Sepia apama: the giant Australian cuttlefish

We are looking to reconcile conflicts between ecotourism and fishing of this iconic species.

Each year, during the winter months, Sepia apama (giant Australian cuttlefish) aggregate in the shallow waters near Whyalla to breed. The breeding aggregation is so large at times (one cuttle per square meter) that it has attracted a number of ‘user groups’. Prior to mid 1990s, the aggregation was fished at sustainable levels for snapper bait. However, in the mid 90’s, fishers actively targeted cuttlefish, and large numbers of the breeding aggregation were removed from the system. The lifecycle of many cephalopods (squid, cuttlefish and octopus) is very short, and their lives end after laying eggs. This means if you fish out one cohort of breeders, the following generation is going to be severely impacted. To avoid long-term population decline, even local extinction, a renewable moratorium preventing fishing was introduced. In subsequent years, the cuttlefish numbers increased again, and ecotourism in the area began to thrive.

Why are the cuttlefish so popular?
The sheer number of animals makes the breeding aggregations unique, not just in Australia, but the world. Together with the ability to watch their amazing mating displays and quirky behaviours, the Whyalla cuttlefish have become a global phenomenon, with scientists, naturalists, recreational divers and snorkellers wanting to documenting their activities.

Cuttlefish mating occurs in pairs. With such an enormous population, you can imagine the competition between males to mate with a female is quite intense. This is where the behaviour becomes quite interesting: large males are bigger and easily outcompete other males for female attention. Smaller males, not wanting to miss out on the opportunity to mate, change colours and body patterns to look like a female (hence 'cross-dressing' cuttlefish!). The large male that has paired up with a female allows this extra 'female' to get quite close. When he is distracted, the cross-dressing male quickly reverts back to normal male patterns and colours, mates with the female, and quickly swims away from the unsuspecting large male without a potentially fatal fight.

So, in summary, even on snorkel, you can see a range of cuttlefish antics: instant and dramatic colour changes, cross dressing and 'sneaky sex', guarding and fighting, mating and egg laying.

What the project is doing
While there have been professors (e.g. world-renowned cephalopod biologists Dr Roger Hanlon and Dr Mark Norman), Ph.D and honours students (e.g. Dr Karina Hall and Karin Kassahn, Adelaide University) working on behaviour, and population biology, much remains unknown. For instance, we don’t have a good understanding of where the cuttlefish in the breeding aggregation are coming from. We don’t know the extent of their movements after they hatch from the ‘natal’ area. We don’t know how many populations make up the aggregation. It is critical that we know the answer to these questions if the resource is going to be effectively managed.

The approach we are taking is multidisciplinary, with 5 main questions addressed. By using molecular, chemistry and morphological information, we will provide the most detailed description of population structure in any cuttlefish species that will serve as a model for studies of other species, especially in light of the increase in fishing interests in cephalopods globally. With knowledge of migratory movements within and away from the breeding aggregation, we will be able to design and recommend an appropriate marine protected area in the upper Spencer Gulf.

If you have any further queries about our approach to sustain giant Australian cuttlefish in southern Australia, please contact one of our personnel listed below.

Personnel:
Melita de Vries (Southern Seas Ecology Laboratories; University of Adelaide)
Dr Bronwyn Gillanders (Southern Seas Ecology Laboratories; University of Adelaide)
Dr Steve Donnellan (Evolutionary Biology Unit; South Australian Museum)

Funding:
Australian Research Council Linkage Grant
University of Adelaide
South Australian Museum
Department of Environment and Heritage
Nature Foundation
PIRSA
SARDI Aquatic Sciences