Thick-lipped grey mullet: life, behaviour and the long reads

Mullet occupy a niche almost no other fish an inshore angler meets can use, and that is why they are found in places that look unpromising and are not.

THE SALINITY TOLERANCE IS EXTREME. Thick-lipped grey mullet move between full seawater, brackish estuary and genuine fresh water, and they do it routinely rather than as an occasional excursion. That puts them far up estuaries, in harbours, marinas, creeks, drainage outfalls and river systems well above the tidal limit in places.

AND THE FEEDING IS THE OTHER HALF. Mullet graze on detritus, algae, and the film of organic material on surfaces, with a specialised gut and a muscular gizzard-like stomach for processing it. They also take small invertebrates and, notoriously, whatever organic matter accumulates around human activity. A fish that can digest detritus can live where a predator cannot, which is why a harbour with a fish quay holds mullet and holds little else of size.

THE DEPTH IS SHALLOW — typically two to fifteen metres, and often very much less. Mullet are frequently in water that barely covers them, visible, over mud and weed.

WHICH MAKES THEM A SIGHT FISHERY AND A DIFFICULT ONE. They are shallow, visible, in clear or slightly coloured water, and extremely wary. The difficulty is not that they are hard to find; it is that they can see everything, including the angler.

AND THE NURSERY DEPENDENCE MATTERS. Juveniles use estuaries, harbours and brackish creeks as nursery ground, which ties the stock directly to water quality in exactly the places most affected by discharge and development. This species is assessed as Near Threatened, which is unusual among the common inshore fish and is worth knowing before deciding whether to keep one.

Mullet seasonality is a temperature story like most inshore species, but the daily and tidal pattern is far more decisive for this fish than for anything else on the same coast.

THE SEASON. Mullet arrive inshore as water warms in late spring and remain through summer and early autumn, moving offshore and southward as it cools. In the northern part of the range they are effectively a warm-season fish; further south the season is far longer. The trigger is temperature rather than date.

BUT THE TIDE IS WHAT ORGANISES THE FISHING. Mullet follow the flood into shallow ground, creeks, and over mud and weed that were dry an hour before, feeding as they go, and drop back on the ebb. A harbour or creek fishes for a specific part of the tide and is empty for the rest of it. Within that, the last of the flood and the first of the ebb are frequently when fish are most concentrated and most catchable.

DISTURBANCE MATTERS MORE THAN TIME OF DAY. Mullet in a working harbour become accustomed to noise and movement and can be caught in daylight beside considerable activity; the same fish in a quiet creek will not tolerate a shadow. Time of day is a weaker predictor for this species than for most.

CONDITION IMPROVES THROUGH THE SEASON, so late-summer and autumn fish are the heaviest.

WHAT NOT TO CONVERT INTO A CALENDAR. The arrival tracks water temperature across a range running from Iceland to Cape Verde. "They come in May" describes one coast.

AND THE STANDING CAUTION. This species is assessed as Near Threatened, grows slowly and is long-lived. The fishery for it is very largely catch-and-release, and that is a deliberate response to the assessment rather than a convention.

Mullet reproduction separates the adults and the juveniles into different environments, and the environment the juveniles need is the one under the most pressure.

THE STRATEGY. Spawning takes place at sea, offshore, with pelagic eggs released into open water. There is no nest and no parental care. The eggs and larvae drift, and the juveniles move into estuaries, harbours and brackish creeks.

AND THOSE NURSERIES ARE THE CONSTRAINT. Small mullet are most abundant in exactly the brackish, sheltered, organically rich water that adult mullet also exploit, and the dependence is obligatory rather than opportunistic for the early life stage. Water quality, discharge, dredging and the physical modification of estuaries and harbours therefore act directly on recruitment.

WHICH IS WHY THE CONSERVATION STATUS IS WHAT IT IS. A species dependent on estuarine nursery habitat across a range where that habitat is heavily modified is exposed in a way its apparent abundance in a harbour does not suggest. The Near Threatened assessment is a statement about that.

MATURITY IS LATE AND GROWTH IS SLOW. Mullet take several years to mature and large fish are old. Combined with the nursery dependence, that gives a population that recovers slowly from depletion.

AND THE PRACTICAL CONSEQUENCE IS THE FISHERY'S OWN NORM. Mullet angling in Britain and Ireland is overwhelmingly catch-and-release, and the specialist groups that fish for them advocate it explicitly. That is not squeamishness about a fish with a poor culinary reputation; it is a response to a slow-growing, late-maturing, habitat-limited species assessed as Near Threatened.

WHAT THIS SECTION DOES NOT DO. Identify spawning aggregations.

Mullet size is worth stating carefully because the species is widely dismissed and the large fish are, in age terms, among the most impressive an inshore angler will encounter.

THE ORDINARY FISH is thirty to forty-five centimetres and roughly seven hundred grams to one and three-quarter kilograms. That is what most harbours and creeks produce and it is already a fish that has taken years to get there.

A GOOD FISH is over fifty-five centimetres and around three kilograms. Specialists regard a fish of that size as a genuine achievement, and the difficulty is not landing it but deceiving it.

THE RECORDED MAXIMUM is 75 centimetres and 4.5 kilograms in FishBase. Fish at that end are exceptional and old.

WHAT MAKES THE NUMBERS MEANINGFUL IS THE AGE BEHIND THEM. Mullet grow slowly and live a long time, so the weight is a poor guide to what the fish represents. A three-kilogram mullet may be older than a much heavier bass, and it belongs to a species assessed as Near Threatened.

WHICH IS THE ARGUMENT FOR RETURNING THEM. The specialist mullet fishery in Britain and Ireland is very largely catch-and-release, and the reason is the combination above: slow growth, late maturity, dependence on degraded nursery habitat, and a conservation assessment worse than any comparable inshore species.

AND A NOTE ON IDENTIFICATION AFFECTING SIZE CLAIMS. Several grey mullet species occur in the same water and are confused routinely, and weight records attributed to one may belong to another. A size figure for this species is only as good as the identification behind it.

Mullet fishing is the clearest case in British angling of a sea species that must be approached with freshwater technique, and understanding why makes the whole discipline coherent.

THE FISH IS A GRAZER WITH A SMALL MOUTH AND EXCELLENT EYESIGHT. Mullet feed on algae, detritus, small organisms and biofilm, sifting and sucking rather than seizing. They have a small mouth, soft lips and a fine-meshed filtering apparatus, and they are extremely wary in the clear shallow water of harbours and estuaries where they are usually seen. Nothing about that combination suits conventional sea tackle.

SO THE TACKLE AND METHOD COME FROM COARSE FISHING. Light float rods, fine line, small hooks, small baits and a float or freeline presentation are what work — essentially roach tactics applied to salt water. Heavy tackle is detected and refused, and the difference between fine and heavy tackle here is the difference between catching and watching.

GROUNDBAITING IS CENTRAL AND IT TAKES TIME. Mullet are conditioned rather than persuaded: introducing small quantities of bait regularly over a period gets a shoal feeding confidently, and then a hook bait among it is taken. A single cast into a shoal of unfed mullet achieves nothing. Bread, mashed bread and fish-based groundbaits are the standard, and patience is the actual technique.

BAIT IS SMALL AND OFTEN BREAD OR HARBOUR FOOD. Bread flake and mashed bread are the classic; where mullet are feeding on harbour outfalls or on weed and algae, matching what they are actually taking is what converts a fed shoal into a caught fish.

THE TAKE IS SUBTLE AND THE FIGHT IS NOT. Mullet bites are delicate and easily missed, and a hooked mullet then runs hard and long for a fish of its size — powerful, fast and difficult on fine tackle, particularly around harbour structure. The soft mouth means the hook hold is fragile throughout.

AND THE SPECIES IS SLOW-GROWING AND LONG-LIVED, which is a strong argument for release. Mullet are frequently returned by the anglers who target them for that reason. What may be retained is a matter for the competent authority, and in some areas mullet are subject to specific measures.

Mullet are slow-growing and long-lived, with FishBase recording a maximum reported age of 25 years. They mature comparatively late and shoal by size throughout life. Their catadromous habit — moving between salt, brackish and fresh water — means individual fish may use a wide range of habitats over a season.

Spawning takes place at sea, offshore, with pelagic eggs. Juveniles move into estuaries, harbours and brackish creeks, which are the nursery habitat and where small mullet are most abundant. The dependence on estuarine and harbour habitat makes water quality in those places directly relevant to the stock.

Adults feed on benthic diatoms, epiphytic algae, small invertebrates and detritus, grazing surfaces and processing sediment; juveniles feed on zooplankton. The gut is long and the fish has a muscular gizzard-like stomach region for grinding, which is what a diet of algae and sediment requires. This is a grazing animal, and the whole difficulty of catching one follows from it.

Vision dominates and mullet are exceptionally wary in the clear shallow water they favour — a shoal in a harbour will move away from a shadow. They also respond strongly to introduced food, which is the crack in the armour: a mullet shoal that has been fed steadily on bread over an hour behaves very differently from one that has not.

Mullet arrive inshore as water warms in late spring and remain through summer and early autumn, moving offshore and southward as it cools. They tolerate a wide salinity range and penetrate far up estuaries and into fresh water. Within a day, tide state and disturbance matter more than time of day.

A specialist pursuit with a devoted following, fished with freshwater tackle scaled down further than most sea angling would recognise. Mullet are the clearest demonstration in sea angling that matching the feeding behaviour matters more than matching the size of the fish.