We often take for granted today was once severely threatened and continues to demand strong protection. An example of this situation was the countless species of whales commercially exploited during the 19th and 20th centuries, with estimates pointing to more than 2 million whales captured in the southern hemisphere alone. It was not until the 1960s that there was a total ban on whaling, and the start of a slow recovery. Among the species explored is the humpback whale (Megaptera novaeangliae), reaching a size of around 15 meters in length and 40 tons, when adults.
This species, like many other whales, moves within the ocean, between their breeding and feeding grounds. Consequently, humpback whales perform large annual migrations, feeding in the Antarctic polar waters during the austral summer.
Before commercial exploitation, South Georgia and the South Sandwich Islands in the Atlantic part of the Southern Ocean were one of the most important habitats for the humpback whale. This area is rich in Antarctic krill, their main prey. Due to this krill abundance, these islands are also an important area for krill fisheries. Due to the establishment of a marine protected area, the fishery is limited by, for example, some areas permanently closed to fishing.
A recent study sought to understand how measures to protect krill and regulate the fishery in this protected area are protecting humpback whales' feeding grounds. With the use of satellite tags placed near the dorsal fin of humpback whales between 2003 and 2020, it was possible to follow the movements of these whales, from the coast of Brazil, where they reproduce, to the islands of South Georgia and the South Sandwich Islands, where they feed. These movements were then analyzed taking into account the aggregation of krill, and environmental factors (e.g., sea surface temperature, iron concentration, depth, and month).
With these data, it was possible to analyze the existence or absence of humpback whales in various locations and the factors that most influenced their presence in those areas. In the first months of their arrival, the whales were more concentrated in a deep channel of the South Sandwich Island with about 2000 meters, and with high concentrations of iron, which is indicative of high biological productivity, being the possible reason for their presence in this area. As the summer progresses, the whales move to the South Georgia shelf, where >90% of the tagged whales were within the limits of the marine protected area, during a period in which no fishery was taking place. Humpback whales are increasingly frequent in these waters and seem to be recovering to pre-exploitation levels, which is excellent news.
The management of resources in the Southern Ocean does not yet include the various species of whales, unlike penguins, seals, and seabirds, species that also feed on krill. However, in the future, with the right information, it will be possible to move in that direction.
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Source:
Bamford, C. C. G., Jackson, J. A., Kennedy, A. K., Trathan, P. N., Staniland, I. J., Andriolo, A., & Zerbini, A. N. (2022). Humpback whale (Megaptera novaeangliae) distribution and movements in the vicinity of South Georgia and the South Sandwich Islands Marine Protected Area. Deep Sea Research Part II: Topical Studies in Oceanography, 198, 105074. https://doi.org/10.1016/j.dsr2.2022.105074
Author: José Abreu