Discovered by divers in the late 1990s, the upper Spencer Gulf population is the world's only known mass cuttlefish spawning aggregation, with hundreds of thousands of S. apama cuttlefish congregating on subtidal reefs around Point Lowly near Whyalla between May and August.
While outside of the breeding season, the sex ratio is one to one, Spencer Gulf males outnumber females by up to 11 to one in the spawning aggregation.
If this is due to fewer females taking part or to males breeding for a longer period of time than females is not known.
With densities of one cuttlefish per square metre, covering about 61 hectares (150 acres), the sheer numbers of S. apama make this breeding aggregation unique in the world.
As the cuttlefish are oblivious to divers while spawning, they are now a major regional tourist attraction for divers from around the world.
Professor Roger Hanlon of the Woods Hole Oceanographic Institution has called the breeding aggregation "the premier marine attraction on the planet."

The upper Spencer Gulf population displays two alternative lifecycles in both sexes (growth pattern polymorphism).
The first involves rapid growth with maturity reached in seven to eight months with small adults returning to spawn in the first year.
The second involves slow growth with maturity reached in two years, with large adults returning to spawn in the second year.
The upper Spencer Gulf population displays reproductive behaviours unique to this population, possibly as a result of the high spawning densities.
Large males defend females and egg-laying sites, while small males, "sneakers" mimic female colouring and form to gain access to the females being protected by the dominant males, which are extremely territorial.
Male genetic material is deposited in sperm receptacles directly.
The females, which potentially lay hundreds of eggs, extract one egg at a time and fertilise it by passing it over the sperm receptacle before attaching it to the underside of a rock at depths of 2 to 5 m (6 ft 7 in to 16 ft 5 in).

Prior to the mid-1990s, the population was fished for snapper bait, with annual catches of around 4 tonnes (4,000 cuttlefish).
During the 1995 and 1996 spawning seasons, commercial fishing of the spawning grounds harvested around 200 tonnes annually.
Overexploitation was recognised after 245 tonnes were harvested in 1997, leading to 50% of the grounds being closed to commercial fishing in 1998.
Despite half of the grounds being closed, commercial fishers took 109 tonnes in 1998 (about half of the estimated biomass) before dropping to 3.7 tonnes in 1999.
The catch data for 2000 to 2005 have not been released for confidentiality reasons.
Surveys indicated that the cuttlefish biomass remained stable from 1998 to 2001.
A further survey in 2005 revealed a 34% decrease in biomass since 2001 that was attributed to natural variability and illegal fishing during the peak spawning period.
The closure was subsequently expanded to the entire spawning grounds, and anecdotal observations suggested increased numbers in 2006 and 2007; however, a new survey in 2008 found the biomass had decreased a further 17%.

Catch data for the South Australian cuttlefish fishery are reported in annual reports of the Marine Scalefish Fishery, published by SARDI.
The 2014 data are graphed below.
From its establishment in 1987 to the financial year ending June 1992, the fishery caught less than 3 tonnes per annum.


        

        

        

        

        

        

        

        

 


In 2011,  an estimated 33% of the 2010 population had returned to breed, fewer than 80,000 cuttlefish.
Beginning in May, the cuttlefish leave deep water and migrate along coastal reefs to reach their spawning grounds.
Local fishermen claim that a small "finger of land" near Point Lowly extends outside the exclusion zone and that commercial fishers have been targeting the area, intercepting the squid before they can reach the spawning grounds.
Being semelparous breeders, ecologist Bronwyn Gillanders believed the cuttlefish were in danger, stating that determ
Discovered by divers in the late 1990s, the upper Spencer Gulf population is the world's only known mass cuttlefish spawning aggregation, with hundreds of thousands of S. apama cuttlefish congregating on subtidal reefs around Point Lowly near Whyalla between May and August. While outside of the breeding season, the sex ratio is one to one, Spencer Gulf males outnumber females by up to 11 to one in the spawning aggregation. If this is due to fewer females taking part or to males breeding for a longer period of time than females is not known. With densities of one cuttlefish per square metre, covering about 61 hectares (150 acres), the sheer numbers of S. apama make this breeding aggregation unique in the world. As the cuttlefish are oblivious to divers while spawning, they are now a major regional tourist attraction for divers from around the world. Professor Roger Hanlon of the Woods Hole Oceanographic Institution has called the breeding aggregation "the premier marine attraction on the planet."
The upper Spencer Gulf population displays two alternative lifecycles in both sexes (growth pattern polymorphism). The first involves rapid growth with maturity reached in seven to eight months with small adults returning to spawn in the first year. The second involves slow growth with maturity reached in two years, with large adults returning to spawn in the second year. The upper Spencer Gulf population displays reproductive behaviours unique to this population, possibly as a result of the high spawning densities. Large males defend females and egg-laying sites, while small males, "sneakers" mimic female colouring and form to gain access to the females being protected by the dominant males, which are extremely territorial. Male genetic material is deposited in sperm receptacles directly. The females, which potentially lay hundreds of eggs, extract one egg at a time and fertilise it by passing it over the sperm receptacle before attaching it to the underside of a rock at depths of 2 to 5 m (6 ft 7 in to 16 ft 5 in).
Prior to the mid-1990s, the population was fished for snapper bait, with annual catches of around 4 tonnes (4,000 cuttlefish). During the 1995 and 1996 spawning seasons, commercial fishing of the spawning grounds harvested around 200 tonnes annually. Overexploitation was recognised after 245 tonnes were harvested in 1997, leading to 50% of the grounds being closed to commercial fishing in 1998. Despite half of the grounds being closed, commercial fishers took 109 tonnes in 1998 (about half of the estimated biomass) before dropping to 3.7 tonnes in 1999. The catch data for 2000 to 2005 have not been released for confidentiality reasons. Surveys indicated that the cuttlefish biomass remained stable from 1998 to 2001. A further survey in 2005 revealed a 34% decrease in biomass since 2001 that was attributed to natural variability and illegal fishing during the peak spawning period. The closure was subsequently expanded to the entire spawning grounds, and anecdotal observations suggested increased numbers in 2006 and 2007; however, a new survey in 2008 found the biomass had decreased a further 17%.
Catch data for the South Australian cuttlefish fishery are reported in annual reports of the Marine Scalefish Fishery, published by SARDI. The 2014 data are graphed below. From its establishment in 1987 to the financial year ending June 1992, the fishery caught less than 3 tonnes per annum.

        

        

        

        

        

        

        

        

 


In 2011,  an estimated 33% of the 2010 population had returned to breed, fewer than 80,000 cuttlefish. Beginning in May, the cuttlefish leave deep water and migrate along coastal reefs to reach their spawning grounds. Local fishermen claim that a small "finger of land" near Point Lowly extends outside the exclusion zone and that commercial fishers have been targeting the area, intercepting the squid before they can reach the spawning grounds. Being semelparous breeders, ecologist Bronwyn Gillanders believed the cuttlefish were in danger, stating that determ
Sepia apama