Greater amberjack: life, behaviour and the long reads

Greater amberjack are structure-associated pelagic predators, and the combination is what makes them distinctive.

THEY HOLD OVER HARD STRUCTURE IN OPEN WATER. Wrecks, pinnacles, reef edges, offshore banks, oil platforms and drop-offs concentrate them, but the fish occupy the water column above and around the structure rather than sitting on it. A wreck holds amberjack in the twenty metres above it as much as on it.

DEPTH IS MODERATE TO DEEP, typically from around twenty metres down to well over a hundred, with larger fish generally deeper.

CURRENT IS PART OF THE HABITAT. Amberjack hold on the up-current side of structure and feed on what the flow delivers, which is why a mark fishes on a tide and dies at slack.

JUVENILES LIVE A COMPLETELY DIFFERENT LIFE. Young amberjack associate with floating weed and debris in open ocean — sargassum rafts in the Atlantic — living pelagically before recruiting to bottom structure as they grow. That drifting phase is where the year class is determined and it is invisible to any structure-based survey.

THEY ARE FAST SCHOOLING PREDATORS, and schools are size-sorted, so a piece of structure tends to hold fish of similar size.

AND BAROTRAUMA IS A HABITAT-DRIVEN PROBLEM: fish taken from depth need descending devices for release, which is now standard or required practice in the fisheries concerned.

Greater amberjack spawn in aggregations over offshore structure, which places them in the vulnerable category despite their fast growth.

SPAWNING AGGREGATIONS FORM IN SPRING AND EARLY SUMMER in most of the range, over offshore banks, wrecks and reef, with fish gathering from surrounding areas. The aggregations are predictable enough in place and season to be targeted.

SPAWNING IS BATCH AND PELAGIC, with females releasing eggs repeatedly over the season and fecundity high. Eggs and larvae drift in the surface layer.

JUVENILES ASSOCIATE WITH FLOATING WEED AND DEBRIS, spending their early life in that drifting habitat before recruiting to bottom structure. Sargassum in the Atlantic is a genuine nursery habitat and its abundance affects recruitment.

GROWTH IS FAST AND MATURITY EARLY relative to the fish's eventual size, which gives the species more resilience than a slow-growing grouper of comparable weight.

BUT THE AGGREGATIONS STILL MATTER. Concentrating reproductive adults at known offshore structure in a defined season is the standard mechanism by which a resilient species is nevertheless fished down locally, and several stocks have been assessed as overfished.

AND SEASONAL AND SIZE MEASURES APPLY IN SEVERAL MANAGEMENT AREAS as a result. This page describes the biology; the applicable rules come from the relevant authority.

Three separate problems, and the one people prepare for least is the first.

Amberjack are taken from deep structure, and a fish brought up quickly from thirty or forty metres suffers swim bladder expansion it cannot resolve. Released at the surface it floats and dies. A descending device is the answer where release is intended, and choosing to fish shallower is the answer where one is not available.

The second is physical. A large amberjack is heavy, extremely powerful and lands on a moving deck. Support it horizontally and do not lift it vertically; the gill covers cut, and the fish is entirely capable of injuring somebody with its body alone. Heavy jigging tackle with locked drags adds a line-under-tension hazard on top: when a leader parts under that load it returns toward the boat at speed.

The third is not a handling issue at all but belongs in the same decision. Large amberjack in parts of the range accumulate ciguatoxin, which no cooking or freezing removes and which causes serious and sometimes prolonged illness. Whether a particular fish is safe to eat is a local health question, and the honest answer here is to point at local advice rather than to offer a rule.

Amberjack seasonality has two components that anglers experience quite differently: a depth cycle driven by temperature, and a spring aggregation driven by spawning.

THE SPRING SPAWNING AGGREGATION IS THE DEFINING SEASONAL EVENT. Greater amberjack gather in numbers on offshore reefs, wrecks and hard bottom to spawn through spring and early summer, and those aggregations are large, predictable and located on known structure. That is when the biggest fish are most concentrated, and it is why the species is so vulnerable to targeted fishing at that time — the standard aggregating-reef-fish problem, in a fish that grows large and lives a long time.

WHICH IS WHY THIS IS ONE OF THE MOST ACTIVELY MANAGED SPECIES ON SEVERAL COASTS. Seasonal closures, size limits and quotas for greater amberjack are common, are revised frequently, and are set with the aggregation specifically in mind. Nothing in the biology above tells anybody what is currently permitted; that is a matter for the competent authority and it changes.

OUTSIDE THE AGGREGATION, DEPTH TRACKS TEMPERATURE. Amberjack move deeper as surface waters warm through summer and use shallower structure in cooler periods, so the same wreck holds fish at different depths through the year and the shallow-water encounters cluster in the cooler months.

STRUCTURE IS THE CONSTANT AND CURRENT IS THE SWITCH. Amberjack hold on wrecks, reefs, rigs, pinnacles and any substantial relief, and they feed actively when current runs over that structure. Slack water on a good wreck produces very little; the same wreck with a tide running produces a great deal. That is a within-day cycle sitting under the seasonal one.

JUVENILES ASSOCIATE WITH FLOATING WEED AND DEBRIS in open water, a completely separate seasonal habitat that tracks the abundance of drifting sargassum and other floating material.

AND THE PARASITE QUESTION IS SEASONAL FOLKLORE WORTH ADDRESSING PLAINLY. Amberjack commonly carry visible parasites in the flesh, and the widespread belief that this is worse in warmer months is practitioner observation rather than an established seasonal rule. It is a food-preparation matter rather than a season, and the sensible response is inspection rather than a calendar.

Fast-growing and moderately long-lived, maturing at around three to five years and living to about seventeen. Spawns in open water in the warmer months, with pelagic eggs and larvae that associate with floating weed and debris — the same juvenile strategy seen in other Seriola. Adults associate strongly with deep structure and show considerable site fidelity to particular wrecks and pinnacles.

Broadcast spawning in open water in spring and summer, with pelagic eggs and larvae. Juveniles shelter under floating weed and debris well away from the reef habitat adults occupy, which is why small amberjack turn up offshore under drifting material. Adults aggregate on structure, and those aggregations are predictable enough to be depleted.

A powerful predator taking fish, squid and crustaceans, hunting in packs around deep structure and driving prey against it. The pack habit means a hooked fish is frequently followed by others, which is the basis of the standard technique of keeping one fish in the water to hold the school near the boat.

Sight-dominant in the clear water over deep reef, hunting visually at speed and responding strongly to fast-moving lures and to live bait. Amberjack are notably willing compared with many reef predators, which is part of why they are so heavily fished on wrecks and why individual structures can be depleted of large fish.

Present year-round in the warmer parts of the range, with seasonal movement at the margins as water temperature shifts. Spawning aggregations form in the warmer months. Tidal and current flow governs the fishing on any given structure, since the fish position themselves relative to the current sweeping past it.

A major target on deep wrecks and reefs worldwide, taken by vertical jigging, live-baiting and trolling. Its power and its habit of diving for structure make it a benchmark fish for heavy jigging tackle. Regionally significant commercially, and heavily fished on known structures, where local depletion of large fish is a documented effect.