Geographic variation in external morphology of North Pacific and Southern Hemisphere blue whales (Balaenoptera musculus)

Geographic variations in size and proportions of blue whales (Balaenoptera musculus) were investigated using length data acquired from whaling records aerial photogrammetric surveys. Results showed that found the eastern Pacific off Central North America are significantly shorter (by approximately 2m) than at higher latitudes Pacific. support occurrence a morphologically distinct (ENP) whale population which migrates spring/summer warm waters Mexico to temperate feeding grounds along west coast America. Southern Hemisphere sampled with vertical photogrammetry northern Peru Galapagos Islands similar ENP whales. However, affinity these southern remains uncertain. No available for formerly captured Japan Korea. Nonetheless, history diminishing fishery catches lack any recent sightings suggests members geographic is now severely depleted or extinct. Based on comparisons total length, rostrum tail region, be ‘pygmy’ (B.m. brevicauda) described Kerguelen Island region Indian Ocean. ‘Antarctic’ intermedia) Ocean statistically larger their conspecifics high These results hypotheses migrate seas cold those whose distributions limited low mid-latitudes. Differences morphology may reflect selective pressure populations adapt physiologically energy demands associated different migration, environmental ecological regimes. As some come located far apart oceans, questions remain concerning continuity within among ocean basins. Consequently, research approaches such as photogrammetry, telemetry, acoustics molecular genetic analysis should continued better understand worldwide structure.