Northern red snapper

Red snapper are demersal reef-associated fish of the Gulf and south Atlantic shelf, and in that region a very large part of the habitat is man-made.

THEY REQUIRE HARD BOTTOM AND RELIEF. Natural rocky outcrops, ledges, banks and reef hold them, and adults are strongly associated with vertical relief rather than with flat bottom.

ARTIFICIAL STRUCTURE IS A MAJOR HABITAT COMPONENT. Oil and gas platforms, artificial reefs and wrecks across the Gulf function as red snapper habitat at a scale that materially affects the population's distribution, and the relationship between energy infrastructure and this fishery is closer than for any other species in this catalogue.

DEPTH INCREASES WITH AGE. Juveniles occupy shallow shelf habitat including low-relief bottom and shell ridges; adults move progressively to deeper structure, with the largest fish on deep offshore relief.

JUVENILES USE LOW-RELIEF AND SOFT-BOTTOM SHELF as nursery habitat, which is a less obvious dependency than the adult one and matters to recruitment.

THEY SCHOOL AROUND STRUCTURE, size-sorted, and a given piece of relief tends to hold a cohort.

AND BAROTRAUMA IS UNAVOIDABLE FROM THESE DEPTHS. Released red snapper suffer pressure injury and require descending devices to survive, and the mandating of those devices is one of the clearer recent gear interventions in the region's recreational fishery.

Red snapper have an extended warm-season spawning period, and the interesting seasonal fact about them is the gap between their biology and their fishery.

SPAWNING RUNS THROUGH THE WARM MONTHS, from late spring into autumn, with females spawning in batches repeatedly over that whole period rather than in a single event. Frequency is high — individual females may spawn many times in a season.

OLDER, LARGER FEMALES SPAWN MORE OFTEN AND PRODUCE MORE AND BETTER EGGS, so the reproductive contribution of a population is concentrated in its oldest fish. That is the biological argument behind protecting large individuals, and it applies to this species with unusual force.

EGGS AND LARVAE ARE PELAGIC, and settlement onto shelf nursery habitat depends on transport.

SPAWNING IS ASSOCIATED WITH STRUCTURE AND WITH THE SHELF EDGE, in the same general habitat the fishery works.

AND THE FISHERY SEASON IS AN ADMINISTRATIVE OBJECT, NOT A BIOLOGICAL ONE. Federal recreational seasons for this species have at times been measured in days, set by quota and effort rather than by the fish's calendar, and the resulting allocation dispute is among the most litigated fisheries questions in the United States. A reader looking up red snapper seasons is looking at a management decision that changes annually, and this record does not state what any current one permits.

This is the fish that made descending devices a legal requirement in a major fishery, and the reasoning is worth understanding rather than merely complying with.

THE PROBLEM. Northern red snapper are taken from depths at which barotrauma is routine, in a fishery with tight bag and size limits, which means a very large number of fish are caught and released by regulation rather than by choice. Released at the surface with an everted stomach and no ability to submerge, a high proportion of them die. The discard mortality was large enough to matter to the stock assessment, which is how it became a rules question.

WHAT WORKS. Recompression with a descending device, promptly. Federal rules in the Gulf now require descending or venting equipment to be aboard and rigged, and the practical instruction is to have it ready before the first fish comes up rather than to look for it afterwards. Speed matters: the fish's odds fall with every minute it spends distended at the surface.

THE SPINES ARE SHARP AND THE GILL PLATE IS NOT FRIENDLY. Handle from above and behind with a wet cloth, keep fingers clear of the operculum edge, and use pliers rather than hands in the mouth.

WHAT NOT TO ASSUME. That a fish which disappeared under the surface swam away. A fish that sinks may be sinking rather than swimming. The test of a good release is a fish that goes down under its own power from a descender at depth, not one that vanishes from the surface.

AND THE HONEST PART. If you are catching fish you must release at a depth where they will not survive release, the useful change is depth or location, not technique.

Red snapper reproduction is unusually well studied because the species has been at the centre of one of the most contested fishery management arguments anywhere, and the biology is what the argument turns on.

SPAWNING IS BATCHED AND EXTENDED. Red snapper do not spawn once a year; mature females release eggs in repeated batches through a long warm season, spawning many times over several months. That spreads reproductive risk across a whole summer's worth of plankton conditions rather than staking it on one event, and it means a single female's annual output is far larger than a single spawning would suggest.

BATCH FREQUENCY AND FECUNDITY BOTH RISE STEEPLY WITH SIZE AND AGE. A large old female spawns more often and releases more eggs per batch than a small one, and the difference is not marginal — it is a multiple. So a stock's reproductive output is concentrated in its oldest fish to a degree that a simple biomass figure conceals.

WHICH IS WHY AGE STRUCTURE IS THE CENTRAL MANAGEMENT VARIABLE FOR THIS SPECIES. A population rebuilt to the same tonnage but composed of young fish produces far fewer eggs than one containing old ones. Recovering the age structure, not just the biomass, is what the rebuilding effort has been about.

SPAWNING OCCURS OVER STRUCTURE AND HARD BOTTOM in shelf waters, with fish associating with reef, wreck and artificial structure. Artificial reefs and platforms have become significant habitat for this species, which complicates the picture: they concentrate fish, which aids both the fishery and the fishing pressure on it.

MATURITY IS REACHED YOUNG AND LONGEVITY IS LONG — a combination that means a fish can be reproductively active for a very long time if allowed to be, and that a fishery removing fish shortly after maturity captures a tiny fraction of an individual's lifetime output.

BAROTRAUMA IS A REPRODUCTIVE ISSUE HERE, NOT ONLY A WELFARE ONE. Released fish from depth that fail to survive are removed from the spawning stock regardless of the regulation that released them, which is why descending devices and venting practice have become part of the management conversation.

AND THE RULES CHANGE OFTEN AND DIFFER BY AREA AND SECTOR. The competent authority is the only source for what currently applies.