Monofilament Fishing Line

Line is the only link to the angler and the fish that they are aiming to catch, and it is therefore worthwhile spending time thinking about the type, strength and quality of line that will be used. The most popular line in the UK is monofilament (often referred to as simply ‘mono’). This is a line made out of a single fibre of plastic by heating and mixing the polymers and forcing them through tiny holes to produce line of the thickness and strength required. Monofilament is fairly cheap and an effective fishing line, accounting for its popularity throughout the UK, and indeed the world, although braided fishing line has become increasingly popular in recent years. Before monofilament existed anglers had to use line made out of a range of different materials, all of which were vastly inferior and much harder to use than monofilament (see below).

Line for Reels

Fishing Line Strength, Diameter and Stength

The strength of monofilament refers to the maximum weight that this line will hold, but every time a knot is tied in monofilament the strength of the line is reduced. For this reason rigs that use few knots (for example by using trapped swivels rather than dropper knots) will be the stronger than rigs featuring a high number of knots. However, using 15lb line does not mean that fish only up to 15lb can be caught. The weight of the fish is supported by the water and very big fish can be reeled onto beaches using relatively weak line. However, if fish are being winched up from the sea (i.e. up a pier wall) and are not supported by the water then line has a much higher chance of snapping – see the page on Striking, Reeling In and Landing Fish. Monofilament line is not very abrasion resistant and will easily become damaged if it is allowed to scrape over rocks or railings.

The stronger line is the thicker it is. Mono of around 15lb is usually 0.35mm in diameter, with the stronger 30lb mono being around 0.50mm in diameter. This may not sound like too much difference but stepping up the thickness of line has a big impact on casting distances. Monofilament is also stretchy, which is both a strength and disadvantage – the stretchiness allows mono to have some forgiveness in casts and means that there is a buffer between the angler and the fish when striking or playing a fish, but it also means reduced bite detection and contact with the fish. Stretch free braided line is now available on the market, but this brings its own advantages and problems.

Manufacturers and Quality

Unbranded Line

Avoid unbranded line as there is no guarentee of quality.

With line, like many other things in sea fishing, it is certainly better to pay a little more for a quality product from a well-known manufacturer than take a chance on a unbranded make. There are a great number of line manufacturers on the market with Impact, Ultima and Daiwa making quality fishing lines. Others such as Sunset make specialist snood line, such as their Amnesia brand. Extra heavy monofilament and wire line is also available for hooklengths for powerful species with sharp teeth which may be capable of biting through weaker monofilament lines.

Using Monofilament Line

When choosing a line for fishing from the shore with a 12-16ft beachcaster rated to cast 4-8oz there are two ways of setting up a reel with line – a light line and shockleader or a stronger line all of the way through.

Light main line and shockleader: The first way is to use a light mainline of 12 – 18lb monofilament, this line is strong enough to successful reel in a fish, but light and thin enough (usually 0.35 – 0.40mm in diameter) to allow anglers to cast to their maximum distances. However, because this line is so thin and weak the force of a cast will easily snap the line. For this reason a shockleader needs to be used. This is a length of heavy mono, typically 50lb or more in breaking strain, which is attached to the end of the main line to absorb the force of a cast. A shockleader needs to be long enough so that when the weight is in place ready to cast there is at around 6-8 turns of shockleader around the spool. Shockleader is attached to the mainline using a special adaptation of the uni knot, although tapered shockleaders are available which produce a much slimmer knot.

Impact Monofilament

Impact Monofilament 14lb breaking strain is a good choice for main lines when used with a shockleader.

The 12-18lb mainline and 60lb shockleader is a classic setup for shore fishing on clean ground. Working out the strength of shockleader needed is easy as it follows a simple formula of 10lb of breaking strain for every ounce of casting weight (see panel above). Both multiplier and fixed spool reels work well with weaker mainline and a shockleader used. A range of line can be purchased online including 14lb Impact monofilament in clear or hi-vis yellow are a good choice mainlines for anglers using this set up. When it comes to shockleaders Fladen Warbird hi-vis shockleaders can also be purchased, as can WSB Tapered Leaders. These leaders are 50lb breaking strain but then taper down to 15lb breaking strain, meaning that the shockleader knot is smaller and more streamlined and compact, meaning it is less likely to collect weed or catch on rod rings during a cast.

Red Ice

Ultima Red Ice (30lb breaking strain) is an ideal lie to use in a reel used for rough ground fishing.

Straight through line: When fishing rough ground and marks with constant snags many anglers use an alternative setup. This does away with light line and a shockleader and instead has the same strength line all of the way through from the reel to the rig. This line in always stronger and thicker, typically 30lb breaking strain. The reason for this is that when getting snagged with a light line and shockleader the line will always snap at the join between leader and main line as this is the weakest point. In a fishing session where getting snagged is a regular occurrence this will mean constantly going through the fiddly (and costly) job of tying on new shockleaders. For this reason anglers fishing snaggy marks use a straight through line as this will always snap at the rig, meaning the line can be reeled in and a new rig attached with minimum fuss. However, casting distances will be reduced as much thicker line is being used and it is very important that only overhead casts should be performed. It is not safe power cast with 30lb line straight through and no shockleader! Anglers should avoid using line that is too strong to cast with – any stronger than 35lb and line will be so thick it will cut down casting distances considerably, and can also prove very difficult to snap when caught in a snag. Again Impact Monofilament in its 33lb strength is a good choice for anglers looking to use a straight through set up – it is avialble in either clear or hi-vis yellow colour, while Ultima F1 Extreme Strength Surf Monofilamentis a good alternative for anglers looking for a strong, straight through line.

Multiplier reels definitely work better than fixed spool reels when fitted with 30lb line straight through, as the bulkiness of the line makes the line level plummet on a fixed spool reel which seriously reduces casting distances. However, fixed spool reels can still be used with 30lb line as long as anglers are aware that casting distances will be reduced considerably (this may not matter on deep-water rock and pier marks where casting distance is not important).

Line for Bass, Flattie and Spinning Rods

Spinning Reels

Light spinning reels can be used with relatively weak line straight through.

When using lighter rods and monofilament most anglers use straight through line and do not bother with shock leaders. This is because these rods are used to cast relatively light lures and weights and are only used to perform basic overhead casts (not power/pendulum casts). With bass or flattie rods which generally cast lures or weights of 2-4oz anglers usually use line of around 12-18lb breaking strain. With smaller, lighter spinning rods, which may cast lures of only an ounce or so, anglers can step down to a mainline of around 10lbs with no need for a shockleader. With the rising popularity of LRF (Light Rock Fishing) anglers can cast lures weighing just a few grams on monofilament lines of 2-5lb breaking strain. All of these types of rods can of course also be used with braided line, and in this case anglers may choose to add a monofilament shockleader.

Line for Making Rig Bodies

A number of different types of line are used for making rigs, ranging from near-invisible flurocarbon lines for rigs to catch stealthy and shy-biting fish to heavy wire which are used to prevent powerful species with sharp teeth from biting through the line. Read on to find out more about the different types of line used in the construction of sea fishing rigs.


Rig Body

Rig body line is simply the line which makes up the main ‘body’ part of a rig. Due to the fact that rigs will be dragged over the seabed as they are reeled in, and will often have crimps pressed onto them and knots tied into them, anglers usually use line which is at least 60lb breaking strain. Trace Builder Clear Rig Body Line is a good value choice for rig body line. Often anglers buy two spools from the tackle shop and using one for leaders and keeping one to use for making rigs. Obviously, line used for rig bodies needs to be at least as strong as the line being used for the shockleader. There would be safety implications if an angler cast 8oz weights with an 80lb shockleader but used rig body of 40lb line! However, anglers should be aware that it may be difficult to fit crimps and tie knots in very thick line which is over 80lb in breaking strain.


A hooklengths (also known as a snood) is a length of line which is attached to the rig body and terminates in a hook. The vast majority of rigs used in UK sea fishing will incorporate a hooklength which can be attached to the rig body with either trapped swivels or a more simple (and cheaper) dropper knot.


Amnesia is extremely popular for making hooklengths.

Monofilament Hooklengths: The Amnesia brand of line by the American company Sunset is by far and away the most popular for making hooklengths in the UK. This is because Amnesia is memory free, meaning that it stays straight and tangle free in a way that normal monofilament fishing line does not, making it ideal for making hooklengths and snoods. Amnesia is reasonably priced, comes on conveniently sized spools and is commonly available from tackle shops and online retailers. Amnesia is available to order online from Sea Angling Shop in either clear or black colours in 20lb or 30lb breaking strains.

Fluorocarbon: Fluorocarbon is a fairly new development in sea angling, although it has been used in freshwater fishing and fly fishing for a number of years. It is a highly technologically advanced line that is close to invisible when it is in water due to the way it refracts light. For this reason it is becoming increasingly popular as a line to use for snoods, especially for shy biting fish such as mullet and bass, and is now being widely used in LRF (Light Rock Fishing). It is also strong and stiff meaning it stands away from the rig body, lessening the chances of a tangle, and it is also very abrasion resistant and sinks meaning that it helps keep baits on the seabed. However, it is expensive and much of the flurocarbon on the market is designed for freshwater fishing and therefore has a relativley weak breaking strain.

Wire trace hook

A Cronus size 6/0 O’Shaughnessy hook attached to wire line with a crimp.

Wire Line: Wire line is a type of line used to construct hooklengths on rigs designed to target big and powerful fish such as conger, tope or other shark species. The reason for this is that these fish have sharp teeth which can bite through monofilament, leading to many anglers using wire traces to guard against this. As knots cannot be tied with wire line specialist crimps are used instead. An alternative to wire traced is to used heavy monofilament (150-200lb breaking strain), although this will also have to be secured with heavyweight crimps as it is too heavy to tie conventional knots with. With most heavyweight crimps it is also necessary to use specialist heavy crimping pliers.

Weak Link Line

When fishing rough ground anglers almost always use a rig which has a weak link release (rotten bottom) built into it. Often simple weak link releases and the popular Gemini Genie Breakers rely on incorporating a weak link of line which the weight is attached to. If the weight becomes snagged while reeling in the weak link will easily snap, but if no snags are encountered then the weak link will allow the rig and weight to be retrieved. Most anglers have a spool of weak monofilament line of around 10lbs breaking strain which is kept in the tackle box and used to make any weak link releases which are needed during the fishing session.

Power Gum

Power Gum

Power gum is the best choice to make stop knots with.

Power gum is a specialist type of line that is used in freshwater fishing as a way of making shock absorbing sections of line, but is only used in sea fishing as a way of making stop knots. Stop knots made with power gum are very effective as they hold their place well, but can still be moved under a little pressure. Power gum stop knots are based on the uni knot and are ideal for making bait stops or for trapping swivels when constructing rigs and are the best way to secure an impact shield as there is still some room for adjustment. Just like line power gum comes in breaking strains with 10 – 15lb power gum providing the best stop knots, power gum 20lb+ does not knot well as it is too bulky and thick. Buy Drennan Power Gum on Amazon by clicking here.

Line Colour

A quick look around any tackle shop or online tackle dealers will reveal that monofilament line is available in a wide range of colours, ranging from clear to super high-visibility fluorescent yellows and reds. While these high visibility lines make it easier to see where line is (a big advantage on a crowded pier), clear lines allow the reassurance that fish are not spooked or put off by a brightly coloured line. In reality the majority of sea fish are fairly unfussy feeders which are highly unlikely to be put off by line colour, even when fishing in bright daylight. However, anglers targeting shy-biting fish such as mullet (and to a lesser extent bass) generally use clear monofilament, possibly flourocarbon, in order to avoid frightening off any fish.

Before Monofilament Fishing Line

The ubiquitous nature of monofilament means that many anglers do not realise the range of different types of line which anglers used in previous generations – and how difficult these lines were to use compared to mono. The book The Technique of Sea Fishing and Tackle Tinkering by W. E. Davies which was originally published in 1952 and revised in 1962 lists cuttyhunk (flax), cotton, silk, plaited nylon and nylon monofilm (sic.) as all being lines which were commonly used by anglers at the time, although the book warns that nylon monofilm in breaking strains of over 8lb can be “too springy and difficult to handle” (p22). Many of these non-nylon fishing lines would have to be removed from the reel dried after fishing (otherwise they would rot). Indeed, the book provides a method of dressing line to make it last longer and become less water absorbent. Anglers have to mix Stockholm tar, turpentine and methylated spirits in a jar and then coil the fishing line and place it in the solution and leave it there for two days, before removing the line and letting it dry (which took two weeks) and then re-winding it onto their reel through a cloth. It is easy to forget how much easier modern monofilament fishing lines are to use and maintain compared to the lines which were used in the pre-monofilament era.

Sea Fishing Line and the Environment

Bird with Fishing Line

Marine birds tangled up in fishing line create a terrible image of anglers.

Related article: Responsible Sea Fishing

Any kind of fishing line is extremely destructive to the environment and sea fishing line of any type should always be disposed of carefully and never thrown away or left at a fishing mark. Line which has been carelessly (or, even worse, deliberately) left around a fishing area after an angler has left is a real threat to the marine environment, and images of sea birds tangled up in line makes a terrible image of anglers. Images like this are very powerful and can be used by local councils and wildlife pressure groups to get the public onside in campaigns to ban anglers from certain areas. The way of dealing with this situation is simple – anglers must take excess line home with them and dispose of it responsibly.

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