One of the smallest hammerheads, with a semicircular head like a paddle, living in shallow water and mangroves and eating crabs. Endangered worldwide (IUCN); on Brazil's list, Critically Endangered, with catch prohibited.
Also called: cação-martelo-de-aba-curta, tubarão-panã
The bonnethead ("cação-martelo-de-aba-curta" in Portuguese) is one of the smallest hammerheads: it reaches 150 cm and 10.8 kg. The front of the head is a semicircle, without the elongated hammer of its relatives. It lives on shelves, bays, estuaries, mangroves and reefs, over mud and sand bottoms, often in shallow water. At night it looks for invertebrates in shallow seagrass beds, and by day it moves to deeper water. It eats mostly crabs and other crustaceans, also mollusks and small fish, and it was the first shark shown to digest seagrass. It lives in small groups, and the female has 6 to 9 pups. It is harmless to people (FishBase). IUCN classifies it as Endangered (2019), and the Brazilian list as Critically Endangered.
fun facts
It was the first shark shown to digest seagrass, which makes it omnivorous (FishBase).
Males and females separate for much of the time, and the species always lives in small groups (FishBase).
The bonnetheads of southeastern Brazil are a cryptic species and were considered collapsed in the 2000s (Gonzalez et al., 2021).
how to recognize it
identification
The front of the head is a semicircle, like a paddle or a bonnet, without the elongated points of other hammerheads: according to FishBase, no other hammerhead has a semicircular head front. Slim and small body: common length up to 80 cm and maximum of 150 cm (FishBase). In Latin America, "cabeza de pala" and "pala" also name the scoophead (S. media), which has a similar head. FishBase treats the species as a complex with S. alleni (from Belize to Brazil) and S. vespertina (eastern Pacific). When in doubt, release it.
how bonnethead fishing looks
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Each card shows the day's index (0 to 100) and, below it, a strip with the index for each hour, from 0h to 23h. from poor to excellent.
Western Atlantic, from North Carolina (USA) to Belize, according to FishBase, including the Gulf of Mexico and the Caribbean. In FishBase, its sister species S. alleni runs from Belize to Brazil, and S. vespertina lives in the eastern Pacific. The Brazilian national list uses the name S. tiburo, and a 2021 study treats the bonnetheads of southeastern Brazil as a cryptic species (S. aff. tiburo).
Habitat: Continental and island shelves, bays, estuaries, mangroves and reefs, over mud and sand. At night in shallow seagrass beds, by day in deeper water.
calendar and clock
when to fish
best season
time of year
JanFebSeaAprMayJunJulAugSepOctNovDec
Estimate: no known season for Latin America. FishBase gives no seasonality. Catch is banned year-round in Brazil.
best time of day
Nighttime. Spends the night in shallow seagrass beds hunting invertebrates active at night, and by day moves to deeper water; it has a daily activity rhythm (FishBase).
weather, water and behavior
what affects the bonnethead
sensitivity The little bars show how much each factor affects this species. Five full: it feels it a lot.
cold and cold fronts
Subtropical species; cold water keeps it away from shallow areas. Effect poorly measured.
atmospheric pressure
Not well known.
moon
Not well known.
rain
Not very relevant.
water level
Not applicable at sea; it uses shallow bays, estuaries and mangroves.
noise
Not well known.
wind
Rough seas prevent surf fishing and fishing from small boats.
tide
It enters seagrass beds and shallow bays; the rising tide brings the animal into shallow water (estimate).
depth
From 10 to 80 m (FishBase); at night in shallow seagrass beds, by day in deeper water.
technique, gear and bait
how to fish
rod
Catch banned in Brazil; in Mexico, the quota is one shark per day, and releasing it is best.
spinning / baitcasting reel
Not applicable.
line
Not applicable.
leader
Not applicable.
hook
When fishing from shore or a boat, prefer a barbless circle hook (or one with the barb flattened): it makes releasing what cannot be kept easier.
accessories
cutting pliers
long-handled hook remover
tip from an angler
If a hammerhead is hooked by chance, don't bring it out of the water: cut the line close to the mouth or remove the hook with pliers, release it right away and don't waste time on photos.
what the law says
rules for the bonnethead
Summary of the regulations we found, with the source for each. Rules change; before keeping or transporting fish, check with the state environmental agency. Conservation: Global: Endangered (EN, A2bcd), assessed on Jul 2, 2019 (IUCN, via FishBase). It is on the Brazilian national list (Portaria GM/MMA nº 1.667/2026) as Critically Endangered (CR), with catch banned in Brazil. ICCAT excludes S. tiburo from the ban on retaining hammerheads (Rec. 10-08), but that does not apply to Brazil.
Brazil: bonnethead on the national list (CR), catch prohibited
full protection
The national list (Portaria GM/MMA nº 1.667/2026, item 331 of Annex I) classifies Sphyrna tiburo (cação-martelo-de-aba-curta) as Critically Endangered (CR). Under Portaria GM/MMA nº 1.666/2026 (art. 3), VU, EN and CR species have full protection: catch, transport, storage, processing and trade are banned. If you hook one by accident, release it right away, with minimal handling (art. 3, § 4). This entry covers the bonnethead outside Brazil; FishBase does not record it in the country, but the Brazilian list uses the name S. tiburo and southeastern bonnetheads are treated as S. aff. tiburo, so when in doubt, the ban applies. Because the species was already among the bans in Portaria MMA 445/2014 (SEMIL-SP note, 2016), the rule is probably not new; we did not check the earlier list.
1 specimen per angler per day (counts as 5 against the quota of 10)
In recreational sport fishing in Mexican marine waters, the shark limit is one specimen per angler per day, which counts as five toward the total limit of ten fish (no more than five of the same species). Specimens beyond the quota may only be released alive, in good survival condition (catch and release), and sport-caught fish may not be sold. Sport fishing is also not allowed in closed zones and seasons or in protected natural areas without the proper permits. The bonnethead is Endangered worldwide: prefer to release it.
Mexico: NOM-029-PESC-2006 regulates commercial shark and ray fishing
NOM-029 is the rule for shark and ray fishing at commercial scale: it applies to holders of permits for directed fishing of these animals and to those who catch them by chance (section 1.2), and covers commercial fishing vessels (section 4.2.1); sport fishing has its own rule, NOM-017. It prohibits keeping only the fins of sharks (section 4.2.1) and provides closed seasons and closed zones, set by notice in the DOF, for directed fishing (sections 4.2.3 and 4.3.4: no directed fishing during closed seasons, within 5 km of coral reefs, in front of river mouths and lagoons, in front of turtle nesting beaches, and near sea lion colonies). The species is listed in Normative Appendix A (Sphyrna tiburo vespertina in the Pacific, Sphyrna tiburo tiburo in the Gulf of Mexico and the Caribbean Sea).
Mexico: annual closed seasons for sharks and rays (check the dates for the year)
confirm with the agency
NOM-017 (item 4.10 a) prohibits recreational fishing in closed zones and seasons, and NOM-029 (item 4.2.3) requires the authority to set closed seasons for sharks and rays by notice in the DOF; the dates change and vary by coast. On Aug 1, 2025, the Secretaría de Agricultura and Conapesca announced, for the Pacific coast, the use of sharks and rays from August 1 to April 30 (May to July are excluded, our interpretation from the announcement) and, in Tabasco, Campeche, and Yucatán, a closed season from August 1 to 29. We did not find the official notice in force in 2026: confirm the dates with Conapesca before fishing.
Bahamas: sharks protected since 2011, release them all
shark fishing not permitted; a shark hooked must be released unharmedconfirm with the agency
The official fishing guide of the Bahamas states that shark fishing is not allowed, that sharks have been protected since a 2011 amendment, that they may only be taken under special permits for very specific purposes, and that a shark hooked in any fishing must be released unharmed. The page does not cite the number of the rule.
catch and release Releasing the fish alive, quickly and with a wet hand. During a closed season it isn't always allowed: what the regulation says applies.
Small and not much of a fighter, but fragile: release it quickly, in the water, holding it by the body and without touching the gills. In Brazil, catch is prohibited.
in the kitchen
In Brazil, catch and trade are banned. FishBase records human consumption and use in fishmeal, but the species is Endangered: prefer to release it.
calculator
how much it weighs without taking it out of the water
Length-weight relationship W = a·Lb (a = 0.00204, b = 3.1; FishBase (relação peso-comprimento bayesiana, estimativa da própria espécie)). It's an average: a fat or lean fish can vary by 10% to 20%.
estimated weight
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sources and references
The seasonal weights (months), the time of day, the sensitivities (cold, pressure, moon, wind, rain, tide, strong light, murky water and noise), the water temperature range and the common size range are the app's editorial estimates, supported by FishBase and by the literature cited below, with no measurements of our own for this species. The months show when an angler may find the species near the coast, not a catch season. They are not official data and may vary by region and year. Legal rules appear in the rules section, with the norm and a link.
officialPortaria GM/MMA nº 1.666, de 27 de abril de 2026: regras e restrições para as espécies ameaçadas da lista nacionalArt. 3: full protection for EW, CR, EN, and VU species (catching, transporting, storing, holding, handling, processing, and trading are banned); § 4: the restriction does not apply to incidental catch when the animal is released alive; art. 12: for species added to the list by a new ordinance, the art. 3 bans start 180 days after publication. Text checked in the DOU on Oct 13, 2026.
officialSEMIL-SP: Portaria MMA sobre espécies aquáticas ameaçadas volta a vigorar (15/08/2016)Note from the São Paulo Environment Secretariat on Portaria MMA 445/2014 (of Dec 17, 2014, later revoked by Portaria GM/MMA 1.667/2026): it lists the hammerhead sharks (Sphyrna lewini, media, mokarran, tiburo, tudes and zygaena) among species whose catch is prohibited.
officialMéxico: NOM-029-PESC-2006, pesca responsável de tubarões e raias (DOF de 14/02/2007)Copy of the text published in the DOF, on the standardization platform of the Secretaría de Economía. Items 1.2, 4.2.1, 4.2.3, and 4.3.4 and Normative Appendix A checked on Oct 13, 2026. The standard was written for commercial fishing; recreational fishing has its own standard, NOM-017.
