Plas­tic baits will usu­ally pass through both an in­testi­nal sys­tem and a true stom­ach of any fish large enough to in­gest them.

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A U-shaped stom­ach with a slightly en­larged cav­ity, as in sal­mon and trout;

A Y-shaped stom­ach (imag­ine a Y on its side) as found in eels;

No stom­ach, as is the case of cyprinids.

The size and shape of the stom­ach re­lates to the type of food items that the species eats, so fish that feed upon large prey items have tubu­lar cav­i­ties, known as lu­mens, ca­pa­ble of hold­ing large food items and stretch­ing with­out caus­ing dis­tur­bance to other or­gans. Species that pri­mar­ily feed on small items tend to have no true stom­ach, as they do not need to store food. In­stead, they pos­sess a very long in­tes­tine, de­signed to process food items as they pass through it.

Di­ges­tion usu­ally starts in the buc­cal (throat) cav­ity, where food items may be crushed by the pha­ryn­geal teeth and coated

Plas­tic prob­lem

But what of plas­tic and hooks? Both are non-biodegrad­able and tend to pass through the di­ges­tive tract in­tact, mod­i­fied slightly per­haps by chew­ing and acid/en­zyme at­tack, but largely un­touched.

The pres­ence of non­biodegrad­able waste, par­tic­u­larly plas­tic, in the aquatic en­vi­ron­ment is big news. David At­ten­bor­ough’s Blue Planet II alerted the wider pub­lic to the ex­tent of the prob­lem, and when you re­alise that at cur­rent rates of dis­posal there will be more plas­tic in our oceans than fish by 2050, you be­gin to ap­pre­ci­ate the scale we are deal­ing with.

It’s not just the ma­rine en­vi­ron­ment, a re­cent An­gler’s Mail news story (March 27, 2018) high­lighted the fact that Manch­ester’s River Tame was found to con­tain over 500,000 par­ti­cles of mi­croplas­tic per square me­tre – the high­est con­cen­tra­tion ever found. All our rivers are con­tam­i­nated by mi­croplas­tics and, ul­ti­mately, they all drain into the sea and af­fect ev­ery crea­ture in the food chain, from plank­ton to apex preda­tors.

The size and tex­ture of ar­ti­fi­cial baits is such that they will usu­ally pass through both an in­testi­nal sys­tem and a true stom­ach of any fish large enough to in­gest them in the first in­stance. In­deed, look at the size and tex­ture of some items that a carp will ex­crete whole, such as tiger nuts or cray­fish claws, and you re­alise that a small ar­ti­fi­cial bait is un­likely to cause a prob­lem.

But it is not as sim­ple as that. Small plas­tic baits may cause prob­lems with smaller species, we don’t yet know the fate of mi­croplas­tics, and there is a likely chem­i­cal in­flu­ence, too. What we do know is that stud­ies of fish in the North Sea in 2014 found no re­la­tion be­tween the con­di­tion fac­tor of the fish and the pres­ence of in­gested plas­tic par­ti­cles, but it’s early days.

Deal­ing with deep hooks

In re­spect of hooks, lab­o­ra­tory ex­per­i­ments on the im­pact of deep hook re­moval from an oe­soph­a­gus showed that fish were of­ten able to dis­card a hook af­ter a time, rather than it be­ing dis­solved away. In terms of deep hook man­age­ment, fish in which the line was cut and the hook left in place tended to show a much lower mor­tal­ity rate than fish that had been un­hooked be­fore re­turn.

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