|Title||Coastal, offshore, and migratory movements of South African right whales revealed by satellite telemetry|
|Publication Type||Journal Article|
|Year of Publication||2011|
|Authors||Mate B, Best P, Lagerquist BA, Winsor M|
|Journal||Marine Mammal Science|
|Date Published||July 2011|
|Keywords||migratory movements, right whales, Telemetry|
In September 2001, 21 satellite-monitored radio tags were deployed on southern right whales in South African waters, 15 of which transmitted for 25–161 d. Most coastwise movement on the south coast occurred in a westerly direction with cow-calf pairs moving slowest. Three whales tagged on the west coast and one tagged on the south coast moved north into St Helena Bay, a probable feeding ground, where residence times were 36–100 d. Five animals tracked after leaving the coast maintained a bearing of 201°–220° before branching out over the southeast Atlantic from 37° to 60°S and between 13°W and 16°E, traveling 3,800–8,200 km over the ensuing 53–110 d before transmissions ceased. Their locations were categorized as migrating or nonmigrating based on the relative orientation of the track and net speed. An average of 42% of nonmigrating locations were between 37°S and 45°S, and 53% were south of 52°S, possibly associated with the Subtropical Convergence and Antarctic Polar Front, respectively. Whaling data suggest right whales fed largely on copepods at the former and euphausiids at the latter. If the nonmigrating locations represented feeding at these frontal zones, switching between them would seem to have obvious cost-benefit implications.
Most published accounts of the seasonal distribution and movements of southern right whales (Eubalaena australis) have relied on data from late 18th and early 19th century whaling (Townsend 1935), supplemented by information from illegal 20th century whaling (Tormosov et al. 1998). Interpretation of the resultant patterns of movement depends heavily on assumptions regarding the process of whaling and how it might have been affected by influences other than the abundance of whales (Best 1970, Best 1981, Bannister 2001). Other indirect lines of evidence used to investigate possible movement patterns have included stable isotope ratios in baleen (Best and Schell 1996) and combined genetic-stable isotopic analysis of skin (Valenzuela et al. 2009). More recently, direct evidence of individual movement has been obtained from photo-identification matches (Best et al. 1993, Best 1997, Bannister et al. 1999), but the timing, routes, and speeds of migration still remain speculative. Such information is needed to establish patterns of habitat utilization and possibly identify areas of critical importance for the species.
In this paper we report on the movements of southern right whales on and away from the South African coast following the deployment of satellite tags in September 2001. The unprecedented use of this technology with southern right whales provided new insights into cow-calf movements along the coast, and the timing, routes, and migration speeds into offshore areas and different feeding grounds.