Before trying to analyse what marine products are discarded it is important to try to understand the reasons why discarding occurs. What drives the discard process ?
Fish are wasted or discarded for a number of reasons, (Clucas 1996). These may include the following:
Fish of wrong species.(Not of the target species for the particular operator).
Fish are of the wrong size. (Command too low a price on the market to be worth landing or outside the limits imposed by management for capture or landing of that particular species).
Fish are of the wrong sex(Usually where gender is important from the processing and marketing point of view).
Fish are damaged(Caused by gear or predation in nets or mis-handling etc.).
Fish are incompatible with rest of catch(Slime or abrasion could cause damage to target species).
Fish are poisonousor otherwise considered inedible.
Fish spoil rapidly(Causing problems with the rest of the catch).
Lack of space on board (Where fishing operations are successful and target species take precedence over lower value or non-target species).
High Grading(Certain attributes of a fish make it more marketable and therefore more valuable than another and the less valuable is discarded - this is often related to size).
Quotas reached(This may involve discarding of small specimens of the target species to make way for more valuable specimens of the same species for instance - which is often a reason given for high grading).
Prohibited Species(Where quotas are species-based fish may be discarded from one vessel although another vessel with a quota related to the errant species may have been able to land that same fish legally).
Prohibited Season(Where time bound constraints are made on catching particular species, specimens may be discarded if caught in the wrong season).
Prohibited Gear(A quota may be given for capture of a particular species by a particular type of gear - if the wrong gear catches the wrong fish then fish may be discarded).
Prohibited fishing grounds(Fishing ground may be closed for capture of one species but open for others - if the wrong type is caught it can be discarded).
The driving forces behind the practices of discarding can be divided into a number of categories. Crean and Symes (1994) define three main classes as follows:
a) marine biomass caught incidentally while targeting other species and discarded as sea (by-catch discards)
b) quota discards, where part of the catch is returned to the sea to comply with legal requirements relating to permitted quota entitlements of minimum landing sizes
c) pre-market selection, for example high grading, discarding of damaged fish etc.
Discards can be made because of commercial and market considerations by the operator of the fishing business - it is a business decision to discard. Within this category however there are two distinctly different types. Bycatch from shrimp trawling operations which is discarded is an example of the first type. This fish that is almost invariably of lower value than the target and the in investment in sorting preservation and processing may not be rewarded by high enough returns in the market place. Typically, if the bycatch from shrimp trawling has any value at all, it can be twenty or thirty times less valuable than the shrimp.
The other example of market considerations leading to discarding is where fish is discarded which are less valuable than others of the same species because of their size, sex or physical condition. This may be done for instance where there is anticipation of catching fish of higher value later in the fishing voyage or fishing season and in quota fisheries is referred to as high grading.
Often legislation forbids or restricts the landing of the fish and makes it more advantageous for the fishermen to discard fish in anticipation of more valuable fish being caught later against a quota system - this is a legislation reinforced high grading scenario. Where a fishing unit is allocated a quota there is an incentive to maximise the return on that quota and thus an incentive to land the higher quality and more valued fish caught resulting in the discarding of the less valuable or poorer quality specimens. Legislative discarding also occurs in multi or mixed species fisheries where quotas or total allowable catches are given which do not match the actual composition of the catch. This means that a vessel or fleet of vessels may reach the target quota or total allowable catch for one particular species in a mixed catch whilst there is still unfulfilled quota of other species. Rather than forgo the, as yet un-caught, quota the individual or fleet will continue fishing but discard fish for which the quota has been filled. Alternatively the over quota fish may be landed and enter the black market or where a ban on discarding exists it may enter the market through a formalised system specifically designed to accept "illegal fish".
Where discard and waste are associated with the capture of fish prohibited by law this may well lead to the under recording of catches and therefore difficulties with management of the fisheries concerned.
Discards occur because fishing methods and gears are not perfectly selective or because there is pressure on fishermen to catch more of the target species than they can market. Avoiding catching these unwanted individuals at an acceptable cost (be it economic or social) is a major challenge.