A monitoring program being established for the Spotted Handfish in southern Tasmania will provide a basis for population estimates and a vehicle for implementing and tracking the success of conservation initiatives.
Spotted Handfish, (Brachionichthys hirsutus), once were abundant in coastal waters from Southern to north-eastern Tasmania, but now persist only as isolated sub-populations in the Derwent and D’Entrecasteaux estuaries. In 2012, the species was listed as Critically Endangered under the Environment Protection and Biodiversity Conservation Act (EPBC).
Surveys in the past decade have charted a contraction in the range of Spotted Handfish, with only 10 known sub-populations remaining at small, isolated, sites. Three of these sites have very low population densities with only one to three individuals observed in the latest round of sampling. There is a concern that these numbers may now be too low for successful mating.
As well as being scarce and patchily distributed, Spotted Handfish have particular micro-habitat requirements and poor dispersal capabilities. They need three-dimensionally complex, shallow, soft sediment habitats with suitable spawning substrates: primarily stalked ascidians, but also sponges, and seagrasses.
After hatching, the young remain in the same area as the adults, and with no larval phase, they have little opportunity to disperse and colonise new areas. Adult handfish are also poor dispersers, preferring to walk with their modified pectoral fins rather than swim.
Agents responsible for the fragmentation of suitable habitat include introduced predator species such as the North Pacific Seastar, pollution, siltation, historic commercial dredge fisheries, boat moorings and coastal development.
Effective float and GPS-based survey technique
This project will support a monitoring program for Spotted Handfish at the 10 known sites in southern Tasmania which were surveyed as a baseline in 2015. This second monitoring year will determine the adequacy and repeatability of the proposed monitoring program. The surveys will use a new method that uses a towed float and GPS tracker, rather than a physical transect reel. The float method allows for longer transects per dive (two times 300 metres rather than two times 100 m), and in 2015 for the first time made it logistically and financially feasible to survey all 10 known spotted handfish sub-populations in a single season. .
Because individual handfish have distinctive spot patterns and low dispersal, a photographic survey of discovered fish will be analysed using mark-recapture techniques to determine whether abundance can be reliably stimated with this method. (Low recapture rates indicate larger populations and vice versa.) Through synchronisation of the underwater cameras timestamped with the towed GPS, locations of handfish can also be georeferenced and subsequently assessed to estimate any movement between sub-populations.
Georeferenced data collected in the monitoring program will help to guide and track the success of future planned conservation actions such as the placement of artificial spawning habitat, potential capture of brood-stock for captive breeding, replacement of traditional chain yacht moorings with ‘eco-moorings’, and site specific suppression of predators such as the North Pacific Seastar.
The project will also foster community awareness and engagement in Spotted Handfish conservation.