Every year more than 179 million tons of fish are being produced and 156 million tons of that production is used for human consumption. In one way or another, a large portion of the human population is reliant on the fishing industry [1]. To meet the demand of the ever-growing population, several methods have been utilized to catch fish shoal and the school of fishes. One of the most detrimental ways of catching these shoaling fishes is blast fishing.

Blast fishing ensures a large harvest but at the cost of degradation of the underwater habitat. Even though for the fishermen the target is the large fishes, this process also kills the small fishes and marine species [2,3,4,7,6]. This destruction of underwater habitat and marine lifeform leads to the extinction of many species and coral habitat.

Many countries have already made blast fishing illegal but the ease of available materials to produce explosives, lack of proper regulation, and most importantly basic needs and poverty has made it difficult to control this illegal fishing method [5-8]. Due to the destructive nature of this fishing method, hundreds of years of coral growth is being diminished in seconds. As a result, fishes and other animals are losing the habitat, fish eggs and larvae are dying and the underwater ecosystem is losing their natural feeding and mating environment. It is a very negative impact also in the sense that in future there will not be enough food and habitat for the fishes to reproduce and eventually that will lead to more drastic methods of fishing until there is no place to fish anymore and that will happen very quickly if we do not take any measures soon [2,4].

When an explosion occurs, a pressure wave passes through the sea, within a few meters of the area the strength of the shock wave is very high and within this radius, it kills most of the living creatures. The fishermen normally target the school of fishes, the shockwave of the explosion ruptures the swim bladder along with damaging the other internal organs. The dead and injured fishes either floats on the surface or sink to the bottom of the reef [2-4] and become easy prey to the fishermen.

This method of destructive fishing is not only harmful to the underwater habitat but also for the people whose life revolves around it. Excessive fishing in one area will essentially lead to the decline of the growth of new fishes and eventually, that will cause lots of fishermen to lose their jobs. The Fishermen using their homemade explosives also suffer from the lack of knowledge of preparing explosives property, often they lose their limbs due to the unsafe handling process of explosives [9-11]. The chemicals used in these explosives are making the water more polluted and that leads to various health issues. That is certainly creating a negative impact on tourism and ultimately that is affecting the economy [3,6].

Blast fishing or dynamite fishing has been going on for decades. North Korea, Hong Kong, Malaysia, Japan, USA, Papua New Guinea, Philippines, Palau, etc. countries have reported the event of blast fishing as early as 1900. During and after world war I and II, soldiers inspired local habitants to use explosives to catch fish and after the war ended, the local people used the abundant leftover explosives to catch fish and also educated themselves to make their version of explosives [5,6]. Mixed fertilizer with kerosene or diesel essentially creates ammonium nitrate, a very easy to prepare explosive. Plastic bottle, waterproof fuse, and cheap detonator, everything all together cost around the US $3, which can be earned back with only 10 minutes of fishing [14-16]. Acoustic data collected from one research shows that, only in Tanzanian’s coastal area, daily 318 confirmed blasts occurred within 31 days in March and April 2015 [7]. Around 70 million people’s livelihoods are married to the coastal area of the Philippines. The country’s coastline shapes around 18,000 km and coastal water cover an area of 266,000 sq km. Life here is mostly circles around fisheries [12]. The country’s fisheries Bureau estimates that, even after the decline of blast fishing due to the steps taken by the local authority, there are still thousands of big and small dynamite fishing events happening every day [13].

Many Countries have issued laws against blast fishing [5,6,7] but little progress has been made due to the nature of the crime.  Within 10 minutes of the explosion, the fishermen can catch all the fishes and move to a different location before the local authority can even realize. Groups of fishermen catch fishes in the same location until the area has no more fish to offer and they move in between locations so that it becomes difficult for the local authority to monitor their steps. They try to fish around the patrol schedule to avoid getting caught, fishermen also do blast fishing at night to avoid the parting police. If someone dares to report a complain, they are later threatened to hurl explosives in their boats. Even when the fishermen are arrested, they bribe the authority and come back. In many countries, the local authority is trying to educate the local fishermen about the effect of blast fishing, though it sometimes helps, when people are living hand to mouth, they barely can thing about the environment or the future [2]. In the Philippines, the local authority has utilized a different approach to scare off fishermen form using explosives to fish. They have placed the statue of the Virgin Mary in many places underwater across the countries coastline and have advertised the event to the locals. This event reduced the number of blast fishing as most of the fishermen are of Catholic believers and they did not want to risk their faith [14].

In this study a dedicated device has been proposed which has been designed by only using off-the-shelf components that perform all the detection making process independently. This research also proposes a low-cost opensource device with low power consumption and easily repairable compacts that will be able to run in the field independently for a stretch of 1 to 2 months.

This concept of a single board solution will greatly reduce the cost of the process and the open-source availability will ensure a regular update and improvement on the design. CBobby is designed based on the audio spectrum analysis of the underwater acoustic activity. To acquire the data a hydrophone has been chosen with a specific property of wideband frequency response (10Hz to 100K Hz) [15]. It particularly monitors four different properties of any acoustic activity to determine the probability of a blast fishing event and the hypothesis is that only by monitoring those features the device will be able to identify an underwater blast fishing activity with complete accuracy. The first property of an acoustic event that it checks, is the presence of transient change of sound level from the background (or environmental noises). If it detects any kind of transient change then it simultaneously checks the duration of the acoustic event and the audio spectrum of that incident. And in the end, it checks how often does this event occurs within a short period. As for a blast fishing event, the chances of repeatability are quite low for a particular location [8].

At this first iteration of the device, it can detect an explosion based on a controlled environment (Lab) and it can differentiate an explosion from other environmental noises such as boat engine, and propeller noise, etc. and also from the background noise of the environment. The primary goal of the research was to test the device in the Philippines, in an active region where blast fishing is quite common and where trial explosives will not be necessary to test the device. But due to the current travel restriction and potential health concerns, the field test in the Philippines was postponed to a later date. Now, the device is mostly tested in the Lab, in the Spoy Canal (Hochschule Rhein-Waal, Kleve) and the lake (SAMsDIVING, Klosterweg, Goch) with simulated explosions using underwater speakers. In this research, the performance of the device is tested based on multiple natural and man-made acoustic activities including many marine animal’s acoustic activities and six different types of underwater explosions. Other than the underwater explosions, the device was tested with Earthquake, Ice Cracking, Light Rain, Lightning, Waves on a beach, Pile Driving Impact Drop Hammer, Torpedo, Sonar, Large Commercial Ship, 50 HP Outboard Motor, Blue Whale Moans, Bottlenose Dolphin, Common Dolphin Monterey, Humpback Whale Song, Mantis Shrimp and Snapping Shrimp. The Result of those tests is promising. Although CBobby can identify a blast fishing event and differentiate it from some natural and manmade event in a simulated environment, a comparatively small dataset was used to calibrate its parameter and it still was not subjected to a long-term field test.

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