenoptera borealis and B. physalus) presented herein are of particular importance and include the very first of its category on the northern coast of Brazil providing new insights on migration movements on the southern hemisphere.

Evidence of anthropogenic injuries inflicted to cetaceans and also the consumption of marine bushmeat is reported to the north-eastern coast of Brazil. Although the proximity of the northern and the north-eastern Brazilian coasts, results showed that cetacean fauna in northern is more similar with the Caribbean region. Further investigation on movements and distribution patterns should be encouraged.

In this context, beach surveys and stranding network definitely provide relevant information on marine mammals’ richness and diversity is this vast region. The cetacean fauna of north and north-eastern Brazil combines different elements from tropical marine ecosystems under the influence of the most powerful river of the world. Such dynamism requires a proportional research effort to better evaluate and understand its own complexity.

We would like to thank the GEMAM members who helped with field surveys, carcass collections, and processing at the Pará coast. AF Costa is indebted to Herbert Freitas (Quadrado) for his support and the collections made at the Piauí coast, without his help we would not have obtained the diversity of cetaceans in that sector. We are grateful to veterinarians Dr Valíria Cerqueira and Dr Pedro Bezerra and their staff from the Universidade Federal do Pará/Instituto de Medicina Veterinária-Campus Castanhal for their assistance in necropsies and staff of NUBIO/IBAMA/SUPES/PA for all the logistic and technical support for the stranding callings. Thanks to the staff of the MPEG, especially to the Setor de Mastozoologia for the support given to our research group along all these years.

This study was supported by VALE/FAPESPA/FAPEMIG (Process no. 038/2011) and Petrobras (Projeto Bicho D’água: Conservação Socioambiental and Projeto Cetáceos do Maranhão). M Sousa received a scholarship from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior-CAPES. T Giarrizzo is funded by CAPES (PNPD), and receives a productivity grant from Conselho Nacional de Desenvolvimento Científico e Tecnológico-CNPq (310299/2016-0). This article is part of Alexandra Costa’s PhD thesis in Aquatic Ecology and Fishery from the Universidade Federal do Pará. CAPES provided the scholarship for AF Costa during PhD course. Programa de Capacitação Institucional (MPEG/MCTI) provides a research grant to AFCosta (313522/2015-4) and REmin-Lima (313356/2015-7).