Hera Sengers took this photo of a humpback whale breaching in Hervey Bay.
Hera Sengers took this photo of a humpback whale breaching in Hervey Bay.

MARINE MYSTERY: Why whales are giving birth earlier

THIS year seems to have bought about a huge shift in calving areas and more new calves have been observed in southerly waters than what has been traditionally observed.

The female humpback's gestation time is a cycle of 11-12 months.

This will depend on her age, her body mass at the time and when she was impregnated.

We can review several variables in this new occurrence of the females giving birth in southern waters, and only surmise what we think is happening.

The reason for just surmising is unless this happens again next migration season we do not know if this was just down to one factor.

If birthing in the southern waters does occur next season, a long-term study into this would be advisable to understand the full effects.

Starting with the whales, we have several variables here.

If the mum is a first-time mum, she could have got her timing wrong on her migration.

If she is not a new mum, it could be that she was impregnated very early in the previous season and has started her migration and been caught out in the southern waters.

Resources regarding krill in the feeding ground will determine when they are ready to migrate.

Mothers must reach a body mass that will support the constant lactation and feeding of their newborn calf.

If they are still trying to gain enough weight due to lack of resources this could affect the timing of their migration.

Some humpback mothers' calves can, like humans, be stillborn or born with life-threatening defects and will not survive.

They can also be miscarried.

I could go on listing more issues that could possible happen with the whales themselves, but we need to look at external influences that might be causing this early birthing as well.

With climate change, the sea temperatures are changing.

Could the southern waters be warming up enough to trigger this early birthing response?

This would involve data collection over years to confirm this hypothesis.

Are there chemical influences, run-off, herbicides, pesticides, hormonal constituents in the seas now that are affecting the birthing processes?

To understand this phenomenon there would have to be repeated early birthing on the southern migration of the east coast and constant data collection of all variables to point toward the exact cause.

With all that said, this weekend saw the whale-watching season draw to a close and as we say our fond farewells to the humpback whales, we wish them all a safe journey back to Antarctica.

Big thanks for such great memories for us and our visitors.

We want them to survive their long journey to visit Hervey Bay again next year.

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