Observations of Killer Whale (Orcinus orca) Feeding Behavior in the Tropical Waters of the Northern Mozambique Channel Island of Mayotte, Southwest Indian Ocean

Abstract An eddy-permitting, regional ocean model has been used to examine the variability in the source regions of the Agulhas Current on a range of time scales. These source regions are the East Madagascar Current, the flow through the Mozambique Channel, and the recirculation of the southwest Indian Ocean. The effect of variability in these source regions on the interocean leakage at the Agulhas retroflection south of Africa has been quantified using a retroflection index. On the annual mean, the recirculation in the southwest Indian Ocean subgyre is by far the dominant contribution to the volume transport of the Agulhas Current in the model. On average the recirculation also contributes the largest amount of heat, although the difference between the three sources is not as great as that seen in the volume flux since the water in the Mozambique Channel may be warmer than in the recirculation. Local winds seem to be the dominant forcing mechanism of variability in this recirculation, although it is also partly in phase with the zonally averaged wind stress curl over the subtropical Indian Ocean. A strong relationship was found between the transport of the recirculation and that of the Agulhas Current, particularly on interannual time scales. Consistent with observations, the model flow through the Mozambique Channel is dominated by eddies, with a strong annual cycle, lagging the South Equatorial Current by 1 month and a weaker semiannual cycle. The southern limb of the East Madagascar Current also shows an annual and semiannual variation in transport at 20°S, partly in phase with the local winds. South of about 24°S, the East Madagascar Current breaks up into eddies. An investigation into the sensitivity of the flows in the source regions and in the retroflection index to a 2° southward shift in the mean winds was conducted. In the model run with the shifted winds, the transport strengthened in the recirculation subgyre together with increased mesoscale activity as well as reduced leakage into the southeast Atlantic Ocean when the winds were shifted south by 2°.

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Surface-Based Observations Can Be Used to Assess Behavior and Fine-Scale Habitat Use by an Endangered Killer Whale (Orcinus orca) Population

Aquatic Mammals ◽

10.1578/am.42.2.2016.168 ◽

2016 ◽

Vol 42 (2) ◽

pp. 168-183 ◽

Cited By ~ 3

Author(s):

Dawn P. Noren ◽

Donna D. W. Hauser

Keyword(s):

Habitat Use ◽

Killer Whale ◽

Orcinus Orca ◽

Fine Scale

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Family feud: permanent group splitting in a highly philopatric mammal, the killer whale (Orcinus orca)

Behavioral Ecology and Sociobiology ◽

10.1007/s00265-021-02992-8 ◽

2021 ◽

Vol 75 (3) ◽

Author(s):

Eva H. Stredulinsky ◽

Chris T. Darimont ◽

Lance Barrett-Lennard ◽

Graeme M. Ellis ◽

John K. B. Ford

Keyword(s):

Killer Whale ◽

Group Structure ◽

Group Living ◽

Orcinus Orca ◽

Learning Approaches ◽

Killer Whales ◽

Internal Factors ◽

Individual Fitness ◽

Leadership Experience

Abstract For animals that tend to remain with their natal group rather than individually disperse, group sizes may become too large to benefit individual fitness. In such cases, group splitting (or fission) allows philopatric animals to form more optimal group sizes without sacrificing all familiar social relationships. Although permanent group splitting is observed in many mammals, it occurs relatively infrequently. Here, we use combined generalized modeling and machine learning approaches to provide a comprehensive examination of group splitting in a population of killer whales (Orcinus orca) that occurred over three decades. Fission occurred both along and across maternal lines, where animals dispersed in parallel with their closest maternal kin. Group splitting was more common: (1) in larger natal groups, (2) when the common maternal ancestor was no longer alive, and (3) among groups with greater substructuring. The death of a matriarch did not appear to immediately trigger splitting. Our data suggest intragroup competition for food, leadership experience and kinship are important factors that influence group splitting in this population. Our approach provides a foundation for future studies to examine the dynamics and consequences of matrilineal fission in killer whales and other taxa. Significance statement Group living among mammals often involves long-term social affiliation, strengthened by kinship and cooperative behaviours. As such, changes in group membership may have significant consequences for individuals’ fitness and a population’s genetic structure. Permanent group splitting is a complex and relatively rare phenomenon that has yet to be examined in detail in killer whales. In the context of a growing population, in which offspring of both sexes remain with their mothers for life, we provide the first in-depth examination of group splitting in killer whales, where splitting occurs both along and across maternal lines. We also undertake the first comprehensive assessment of how killer whale intragroup cohesion is influenced by both external and internal factors, including group structure, population and group demography, and resource abundance.

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Circulation pattern controls of wet days and dry days in Free State, South Africa

Meteorology and Atmospheric Physics ◽

10.1007/s00703-021-00822-0 ◽

2021 ◽

Author(s):

Chibuike Chiedozie Ibebuchi

Keyword(s):

South Africa ◽

Indian Ocean ◽

Atmospheric Circulation ◽

Southern Africa ◽

Austral Summer ◽

Free State ◽

Austral Spring ◽

Study Region ◽

Southwest Indian Ocean ◽

South Indian

AbstractAtmospheric circulation is a vital process in the transport of heat, moisture, and pollutants around the globe. The variability of rainfall depends to some extent on the atmospheric circulation. This paper investigates synoptic situations in southern Africa that can be associated with wet days and dry days in Free State, South Africa, in addition to the underlying dynamics. Principal component analysis was applied to the T-mode matrix (variable is time series and observation is grid points at which the field was observed) of daily mean sea level pressure field from 1979 to 2018 in classifying the circulation patterns in southern Africa. 18 circulation types (CTs) were classified in the study region. From the linkage of the CTs to the observed rainfall data, from 11 stations in Free State, it was found that dominant austral winter and late austral autumn CTs have a higher probability of being associated with dry days in Free State. Dominant austral summer and late austral spring CTs were found to have a higher probability of being associated with wet days in Free State. Cyclonic/anti-cyclonic activity over the southwest Indian Ocean, explained to a good extent, the inter-seasonal variability of rainfall in Free State. The synoptic state associated with a stronger anti-cyclonic circulation at the western branch of the South Indian Ocean high-pressure, during austral summer, leading to enhanced low-level moisture transport by southeast winds was found to have the highest probability of being associated with above-average rainfall in most regions in Free State. On the other hand, the synoptic state associated with enhanced transport of cold dry air, by the extratropical westerlies, was found to have the highest probability of being associated with (winter) dryness in Free State.

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Variability in the Mozambique Channel Trough and Impacts on Southeast African Rainfall

Journal of Climate ◽

10.1175/jcli-d-19-0267.1 ◽

2020 ◽

Vol 33 (2) ◽

pp. 749-765 ◽

Cited By ~ 3

Author(s):

Rondrotiana Barimalala ◽

Ross C. Blamey ◽

Fabien Desbiolles ◽

Chris J. C. Reason

Keyword(s):

Indian Ocean ◽

Austral Summer ◽

Western Indian Ocean ◽

Strong Relationship ◽

Ocean Basin ◽

Moist Convection ◽

South Indian Ocean ◽

Mozambique Channel ◽

Mascarene High ◽

South Indian

AbstractThe Mozambique Channel trough (MCT) is a cyclonic region prominent in austral summer in the central and southern Mozambique Channel. It first becomes evident in December with a peak in strength in February when the Mozambique Channel is warmest and the Mascarene high (MH) is located farthest southeast in the Indian Ocean basin. The strength and the timing of the mean MCT are linked to that of the cross-equatorial northeasterly monsoon in the tropical western Indian Ocean, which curves as northwesterlies toward northern Madagascar. The interannual variability in the MCT is associated with moist convection over the Mozambique Channel and is modulated by the location of the warm sea surface temperatures in the south Indian Ocean. Variability of the MCT shows a strong relationship with the equatorial westerlies north of Madagascar and the latitudinal extension of the MH. Summers with strong MCT activity are characterized by a prominent cyclonic circulation over the Mozambique Channel, extending to the midlatitudes. These are favorable for the development of tropical–extratropical cloud bands over the southwestern Indian Ocean and trigger an increase in rainfall over the ocean but a decrease over the southern African mainland. Most years with a weak MCT are associated with strong positive south Indian Ocean subtropical dipole events, during which the subcontinent tends to receive more rainfall whereas Madagascar and northern Mozambique are anomalously dry.

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