Actinopyga miliaris: The Blackfish That Disappeared from the Rowley Shoals

In 2023, researchers conducting standardized benthic surveys across the three protected atolls of the Rowley Shoals in northwestern Australia made a finding that captured the trajectory of Actinopyga miliaris more precisely than any population model could. The blackfish Actinopyga miliaris, a targeted species currently facing a high risk of extinction in the wild, completely disappeared from monitoring sites in the most recent surveys.

The Rowley Shoals are not an easy place to fish. Located approximately 260 kilometers off the Western Australian coast, historically regarded as among the most unimpacted coral reef systems in the world, and within a formally protected marine area, these three atolls were expected to function as refugia — places where sea cucumber populations could persist even as surrounding fishing grounds were depleted. The disappearance of A. miliaris from all monitoring sites there, documented in research published in Limnology and Oceanography Letters (Wiley, 2026), is the most recent data point in a story that the global literature on this species has been building for two decades.

Taxonomy, Morphology, and the Blackfish Name

Actinopyga miliaris belongs to the family Holothuriidae, within the genus Actinopyga — the same genus as A. lecanora (surf redfish / stone fish, profiled in article 24) and A. mauritiana (surf redfish, profiled in article 33). In commercial trade, it is known as blackfish or hairy blackfish, names that distinguish it from the other dark-colored commercial species — the black teatfish (H. whitmaei and H. nobilis) — by referring to the characteristic hairy texture of its body wall surface.

The body reaches 250 to 350 millimeters in length, with a maximum body wall thickness of 9 millimeters — thicker than A. lecanora but thinner than the teatfish species. The dorsal surface is uniformly black, covered in mucus and fine sediment that adheres to the surface and contributes to the hairy appearance. The ventral surface is white, covered in long thick tube feet. Like A. mauritiana, A. miliaris lacks functional Cuvierian tubules — the defensive sticky threads present in many other sea cucumber species — relying instead on its firm, heavily built body wall as its primary defense against predation.

The common name "blackfish" creates potential confusion with Actinopyga miliaris and the black teatfish species because all appear black dorsally. The distinction in commercial trade rests on body shape and size: blackfish are smaller and more cylindrical than teatfish, with a rounded rather than squared cross-section, and without the pronounced lateral teat-like protrusions that define the Microthele subgenus. In dried form, the distinction is partially maintained through body wall thickness — teatfish have substantially thicker body walls — but morphological authentication of dried product requires expertise, and molecular barcoding remains the most reliable authentication method for processed material.

Distribution and Habitat

Actinopyga miliaris is distributed throughout the tropical Indo-Pacific, from the East African coast across the Indian Ocean, through the Indonesian archipelago and broader Southeast Asia, to the Pacific Islands and northern Australia. Within this broad range, it occupies sandy lagoons and reef flats at depths from the intertidal zone to approximately 10 meters, most commonly in less than 4 meters of water.

This shallow, accessible habitat is both ecologically characteristic and commercially consequential. Unlike white teatfish or prickly redfish, which occupy reef slope and deeper lagoon environments that require more skilled diving to access, A. miliaris is found in water shallow enough for collection by wading and hand-picking in many of its coastal habitats. This accessibility has historically made it one of the earliest species targeted in any new commercial sea cucumber fishery, and one of the first to be depleted as a result.

In Indonesian waters, A. miliaris is documented across multiple producing regions and appears in the inventories of commercially exploited species documented in research from the Fisheries Research Institute (Puslitbang KP). Research published in Fisheries Research (Elsevier, 2024) on commercial sea cucumber diversity across Indonesia confirmed A. miliaris presence within the assemblage of species harvested nationally, noting the broader pattern of depletion observed by fishers in the preceding decade for high-value species across Indonesia's producing regions.

The Red Sea Evidence: From 48 to Zero in Sixteen Years

The most quantitatively precise documentation of A. miliaris population collapse in the research literature comes from the Red Sea, where a longitudinal study conducted surveys at the same sites in 2000, 2006, and 2016. The data is stark.

In 2000, A. miliaris was present in the survey area with a recorded relative abundance of 3.03% of the total sea cucumber assemblage. By 2006, its relative abundance had declined further as overall populations fell. By 2016, A. miliaris recorded zero individuals at the surveyed sites — a complete local disappearance over sixteen years of commercial harvesting. The total abundance of all sea cucumber species at the same sites fell from 13,880 individuals in 2000 to only 2,420 individuals in 2016, a loss of 82.6% of the original population. A. miliaris, present at the start of the monitoring period, was among the species that contributed to this collapse and was absent by its conclusion.

This Red Sea trajectory is not unique. It is the documentation of a pattern that the research literature consistently identifies for A. miliaris wherever the species has been commercially exploited and subsequently monitored: relatively rapid depletion of accessible populations, with no documented recovery in areas where exploitation has continued.

The IUCN Assessment and What 80-90% Means

The IUCN Red List assessment for Actinopyga miliaris, conducted in 2013 and cited in CITES COP19 documentation, concluded that the species has declined by 80-90% in at least 50% of its range and is considered overexploited in at least 30% of its range. These are the quantitative thresholds that inform the Vulnerable classification under IUCN criteria A2bd, which assesses decline based on observed population reduction over the past three generations, inferred from indices of abundance and levels of exploitation.

An 80-90% population decline across the majority of a species' range is not a preliminary warning. It is a late-stage indicator — the kind of data point that, in the history of fisheries management, more often precedes collapse and regulatory intervention than recovery and stabilization. The CITES COP19 documentation presented this evidence as part of the proposal to list Actinopyga miliaris under Appendix II — a proposal that was not adopted at COP19 — meaning that despite the IUCN Vulnerable classification and the documented population declines, the species currently remains without CITES trade controls.

The absence of CITES listing for A. miliaris is not a determination that the species is not at risk. It reflects the political and scientific process of CITES listing, which requires evidence meeting specific criteria for inclusion. The IUCN assessment, the Red Sea longitudinal data, and the Rowley Shoals disappearance together constitute a body of evidence that, regardless of its regulatory status, defines the conservation context within which any commercial sourcing of A. miliaris occurs.

Why A. miliaris Declined Faster Than Many Other Species

Several biological characteristics of A. miliaris contributed to the speed and extent of its documented population declines. Its shallow, accessible habitat made it among the first species targeted in new fisheries and among the easiest to harvest comprehensively once commercial demand created incentive to do so. Its IUCN assessment describes it as having a generation time likely exceeding 10 years, meaning that the 80-90% population decline documented by 2013 occurred within a timeframe shorter than two full generation cycles for many populations.

The blackfish A. miliaris declined severely in surveys at the Rowley Shoals, raising concerns about recovery potential, alongside H. whitmaei — both species being consistently found at densities below 0.3 individuals per 100 square meters, a threshold that research in New Caledonia has defined as at or near a critical level for effective population recovery. When a population falls below this density, the probability of successful spawning and fertilization declines because mature adults become too sparse to reliably encounter one another during reproductive periods.

This Allee effect — where population recovery becomes increasingly difficult as density falls below a critical threshold — is particularly well-documented in broadcast-spawning marine invertebrates like sea cucumbers. The combination of A. miliaris accessibility for harvest, slow generation time, and susceptibility to Allee effects at low population densities creates a biological profile that responds poorly to anything short of complete harvest cessation for extended periods.

The Rowley Shoals Finding and What It Signals

The 2026 publication in Limnology and Oceanography Letters (Wiley) documenting the disappearance of A. miliaris from all monitoring sites across the three protected atolls of the Rowley Shoals is significant beyond the local finding. The Rowley Shoals are remote, formally protected, and historically unimpacted — precisely the conditions under which a population facing harvesting pressure elsewhere might be expected to persist. Their documented disappearance from all monitoring sites there, attributed to illegal fishing pressure that the Australian Fisheries Management Authority documented through seizures during the same period, illustrates that the conservation infrastructure surrounding A. miliaris populations is insufficient to prevent their continued decline even in nominally protected environments.

Documented seizures of illegally harvested holothurians by the Australian Fisheries Management Authority over the period between 2018 and 2023 suggest that illegal fishing pressure likely contributed to the observed declines, with the blackfish A. miliaris completely disappearing from monitoring sites in the most recent surveys.

For supply chain operators evaluating A. miliaris as a sourcing option, the Rowley Shoals finding is not an abstract conservation concern. It is the most recent data point in a trajectory that has consistently pointed in one direction across every geographic area where this species has been commercially harvested and subsequently monitored.

Sourcing Actinopyga miliaris from Indonesia

A. miliaris is present in Indonesian waters and documented in commercial catch records across multiple producing regions. It is traded as a mid-tier species, above the lowest-value holothurians but below the premium CITES-listed species in both price and documentation requirements. It is not currently subject to CITES Appendix II controls, which reduces the formal documentation burden compared to sandfish, teatfish, and prickly redfish.

For supply chain operators evaluating A. miliaris sourcing, the absence of CITES controls does not reduce the significance of the conservation evidence. The combination of IUCN Vulnerable classification, documented 80-90% population decline across the majority of its range, and the Rowley Shoals disappearance constitute a conservation risk profile that is among the most serious for any commercially traded sea cucumber species not currently subject to CITES controls. Organizations with sustainability procurement commitments or ESG reporting requirements should weigh this evidence explicitly when evaluating supply chain exposure to this species.

Sepanjang's approach to sourcing encompasses awareness of the conservation status of all commercially traded species in our operating environment, including those not currently subject to formal CITES controls. We welcome conversations with organizations seeking to understand the conservation dimensions of their sea cucumber supply chain beyond the regulatory baseline.

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Sepanjang — Indonesia's Specialty Ocean Products Co. Sourcing high-quality sea cucumber directly from Indonesian waters for over 20 years.

PT Sepanjang Laut Nusantara is an Indonesia's Specialty Ocean Products Co. specializing in Sea Cucumber, Seaweed, Abalone, and Seashell from Indonesia — for domestic and international B2B markets.

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