Keywords

Introduction

Top predators, such as cetaceans, are known to seek and associate with predictable regions of high biological activity (“hotspots”). Oceanic islands are topographic features that result in localized upwellings, eddies, and convergence zones, which in turn may cause enhanced primary productivities that promote biomass accumulation and congregate biodiversity in their vicinity (Doty and Oguri 1956; Caldeira et al. 2002; Palacios 2002).

The Gulf of Guinea is a globally important region that hosts high concentrations of rare, range-restricted, and threatened marine species, such as sea turtles, elasmobranchs, and marine mammals (Weir 2010; Lucifora et al. 2011; Selig et al. 2014; Polidoro et al. 2017) and is considered a marine biodiversity hotspot (Roberts et al. 2002). The waters of the Gulf of Guinea support key life-history stages for several cetacean species (Jefferson et al. 1997; Weir 2010, 2011). However, the cetacean fauna along the west coast of Africa, as well as of the oceanic islands of the Gulf of Guinea, is incompletely described and, despite historical information and verbal descriptions of great diversity, there is relatively little scientific information about the ecology of species from this group occurring in the region (Hoyt 2005; Weir 2010).

The nation of São Tomé and Príncipe is composed of two main islands and several small islands and islets. Due to their volcanic origin, the islands display high relief and the littoral surrounding fringe is very narrow with depths of around 200 m close to the shore (Afonso et al. 1999). The country has an Exclusive Economic Zone (EEZ) of almost 165,000 km2, and a strong dependence on fishing; however, knowledge related to its marine fauna is limited, and only a few studies have been conducted in recent years (e.g., Afonso et al. 1999; Maia et al. 2018; Hancock et al. 2019; Quimbayo et al. 2019).

This chapter provides a brief summary of historical whaling activity in the Gulf of Guinea region, an updated review of the occurrence of cetaceans in the waters of São Tomé and Príncipe (no studies available for Annobón), and a brief history of cetacean research in the archipelago. It also identifies priorities for future research and conservation of cetaceans in the region.

Cetacean Occurrences Based on Historical Whaling Data

Background on Historical Whaling in the Gulf of Guinea

Early written references to cetaceans in the Gulf of Guinea include observations of “big fishes such as porpoises” (Dias 1934 in Brito 2009) and “many whales, large and small, that it is a wonderful thing to say” (Anonymous 1812). As with other Atlantic islands and the coast of the African mainland, cetaceans stranded on the shore were probably used by local people and settlers, who consumed the meat and transformed blubber into fuel (Brito et al. 2017; Vieira 2020).

By the second half of the eighteenth century, the Governor of São Tomé and Príncipe reported the presence of English vessels hunting whales around Cap Lopez (Gabon) and Fernando Po (Bioko) Island (Ferreira 1773). Those operations followed “American whaling” techniques, which included the persecution of animals from open boats and hand harpooning (Macy 1835; Townsend 1935). Humpback Whales Megaptera novaeangliae (Borowski, 1781) were one of the main targets along equatorial West Africa, due to their seasonal migratory movements, preference for coastal waters during migration and breeding, and slower swimming speed compared with other baleen whales (Townsend 1935; Tønnessen and Johnsen 1982). The combination of these factors made this species an easy target for coastal whaling globally during the nineteenth century (Reeves and Smith 2006), including in the waters of São Tomé and Príncipe, for instance during the voyage of the Vessel Admiral Blake. The Vessel arrived at São Tomé on June 22, 1869, and anchored on Príncipe Island on June 24, 1869. The crew went on “bay whaling” until the end of August hunting humpback cow and calf pairs (Anonymous 1869–70).

Starting in the mid-1800s, whaling became dramatically more effective due to several innovations, including explosive harpoons and modern steam-driven whaling boats (Tønnessen and Johnsen 1982; Clapham and Baker 2002). This allowed the capture of previously unattainable fast-swimming species, especially Balaenoptera whales including Blue Whale Balaenoptera musculus (Linnaeus, 1758), Sei Whale Balaenoptera borealis (Lesson, 1828), Bryde’s whale Balaenoptera edeni (Anderson, 1879), and Fin Whale Balaenoptera physalus (Linnaeus, 1758).

In the early twentieth century, engine-powered Norwegian floating factories (moored near shore or working in the open sea) accompanied by fleets of catcher boats with deck-mounted harpoons began operations in the Gulf of Guinea. During this time whaling went through periods of expansion and crisis (Rocha et al. 2015). Despite the breaks in whaling activity resulting from World Wars I and II, after years of intense captures, the following seasons were significantly less successful. Pelagic and coastal whaling operations were conducted from Cap Lopez (Gabon) in 1912 and took place in 1912–1914, 1922–1926, 1930, 1934–1937, 1949–1952, and 1959. Whaling operations took place mostly between the end of June and November, with a peak in July/August (Budker and Collingon 1952), corresponding to the breeding period of Humpback Whales, the main target of the catch. Bryde’s, Sei, Sperm Physeter macrocephalus (Linnaeus, 1758) and Fin whales were also taken (Budker 1953; Tønnessen and Johnsen 1982). During the whaling seasons, high fluctuation of total catches, with a substantial decline not only in numbers but in the mean length of the individuals caught indicated the depletion of the Humpback Whale stock (Budker and Collignon 1952; Budker 1953).

In the late 1960s, overexploitation was notorious, and almost every whale stock was depleted or had already collapsed. The International Whaling Commission (IWC), an intergovernmental organization established in 1946 to provide conservation of whale stocks and management of the whaling industry, began to impose restrictions on whale catches. Restrictions for Blue and Humpback whales were imposed in the 1960s, Sei and Fin whales in the 1970s, and in 1986 the moratorium went into effect with zero catch quota for both pelagic and coastal whaling (Clapham and Baker 2002). In the 1970s, illegal captures, mostly of Bryde’s and Sei whales, continued by the catcher/factory vessel Run/Sierra in the Gulf of Guinea (Tønnessen and Johnsen 1982; Best 2001).

In addition to commercial whaling, an aboriginal whaling operation in Annobón has been reported since the late nineteenth century (Doce 1932, 1951; Aguilar 1985), and with recent evidence of continuing until today (Collins et al. 2019; Fielding and Barrientos 2021). The Annobonese retained the skills and practices of hunting whales from their experience on foreign whaling vessels, and the activity was integrated into local culture. Small rowing boats with two rowers and one harpooner were used in July and August, targeting coastal Humpback Whales, mainly calves (Aguilar 1985). However, the status of this hunt is uncertain and more information is needed.

Industrial Whaling in São Tomé and Príncipe

First attempts to promote modern whaling in São Tomé using a factory-ship and catchers date to the 1930s (Henriques 2016) but not much is known from that period. From 1945, the company Grémio dos Armadores da Pesca da Baleia of Lisbon, regulated the activity in mainland Portuguese waters and overseas (Henriques 2016).

There are some references on whaling operations off São Tomé and Príncipe in the 1940s. Tenreiro (1961) mentioned that local fishermen and Norwegian companies established on São Tomé hunted Sperm Whales and sharks. He notes that 1946 was an excellent year when they caught 100 cetaceans, which generated 1079 tons of oil, produced in the factory in the town of Neves (Fig. 23.1, 1). In 1951, a decree granted a Norwegian company the right to hunt whales in the archipelago for a period of 10 years, with one of several conditions being the distribution of whale meat to the local population (Henriques 2016). The operation was supported by the modern factory in Praia Rosema (Neves), in the northeast of São Tomé Island (Figueiredo 1960; Henriques 2016). Among the workforce were local people, Portuguese, and foreigners (Boletim Semanal 1951). The factory operated between July and October of 1951, processing an average of seven animals per day, with a total of 714 animals: 336 Bryde’s Whales, 323 Humpback Whales, 53 Sperm Whales, and 2 Fin Whales (Figueiredo 1960).

Fig. 23.1
A photograph illustrates a whaling factory in Sao Tome located in an industrial area with a large tank near the banks of a river.

Whaling industry on São Tomé: (1) Whaling factory at Praia Rosema (Neves, São Tomé; Tenreiro 1961); (2–5) Remains of the whaling factory in 2005. Photo credits: (2–5) Inês Carvalho

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The Humpback Whales killed in the waters of São Tome and Príncipe belong to the Gabon stock that by 1951 the IWC had already identified as being depleted. Nevertheless, at the time, Portugal was not a member of the IWC (joining only in 2002) and despite the criticism, whaling was allowed in STP waters (Budker and Collignon 1952). However, with increasing international criticism, the competition with French enterprises in the Gulf waters, and the low number of captures, the factory closed in that same year (Budker and Collignon 1952; Henriques 2016). Its remains are still part of the São Tomé seascape (Figs. 23.1, 2–5).

Historical Catches of Cetaceans in the Gulf of Guinea Region

Whaling data provides valuable information on species identification, distribution, migration, life history, and population status of whale stocks around the world (e.g., Townsend 1935; Josephson et al. 2008; Gregr 2011; Smith et al. 2012). To gather information on the occurrence and distribution of cetacean species in the eastern Gulf of Guinea area during the whaling period, two databases were used. The first was the American Offshore Whaling Logbook database (Lund et al. 2021), which includes information from 1381 logbooks from American offshore whaling voyages (1784–1920) extracted from original whaling logbooks from three different sources: Matthew Maury (1850s), Townsend (1930s), and the Census of Marine Life project (Barnard et al. 2002). The second database was the IWC compilation of worldwide whale catches since 1900 (Allison 2016a, b). The IWC data is continually updated (Allison and Smith 2004) and consequently, the total number of catches reported has changed over time (e.g., Findlay 2000; Best 2001; Weir 2010). Whaling records and species identifications were accepted as published, despite the likely misidentification between Sei Whale and Bryde’s Whale in the whaling statistics (Best 2001). Prior to 1960, whalers could not reliably distinguish between the two species (Best 2001; Weir 2010). This led to records of “Sei Whales” along the coast of West Africa likely being misidentified Bryde’s Whales; thus, records of the two species were merged. Since several cetacean catches are represented by the same geographic positions, the data were separated into two seasons for better visualization (Fig. 23.2): June to October, representing the breeding season for Humpback Whales; and November to May.

Fig. 23.2
Two geographical maps illustrate the whaling catch sites of different species of whales for two seasons around the Gulf of Guinea Islands. From June to October, humpbacks,Bryde’s/Sei,Sperm and fin whales are recorded, and from November to May, Bryde’s/Sei Whales are recorded in the highlighted region.

Distribution of whale catch positions around the Gulf of Guinea Islands. Data from American Offshore Whaling Logbook database (https://whalinghistory.org/av/logs/aowl/) and IWC database (Allison et al 2016b), representing N = 11845 catches (10553 Humpback whales; 1010 Bryde’s/Sei whales; 261 Sperm whales; 15 Fin whales; 2 Pilot whales; 1 Blue whale; 1 Right whale (Eubalaena australis Desmoulins, 1822); 1 Minke whales; 1 Killer whale). Top map-whaling catches between June-October, Bottom map-whaling catches between November-May. The symbol ○ (on top map in red) represents the records without specific geographic coordinates provided by IWC. Blue, Right and several Humpback whale catches were recorded with this point, which indicates that they were caught in the area but there was no specific location

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Humpback Whale was the main target species of whaling in the Gulf of Guinea region with more than 10,000 animals captured mostly near the coast of Gabon and around Príncipe Island between June and October (Fig. 23.2, top). Bryde’s/Sei Whales were caught throughout the year, mainly off the southern coast of Gabon, the offshore waters off the west coast of São Tome, and between the islands of São Tomé and Annobón (Fig. 23.2). Sperm and Fin Whale catches were more infrequent and spread in offshore waters across the entire region, while catches of other cetacean species were rare (Fig. 23.2).

Recent Data from Fieldwork on São Tomé and Príncipe

There is limited information about the spatial and temporal patterns of the distribution and abundance of cetaceans in the Gulf of Guinea, and most of the available information is based on whaling data (e.g., Townsend 1935; Budker and Collignon 1952), reports on strandings, by-catch data, and some dedicated cetacean research (e.g., Walsh et al. 2001; Van Waerebeek et al. 2009; Segniagbeto and Van Waerebeek 2010; Weir et al. 2010; Weir 2011; Sohou et al. 2013; Rosenbaum et al. 2014; Escalle et al. 2015; De Boer et al. 2016; Collins et al. 2019; Trew et al. 2019).

In 2002, the first field study dedicated to cetaceans of São Tomé Island started with the objective of collecting baseline data on the occurrence of cetaceans in these waters. The fieldwork of this project was based at Rolas Islet, and the boat surveys in 2002 and 2003 were conducted in the south region of São Tomé. Data on occurrence, movements, seasonality, and behavior (including acoustic behavior) of several species were collected and analyzed (Picanço et al. 2009). In 2004, a PhD focusing on the population structure of the Humpback Whale on the West African coast was initiated, in collaboration with the Wildlife Conservation Society and the American Museum of Natural History. Fieldwork was conducted between 2004 and 2006 in São Tomé waters to collect data on the occurrence, distribution, behavior, and genetics of humpback whales (Carvalho et al. 2011, 2014; Carvalho 2012; Kershaw et al. 2017). In 2012, a partnership between the NGOs MARAPA (São Tomé) and Associação para as Ciências do Mar (APCM; Portugal) started the project “Operação Tunhã.” The aim of the project was to establish a program to collect systematic baseline data on cetaceans in São Tomé, to assess the local capacity to develop a sustainable whale watching activity, and at the same time to raise awareness among stakeholders on local cetacean conservation.

In Príncipe Island, data collection about cetaceans has been more limited. Some sighting and stranding records have been collected intermittently over the years by Fundação Príncipe (Vanessa Schmitt pers. comm.). In 2020, between August and November, a field survey was carried out in the archipelago’s waters to collect visual and acoustic data on cetaceans, for the South Atlantic Cetacean project by the Edmaktub Association (Sesani et al. 2020).

Cetacean Species Recorded in São Tomé and Príncipe Waters

To date, the presence of 12 cetacean species has been confirmed (Fig. 23.3, Appendix), based on data collected by the authors during 2002–2006 and 2012–2015 around São Tomé Island. Five of those species were only confirmed recently by the authors: Striped Dolphin Stenella coeruleoalba (Meyen, 1833), Rough-toothed Dolphin Steno bredanensis (Lesson, 1828), Risso’s Dolphin Grampus griseus (G. Cuvier, 1812), Pygmy Killer Whale Feresa attenuata (Gray, 1874), and Dwarf Sperm Whale Kogia sima (Owen, 1866).

Fig. 23.3
A geographical map illustrates 12 species of whale and dolphin sightings around Sao Tome Island. Rolas Islet has the maximum population of humpback whales and bottlenose dolphins, with very few pantropical spotted dolphins.

Cetacean sightings and strandings in São Tomé Island recorded from 2002 to 2006 and from 2012 to 2015 (N = 215; Picanço et al. 2009; Carvalho et al. 2014; Collins et al. 2019; Associação para as Ciências do Mar, Portugal unpublished data)

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Megaptera novaeangliae

Humpback Whales (Fig. 23.4, 1) in the Southern Hemisphere migrate between summer feeding areas in the nutrient-rich waters of the Southern Ocean and winter breeding areas in tropical waters (Townsend 1935). The Gulf of Guinea region is known as a breeding area for the Humpback Whale B stock (IWC 2001). Catch histories and recent genetic data suggest that this stock may be sub-structured (Findlay 2000; Carvalho et al. 2014) with some temporal and spatial segregation; Humpback Whales use two different migration corridors and different feeding areas, in South Africa and Antarctica (Barendse et al. 2011; Rosenbaum et al. 2014; Carvalho et al. 2014). Between 2002 and 2014, 74 sightings of Humpback Whales were collected around São Tomé waters (Carvalho et al. 2011; APCM unpublished data). In 2020, 63 sightings were collected mostly around Príncipe Island (Sesani et al. 2020). The sightings were collected between July and late November. São Tomé appears to be used primarily by mother/calf pairs, as a calving, nursing, and resting area. This is suggested by the high frequency of observed groups with a calf present (more than 70%) and long occupancy of several weeks in the area by these groups (Carvalho et al. 2011; Sesani et al. 2020). Female Humpback Whales with calves prefer shallow waters (Ersts and Rosenbaum 2003), being sighted mostly around Rolas Islet (sometimes very close to the shore), near São Tomé city (northeast), and around Príncipe Island (Picanço et al. 2009; Carvalho et al. 2011; Sesani et al. 2020).

Fig. 23.4
A photograph of different species of dolphins and whales in Sao Tome waters. It includes Humpback Whale,Bottlenose Dolphin,Pantropical Spotted Dolphin, Rough-toothed Dolphin, Killer Whale, Pygmy Killer Whale,Short-finned Pilot Whale, and Sperm Whale

Cetacean species photographed in São Tomé waters: (1) Humpback Whale; (2) Bottlenose Dolphin; (3) Pantropical Spotted Dolphin; (4) Rough-toothed Dolphin; (5) Killer Whale; (6) Pygmy Killer Whale; (7) Short-finned Pilot Whale; (8) Sperm Whale. Photo credits: (1) Maria Pimentel, (2, 5, 7) Inês Carvalho, (3) Cristina Picanço, (4, 6, 8) Bastien Loloum

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Physeter macrocephalus

The Sperm Whale (Fig. 23.4, 8) is a cosmopolitan species but shows differential sex-and age-related distributions. Females and immature individuals inhabit primarily warm waters in tropical to subtropical areas (Whitehead 2002). As males get older, they disperse from these warmer areas to higher latitudes (Whitehead 2002). There are three stranding records of Sperm Whales in São Tomé (2002, 2010 and 2013; Fig. 23.4) and one in Príncipe in 2014 (Collins et al. 2019). Two sightings of single animals were recorded off the north coast of São Tomé Island, one reported in 2005, at 1500 m depth (Picanço et al. 2009), and another one in 2013 at 980 m depth (APCM unpublished data). These records suggest the occurrence of the expected “nursery groups,” as young calves were recorded from strandings and immature animals and adults were recorded from sightings. Sesani et al. (2020) described a sighting of two individuals in 2020, 80 km off the east coast of São Tomé Island at 2500 m depth, with no information on age and sex.

Kogia spp.

Two Kogia species are currently recognized: the Dwarf Sperm Whale (Kogia sima) and the Pygmy Sperm Whale Kogia breviceps (de Blainville, 1838) (Rice 1998). Both occur in deep temperate and tropical waters worldwide, with overlapping distributions, and they are very difficult to distinguish. The Dwarf Sperm Whale is smaller and has a more prominent dorsal fin, whereas the Pygmy Sperm Whale is slightly larger and has a smaller and rounded dorsal fin. There were two confirmed records of the Dwarf Sperm Whale off São Tomé, one sighting in February 2012, off the northwest coast, at around 150 m depth, and one a by-catch record in the southern region in February of 2014 (APCM unpublished data). Four additional sightings of Kogia spp. were recorded off the north region of São Tomé Island, two in March and April of 2012 and two in January of 2014 (APCM unpublished data), but the species could not be fully confirmed.

Orcinus orca (Linnaeus, 1758)

The Killer Whale (Fig. 23.4, 5) is distributed across oceans (Rice 1998), but reports are less common in tropical waters (Weir et al. 2010). Six sightings were reported around São Tomé (Picanço et al. 2009; Weir et al. 2010): one in November, four in December, and one in January. Four of the six sightings occurred around Rolas Islet, in the south, and the remaining on the east and northwest coasts (Fig. 23.4). Four sightings occurred in shelf edge habitat (270–790 m), one in shallow waters (55 m) and another one in deep-water (1200 m; Weir et al. 2010). The average group size was estimated at six animals and included adults and calves. Weir et al. (2010) photo-identified 13 animals. Two animals were first photo-identified together in 2002, and then in 2004; one of these individuals was also photographed in 2003. The four sightings during December 2002 were the result of repeated encounters on successive dates with a single group of Killer Whales. A predation event was observed off São Tomé during January 2003, when an adult–calf pair of killer whales was observed feeding on an Ocean Sunfish Mola mola (Linnaeus, 1758) at the surface (Weir et al. 2010). Repeated sightings of the same group of killer whales around São Tomé suggested the regular use of that area (at least seasonally) by a particular group of animals. In 2020, there were two recorded sightings off western São Tomé, one individual in October and two individuals in November (Sesani et al. 2020). The three individuals were photo-identified, but there was no cross-checking with photographs from previous years.

Steno bredanensis

The Rough-toothed Dolphin (Fig. 23.4, 4) inhabits primarily warm oceanic waters worldwide (Rice 1998). Four sightings of this species were recorded, off the north coast of São Tomé Island, in August and September of 2012 and within the 200 m bathymetry. Three of the sightings comprised average groups of eight individuals, all adults. The fourth sighting was a larger group of around 20 adults and juveniles sighted together with a group of 8–10 Pygmy Killer Whales, at around 2 km from the coast and depths under 100 m (APCM unpublished data). In October of 2008, there was one offshore sighting of a group of 35 individuals, west of São Tomé at 3271 m depth (Weir 2011).

Grampus griseus

The Risso’s Dolphin inhabits temperate and tropical waters worldwide and generally prefers deeper offshore waters, especially close to the continental shelf edge and slope (Jefferson et al. 2008). One individual was stranded on the north coast of São Tomé (Fig. 23.3) in February 2015 (Collins et al. 2019).

Pseudorca crassidens (Owen, 1846)

The False Killer Whale inhabits primarily tropical to subtropical waters, and sometimes also occurs in warm temperate waters (Rice 1998). The first record of this species was a sighting of 6–8 adult animals engaged in feeding activities (some animals had fish in their mouths) off the north coast of São Tomé Island in April 2012 (APCM unpublished data). The two subsequent records, in 2013 and 2014, came from strandings in the same coastal region (Collins et al. 2019). The most recent sightings were recorded in 2020, one south of Rolas Islet (on São Tomé) and another on the southwestern coast of Príncipe (Sesani et al. 2020). The estimated group size of these sightings was 30 and 20 individuals, respectively. The group observed off Príncipe was composed of adults and calves (Sesani et al. 2020). All the sightings of this species were within the 250 m bathymetry.

Feresa attenuata

The Pygmy Killer Whale (Fig. 23.4, 6) occurs mainly in deep warm tropical waters (Rice 1998). Off the north of São Tomé Island, two groups of eight (in August) and 12 animals (in December) were recorded in 2012 (APCM unpublished data). The eight Pygmy Killer Whales were sighted together with rough-toothed dolphins at less than 100 m depth. The other 12 animals were sighted around 450 m deep.

Globicephala macrorhynchus (Gray, 1846)

There are two species of pilot whales: the Short-finned Pilot Whale (Fig. 23.4, 7), which is mostly found in tropical waters, and the Long-finned Pilot Whale, Globicephala melas (Traill, 1809), which inhabits colder waters. Picanço et al. (2009) reported a sighting in January 2003 of around 20 pilot whales as Long-finned Pilot Whales, mixed with Bottlenose Dolphins, off the southeast coast of São Tomé, over the shelf edge (975 m). During this sighting, eleven individuals were identified by photographs of the dorsal fins. The second sighting of pilot whales was recorded in February 2012, a group of eight Short-finned Pilot whales, including calves, traveling off the east coast of São Tomé (APCM unpubl. data). Photographs confirmed that both sightings refer to Short-finned Pilot Whales and that the most conspicuous individual identified in 2003 was re-sighted after 9 years, suggesting long-term site fidelity that could also apply to other individuals of the group.

Stenella attenuata (Gray, 1846)

The Pantropical Spotted Dolphin (Fig. 23.4, 3) occurs in tropical and subtropical waters (Rice 1998). This species is one of the most frequently observed cetaceans in São Tomé, and it is present throughout the year. Since 2002, a total of 37 sightings have been recorded off São Tomé Island; 14 sightings recorded by Picanço et al. (2009) and 23 afterward. Most sightings were recorded over the slope (400–2000 m) to the north of São Tomé (APCM unpublished data). More recently, this species was also recorded around Príncipe, with five sightings (Sesani et al. 2020). The Pantropical Spotted Dolphin can form large groups, ranging from a few animals to several hundred animals. The majority of the sightings were groups of more than 100 animals. In 2012, one animal died from by-catch in the south of São Tomé (Collins et al. 2019).

Stenella coeruleoalba

The Striped Dolphin is a mostly oceanic species and occurs in deep warm temperate, subtropical, and tropical waters worldwide (Rice 1998). There was a single record of one stranded individual in March 2012, off the east coast of São Tomé (Collins et al. 2019).

Tursiops truncatus (Montagu, 1821)

The Common Bottlenose Dolphin (Fig. 23.4, 2) is a cosmopolitan species with a worldwide distribution in tropical and temperate regions (Rice 1998). It is the most commonly sighted small cetacean species around São Tomé and occurs regularly throughout the year (Pereira et al. 2013). The average group size for this species was estimated at 45 individuals. Calves and juveniles were sighted regularly with adults. Pereira et al. (2013) photo-identified 140 individuals during sightings from 2002 to 2006 and 2012 around São Tomé. The sightings occurred mainly around Rolas Islet and to the northeast of São Tomé (adjacent to São Tomé city), sometimes very close to shore. Most sightings around São Tomé were recorded below the 200 m bathymetry. Some of the individuals identified showed a degree of site fidelity (Pereira et al. 2013). Eight individuals recorded from 2002 to 2006 were resighted in 2012, and one of them was sighted in every survey year. On several occasions, Bottlenose Dolphins were sighted in mixed groups with other species, such as Sperm Whales (on two occasions), Pantropical Spotted Dolphins, and Short-finned Pilot Whales. In 2020, there were five sightings of this species along the northeastern coast of São Tomé, around the 250 m bathymetric, but none around Príncipe (Sesani et al. 2020).

Threats, Conservation Needs, and Future Research

The Gulf of Guinea is one of the 18 global hotspots for marine biodiversity conservation (Roberts et al. 2002). Globally, it is also one of the fastest developing marine regions, and a highly productive ecosystem, that includes some of the most productive coastal and offshore fisheries (Aryeetey 2002). This region also has substantial oil and gas reserves. Marine species are therefore subject to a range of pressures, such as incidental capture (by-catch) in fisheries, overfishing of their prey, direct catch (meat and other products), as well as habitat loss and pollution, namely linked to intense deep-water oil and gas exploration (Weir and Pierce 2013; Escalle et al. 2015). The expansion of offshore hydrocarbon extraction activity has been a concern for the populations using the waters of central Africa and the eastern Gulf of Guinea (Findlay et al. 2006). Seismic surveys use high-amplitude sound sources, that can have negative impacts on acoustically-sensitive animals such as cetaceans, which can result in changes in habitat use, including spatial avoidance (Weir 2008; Kavanagh et al. 2019), and behavioral changes (Cerchio et al. 2014; Dunlop et al. 2017). In recent years, several seismic surveys have been conducted in the EEZ of São Tomé and Príncipe for future oil exploration (e.g., Anonymous 2018). Although there was no assessment of the impact seismic surveying had on cetaceans in the area, it is most likely that such extended surveys resulted in some degree of responses by the animals.

In São Tomé and Príncipe, fishing provides more than 80% of the animal protein consumed by the population (Maia et al. 2018). From 1955 to 2010, the number of artisanal fishers in the archipelago increased by about 116%, from 1127 to 2428 (Maia et al. 2018). Moreover, catches by national semi-industrial fishing and foreign industrial fishing (by the European Union, Japan, and China) have continued to increase during recent decades (Carneiro 2011; EU 2019), despite a reduced capacity for monitoring, control, and surveillance by national authorities (Belhabib 2015). Maia et al. (2018) suggested a potential decline in the catch trends (mainly coastal) in São Tomé and Príncipe’s artisanal fisheries. Declining catches and increasing fishing efforts can lead fishermen to expand their fishing grounds further offshore, use destructive fishing practices (such as explosives and grenades), use illegal gillnets, and sometimes target different species (Santos 2017). Most sightings of cetaceans in northern and southern São Tomé coincide with areas of intense artisanal fisheries. Episodes of cetacean by-catch (Collins et al. 2019) and direct hunting of cetaceans (APCM unpublished data) have been described in recent years. Fishermen themselves recognize that the problem of overexploitation of marine resources should be addressed through the creation of marine reserves (Maia et al. 2018). So far, São Tomé and Príncipe has not created any marine protected areas (MPAs), but presently efforts are being made by local and international NGOs together with the government to propose a network of co-managed coastal MPAs (de Lima et al. 2022). Well-managed MPAs have been reported to lead to increases in marine biodiversity, abundance, and biomass (Ballantine 2014; Grorud-Colvert et al. 2021), benefit fisheries (Harrison et al. 2012), and improve the local economy.

In 2018, at the 67th IWC meeting, several countries from the Gulf of Guinea (São Tomé and Príncipe included) voted, along with whaling nations, to re-establish appropriate catch limits for some stocks/species, and voted against the proposal to create a Whale Sanctuary in the South Atlantic (IWC 2018). Cetaceans in the waters of São Tomé and Príncipe have no specific legal protection, although there are laws regarding general aspects of environmental protection (Brito et al. 2010; Decree-Law N° 11/1999—Fauna and Flora conservation and protected areas; Decree-Law N° 6/2014—Marine turtles protection and Decree-Law N° 22/XI/5a/2021—new fisheries law mentions the creation of protected areas for cetaceans in important regions for migration and/or feeding). There is a clear need for action at national and regional levels to quantify the impact of human activities (especially by-catch and direct take) and to implement legislation and measures for the protection of cetaceans.

Cetacean research in the Gulf of Guinea has focused mostly around São Tomé waters and in coastal areas, with some research on Príncipe and none at all on Annobón. Broadening the survey area to include the islands of Príncipe and Annobón, and covering a wider temporal window, may provide important information on the level of population structure, habitat use, and seasonal dynamics of several cetacean species. In addition, extending the survey area to offshore waters will provide new information on the more oceanic species (Bryde’s and Sperm Whales, for example) that are present in other regions of the Gulf of Guinea, and are expected to occur around the archipelago. Establishing the year-round monitoring of species composition, distribution, and abundance as well as identifying critical habitats for cetacean survival and its overlap with human activities (specially by-catch and direct takes) should be a priority for future research. This is especially important since whale catches and recent sightings indicate that the region may be important for several cetacean species (Picanço et al. 2009; Carvalho et al. 2011). For the implementation of long-term population monitoring, it will be essential to promote greater conservation efforts by involving local biologists and NGO technicians in training programs that include species identification, photography techniques, and collection of samples from stranded animals. Moreover, it is crucial to engage with the local population and fisheries communities by developing conservation campaigns and targeting different stakeholders. By allying consistent research and local awareness it will be possible to better understand and protect the cetaceans of this region.