Assessment of the level of surface activity in humpback whales during the breeding season

Abstract

-Between 1991 and, the reproductive behavior of the humpback whale was studied during the breeding season off the coast of Ecuador, South America (02°S, 81°W). During the sighting period the level of surface activity exhibited by the whales was assessed according to the type of display performed and its frequency. Five displays that produce percussion sounds and used likely for communication were considered: breaching, head-lapping, tail-slapping, flipper-slapping and tail slashing. A total of 289 selected sightings were included in one of four levels according to a scale of intensity designed for the purpose. To determine what social conditions increased or reduced the activity, groups were organized according to their size and age-class composition. Singletons and groups of three and four whales showed a significantly higher surface activity than pairs or larger than four for the highest intensity level (P<0.05). Differences were also found when age-classes were compared, with subadults showing significantly higher surface activity than other classes (P<0.01). Groups that increased members showed a significant difference respect to decreasing groups at the lowest level of intensity of the scale (P<0.05). Competitive groups showed a significant higher occurrence at intensity level 2 than other groups (P<0.05). No relationship was found between whale speed and surface activity. The possible influence of environment factors such as day hour, sea state, moon phase and "El Niño", was also assessed; none of which showed a clear trend to affect the intensity of whale surface activity. A discussion about the implications of these findings is provided as well as interpretations of possible meanings of some displays under different social contexts. This analysis indicates that social aspects rather than environment factors drive the surface activity of the humpback whales during the breeding season.Resumen -Entre 1992 y 2002, se estudió el comportamiento de las ballenas jorobadas durante su temporada de reproducción en la costa de Ecuador, Sudamérica (02°S,81°W). Para ello se analizó la actividad de superficie exhibida por las ballenas de acuerdo al tipo de pautas mostradas y su frecuencia. Cinco pautas que producen sonidos de percusión y que son utilizadas probablemente como una forma de comunicación fueron evaluadas: salto de espaldas, salto de vientre, golpe de cola, golpe de aleta pectoral y latigazos con la cola. Un total de 289 avistamientos fueron usados en el análisis. Con el afán de determinar que condiciones sociales fueron causantes del incremento o la ausencia de la actividad de superficie, los grupos fueron organizados de acuerdo al tamaño del grupo y al tipo de individuos presentes. Los individuos solitarios así como los grupos formados por tres y cuatro ballenas mostraron un nivel de actividad de superficie significativamente más alto (P<0.05). Diferencias significativas también fueron encontradas cuando se comparó los grupos por clases de edades, siendo los subadultos quienes mostraron el mayor ...

Short Note: Evaluating Humpback Whale (Megaptera novaeangliae) Social Behaviour Through Sexing Active Individuals

“…The inverse relationship between group size and surface activity found in this study-particularly in groups where males were sampledsupports the belief that one role of surface activity is to act as a joining mechanism through the generating of acoustic signals for long-distance inter-group communication (Herman & Tavolga, 1980;Helweg & Herman, 1994;Félix, 2004;Dunlop et al, 2008). This would be one way in which individuals could use social recognition by conspecifics in order to establish new social interactions.…”

“…This was an unexpected result as traditionally researchers have associated certain surface displays in this species with intraspecific competition between males (Darling et al, 1983;Tyack & Whitehead, 1983;Baker & Herman, 1984;Silber, 1986;Clapham, 1996;Félix, 2004). However, in order to optimize their contact with males during the breeding season, receptive females may use surface activity to attract males, promote competition, and/or choose a mate (Darling, 2001;Deakos, 2002;Cerchio et al, 2005).…”

“…Humpback whales (Megaptera novaeangliae) have been studied off Ecuador for 20 y (see Félix & Haase, 2001Félix, 2004;Félix & Botero, 2011;Félix et al, 2012). These whales belong to the so-called Breeding Stock G (International Whaling Commission [IWC], 2008) that migrates along the west coast of South America between the eastern tropical Pacific where breeding grounds are located and their feeding grounds along the northwestern Antarctic Peninsula (Stevick et al, 2004).…”

“…Surface displays by humpback whales have been associated with a variety of social contexts and emotional states, including aggression, courtship, and dominance ranking (e.g., Herman & Antinoja, 1977;Herman & Tavolga, 1980;Darling et al, 1983;Tyack & Whitehead, 1983;Baker & Herman, 1984;Whitehead, 1985;Silber, 1986;Clapham et al, 1992;Frankel et al, 1995;Darling, 2001;Clapham, 2002;Félix, 2004). The nonvocal sounds produced when an individual hits the water surface after executing an active surface behaviour are used for communication and can be heard several kilometers away from the source (Herman & Tavolga, 1980;Dunlop et al, 2008).…”

“…It was also sampled 4.6 times more frequently (but not significantly) in males than in females in all adult groups, supporting the belief that it is used as a form of aggression or warning toward adversary males (see Darling et al, 1983;Tyack & Whitehead, 1983;Baker & Herman, 1984;Silber, 1986). Clapham et al (1992) suggests that females use tail slashing to reject male advances or potential escorts.The execution of this display by females in groups containing a mother/calf pair suggests that it is also used by adult females to reject male escorting; for calf protection; and, in the case of mother/calf pairs alone, as a defensive or warning response to boat presence (Félix, 2004).…”