cottonmouth jack
Uraspis secunda · Carangidae · predator
Dark open-sea jack that stays near islands, of sport interest. It usually lives alone or in small groups.
Also called: xaréu-boca-de-algodão, jurel boca algodón, cottonmouth jack
- maximum
- 50 cm
- record/max.
- 2.0 kg
- depth
- 2–15 m
the right time
to be on the water
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.
Reading the weather across 3 global models and 31 simulations…
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hour by hour
slide your finger or mouse over the chart to see each hoursee hour-by-hour table
why this index at —?
choose the day
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.
the fishing month at a glance
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.
everything about the cottonmouth jack
who is the cottonmouth jack
The cottonmouth jack belongs to the family Carangidae and reaches 50 cm and 2 kg. It occurs in warm waters worldwide, at the surface and down to 50 m, often near islands. Adults are pelagic but sometimes stay near the bottom. They live alone or in small schools. Juveniles have dark bands on the body. It has sport interest and little commercial use, which is why it turns up on the line of anglers fishing near islands.
Essential profile. Identification, where it occurs and rules, with data from FishBase and the cited regulations. Season, time of day, technique and bait are added once we have a good source for the cottonmouth jack.
fun facts
- Adults are dark and juveniles have bands, a clear difference between the ages.
identification
Dark adults, from dark gray to blue-black. Juveniles have six to seven dark bands on the body, with pale spaces between them. The popular names of the species (boca de algodón, boca blanca) refer to the white mouth. It lives in open sea, near islands, alone or in small groups.
where found
It occurs in warm waters worldwide. In Latin America, it appears from Brazil to Mexico and the Pacific, near islands.
Habitat: Warm oceanic waters, from 1 to 50 m, near islands.
coast
rules for the cottonmouth jack
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: Not on the Brazilian national list (Ministerial Ordinance GM/MMA No. 1.667/2026).
We found no species-specific rule beyond the region's general rules.
catch and release
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.
No danger to anglers. Hold it with care, because the dorsal fin has firm spines.
how much it weighs without taking it out of the water
Length-weight relationship W = a·Lb (a = 0.01318, b = 2.96; FishBase (relação peso-comprimento bayesiana, estimativa)). It's an average: a fat or lean fish can vary by 10% to 20%.
estimated weight
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sources and references
Essential profile: size, length-weight, depth, countries and conservation come from FishBase and the cited regulations, and the texts were written from those sources. Season, time of day, sensitivities, technique and baits and lures are not included yet, because we did not find a good source for this species.
- scientific FishBase: Uraspis secunda (ficha da espécie)Size, length-weight, depth, habitat, distribution, biology, and IUCN status. Page checked on Oct 13, 2026.
- scientific FishBase: nomes populares de Uraspis secundaNames by country and language.
- official Portaria GM/MMA nº 1.667, de 27 de abril de 2026: Lista Nacional Oficial de Espécies da Fauna Ameaçadas de Extinção (peixes e invertebrados aquáticos)The species is not on the list. Checked in the DOU of April 28, 2026.
where each number comes from
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.
sources for this lookup
how accurate the forecast is
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: