CuttleFest – The Great Migration
Every winter tens of thousands of Giant Australian Cuttlefish migrate to one location along South Australia's rocky coastline to aggregate
Giant Australian Cuttlefish Aggregation by Stefan AndrewsOriginal Source: @ocean_imaging
A Special Spot
In South Australia’s Northern Spencer Gulf, there is a section of rocky reef that provides an important breeding ground for Australia’s Giant Cuttlefish (Sepia apama). It is within and underneath these rocks where the cuttlefish lay their eggs.
Males outnumber females at around 7:1 but the ratio can be as high as 11:1 early in the mating season. Females reject around half of all matings.
Making a move
Males pair with, and defend females, rather than egg laying sites. Large males paired with females spend the most time guarding the female from other males with spectacular visual displays.
South Australia's Giant Cuttlefish Aggregation. How Populations Crashed and Recovered.Great Southern Reef Foundation
The story of Australia's giant cuttlefish aggregation
Discover how populations crashed and recovered.
A pair of cuttlefish mating by Stefan AndrewsOriginal Source: @ocean_imaging
Fussy cuddlers
When mating does occur, the couple ‘cuddle’ in a head to head embrace. The act involves the male jetting water from his funnel towards the mouth region of the female and the transfer of sperm packages.
Males may actively try and prevent females from mating with other males (guarding). They may attempt to displace the sperm of rival males, for example by flushing water through the female during mating, thereby increasing the chances of fertilisation by their own sperm.
Cuttlefest (2019), Whyalla, SA by Stefan AndrewsOriginal Source: @ocean_imaging
Strength vs. Stealth
A number of strategies are used by smaller male cuttlefish to gain more female partners including;
Open stealth, where the smaller male approaches the guarded female while the consort male is fending off other males; hidden stealth, the smaller male meets potential female partners underneath the cover of rocks and reef and the most interesting...
Female mimicry, where the smaller males mimic the appearance of a female to prevent larger guarding males from challenging them directly.
Cuttlefish guards eggs by Stefan AndrewsOriginal Source: @ocean_imaging
Females do not necessarily engage in immediate egg-laying following mating, but can mate multiple times before commencing egg-laying. Eggs are deposited on the underside of rocks or in rock crevices.
Cuttlefish laying their eggs by Stefan AndrewsOriginal Source: @ocean_imaging
Females move around in search of egg laying sites and do not deposit all their eggs in the same location.
Females may lay 5-39 eggs a day with these eggs being sired by multiple males. The eggs develop for 3-5 months and hatch from mid-September through to early November.
Cuttlefish, Whyalla, SA by Stefan AndrewsOriginal Source: @ocean_imaging
Boom and bust
In the late 90s the population estimate was around 180,000 and appeared stable. In 2005 the population dipped a little, but from about 2009 onwards the scientists started to see a concerning decrease in the population.
Many questions were raised about what was causing that decline. Was it pollution, disease, aquaculture, fishing? Because the area is highly utilised by many different people and organisations, there was a lot of speculation.
Precautionary principle
While studies show no definitive link that fishing pressure caused the cuttlefish population to decline, it was more of a precautionary approach to implement protective bans on fishing in the breeding areas.
From 1998 onwards, the sanctuary zone within the aggregation site has been in place. In March 2013 following record low levels of cuttlefish, the entire northern Spencer Gulf (the line between Wallaroo and Arno Bay) was closed to the taking of the species.
Kids see giant cuttlefish mating. This is how they react.Great Southern Reef Foundation
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Imagery by Stefan Andrews and Mike Jones
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