**1. Introduction**

Plastic pollution in the sea is a widespread problem that has gained much focus recently. One of the most prominent sources of this pollution is fishing gear accounting for about 18% of the total marine plastic debris [1]. This plastic pollution causes lots of damage to the wildlife in and around the oceans. Some review papers discussing this damage are [2–8]. Furthermore, several studies have reported on the occurrence of microplastics in marine animals from the Middle East [9], Europe [10–15], Asia [16], South America [17], Africa [18], and Australia [19].

This chapter reports the plastic pollution caused by fishing gear during ordinary fishing activities, that is, wear and tear from the plastic ropes due to sea bottom contact and abrasion caused by the hauling equipment. Modern fishing gear is composed of different plastics, with polyethene (PE), polypropylene (PP), and polyamide (PA) being the most widely used [1]. These plastic ropes are worn during everyday use and regularly replaced when the wear gets too high. The amount of microplastics originating from fisheries is difficult to estimate, and the literature reports very little on the subject. However, a recent report from the University of Plymouth states that the total number of microplastic fragments in the oceans originating from the use of fishing gear in the United Kingdom can range from 326 million to 17 billion pieces annually [20]. Another study from the University of Alicante shows that the concentration of microplastics in

marine sediments on the coast of Spain is higher close to the three coastal fish farms investigated [21]. There are also other sources of plastic pollution caused by fishing that we do not consider, such as lost and abandoned gear that remains in the ocean indefinitely. Lost and abandoned gear causes severe problems, such as ghost fishing [22] and entanglement [2]. A recent report claims that lost and abandoned fishing gear contributes to more than 45000 tons of plastic pollution annually [23].

The objective of this chapter is to determine the number of microplastics in the sea originating from fishing gear globally. Due to the complexity, it must be considered a first approach, aiming for better and more accurate calculations in the future. We omit small-scale fishing and consider commercial fishing only, that is, fishers having a quota and regularly delivering catch registered in the catch statistics.
