Pelagic Fish Schools Research Articles

ITSASDRONE, an autonomous marine surface drone for fish monitoring around wave energy devices

The ocean energy development is one of the main pillars of the EU Blue Growth strategy. However, while the technological development of devices is growing fast, their potential environmental effects are not well-known. The nascent status of the Marine Renewable Energy (MRE) sector and Wave Energy (WE) in particular, yields many unknowns about its potential environmental pressures and impacts, some of them still far from being completely understood. Wave Energy Converters’ (WECs) operation in the marine environment is still perceived by regulators and stakeholders as a risky activity, particularly for some groups of species and habitats. The SafeWAVE project aims to improve the knowledge on these impacts trough an Environmental Research Demonstration Strategy based on the collection, processing, modelling, analysis and sharing of environmental data collected in WE sites from different European countries where WECs are currently operating (Mutriku power plant and BIMEP in Spain, Aguçadoura in Portugal and SEMREV in France) representing different types of technology, different types of locations and different types of project scales, therefore, different types and/or magnitudes of environmental impacts. As part of SafeWAVE project, environmental monitoring plans relative to electromagnetic fields, acoustics (noise), seafloor integrity and fish communities need to be put in place. In the case of fish communities, generally speaking, any artefact located in the sea may cause an attraction effect on fish communities, especially if it is floating. In the case of Marine Renewable Energy Devices, during the operation phase, in general, the placement of any artefact in the sea can result in an attracting effect on fish communities, especially if it is floating. In order to study this possible effect, fish communities monitoring around the Penguin WEC-2 of WELLO-Oy localized in BiMEP test site with the ITSASDRONE surface drone developed by AZTI was planned. The study was designed to carry out the tunning and conditioning of the ITSASDRONE and to discover the associations between WECs and fish aggregations. Penguin WEC-2 of WELLO was removed from BiMEP test site due to an alarm of leakage. Consequently, we decided to carry out the monitoring work around the HarshLab, a floating laboratory device constructed by Tecnalia and localized also in BiMEP test site. The study allows us to validate the ITSASDRONE as a viable autonomous vehicle for fish school monitoring. It still needs some technological improvement related to navigation system, but in general, the ITSADRONE meets the objectives for which it was conceived and could be an excellent monitoring technique due to its capacity to work remotely and in near shore areas. Schools of unidentified small pelagic fish were observed distributed throughout the water column, predominantly near the bottom in the device area. But, future studies are needed to further explore the association between WECs and fish aggregations. The aim of this communication is to show the work done by an autonomous marine surface drone, ITSASDRONE, in relation to fish monitoring in BiMEP area.

Schooling of light reflecting fish.

One of the hallmarks of the collective movement of large schools of pelagic fish are waves of shimmering flashes that propagate across the school, usually following an attack by a predator. Such flashes arise when sunlight is reflected off the specular (mirror-like) skin that characterizes many pelagic fishes, where it is otherwise thought to offer a means for camouflage in open waters. While it has been suggested that these 'shimmering waves' are a visual manifestation of the synchronized escape response of the fish, the phenomenon has been regarded only as an artifact of esthetic curiosity. In this study we apply agent-based simulations and deep learning techniques to show that, in fact, shimmering waves contain information on the behavioral dynamics of the school. Our analyses are based on a model that combines basic rules of collective motion and the propagation of light beams in the ocean, as they hit and reflect off the moving fish. We use the resulting reflection patterns to infer the essential dynamics and inter-individual interactions which are necessary to generate shimmering waves. Moreover, we show that light flashes observed by the school members themselves may extend the range at which information can be communicated across the school. Assuming that fish pay heed to this information, for example by entering an apprehensive state of reduced response-time, our analysis suggests that it can speed up the propagation of information across the school. Further still, we use an artificial neural network to show that light flashes are, on their own, indicative of the state and dynamics of the school, and are sufficient to infer the direction of attack and the shape of the school with high accuracy.

Spatiotemporal Distribution of Small Pelagic Fish Schools in the Western Algerian Coast

Spatiotemporal Distribution of Small Pelagic Fish Schools in the Western Algerian Coast

Short-Range Movement Pattern of Amphidromous Lagoon Fish Schools: Ecological Applications

High-resolution multibeam sonar allows estimating movements of pelagic fish schools at short range. Taking advantage of this methodology, we calculated a Straightness Index (SI) to quantify the proportion of schools migrating actively from those residents in lagoon channels. This information enhances our knowledge of both fish school displacements and migration processes, which are essential to improve our understanding of ecosystem functioning. Most fish schools (65%) exhibited a SI value demonstrating oriented swimming behavior through the channels displayed by schools reaching the sea during fall migration. This trend appears as an intrinsic property of school movements, allowing monitoring of the school migration process in a channel to provide information for manager vs. fishing regulation measures or lagoon planning. The result strengthens the ‘multi-transit’ hypothesis, as 35% of schools show sinuous trajectories representative of schools staying in the channel or displaying high exploratory behaviors. Lastly, the fish school Exploration Swimming Speed (ESS) was tested as a fishery-independent sampling method to evaluate the proportion of different fish species monitored using hydroacoustics. This approach demonstrates the interest in using swimming behavioral characteristics of fish schools for ecological and management purposes.

SPECIFICATIONS AND OPERATIONS PURSE SEINE IN KM KARYA MAJU DISTRICT SIBOLGA

Fish landing activities in Sibolga Fishing Port are dominated by small pelagic fish, used purse seine. Purse seine is one of the most widely used fishing gear in Sibolga. The reason for the large number of fishing gears is because this fishing gear is considered to be quite effective in use and also the availability of potential to support it in carrying out its operation. Fishing using purse seine is one of the fishing methods aimed at large schools of pelagic fish. The purpose of this study was to determine the specifications of the purse seine at KM Karya Maju and to determine the method of operation of the purse seine at KM Karya Maju. The research was carried out March-April 2019 at KM Karya Maju. The purse seine specifications at KM Karya Maju consist of upper rope, lower rope, buoys, ballast rope, self edge, ring rope, ropes, buoys, sinkers, rings. The purse seine operation area is located at WPP 572, from Nias island to North Natuna. Purse seine at KM Karya Maju is operated at night, using FADs. The principle of operation of KM Karya Maju's purse seine is by circling a group of fish into a pocket- shaped net.
 
 Keywords: KM Karya Maju, Operation, PPN Sibolga, Purse seine, Specification

Development of species‐specific multiplex real‐time PCR assays for tracing the small pelagic fishes of North Pacific with environmental DNA

AbstractEnvironmental DNA (eDNA) has become a popular non‐invasive method to study the presence of organisms in the environment. To study the ecological behavior and migration routes of small pelagic fishes that are difficult to trace with traditional capturing methods, we developed multiplex real‐time PCR assays to measure the eDNA of chub mackerel, blue mackerel, Japanese jack mackerel, Japanese anchovy, Japanese sardine, and Pacific saury. To test the validity, eDNA samples collected from the water near fisherman set nets in Northeast Japan between 2018 and 2019 were analyzed. Warm‐climate species including blue mackerel, jack mackerel, and anchovy were prominent in autumn, while cold‐climate species such as chub mackerel and sardine were richly present in winter. Pacific saury is an off‐coast species and was not detected in the coastal set net area. The eDNA data were partially correlated to the fishery catch records, suggesting that the eDNA quantities are relevant to the biomass of the fish schools, and our PCR assays can quantify the biological traces left by the small pelagic fish schools. Different patterns of eDNA occurrence were observed between the chub and blue mackerels, indicating that the specificity of the multiplex assay is applicable to field samples to measure the presence of the two closely related species separately. The methods are useful to evaluate the eDNA samples collected from the open water in the North Pacific to elucidate the life cycles and monitor the sustainability of the small pelagic fishes, which not only are important food sources, but also carry a role in the Japanese food culture.

Foraging behaviour and movements of an ambush predator reveal benthopelagic coupling on artificial reefs

The behaviour of coastal fishes to new habitats and trophic opportunities provided by artificial reefs may reveal the key processes which sustain fish production at these reefs. We quantified the trophic link between benthic predators and pelagic forage fish from the movement and foraging behaviour of an ambush predator, the bluespotted flathead Platycephalus caeruleopunctatus, around an artificial reef in relation to schools of small pelagic fish. We used a network of acoustic receivers to monitor the fine-scale movements of 48 acoustically tagged flathead around 5 groups of artificial reef modules for 8 mo in conjunction with acoustic surveys of pelagic baitfish and sustained monitoring of current speed and direction. Flathead were highly associated with the artificial reef, with 44% of detections within 10 m of the modules. Flathead had a considerable degree of fidelity to the reef system, with an average residency period of 84 d yr-1 (residency index = 0.23, SD = 24 d). Low activity was recorded by accelerometers in the north-east of the artificial reef. This coincided with high densities of forage fish which were also found inside the stomachs of the flathead. Artificial reefs with high vertical relief allow planktivores to feed through more of the water column, fixing more pelagic biomass into the system. Defining the residency and trophic connectivity of fish at artificial reefs is critical to clarify the production-attraction debate and the sustainability of fishing at artificial reefs.

Effect of environmental variables on the number of births at California sea lion (Zalophus californianus) rookeries throughout the Gulf of California, Mexico

Abstract The 13 California sea lion breeding colonies in the Gulf of California (GoC), Mexico are each characterized by different population growth trends, including a variable number of births. Despite being located in a highly productive marine area, both the species’ population and the number of births have declined significantly over the past few decades. The goal of this study was to assess the effects of certain environmental variables on the number of births at colonies in three regions (northern, central and southern) of the GoC (1995–2018). Data on diet, small pelagic fish catches by fisheries, the density of small pelagic fish schools, remotely sampled values of sea surface temperature and chlorophyll‐a concentration and El Niño Southern Oscillation events were collected in order to evaluate whether these variables had an effect on the number of births using correlations and generalized linear models. No significant relationships were found between the environmental variables and the number of births. However, the number of births decreased when the sea surface temperature anomalies exceeded 1°C in the northern and central regions of the GoC. Although no significant relationships were found between the small pelagic fish catches and the number of births, positive trends were observed between sardine catches and the number of births during certain periods in the central region. A positive correlation between the density of small pelagic fish schools and the number of births suggests a possible relationship between prey availability and reproductive success in the central region. A Programme of Action for the Conservation of the Species should be promoted by the Federal Government and carried out in order to implement specific management actions. Specifically, surveillance efforts should increase, fishing gear conversion plans should be established and sea lion exclusion devices should be introduced, among other measures.

The Arctic Front and its variability in the Norwegian Sea

Abstract. The Arctic Front (AF) in the Norwegian Sea is an important biologically productive region which is well-known for its large feeding schools of pelagic fish. A suite of satellite data, a regional coupled ocean–sea ice data assimilation system (the TOPAZ reanalysis) and atmospheric reanalysis data are used to investigate the variability in the lateral and vertical structure of the AF. A method, known as “singularity analysis”, is applied on the satellite and reanalysis data for 2-D spatial analysis of the front, whereas for the vertical structure, a horizontal gradient method is used. We present new evidence of active air–sea interaction along the AF due to enhanced momentum mixing near the frontal region. The frontal structure of the AF is found to be most distinct near the Faroe Current in the south-west Norwegian Sea and along the Mohn Ridge. Coincidentally, these are the two locations along the AF where the air–sea interactions are most intense. This study investigates in particular the frontal structure and its variability along the Mohn Ridge. The seasonal variability in the strength of the AF is found to be limited to the surface. The study also provides new insights into the influence of the three dominant modes of the Norwegian Sea atmospheric circulation on the AF along the Mohn Ridge. The analyses show a weakened AF during the negative phase of the North Atlantic Oscillation (NAO−), even though the geographical location of the front does not vary. The weakening of AF during NAO− is attributed to the variability in the strength of the Norwegian Atlantic Front Current over the Mohn Ridge associated with the changes in the wind field.

Identifying small pelagic Mediterranean fish schools from acoustic and environmental data using optimized artificial neural networks

The Common Fisheries Policy of the European Union aims to exploit fish stocks at a level of Maximum Sustainable Yield by 2020 at the latest. At the Mediterranean level, the General Fisheries Commission for the Mediterranean (GFCM) has highlighted the importance of reversing the observed declining trend of fish stocks. In this complex context, it is important to obtain reliable biomass estimates to support scientifically sound advice for sustainable management of marine resources. This paper presents a machine learning methodology for the classification of pelagic species schools from acoustic and environmental data. In particular, the methodology was tuned for the recognition of anchovy, sardine and horse mackerel. These species have a central role in the fishing industry of Mediterranean countries and they are also of considerable importance in the trophic web because they occupy the so-called middle trophic level. The proposed methodology consists of a classifier based on an optimized two layer feed-forward neural network. Morphological, bathymetric, energetic and positional features, extracted from acoustic data, are used as input, together with other environmental data features. The classifier uses an optimal number of neurons in the hidden layer, and a feature selection strategy based on a genetic algorithm. Working on a dataset of 2565 fish schools, the proposed methodology permitted us to identify the these three fish species with an accuracy of around 95%.

Interaction between small pelagic purse seine fishery and its top predators

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.

Acoustic observations of the vertical distribution and latitudinal range of small pelagic fish schools in the Midriff Islands Region, Gulf of California, Mexico

Within the Gulf of California, the Midriff Islands Region (MIR) is characterized by mixing conditions of water masses that lead to high primary productivity, which fosters the presence of sardines, anchovies, and their predators. Using acoustic tools, we analyzed the presence and characteristics of schools detected in three surveys carried out in late spring of 2012 and 2013 and early summer of 2014. We sought to relate changes in the geographical distribution of schools with Sea Surface Temperature (SST) and Net Primary Productivity (NPP). The largest number of schools was observed in 2012, coinciding with the highest and most extensive NPP, while the following years were associated with lower NPP coupled with a lower number of detections. During the study period, the Ballenas-Salsipuedes Channel and its area of influence showed the lowest SST and higher NPP even toward the summer as compared to the rest of the MIR, favoring the presence of fish schools and supporting the importance of this site as a feeding center for these species. As for their vertical distribution, it was found that during the day schools reach greater depths, while during the night these are concentrated in surface waters. However, no differences in size, density, or other characteristics were detected either between periods or between years. Finally, we found a high proportion of schools during the night (61%), which departs from the typical nocturnal dispersal behavior described for similar species in other areas.

Detection of Schools of Marine Fish Using Polarization Laser Sensing

General regularities of lidar returns in the sensing of the water column containing pelagic fish schools are investigated by the Monte Carlo method. Based on results of statistical simulation of depth profiles of lidar return power and depolarization, we propose a method of polarization laser sensing of marine fish schools based on a comparison of numerical values of the lidar return power and depolarization with their threshold levels determined by the sea water extinction index in the fishery region.

Coagulation\u2013Fragmentation Model for Animal Group-Size Statistics

We study coagulation–fragmentation equations inspired by a simple model proposed in fisheries science to explain data for the size distribution of schools of pelagic fish. Although the equations lack detailed balance and admit no H-theorem, we are able to develop a rather complete description of equilibrium profiles and large-time behavior, based on recent developments in complex function theory for Bernstein and Pick functions. In the large-population continuum limit, a scaling-invariant regime is reached in which all equilibria are determined by a single scaling profile. This universal profile exhibits power-law behavior crossing over from exponent -frac{2}{3} for small size to -frac{3}{2} for large size, with an exponential cutoff.

Three dimensional observation of pelagic fish schools by multibeam echosounder ME70

In this study, three-dimensional observation of pelagic fish using a multibeam echosounder with a quantitative echosounder are discussed. Multibeam echosounder originally has been developed for bathymetry survey, transmits and receives fan-shaped acoustic beam, and has extensive search area compared with single beam conventional echosounder. SIMRAD ME70 used in this study was developed specifically for fisheries research while maintaining the characteristics of fan-shaped wide multibeam. Because the calibration software is built in the ME70 for quantitative analysis of the acoustic beams, the output data can be compared with that from the quantitative echosounder like the EK60. Therefore, the ME70 and the EK60 are installed in the R/V YOKO-MARU used in alternate transmission, and carried out the observation for the same fish schools. Echograms were obtained from both echosounders and compared in terms of differences in characteristics of these echograms. Multibeam echosounder covered a widespread area to the side way of the vessel that the conventional echosounder could not observe and allowed to express fish schools in three dimensions.

Effects of Sound on the Behavior of Wild, Unrestrained Fish Schools.

To assess and manage the impact of man-made sounds on fish, we need information on how behavior is affected. Here, wild unrestrained pelagic fish schools were observed under quiet conditions using sonar. Fish were exposed to synthetic piling sounds at different levels using custom-built sound projectors, and behavioral changes were examined. In some cases, the depth of schools changed after noise playback; full dispersal of schools was also evident. The methods we developed for examining the behavior of unrestrained fish to sound exposure have proved successful and may allow further testing of the relationship between responsiveness and sound level.

Species identification of small pelagic fish schools by means of hydroacoustics in the Eastern Mediterranean Sea

Reliable biomass estimates by means of hydroacoustics largely depend on the correct identification of acoustic targets. Data collected during five summer acoustic surveys (2004-2008) in the North Aegean Sea (Greece) were analyzed to explore effective discrimination of small pelagic fish schools according to the species they belong. Discriminant Function Analyses (DFA) using bathymetric, energetic and morphometric school descriptors as explanatory variables were applied per research cruise as well as to pooled data from all surveys. Results revealed that the schools can be successfully classified into the five species considered (anchovy Engraulis encrasicolus, sardine Sardina pilchardus, round sardinella Sardinella aurita, blue whiting Micromessistius poutassou, and Atlantic mackerel Scomber scombrus). The percentage of correct classifications in terms of number of schools was higher in the analyses of the annual cruises (75.6%-95.36%) than in the analysis of pooled data (≈72%). This is because of (i) the lower number of species, as well as (ii) the reduced intraspecific variability, occurring in each separate cruise. Significant differences were detected among school descriptors for the different species, revealing discrete aspects of schooling behaviour for each species. The benefit of the specific approach is that the classification functions of the DFAs can be used to classify a larger set of schools, which has not been possible to assign to specific species. Overall the approach constitutes an objective, more automated and less time consuming procedure for the analysis of acoustic data and can contribute to the improvement of biomass estimates in the area.

African PenguinsSpheniscus demersus, Bait Balls and the Allee Effect

We report co-operative group foraging in the African Penguin Spheniscus demersus. Groups of approximately 25–165 African Penguins were observed circling schools of pelagic fish, sometimes forcing them to the surface. During this behaviour 66–75% of penguins were underwater at any given time. Smaller numbers of African Penguins also joined foraging groups of Cape Gannets Morus capensis and Cape Cormorants Phalacrocorax capensis, but did not appear to corral fish schools when outnumbered by these species. African Penguins are listed as Endangered due to ongoing rapid population decreases. If group foraging confers an advantage to African Penguins, their dwindling populations may suffer from an Allee effect as colonies become too small to support sufficient densities of birds for foraging groups to form.

Spatial Statistics of Objects in 3-D Sonar Images: Application to Fisheries Acoustics

In this letter, we address the characterization of objects in 3-D sonar images of the water column obtained by a multibeam echo sounder. Compared with classic 2-D images from a monobeam echo sounder, these 3-D images provide finer scale observation of the pelagic biomasses and new tools to characterize 3-D distributions. By viewing object patterns as realizations of spatial point processes, we investigate descriptive spatial statistics. This method is then applied to 3-D fisheries acoustics data set for characterization of the distribution of pelagic fish schools. Reported experiments illustrate the relevance of the proposed descriptors. The comparison of our method with 2-D sonar data analysis further demonstrates the information gain from using 3-D sonar imagery.

Three‐dimensional internal spatial structure of young‐of‐the‐year pelagic freshwater fish provides evidence for the identification of fish school species

Active acoustic detection and characterization in three dimensions (3D) with multibeam sonars is a powerful technique for ecological studies of schooling fish. The alpine Lake Annecy provides ideal conditions for sampling fish with active acoustic methods: it has calm water, low species diversity, and the density of pelagic fish schools is high. We carried out investigations on the internal 3D morphological characteristics of young‐of‐the‐year (Y‐O‐Y) pelagic fish schools, using high resolution multibeam sonar in the vertical plane. The objective was to discriminate between the two fish species that school in the lake: perch (Perca fluviatilis) and roach (Rutilus rutilus). To discriminate between these Y‐O‐Y fish species, we used only one characteristic of their internal spatial structure: the total number of vacuoles, defined as empty volumes inside the school, relative to the school volume. Two distinct linear relationships between school volume and the total number of vacuoles were determined. These two types were consistent with the proportions of the percentage occurrence of the two different species as obtained from pelagic trawl sampling in 2004. In 2008, perch was dominant (93%) in the lake, and only one relationship was detected: this relationship corresponded closely to the one in 2004 attributed to perch. Thus, we assume that the schooling behavior is a phenotypic expression that could be used for remote fish species identification.