Age is one of the most important life history parameters for assessment and management of marine living resources. Counting of the growth layers deposited in the earplugs is the most accepted technique for determining chronological age of baleen whales. However unreadable growth layers form in the earplugs of some individual whales. In such cases, alternative methods of age estimation are required. The objective of the present study was to examine the utility of the DNA methylation technique as a proxy to estimate chronological age in the Antarctic minke whale. For this purpose, skin tissues of a total of 100 Antarctic minke whales sampled in the Pacific region of the Antarctic by JARPAII surveys were used. Earplug-based age data from the same whales were used for calibration purposes. Seven CpG sites in three genes (TET2, CDKN2A and GRIA2) were selected for the analysis. In a previous study, these sites showed significant correspondence between methylation levels and age in humpback whales. Methylation levels of the seven CpG sites were scored successfully. Four CpG sites showed significant regressions with age, which contrasted with the case of the humpback whale where all seven sites showed significant regressions with age. The assay predicted age from skin samples with a standard deviation of 8.865 years. This low precision makes the age estimated by the CpG methylation technique unsuitable for use in population dynamics models such as the statistical catch-at-age (SCAA). Furthermore CpGs methylation levels fluctuated among body positions of the whale, particularly between dorsal (exposure to sunlight) and ventral sides. The precision of the CpG methylation technique for age estimation could be improved by increasing the number of CpG sites showing a good correlation with age, and this work is ongoing. In addition, other factors including variation of CpG methylation levels between different tissues should be examined to further evaluate the utility of the DNA methylation techniques as a proxy of age estimation in baleen whales.

This paper examined the geographical distribution of several whale species in the Indo-Pacific region of the Antarctic during the austral summer. The analyses were based on sighting data collected systematically by JARPA and JARPAII surveys in the longitudinal sector of 35°E–145°W, south of 60°S, between 1987/88 and 2008/09. The searching effort comprised a total of 353,134 n.miles. The Antarctic minke whale was the species most frequently sighted, followed by killer, humpback, unidentified beaked, fin, sperm, southern bottlenose, blue, southern right and sei whales. Density index of whales (DIW: no. of individuals sighted/100 n.miles) was calculated using all primary effort and sightings data and its geographical distribution plotted on maps with Lat. 1 degree × Long. 1 degree squares for each species. These maps are more detailed compared to those of the previous maps which used 5° × 5°squares in the 1960s. The geographical distribution was described for each whale species together with some features of their distribution. For example, sei, dwarf minke, humpback and southern bottlenose whales were not sighted in the Ross Sea, distribution areas of southern right whales were limited to the sector 80°E and 135°E, and high-density areas of humpback whales were observed between 80°E and 110°E. The large scale and long-term sighting data set has made a substantial contribution to understanding the geographical distribution patterns and habitat use of whales in the Antarctic ecosystem.

Concentrations of PCB congeners and DDT, HCH, HCB and CHL isomers in the blubber of five mature males of each of common minke, sei and Bryde's whales taken by the Japanese Whale Research Program under Special Permit in the western North Pacific-Phase II (JARPNII) in 2011 were determined. For comparison, concentrations of these compounds in the blubber of five mature male Antarctic minke whales taken by the Japanese Whale Research Program under Special Permit in the Antarctic-Phase II (JARPAII) in 2010/11 in the Pacific sector of the Antarctic were also determined. Concentrations of PCBs were highest among organochlorines in the whales from the western North Pacific, and were much higher than PCBs concentrations in the Antarctic minke whales. Concentrations of HCB, DDTs and CHLs in Antarctic minke whales were higher or of the same order as North Pacific sei and Bryde's whales but much lower than those in North Pacific common minke whales. Differences are explained by the different trophic levels of the species and or the source of the pollutants. The accumulation of detectable 112 PCB congeners in the whale blubber samples was investigated by principal component analysis (PCA). Two significant factors, in which 72.5% (PC1) and 8.5% (PC2) of the total variance in the data were found. These were attributed to possible trophic level and pollution sources. The main component isomers from pesticide products originating in DDTs and HCHs were comparatively lower, although high levels of trans-chlordane contained in an insecticide were not detected in the whales from the western North Pacific. These results suggest that in the western North Pacific, a great deal of time has passed since the release of DDTs, HCHs and CHLs into the environment.