Today, the humpback whale has one of the largest geographical ranges in the animal kingdom, summering in prey-abundant high latitude waters and then migrating to tropical waters in the winter to breed and give birth, performing one of the most impressive migrations of any animal (Rasmussen et al. 2007). Discrete humpback “stocks” are designated by the International Whaling Commission (IWC) for assessment and management purposes. Our project focuses on stock B, which occurs in the southeast Atlantic. More specifically, we are focusing on a population that comes to São Tomé and Príncipe to breed and given birth (Carvalho et al. 2011).
The Gulf of Guinea and the surrounding waters were subjected heavily to commercial whaling from the 18th into the 20th century (Townsend 1935). Since the cessation of whaling in this area in 1959, limited scientific studies have been completed. This lack of data is highlighted further when compared to the volume of studies that originate from humpback hotspots such as Hawaii or Mexico. Humpbacks generally arrive to the Gulf of Guinea in June and leave in October, however there have been instances of humpbacks sighted in the north of the Gulf into December (Rosenbaum and Collins, 2006; Weir, 2010).
The first official study conducted in São Tomé waters was only recently published in 2009 by Picanço et al and consisted of a cetacean diversity study. Carvalho et al. 2011 suggested that the waters of São Tomé served as a nursery or resting ground for humpbacks, due to the high occurrence of cow/calf pairs and limited displays of breeding behaviors. Our project aims to provide further analysis of humpback behavior and prevalence in these waters.
Given the geographical proximity of the Gulf of Guinea to the Cape Verde Islands, it has been suggested that there may exist a population overlap between stock B and the eastern North Atlantic humpback population that winters in Cape Verde. When suggesting a population overlap between these two populations, Hazevoet et al. (2011) cited 4 instances of humpback whale sightings (2 of which were cow/calf pairs) outside of the established winter season.
Humpbacks are thought to be found in the Cape Verde Islands from January to May, whereas these 4 sightings were from June through to August. It is suggested that these rare sightings outside of the established winter time frame could be due to:
However, to date, there has been no genetic testing, photo identification, or acoustic studies to determine if there exists any population overlap between these two populations. By utilizing citizen science and scientific surveys to gather and analyze photo identification and acoustic data year-round in São Tomé, this project aims to provide more information on the possible inter-population movements of these whales.
While on their low-latitude breeding grounds, male humpback whales will sing their characteristic songs (Payne & McVay, 1971). While there is dispute in the scientific community, it is generally accepted that these songs serve as an attractant to females. It is accepted that separate populations will sing distinctive songs, with similarity being inversely associated with the geographic distance between two given populations (Winn et al. 1981; Payne & Guinee, 1983; Noad et al. 2000). Therefore, establishing song structure for a given region will facilitate easy comparisons between other populations and could provide insights into cultural transmission between populations. Given this, song similarities spanning ocean basins can give insights into the acoustic contact of the singers with other populations.
To date, the mechanisms of song transmission are not fully understood, yet there are three generally accepted hypotheses: (1) males are moving between breeding grounds inter-seasonally and thus do not display site fidelity (2) males are moving between breeding grounds intra-seasonally (3) songs are transmitted during migration or at feeding grounds (Payne & Guinee, 1983).
Through the first classification of the breeding song of São Tomé, this project aims to facilitate cross-comparison of this song to that of the Cape Verde Islands and other populations to examine possible acoustic overlap.
The Gulf of Guinea and the surrounding waters were subjected heavily to commercial whaling from the 18th into the 20th century (Townsend 1935). Since the cessation of whaling in this area in 1959, limited scientific studies have been completed. This lack of data is highlighted further when compared to the volume of studies that originate from humpback hotspots such as Hawaii or Mexico. Humpbacks generally arrive to the Gulf of Guinea in June and leave in October, however there have been instances of humpbacks sighted in the north of the Gulf into December (Rosenbaum and Collins, 2006; Weir, 2010).
The first official study conducted in São Tomé waters was only recently published in 2009 by Picanço et al and consisted of a cetacean diversity study. Carvalho et al. 2011 suggested that the waters of São Tomé served as a nursery or resting ground for humpbacks, due to the high occurrence of cow/calf pairs and limited displays of breeding behaviors. Our project aims to provide further analysis of humpback behavior and prevalence in these waters.
Given the geographical proximity of the Gulf of Guinea to the Cape Verde Islands, it has been suggested that there may exist a population overlap between stock B and the eastern North Atlantic humpback population that winters in Cape Verde. When suggesting a population overlap between these two populations, Hazevoet et al. (2011) cited 4 instances of humpback whale sightings (2 of which were cow/calf pairs) outside of the established winter season.
Humpbacks are thought to be found in the Cape Verde Islands from January to May, whereas these 4 sightings were from June through to August. It is suggested that these rare sightings outside of the established winter time frame could be due to:
- North Atlantic humpbacks overstaying the winter season
- Humpbacks from stock B journeying farther north than previously thought
- A mixture of both hypotheses (Hazevoet et al. 2011).
However, to date, there has been no genetic testing, photo identification, or acoustic studies to determine if there exists any population overlap between these two populations. By utilizing citizen science and scientific surveys to gather and analyze photo identification and acoustic data year-round in São Tomé, this project aims to provide more information on the possible inter-population movements of these whales.
While on their low-latitude breeding grounds, male humpback whales will sing their characteristic songs (Payne & McVay, 1971). While there is dispute in the scientific community, it is generally accepted that these songs serve as an attractant to females. It is accepted that separate populations will sing distinctive songs, with similarity being inversely associated with the geographic distance between two given populations (Winn et al. 1981; Payne & Guinee, 1983; Noad et al. 2000). Therefore, establishing song structure for a given region will facilitate easy comparisons between other populations and could provide insights into cultural transmission between populations. Given this, song similarities spanning ocean basins can give insights into the acoustic contact of the singers with other populations.
To date, the mechanisms of song transmission are not fully understood, yet there are three generally accepted hypotheses: (1) males are moving between breeding grounds inter-seasonally and thus do not display site fidelity (2) males are moving between breeding grounds intra-seasonally (3) songs are transmitted during migration or at feeding grounds (Payne & Guinee, 1983).
Through the first classification of the breeding song of São Tomé, this project aims to facilitate cross-comparison of this song to that of the Cape Verde Islands and other populations to examine possible acoustic overlap.
Research Methodologies
Fin Identification
To determine individual identification, photographs will be taken of flukes as well as dorsal fins (Katona and Whitehead, 1981). Occurrence and occupancy, as defined in Carvalho et al. 2011, of each individual will be determined by comparing photographs to an ongoing seasonal catalog.
This catalog will then be compared against both the Antarctic Humpback Whale Catalog (Allied Whale) and the North Atlantic Humpback Whale Catalog to determine the stock of each individual. If no matches are found in either catalog, whales occurring in Sao Tome from June to December will be assumed Antarctic humpbacks based on previous studies (Weir 2010; Carvalho et al. 2011) and humpbacks observed from January to May will be considered North Atlantic humpbacks based on previous studies (Hazevoet and Wenzel 2000).
Through year-round survey efforts, both in scientific and citizen science-based approaches, further understanding of a suggested overlap of these two populations (Hazevoet et al. 2011) will be achieved.
Acoustics
Acoustic data from both a Passive Acoustic Monitoring device and a handheld hydrophone will be used to examine if any breeding songs are present. Any songs recorded would be classified into the hierarchical structure of units, phrases, and themes as first described in Payne and McVay 1971. Recordings used in analysis will be separated by 24 hours to minimize the risk of sampling the same whale twice.
Only recordings with visible harmonics will be used to ensure quality analysis. From these recordings, only samples that have at least 1 full song cycle by a single whale will be used in the final analysis. Songs will then be classified manually using Raven 1.5 (2016; Cornell Lab of Ornithology). Units will be first established, followed by phrases, and themes. Song units are defined as the smallest continuous sound to the human ear.
Phrases are defined as the smallest number of repeated units organized in such a fashion to avoid “lone” units. Themes are defined as grouping of similar phrases. The following acoustic parameter data will be extracted for each unit following Oviedo et al. 2008: duration, minimum frequency, maximum frequency, peak frequency, and unit occurrence.
This song classification will then facilitate cross-comparison to the breeding song on the Cape Verde Islands, first described in Ryan et al. 2019. A high occurrence of theme sharing could suggest acoustic overlap between the two populations, whereas a low degree of similarity would suggest acoustic and geographic isolation.
To determine individual identification, photographs will be taken of flukes as well as dorsal fins (Katona and Whitehead, 1981). Occurrence and occupancy, as defined in Carvalho et al. 2011, of each individual will be determined by comparing photographs to an ongoing seasonal catalog.
This catalog will then be compared against both the Antarctic Humpback Whale Catalog (Allied Whale) and the North Atlantic Humpback Whale Catalog to determine the stock of each individual. If no matches are found in either catalog, whales occurring in Sao Tome from June to December will be assumed Antarctic humpbacks based on previous studies (Weir 2010; Carvalho et al. 2011) and humpbacks observed from January to May will be considered North Atlantic humpbacks based on previous studies (Hazevoet and Wenzel 2000).
Through year-round survey efforts, both in scientific and citizen science-based approaches, further understanding of a suggested overlap of these two populations (Hazevoet et al. 2011) will be achieved.
Acoustics
Acoustic data from both a Passive Acoustic Monitoring device and a handheld hydrophone will be used to examine if any breeding songs are present. Any songs recorded would be classified into the hierarchical structure of units, phrases, and themes as first described in Payne and McVay 1971. Recordings used in analysis will be separated by 24 hours to minimize the risk of sampling the same whale twice.
Only recordings with visible harmonics will be used to ensure quality analysis. From these recordings, only samples that have at least 1 full song cycle by a single whale will be used in the final analysis. Songs will then be classified manually using Raven 1.5 (2016; Cornell Lab of Ornithology). Units will be first established, followed by phrases, and themes. Song units are defined as the smallest continuous sound to the human ear.
Phrases are defined as the smallest number of repeated units organized in such a fashion to avoid “lone” units. Themes are defined as grouping of similar phrases. The following acoustic parameter data will be extracted for each unit following Oviedo et al. 2008: duration, minimum frequency, maximum frequency, peak frequency, and unit occurrence.
This song classification will then facilitate cross-comparison to the breeding song on the Cape Verde Islands, first described in Ryan et al. 2019. A high occurrence of theme sharing could suggest acoustic overlap between the two populations, whereas a low degree of similarity would suggest acoustic and geographic isolation.