Rediscovery off Papua New Guinea: The sailback houndshark is back

One of the rarest shark species in the world has reappeared off the coast of Papua New Guinea after more than 50 years: the sailback houndshark (Gogolia filewoodi). A WWF team led by marine biologist Jack Sagumai documented a total of six specimens near the mouth of the Gogol River in Astrolabe Bay (Madang Province) in 2020 and 2022.

G. filewoodi is the only representative of its genus—a monotypic species in the houndshark family (Triakidae). It therefore represents a globally unique evolutionary lineage. Its defining feature is the extraordinarily long-based first dorsal fin, which is also reflected in its German and English names.

Known only from a single specimen until 2020

Until its rediscovery in 2020, the sailback houndshark was known only from a single specimen, likewise caught near the mouth of the Gogol River in 1970—a pregnant female. Based on this, the American shark researcher Leonard Compagno published the original scientific description in 1973.

Even today, little is certain about the biology of these animals. The species is aplacental viviparous (ovoviviparous): the embryos are nourished by their yolk sac in the uterus, hatch shortly before birth, and are born alive. The holotype contained two well-developed embryos—an indication of at least two young per litter.

In the decades that followed, the species remained untraceable: neither extensive deep-sea surveys between 2010 and 2014—including in Madang Province—nor a targeted shark and ray study from 2013 to 2017 produced any records. As a result, specialists assumed a possible extinction due to overfishing.

The rediscovery: data and location

The records come from landing-site and market surveys conducted by WWF and accompanied by local fisheries officers. In March 2020, five female animals were documented, and in September 2022 an adult male. The females were caught at depths of around 80 meters, the male at about 200 meters.

The animals were caught as bycatch: a local fisher was targeting croakers (Sciaenidae) with hand lines for trade. These are the first confirmed records of this rare species since the original description—and the first male specimen ever recorded.

The sailback houndshark apparently lives on the continental shelf—the relatively shallow marine zone directly off the coast—and uses the nearshore deep channels of Astrolabe Bay, especially around the mouth of the Gogol River. All confirmed records come from this single stretch of coastline. Despite intensive surveys and broad fishing activity elsewhere in Papua New Guinea, the species has been recorded only here; the new findings also lie close to the type locality (1970). This points to a very small range and possible micro-endemism—and explains its particular sensitivity to increasing fishing pressure.

Sailback houndshark: protection status and risks

The IUCN lists the sailback houndshark as data deficient because data on population size and trend are lacking. The new study in the Journal of Fish Biology provides the first recent records, but basic information on the species’ ecology, way of life, and exact distribution is still missing.

According to fishers, sailback houndsharks are occasionally caught as bycatch in Astrolabe Bay, especially between March and July and during the dry season from August to November. During this time, local boats target croakers whose dried swim bladders (fish maw) are considered a delicacy in Asian cuisines.

The fact that five females were caught as bycatch within only two days suggests the species occurs regularly at least near the Gogol estuary and may be a frequent bycatch in the fish-maw fishery. At the same time, the fish-maw fishery is expanding in Papua New Guinea, where it is regarded as an important pressure factor on threatened sharks and rays. For a rare species such as the sailback houndshark, with its presumably small range, this is an acute risk factor that could make it vulnerable to population declines as fishing activity increases.

Not a target species, but still at risk: fishers report that the flesh of the sailback houndshark is not in high demand and is often given away if there is too much of it. Its fins also have little value in the shark-fin trade, so targeted fishing is unlikely. The threat comes from bycatch.

In addition, the sailback houndshark is an aplacental viviparous shark species, which is often associated with long gestation periods and late maturity—population recovery is therefore probably slow, which could make it especially sensitive to additional fishing pressure.

How should the sailback houndshark be protected?

Rare, locally restricted species are especially sensitive to additional fishing pressure. A recent IUCN report on the global status of sharks, rays, and chimaeras underscores this: overfishing and habitat loss are seen as central drivers; since 1970, the populations of many groups have declined sharply, and a large proportion of species are considered threatened with extinction. Against this background, and given the species’ rarity and possible micro-endemism, the study authors recommend precautionary monitoring and management for the sailback houndshark.

This could look like the following:

• Continuous bycatch recording in Astrolabe Bay
• Seasonal and spatial protection measures around the mouth of the Gogol River, such as closed seasons or protected zones
• Awareness-raising in local communities (low fin value; flesh sometimes given away; live bycatch should be released whenever possible)
• Targeted research on reproduction, growth, habitat use such as depth or temperature, or the genetic structure of the population

The goal is to become capable of acting early and to secure a potentially micro-endemic population—before fishing pressure increases further.

Rediscovered—now act

The rediscovery of the sailback houndshark is the result of consistent cooperation between local fishers, WWF teams, and research, and shows how community-based local surveys in poorly studied regions can reveal hidden populations. Now the focus must be on protecting the species.

For Papua New Guinea, Gogolia filewoodi could thus become an iconic indicator of sustainable use of the nearshore sea—provided that the data gaps are closed quickly and cooperative management with coastal communities is implemented.

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Sources

• Compagno, L. J. V. (1973). Gogolia filewoodi, a new genus and species of shark from New Guinea (Carcharhiniformes: Triakidae), with a redefinition of the family Triakidae and a key to triakid genera. Proceedings of the California Academy of Sciences, Series 4, 39: 383-410. https://biostor.org/reference/78225
• Sagumai, J., Samuel, R. H., White, W. T., & Grant, M. I. (2025). Rediscovery of one of the world’s rarest sharks, the sailback houndshark Gogolia filewoodi, in Papua New Guinea. Journal of Fish Biology. Advance online publication. https://doi.org/10.1111/jfb.70196