The Spotted Handfish (Brachionichthys hirsutus) is a small fish that lives on the sea bed in the cool, sheltered waters of south-east Tasmania. It has modified pelvic fins that look like “hands”, hence the name. While the handfish can swim when required, it usually uses the “hands” to “walk” across the seabed in search of food such as mysid shrimps.
The main habitat for this species is sandy to silty sea bed in the Derwent River estuary near Hobart, where it forms small, localised populations. This highly-localised distribution is quite uncommon for fish. The reason appears to be the fact that the adults are sedentary, they don’t move around very much. Also the larvae develop completely within the egg mass laid by the females.
Spawning females attach an egg mass of up to 200 eggs onto an appropriate object such as a stalked ascidian (or sea squirt), and then guard the eggs for up to six weeks until they hatch.
The pattern of spots on each Spotted Handfish appear to be unique, meaning we can identify individuals. They are members of the group of fish including deep sea anglerfish. There are a number of handfish species found in Australian waters, with the majority of these being rare and restricted to the south-east.
There are a number of reasons the handfish is listed as endangered. A small population, restricted distribution and vulnerable life cycle are key. Habitat degradation and pest species have contributed to the species’ decline.
The greatest threats to the handfish appear to be siltation and invasive species. The Derwent Estuary where the fish lives is highly urbanised and industrialised, and a range of marine pests have been introduced through shipping.
One key pest is the Northern Pacific Seastar (Asterias amurensis), a particularly large and voracious predator that is now abundant in the estuary. Studies by CSIRO show that the seastars eat the stalked ascidians that the handfish use to attach their eggs.
The egg mass itself is highly vulnerable to predators during the six weeks the eggs take to develop. Increasing numbers of seastars and introduced crabs pose a significant and ongoing risk.
One of the first strategies to conserve the handfish was to give them full protection under fisheries legislation, preventing collection for aquariums. The species’ restricted distribution has worked in its favour, encouraging interest from the local community to clean up the estuary.
Artificial sticks for attaching eggs have been developed by CSIRO and planted throughout the estuary. There is some evidence that the handfish are already using the sticks, although it is unknown whether the eggs survive to hatching.
It is difficult to monitor the handfish’s population because diving is involved, but in recent years some populations have been monitored as part of volunteer programs such as Reef Life Survey. Current results suggest the populations in the centre of the estuary are stable, but more surveys are always needed.
Life in a degraded estuary, full of introduced pest species, is fraught with difficulty, especially where a species is dependent on that localised habitat. But, recent surveys do indicate that viable populations of this species continue to exist, and this gives some significant hope that the handfish can survive in the long term.
With time, improvements in the water quality within the Derwent should flow through to improved habitat for the Spotted Handfish, and perhaps to a reduced threat from introduced pest species as more natural assemblages of species return. Meanwhile, monitoring and artificial egg sticks offer the best chance of avoiding the loss of the species.
The Conversation is running a series on Australian endangered species. See it here.