There was great excitement at the North Mole in Whanganui last week with the unusual and unexpected appearance of a massive whale and her calf close to shore.

Spectators watched for about an hour until the pair slowly began making their way westwards along the coast.

Judging by the adult's size, lack of dorsal fin and the presence of callosities (large, white, rough growths) on the skin around the adult's head, it was suggested they were Southern right whales.

Tohora, or Southern right whales (Eubalaena australis), are a New Zealand native migrant species. They live mostly in sub-Antarctic waters around Auckland and Campbell Islands and breed during winter and spring.

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Tohora are the only large baleen whales that are seen from our beaches, and there are occasional sightings around mainland New Zealand. A few months ago, Wellington residents were entertained for several weeks by a tohora frolicking in the harbour.

During August another two mothers and their calves were seen offshore, one at Petone and one off the Kāpiti Coast. This was the first recorded sighting of a tohora mother and calf in Wellington Harbour in modern times.

A century ago, tohora were hunted almost to extinction because they were the "right whale" to catch. Previous to that, they were common enough for the South Taranaki Bight to be called "Mothering Bay" because of the large numbers of mother whales and their calves that gathered here.

Recent marine studies have revealed there is also a resident population of pygmy blue whales in the South Taranaki Bight. They feed on an up-welling ocean current that produces massive amounts of krill, the tiny crustacean that blue whales eat.

By using biopsy darts to collect DNA samples and recording whale-songs, researcher Leith Torres from Oregon State University was able to identify 151 individual blue whales in the area.

Her study demonstrated that this is a genetically distinct population, estimated at around 718 whales, and could possibly be a new sub-species of pygmy blue whales.

With the reappearance of tohora off the Whanganui coastline and the significant discovery of a resident blue whale population in our area, it is even more imperative that public pressure is applied to prevent Trans-Tasman Resources Ltd from mining the seabed of the South Taranaki Bight for iron sand.

The company's website claims their operation to remove 50 million tons of sand per year will create 1,600 jobs and increase New Zealand's GDP by $150 million per year.

The company states this will translate to over 290 jobs in the Whanganui and South Taranaki area, and increase GDP locally by $150 million per year.

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There is no detail provided to support these claims. While the High Court has recently overturned the Environmental Protection Authority's decision to allow mining to proceed, the company is launching an appeal to the High Court. So it's not time to celebrate yet.

If we want the South Taranaki Bight to be a healthy marine habitat for such stupendous and amazing creatures as Southern right whales and pygmy blue whales, we need to continue applying public pressure and defending the right of these incredible creatures to remain living undisturbed in their own patch of ocean.