|Scientific Name:||Sphyrna tiburo|
|Species Authority:||(Linnaeus, 1758)|
Squalus tiburo Linnaeus, 1758
|Taxonomic Source(s):||Eschmeyer, W.N., Fricke, R. and Van der Laan, R. (eds). 2016. Catalog of Fishes: genera, species, references. Updated 1 July 2016. Available at: http://researcharchive.calacademy.org/research/ichthyology/catalog/fishcatmain.asp. (Accessed: 1 July 2016).|
|Red List Category & Criteria:||Least Concern ver 3.1|
|Assessor(s):||Cortés, E., Lowry, D., Bethea, D. & Lowe, C.G|
|Reviewer(s):||Vásquez, V.E. & Carlson, J.|
|Facilitator/Compiler(s):||Kyne, P.M., Ebert, D.A., Walls, R.H.L. & Dulvy, N.K.|
The Bonnethead Shark (Sphyrna tiburo) is a very abundant, small hammerhead that is found in shallow estuaries and bays on the Atlantic and Pacific Ocean coasts of the Americas as well as in the Gulf of Mexico. Despite pressure from both target and bycatch fisheries, this is an abundant species with some of the highest population growth rates calculated for sharks, making it much less susceptible to removals than most other species of sharks. Given its high rate of population increase and short generation length relative to other shark species, and the fact that it is considered not overfished and with overfishing not occurring in regions where stock assessments are available, this species is currently assessed as Least Concern.
|Previously published Red List assessments:|
This species occurs off the American continents only. In the western Atlantic Ocean it has been reported from southern Brazil to North Carolina, USA, and occasionally as far north as Rhode Island (Ebert et al. 2013). It is also common in the Gulf of Mexico and much of the Caribbean. In the eastern Pacific Ocean it is reported from southern California to Ecuador (Ebert et al. 2013).
Native:Aruba; Bahamas; Belize; Bermuda; Bonaire, Sint Eustatius and Saba; Brazil; Colombia; Costa Rica; Cuba; Curaçao; Ecuador; El Salvador; French Guiana; Guatemala; Guyana; Honduras; Mexico; Nicaragua; Panama; Peru; Suriname; Trinidad and Tobago; United States (Alabama, California, Connecticut, Delaware, Florida, Georgia, Louisiana, Maryland, Mississippi, New Jersey, New York, North Carolina, South Carolina, Texas, Virginia); Venezuela, Bolivarian Republic of
|FAO Marine Fishing Areas:|
Atlantic – western central; Atlantic – northwest; Atlantic – southwest; Pacific – eastern central; Pacific – southeast
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Regional estimates of abundance from stock assessment models are available for the United States (South Atlantic, Gulf of Mexico, and Caribbean) as defined by NOAA Fisheries. In the region, predicted 2011 abundance was ~4.9 million animals, which had remained relatively stable over the past ~25 years (SEDAR 2013). Predicted abundance and spawning stock fecundity show slight depletion from 1950 to 1972, followed by a decreasing trend through the late 1990s, and a progressive increase in the last decade (SEDAR 2013).|
At the time of this assessment Bonnethead Sharks in the Gulf of Mexico and western North Atlantic are not considered overfished, and overfishing is not occurring (SEDAR 2013, Frazier et al. 2013a). U.S. Atlantic and Gulf of Mexico recreational shark catch estimates from several surveys indicate that about 60,000 Bonnethead Sharks were caught annually from 1981-2011, ranging from a minimum of about 7,000 sharks in 1984 to a peak of about 131,000 sharks caught in 2001 (SEDAR 2013). Additionally, bycatch estimates from the shrimp trawl fishery operating in the Gulf of Mexico indicate that about 537,000 individuals were caught annually from 1972-2011 (SEDAR 2013).
United States Atlantic and Gulf of Mexico annual overall catch from 2000-2011 averaged >500,000 individuals (SEDAR 2013). Commercial landings of this species indicate that Bonnethead Shark accounted for over 50% of all landings of small coastal sharks in the southeastern USA in 1995, but was the least important small coastal species of shark represented in commercial landings from 1996-2011. The number of individuals landed commercially averaged about 29,000 sharks annually from 1995-1999, and ~14,000 sharks annually from 2000-2011 (SEDAR 2013).
|Current Population Trend:||Stable|
|Habitat and Ecology:||The Bonnethead Shark is an abundant, small coastal shark commonly found in shallow estuaries and bays over seagrass, mud and sandy bottoms at depths ranging from 10-80 m (Compagno 1984). Hueter and Manire (1994) determined this species was very abundant in shallow estuaries along Florida’s Gulf of Mexico coast during the summer months, moving to deeper water off the beaches in winter. More recently, Bonnethead Sharks have been shown to be one of the top three most abundant species in the Gulf of Mexico coastal areas from Mississippi Sound south to Anclote Key, Florida (Bethea et al. 2014) and northeast coastal Florida (despite longline gear bias, McCallister et al. 2013). This species shows geographic sexual segregation (Hueter and Manire 1994, Bethea et al. 2014). Froeschke et al. (2010), found this species from Sabine Lake at the Louisiana Texas border southwest to Lower Laguna Madre, Texas.|
Several factors such as water temperature (Ward-Paige et al. 2014), salinity (Ubeda et al. 2009, Froeschke et al. 2010, Bethea et al. 2014), depth (Froeschke et al. 2010, McCallister et al. 2013), distance to tidal inlet (Froeschke et al. 2010), and water clarity (Bethea et al. 2014) have been shown to have an important role in Bonnethead Shark movement, distribution, and abundance. The shallow sea grass habitat off Florida’s Gulf of Mexico coast are documented nursery grounds for this species, which probably utilizes similar habitats as nursery areas throughout its range (Hueter and Manire 1994, Bethea et al. 2014).
The Bonnethead Shark is a small coastal sphyrnid that reaches about 150 cm natural total length (TL; Ebert et al. 2013), though on the southeastern coast of North America (North Carolina to Florida) individuals are typically smaller (Frazier et al. 2014b). The life history of this species in the Gulf of Mexico has received considerable attention. In the eastern Gulf of Mexico, female Bonnethead Sharks seldom exceed 130 cm TL, whereas males rarely surpass 110 cm TL. Females generally mature between 80–95 cm TL (or 2-3 years of age) and males mature between 68-85 cm TL (two years of age) depending on geographic area. In the Gulf of Mexico, maximum observed ages are 7-8 years or more for females and 5-6 years or more for males, whereas theoretical longevities derived from von Bertalanffy growth curves range from 5-6 years for males and from 10-12 years for females (Lombardi-Carlson et al. 2003). Recent work off the southeastern coast of the United States has produced validated age estimates of 17.9 years for females and 16.0 years for males (Frazier et al. 2014b). Empirical data for populations of this species in the eastern Gulf of Mexico reveal a latitudinal increase in maximum size, size at maturity and offspring size (Lombardi-Carlson et al. 2003). Based on growth and age parameter variation between the Gulf of Mexico and western North Atlantic, as well as a demonstrated lack of movement between the two areas resulting in genetic differentiation (SEDAR 2013), it is likely these populations represent two distinct stocks. Providing further evidence to this, Escatel-Luna et al. (2015) found significant genetic variation between Bonnetheads from the Atlantic coast of Florida, the Gulf Coast of Florida and the southwestern Gulf of Mexico.
The Bonnethead Shark is a placental viviparous species that reproduces annually. The gestation period of this species is one of the shortest known in sharks, lasting ~4.5-5 months; litter size averages 9.7 in the Gulf of Mexico and 8.8 in the Atlantic Ocean off the southeast United States (SEDAR 2013). The timing of parturition also varies latitudinally, taking place in mid-to-late August in Florida Bay (southernmost location), early September in Tampa Bay (middle location) and mid-to-late September off north-west Florida (northernmost location; Lombardi-Carlson et al. 2003). Size at birth ranges from an average of 21.5 cm FL in Florida Bay to 29.7 cm FL in Tampa Bay (Lombardi-Carlson et al. 2003). Parsons (1993) and Manire et al. (1995) found that mating occurs in November and sperm is stored until ovulation/fertilization the following March or April. Ongoing tagging studies along the Gulf of Mexico coast of Florida indicate that individuals of this species are highly site-attached, with little evidence for long-distance migrations and mixing of populations (Heupel et al. 2006, SEDAR 2013).
Cortés and Parsons (1996) compared the demography of two populations off Florida’s west coast and found short generation times (4-5 years) and high population growth rates (1-28% per year). Demographic studies of this species by Cortés (2002) incorporating uncertainty in estimates of vital rates indicate that the Bonnethead Shark has very high rate of population growth (mean=1.304 yr-1; 95% confidence interval=1.150-1.165 yr-1) and short generation times (mean = 3.9 years, 95% CI=2.6-4.5 years). Annual survivorship values for Tampa Bay, Florida, were estimated to be 0.489 (95% confidence limits: 0.393-0.631) for 1-year-old females (Cortés and Parsons 1996).
|Generation Length (years):||3.9-4.55|
|Use and Trade:||This species is targeted for its meat.|
In the USA, Bonnethead Sharks are caught in commercial (gillnet and hook and line) and recreational fisheries and also as bycatch, especially in shrimp fisheries.
The Bonnethead Shark is also exploited in Mexico. In Mexican coastal waters, off the Gulf of Mexico, this is the second most important species in the artisanal fisheries accounting for 15% of the landings numerically (Castillo-Géniz et al. 1998). Targeted fisheries for this species have also been documented for Trinidad and Tobago (Shing 1999) and Ecuador (Martinez 1999). Bycatch in other fisheries, mainly from shrimp trawling, is probably also significant in other fishing nations within this species range.
Nursery areas for this species are located inshore and adults frequent inshore waters, making this species vulnerable to exploitation and human-induced habitat degradation. Results of ongoing work on the reproductive endocrinology of this species off Florida’s west coast show that high levels of organochlorine contaminants are present in tissues of sampled individuals; however, there have been no documented indications of resulting physiological impact (Gelsleichter et al. 2005).
In the USA, the Bonnethead Shark is classified as a small coastal species in the Federal Management Plan (FMP) for Sharks of the Atlantic Ocean, Gulf of Mexico and Caribbean, together with the Blacknose Shark (Carcarhinus acronotus), the Finetooth Shark (C. isodon), and the Atlantic Sharpnose (Rhizoprionodon terranovae; NMFS 2006). The Bonnethead Shark has been assessed individually since 2007 and the population in the northwest Atlantic Ocean was determined to be not overfished with no overfishing occurring (SEDAR 2013).
|Citation:||Cortés, E., Lowry, D., Bethea, D. & Lowe, C.G. 2016. Sphyrna tiburo. The IUCN Red List of Threatened Species 2016: e.T39387A2921446.Downloaded on 25 October 2016.|
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