The hammerhead with a notch in the middle of its head. Critically Endangered in Brazil since 2014: catch prohibited. Pups show up in shallow water in the South and Southeast and get caught on beach lines.
Also called: tubarão-martelo-recortado, tubarão-martelo, cação-martelo, cação-martelo-entalhado, cambeva, cambeba, cornudo, rudela
Choose the place and the species. The index, from 0 to 100, combines weather, sun, moon and tide with each fish's habits. Up to 28 days, with each day's confidence.
location
Sample location: choose yours to see the forecast for where you fish.
period
Reading the weather across 3 global models and 31 simulations…
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index Score from 0 to 100 for the fishing conditions of each hour. It reads weather, sun, moon, tide and the species' habits. It doesn't promise fish: it tells you when the water is on your side. 0–24 poor · 25–44 fair · 45–64 good · 65–84 very good · 85–100 excellent.
today
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confidence —
confidence How much you can trust the weather forecast for the day. It drops with distance and when the models disagree. It is not the chance of catching fish.
models and trend Up to 16 days, three global weather models (the European ECMWF, the American GFS and a high-resolution blend) read hour by hour; when they disagree, the light band on the chart widens. Beyond that it's a trend: 31 runs of the American GEFS model. Confirm when it's 1 week out.
window Consecutive hours with the index near the day's peak and no danger alert. It is the time to have the bait in the water.
hour by hour
slide your finger or mouse over the chart to see each hour
see hour-by-hour table
why this index at —?
next 7 days
choose the day
chart: bar height = day's index · line = variation between models · striped = trend · fainter = less confidence
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.
4-week calendar
the fishing month at a glance
plan a trip
what's the best window for the crew?
Choose how many fishing days. We compare each stretch by its average index, discount days with a warning or closed season, and show the 3 best.
trend for the coming weeks
Line: the middle value of 31 simulations of the American GEFS model. Band: where 8 out of 10 fall. Narrow, firm trend; wide, high uncertainty.
the species
everything about the scalloped hammerhead
overview
who is the scalloped hammerhead
The scalloped hammerhead lives in warm seas worldwide. Adults form schools by day around islands and seamounts, then spread out at night to hunt fish and squid. Females give birth in shallow bays and beaches, and pups stay near the coast for their first months, where they are heavily caught in gillnets and beach lines. In Brazil it occurs along the whole coast. Fishing has reduced its populations so much that it is Critically Endangered in Brazil and worldwide, and it is listed in CITES Appendix II. Hammerheads are especially sensitive to capture stress: many die after release if the fight is long. For anglers, the job is to recognize it and release it right away.
fun facts
The hammerhead spreads its eyes and nostrils apart and enlarges its area of electrosensors, which help it find buried prey.
Adults form schools of hundreds of animals around islands and seamounts, a spectacle for divers.
In a study of five species, the great hammerhead, a close relative, built up the most lactic acid during the fight.
how to recognize it
identification
A flat, wide head shaped like a hammer, with the eyes at the tips. The front edge of the hammer is arched and has a notch in the middle, plus two smaller notches at the sides. Dark tips on the underside of the pectoral fins. The smooth hammerhead (S. zygaena) lacks the central notch; the great hammerhead (S. mokarran) has a nearly straight hammer and a very tall, sickle-shaped first dorsal fin. All are protected in Brazil.
The entire Brazilian coast. Pups in beaches, bays and shallow estuaries, with frequent records in the South and Southeast; adults on the continental shelf, around oceanic islands and seamounts. In the western Atlantic it ranges from the United States to Uruguay; in the Pacific, from California to Ecuador, probably as far as Peru.
Habitat: Pups in shallow beaches, bays and estuaries; adults on the shelf, around islands, shoals and seamounts.
coast
North CoastNortheast CoastSoutheast CoastSouth Coastcoastalshelfoceanic
states
Amapá, Pará, Maranhão, Piauí, Ceará, Rio Grande do Norte, Paraíba, Pernambuco, Alagoas, Sergipe, Bahia, Espírito Santo, Rio de Janeiro, São Paulo, Paraná, Santa Catarina, Rio Grande do Sul
calendar and clock
when to fish
best season
time of yearbest: Nov–Feb
JanFebSeaAprMayJunJulAugSepOctNovDec
Estimate: in the South and Southeast, newborn pups appear in shallow water in spring and summer. Biological information: catch is prohibited year-round.
best time of day
Night and twilight. Adults form schools by day and hunt at night; pups stay in shallow water all day.
weather, water and behavior
what affects the scalloped hammerhead
sensitivity The little bars show how much each factor affects this species. Five full: it feels it a lot.
cold and cold fronts
A warm-water species; cold water keeps pups out of the shallows.
atmospheric pressure
Not very relevant.
moon
Not well known.
rain
Not very relevant.
water level
Pups use shallow bays and estuaries as nursery grounds.
noise
Adults in schools move away from noisy boats and divers.
wind
Not very relevant.
tide
Pups follow the tide in bays and at estuary mouths.
depth
Pups live from 0 to 25 m; adults descend to hundreds of meters.
technique, gear and bait
how to fish
rod
Catch prohibited in Brazil.
spinning / baitcasting reel
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line
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leader
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hook
For any beach or boat fishing, prefer a barbless circle hook: it makes it easy to release what can't be kept.
accessories
cutting pliers
long hook remover
tip from an angler
If a hammerhead is hooked by accident, don't lift it out of the water: cut the line close to the mouth or remove the hook with pliers, release it immediately, and don't waste time on photos. In Argentina, where catch and release is allowed, the same applies: hammerheads die easily after a long fight.
what the law says
rules for the scalloped hammerhead
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: Catch prohibited throughout Brazil. Global: Critically Endangered (IUCN, November 8, 2018). Listed in CITES Appendix II. ICCAT prohibits retaining hammerheads in tuna fisheries (Rec. 10-08).
Threatened species (CR): catch prohibited in Brazil
catching, transport, holding and trade prohibited
The scalloped hammerhead (Sphyrna lewini) is on the national list as Critically Endangered (CR) (it was already on the previous list, Portaria MMA 148/2022). Ministerial Ordinance GM/MMA 1.666/2026 (art. 3) prohibits catch, transport, storage, possession, processing and trade throughout Brazil. Anyone who hooks one by chance must release it alive immediately (art. 3, § 4). The rule does not authorize targeted fishing, even with release: in Brazil, do not seek this species.
Besides the scalloped, the national list includes as Critically Endangered the smooth hammerhead (S. zygaena), the great hammerhead (S. mokarran), S. gilberti, S. media, S. tiburo and S. tudes. Any hammerhead hooked in Brazil must be released alive immediately. The old 60 cm minimum size in IN MMA 53/2005 does not authorize capture.
Finning prohibited: shark only whole, with its fins
fins naturally attached to the body
In Brazil, finning is prohibited (cutting off the fins and discarding the body). Every shark or ray landed must arrive with its fins attached to the body; it is prohibited to carry on board an animal without fins or with loose fins, and to transfer sharks between vessels. It applies to any shark that may be kept.
Buenos Aires (AR): mandatory release of large coastal sharks
mandatory release; killing prohibited
On the Buenos Aires Province coast (and in the Plata, Bahía Blanca and Mar Chiquita estuaries), escalandrún, bacota, gatopardo, cazón and hammerheads are "reserved directed fishing": release is mandatory, and killing is prohibited even for incidental catch. Gear rules: one rod per angler on a boat and two from shore; single-hook rigs only (tandem rigs prohibited); circle or biodegradable hook 12/0 to 14/0 with the barb flattened; a stopper float 25 cm above the hook is recommended on bottom lines, along with nylon line of at least 0.70 mm. Gaffs are prohibited. Remove the hook only if there is no risk; otherwise cut the line close to the hook, avoiding lifting the shark out of the water.
1 specimen per angler per day (counts as 5 against the quota of 10)
In recreational sport fishing in Mexican saltwaters, the limit for sharks is one specimen per angler per day, which counts as five toward the total limit of ten fish. Fish caught in sport fishing may not be sold. Catch and release does not count toward the limit: prefer releasing.
commercial or sport extraction not permittedconfirm with the agency
In 2021 Colombia stopped considering sharks and marine rays a fishery resource and began treating them as a hydrobiological resource; the recitals of Decree 281/2021 state that they may not be extracted for commercial or sport purposes, and the decree created an environmental protection plan. Later AUNAP rules dealt with incidental catch in artisanal fishing; we did not check the consolidated text. When in doubt, release it into the water.
North CoastNortheast CoastSoutheast CoastSouth Coast
Many sharks and rays are on the national list (CR, EN or VU), with catching, keeping and transport prohibited, including those listed here. Species added to the list only in 2026 follow the 180-day deadline (until about Oct 25, 2026). If unsure of the species, release it.
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.
This is not catch and release: it is release of incidental catch. Hammerheads are among the sharks most sensitive to stress: end the fight as quickly as possible, leave the animal in the water, cut the line close to the mouth, and don't hold it for a photo.
in the kitchen
Catch and trade prohibited. Don't buy "cação" of unknown origin: DNA studies found threatened species sold under that name in southern Brazil.
calculator
how much it weighs without taking it out of the water
Length-weight relationship W = a·Lb (a = 0.00347, b = 3.1; FishBase (estimativa bayesiana para a espécie, comprimento total)). 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), time of day and sensitivities (cold, pressure, moon, wind, rain, tide, strong light, murky water and noise) are the app's editorial estimates, based on the literature below and on field experience of anglers and guides. The months indicate the time of year when the angler usually finds the species near the coast, not a catch season. They are not official data or measurements made for this species and may vary by region and year. Legal rules appear in the rules section, with the regulation and link.
officialPortaria GM/MMA nº 1.666, de 27 de abril de 2026 — regras de proteção das espécies ameaçadas da lista nacionalArt. 3: full protection for VU, EN and CR species; § 4: incidental catch with immediate release of the live animal. The 180-day transition rule for species newly added to the list was verified from official summaries (Fiperj) and technical sources; the DOU (Brazil's Official Gazette) page did not open during verification.
The weather comes from three independent global models, cross-checked hour by hour: when they agree, confidence goes up; when they diverge, the band between them shows on the chart. Beyond 16 days, we use the GEFS ensemble of 31 simulations: if 20 of the 31 predict rain, the chance of rain is 65%. Sun and moon are calculated astronomically, with no uncertainty.
The index adds up, weighted for each species: time of day (species curve anchored to real sunrise and sunset), moon (transits, rise and set, phase), pressure (3 h trend and 24 h swing), water temperature (in rivers, estimated from air temperature; at sea, estimated by an ocean model), wind, rain, clouds, tide and the month in the species' cycle.
Accuracy measured in the reference project (4 regions, 93 days, forecast vs. observed): maximum temperature is off by 0.6 °C on average the next day and 1.7 °C at 7 days; rain of 5 mm or more is detected 76% of the time the next day and 57% at 7 days. Detection isn't everything: the false alarm rate isn't published here yet, and 93 days in 4 regions is still a small sample. We now also measure every day, at the app's destinations:
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Your location is saved only on this device and feeds the forecast, the map and the "today" on the home page.
