Exploring Edible Crustaceans of Sydney Harbour: Crayfish, Prawns, and Crabs
Port Jackson, better known as Sydney Harbour, boasts an incredibly rich and diverse marine fauna. This semi-enclosed body of water is likely unparalleled worldwide in terms of its extensive and varied marine life. Sydney Harbour is a naturalist’s paradise, with more than 300 fish species and hundreds of types of crustaceans, molluscs, sea urchins, medusae, sea anemones, sponges, sea worms, bryozoans (sea mosses), and other invertebrates.
The harbour is also home to various mammals, including schools of dolphins (genus Delphinus), and occasionally seals or sea bears (Otaria), leopard seals, bottlenose dolphins, killer whales (Orca), and humpback, black or southern right, and sperm whales. Occasionally, reptilian visitors such as the edible green turtle and the hawksbill turtle make an appearance. The avian population is equally diverse, with frequent sightings of little (blue) penguins, albatrosses, and other bird species.
While it’s tempting to go into the general wonders of this fascinating region, we’ll focus specifically on the crustaceans of Sydney Harbour—particularly those species notable for their size or abundance and regarded as edible or commercially valuable. Sydney Harbour offers a magnificent variety of crustaceans, including crabs, prawns, shrimps, crayfishes, and sandhoppers. These species vary widely in form, size, colour, and other characteristics.
Crayfishes
Two kinds of crayfish, or lobsters, are found in Sydney Harbour, though only one is common. The prevalent species, often seen in New South Wales markets, is the Common Crayfish or Green Crayfish. Most of those found in Port Jackson are relatively small, but occasionally, larger specimens are caught. This crustacean has a limited geographical distribution, ranging intensively from Port Macquarie in the north to Bateman’s Bay in the south.
Size and Distribution
A remarkable phenomenon observed in this species is that the largest examples are typically found in the northern part of its habitat, while those around Bateman’s Bay are generally smaller, dark greenish or blackish, and sexually immature. This distribution pattern is particularly interesting to naturalists.
The primary spawning grounds are located from Newcastle to Port Macquarie, especially near Port Stephens and Seal Rocks. Female crayfish attach tiny eggs to the swimmerets on the underside of their tail, which then release near-microscopic free-swimming larvae within a few days. These larvae bear no resemblance to their parents and soon join the vast array of small marine organisms carried by the south-flowing ocean current along the coastline. After many months and several larval stages, the surviving young reach the “glass crab” stage, characterized by shield-shaped, glassy bodies about three-quarters of an inch across. At this point, they are ready to molt into the recognizable crayfish form and begin life on the ocean floor. When they first resemble their parents, they are about an inch long, which explains why fishermen rarely see them at a smaller size—they are still in the floating larval stage.
Migration and Growth
One of the most fascinating aspects of the crayfish lifecycle is the long, free-swimming phase, during which they can be carried far south of their birthplace. Consequently, where they “go ashore” may be hundreds of miles from where they were spawned. This drift necessitates a compensatory northward migration of the young crayfish to maintain the population within its natural habitat. This explains the smaller sizes observed in southern regions and around Botany Bay and Port Jackson compared to the larger sizes seen further north.
Crayfish undergo interesting color changes throughout their lives. Young specimens are deep olive green, with occasional deep reddish-brown individuals. As they grow, yellow mottling spreads from the lower surface up over the sides and around the head, with the rest of the body becoming a much lighter green. These crustaceans can grow quite large, up to 14 pounds or more.
The Southern Crayfish
The Southern Crayfish, also known as the Tasmanian Crayfish, is abundant in the south but rare in Port Jackson. It has been occasionally found as far north as Port Macquarie, though this is a rarity. This species can be easily recognized by its deep reddish tint and the short, bristly hairs covering its body, particularly around all the protuberances. The tail portion is also beautifully sculptured.
Other Crayfish-like Species
Other crayfish-like forms found in Port Jackson include the large Scyllarus and the curiously flattened and armored Ibacus. These species are occasionally brought to market as curiosities. The Ibacus is especially noteworthy to naturalists because the appendages, which in crayfish are long, fine tactile antennae, are transformed and reduced into strong, armored plates.
Prawns
Sydney Harbour is home to several species of prawns from the genus Penaeus, along with other shrimp-like crustaceans of edible size. Among these, three commercial prawns are of notable importance. These prawns live in various parts of Port Jackson but migrate to the ocean for breeding at the end of summer. Unlike some shrimp and crabs, these prawns do not have ripened gonads or eggs attached beneath their tails when found in the harbour. Instead, they spawn at sea, releasing their eggs directly into the water.
Breeding and Larval Stages
The surface ocean plankton off Sydney Harbour frequently contains large numbers of prawn larvae at various stages of development, as well as young prawns immediately after their final moult. In 1905 and later years, many of these larvae were collected with silk tow-nets and exhibited before the Naturalists’ Society, mainly from areas one to three miles off Sydney Heads.
King Prawn
The King Prawn, although not the largest, is the most prominent prawn in Sydney Harbour. It commonly reaches lengths of 8 to 9 inches and is caught abundantly using sunken nets (“diver nets”) on muddy bottoms. The King Prawn is distinguished by its beautiful tinting, especially on the swimmerets (under the abdomen) and tail. It can be readily identified by the narrow channel or groove running along the back of the “head” to the rostrum or beak.
Tiger Prawn
The largest prawn, the Tiger Prawn, is less common in Sydney Harbour as it is more typically found in tropical regions. I have caught them in large numbers in the Malayan region, and one specimen from Port Jackson measured nearly 30 cm long. The Tiger Prawn is aptly named for the large vertical brown stripes that adorn its body. Unlike the King Prawn, it has a prominent crest along the middle of its back, which becomes very high and noticeable on the strongly toothed beak.
School Prawn
The most abundant prawn in the upper waters of the harbour is the School Prawn. It thrives on muddy bottoms in water depths of 5 to 7 meters and is the smallest of the commercially significant prawns. The School Prawn is semi-transparent and covered with small reddish spots, with a fine, drawn-out beak.
Crabs
While only two types of crabs in Sydney Harbour are commercially significant, several other species are excellent for eating. The largest of these is the Mangrove Crab (Scylla), which is abundant along Australia’s tropical and temperate coasts. However, reclamation projects in Port Jackson have significantly reduced their numbers in that area. These crabs prefer shallow mudflats, where they create basin-shaped hollows for their homes. Mangrove Crabs are typically deep olive green or dark brown. In the Malayan region, they are captured in large numbers using a simple net called a Bintoh, which traps the crabs when baited and lifted quickly.
Blue Swimming Crab
The Blue Swimming Crab is very common in Port Jackson and is the only crab regularly found in local markets. This species has a carapace with long, acutely pointed spines on each side. The males, with their longer nipper arms, are attractively marked with blue, brown, and other mottlings. They are often caught in Middle Harbour using lines from boats and are lifted out with landing nets.
Other Notable Crabs
Several other crab species are worth mentioning for their unique features:
- Blood-Spotted Swimming Crab: This beautiful relative of the Blue Swimming Crab can be recognized by its three blood-like spots surrounded by bluish rings on its carapace.
- Cross-Bearing Swimming Crab (Charybdis): Known for its delicate colours, this crab has several milk-white or cream-coloured bars running from front to back on its carapace. The central bars resemble a cross, giving the crab a porcelain-like appearance.
- Two-Spotted Swimming Crab: Common in the sand below the low-tide mark on beaches, this crab is easily identified by its rounded carapace and two irregular red spots near the posterior edge. The rest of the carapace is yellowish.
Sydney Harbour’s diverse marine fauna includes an impressive array of edible crustaceans, from the impressive Mangrove and Southern Crayfish to the commercially significant King, Tiger, and School Prawns, and the abundant Blue Swimming Crab. These species, each with unique habitats, sizes, and characteristics, contribute significantly to both local biodiversity and commercial fishing industries. The rich variety of crustaceans in Sydney Harbour underscores its status as a naturalist’s paradise and a vital resource for seafood lovers. Exploring and understanding these crustaceans not only highlights the ecological richness of the harbour but also emphasizes the importance of preserving this unique marine environment.
