European sardine

A sardine's habitat is a water mass rather than a piece of ground, and that is the single most useful thing to understand about finding them.

THEY LIVE IN THE OPEN WATER COLUMN, typically over the continental shelf, from the surface down to a few tens of metres. They are not associated with reef, wreck, weed or bottom structure in the way most angling species are, because their food is not either.

WHAT THEY FOLLOW IS PLANKTON, and plankton concentrates where physical processes put it: at upwelling cells, along fronts where two water masses meet, at the edges of eddies, and in the tide-driven convergences that form near headlands and banks. A sardine shoal sits where the water is productive, and when that water moves the shoal moves with it.

DEPTH CHANGES THROUGH THE DAY. Shoals commonly rise towards the surface at night as the plankton they feed on migrates upward, and drop deeper during daylight — the same vertical migration that governs much of the open ocean, and one reason that a shoal marking on a sounder at dawn may be unreachable by mid-morning.

INSHORE OCCURRENCE IS SEASONAL AND PATCHY, which is why shore anglers encounter them irregularly. Where upwelling or a productive front comes close to the coast, sardines can be within reach of a pier or a small boat; where it does not, they may be many kilometres offshore all year.

AND THE PRACTICAL CONSEQUENCE for an angler is that sardines are found by watching rather than by returning to a mark. Working birds, surface disturbance, predators showing, and bait registering on a sounder are the signals; a spot that held them last week carries no promise at all.

Sardine size is unusually consequential for a small fish, because the name changes with it and so does the use.

THE ORDINARY RUN IS 15 TO 20 CENTIMETRES. That is the size the commercial fishery is built around, the size that goes into a tin, and the size most anglers meet either as bait or in a shoal taken on feathers.

AROUND 22 TO 25 CENTIMETRES the fish is large enough to be sold and described differently. In British usage that larger fish is a pilchard and the smaller one a sardine, which is a commercial convention rather than a biological distinction — the Cornish pilchard and the Portuguese sardine are the same species at different ages.

THE MAXIMUM RECORDED IN THE SCIENTIFIC LITERATURE is around 27 to 28 centimetres, and figures beyond that should be treated with caution: sardines are rarely measured individually outside a survey, and larger claims usually rest on somebody's recollection rather than on a record.

GROWTH IS FAST AND LIFE IS SHORT. A sardine reaches usable size within its first year or two and lives a handful of years rather than decades, so the size of the fish in a shoal is mostly a statement about which year class is dominant. A run of large sardines usually means a strong cohort from a good recruitment year rather than exceptional individuals.

FOR BAIT THE SIZE DECIDES THE PRESENTATION. A whole small sardine suits a modest bait for bass or smoothhound; a large one is usually cut, either as fillet or as a head-and-guts section for conger and bigger ground. Matching the bait to the mouth is the ordinary discipline, and a sardine gives a usefully wide range without changing species.

Sardine reproduction is a broadcast strategy taken to its logical conclusion, and understanding it explains why the stock swings the way it does.

SPAWNING HAPPENS IN OPEN WATER with no nest, no site and no parental care. Eggs are released into the water column, fertilised there, and float. Nothing about the process is tied to a piece of ground, which is why sardines have no spawning site an angler can identify or avoid.

THE SEASON IS LONG RATHER THAN SHARP. Rather than a concentrated spawning period, sardines spawn in batches over an extended part of the year, and the timing shifts with latitude and temperature: broadly the cooler months in the warmer parts of the range and the warmer months further north. That spread is itself a strategy — it hedges against any single batch meeting bad conditions.

EGGS AND LARVAE DRIFT, AND THAT IS WHERE THE FISHERY IS DECIDED. Survival depends almost entirely on whether the currents carry the larvae somewhere with enough plankton to eat and few enough predators to escape. Good years and bad years differ by orders of magnitude, and the difference is physical oceanography rather than the number of adults that spawned.

THAT IS WHY RECRUITMENT DOMINATES THE STOCK. A single strong year class can carry a fishery for several seasons, and a run of poor ones can collapse it while the spawning population still looks adequate. It is also why sardine stocks fluctuate on decadal cycles that fishing alone does not explain, and why management measures on these stocks change in response to scientific advice rather than staying fixed.

FECUNDITY IS HIGH BECAUSE MORTALITY IS ENORMOUS. Releasing very large numbers of small eggs is the correct answer when almost none of them will survive, and it is the same answer most open-water shoaling fish have arrived at.

The sardine year is organised by water temperature and by the productivity that drives their food, not by a calendar an angler can carry between coasts.

IN THE WARMER MONTHS shoals generally move closer inshore and nearer the surface across much of the range, which is what brings them within reach of piers, small boats and shore marks at all. This is when most anglers encounter them, and when the predators that follow them — bass, bonito, mackerel and larger fish — are most accessible as a consequence.

IN COLD WATER they move deeper, further offshore, or both. The shoals do not disperse; they relocate, and a coast that was full of bait in August can have none within reach in February while the same fish are a few miles out.

UPWELLING SEASONALITY DOMINATES ON THE PRODUCTIVE COASTS. Where the fishery rests on wind-driven upwelling, the sardine season is effectively the upwelling season: the shoals concentrate while the wind drives the system and disperse when it relaxes. That makes the fishing calendar a wind calendar, and it varies between years in a way a month table cannot capture.

SPAWNING SHIFTS THE PICTURE AGAIN, because the extended batch-spawning season overlaps with feeding movements rather than replacing them, and fish in spawning condition behave and feed differently from fish that are not.

AND THE LONG-TERM TREND IS PART OF THE SEASONALITY NOW. Northern occurrence around the British Isles has varied considerably over the past century with sea temperature, and the fishery that supported Cornish pilchard cellars is not the same fishery as the one there today. Anybody reading a historical account of when sardines appear on a coast should treat the dates as evidence about that period rather than as a forecast.

European sardine size is the subject of a naming convention that confuses a great many people, and it is worth settling.

A SARDINE AND A PILCHARD ARE THE SAME FISH. Sardina pilchardus is called a sardine when small and a pilchard when large, and the boundary is commercial convention rather than biology. The Cornish pilchard fishery and the Portuguese sardine fishery were fishing the same species at different sizes.

A TYPICAL FISH IS 15 TO 22 CENTIMETRES. Over 25 centimetres is large, and the reported maximum for the species is around 27 centimetres.

THEY ARE FAST-GROWING AND SHORT-LIVED, maturing at one to two years and rarely exceeding eight. That short life is why sardine stocks fluctuate so sharply: a population dominated by one or two year classes responds to a good or bad spawning year within a season or two, with none of the buffering a long-lived species has.

WHICH IS THE MECHANISM BEHIND THE HISTORICAL COLLAPSES. The Cornish pilchard fishery, at its height one of the largest in Britain, declined for reasons that combined fishing pressure with the natural volatility of a short-lived pelagic stock — and the same pattern of boom and collapse has recurred in sardine and anchovy fisheries worldwide.

FOR AN ANGLER THE SIZE MATTERS IN TWO WAYS. Sardines are taken on very small feathers and sabiki rigs, and hook size is the entire limitation — a fish this small cannot take a mackerel feather. And a sardine is one of the most effective baits available for larger species, fresh or frozen, which is what a great many are caught for.

Sardines deteriorate faster than almost any fish a shore angler will catch, and the two reasons compound.

THEY ARE SMALL AND OILY. A small fish warms through instantly and has no thermal mass to buy time, and an oily fish has a high proportion of fats that begin oxidising at death. Together those mean a sardine goes from excellent to poor within an hour or two on a warm day.

AND THEY BELONG TO THE HISTAMINE GROUP. Sardines are among the fish the FDA guidance associates with scombrotoxin formation, on the strength of the same dark-muscle chemistry that puts mackerel in it. That means the deterioration is not only a quality question: a sardine left warm can accumulate histamine, which no amount of cooking removes.

SO THE HANDLING IS SIMPLE AND IT IS NOT OPTIONAL. Into an ice slurry immediately, not into a bucket and not into a bag. Where sardines are being caught in numbers on feathers or sabikis, the ice needs to be there before the fishing starts, because there is no version of this that works retrospectively.

THE BAIT CASE IS THE SAME CASE. A sardine intended as bait is worth far more if it was chilled hard the moment it was caught: it stays intact on a hook, it leaks the oils that make it effective, and it does not go soft. Anglers who treat bait fish carelessly and then wonder why frozen shop sardines out-fish their own fresh ones have usually answered their own question.

AND THE SPINES AND SCALES ARE A MINOR NUISANCE RATHER THAN A HAZARD — sardine scales are deciduous and come off on everything, which is cosmetic, and the fish is otherwise harmless to handle.