Net Fishery Research Articles

Assessing the vulnerability of Elasmobranch species in the Bay of Bengal: Insights from Lakkha gill net fishery of Bangladesh

The elasmobranch population is declining in the Bay of Bengal of Bangladesh due to large-mesh gill net fishing, locally known as the Lakkha net, which primarily targets Indian threadfin (Leptomelanosoma indicum). This study was the first attempt to identify megafaunal bycatch in Lakkha fishing and assess its vulnerability using Productivity Susceptibility Analysis. A total of 40 elasmobranch bycatch species were identified, with sharks comprising 13 species from three families, while 27 rays belonged to six families, with the majority belonging to the Myliobatiformes order (60 %). Productivity and susceptibility scores were assigned to all identified species, with values ranging from 1.27 to 2.73 and 1.50 to 2.63, respectively. The target Lakkha fish exhibited the highest susceptibility score, followed by several pelagic sharks and eagle rays. Vulnerability assessment revealed that 31.7 % (n = 13) of species were highly vulnerable, while 43.9 % (n = 18) were classified as moderate, and 24.4 % (n = 10) were considered to have low vulnerability. All the high-risk megafauna species (n = 13) are classified as threatened by the global IUCN Red List. Sensitivity analysis highlighted susceptibility as a major contributor to species’ vulnerability. Alterations in susceptibility scores led to significant changes in the vulnerability status of many species. The overall data quality assessment indicated moderate data quality across species, with variability observed between productivity (76 % of species received a poor data quality score) and susceptibility attributes. However, vulnerability of these species can be reduced through adequate gear modification, shorter net deployment periods, adoption of safe discharge techniques, identification of critical habitats, and establishment of marine protected areas within this region. This study provides valuable insights into the species composition and vulnerability of elasmobranchs in the Lakkha gill net fishery, emphasizing the need for conservation measures to mitigate bycatch impacts on threatened species.

Stake Net Fishery of Central Kerala – Costs, Returns and Seasonality

Stake Net Fishery of Central Kerala – Costs, Returns and Seasonality

Identification of static netters fishing trajectories with high resolution data and their evolution in the Bay of Biscay since 2015: Potential implications for short-beaked common dolphin bycatch

Since winter 2016, an increase in strandings of small cetaceans has been recorded along the French Atlantic seaboard. This mortality, which concerns mostly the short-beaked common dolphin (Delphinus delphis), is mainly due to bycatch in fishing gears. Highly vulnerable towards this issue, this protected species is more and more threatened in the Bay of Biscay. Fine scale knowledge on fisheries practices, which are ever evolving, is paramount to address the bycatch issue. The objective of this study was to identify the individual trajectories of static netters flying the French flag and to highlight possible changes in their practices between 2015 and 2019, during the winter period. An analysis of AIS data from vessels over 15 m of length, using a clustering method (HCPC), enabled us to define a typology of the static net fishery trajectories. The possible main trajectories of static netters flying the French flag were identified. Among these, one trajectory was linear with a constant navigation path and was used by offshore gillnetters targeting hake. This trajectory increased in frequency between 2015 and 2017. This study improves knowledge on practices of passive fishing gears that present a risk of short-beaked common dolphin bycatch such as gillnets and trammel nets in the Bay of Biscay. Further analysis of AIS data from other years and fishing fleets, adding environmental data or even dolphin distribution, are needed for a full understanding of the bycatch issue and towards the implementation of efficient mitigation measures.

Characterization of small-scale net fisheries off the coast of Guyana

Characterization of small-scale net fisheries off the coast of Guyana

Evaluating dolphin interactions with bottom-set net fisheries off Southern Iberian Atlantic waters

The present study, covering 2018–2022, evaluated the cetacean interactions with a bottom-set net fishery along the mainland Portuguese Southern coast (Algarve), estimating bycatch, depredation, gear damage and net length influence on Landing per Unit Effort (LPUE). The fishery employed various métiers (gillnets - mesh sizes: < 60, 60–75, 80 and 220 mm; trammel nets - 120 inner and 640 mm outer panels). Observations from 655 hauls revealed depredation by bottlenose dolphins in 17.7 % of hauls, while bycatch (isolated events of 4 bottlenose dolphins and one common dolphin) occurred in < 1 %. Depredation typically results in heavy damage to the net and occurs throughout the year, with elevated rates observed during the spring and winter months. Depredation rates varied among métiers, being higher in gears targeting red mullet and hake. The impact of depredation on LPUE varied based on net length and the targeted fish species. However, when comparing LPUE in hauls without depredation, there was no significant influence on the total and hake LPUE for nets shorter or longer than 6 km (p > 0.05). Interestingly, in hauls targeting red mullets without depredation, nets shorter than 6 km had a significantly higher LPUE (p < 0.01) compared to nets 6 km or longer, suggesting that longer nets increase fishing effort due to prolonged soaking times and a higher likelihood of depredation.

Disappearing fish: Grey seal depredation in a Baltic net fishery

Grey seals (Halichoerus grypus) in the Baltic Sea commonly attempt to steal fish captured in net fisheries. Seal depredation reduces economic yields for small-scale net fishers in a region already highly impacted by the collapse of important fish stocks. Visible damages in looted nets consist of injured fish with bite marks, or holes in the gear, but additional losses from seals eating entire fish without leaving a trace can often remain unnoticed. In this study, we estimated the daily rates of injured and of stolen fish in a commercial gillnet fishery operating off coast of Bornholm in the Central Baltic Sea in 2021–2022. Our results show that the Atlantic cod (Gadus morhua) is generally preferred over other target species [here, European plaice (Pleuronectes platessa), European flounder (Platichthys flesus), and turbot (Scophthalmus maximus)]. Although the observed ratio of 5.65 cods disappearing for each cod retrieved with seal bite marks is similar to a study from the 2000’s, we show that average daily cod disappearance rates are linked to the duration a gear is left soaking in the same location.

Unraveling the environmental influence on inter-annual fishery yield in a small-scale gillnet fishery under Rio de la Plata influence, South America

The study focuses on understanding the influence of the environment on the relative yields of a gill net fishery operating in San Antonio Cape, Argentina. The research was conducted during five austral warm periods covering spring to summer from 2008 to 2013, aiming to assess the potential impacts of climate change on small-scale fisheries. The hierarchical species composition of 563 fishery landings encompasses 41 registered species. Among these species, Cynoscion guatucupa, Micropogonias furnieri, Mustelus schmitti, and Parona signata were found to be dominant. The species composition showed a similarity ranging from 36.22% to 57.59%, with significant differences observed among most of the warm seasons. The Multivariate Regression Tree analysis showed that the temperature was the variable with the greatest influence on the composition of the landings. During warmer conditions (>20.4 °C), the location of the draft became a significant factor, while variation in turbidity played a role in the northern zone. In colder warm conditions (<20.4 °C), the composition differed based on the volumes of Río de la Plata discharge. Specifically, the freshwater outflow was further differentiated by depth (∼9 m) at lower volumes (<20 649 m3/s) and by turbidity at intermediate values (20 649–22 908 m3/s). The vulnerability of the fishery was explained by a combination of specific ranges of various stressors. These stressors led to significant variations in the composition of fishery landings, ultimately affecting the economic income of the fishermen. By understanding the relationship between environmental factors and fishery yields, this study provides valuable insights into anticipating the potential impacts of climate change on small-scale, vulnerable fisheries.

Age Readings and Assessment in Coastal Batoid Elasmobranchs from Small-Scale Size-Selective Fishery: The Importance of Data Comparability in Multi-Specific Assemblages

The large variation in vertebral shape and calcification observed among elasmobranch species prevents using a single method for enhancing growth bands and reading age. Further, estimating age and growth parameters can be difficult or impractical when samples are incomplete due to the bycatch of a size-selective fishery. Using a single and rapid method, age readings were obtained on the vertebrae of four batoid species, namely 53 individuals of Dasyatis pastinaca, 51 of Raja asterias, 15 of Torpedo marmorata, and 55 specimens of Torpedo torpedo, from the local small-scale trammel net fishery in the coastal waters (5–20 m depth) of the Central Tyrrhenian Sea during 2019–2021. Based on these data, a statistical routine was developed to obtain multiple estimates of age and growth parameters for incomplete samples due to size-selective fishing. The acceptable agreement between and within readers (intra and inter-reader disagreement &lt; 5%) and the rate of increase in vertebral size with body size (differently ranked across species) demonstrated the consistency of the enhancing method. The parameters estimated by the Von Bertalanffy and Gompertz growth models matched the data available in the Mediterranean Sea for the species studied, with D. pastinaca, T. torpedo, and R. asterias showing the lowest (k = 0.05–0.12), intermediate (k = 0.112–0.19), and highest (k = 0.18–0.23) growth rates, respectively, in line with the life history traits of these species. Overall, the method proved effective both in delineating band pairs in vertebrae of different species and in reliably estimating the age and growth parameters of problematic samples due to size-selective fishing. The proposed method supports the collection of comparable demographic data from other areas where similar multi-specific assemblages are bycatch of size-selective fisheries impacting potential nursery areas and other essential habitats for elasmobranchs.

Assessing nine devices to reduce bycatch in the pink shrimp Penaeus paulensis fisheries: Lessons from field experiments with fyke nets

The adoption of bycatch reduction devices (BRD) has been widely used to reduce bycatch in several fisheries worldwide, especially in trawl nets targeting shrimps. However, the efficiency of these devices has rarely been assessed in passive nets, such as fyke nets using light attraction. This study tested the efficiency of nine BRDs in a passive fyke net fishery performed in southern Brazil, targeting the pink shrimp Penaeus paulensis. The abundance of fishes, swimming crabs and shrimp was compared using the National Oceanic and Atmospheric Administration (NOAA) testing protocol across 1) three different light attraction colours; 2) two fisheye models; 3) two square-mesh models, and; 4) two grid models. A significant reduction in bycatch was recorded when using fisheye and square mesh, however it was also noticed an important reduction in target species. A reduction in total bycatch biomass was also recorded for both grid models (85 % for a grid angle of 50° and 61 % for a grid angle of 32°), with no significant reduction in target species when using grid angle of 32°. The extensive testing performed supports the ecological benefits of BRDs adoption and tools for management in small scale fisheries.

Incidental take of Giant Sea Bass in the gill net fishery

The Giant Sea Bass is an apex predator of southern California kelp forests that historically supported large commercial and recreational fisheries but whose population was drastically reduced due to overfishing. Although regulations have been in place to protect Giant Sea Bass for over 30 years, there is concern for continued allowance of their incidental take in commercial gill net fisheries. Through landing records, logbooks, and federal observer data, we examined the commercial take of Giant Sea Bass to determine the: magnitude, location, age, and disposition of catch; whether this take was incidental or targeted; and its impact on the current population. We found that Giant Sea Bass landings declined since gill netting was banned in state waters in 1994 and their overall landings decreased by 75% since becoming protected in 1981. Over time, a greater proportion of older fish was seen in the landings with an increase in mature individuals over 13 years of age since 2000. We found no evidence that commercial fishers are targeting Giant Sea Bass. On average, Giant Sea Bass were landed on 4.2% of gill net trips from 1994 to 2021. Additionally, over the past decade the majority of Giant Sea Bass landings came from only 15 permit holders, but this made up only ~2% of their total landings in pounds as these are the most active permittees, bringing in the highest landings of White Seabass or California Halibut. Assessing gill net observer data, we found the mortality of released Giant Sea Bass is high at 72%, although despite this level of mortality, multiple fishery independent sources indicate Giant Sea Bass populations are increasing, suggesting that current protection measures may be effective. Despite these findings, it is challenging to interpret the full impact of the commercial fishery on Giant Sea Bass as an accurate measure of total discards is unknown without consistent observer coverage.

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.

The dynamics of arabesque greenling fishery off south Kuril Islands

The purpose of this work was to characterize the biological and commercial indicators of arabesque greenling in the Kunashir Strait during 1998–2022.The basic material for the article was the data collected during the net fishery of arabesque greenling by the fleet of small-tonnage vessels of the Japanese fishing cooperative in the city of Rausu in the eastern (Russian) zone of the Kunashir Strait.Results: It is shown that the stock resources of arabesque greenling in the waters of the southern Kuril Islands have been declining during for a long period of time. Despite a short-term growth of catch per effort in 2018–2021, in 2022 there was again a decrease of fishery indicators. The negative trend of catch per effort is directly associated with the features of dynamics of arabesque greenling resources distributed in Kunashir Strait and in the Sea of Okhotsk waters of Hokkaido.Practical significance: The new information makes it possible to determine the current trends in total biomass changing for commercial fish and to clarify the fishery capabilities of the area in the nearest future.

Eutrophication in Lake Batur: Current status and management strategies

Lake Batur, designated as one of the National Priority Lakes in Indonesia, has experienced significant eutrophication in recent years. Waste generated from various anthropogenic activities, including agriculture, domestic, tourism, and floating net fishery (FNF), have collectively contributed to the decline in water quality and the eutrophication status of the lake. Our study aimed to evaluate the current eutrophication status of Lake Batur by analyzing the spatial and temporal variations in nutrient parameters, water transparency and phytoplankton biomass. Then we assessed strategies in controlling eutrophication in the lake using the Driving forces-Pressure-State-Impact-Response (DPSIR) framework. Currently, Lake Batur has reached mesotrophic to hypereutrophic levels. We identified that the main driving forces behind these concerning conditions were the significant increase of agricultural and FNF activities, particularly since the outbreak of the COVID-19 pandemic. The main environmental pressures showed that agriculture waste was the most dominant nutrient source to the lake (93.05 % of N and 89.96 % of P loads). The state analysis indicated that high nutrient concentrations and subsequent algal growth led to oxygen depletion, resulting in mass mortality of fish, loss of amenity and tourism value, and reduced availability of clean water. Short-term and long-term strategies for effectively managing eutrophication in Lake Batur has been proposed in this study. However, the best scenario will be chosen by considering both eutrophication issue and social implications.

COMPOSITION OF THE NEW DESIGN OF PAYANG CATCHES IN MAJENE WATERS, MAKASSAR STRAIT

In this study, a new design scottish seine net was used with larger than the general size of the Scottish seine net in the research location. The purpose of this research was to analyze the total catch, species composition and the length of the catch. The study was conducted on one case of a Scottish seine net fishery unit by making a new design of Scottish seine net and then operating it with Scottish seine net fishers in the waters of Majene Makassar Strait. The parameters observed were the fish species caught and the length of each species. From the study results, it was found that the catch of 8 species of fish with total of 15,253 fish in the other bag. The species composition consisted of Shortfin scad (Decapterus macrosoma) 66.48%, Indian mackerel (Rastrelliger kanagurta) 14.42%, Rainbow runner (Elagatis bipinnulata) 7.09%, Mackerel tuna (Euthynnus affinis) 3.83%, Malabar trevally (Carangoides malabaricus) 2.39%, Unicorn leatherjacket (Aluterus monoceros) 2.29%, Skipjack tuna (Katsuwonus pelamis) 2.19% and Goldstripe sardinella (Sardinella gibbosa) 1.31%. The length of the dominant catch Shortfin scad (Decapterus macrosoma) as much as 66.48% ranged from 12.5 - 27 cm with a catchable percentage of 82.53% while Indian mackerel (Rastrelliger kanagurta) as the second highest catch was 14.42% only about 2 ,64% worth catching.

Assessing the Fishing Impact on the Marine Ecosystem of Guishan Island in the Northeastern Waters of Taiwan Using Ecopath and Ecosim

The northeastern waters of Guishan Island constitute one of the crucial fishing grounds for coastal trawl fishery in Taiwan and have been exploited for many decades. To construct the marine ecosystem and to examine the interactions among trophic levels of fisheries resources in the waters of Guishan Island, historical catch, catch composition, biological information, fishing effort, environmental data such as sea surface temperature, salinity, and nutrients were analyzed using Ecopath with Ecosim. The results indicated that the longline and drift net fisheries have a very minor incidental catch of cetaceans, with a fishing mortality (F) of 0.01 year−1 and an exploitation rate (E) of 0.03. The F and E were 0.308 year−1 and 0.617 for small skates and rays, and were 0.261 year−1 and 0.580, respectively, for small sharks. The F and E of the dolphinfish, Coryphaena hippurus, an important pelagic species, were 0.411 year−1 and 0.245, respectively. Fisheries had negative impact on major commercial species except the dolphinfish and the oil fish, Lepidocybium spp., which benefited from the reduction of their predators or competitors. The keystone species of the Guishan Island marine ecosystem is phytoplankton, which has the lowest trophic level and great biomass, and is an important energy source of the ecosystem. The influences of zooplankton and anchovy rank as second and third, respectively, with regard to the keystone species in the ecosystem due to their great biomass. Regarding the biomass of less abundant species, carangids had the highest influence followed by hairtail due to their feeding habits. The results of simulations using Ecosim indicated that the hairtail, small sharks, skates and rays, mackerels, and marine eels will benefit if fishing efforts are reduced by 30%. On the other hand, the biomass of phytoplankton, zooplankton, demersal benthivores, and shrimps will decrease due to the increase in the biomass of their predators.

Winter-autumn fishery of walleye pollock &lt;i&gt;Gadus chalcogrammus&lt;/i&gt; (Gadidae) by bottom gill nets in the Kunashir Strait in 1999–2022

Japanese gill net fishery of walleye pollock in the Kunashir Strait, also well-known as local spawning grounds of this species, has been carried out in the eastern (Russian) part for more than 20 years. The results of the fishery allow us to consider general trends in the long-term changes of the local stock in mentioned dynamic and still underexamined area on the border of the Sea of Okhotsk and the Pacific Ocean. The use of a large series of standardized catch per effort as an index of stock biomass indicates specific dynamics of walleye pollock stock biomass in the Kunashir Strait, different from the behavior in the adjacent ocean waters of the southern Kuril Islands. On the background of a long-term trend of decreasing catch per effort in the Kunashir Strait, the CPUE in the ocean waters of the islands, as well as in the southern part of the Sea of Okhotsk, demonstrates opposite trend of increase of this parameter.

Looking into the prevalence of bycatch juveniles of critically endangered elasmobranchs: a case study from pelagic longline and trammel net fisheries of the Asinara Gulf (western Mediterranean)

Bycatch of cartilaginous species is considered one of the main drivers for the dramatic declines observed in many populations. Pelagic longlines and passive nets impact many species depending on their life stage and habitat use. Here, we present an updated list of incidental catches collected through a 4-year fishery-dependent survey. We documented the bycatch of four critically endangered species, particularly 13 individuals of Isurus oxyrinchus, Prionace glauca, and Mobula mobular by longlines and one specimen of Lamna nasus by trammel nets in the Asinara Gulf (Northern Sardinia, Italy). As almost all specimens were juveniles or newborns, we explored and discussed the potential drivers explaining their prevalence in the sample. Despite our low sample size, of the four possible options discussed, the role of the Asinara Gulf as an Important Shark and Ray Area (ISRA) for large pelagic elasmobranch species is one worth considering.

Mitigating bycatch in Mediterranean trammel net fisheries using species-specific gear modifications.

Small-scale fisheries (SSF) use static gear which are thought to interact with marine ecosystems more benignly than towed gear. Despite this, trammel nets, one of the most extensively used type of fishing gear in the Mediterranean SSF, generate large amounts of discards, which can account for 25% or more of the captured biomass. Discarded organisms may include endangered or threatened species such as elasmobranchs, as well as non-commercial invertebrates that damage fishing gear or cause disentanglement delays. We evaluated various trammel-net gear modifications, including (i) the use of a guarding net attached to the footrope, (ii) increasing the length of the rigging twine between the footrope and the netting panel, and (iii) decreasing the mesh size of the outer panels. The last two modifications were successful in lowering captures of the marbled electric ray Torpedo marmorata, which is commonly discarded in the study area. Both sorts of modifications are relatively simple, their manufacturing does not represent an added cost to implement, and most importantly they do not negatively affect the catch of the target species. The current study shows that prior evaluation of the discard profile of distinct métiers is essential to accomplish species-specific gear modifications and underlines the importance of collaboration among scientists, fishers and gear manufacturers.

Pacific Lamprey and Western River Lamprey marine ecology: Insight from new ocean collections

AbstractObjectiveLittle is known about the marine ecology of anadromous Pacific Lamprey Entosphenus tridentatus and Western River Lamprey Lampetra ayresii. This information is needed to determine how marine life regulates adult abundances and to identify management actions that may benefit declining populations.MethodsTo address this deficit, we compiled historic data, collected lamprey from marine stock assessment surveys and commercial fisheries, and documented fish with Pacific Lamprey wounds.ResultPacific Lamprey were most commonly caught by midwater trawls targeting Pacific Hake Merluccius productus along the continental shelf break from northern California to northern Washington. Pacific Lamprey ranged in size from 115 mm total length (TL) and 2.9 g to 714 mm TL and 655 g (n = 1912) and were expected to represent multiple ocean ages. The vast majority (93%) of Pacific Lamprey were small (≤300 mm TL) and thus were likely in their first year in marine waters. Growth for small Pacific Lamprey was estimated as 0.37 mm/day and 0.13 g/day over the summer. Gut fullness for Pacific Lamprey was high (5.5% of body weight [BW]), but it was highly variable for larger individuals (range = 0–55% BW). Our results suggest that there is a positive relationship between calendar day and lamprey length and condition factor in most years, while the effect of latitude varies by life stage. We documented Pacific Lamprey wounds on 240 individual fish representing 16 species, of which six species are newly identified as lamprey hosts. We had comparably few records for Western River Lamprey (n = 72; mean length = 285.5 mm TL), which were primarily found in surface waters on the continental shelf from northern California to southern British Columbia.ConclusionOur results have implications for both fisheries and conservation management, including development of best practices for lamprey caught by net fisheries and the use of new marine information to inform conservation actions.

Exploring the Structure of Static Net Fisheries in a Highly Invaded Region: The Case of Rhodes Island (Eastern Mediterranean)

Experimental fishing was conducted in three different locations along the coastal marine waters of eastern Rhodes Island, Levantine Sea, Hellas, from April 2021 to March 2022 on a monthly basis. Twelve samplings with gill nets and 12 with trammel nets at each of three selected locations resulted in a total of 72 samplings. The numbers of indigenous and non-indigenous species, as well as their abundances, biomasses and frequencies of occurrence, were recorded. Overall, the samplings yielded 71 species, of which 14 were non-indigenous. The total abundance was 1879 individuals, corresponding to a fish biomass of 433.57 kg. Fistularia commersonii, Sparisoma cretense and Pterois miles exhibited the highest numbers of individuals, whereas three of the invasive alien species in the Hellenic seas, namely, F. commersonii, Lagocephalus sceleratus and P. miles had the highest biomasses. The results exhibited a strong presence of P. miles in the Rhodian fisheries as the dominant invasive species based on the examined indicators (i.e., abundance, catches and frequency of occurrence). Comparisons in regard to the collected biomass between the locations, seasons, species origins and types of fishing gear were performed. All three locations were characterized by a good ecological status based on the relationship between abundance and biomass. The results of this study contribute valuable information on the ongoing changes in small-scale fisheries in the marine waters of Rhodes Island, which is one of the Eastern Mediterranean regions most affected by biological invasions.