Conservation of Spotted Handfish

Spotted Handfish are the subject of a national recovery plan implemented by the National Handfish Recovery Team. Numerous planning, and development authorities, and development proponents and opponents, require advice on how activities may affect Spotted Handfish populations.

The species is relatively short-lived, (5–10 years) and matures at more than two years’ old. This leaves a short window for reproduction, which relies on egg masses laid on seafloor structures such as stalked ascidians. If spawning fails, population declines may occur rapidly. With no planktonic life stage to aid dispersal, and low adult dispersal, outside recruitment to re-establish collapsed populations is unlikely.

Analysis of 23 years of Spotted Handfish survey data (1997–2019) supported by the Marine Biodiversity Hub (a forerunner of the Marine and Coastal Hub) showed that periodic collapses and booms occur across local populations. The rates of change suggest that annual surveys are required to effectively respond with management interventions.

This project continued the monitoring and review of Spotted Handfish populations and conservation actions. While the population appears to have stabilised in response to the planting artificial spawning habitat each isolated population group is highly vulnerable to being lost to a chance event.

As local populations can be dynamic, the functional life span of artificial spawning habitat is limited, and threats to the species are chronic, stochastic and existential through climate change, Spotted Handfish may be a ‘conservation reliant’ species that require ongoing management. A robust captive population program is required. Operational governance models, rather than short-term research projects, are needed to conserve the Spotted Handfish, due to the dependence on interventions and the long time-scale required to even stabilise the population.

Approach and findings

This project continued a range of activities designed to answer key research questions important to the conservation management of Spotted Handfish. These include:

• recommencing surveys of nine Spotted Handfish populations in the Derwent estuary and surrounds, after a two-year gap, to allow population modelling, and support the assessment of management actions, and the impacts of development;
• counting ascidians during surveys to target future artificial substrate habitat plantings at locations with low densities of natural spawning habitat (a possible stabilisation of Spotted Handfish populations may be linked to the planting of ASH);
• providing advice on mitigation for government and industry regarding any observed impacts on local Spotted Handfish populations;
• maintaining ambassador fish and captive breeding populations in partnership with industry; and
• fostering engagement to identify any unknown local populations of Spotted Handfish, publications, community outreach and the National Handfish Recovery Team.

Surveys

Surveys recommenced in 2022 showed continued persistence of all monitored local populations in line with the stabilisation trend. Genomics of local populations indicate that even within the Derwent estuary local Spotted Handfish populations are genetically isolated from one another, and therefore vulnerable to local extinctions due to chronic pressures and/or stochastic events.

Pressures

Activities including the building of jetties, moorings, and wharfs, marine pipelines and cables, and large developments such as marinas and aquaculture have the potential to hamper Spotted Handfish movements, destroy habitat, and fragment their populations. Anchoring of vessels on top of near-shore habitat may also affect populations, especially in the breeding season. Habitat degradation includes the reduction in suitable spawning substrates through declines in seagrasses and predation on stalked ascidians by the introduced northern Pacific seastar (Asterias amurensis). Additional pressures are storm events and blooms of filamentous algae and other species that rot and turn the habitat anoxic.

Climate change

Spotted Handfish are highly vulnerable to extinction due to rapid climate change. Already on the edge of their temperature tolerance (~18°C) in summer, their cool temperate marine niche and, based on historical records, their known range, has contracted poleward as rapid climate change has occurred. As they are a shallow water coastal species, they have no available habitat south of Tasmania. Future marine heatwaves may cause extinction or severe depletion of remnant populations.

Environmentally friendly moorings

Following four years of development an environmentally friendly mooring (EFM), with a cost neutral design and mature deployment and servicing methods, will undergo testing in Tasmanian and New South Wales waters. This will provide generic build advice (depth, vessel size, exposure) for widespread mooring replacement.

Coastal development

On several occasions the project leader, in coordination with the chair of the National Handfish Recovery Team, provided advice to permitting and development proponents and authorities that protected Spotted Handfish populations from coastal development activity. For example, seven of the nine long term Spotted Handfish monitoring sites are adjacent to the Clarence City Council boundary, with extensive exposure to potential development interactions.

Captive husbandry

Captive husbandry in aquariums is a further strategy to manage both the risk of extinction from localised stochastic events and the existential risk of marine heat waves. Following development of husbandry methods at Seahorse World and SEA LIFE Melbourne Aquarium, successful captive breeding events have occurred and ~31 juveniles are being raised in captivity for potential release or transfer to other aquariums in 2023. Otolith and age and growth work suggest that >5 years old is geriatric for Spotted Handfish, and all the original captive brood stock collected in 2018 are now dead.

Artificial spawning habitat

As local populations can be dynamic, the functional life span of artificial spawning habitat is limited and threats to the species – chronic, stochastic and climate – are ongoing, Spotted Handfish are a ‘conservation reliant’ species. They require annual site-specific monitoring, in situ interventions and ex situ captive husbandry. They are particularly dependent on the conservation interventions of artificial spawning habitat, (~14,000 deployed since 1998), which has not occurred since 2019.

Outcomes

This project has updated the evidence base for Spotted Handfish conservation, through implementation of the national recovery plan by the National Handfish Recovery Team. It provides stakeholders with a shared understanding of conservation needs. Recommendations include:

• replacement of all chain moorings with environmentally friendly moorings between Battery Point and Sandy Bay;
• eradication or massive suppression of Asterias amurensis, restoration of seagrasses, removal of moorings and consideration of other threats would be needed if artificial spawninbg habitat planting were to be permanently abandoned; and
• further collection of individuals from the wild in order to extend the genetic diversity of existing captive ‘insurance’ populations.

Greater acceptance may be needed that recovery of endangered species are often ‘wicked problems’ that are not solvable but rather require o-going conservation interventions. Operational governance models, rather than short-term research projects, are needed to conserve the Spotted Handfish, due to the dependence on interventions and the long time-scale required to even stabilise the population.

Project location

Derwent estuary and surrounds, south-eastern Tasmania