Straight-tooth weasel shark

About the Straight-tooth weasel shark

The Straight-tooth Weasel shark is a weasel shark of the family Hemigaleidae, found in the tropical western Pacific Ocean. It can reach a length of 88 cm/2.89 ft.

Biology and description:

The Straight-tooth Weasel shark reaches about 92 cm/3 ft in length, is viviparous and gives birth to litters of two pups, but little else is known of its biology. This species is of grey or brown above colour and light below. No prominent marking on body and fins.

Habitat:

This is an inshore species but its depth range has not been reported. Its distribution ranges from Japan to Viet Nam, including Hong Kong and Taiwan. Thi is a demersal species and occurs mainly in tropical waters.

Conservation:

Taken as bycatch in fisheries throughout much of its range, including Hong Kong, Taiwan, Province of China, and Japan. It is retained and utilised for its meat and fins, but no data is available. There are no known conservation measures within the range of this species.

The species is a bycatch of a range of artisanal and industrial gears including demersal trawl, longline, and gillnet and is retained for human consumption and fish meal. There are no species-specific time series. Landings data of all sharks combined from the Taiwan Exclusive Economic Zone (EEZ) and reconstructed catches of all sharks, skates and rays from the Japan, China, and Viet Nam EEZs infer declines of 26–96% over the past three generation lengths (26 years). These levels of declines are not species-specific but are informative for understanding the broader levels of decline in sharks in the region. Fishing pressure is very high across the entire spatial and depth range of the Straight-tooth Weasel Shark. Its restricted inshore distribution means it has no refuge from intense fishing pressure and is possibly now extinct in Taiwan. The inshore trawl bans in Taiwan and China waters may afford the species some refuge from fishing pressure. The inferred relatively short generation length may provide it some resilience to fishing pressure. Dramatic levels of habitat loss in the region are likely a threat to this species. It is suspected that the Straight-tooth Weasel Shark has undergone a population reduction of 50–79% over the last three generation lengths (26 years) due to levels of exploitation, and it is assessed as Endangered A2d.

No specific measures are in place. In China, since the late 1990s, regulations have specified varying annual seasonal fishing closures on commercial demersal trawling in the East China Sea, and in the South China Sea to 12⁰N (Yu and Yu 2008). The closure times have varied over the years and between regions, but most now commence in May and are in place for 3–4 months. In 2018, this seasonal closure was widened to also include all other commercial fishing gears (e.g. gillnet and longline) with the only exception being for rod and reel to allow small-scale artisanal fisheries and recreational fisheries (Zhang unpubl. data 2019). Since 2017, enforcement of the seasonal closure has strengthened (Chen unpubl. data 2019). The effectiveness of the closures is debatable as overfishing remains a threat (Yu and Yu 2008, Pauly and Liang 2019). Some of the species range may be protected along the China coastline as it is estimated that ~20% of the coastline is included in Protected Areas (MacKinnon et al. 2012).

In Taiwan, there is a prohibition on using any net fishing gear (e.g. trawls, seine nets) in 68 reef areas (Fisheries Agency 2019). Since 1999, all demersal trawling is prohibited within 3 nautical miles (nm) of the coast and within 12 nm for trawlers larger than 50 Gross Registered Tonnage (Fisheries Agency 2019, Liao et al. 2019). Since the mid–2000s, gillnets have been banned within 3 nm in parts of five counties with a policy of gradual removal of gillnets from within 3 nm of the entire coast and government assistance to transition to line and troll fishing (Fisheries Agency 2019, Liao et al. 2019). Since 2005, shark fins must be naturally attached on vessels that use ice to preserve the catch (Fisheries Agency 2019, Liao et al. 2019). This species may be protected in some of the ~32 Protected Areas which cover ~38% of the Taiwan coastline and ~47% of Taiwan territorial seas, with no-entry and no-take areas accounting for 0.9% and 4.6% of the territorial seas, respectively (MacKinnon et al. 2012, Fisheries Agency 2019, Liao et al. 2019).

In Japan, management measures have been implemented since the mid-1990s to control fishing effort that include total allowable catches, seasonal closures, and gear restrictions (White Paper 2015). In Viet Nam, there is a prohibition on destructive fishing practices, and some fisheries regulations, however, enforcement and compliance is limited (Teh et al. 2014). There are at least three Marine Protected Areas (Hon Mun, Cu Lao Cham, and Con Dao) with an aim to preserve 2% of the marine area (FAO 2020). In Thailand, all commercial fishing vessels greater than 10 gross t are prohibited to fish within three nautical miles from the shore (DoF 2015). Further research is needed on population size and trends, life history, and catch levels should be monitored.

To conserve the population and to permit recovery, a suite of measures will be required which may include species protection, spatial management, bycatch mitigation, and harvest and trade management measures (including international trade measures). Effective enforcement of measures will require ongoing training and capacity-building (including in the area of species identification). Catch monitoring is needed to help understand population trends and inform management.

 

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