Search

Jůza T, Blabolil P, Čech M, Draštík V, Holubová M, Kočvara L, Kubečka J, Malinovskyi O, Policar T, Rychtecký P, Říha M, Sajdlová Z, Tušer M, Vašek M. 2024. Assessing the efficacy of spring stocking of pikeperch (Sander lucioperca) into a eutrophic reservoir. Lake Reserv Manage. 40:196–204. The survival of stocked fish is one of the crucial problems of management measures. In April 2023, approximately ten thousand 1-yr-old pond-reared pikeperch fry were marked and stocked into the small, eutrophic Hubenov Reservoir in the Czech Republic. Later that year, in August, the abundance of the stocked pond-reared pikeperch in the reservoir was estimated through beach seining, electrofishing, and gillnetting. Gillnet results showed that pikeperch avoided pelagic and deeper benthic habitats. Consequently, the most quantitative results were obtained by night beach seining. Our captures indicated that approximately 688 stocked pikeperch individuals were present in the entire reservoir in August, representing 6.5% of the stocked fish. These pikeperch displayed good growth and condition, primarily feeding on European perch fry, the most abundant 0+ fish in the reservoir. Our findings elucidate a relatively high mortality of 1-yr-old pond-reared pikeperch in the reservoir after spring stocking. Despite this mortality, the stocked pikeperch represented 85% of all 1-yr-old pikeperch in the reservoir. This highlights the effectiveness of spring stocking as a valuable tool for supporting the pikeperch population in reservoirs, emphasizing the stocking of an adequate quantity of pond-reared fish to compensate for the observed mortality. [ABSTRACT FROM AUTHOR]

Raiding seals pose a big problem to gillnet fishers in areas with high seal abundances. As moving to active gears could be a potential solution for that problem, one gear of particular interest in areas with relatively flat sea bed structure is the so-called “MiniSeine” – a demersal seine that is reduced in size so it can be operated from small vessels. Besides its ability to catch most of the species targeted by gillnet fishers, it offers various advantages compared to other active gears. To reduce the gear in size to fit on a small vessel, the present study assessed how seine rope length (4 coils vs 8 coils), seine rope diameter (18 mm vs. 22 mm) and seine net configurations of different sizes and shapes (three different designs) affect the catch efficiency and the ratio of fish below minimum conservation reference size (MCRS). In general, shorter seine ropes (4 coils) resulted in significantly lower catches than longer ones (8 coils), except for the smallest seine configuration. Larger seine net configurations and longer seine ropes caught generally less fish below MCRS, both up to around 10 %. The seine rope diameter did not affect catches significantly. As potential “adjusting screw” to counteract lower catches due to shorter seine ropes, the effect of different layout patterns of the seine ropes on the catch efficiency was assessed. Laying out the second seine rope perpendicular to the first one can increase the fishing area to more than three times while CPUE showed a tendency to be increased compared to the standard layout pattern. Besides its importance for a successful development of the MiniSeine, these findings are of equal interest for the large-scale demersal seine fishery.

As a commercial fish, bullet tuna is constantly caught in purse seine fisheries to provide economic benefits for coastal communities. Biological information such as food preference has to be known due to their sustainability in the future. This research aims to figure out the food composition and preference of bullet tuna (Auxis rochei Risso, 1810) in Prigi Coast, Trenggalek Regency East Java. A total of 294 fish landed by purse seine fishermen have been collected from March up to May 2018. Each individual was measured in its total length and weight, then was dissected for sex determination, measured the length of intestine, and analyse the stomach content. The data analysis encompasses frequency distribution of total length, relative gut length, frequency of occurrence, index of preponderance, trophic level, niche breadth, and food overlapping. The research result indicates that the main foods of Auxis rochei are fish and crustacean, while the complementary and additional foods were copepod, mollusc, annelid, and debris. Bullet tuna was a carnivorous fish with the trophic level of 3.7 and shows the existence of competition for food resources. Overlapping of feeding occurred in the 19-20 cm long group against the 23-24 cm long group in male fish and the 19-20 cm size group against the 21-22 cm length group in female fish. Bullet tuna use the same feed resources among the size groups of fish, where females use feed over a wider area than males. [ABSTRACT FROM AUTHOR]

Raiding seals pose a big problem to gillnet fishers in areas with high seal abundances. As moving to active gears could be a potential solution for that problem, one gear of particular interest in areas with relatively flat sea bed structure is the so-called "MiniSeine" - a demersal seine that is reduced in size so it can be operated from small vessels. Besides its ability to catch most of the species targeted by gillnet fishers, it offers various advantages compared to other active gears. To reduce the gear in size to fit on a small vessel, the present study assessed how seine rope length (4 coils vs 8 coils), seine rope diameter (18 mm vs. 22 mm) and seine net configurations of different sizes and shapes (three different designs) affect the catch efficiency and the ratio of fish below minimum conservation reference size (MCRS). In general, shorter seine ropes (4 coils) resulted in significantly lower catches than longer ones (8 coils), except for the smallest seine configuration. Larger seine net configurations and longer seine ropes caught generally less fish below MCRS, both up to around 10 %. The seine rope diameter did not affect catches significantly. As potential "adjusting screw" to counteract lower catches due to shorter seine ropes, the effect of different layout patterns of the seine ropes on the catch efficiency was assessed. Laying out the second seine rope perpendicular to the first one can increase the fishing area to more than three times while CPUE showed a tendency to be increased compared to the standard layout pattern. Besides its importance for a successful development of the MiniSeine, these findings are of equal interest for the large-scale demersal seine fishery., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors.)

Aquatic ecosystems are deteriorating, with the most impacted species and populations having insufficient data to inform conservation and management. Monitoring aquatic biodiversity and evaluating anthropogenic impacts typically rely on time-consuming, logistically challenging, and invasive methods (e.g., seining, trawling or electrofishing). Environmental DNA (eDNA) methods have been touted as an important advancement, especially in fish biodiversity assessment. We compare eDNA metabarcoding and seining methods along a 350 km section of the Upper St. Lawrence River (Canada) for: i) mapping the distribution of invasive and threatened fish species, ii) describing species richness and fish community structure, and iii) assessing the effect of habitat type and anthropogenic degradation of riparian zones on fish community composition and richness. eDNA detected more fish species (n = 67) than seining (n = 38) and revealed higher fish diversity in samples adjacent to intact, natural riparian zones. Fish assemblages were influenced by habitat type according to analyses using eDNA, while no effect of any environmental predictor on fish community composition was found using seining. Altogether, our results support eDNA metabarcoding as a powerful, complementary tool in fish monitoring and testing for the impacts of anthropogenic disturbances. [ABSTRACT FROM AUTHOR]

Studies dealing with invasive species usually focus on changes caused by invasion, however, natural recovery of the system after the initial population explosion (boom) has been much less studied. Ruffe dominated the benthic fish community in De Gijster Lake (Biesbosch National Park, the Netherlands) before a round goby invasion indicated by catches in both seines and gillnets. In 2012, the round goby was found for the first time and it was observed to undergo a boom in 2014, when ruffe almost completely disappeared. Nevertheless, gillnet sampling in 2016 indicated a decreasing trend in the number of round gobies and an increase in ruffe. These changes were confirmed during monitoring in 2019, when the density of round goby decreased seven times in comparison with 2014 indicated both in seine and gillnet catches. At the same time, the density of ruffe increased six times in gillnets and from zero to 396 ind/ha in seine catches. Densities of both species were clearly negatively correlated and the approximate theoretical threshold-values for coexistence of both species were estimated as 750 ind/ha in the littoral zone and 120-140 ind/1000 m² of standard CEN gillnets. Our results show the recovery of a native fish population after a natural decline of the invasive species density, which could be important when considering the management of invasive species. [ABSTRACT FROM AUTHOR]

On the upper Niger, two river sections in Mali and Guinea are affected by family and entrepreneurial seine fishing practices leading to seasonal migration phenomena. Although the physical, cultural, social and political contexts are obviously not the same, the existence of entrepreneurial fishermen, owners of large seines – the joba – in Mali and of a smaller size in Guinea – the jolé – is the result of similar processes in terms of their economic organisation and their exploitation of the river environment. The different practices of fishing with the jolé and joba seine nets are important technical indicators of the degree of cohesion and consultation between fishing villages in the same region. In fact, the study of their practices and the places where they are practised informs us of the state of power relations existing on the river and the management of common aquatic territories. [ABSTRACT FROM AUTHOR]

This paper considers the contribution of legal pluralism scholarship to the field of socio-technical transition studies. Making use of a case study on the changeover to ring seine fishing in India, it pays particular attention to the implications of legal pluralism – or the co-existence of multiple legal systems in a societal field – for the stability of such transitions. Ring seine fishing developed in particular niches in the 1970s to spread swiftly throughout the subcontinent, dividing the fisher population into fervent protagonists and antagonists. Arguing that socio-technical innovations are often contested and that rival parties make use of alternative legal systems to advance their rights, the paper suggests that so-called regimes function as arenas for deliberating and battling alternative futures in fishing. Rather than creating stability for a particular socio-technical transition, such regimes may actually mask deep socio-legal divides. [ABSTRACT FROM AUTHOR]

This study identifies differences in vessel efficiency amongst purse seiners in Vietnamese fishery. Deterministic data envelopment analysis (DEA) was used to assess relative capacity utilisation of each vessel, and double bootstrap DEA was adopted to overcome some of the drawbacks of nonparametric DEA. The study was based on a survey of costs and earnings from 52 purse seiners in 2016, revealing an average vessel profit margin of 11%. By adopting double bootstrap DEA while assuming variable returns to scale, mean capacity utilisation was found to be 0.72 (with 95% confidence interval from 0.67 to 0.79). This indicates that to sustain the current catch levels, expected inputs should be reduced by 21-33%. The study shows that vessel size, fishing experience, and family size of skippers, all are factors affecting the capacity utilisation. [ABSTRACT FROM AUTHOR]

Light seine fishing, one of the most efficient methods used in modern fisheries, is performed based on fish phototaxis. In this study, the East China Sea was selected as the study area, and fishing vessel pixels (pixels representing light seine fishing vessels) were detected in five years of Visible Infrared Imaging Radiometer Suite (VIIRS) day/night band (DNB) imagery according to three indicators: the Spike Median Index (SMI), Sharpness Index (SI), and Spike Height Index (SHI). Subsequently, cluster, barycenter, range and direction, and density analyses were conducted to comprehensively evaluate the spatiotemporal patterns of potential light seine fishing areas in the East China Sea. The following conclusions were drawn from the study: (1) the number of fishing vessel pixels exhibited obvious monthly characteristics that are consistent with the fishing moratorium that has been enforced in this region; (2) at the study area scale, light seine fishing occurred in one cluster, and the pattern in the interior of the cluster exhibited spatiotemporal periodicity; (3) the barycenter of the fishing areas displayed opposing movement trends in the first half and the second half of the year, and the movements were closely linked to water temperature changes. In addition, seasonally concentrated fishing areas were observed in winter, spring and summer; (4) the peak fishing month advanced from September to August beginning in 2014, and the fishing areas displayed a strong tendency in orientation that was highly consistent with the distribution of the Kuroshio Front in the East China Sea; and (5) light seine fishing activities were mainly concentrated in the second half of the year, especially in summer, but the intensity has declined in recent years. Our results are in good agreement with the results of other scholars and provide reliable information concerning where and when light seine fishing occurs. These results also suggest that VIIRS DNB imagery can be effectively used to detect light seine fishing areas. [ABSTRACT FROM AUTHOR]

Productivity-susceptibility analysis (PSA) is a widely used data-limited method to assess the relative vulnerability of species impacted by fisheries. Despite its widespread use, few authors have evaluated the impacts of attribute weightings and correlation of productivity attributes that may bias species' vulnerability scores. We evaluated the PSA methodology and performed sensitivity analyses to determine the impacts of correlation among productivity attributes used in the PSA, given that several of these attributes are strongly correlated. A PSA for species caught in the eastern Pacific Ocean tuna purse-seine fishery was used as an example to assess potential bias introduced by attribute weightings and correlation of productivity attributes on species' vulnerability scores. Redundancy was observed among three pairs of attributes. We demonstrated that manipulation of attribute weightings and removal of correlated attributes did not appreciably change any species' overall vulnerability status. Our results suggest that after removal of redundant attributes, PSAs can be conducted more rapidly with fewer data inputs than previous implementations, while retaining comparable vulnerability scores. [ABSTRACT FROM AUTHOR]

Fish aggregating devices (FADs) and other floating objects (OTHs) are used in tuna purse seine fishing because they are effective in attracting tunas. The objective of this study was to describe the fish species associated with FADs and OTHs in the Eastern Indian Ocean. A total of 25 FADs were deployed during fishing surveys in March-May 2012 and March-April 2013 operated by FRV Mahidol. Fifteen deployed FADs were tracked and observed, and three OTHs with fish schools were found and recorded during the fishing surveys. A total of 15 species of fish, including three species of cartilaginous fish and 12 species of teleost fish were recorded through visual census technique, trolling line and purse seine fishing around FADs and OTHs. For tuna species, skipjack and yellowfin tunas were found around FADs and OTHs at similar frequency of occurrence, while bigeye tuna was found only around FADs. Results revealed that there was no statistically significant difference in taxa richness or frequency of occurrence of 11 species of fish between FADs and OTHs. This study demonstrated that FADs and OTHs can be used to attract tunas and also other fish species in the Eastern Indian Ocean. Among the 15 species of fish, silky shark and devil ray were considered as non-target species, which are listed on Appendix II of CITES. The findings of this study could support the establishment of subsequent conservation and management measures of the Indian Ocean Tuna Commission in reducing the impact of bycatch through the efficient use of FADs in the tuna purse seine fishery in the Indian Ocean. [ABSTRACT FROM AUTHOR]

Due to very good collaboration with one commercial purse seiner, using "Srdelara" and operating in fishing zone G, preliminary data concerning the interaction between small pelagic purse seine fishery and its predators were obtained. According to the notes taken by experience observer on-board in period from year 2013 to 2016, seems that tunas, dolphins and swordfish were the faithful companions of purse seiner fisherman with abundance of 68.6%, 22.0% and 9.4%, respectively. Although they were present all year round, their monthly pattern of appearance indicated that less tunas were recorded in May-June, more dolphins were noted from July to October while swordfish were mostly abundant in winter (January-March). Within the investigated period, slightly increasing trend of tuna and dolphins' appearance was recorded, although statistically not significant. Analysing possible correlation between purse seine catches and predator's abundances, revealed that appearance of tuna had negative impact on the catches (dispersion of schools), while realised catches in presence of dolphins were quite good so it seems that they tend to round up small pelagic fish schools. [ABSTRACT FROM AUTHOR]

Highlights • Shooting trajectories of purse seines for unassociated (FAD-free) tuna schools were predicted. • Shooting methods were proposed according to the speed of the fish school. • Shooting trajectory was suggested according to the net sinking depth. Abstract Purse seine fishing is very effective in catching large volumes of pelagic fish. In Korea, as in many other countries, it is frequently used in catching tuna, a fish with high added value. To make a successful catch in purse seine fishing, it is important to choose the initial gear shooting position and trajectory for the purse seine based on the speed and direction of the swimming fish and the speed of the ship. In the field, the initial shooting position typically depends on the experience of the captain. With increasingly strict global regulations for fish aggregating devices (FADs), greater precision in predicting the purse seine shooting trajectory is required to improve the catch success rate for unassociated (FAD-free) schools. In this study, we propose trajectories with high potential for application in purse seine fishing, based on the speed and direction of the fish school. Two distinct gear shooting methods are proposed according to the speed of the fish. The first gear shooting method is applicable for fish moving at a moderate speed and with less changes in direction; the second method can be applied to fast-swimming schools. In addition, when the depth covered by the sinker line is known through the analysis of the gear behavior, the gear shooting trajectory can be modified according to the depth of the sinker line. The results from this study may be used as a technological alternative to FAD operations by assisting in tuna resource management and reducing the capture of non-targeted species. [ABSTRACT FROM AUTHOR]

Vessel monitoring systems (VMS) represent a tool that can provide information on the spatial and temporal distribution of fishing activity and a quantitative evaluation of the fishing effort at both spatial and temporal scales. The aim of this study was to characterise the spatio‐temporal structure of the Catalan purse seiner fishing effort directed towards anchovy or sardine, which was estimated by filtering VMS data (from 2012 to 2014) by species and seasons. The results showed that the mean location of the fishing effort directed towards anchovy did not vary among the summer seasons, in contrast to the efforts in spring and autumn, whereas the mean location of the effort directed towards sardine was constant over the seasons. The concentration curves indicated that similar fishing effort patterns occurred during all seasons when directed towards sardine, whereas the effort directed towards anchovy was more concentrated in summer. The ranges of the variograms indicated that the fishing effort directed towards both species formed patches. The dimensions of these patches changed from season to season, with the smallest magnitudes during the summer seasons. In this study, a seasonal distribution pattern of the fishing efforts was recognised that adequately captured the features of the distributions of small pelagic populations. [ABSTRACT FROM AUTHOR]

Abstract A number of restrictions envisaged by Council Regulation 1967/2006 (Mediterranean Regulation, MR) have been introduced to reduce the fishing effort and the catch of juveniles in the Mediterranean Sea. A large proportion of the purse seiners of the Adriatic fleet that target small pelagic species may be using gear that does not comply with regulatory provisions. This study provides a thorough overview on Adriatic purse seine designs and fishing practices. Moreover, since no detailed information was available about their environmental impact, an ad hoc study was also performed to examine the issue in relation to Mediterranean Regulation provisions. Analysis of the technical data confirmed the vast majority of the nets used by the Adriatic purse seine fleet do not comply with regulatory provisions. However, data analysis highlighted that the technical features and operational characteristics of these fisheries do not justify the application of MR restrictions. In fact, i) spatial analysis of the fishing effort demonstrated that purse seiners operate more than 3 nautical miles off the coast, i.e. further than the area covered by the restrictions; and ii) data from sensors and video cameras documented that purse seines do not exert adverse impacts on critical habitats such as Posidonia meadows and that the groundrope impact on the seabed is so slight and short-lived as to be negligible. Moreover, the extensive changes required to make purse seines compliant with the MR would entail steep costs and would ultimately render the nets unsuitable for commercial fishing, thus involving highly negative socioeconomic consequences. [ABSTRACT FROM AUTHOR]

Fishing on floating objects (FOBs) dominates catch in tropical tuna purse seine fisheries. One frequently cited advantage of deploying GPS-monitored FOBs is that the position information can be used for directed fishing to reduce search time for tuna. However, purse seiners also fish on foreign objects for which position information is not available. It is critical to quantify the prevalence of fishing on GPS-monitored versus unmonitored FOBs to understand how they impact fishing effort and catch per unit effort. We analyzed French commercial, observer, and FOB trajectory data in the Atlantic and Indian oceans to determine how often purse seine vessels fish on GPS-monitored FOBs. Only 2.7%–20.4% of French FOB fishing sets over 2007–2013 in both oceans were made on GPS-monitored FOBs. Though increasing over time, the low percentage suggests that French vessels do not primarily use GPS-monitored FOBs to reduce search time for tuna. We hypothesize that fishery-wide FOB deployments have important collective consequences for overall fishing effort and recommend that future effort metrics should be based on fishery-wide FOB activities. [ABSTRACT FROM AUTHOR]

Recommendations and regulations regarding handling of non-target fish (i.e. bycatch) are often vague and subjective in commercial fisheries. Identifying how different components of capture influence the condition of discarded fish can help develop specific guidelines and best handling practices. Using an experimental approach, we modified the severity of capture stressors in commercial purse seine fisheries for Pacific salmon and monitored indices of injury and reflex impairment in chum salmon ( Oncorhynchus keta ), a species commonly discarded from these fisheries. Study fish were held for 5 or 10 days. Modeling of changes in injury and impairment sought to disentangle the latent effects of capture stressors and the role of sex and maturity. Thresholds in physiological responses to times (i) pursed in the net and (ii) air exposed on deck were also evaluated. Injury progressed throughout holding, was more extensive in females, and accelerated faster in less mature fish. Both crowding severity and set size (i.e. estimated number of fish caught) increased injury and impairment, effects that were exacerbated with time pursed. Physiological indicators of exhaustion also increased with time pursed and 15 min was identified as an important transition point, potentially representing the temporal limit to anaerobic exercise. The time between 1 and 3 min of air exposure was identified as being important to survival, and after 6 min of air exposure, endogenous energy stores may have become exhausted. Resulting recommendations include keeping nets loose during sorting, releasing fish prior to 15 min of being pursed, and keeping air exposure within the range of 1–2 min, or less. Additionally, females and less mature fish appear to be more susceptible to the injurious effects of capture. [ABSTRACT FROM AUTHOR]

Concerns about the ecological impact of recent increases in the use of drifting fish-aggregating devices (FADs) have led to implementation of FAD limits worldwide in purse-seine fisheries targeting tropical tunas. However, quantitative analyses supporting such management measures are needed. Analyses of observer data for purse-seine vessels operating in the eastern Pacific Ocean (EPO) during 2012–2015 were conducted. FAD fishing strategies identified in this analysis were found to vary with distance to the coast. Vessels that operated furthest offshore made a large number of FAD deployments and fished primarily on FADs they deployed themselves. Vessels that operated closest to the coast made the fewest FAD deployments and fished about equally on FADs they deployed themselves and on FADs deployed by other vessels. Independent of the FAD fishing strategy, the estimated relationship between deployments and sets was increasing but nonlinear, with a reduced rate of return beyond about 200 deployments. An analysis of the relationship between deployments and standardized catch per successful set, however, provided some support for the hypothesis that more deployments may allow vessels to optimize fishing efficiency. These results highlight the complexity of EPO FAD fishing strategies and have management implications for limits on FAD usage globally. [ABSTRACT FROM AUTHOR]

Seining is a commonly used method for sampling fishes in shallow water, but studies that rely on data collected by seining rarely include corrections based on varied capture efficiencies for species or size classes, or account for false negative errors of detection. We sampled fishes in shallow, nearshore areas of a large river using a fine-mesh seine within a blocknet to estimate capture efficiencies for age-0 and yearling-and-older (YAO) fishes, make comparisons among species (within age groups), and determine if capture efficiencies were affected by water depth and aquatic vegetation cover. We also estimated the proportions of sites that individuals were present but not detected for each species, compared estimated taxa richness and Shannon diversity index values to true values, and determined if richness estimates were affected by water depth and aquatic vegetation cover. We found that capture efficiencies of age-0 fishes were not affected by depth, but did differ among four levels of vegetation cover and these relationships differed among species. Capture efficiencies differed among YAO species (range of species-specific means = 0.17–0.93), but were not affected by vegetation cover or depth. Total abundance of age-0 and YAO fishes (summed across species) captured during the first seine haul were highly correlated with true abundance (age-0 r  = 0.96; YAO r  = 0.95) but underestimated. Species and age-specific captures from the first seine haul were also highly correlated with true abundance. Finally, proportions of false negative errors of detection were typically higher for YAO than age-0 fishes, and estimated taxa richness and Shannon diversity were correlated with true values, but generally underestimated. Numerous biotic and abiotic factors appear to drive wide variations in capture efficiencies and false negative errors of detection among species, so results from any one study are likely only applicable to particular species. However, seining is an adequate method for investigating within species or total relative abundance (summed across species) trends. Further, seining-based abundance estimates are likely adequate for identifying habitat features associated with relatively high and low catches for a given species. Therefore, seining may be an effective method for comparing these values across sites to gain insights about what types of habitat or locations are most productive for nearshore fishes. [ABSTRACT FROM AUTHOR]

Fishing activities are important for food resources and economics globally, with more than 120 million people depending on fishing for their livelihood. Fisheries management, and the related crackdown on illegal fishing has been rapidly evolving in the last several years, particularly in Indonesian waters. This is critically important because of the significant fisheries resources within the region (estimated at more than $2 billion USD per year). The changes in regulations, including a moratorium on foreign vessels and on transhipment by foreign vessels, as well as changes in legislation related to domestic vessel activities means that Indonesia is in the limelight on addressing illegal, unreported and unregulated (IUU) fishing activities. An expert group identified key behaviours by vessel operators that indicate violations of these regulations, in particular the regulations on foreign and domestic transhipment. In this paper the transhipment indicators in purse seine and long line vessels developed in the workshop are characterised, governance changes are discussed, and the perverse consequences and impacts of new policies that have recently been implemented are highlighted. [ABSTRACT FROM AUTHOR]

The higher proportion of males of the invasive round goby Neogobius melanostomus in samples from two activity selective passive fishing gears compared with one activity non‐selective fishing gear in three Dutch lakes is related to higher male locomotory activity and is a sex‐dependent trait. This difference in activity reflects the different ecology of male and female N. melanostomus. [ABSTRACT FROM AUTHOR]

Biodiversity loss is a serious issue for freshwater fishes in temperate climates and there is a need for more information in this area. A study was conducted to assess fish community changes in the littoral zone of 22 lakes over a 45 year period (compared years 1969-1979 and year 2014). To compare fish communities, historical seining records were compiled for 22 inland lakes and compared with contemporary data sampled using the same protocol. Fish abundance data analyzed using a multivariate approach identified a shift from cyprinid-dominated communities to centrarchid-dominated communities between time periods. There was no evidence to support a strong influence of invasive species on these communities, but there have been significant changes in temperature and land use around these lakes since the historical data sets were collected. This is an important contribution to our understanding of biodiversity change in North American freshwater fish communities and may influence fisheries management approaches in the future. [ABSTRACT FROM AUTHOR]

Purpose: The main purpose of this article is to assess the environmental impacts associated with the fishing operations related to European anchovy fishing in Cantabria (northern Spain) under a life cycle approach.Methods: The life cycle assessment (LCA) methodology was applied for this case study including construction, maintenance, use, and end of life of the vessels. The functional unit used was 1 kg of landed round anchovy at port. Inventory data were collected for the main inputs and outputs of 32 vessels, representing a majority of vessels in the fleet.Results and discussion: Results indicated, in a similar line to what is reported in the literature, that the production, transportation, and use of diesel were the main environmental hot spots in conventional impact categories. Moreover, in this case, the production and transportation of seine nets was also relevant. Impacts linked to greenhouse gas (GHG) emissions suggest that emissions were in the upper range for fishing species captured with seine nets and the value of global warming potential (GWP) was 1.44 kg CO2 eq per functional unit. The ecotoxicity impacts were mainly due to the emissions of antifouling substances to the ocean. Regarding fishery-specific categories, many were discarded given the lack of detailed stock assessments for this fishery. Hence, only the biotic resource use category was computed, demonstrating that the ecosystems’ effort to sustain the fishery is relatively low.Conclusions: The use of the LCA methodology allowed identifying the main environmental hot spots of the purse seining fleet targeting European anchovy in Cantabria. Individualized results per port or per vessel suggested that there are significant differences in GHG emissions between groups. In addition, fuel use is high when compared to similar fisheries. Therefore, research needs to be undertaken to identify why fuel use is so high, particularly if it is related to biomass and fisheries management or if skipper decisions could play a role. [ABSTRACT FROM AUTHOR]

This paper assesses the effect of Marine Stewardship Council certification on the allocation of fishing effort by Filipino purse seine fishers operating in the waters of the Parties to the Nauru Agreement. Targeting skipjack tuna, these purse seiners allocate effort under a vessel day scheme to either MSC certified free school fishing or non-MSC certified fishing on fish aggregating devices (FADs). Based on historical catch and price data, the optimal set of fishing activities are determined in terms of the mean and variance of fishers’ gross margin at given levels of risk aversion. The results show that MSC certification stimulates fishers to reduce their allocation of effort on non-MSC compliant FADs, and consequently convert this effort to MSC compliant free school purse seining. In general, the MSC also increases the yearly gross margin of fishers as compared to the situation without MSC certification. The MSC therefore appears to be effective to a certain extent in promoting a transition to more sustainable fishing practices. However, the results also indicate that the risk profile of fishers is a key but underexplored dimension of assessing the potential impact of MSC certification on effort allocation. [ABSTRACT FROM AUTHOR]

The shortbill spearfish (Tetrapturus angustirostris) is a rare, large pelagic fish that inhabits the tropical and temperate waters of the Pacific and Indian Oceans, and it is seldom incidentally captured by the purse seine and longline tuna fleets. It is listed on the International Union for the Conservation of Nature red list as data deficient, with the population likely decreasing. The main objective of this paper is to contribute basic knowledge of the species catch rate, spatial distribution, temporal trends, and association with different types of fishing sets. A 23-year (1993-2015) database of incidental catches was analyzed; data was gathered by the observers from the Inter-American Tropical Tuna Commission aboard vessels from the international tuna purse seine fleet in the eastern tropical Pacific Ocean. We also analyzed time series of sea surface temperature (SST) from different Niño regions, and 2 climatic indices, the Oceanic Niño Index (ONI) and the Pacific Decadal Oscillation (PDO). The database included information from a total of 422,970 sets; of these, ~1% resulted in a catch of 687 spearfish. Most incidental catches occurred in waters close to the equator (10°S to 10°N), with no apparent seasonal distribution pattern. Time-series analyses showed a significant positive trend in incidental catch (~4% per year). Weak negative correlations of incidental catches with El Niño SST and ONI suggest that spearfish prefer cool waters in zones near the Equator. The PDO seemed to be more important to spearfish than El Niño events, and it is likely playing an important role in the positive trend of incidental catches. Most spearfish catches were associated with sets made on floating objects, mainly south of the equator and west of 100°W, highlighting the oceanic behavior of this species. [ABSTRACT FROM AUTHOR]

Background. Purse seining with the use of light is among the most common fishing practices around the world, but there is lack of studies on the effect of light on the feeding of the target species in this kind of fishery and the possible consequences for other prey species. The presently reported investigation intended to provide indications on this issue by studying the diet of Atherina boyeri Risso, 1810, which is the target species of professional purse seine fishery, conducted using light in Lake Trichonis (Greece), and by comparing the acquired results with those of previous studies where the samples were taken without using light. Materials and methods. A seven-month (June through December 2014) purse seining fishing was conducted at night around two lamp rafts: 1) a traditional lamp raft producing white LED light and 2) an autonomous photovoltaic-battery-LED lamp raft producing green LED light. Stomach content analysis was conducted on 100 randomly selected specimens from each sample and the relative prey abundance and frequency of occurrence for each prey category was estimated. Calculations of predation pressure of A. boyeri upon the fish larvae of a goby, Economidichthys trichonis Economidis et Miller, 1990, were performed. Results. The study revealed the intense effect of light on the attraction and capture of prey species rarely found in previous studies, such as the larvae of the native and endangered fish E. trichonis, amphipods, and copepod nauplii. No significant differences were observed between the two light colours. A preference shift to larger prey with the increase of ontogenetic stage of A. boyeri was observed. Several thousands of pre-recruited E. trichonis larvae may be preyed upon each night around a single lamp especially during summer. Conclusion. Fishing with light may alter the dietary preference of the target fish species and even of the entire fish community. This may have serious consequences on the younger ontogenetic stages of other fish populations, especially when it coincides with their reproductive period. Considering the lack of similar field studies, the present results may stimulate analogous investigations on the effects of fishing lights in other marine and freshwater ecosystems worldwide. [ABSTRACT FROM AUTHOR]

Purse-seine vessels commonly interact with dolphins. The total number of dolphins accidentally killed in the world's purse-seine fisheries may be substantial, even if interaction rates are generally low. This paper describes an industry Code of Practice (CoP) that was established in Australian purse-seine fishery after an observer program detected high dolphin interaction rates that had not been reported in fishery logbooks. Key features of the CoP are search and delay procedures designed to prevent encirclements and release procedures that minimise mortalities. Extrapolation from observer data (3.9% of net sets observed), suggested that 449 dolphin encirclements and 423 mortalities occurred in 2004-05, the year before the CoP was established. A decade later, observer data suggest that annual encirclements and mortalities had been reduced by 87% and 97%, respectively. Searches were highly effective in detecting the presence of dolphins. Dolphins were not encircled in > 85% of net-sets made after searches determined that dolphins were absent from the fishing area. Opening the front of the net resulted in the successful release of all dolphins in > 86% of encirclement events. Discrepancies between interaction rates estimated from observer data and those recorded in logbooks have decreased over time. This study demonstrated that codes of practice that specify changes in fisher behaviour can be effective in mitigating the interactions of purse-seine fisheries with dolphins. The avoidance and release procedures documented in the CoP for the South Australian sardine fishery are simple and, if adopted in other purse-seine fisheries, could substantially reduce global mortality of dolphins. [ABSTRACT FROM AUTHOR]

There are three main types of tuna purse seine operations: setting on free-swimming schools, setting on fish aggregation devices, or setting on marine mammal associated schools. In this research, we measured sinking performance of 88 purse seine sets on free-swimming skipjack ( Katsuwonus pelamis ) schools in the western and central Pacific Ocean from October 2006 to May 2013. The sinking behavior of a purse seine is influenced by many factors (e.g. netting materials, sinker weight, length-height ratio, mesh size, purse line length, setting position, setting speed, current, wind, etc.), it may be difficult to quantify the effect these factors have on the sinking performance. A purse seine set is considered to have a better sinking performance if its purse line reaches a greater depth in a shorter time period, i.e., higher sinking speed and greater sinking depth. A generalized additive model (GAM) was used to analyze sinking depth and sinking speed under different sea conditions (current speed and direction at different layers), gear design (length-height ratio, towing line length and purse line length), and operational methods (shooting duration and setting speed). The results in this study showed that the sinking performance of a purse seine with a lower length-height ratio was better than a seine with a higher ratio, current speed at 120 m depth was the most important environmental factor affecting sinking depth of the purse seine. Sinking depth was strongly associated with length-height ratio, shooting duration and purse line length. Sinking speed was related to length-height ratio, shooting duration, current speed at 60 m, purse line length and towing line length. The sinking performance models obtained from this study can be used to predict sinking behavior in relation to operational and environmental conditions, which is essential for the success of tuna purse seine operation on free-swimming tuna schools. [ABSTRACT FROM AUTHOR]

The codend is generally presumed to be the place where the main selectivity of fish occurs in towed fishing gears, but other parts of the net have been found to contribute to the selectivity process of several invertebrate species. This means that conventional selectivity or survival studies may ignore the selectivity of net parts other than the codend for certain species. By attaching 12 small meshed collecting bags to different parts of a Danish anchor seine net and conducting normal commercial fishing activities, this study showed that there is a substantial escapement of fish and (especially) invertebrates from the forward parts of the seine net. For seven species of demersal fish, most fish escaped through the lower panel close to the codend. All invertebrate species were found in higher numbers in the collecting bags than in the codend where many organisms escaped in the lower panel of the wings or the belly. Mean levels of visible damage ranged from 1.00 to 3.25 for collected invertebrates and were similar for all gear parts. Common starfish (Asterias rubens), however, showed highest damage in the extension part of the net. [ABSTRACT FROM AUTHOR]

By focusing on a single species and multiple fisheries, this study provides a stock assessment of the Spanish mackerel caught mostly by Korean large trawl (LT), large purse seine (LPS), and large pair trawl (LPT) fisheries. We standardize the fishing efforts for the three fisheries by using a general linear model. We also employ a surplus production model, the Clarke-Yoshimoto-Pooley (CYP) model, based on the Gompertz growth function. The CYP model estimates the maximum sustainable yield, allowable biological catch (ABC), and associated fishing efforts, while a bioeconomic model is used to estimate the maximum economic yield and associated fishing efforts. Furthermore, the study analyzes the economic interactions among the LT, LPS, and LPT fisheries in the Republic of Korea. The economic analysis compares the net profits of the three different axes accruing to the three fisheries from the estimated ABC. The results show that fishing efforts to catch Spanish mackerel have recently risen in the seas of Korea; however, the stock has reduced because of overfishing. Thus, the study's findings suggest that total allowable catch management is necessary for single species and multiple fisheries in order to preserve the Spanish mackerel stock in Korea. [ABSTRACT FROM AUTHOR]

Seagrass beds are subject to numerous anthropogenic influences, including nutrient pollution, shoreline development and modification, and overfishing. Direct human impacts on seagrass though, such as through contact with boat propellers and fishing gear, remains relatively uninvestigated. Here, we use 26 years of aerial imagery and 3 years of ground surveys to explore the degree, distribution, and recovery of scarring in seagrass beds as the result of boat propellers in lower Chesapeake Bay, USA, specifically from commercial haul seine fishing activity. We find that propeller scarring is extensive, particularly on the western shore of the Bay, where pressure from haul seining is more intense. In two areas with the most intense scarring, Browns Bay and Poquoson Flats, annual total length of scars averaged 5575 and 3206 m, respectively. Despite the considerable presence of observable scarring, an individual scar generally persisted for only 2.7 years on average, implying quick recovery, aided by the diverse reproductive habits of the two seagrasses in this region, Zostera marina and Ruppia maritima. Moreover, regulations adopted by the regulary agency responsible for protecting marine habitats in Chesapeake Bay, the Virginia Marine Resources Commission, concerning the timing of haul seining in response to these findings reduced the frequency of new scars 43% at Browns Bay and 90% at Poquoson Flats since 2003. These results demonstrate that swift and decisive management action, in cooperation with relevant science, can lead to effective conservation of underwater grasses. [ABSTRACT FROM AUTHOR]

The demand for mud crabScylla serrata(Forsskål 1775) in the global market has increased, hence there is growing momentum to farm the species in Africa. Aquaculture production in Kenya and elsewhere in East Africa currently relies on juvenile seeds sourced from the wild. Wild-seed collection calls for management of the juvenile crab industry founded on knowledge of the species’ ecology, so as to achieve a sustainable seed supply and recruitment to the capture fishery. This study investigated the tidal, diurnal and seasonal occurrence of juvenile crabs in three habitats (intertidal-flat boundary zones, inside the mangroves, and in channels) in small creeks (Mida, Kilifi and Mtwapa) and Gazi Bay, on the coast of Kenya. Sampling was done with scoop nets and seining at receding tides and via burrow searches at low spring tides (day and night). Juveniles in the mangrove/intertidal-flat boundary zone were found sheltered under mangrove leaves or debris, or in shallow burrows during low spring tides, whereas at receding tides they could be seen moving out with the tide or searching for sheltering substrate or burrows. Catch per unit effort at high-abundance sites varied between 59 and 68 crabs fisher−1day−1. More juvenile crabs, sized 10–80 mm internal carapace width (ICW), occurred at night during the receding tide. Net-seining was effective in the collection of juvenile mud crabs <30 mm ICW, whereas burrow sampling was effective for gathering larger crabs. However, collection of juveniles by seining reduced the quality of the crabs caught due to frequent loss of chelipeds, as compared with retrieving individual crabs by searching burrows. Some juveniles collected in the intertidal-flat boundary-zone habitat were either in the process of moulting or had just moulted, indicating the significance of this habitat for mud crabs at this physically delicate life stage. [ABSTRACT FROM AUTHOR]

This study attempted to determine certain characteristics of the species caught in the boat seine fishery in the İstanbul Strait during the 2009–2010 fishing season, including catch composition, commercial and nontarget catch ratios, catch per unit effort (CPUE), and the length distributions of commercial species. A survey of 20 boat seine operations detected species belonging to the following 3 different taxonomic groups: 26 Osteichthyes, 2 Crustacea, and 1 Mollusca. Of all of the nontarget species, 13 were commercial, 14 were noncommercial, and only 1 was under threat. Of the total catch, the proportion of the commercial species in the nontarget catch was 31.3% and that of the discarded catch, which the fishermen did not take into account, was 2.8%. According to the Spearman rank correlation test, there was a significant correlation between the total catch and the discarded catch (r = 0.759); the size of discarded catch increased as the catch increased (P = 0.000). It was clear from the data that overfishing was seen in the commercial species. [ABSTRACT FROM AUTHOR]

Demersal Seining is an active fishing method applying two long seine ropes and a seine net. Demersal seining relies on fish responding to the seine rope as it moves during the fishing process. The seine ropes and net are deployed in a specific pattern encircling an area on the seabed. In some variants of demersal seining the haul-in procedure includes a towing phase where the fishing vessel moves forward before starting to winch in the seine ropes. The initial seine rope encircled area, the gradual change in it during the haul-in process and the fish's reaction to the moving seine ropes play an important role in the catch performance of demersal seine fishing. The current study investigates this subject by applying computer simulation models for demersal seine fishing. The demersal seine fishing is dynamic in nature and therefore a dynamic model, SeineSolver is applied for simulating the physical behaviour of the seine ropes during the fishing process. Information about the seine rope behaviour is used as input to another simulation tool, SeineFish that predicts the catch performance of the demersal seine fishing process. SeineFish implements a simple model for how fish at the seabed reacts to an approaching seine rope. Here, the SeineSolver and SeineFish tools are applied to investigate catching performance for a Norwegian demersal seine fishery targeting cod (Gadus morhua) in the coastal zone. The effect of seine rope layout pattern and the duration of the towing phase are investigated. Among the four different layout patterns investigated, the square layout pattern was predicted to perform best; catching 69%-86% more fish than would be obtained with the rectangular layout pattern. Inclusion of a towing phase in the fishing process was found to increase the catch performance for all layout patterns. For the square layout pattern, inclusion of a towing phase of 15 or 35 minutes increased the catch performance by respectively 37% and 48% compared to fishing without a towing phase. These results highlights the importance of the selected seine rope layout pattern and the duration of the towing phase when fishermen try to maximize the catch performance of their fishery. To our knowledge this is the first time the combination of models for the physical behaviour of seine ropes and for fish behaviour in response to seine rope movements have been applied to predict catch performance for demersal seining. [ABSTRACT FROM AUTHOR]

Balancing sustainability and conservation concerns with the socioeconomic needs of small-scale fishers is a dilemma that is commonly faced by fisheries managers. In this paper, we present a case study on managing the developing small-scale purse seine (or ring net) fishery introduced to Kenya by migrant fishers. The fishery, which primarily targets coastal pelagics in offshore waters, was deduced to have the potential of reducing fishing effort on nearshore demersal reef fish stocks while enhancing fisheries production and fisher livelihoods. The expanding fishery elicited much controversy resulting in resource use conflicts related to gear competition and concerns about the environmental impacts of the gear. We detail the consultative planning process that was undertaken to develop a gear-based management plan spanning over 10 years from 2004 to 2016. We briefly document the catch dynamics and evolution of the fishery, and further detail the challenges and key outcomes of the decision-making process. Regulatory measures agreed by stakeholders include restrictions on gear dimensions as well as spatial restrictions defining the distance and depth of operation. Effective implementation and enforcement of the measures will require collective action from all stakeholders. Future considerations should focus on harmonization of proposed measures in transboundary areas. [ABSTRACT FROM AUTHOR]

This study compares the effectiveness and representativeness of electrofishing, snorkelling, seining, baited lift netting, multi-mesh gillnetting, baited fish traps, fyke netting, angling and longline fishing, considering three typical lentic flood-plain habitats at different times of day. Electrofishing was by far the most effective method yielding highest species richness, species trait representation and catch per unit of effort ( CPUE), followed by seining. For single species like dace Leuciscus leuciscus, European ruffe Gymnocephalus cernua, common bream Abramis brama and silver bream Blicca bjoerkna, seining was more effective than electrofishing. With both methods, some species were more consistently caught during night, dusk or dawn than during daylight. All other methods tested cannot be generally recommended for fish community assessments in shallow backwaters due to their low representativeness of species inventory and generally low CPUE. Based on these results, electrofishing of 30 m transect replicates at different times of day for monitoring the fish community in shallow backwaters, can be recommended, enabling the maximum possible comparability to adjacent river habitats. Seining should be considered as an alternative if accessibility of habitats is restricted or electrofishing is prohibited. The 25 species detected in the backwaters also suggest that these habitats contribute a large proportion of fish diversity and should be included in standard assessments of river ecological status. [ABSTRACT FROM AUTHOR]

Many capture fisheries worldwide have declined sharply in recent decades or have already collapsed from overfishing, and major fishing grounds are concentrated in zones threatened by pollution, habitat, and coastal zone modification. In Portugal, the European pilchard or sardine (Sardina pilchardus), which is mainly captured by purse seiners (∼98%), is among the species most consumed (along with dried and salted cod), and commercially, it is the most important fish landed in national ports. Besides its consumption as fresh, canned sardine stands out among Portuguese seafood major exports. Although sardine has neither total allowable catch (TAC) nor quota, the Portuguese catch limits for sardine are regulated by the International Council for the Exploration of the Sea (ICES) at the request of the European Union (EU). Therefore, in practice, the ICES advice works as a theoretical TAC. The aim of this article is to diagnose the current state of sardine stocks in the areas where the Portuguese seine fishing is exerted and simultaneously assess if the structural changes induced on the purse seining fleet capacity, in response to the management system currently in force for this fishery, are aligned with its sustainable development. Our major findings conclude that sardine stocks are still exploited at levels that jeopardize the Maximum Sustainable Yield (MSY). Once the unavoidable restructuring of the Portuguese purse seine fleet will inevitably increase unemployment among fishers, we also stress the need to reshape the current Community-Led Local Development (CLLD) program, funded under the EU fisheries structural aid, to make it more effective in minimizing the severe social impacts potentially coming out. [ABSTRACT FROM AUTHOR]

Tuna fisheries catch over three million tonnes of skipjack tuna (Katsuwonus pelamis) each year, the majority of which come from purse-seine vessels targeting fish associated with man-made fish aggregating devices (FADs). A significant challenge for fisheries management is to maximize the efficiency of skipjack tuna catches whilst minimizing the bycatch of small and immature bigeye (Thunnus obesus) and yellowfin (T. albacares) tuna, for which long-term sustainability is uncertain in 75% of the world’s stocks. To better manage the issues common with this fishing method, an improved understanding of tuna behaviour around FADs is necessary. We probabilistically classified the vertical behavioural patterns of 50 bigeye and 35 yellowfin tuna (mean fork length 72cm and 70cm, respectively) electronically tagged throughout the western and central Pacific Ocean into shallow and deep states, using a state-space modelling approach. The occurrence of surface-association behaviours, defined as an individual remaining in a shallow state for 24-hours, was examined in relation to known capture events and FAD density. In general, surface-association events for both species were short and lasted on average less than three days, although events as long as 28 days were observed, and were more common in yellowfin when in archipelagic waters. Events were longest immediately following tagging in 62% and 17% of bigeye and yellowfin, respectively. Surface-association behaviour was not generally estimated just prior to recapture, being either non-existent or shorter than two days for 85% of bigeye and 74% of yellowfin. Current management measures in purse-seine tuna fisheries involve periodic or spatial closures for FAD use. If the chief benefit to purse-seine fishers of surface-association around floating objects is in locating schools in horizontal space at short-term time-scales, rather than holding fish near the surface for extended periods, controlling the number of sets made on FADs should be explored further as an additional management tool. [ABSTRACT FROM AUTHOR]

An experimental study was conducted to assess the physical and biological impacts of muddy fine sand dredged material dumped on a medium sand site Machu offshore the Seine Estuary. Complementary trophic web modelling tools were applied to the Machu ecosystem to analyse the effects of dumping operations. Results show that, after the dumping operations, the biomass of fish increased while invertebrate biomass remained relatively stable through time. Nevertheless, the biomasses of benthic invertebrates, omnivores/scavengers and predators showed some increases, while non-selective deposit feeders and filter feeders decreased. At the ecosystem level, results show that the total ecosystem activity, the ascendency and the overall omnivorous character of the food-web structure increased after dumping operations, whereas recycling subsequently decreased. Finally, the fine and medium sand habitat offshore from the Seine estuary, which undergoes regular natural physical perturbations, shows a high resilience after a short dumping phase. [ABSTRACT FROM AUTHOR]

Multi-beam sonar is commonly used in purse seine fishing to visually evaluate school size and biomass. However, quantitative analyses of the across-beam school dimensions may provide more accurate estimates of school volumes. These may help fishers improve their estimates of fish biomass prior to setting a purse seine set; and assist scientists to more accurately assess the distributions and abundances of pelagic schooling fishes. Fish-school volumes are evaluated using data from a simulated Simrad SX90 sonar. The accuracy of the estimates is dependent on the number of ensonifying beams, and therefore dependent on the school size and range from transducer. We present two models, derived through simulations, to correct for distortions of the target dimensions, both horizontally and vertically. The corrected school heights and widths have precisions of 8.5-10.5% vertically and 6.6-8.7% horizontally. [ABSTRACT FROM AUTHOR]

Danish seining (or anchor seining) is a fishing technique that is gaining increasing attention because it is considered to be a fuel-efficient fishing method with low environmental impact. However, scientific documentation of the selectivity characteristics of Danish seines is lacking, and the gear generally is grouped with bottom trawls and Scottish seines in fisheries management legislation. In this study, we developed a codend cover to estimate the selectivity of a standard commercial Danish seine codend for four fish species. The data for the dominant species, dab ( Limanda limanda ) and plaice ( Pleuronectes platessa ), was best described by models that combine two or three logistic models, which indicated that more than one selection process was at work. Selectivity of cod ( Gadus morhua ) was best described by a Richard curve and selectivity of red gurnard ( Chelidonichthys lucernus ) by a logistic curve. The estimated selectivity curve of dab indicated, contrary to cod and plaice, low retention of individuals below MLS. Confidence limits for larger length classes of cod and red gurnard were relatively wide. For plaice, the estimated selection factor, which is the length with 50% retention divided by mesh size, was comparable to literature values from trawl studies. The average value for cod was similar for Danish and Scottish seines, but lower for trawls. The results are discussed in the context of fisheries management with focus on the landing obligation of the new Common Fisheries Policy. [ABSTRACT FROM AUTHOR]

Mobulid rays are protected in New Zealand, but the spinetail devilray Mobula japanica is caught as bycatch in skipjack tuna purse seine fisheries., Between 2005 and 2014, rays were recorded in 8.2% of observed purse seine sets. Rays were caught during summer, with a 'hotspot' (24.3% of sets) near the shelf edge off North Island over seabed depths of 150-350 m. Rays were usually brailed aboard with the tuna catch from successful sets, but were often entangled in the bunt of the net during unsuccessful sets., Observers tagged nine rays with popup archival tags to obtain preliminary information on their post-release survival, and spatial and vertical movements. Seven of the nine tags reported data, and four of those rays died within 2-4 days of release. All four rays that died had been brought aboard entangled in the bunt. The three surviving rays were all brailed aboard with the tuna catch., One surviving ray remained near New Zealand for 2.7 months during summer, and the other two migrated 1400-1800 km northward to tropical waters near Vanuatu and Fiji at minimum speeds of 47 and 63 km day−1 at the end of summer., Archive data from one ray showed that it made regular vertical movements of 25-100 m amplitude, but spent most of its time shallower than 50 m, more so during the night (89.6%) than the day (76.6%), and mainly experienced temperatures of 18−22 °C. Dives deeper than 200 m were usually made during the day or twilight., All three surviving rays typically moved between the surface and 200-300 m daily, and reached greatest depths of 649 m, 1000 m and 1112 m, respectively, substantially exceeding the previous depth record for this species of 445 m., Recommendations are made for reducing purse seine mortality of mobulid rays by avoiding areas of high ray abundance, avoiding setting on ray-associated tuna schools, and adopting best-practice methods of returning rays to the sea from the net or vessel., Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]