Grouper: water temperature and season

Ledges and wrecks. Flat seas, hold the bottom. Anglrithm scores grouper at reef and offshore spots, on the Atlantic, in the Keys and on the southwest Gulf coast. This page sets out what that score weighs and the cited studies behind it.

Water temperature

Evidence tier Well established

No tagging study gives a surface temperature band for grouper. The score uses a working range of 66-80 °F, a fishing opinion rather than a tagged band, and its credit falls away above that range as well as below it.

Season

Best May to Nov, by the score's season weight.

When they spawn

Spawning months on record: Feb and Mar. A calendar from the studies linked, months and moon only, never a site; not a catch forecast.

Black grouper spawn in late winter, most in February and March, from the full moon to a few days after the new moon (studied off Belize). Paz & Sedberry 2008 (outside South Florida)

The score's season weight by month, from the studies cited in the species profile; the outlined months are at 90% of its peak or better.

What the score weighs

SeasonWell establishedkeeps 100%
CurrentSmall real effectkeeps 50%
SeasSmall real effectkeeps 50%
WindSmall real effectkeeps 50%
TideReal, but localkeeps 100%
Water tempWell establishedkeeps 100%

Why each tier

Season: Season is the strongest single predictor in most recreational datasets, because it carries water temperature, migration and spawning together. Shaw et al. 2021, PLOS ONE 16:e0257882.
Current: No study we found ties a current speed or direction to catch for any fish in this app. Current decides whether you can hold a bait where you want it and how a drift sets up: off Southeast Florida the Gulf Stream runs fast close to the coast, and deep-drop boats stay under power to hold position. Treat a current pattern as a fact about your fishing more than about the fish. Davis, Cudney & Blankinship 2017, Bulletin of Marine Science 93:539-555. Lerner et al. 2013, Transactions of the American Fisheries Society 142:95-104.
Seas: Sea state mostly decides whether the trip happens and whether you can fish it well. Treat a sea-state pattern in your own log as a fact about your fishing, not about the fish. No direct angling-scale study found; labelled from mechanism.
Wind: Wind has a measurable effect on fish movement, apparently through dissolved oxygen, but it is small. The larger effect in any personal log is on you: wind decides where you can fish and whether you go at all, so a wind pattern in your own data is at least as likely to be about your choices as about the fish. Milardi et al. 2019, Aquatic Ecology 53:251-263. Shaw et al. 2021, PLOS ONE 16:e0257882.
Tide: Tide moves fish through cuts and over structure, and the effect can be strong at a particular spot. It is not a species-wide rule: the published work finds the pattern flips by species, site and season, and one high-velocity channel study found no link to current speed at all. Trust it where you fish; do not trust it as a fact about the fish. Becker et al. 2016, Estuaries and Coasts 39:1199. Milardi et al. 2018, ECSS. Viehman & Zydlewski 2017, PLOS ONE 12:e0176405.
Water temp: Fish are ectotherms, so appetite and digestion track water temperature along a dome: rising to an optimum, then falling away again. Warmer is not simply better. Snook energy demand roughly tripled from 15 to 25 C, and they were more likely to have empty stomachs when the water ran hot. Volkoff & Ronnestad 2020, Temperature 7:307-320. White et al. 2025, Marine and Coastal Fisheries 17:vtaf031, doi:10.1093/mcfafs/vtaf031.

Each factor's weight is multiplied by its evidence tier: well established and real but local keep all of it, a small real effect keeps half, and a popular belief that is not supported keeps a fifth. Guidance from the studies sits beside the score, never in it.

Rules and depth

Shallow-water grouper (gag, black, red and others) are closed Jan 1 to Apr 30 in Atlantic and all Keys state waters, and you may not fish for them in Atlantic federal waters then. 3 grouper per person, only 1 gag or black; from Oct 28, 2026 no more than 2 gag or black per boat in federal waters. Gag and black 24 in, red 20 in. No Nassau or goliath. Carry a descending device. Check FWC before you keep one.

Red grouper live on shallow reefs as juveniles (10 to 59 ft) and move deeper than about 118 ft as they mature. Kilfoyle et al. 2017

Seasons, sizes and bag limits change: check the FWC saltwater regulations before you keep a fish.

From the research programs

Gag spawn mainly January through April, peaking February and March, on shelf-edge reefs deeper than about 131 ft. GCOOS, no date (Gulf of America, outside South Florida)
Female gag migrate offshore to spawn while males tend to stay near aggregation sites year-round. GCOOS, no date (Gulf of America, outside South Florida)
Young gag grow up in estuaries and seagrass beds before moving to reefs. GCOOS, no date (Gulf of America, outside South Florida)
Gag start life as females; spawning groups pair one male with several females. GCOOS, no date (Gulf of America, outside South Florida)
Deep-caught grouper suffer barotrauma; Florida Sea Grant promotes descending devices to send them back down. University of Florida, no date
In the Gulf of America, black grouper spawn from December through April, with the peak spawning season January to March. GCOOS, no date (Gulf of America, outside South Florida)
Aggregations form around the full moon on shelf-edge reef points, with spawning roughly 10 to 12 days later near sunset. GCOOS, no date (Gulf of America, outside South Florida)
Juvenile black grouper use mangroves; adults live on rocky and coral reefs. GCOOS, no date (Gulf of America, outside South Florida)

Findings in our own words from the programs linked, area and season only; cited, not endorsed. None of these lines is in the score.

The studies

Southeast Florida reefs hold fewer species and fewer young target fish than protected reference reefs; adult target fish are scarce in the Keys too.
SE Florida; Florida Keys; Dry Tortugas · field · full text read
Grove et al. 2024
Severe red tides knock down shelf fish biomass and catch, with 2005 the worst year; young gag take the heaviest hit.
West Florida Shelf · model · full text read
Vilas et al. 2023
Female gag stack up in shallow water in early winter before moving deep to spawn February to mid-April; males are scarce.
eastern Gulf of Mexico (West Florida Shelf) (outside South Florida) · field · full text read
Lowerre-Barbieri et al. 2020
Black grouper courtship peaks about a week to ten days after the full moon, in late afternoon, during winter and spring.
Florida Keys; Puerto Rico (out of region) (outside South Florida) · field · full text read
Sanchez et al. 2017
Red grouper and scamp are the main game fish on the Pulley Ridge mesophotic reef at about 60-105 m.
Pulley Ridge, SW Florida shelf (Gulf) · field · full text read
Harter et al. 2017
Solution holes with a red grouper held more juvenile reef fish, and a grouper offset the losses a lionfish caused.
Florida Bay · experiment · full text read
Ellis & Faletti 2016
Per trip, east Florida yellowtail peak September-October, gray snapper late summer, and mutton in winter.
Florida Atlantic coast (MRIP South Atlantic Florida, excludes Monroe County) · agency · agency document
NOAA Fisheries Marine Recreational Information Program 2025
In Florida's Gulf plus Keys domain, dolphin catch per trip peaks July-August and blackfin and wahoo peak September-October.
Florida Gulf coast including Monroe County (Keys) as one MRIP domain · agency · agency document
NOAA Fisheries Marine Recreational Information Program 2025

The whole evidence library

Entries read in full text or published by an agency. Entries read only in their abstract are listed on the science page with their numbers withheld.

Where it is scored

Today's score at any of them is free with an account; every fish has a page like this one.

Display only, not for navigation. Every figure here names its source; check the NWS marine forecast and the posted rules before you leave the dock.