Bait size, and what it selects for

SIZE FILTERS IN BOTH DIRECTIONS, AND THAT IS WHY IT IS SUCH A POWERFUL CONTROL.

THE FLOOR. A bait cannot be taken by a fish whose mouth will not accommodate it. Increasing bait size is the standard and effective response to being pestered by small fish, and it works mechanically rather than by preference.

THE CEILING IS SOFTER AND OFTEN MISSED. A large predator will take a small bait quite happily — large fish do not refuse easy food — so a big bait does not exclude small fish so much as it discourages them. What a big bait genuinely does is reduce the NUMBER of fish willing to attempt it, which trades bites for average size. That is a real trade and it should be made deliberately.

'BIG BAIT, BIG FISH' IS HALF RIGHT AND THE HALF IT GETS WRONG MATTERS. Predators select prey by an energetic calculation — how much food for how much effort and risk — and there is good evidence that predatory fish take prey across a wide size range with a preference well below the maximum they could physically manage. A bait at the top of what a fish can swallow is not the optimum; it is the extreme. The practical version is that a bait somewhat larger than the prevailing natural food frequently sorts for larger fish, and a bait dramatically larger frequently just stops bites.

WHAT ELSE SIZE CHANGES, which is usually overlooked.

HOOK SIZE, and therefore hooking behaviour. A large bait needs a hook whose gape is not masked, and a large hook needs a fish whose mouth can accommodate it. These constraints chain.

TIME BEFORE A DECISION. A fish takes longer to deal with a large bait, which changes when a strike should come and increases the chance of a deep hook hold if it is left too long.

WHAT SURVIVES THE CAST. Large soft baits fly badly and come off.

HOW LONG IT LASTS AGAINST SMALL FISH AND CRABS. This is often the real reason for going bigger in the sea, and it is a durability decision wearing a selectivity costume.

AND THE SITUATION WHERE SMALL IS THE ANSWER: when fish are feeding on something specific and abundant — a run of small fry, a hatch, a tide bringing one item in quantity — a bait noticeably larger than the natural food gets refused. The correction there is down rather than up, and it is the same correction a fly angler makes when nothing is taking.