Most bass spend their early years in estuaries, penetrating quite deeply inland into brackish waters, where they are safe from the majority of marine predators. (This is because only a few species can survive in this type of water.) Here, several miles from the sea, they only have to contend with aerial attack, particularly from cormorants, and an occasional foray from seals venturing far up the river.
The fish who share these brackish waters – mullet, flounders, silver eels, the occasional shad or lampreys etc. – pose no threat to the young bass, though they may have to be careful of the occasional sea trout or a quick-tempered salmon. The result is that the estuaries become a safe haven, which is probably why the majority of bass spawning grounds are believed to be close to the mouths of estuaries.
As the bass grow, so they change position within the estuaries before leaving them altogether. In the winter, for example, when heavy rain reduces the salinity – the level of salt present in the water – of the upper reaches, the young bass swim downstream, ahead of the flood. They then take up position in the reaches nearer to the sea. Fortunately for them this takes place at a time when the number of marine predators is at a minimum so they are still relatively safe.
This change of location carries with it a change of diet. Instead of feeding heavily upon smaller fry, earthworms and river ragworm, the young bass start to encounter prawns, shrimps, lugworms and the fry of saltwater species. Pretty soon after that, weighing about a pound or slightly larger, the bass venture forth from the estuary into the open sea, congregating in large shoals which may, on occasion, mix with different year groups, so that you can find several different sizes of bass in a single location, often within harbours or natural ports.
The growing bass then start to develop distinctly migratory habits, with the exact migration paths determined by instinct, food supply and their original hatching grounds. In the winter, for example, they will move into deeper water, following the clouds of baitfish upon which they predate.
In the Spring, once spawning is complete, they will move into rocky areas, where the numbers of prawns and peeling crabs attracts their attention. Then, in the Summer, when sandeels are thick on beaches or the sandbanks off the mouths of estuaries, they will pursue these in the same locations, eventually developing semi-territorial routes which will explore both beaches (usually at night) and rocky areas (either day or night).
Eventually bass reach sexual maturity, usually when they are between 16 and 18 inches long, and breeding takes place so that the cycle starts all over again. If you are an angler then this is something that you should bear firmly in mind. If you put back all fish that are smaller than 18” then they will, eventually, get a chance to breed!