**7. Conclusions**

*Glaciers and the Polar Environment*

• Humpback whales from Population D (Area IV) have expanded their geographical distribution to the south in recent years, while the distribution of the Antarctic minke whales of the Eastern Indian Ocean population (Area IV) has remained stable in the open sea. Larger number of Antarctic minke whales are

• The nutritional conditions of Antarctic minke whales has been deteriorating as

7–8 years old until the 1998 cohort, and the PPF of Antarctic minke whale has

• The ASM of Antarctic minke whale has remained low and stable around

Deteriorating nutritional conditions of the Antarctic minke whales suggest less food available for this species in recent years. Less availability/abundance of Antarctic krill could be a response to environmental changes (e.g. global warming) and/or competition for food with the increasing large whale species such as Antarctic blue, fin and humpback whales. No evidence of global warming exists for the Indo-Pacific sector of the Antarctic [31], so competition for food could be a more plausible interpretation for the results of nutritional deterioration in the Antarctic minke whale. This reflects the end of the period of a krill surplus hypothesised during the past century. Nutritional deterioration as a consequence of competition is not entirely consistent with the low ASM and high APR of the Antarctic minke whale over more recent years. Under the competition hypothesis, this could be the result of a temporal phenomenon in that the response of ASM and APR to environmental

distributed in polynias within the pack-ice in recent years.

remained high (over 0.9), and stable.

evidenced by a decreasing trend of several nutritional indices.

changes producing a nutritional deterioration may be subject to time lags.

Direct competition occurs when two predators are present in the same area as a prey species, and may interfere with each other's access to the prey. Indirect competition may occur when two predators occur in different parts of the area of prey, but because the prey's production is limited, consumption by the one predator limits the production available for the other, and *vice versa* [32]. To investigate the plausibility of the competition hypothesis, estimates of krill biomass trends in the research area are required. There is some partial information on krill abundance based on dedicated krill surveys in the past, but the information is scattered and needs to be combined with that from new surveys in a comprehensive and consistent way so that time series data can be obtained. The period of these demographic changes in the Antarctic minke whales coincides with the post whaling era (1970's-) which has been characterized as 'unfavorable climate conditions and increasing competition for krill' [3].

Antarctic minke whales could also be using alternative feeding areas (e.g. polynias within the pack-ice) in response to the increase in abundance and geographical expansion of these other large whale species. This could provide an alternative explanation from sighting surveys and population models of a decrease and then re-stabilization of Antarctic minke whales abundance in open areas since the 1970's. The increase of the Adelie penguins (*Pygoscelis adeliae*) in East Antarctic in recent decades [33] seems immediately not to be consistent with the competition hypothesis. The authors of the Adelie penguin study provided two explanations for the increase of this species: (i) harvesting of baleen whales, krill and fish across East Antarctic waters through the 20th century could have reduced competition between Adelie penguins and other predators for food, improving prey availability, and (ii) a proposed reduction in sea-ice extent in the mid-20 century may also have benefited Adelie penguins by enabling better access to the ocean for foraging. Since recovery of krill-eating large baleen whales has been reported since the 1980's, it is suggested that their explanation of environmental factors for the demographic changes of Adelie penguins since the

**98**

This review of the scientific evidence for ecosystem changes in the Indo-Pacific sector of the Antarctic has highlighted the importance of long-time monitoring research programs focused on the collection of biological data for krill predators (both land-based and sea-based predators) as well as data on sea ice cover and environmental variables. The hypothesis proposed for the recent demographic changes found in whales is competition. To investigate this hypothesis further, estimates of krill abundance as well additional data collection of the predators and improved modelling analyses are required (see [34]). Also, oceanographic data obtained for more than 30 years in the Indo-Pacific sector of the Antarctic by JARPA/JARPAII surveys should be analysed to explore further the possible effect of global warming on the pattern of demographic changes found in whales.

In this context, Japan has started a new non-lethal research program to continue studying whales and the environment in the Indo-Pacific sector of the Antarctic. The program called JASS-A (Japanese Abundance and Stock structure Survey in the Antarctic) started in the austral summer of 2019/20, and will continue for at least eight years. It will conduct systematic sighting surveys for abundance estimates, biopsy sampling for genetic analysis of population structure, oceanographic and marine debris surveys, satellite tracking and photo-identification for studies on stock structure, distribution and movement of large whales, and Unmanned Aerial Vehicle (UAV) to observe whales outside of the main survey area. The analyses of the data to be collected will assist to examine the plausibility of the hypothesis proposed in this study further, in particular the observation that Antarctic minke whales have been moving into polynias within the pack-ice in recent years.
