**2. Characterization of the research area**

The present study is focused on the Indo-Pacific sector of the Antarctic, in the longitudinal range 35°E-145°W (**Figure 1**), south of 60°S, which is the approximate position of the Antarctic Convergence (AC). This longitudinal range includes International Whaling Commission (IWC) management Areas III (east part), IV, V and VI (west part) (**Figure 1**).

Prydz Bay is located at the west boundary of the research area while the Ross Sea is located at its east boundary. The research area is strongly influenced by the southern boundary of the Antarctic Circumpolar Current (SBACC), which interacts with the coastal East Wind Drift (EWD) in a series of fronts and eddies (**Figure 1**). A series of gyres link the EWD and the SBACC, e.g. the Prydz Bay and the Ross Sea gyres. Krill concentrations appear to track gyral systems off the East Antarctic, for example in the sectors between 30°-90°E or 80°-115°E [6].

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*Whales as Indicators of Historical and Current Changes in the Marine Ecosystem…*

**3. Krill-eating baleen whale species in the Indo-Pacific sector of the** 

*Schematic representation of the research area (dashed in blue). The figure shows the Southern Hemisphere Areas that the International Whaling Commission (IWC) uses for the management and conservation of baleen whales (except the Bryde's whale, B. edeni). The research area is influenced by the southern boundary of the Antarctic Circumpolar Current (SBACC) (dashed arrow), which interacts with the coastal East Wind Drift* 

Baleen whale species, except the Bryde's whale, migrate seasonally between low latitude breeding areas in winter to high latitude feeding areas in the Antarctic in summer. The main prey species of baleen whales such as Antarctic blue, fin, humpback and Antarctic minke (*B. bonaerensis*) whales (**Figure 2**) is the Antarctic krill. Therefore the summer migrations of these whales to the Antarctic are related to areas of krill concentrations, which in turn are associated with gyral systems.

This is the largest baleen whale species. The record for a whale killed in the Southern Hemisphere in the first half of the past century was a body length of more than 30 m and weigh of nearly 180 tons. During the austral summer Antarctic blue whales are distributed between the AC and the ice edge. There is limited informa-

This is the second largest baleen whale species, with a maximum length of more than 27 m and weight of nearly 120 tons. During the austral summer, fin whales are found extensively south of 50°S, but most commonly north of 60°S. There is limited

This species presents a maximum body length of 17 m and weight of 40 tons. During the austral summer humpback whales are distributed from south of the AC to the ice edge, but just to the north of the main distribution area for Antarctic minke whale. The IWC has identified seven populations of humpback whales in the Southern Hemisphere, which are denominated with alphabetic letters from 'A' to 'G' [7]. The populations occurring in the Indo-Pacific sector of the Antarctic are Populations 'C' (mainly in Area III), 'D' (mainly in Area IV), 'E' (mainly in Area V), and 'F'

*DOI: http://dx.doi.org/10.5772/intechopen.94323*

*(EWD) (dotted arrow) in a series of fronts and eddies.*

**Antarctic**

**Figure 1.**

**3.1 Antarctic blue whale**

**3.2 Fin whale**

**3.3 Humpback whale**

tion on the population structure of this species.

information on the population structure of this species.

*Whales as Indicators of Historical and Current Changes in the Marine Ecosystem… DOI: http://dx.doi.org/10.5772/intechopen.94323*

#### **Figure 1.**

*Glaciers and the Polar Environment*

Antarctic ecosystem [1, 2].

part of the Antarctic.

lished hypotheses.

vulnerable species affected by a warming climate [3].

**2. Characterization of the research area**

example in the sectors between 30°-90°E or 80°-115°E [6].

and VI (west part) (**Figure 1**).

(*Euphausia superba*) is a key prey species, supporting different species of baleen whales, pinnipeds, birds and fish. Changes in the ecosystem can result from human interventions or from natural causes. One example of human intervention is the large-scale harvesting of whales in the first half of the 20th Century, which has been discussed by several authors [1, 2]. This harvesting started in the Antarctic Ocean in 1904. Several species of krill-eating large whales, such as the Antarctic blue (*Balaenoptera musculus intermedia*) and humpback (*Megaptera novaeangliae*) whales were heavily reduced in number by commercial whaling during the first half of the past century. Other species such as the fin whales (*B. physalus*) were reduced during the second half. Over more recent decades, the populations of some large whales have started to recover [3]. Changes in the biomass of whale species also seem to have had strong effects on the demography of other krill-eating predators in the

An example of the effects of natural causes is the increases in the chinstrap penguins (*Pygoscelis antarctica*) populations of the Scotia and Weddell Seas over the last four decades (1950's-1990's), which has been attributed to a gradual decrease in the frequency of cold years with extensive winter sea ice cover resulting from environmental warming [4]. However, more recent analyses in the Antarctic Peninsula and Scotia Sea conclude that the chinstrap penguin instead may be among the most

In studying the changes in the Antarctic ecosystem, there needs to be differentiation between West and East Antarctic, as well between land-based and sea-based krill predators. The West Antarctic Peninsula represents one of the regions of the planet where the fastest warming has been observed in the last 50 years [5]. For this reason the studies documenting ecosystem changes in the West Antarctic have considered environmental variables in addition to demographic information on land-based krill predators (mainly penguin species) [3, 4], on which environmental factors could have a larger impact. Warming has not been reported for the East Antarctic, so that environmental factors would not be expected to play the predominant role in the ecosystem changes in this

Here historical and current ecosystem changes in the Indo-Pacific sector of the Antarctic (involving mostly East Antarctic) are documented through the examination of biological and demographic parameters of sea-based predators (whales). These changes in parameter values are interpreted in the context of some estab-

The present study is focused on the Indo-Pacific sector of the Antarctic, in the longitudinal range 35°E-145°W (**Figure 1**), south of 60°S, which is the approximate position of the Antarctic Convergence (AC). This longitudinal range includes International Whaling Commission (IWC) management Areas III (east part), IV, V

Prydz Bay is located at the west boundary of the research area while the Ross Sea is located at its east boundary. The research area is strongly influenced by the southern boundary of the Antarctic Circumpolar Current (SBACC), which interacts with the coastal East Wind Drift (EWD) in a series of fronts and eddies (**Figure 1**). A series of gyres link the EWD and the SBACC, e.g. the Prydz Bay and the Ross Sea gyres. Krill concentrations appear to track gyral systems off the East Antarctic, for

**86**

*Schematic representation of the research area (dashed in blue). The figure shows the Southern Hemisphere Areas that the International Whaling Commission (IWC) uses for the management and conservation of baleen whales (except the Bryde's whale, B. edeni). The research area is influenced by the southern boundary of the Antarctic Circumpolar Current (SBACC) (dashed arrow), which interacts with the coastal East Wind Drift (EWD) (dotted arrow) in a series of fronts and eddies.*
