The smooth hammerhead (Sphyrna zygaena) is listed by the IUCN on its Red List of Threatened Species as Vulnerable as its population worldwide may drastically decline unless efforts are put in place to secure its survival. Sphyrna zygaena is a large-bodied and highly mobile hammerhead shark with active and strong swimming capacities. The maximum reported size of the species is 4.20m but usually ranges between 2.5m to 3m. It is found in temperate and tropical waters, and according to Clarke et al. (2015), this is the most oceanic of all hammerhead sharks, as well as the most temperature tolerant species. It is most common in waters of 16–22°C, but has also been reported in cooler waters of 13–19°C off South Africa (Diemer et al., 2011). This species is reported to be migratory although no group migration has been recorded (Miller, 2016). Santos & Coelho (2018) recorded the longest migration ever documented for this species (> 6600 km) across hemispheres. This study and previous ones have shown this species crosses international borders and carries out inshore and offshore migrations. There is also evidence of north-south movements, which may be seasonal migrations.
It is estimated that S. zygaena individuals reach sexual maturity at 9 years old (Cortés et al., 2015), and have a gestation period of 10-11 months. It is viviparous, as such it gives birth to live young. The longevity is uncertain but the species has been aged to at least 18 years for males and 21 years for females (Coelho et al., 2011). Like many large-bodied shark species, S. zygaena is among the top predators in the marine food web (Cortés, 1999). The species feeds on a large variety of teleosts (i.e. bony fish), elasmobranchs, crustaceans and cephalopod species (Smale and Cliff, 1998; Cortés, 1999).
Smooth hammerhead sharks are taken as direct catch or incidental catch in domestic and artisanal fisheries, as well as industrial pelagic fisheries on the high seas. The majority of catches are from longline and gillnet fisheries, with sporadic catches reported in purse seine fisheries. The meat quality is deemed low buts its high fins are of high value due to their large size and high fin-ray count (Rose, 1996). In an analysis of the trade through the Hong Kong fin market, Clarke et al. (2006a) estimated that 4–5% of all fins traded were from S. zygaena or S. lewini each year. This would account for an estimate of 49 000 and 90 000 tons of smooth hammerhead shark taken each year which would amount to between 1.3 and 2.7 million individual animals (Clarke et al. 2006b).
Habitat degradation and pollution affect coastal ecosystems that juvenile S. zygaena sharks occupy during early life stages. However, the effects of these changes and their ultimate impact on populations of S. zygaena are currently unknown.
Reduction of threats
Reducing bycatch mortality for hammerhead sharks is hampered by the high mortality rates for these sharks after being caught in fishing gears. A study by Coelho et al. (2012) found an at vessel mortality of 71% in longline fisheries, and post-release mortality would increase this number further. Effective management for this species should therefore focus on avoiding unintended capture. However, it is evident that a lack of species-specific data collection is hampering management for this species. Thus, the priority would be to gather more data on the species for improved conservation efforts.
|CMS Instruments||Sharks (2018)|
|Countries||Albania, Algeria, Argentina, Australia, Bahrain, Brazil, Canada, Chile, China, Croatia, Cyprus, Democratic People's Republic of Korea, Egypt, France, Greece, Iceland, India, Iran, Iraq, Ireland, Israel, Italy, Japan, Kuwait, Lebanon, Libya, Madagascar, Mexico, Montenegro, Morocco, Mozambique, Namibia, New Zealand, Oman, Pakistan, Peru, Portugal, Qatar, Republic of Korea, Russian Federation, Saudi Arabia, Slovenia, South Africa, Spain, Syrian Arab Republic, Tunisia, Turkey, United Arab Emirates, United Kingdom, United States of America, Uruguay|
No pictures for Sphyrna zygaena
|English||Smooth hammerhead shark|
|French||Requin marteau commun|
|Spanish||Tiburón martillo liso|
|Formerly listed as||Sphyrna zygaena|
|Scientific name||Sphyrna zygaena|