SOS#Redes
Alborán

SOS#Redes

Effects of ALDFGs

Types of fishing techniques and equipment

This section provides information on what type of instruments are used in the fishing sector and what they are used for, and explains the various fishing techniques, types of debris, and their potential effects on the marine environment and its species.

Links to further information concerning each element is found in the References and glossary section.

01. Possible Effects

Direct effects
Indirect effects

02. Fishing techniques and materials

02.1 Profesional fishing

Remains of techniques with net or mesh
Remains of techniques with hook and line

02.2 Recreative / sport fishing

Remains of equipment with line and other techniques

01. Possible effects

We distinguish between direct and indirect effects or damage that can be caused by lost or abandoned fishing gear on species, habitats and/or marine ecosystems.

Direct effects

Those effects that occur directly on marine fauna and flora, whose consequences can be observed immediately or within a short time.

Burial

Large sections of fishing gear can bury and crush habitats and/or species. In addition, and within a short period of time, this debris can prevent the buried organisms from developing their biological activities and physicochemical exchanges (for example, on seagrass and coralligenous ocean meadows) necessary for survival.

Grazing and/or tearing

Rigid species can be ripped, torn away or damaged through friction with fishing gear that is dragged or moved by currents and/or wave movement, thereby provoking the total or partial elimination of the species (for instance corals, gorgonians, bryozoans, sponges, and molluscs).

Ghost Fishing

For a time, which has yet to be estimated, abandoned gear may continue fishing, thereby sacrificing species which are not destined for the market. Moreover, larger fish, molluscs and/or shellfish can be attracted to feed on the smaller fish that have been caught, and can also become caught.

Indirect effects

Those effects caused by abandoned or lost fishing gear in the medium to long term, which is more difficult to monitor or verify.

“Priming”

Trapped fishes can become the “bait” for larger organisms. This is the basis of ghost fishing. In a recent experiment in Canada, where ghost fishing was simulated using pots targeted at a species of crab, losses due to ghost fishing were estimated at seven percent of total landings.

Bio-accumulation

Sinkers, used for fixing fishing gear to the seabed are made of lead, a heavy metal that can kill species through its toxicity or be bio-accumulated in species and even reach consumers of the fish. This issue remains to be studied.

02. Fishing techniques and materials

Fishing technique is considered as the method consisting of a set of elements used for fishing in a certain way for (a) determined species, and gear as each of the parts of which a certain fishing technique is composed. Therefore, the debris found at sea is the whole or partial remains of the gear of a particular fishing technique.

02.1. Professional fishing

This is the most important activity at regional level although perhaps not so much at local level, especially in certain locations and at a certain depth.

It is for this reason that the SOS_redes project is focused on fishing at the artisanal (non-industrial) scale: fishing also known as “coastal”. This concept has led to controversy in the latest statement of the Common Fisheries Policy of the European Union (PPC), so for us this scale fishing will be understood as that carried out by fishing vessels in which there is no more than a day of continued fishing, and there are no frozen fishery products.

With these premises, the techniques and/or fishing gear that can be found on the seabed are:

Remains of techniques with net or mesh

Techniques that capture the species with a net and/or mesh, regardless of how they work and what equipment they involve.

Purse Seine

The purse seine fishing technique consists of encircling shoals or stocks of pelagic species. The method consists of surrounding the shoal, locking it into a circle to form a kind of pocket, thereby capturing all of a large part of the shoal. In the Alboran Sea, this method is used to catch sardines, anchovies, frigate tuna, mackerel, and horse mackerel.

The purse seine is composed of the following materials, which can appear on the seabed: nets, nylon ropes, sinkers (cylindrical or conical) or a steel chain, steel rings or shackles, and buoys or floats.

This technique, with its different modalities for each area and target species, is used all along the coast of Alboran and the Gulf of Cadiz.

Trammel

Technique consisting of three overlapping netting layers; the outer two have the same mesh and the centre is thicker and larger. Thus, when the three nets are assembled together, they form “bags” in the central net, where fish are caught. This is a seabed fishing technique. Trammel fishing is based on the fish not perceiving the net and when they bump into it they push against the thick central material which forms bags from which they cannot escape. With the trammel technique, various groundfish species are caught, such as bream, plaice, cuttlefish, sole, sea bream, mullet, and sea bass. Prawns and crabs are also usually fished with this technique.

The trammel technique consists of the following materials, which can appear on the seabed: nylon net in various materials, nylon ropes, sinkers, anchor to deploy the gear, steel rings or shackles, buoys or floats.

This technique, with its different modalities for each area and target species, is used all along the coast of Alboran and the Gulf of Cadiz.

Gillnets

Similar to trammel, these consist of a single piece of net. Their use and the characteristics of the size of the mesh depend on the species to be fished. Some of the species cited in the Trammel technique are also fished with these techniques. Therefore, the debris generated is similar to that of the trammel technique.

This technique, with its different modalities for each area and target species, is used all along the coast of Alboran and the Gulf of Cadiz.

Trawling

This technique includes conical nets closed by a bag, the mouths of which expand and are dragged along the seabed, towed by a boat.

Trawling seeks to cross stocks of fish and other animals, in order to trap them inside the conical net. It catches species living on the seabed, very close to the seabed, or buried, such as hake, plaice, cuttlefish, shrimp, octopus and squid.

Trawling consists of the following materials, which can be appear on the seabed: nylon or plastic nets and ropes , steel wires, sinkers, steel chains, rings, doors or meshes of steel or iron, and floaters. This is a technique that requires great skill and ability; it cannot be used at less than 50 m depth and never on certain marine habitats, such as seagrass (marine plants) or coralline.

This technique, with its different modalities for each area and target species, is used all along the coast of Alboran and the Gulf of Cadiz.

Almadraba and Moruna

Traditional fishing techniques considered as passive fishing traps. Both are composed of a network structure (of different dimensions) located offshore to intercept the path of migratory species (tuna, bonito). The labyrinth structure, squeezed in at the bottom, forces the species to gradually move into an increasingly smaller space, where it is easier to catch.

The techniques of Almadraba and Moruna are made of the following materials, which can appear on the seabed: nylon nets, sinkers, steel cables and nylon ropes, anchors, rings, shackles and steel chains, buoys or floats.

This technique, with its various modalities for each area and target species, is used exclusively in Cadiz (Almadraba) and Almeria (Moruna).

Dragnet

A fishing technique that scrapes, turns over or scours the seabed to collect shellfish. The equipment contains an enclosed area where the species are trapped. There are manual dragnets (traction is carried out by fishermen on foot or from a boat) and mechanized dragnets (traction is performed by a boat), with obvious differences in size of materials and catches.

Dragnet techniques consist of the following materials, which can be found on the seabed: steel claws , nylon ropes, steel rods and structures, steel rings and shackles, nylon or plastic mesh or netting, of different sizes. This technique, with its different modalities for each area and target species, is used all along the coast of Alboran and the Gulf of Cadiz.

Pots

Passive fishing equipment which attract prey through bait, usually creating a structure with accessible entry but with a difficult means of exit.

There are many kinds of these traps for each type of target species (shrimp, small crab, lobster, octopus, cuttlefish).

Pots are basically composed of the following materials, which can be found on the seabed: nylon or plastic rope, wooden or iron structures, lead steel or cement weights, plastic or nylon meshes of different thickness and diameter.

These passive techniques with their various forms for each area and target species, are mainly used along the coast of Huelva, Cadiz, Granada and Almeria.

Remains of techniques with hook and line

Fishing techniques and professional gear that catch with hook and line that can potentially lose parts and end up on the seabed:

Lifting hook

Framed within the so-called minor techniques, these are hooks that, through natural or artificial bait, catch species by hooking fish in the mouth. There are several variations, with a single hook and line or with several lines and hooks attached to a main line. This technique can also be used at the bottom, remain vertical or horizontal (longline), or be moving from a boat (trolling).

With these techniques, many (normally very specific) species are caught depending on the size of the hook, type of bait and method of fishing. These include bream, sharks and rays, tuna, mackerel, and grouper fish.

The different forms of these minor techniques are essentially composed of the following materials, which can be found on the seabed: nylon and plastic ropes, sinkers and weights, rods and crowns of steel or lead, fishing lines of different thicknesses and lengths (some of hundreds of metres) and stainless steel hooks highly diverse in thickness and length. This technique, with its different modalities for each area and target species, is used all along the coast of Alboran and the Gulf of Cadiz.

Octopus traps

The remains of other types of fishing equipment that can damage biodiversity may be found on the seabed: examples include octopus traps (plastic or clay pots that are placed on the seabed and tied with a rope to catch octopus).

This technique is used all along the Gulf of Cadiz and the coasts of Málaga.

02.2. Recreative / sport fishing

Significant at local level and highly concentrated in certain areas; the remains of this type of fishing gear is also highly visible and detectable by recreational divers.

Remains of equipment with hook and line

Rod fishing (from a boat and from land).

There are a multitude of variants according to the species to be caught, but its components are essentially: nylon fishing lines (of different lengths and thicknesses), hooks, sinkers, etc., which can frequently appear on the seabed, and accumulate in rocky areas, which tend to hitch hooks and lines.

Other fishing techniques

Spear fishing, is a poorly regulated recreational fishing technique with numerous little-known effects (destruction of coralline, reduced fry, fishing for protected species or in forbidden zones and seasons) in addition to the possible loss of materials. The method is based on the projection of a harpoon or spear with a firing mechanism that spears through the prey, with the help of a rubber sling or compressed air.

Both the harpoon and the materials employed in its projection may become detached (accidentally or voluntarily), and end up on the seabed.