Author: Evan John
One of the most spectacular events of the natural marine world takes place annually between May and August in the reef areas of upper Spencer Gulf, around Black Point, Point Lowly and Fitzgerald Bay, north of the town of Whyalla, on Eyre Peninsula, South Australia.
Fig. 1. Sepia Apama
It is here that the giant Australian cuttlefish, Sepia apama, migrate in the thousands to mate and spawn. The low rocky reef areas provide a hard rocky surface on to which the cuttlefish can attach their eggs, for much of the rest of upper Spencer Gulf is sand, sea grass flats and mud banks. It is an amazing spectacle, as these unique marine animals can be observed changing colour, shape and texture, and performing mating rituals. It is believed that this kind of aggregation occurs nowhere else in the world in such numbers.
Sepia apama is the largest species of marine animals commonly called cuttlefish; it is believed that specimens as large as 1.5 metres have been recorded. S. apama is a mollusc – and is, therefore, a closer relative to the common garden snail, rather than to its marine compatriots, the fish. It belongs to the Class Cephalopoda, a group which presents a complete contrast to the majority of the molluscs in habits, and in many respects, points of organization. Cephalopods have the power of rapid movement, no external shell, (although they do have an internal supportive structure, (the cuttlebone or gladius), and a circle of four pairs of fleshy arms and two elongated tentacles that surround the mouth, which contains a pair of mandibles or “beaks” somewhat similar to parrots. They also have a relatively well-developed nervous system, and their eyes are quite specialized, in that they have a lens, cornea, retina, and distinctive “W-shaped” pupils. This suggests that the eyes are used for observation as well as just transmitting light sensations to the nervous system like snails. Vision is believed to be highly developed, rivalling that of humans, and divers have described meeting the gaze of a cuttlefish as one which is that of a highly intelligent creature “in there looking back”. Cuttlefish and octopus are used in medical eye research because of the similarity to the human eye.
The word Cephalopod is constructed from the Greek words kephale (head) and podos (foot). This conveys the notion that the limbs emerge from the face, which, in effect, is what happens. Cuttlefish have a body shape something like a flattened football, with eyes and arms and tentacles at one end, and a “fin” which runs along each side. This lateral “fin” undulates, and propels the animal through the water. In addition, the cuttlefish “bone”, (often washed up on the beach and used as a source of beak strengthening and diet calcium for caged birds,) is honeycombed with gas-filled cells, producing neutral buoyancy, thus allowing precision and delicacy of movement when desired. When rapid propulsion is necessary, the animal is able to draw water into the mantle cavity, and force it out through a “nozzle” or siphon in the side of the body underneath the eye. This siphon can be swivelled to change direction, and relaxed or constricted when control of speed is desired.
Probably the cuttlefish’s most fascinating behaviour is its ability to change colour. There seems to be a variety of stimuli which start this amazing display, ranging from movement between light and dark areas, an apparent attempt to hide and camouflage, and probable mating activity. On some occasions, waves of coloration changes pass over the length of the body, in less than a second, moving from head to rear, probably associated with a warning display. Colour variation is due to a system of chromatophores, minute multi-nucleate pigmented cells, red, brown, yellow or blue, embedded throughout the animal’s skin. These are surrounded by small radial muscles, connected to the central nervous system. When the muscles contract, the cell expands, and the pigment it contains becomes more apparent. Chromatophores are organized into three layers, each containing a different pigment colour. The ability to manipulate each layer independently means that quite a large range of colours are possible as a result of the blending effect of the different pigments. This colour composition is enhanced by the presence of small cells called iridocytes, that lie above and below the chromatophores, creating a mirror-like effect. It is incredible to watch a cuttlefish rest in a shaft of light – the part of its body in the light changes quite quickly to a distinct, patterned colouration, whilst that in the dark stays a continuous duller colour.
Fig. 2. Male cuttlefish displaying
In addition, these remarkable creatures can change the texture of their skin. Small wart-like protuberances called tubercles on the skin can be made to expand and contract, resulting in the skin of the body becoming more “bumpy” when against a background of marine plants like Caulerpa or Ecklonia or Hormosira.
As previously mentioned, the area around Whyalla is quite unique because it is one of the relatively few areas in southern Australia where S. apama congregate to mate and to spawn. During mating, males and females lock tentacles, and the male uses one of its longer tentacles to transfer a packet of sperm into the body of the female. She then lays between 100 and 300 eggs, attaching them under a rock or to the roof of a cave in the shallow reefs or some other such sheltered location. It is believed that the species takes about four years to reach sexual maturity.
Fig. 3. Cuttlefish eggs
After mating, both male and female animals become lethargic, their appearance takes on a greyish, worn and tattered look, and they then die.
Cuttlefish are an important link in the food chain. From stomach analyses, it seems that they are a prime food source for snapper, yellow-tail, dolphins and sea birds. Research also shows that cuttlefish make up a significant proportion of the diets of Australian fur seals and sea lions. There is little doubt that their biomass component is critical to maintaining viable breeding populations of animals at the upper end of the marine food chain, in marine ecosystems of which they are a part.
Fortunately, up until about 1996, cuttlefish fishing was pretty much restricted to bait fishing by local fishermen, with some recreational catching and a very limited commercial catch. However, in 1997, commercial markets were established in S.E. Asia, and the recorded catch was 255 tonnes, or over 250,000 cuttlefish, by relatively few boats. Commercial exploitation of this resource was at the time unrestricted and unmanaged.
In 1998, there was a doubling of the fishing effort, with many more boats and fishermen per boat! At the beginning of the season in early May, fishermen were ready for the cuttlefish to arrive, and within four weeks had so reduced the stock that they voluntarily stopped fishing for 10 days to allow stocks to recover. By early June the catch was so low that the fishermen had stopped fishing in any significant numbers. Despite this self-imposed moratorium the fishing did not improve to any noticeable degree, and it was at this point, with ongoing lobbying by a number of organizations, that the then South Australian Government announced the closure of the fishery until September 1998, whilst at the same time initiating a three year study of the cuttlefish population, to determine the effects of commercial fishing and the possibility of sustainable exploitation in the long-term. Researchers at Melbourne University, who had studied Whyalla’s cuttlefish aggregation over two seasons, had written to the Premier of South Australia in 1998 pointing out that “the rapid recent rise in exploitation of this spawning aggregation is likely to destroy this unique natural event before the impacts of this harvest are fully understood. Cuttlefish catches from this small area of rocky reef have risen unchecked from negligible levels to more than 200 tonnes per year in less than three years. More than a quarter of a million cuttlefish were pulled from this small, region last year (1997). Signs of collapse are already evident this year …”.
As a consequence, responding to many expressions of community concern, a Sanctuary near Point Lowly was set aside to protect some cuttlefish stocks.
Fig. 4. Cuttlefish mating
Unfortunately the area of the Sanctuary contained large areas of sandy beach, quite unsuitable for cuttlefish to breed. In February 1999, the South Australian Government made the decision to close the local cuttlefish spawning grounds and stop commercial fishing during the 1999 and 2000 seasons, so further research on Sepia apama could be undertaken by the South Australian Research and Development Institute (SARDI).
Anecdotal weekly observations by the divers during the 2000 season indicated that the biomass had not recovered at all in the two and a half years that the spawning grounds have been closed.
That this unique congregation of Sepia apama must be protected from commercial exploitation appears obvious for at least two sound biological reasons:
- Taking the animals as they arrive at the breeding site gives them no time to mate and spawn, hence limiting future population numbers.
- Given the short life-span and low reproductive rate, (they lay relatively few eggs), and the disproportionately high predation rate of young cuttlefish, current stocks may well be unsustainable.
There are other valid reasons why the nurturing of current stocks of S. apama at Whyalla is essential.
There is significant scientific and educational interest
SARDI research to date, the lack of other data and research material on the animal, and the acknowledged limitations of the scope of the current research work, make it clear that there will be insufficient information to make informed and safe management decisions on this resource from the point of view of allowing any form of commercial exploitation. In addition, there has been, and continues to be, unprecedented interest from the scientific and documentary film – making communities, research groups and media from around the world.
The animal’s behaviour is unique, recognized by marine scientists both nationally and internationally. The site also has substantial existing value for research and monitoring, and is unique for its accessibility and scale.
S. apama is ecologically significant – in the marine food chain of S.A. waters
There is substantial potential for sustainable eco-tourism
Divers from across Australia, North America, Chile and Europe have travelled to Whyalla for no other reason than to dive with the cuttlefish – regarded as the “chameleons” of the sea. Feedback from these visitors suggest that they are the forerunners of thousands of diving enthusiasts who will travel around world to experience this unique marine event.
The animals are vulnerable to fishing
Permanent protection is essential for the animal’s survival.
It is well worth taking the effort to visit Whyalla during the breeding season of the giant Australian cuttlefish, Sepia apama. Local diving and boating organizations run charters to the area, enabling divers and snorkellers to witness this unique phenomenon.
Author’s note
I must acknowledge the assistance of two extremely dedicated people, for their comments, thoughts and material in my preparation of this article:
Tony Bramley, of Whyalla Diving Services, who, with his diving colleagues, has worked tirelessly with local and overseas scientists and the S.A. Government, to ensure the protection of the cuttlefish breeding grounds, and Ron Hardman, who has recorded cuttlefish and their activities in a series of brilliant copyrighted photographs and videos. He has very kindly allowed me the use of some of his photos in this article.