During the capture process of different fishing gear, fish species usually have varying behaviours that lead either to their escape or retainment (capture). The images and videos of this section show two different types of fishing gear – trawl fishing (active) and fish pots (passive). For both gears there are examples of different modifications that have varying goals.

The fish pot images (Figure 8, 9 and 10) may look very similar but are actually modifications. Figure 8 shows a fish pot with a modified pot entry – the funnel that leads to the entry is longer than other fish pots. There are many different designs to try and improve the efficiency of fish pots, for example the length or the colour of the pot entry. The response to these designs usually differs for different fish species, with some being more likely to enter a longer entry and others less likely. Another alteration that can be used to try and encourage entry to the fish pot is the addition of bait or light, which also has different effects.

Figure 9 is of a fish pot with a Fish Retention Device (FRD) made of transparent acrylic ‘fingers’ that are designed to allow easy entry and reduce possible escape. Similar to other alterations, different colours of the FRDs have been deployed (Figure 10), but these seemed to deter the fish from entering the fish pot, as many were observed to abort their entry attempt.

Research to improve the efficiency and attractiveness of fish pots has increased because they are more environmentally friendly and experience very little bycatch compared to passive or active nets. However, they currently can not match the catch of these gears, as they cover a smaller area thus have a lower chance of possible encounters with fish. Hence why different designs and visual or olfactory attractants are being tested to try and improve their catch. There is particular focus on olfactory bait due to the greater distance it can act over to attract fish.

Trawls (towed nets) can also be modified.

The first modification is the FLEX (FLatfish EXcluder), which was altered by adding a ‘window’ to the bottom panel of the net to encourage the escape of flatfish (Figure 11 and 12). From previous video footage of trawls that catch flatfish (bycatch) and cod (target) it was observed that flatfish behave in a very particular way during the capture process. This is because they seem to stay near the bottom part of the trawl net, usually in contact with the net. The FLEX in Figure 11, 12 and Video 1 is the second version, as it has an extension of the net past the window, which was not present in the first. During the first FLEX trawl it was observed that the flatfish would escape through the window but then swim back into the net. Based on this and previous behaviour it was concluded that the sudden loss of the net changed their behaviour. The second version shows that this conclusion is likely true, as the escape of flatfish increased when the ‘flying carpet’ was added, whilst there was little impact on cod capture.

Video 2 shows a modified trawl called ROOFLESS, where a section of the top panel of net was removed to encourage the escape of cod, whilst retaining flatfish. For both of these adaptations the behaviour differences of cod and flatfish during the trawl were used, as cod are observed to avoid the net and stick to the middle of trawl. Similarly, this modification increased cod escape but had little effect on the capture of flatfish. The ROOFLESS design is being tested due to new changes in cod guidelines in the Baltic Sea, which is causing some fisheries to want to try and capture flatfish instead of cod, hence the cod capture must be decreased.

By recording and classifying these behaviours using video analysis software, such as BORIS (a behavioural observation research interactive software) (Figure 13) and then analysing them using different R packages, they can be used to help make decisions about possible gear modifications to increase their efficiency and sustainability. R can also be used to create visual representations of a species behavioural sequence during the capture process and this called a behaviour tree (quantitative method) (Figure 14). The 'leafier' the tree is the more behavioural events that occurred in relation to the fishing gear. This method also considers the probabilities of a behaviour occurring, along with the probability that another behaviour may occur after the previous one (the behavioural sequence). It is used to assess the functioning of a certain gear, but it can also be used to assess the fish, for example their possible stress (observed from their behaviour). This all aids with the goal of creating energy efficient, environmentally friendly, sustainable fishing gear.