Set-net Fishery Research Articles

Length–weight relations of underutilized nine fish species (Actinopterygii) from set-net fishery, Mie, Japan

Bycatch, the unintentional capture of non-target species, poses a significant challenge in fisheries management worldwide. Underutilized bycatch species often lack biological information, hindering the assessment of their stock status and the implementation of appropriate management strategies. This study investigated the length–weight relations (LWRs) of 9 of 14 underutilized bycatch fish species collected from set-net fisheries in Nishiki, Mie Prefecture, Japan, during the 2018–2020 fishing seasons. The following fish species were studied: Hyperoglyphe japonica (Döderlein, 1884); Labracoglossa argenteiventris Peters, 1866; Macroramphosus sagifue Jordan et Starks, 1902; Microcanthus strigatus (Cuvier, 1831); Ostorhinchus semilineatus (Temminck et Schlegel, 1843); Parapriacanthus ransonneti Steindachner, 1870; Rexea prometheoides (Bleeker, 1856); Siganus fuscescens (Houttuyn, 1782); Upeneus japonicus (Houttuyn, 1782). A total of 251 fishing operations were conducted, and the collected fish specimens were measured for length (fork length) and wet weight. Simple regression analysis was performed on the logarithm of length and weight data to estimate the LWR parameters (a, b, and R2) for each species. The estimated values of the relative growth coefficient (b) ranged from 2.862 to 3.311, and the coefficients of determination (R2) were above 0.8 for all species, indicating robust LWR estimations. Notably, five species were not previously listed or credibly described in FishBase, and four were new records for the Japanese coast. This study provides new biological information on LWRs for underutilized bycatch fish species, contributing to our understanding of their population dynamics and supporting future management efforts for sustainable fisheries and biodiversity conservation.

Classification of set-net fish catch volumes in Iwate Prefecture, Japan using machine learning with water temperature and current distribution images at migration depth

Efficient management of set-net fisheries can be achieved by predicting fish catches in advance. We aimed to estimate fish catch volumes using machine learning based on the data obtained from past set-net fisheries. We also suggested that the estimation can be conducted without the installation of special sensors, such as fish finders, sonars, and cameras, in the set nets. Therefore, a special feature of this study is the construction of a machine learning model using marine environmental images around the set net. In particular, the distribution images of water temperature and current at a certain water depth were applied to the model. In set-nets where migratory fish are caught, ocean data related to migration routes can be useful for estimation. The images used in this study included the water temperature at a depth of 100 m, absolute velocity at a depth of 50 m, and sea surface temperature for comparison. We then classified the fish catch into three classes as follows: chum salmon, yellowtail, and Japanese common squid in Iwate Prefecture, Japan. Consequently, our results achieved an accuracy of approximately 70–80% compared with the validation and test dataset with the water temperature at depths of 100 m. They showed higher accuracy than the sea surface temperature and absolute velocity at a depth of 50 m. This study indicates the usefulness of image-based classification for predicting the volumes of fish caught by set nets.

A negative trend in abundance and an exceeded mortality limit call for conservation action for the Vulnerable Belt Sea harbour porpoise population

The management and conservation of biodiversity relies on information on both the abundance of species and the potential impact of threats. Globally, one of the largest threats towards marine biodiversity is bycatch in fisheries. Under the Marine Strategy Framework Directive (MSFD), EU Member States are required to assess the status of species, such as the harbour porpoise (Phocoena phocoena), in relation to their abundance and mortality due to bycatch every six years. The Vulnerable (HELCOM) Belt Sea population of harbour porpoise has been surveyed to determine its abundance six times using dedicated aerial or ship-based line-transect distance sampling surveys. Here, we estimated the first trend in population abundance over an 18 year period (2005-2022). Using the most recent abundance estimate, we computed a mortality limit applying the modified Potential Biological Removal (mPBR) method based on the regionally agreed conservation objective to restore or maintain 80% of carrying capacity over 100 years with an 80% probability. Over the past 18 years there has been a strong negative trend (-2.7% p.a.; 95% CI: -4.1%; + 1.3%) in abundance, with a 90.5% probability. The mortality limit was estimated to be 24 animals, which the current bycatch estimates (~900 porpoises/year from the commercial Danish and Swedish set net fishery fleets, with no data from Germany and other fishery types) exceed by far. The frequency and quality of data available on abundance for this population are higher than those available for the majority of marine species. Given the observed population decline and likely unsustainable levels of bycatch, the results presented here provide a strong basis to make informed, evidence-based management decisions for action for this population. Such action is needed urgently, before the dire situation of other porpoise species and populations around the globe is repeated.

Water-Tank and Semi-Field Experimental Investigation of a Hose Net Fish-Hauling Device for Next-Generation Set-Net Fishing

The flexible fire hose and net (hose net) is a novel fish-hauling device developed for set-net fishery. The hose net is placed inside the box chamber net, air is injected from one edge of the hose net, the hoses are inflated, and the buoyancy force is increased. The net floats up gradually, cornering the fish on the other edge. In previous studies, we have conducted a series of floating-up and sinking-down experiments to evaluate the performance of the hose net in calm water. In this study, aimed at the practical implementation of the hose net fish-hauling system, we conducted a water tank experiment and a semi-field test to confirm the operation of the hose net, which was installed inside a box chamber net model. The results demonstrated that the net could float up gradually in an ideal form and stretched on the surface of the box net. The time taken to float up processes varied with the air injected into the auxiliary hose and hose net, so that the motion of the hose net could be controlled by adjusting the air at different parts of practical operation. Furthermore, semi-field trials were conducted to verify its performance in the natural marine environment and its ability to capture schools of fish. Overall, this innovative hose net fish-hauling device is expected to be valuable for next-generation set-net fishing.

Analysis of the positioning factors affecting the sustainable fishing gear-Set net

Using a passive method to catch fish, the set-net fishery is an environmentally friendly fishery posing little risk to the marine ecosystem. To date, no studies have been conducted by industry, government, or academia to formulate a set of physical selection criteria for the installation of set nets. In this study, meteorological and sea condition data were collected around existing set-net fishing grounds in Taiwan, and binary logistic regression analysis and sequential logistic regression methods were used to determine the factors that affect the installation of set nets to confirm the future development of this fishery. According to the results of binary logistic analysis and comparison of physical factors in the waters near Xiaoliuqiu, Pingtung County, Nanliao City, Hsinchu City, Qixingtan City, and Hualien City, where there are set-net fishing grounds, ocean temperature (OCT) and sea surface factors, namely, maximum wind speed (OSWm), wave (WV), air temperature (TEMP) and air pressure (PRES), are the primary factors affecting the installation of set-nets. The results of sequential logistic regression and odds ratio analysis were also used to verify the degree of influence of the determinants of these three sea areas on the nearby set-net fishing grounds. The fish catch data from the fishing grounds studied fitted very well to the examined physical factors in different regions.

An Innovative Designed Velocimeter Application for Set Net Fishery

This article is aimed at the problems encountered by the fishing ground of set nets in Taiwan when the set net operators need to work when the weather is bad at sea. We developed a velocimeter that can be placed in the ocean for a long time and change sensing directions with the flow direction. The self-designed velocimeter has advantages, such as simple operation, low cost, and easy maintenance. With wireless monitoring and an early warning system, it can monitor current velocity, flow direction, sea temperature, and displacement. The data is transmitted back to the operator through the radio transmission module as a basis for dispatching personnel to go out to sea for fishing. To prevent the set net from drifting into the open sea due to bad weather, a GPS module is used to monitor the current location of the set net. If the waves wash away the set net, the warning signal can be received the first time to prevent the floating set net from endangering the safety of ship navigation and the survival of marine life. This innovative technology aligns with SDG 14, which aims to “conserve and sustainably use the oceans, seas, and marine resources for sustainable development”.

Bycatch of short-beaked common dolphin (Delphinus delphis) in the pair bottom trawl fishery of the Bay of Biscay and its mitigation with an active acoustic deterrent device (pinger)

Bycatch of common dolphin (Delphinus delphis) in commercial trawl fisheries in the Bay of Biscay (NE Atlantic) is of concern and its mitigation a priority. Active acoustic deterrent devices (pingers) attached to fishing gear seem to be promising for bycatch mitigation, as they have demonstrated to effectively reduce cetacean bycatch in some set-net fisheries. However, the low occurrence of common dolphin bycatch in many trawl fisheries, coupled with the extensive amount of time needed to monitor them, makes it difficult to prove the effectiveness of pingers. Remote electronic monitoring (REM) systems in fisheries can substantially increase onboard observation, providing access to extensive databases to comprehensively address bycatch mitigation studies. In this study, the effectiveness of DDD®03H Dolphin Dissuasive Device (hereinafter DDD pingers) to reduce common dolphin bycatch was evaluated in a demersal pair trawler in FAO Division 27.8.c. In 195 fishing days, one of the vessels in the pair operated with a set of DDD pingers whereas the other operated without them, and the bycatch of common dolphin was monitored through the REM system. In total, 660 fishing hauls were conducted of which 223 hauls had the DDDs attached. The results showed that the DDDs reduced common dolphin bycatch by more than 90%, with both bycatch frequency and the number of individuals bycaught per haul being significantly lower. The results also showed that common dolphin bycatch in this fishery is related to factors such as the fishing zone and depth, whereas the type of net deployed, time of day and haul duration were found to not significantly affect the bycatch of this species.

Initial experiments to assess potential short-term discard survival of cod (Gadus morhua) in the Baltic Sea set-net fishery

The European Union’s landing obligation includes an exemption for species with documented high survival rates. This is highly relevant for the cod (Gadus morhua) stock in the Baltic Sea, being in a critical state. This study provides initial information on potential discard survival rates for cod (Gadus morhua) caught in trammel nets in the Baltic Sea. Catch-damage-index (CDI) and Reflex Action Mortality Predictor (RAMP) scores were used to assess fish condition immediately after capture and at the end of observation periods. A total of 61 cod were caught in eight different net fleets fished during three trials. Two cod died in the net and three cod died during the observation period from two to 10 days. The results indicate a potential in dedicating resources to cod discard survival studies.

A multi-species catch reduces risk and enhances stability in the fishery? Implications from a portfolio analysis of the Hokkaido setnet fishery

A multi-species catch reduces risk and enhances stability in the fishery? Implications from a portfolio analysis of the Hokkaido setnet fishery

An investigation of acoustic deterrent devices to reduce cetacean bycatch in an inshore set net fishery

In Europe, problems with the use of pingers on larger fishing vessels have raised the question as to whether pingers would be practical on smaller vessels, which are a large proportion of the European static net fishing fleet. In this study, four netting vessels less than 10m long used AQUAmark pingers on part of their nets off the southwest coast of Britain over a 12 month period. Boat skippers recorded ease of use. Acoustic click detectors were deployed on test and control nets to assess the response of cetaceans to the pingers. No significant practical problems, apart from premature failure of pingers, were encountered. During the study, only one harbour porpoise was bycaught, in an unpingered net. In 650 days of acoustic data from pingered and non-pingered nets, matched by location, date and boat, there was a highly significant reduction in the number of porpoise clicks recorded at nets with pingers to 48% of the number predicted from the number recorded at control nets (range 35–51%). To assess habituation, single, modified pingers that were active for alternate seven hour periods were moored below a click detector at two sites, one of which has strong tides and high levels of associated ambient noise. This study showed a stronger pinger effect at the quiet site and a much reduced effect at the noisy site. There was evidence of a period of exclusion of porpoises following pinger use that could exceed seven hours, and no evidence of habituation. Results suggest that pingers are practical on small vessels, that they reduce harbour porpoise activity around nets and are therefore likely to reduce bycatch. Easier means of detecting pinger failure are needed. Pingers should be considered as a bycatch mitigation method in small vessel fisheries using bottom set nets.

Seasonal Variations in the Fish Species Composition and Community Structures on the Eastern Coast of South Korea

The seasonal variations in the species composition of set net fisheries were investigated on the Eastern coast of Korea, from 2007 to 2008. In total, 51 species were found that were classified into 15 orders and 33 families. The water temperature of the study area was 0.1–1.8 °C in 2007 and 0.6–2.1 °C in 2008, which was higher than the average water temperature in the previous decade. The monthly variation in the number of species peaked twice, in May (spring) and November (autumn) when the water temperature increased and decreased, respectively, and the monthly variation in the number of individuals showed a remarkably high trend in winter and autumn and was mainly caused by large migratory species. Based on the cluster analysis of the 18 most dominant species with more than 0.4% of the total number of individuals, we divided the species composition and community structures into three groups: fishes with a temporary appearance (Group A), fishes with a long-term appearance (Group B), and dominant pelagic fishes appearing with a long-term appearance (Group C). We could conclude that the seasonal variation in the structure of the fish community was mainly caused by the pelagic migration of species under high water temperature conditions during the study period.

Initial experiments to assess short-term survival of discarded plaice (Pleuronectes platessa) caught in trammel nets during winter season

European plaice (Pleuronectes platessa) is a key species in commercial fisheries in the North Sea, Skagerrak, Kattegat, and Baltic Sea. The reformed European Union Common Fisheries Policy includes the possibility of exemptions from the landing obligation for “species for which scientific evidence demonstrates high survival rates”. Discard survival from set-net fisheries is poorly studied. Trials were conducted on two commercial fishing vessels over seven trips from November to February 2017–2018 in the Baltic Sea. The nylon trammel nets had a nominal bar size for the inner/outer wall of 75/350 mm and 85/400 mm. Soaking time was 23–47 h, water depth 7–18 m, and deck temperature was −0.1–6.0 °C. Following commercial practice, the trammel nets were hauled back onto the vessel, after which netting and fish passed through a net hauler onto a steel sorting table where the entire fish catch were manually untangled by the fishers and plaice collected by scientists. We used a storage system for housing the captured fish inside fishing harbours during observations. Catch-damage-index (CDI) and Reflex Action Mortality Predictor (RAMP) scores were used to assess fish condition immediately after capture and at the end of observation periods. All plaice below 40 cm were sampled with a total number of 118 individuals from 13 fleets (several nets joined together). The fish were assessed for short-term survival for 4–10 days with full survival (100%). The majority of fish exhibited no reflex impairments. Minor bruises, fraying, and net marks were frequently observed on captured fish. The overall condition of the fish did not change during observation periods.

Impact of summer moratorium on set-net fishery in Haizhou Bay, China

Impact of summer moratorium on set-net fishery in Haizhou Bay, China

Catch Composition of Set Net Fisheries during Normal Season in Sungai Sembilang Waters, Selangor, Malaysia

Highlight ResearchThe Set Net was identified and recorded.Length and weight of the catch of set net was analyzed. AbstractSet net fisheries are made according to traditional fishing gears method in the coastal waters of Sungai Sembilang, Selangor, Peninsular Malaysia. These fisheries system are the passive structure of gear used to catch fish that swim in shallow water with muddy substrate. This study focused on determining the species variety and the possible future of set net fisheries in Sungai Sembilang. Catch composition of set net was investigated based on the catch data during July to December 2020 and continued from January to February 2021. The catch data was recorded by a research assistant on site during fishing season. The data consist of species, length and weight of all catches recorded. Total catch of 60 fish species belonging to 23 families were captured during this study period. Ariidae (31.73%), Clupeidae (11.56%), and Scatophagidae (7.96%) were determined as dominant families caught this set net. The total dominant catch amount of species Plicofollis argyropleuron (18.71%), Nemapteryx caelata (9.96%), and Anodontostoma chacunda (8.92%) compromised 37.6% of the total catch. This type of fishing gear can be used by local fisherman to catch fishes and can prevent trawl net from come closer to the shore. This study would provide some general useful information about the status of set net fisheries as well as the species abundance caught from the set net.

Performance and Feasibility Study of a Novel Automated Catch-Hauling Device Using a Flexible Hose Net Structure in Set-Net

The labor-intensive catch-hauling method in set-net fisheries faces problems of lower productivity, lower efficiency, and higher operational risk due to aging problem and labor insufficiency. To solve such problems, a novel catch-hauling device using the flexible fire hose and net (hose net), which is placed in the box chamber, was proposed in this study. The hoses were inflated with air injected into one edge of the hose net, and the buoyancy force increased: the net gradually floated up, cornering the fish in the opposite edge. To corner and harvest the fish efficiently and safely, the changing formation and motion parameters of the hose net are significant. A series of floating up, sinking experiments, and catch-hauling tests were conducted to evaluate the performance of this device. The results showed that the hose net could gradually float in an ideal form and sink smoothly through natural exhaust and stretched on the bottom of the water tank. The time spent and average speeds in floating and sinking processes varied with air pressure and airflow rate, allowing the hose net motion to be controlled in practice by adjusting the airflow. Through the catch-hauling test using live fish, most of the fish were directed into the fish bag. Two main capture failure phenomena were also observed. Overall, this newly developed automated catch-hauling device is expected to be successful for use in modern fisheries.

Measures for co-existence between seals and coastal large-scale salmon set net fisheries: Mitigation of catch damage by the use of rope grid

In recent decades, conflict between Kuril harbor seals (Phoca vitulina stejnegeri) and local fisheries have become a serious problem in Hokkaido, northern Japan. Catch damage in large-scale salmon set nets may be mitigated by attaching a rope grid to set net funnels. We investigated the effectiveness of different rope grids on catch damage caused by seals, and evaluated hidden impacts on catch caused by the seals using an underwater camera for observation of seal and salmon behavior coupled with on-board observations of catch and catch damage. The rate of seal prevention was highest for rope grid with 20 cm × 20 cm spacing (97.5 %). The percentage of catch damage in the set net with this rope grid was significantly lower than that for the set net with other rope grid which was easy to enter for seals. We concluded that it is effective to attach an appropriate rope grid to set nets to prevent seals from entering fish bags and to ensure salmon catch amounts. The existence of “hidden damage” was quantitatively revealed via the underwater observation of seals removing salmon from the fish bag, and by comparing the number of salmon between underwater observation and on-board observation.

Investigating the utilization of polyethylene pipe for automated hauling system in set net fishery

The use of an automated net-hauling system using four polyethylene (PE) pipes is proposed in this study to increase the efficiency of set net fishery. In this system, the pipes are installed on the seabed beneath a box chamber net. Compressed air is injected into the first pipe at the slope net and then into the other pipes in succession. In this system, the fish are cornered between the fourth pipe and the end of the box chamber net. The performance of the system from the second to the fourth pipe is evaluated using numerical analysis, water tank tests, and field experiments. In addition, a static numerical model for the deformation of the PE pipes is developed using the theory of finite deformation and is validated by the results of the water tank and coastal sea experiments. The results show that the maximal bending stress of the full-scale pipe is about 10 MPa, which is within the allowable range of 23 MPa, indicating that the risk of pipe breakage in the automated net-hauling system is considerably low. Therefore, the automated net-hauling system developed in this study has high application value and development potential in set net fishery.

Seasonal dynamics in fish distribution and abundance revealed by an acoustic survey in coastal waters of the Suzu Area, Kochi Prefecture, Japan

For Japan's fishery, it is essential to conduct sustainable and efficient fishery owing to the decline in fish catch as well as the fisher population. To obtain information that contributes to sustainable and efficient fishery, we researched appropriate set-net locations with regard to fish distribution, abundance, and environmental characteristics. We conducted surveys from 2017/5 to 2018/2 in the Suzu coastal area, Kochi Prefecture, where the only main industry is set-net fishery. We investigated the seasonal relationships between fish school characteristics, including distribution and size, and marine environmental conditions in the Suzu coastal area, using a quantitative echo sounder (KSE300 SONIC, 38 kHz) and other devices. We observed that every season showed similar trends in the horizontal structure; fish densities were higher on the coast side, and in some seasons, these were higher at approximately 2000 m offshore. In addition, fish densities were higher in seas at depths up to 30 m. Set-net fishery is conducted in Suzu District at 300 m from the shoreand at a depth of approximately 35 m. The point of installation of set-nets is based on fish school distribution. In our study, we determined the most appropriate set-net installation points. This study not only provides a scientific basis for point selection but could also enhance the existing fishery that is limited to an aging fisher population and catch instability.

어업관리수단으로서의 어업권제도의 의의와 개편 필요성

Korea"s fishery management system is operated by managing fishery catch effort through license, permit, and reporting system. Fishery license system, also called the fishery right system, includes village fishery, set-net fishery, and aquaculture. The fishery right system, which was introduced over 110 years ago, has many problems. Evaluating in terms of fishery management, the system lacks in efficient resource allocation, fair income distribution, and effective fishing ground management. It cannot actively adapt to market changes since only the property rights of those with fishing permits are reinforced. For improvement, strict enforcement of and fishermen"s compliance with laws and regulations is necessary, and in the long run, should be changed into the fishery permit system. Since there were more problems than advantages with the fishery license system, the fishery permit system will reduce the side-effects and help achieve the purpose of fishery management.

A newly developed soft-type turtle releasing device (Soft-TRD) for setnet fisheries

This study investigated a newly developed soft-type turtle releasing device (Soft-TRD) for setnets. Some setnet fish chambers (bag nets) are open at the sea surface, while others are closed (with ceiling netting) and submerged. Sea turtles that stray into submerged bag nets often drown because the ceiling netting prevents them from swimming up to the surface to breathe. The Soft-TRD has a slit that functions as an escape outlet at the center of a 2 m × 2 m netting. The escape slit remains closed, due to the buoyancy of a float attached at each end of the slit, and prevents fish from getting out. Turtles can push the escape slit upward, which opens and allows the turtles to escape. To decide the optimum design of the Soft-TRD, a turtle releasing trial was conducted in an outdoor water tank. Four loggerhead turtles (Caretta caretta) (standard carapace length (SCL): 67.1–72.8 cm) and five green turtles (Chelonia mydas) (SCL: 42.4–63.4 cm) were used for the trial. A single turtle was placed into the experimental bag net where the Soft-TRD (six models in total) was mounted at the center part of the ceiling, and its behavior was observed. All turtles successfully escaped the model with a 150 cm length escape slit, 10 cm overlaying width, and a 4 kgf buoyancy float at each end. The escape slit immediately closed after the turtles escaped. A sea trial (same model) was also performed using a submerged bag net (30 × 10 × 10 m) for two months. Approximately 90% (seven of the eight) of the entrapped loggerhead turtles successfully escaped out through the Soft-TRD. Fishing was not interrupted by the introduction of this device. The use of the Soft-TRD would be helpful in releasing sea turtles from the setnets and contribute to sea turtle conservation efforts.