Fish Aggregation Research Articles

Distribution, population structure, and some biological distinctions of pikeperch Sander lucioperca of the channel part of the Akhtuba River (Volga-Akhtuba water system)

Biological traits (distribution, reproduction, age composition, body length and weight) of pikeperch Sander lucioperca from channel parts of the Akhtuba River, remote from the Volga Delta, are investigated. In the investigated stretch of the river, movements of most specimens of pikeperch are local and occur in the deep part (4−10 m) of the channel. Aggregations of fish are not confined to any definite points but move along the extensive stretch of broads. Pikeperch prefer near-bottom biotopes confined to the zone of stable hydrodynamic eddies in places of complicated bottom relief—transverse crests and longitudinal channel crests. For the first time, it is found that pikeperch in the under-ice period move to the shallow zone of submersed inshore shrubs. The age structure and body length and weight of pikeperch differ from those in the Volga Delta and correspond more to the populations from northern and northwestern parts of the species area. Pikeperch spawn only in temporary water bodies of the accessory system, within a short period at the temperature 11−17°С. The data on biology of pikeperch from the Akhtuba channel indicate the populational level of differences from the Volga Delta pikeperch.

Maximum Likelihood Deconvolution of Beamformed Images with Signal-Dependent Speckle Fluctuations from Gaussian Random Fields: With Application to Ocean Acoustic Waveguide Remote Sensing (OAWRS)

Wide area acoustic remote sensing often involves the use of coherent receiver arrays to determine the spatial distribution of sources and scatterers at any instant. The resulting acoustic intensity images are typically corrupted by signal-dependent noise from Gaussian random field fluctuations arising from the central limit theorem and have a spatial resolution that depends on the incident direction, sensing array aperture and wavelength. Here, we use the maximum likelihood method to deconvolve the intensity distribution measured on a coherent line array assuming a discrete angular distribution of incident plane waves. Instantaneous wide area population density images of fish aggregations measured with Ocean Acoustic Waveguide Remote Sensing (OAWRS) are deconvolved to illustrate the effectiveness of this approach in improving angular resolution over conventional planewave beamforming.

A designed artificial reef is among the most productive marine fish habitats: new metrics to address ‘production versus attraction’

It was recently demonstrated that oil platforms are among the most productive marine fish habitats (Claisse et al. in Proc Natl Acad Sci USA 111:15462–15467, 2014). Designed artificial reef systems are similar, albeit smaller, modified habitats designed to accommodate fish assemblages. We compared fish production at a large designed reef to reported production at oil platforms. Given the focus in artificial reef research on distinguishing between new and aggregated fish production, we used a different approach to that of Claisse et al. (Proc Natl Acad Sci USA 111:15462–15467, 2014) to calculate production, based on a steady-state assumption. This assumption simplifies the analysis and distinguishes ‘local production’, ‘new production’, and ‘biomass flux’. Comparing biomass flux with standing stock biomass enables a new approach to address the production versus attraction debate, by revealing how much biomass is exposed to fishing compared to how much has local production. The local fish production at this artificial reef was 384 g m−2 year−1, which is within the 105–887 g m−2 year−1 range reported by Claisse et al., although our study included visitor species not included by Claisse et al. We estimate that the fish production new to the ecosystem may only be 4–5 % of the local production, due to the large abundance of visitor species on this reef. The annual flux of biomass across this reef was very large, ~380 times greater than the standing stock biomass, meaning that this reef is vulnerable to overexploitation from fishing. Our results show that like oil platforms, designed artificial reefs can be very productive marine habitats, but may not greatly increase the net fish production in a system. The method detailed here will allow similar studies to be done relatively simply at other marine habitats, including fish aggregation devices.

Benthic and fish aggregation inside an offshore wind farm: Which effects on the trophic web functioning?

As part of the energy transition, the French government is planning the construction of three offshore wind farms in Normandy (Bay of Seine and eastern part of the English Channel, north-western France) in the next years. These offshore wind farms will be integrated into an ecosystem already facing multiple anthropogenic disturbances such as maritime transport, fisheries, oyster and mussel farming, and sediment dredging. Currently no integrated, ecosystem-based study on the effects of the construction and exploitation of offshore wind farms exists, where biological approaches generally focused on the conservation of some valuable species or groups of species. Complementary trophic web modelling tools were applied to the Bay of Seine ecosystem (to the 50km2 area covered by the wind farm) to analyse the potential impacts of benthos and fish aggregation caused by the introduction of additional hard substrates from the piles and the turbine scour protections. An Ecopath ecosystem model composed of 37 compartments, from phytoplankton to seabirds, was built to describe the situation “before” the construction of the wind farm. Then, an Ecosim projection over 30 years was performed after increasing the biomass of targeted benthic and fish compartments. Ecological Network Analysis (ENA) indices were calculated for the two periods, “before” and “after”, to compare network functioning and the overall structural properties of the food web. Our main results showed (1) that the total ecosystem activity, the overall system omnivory (proportion of generalist feeders), and the recycling increased after the construction of the wind farm; (2) that higher trophic levels such as piscivorous fish species, marine mammals, and seabirds responded positively to the aggregation of biomass on piles and turbine scour protections; and (3) a change in keystone groups after the construction towards more structuring and dominant compartments. Nonetheless, these changes could be considered as limited impacts of the wind farm installation on this coastal trophic web structure and functioning.

The Physical Behavior of Seine Ropes for Evaluating Demersal Seine Fishing1

Demersal seining is an active bottom fishing method, which applies seine ropes and a seine net. The seine ropes and net are laid out on the fishing ground with the seine ropes encircling an aggregation of fish on the seabed. The area on the seabed encircled by the seine ropes is typical much larger than the swept area that will be covered by the seine net during the fishing process. Therefore, the catching performance of a demersal seine depends on the efficiency by which the seine ropes are able to herd the fish into and maintain them in the path of the net until they are overtaken by it in the late stages of the fishing process. This article describes flume tank experiments to validate a numerical model. This model simulates the physical behavior of seine ropes during the fishing process. The experiments are conducted for varying physical properties of the ropes and for different layout patterns. The seine ropes are hauled back at different speeds. A motion tracking system, based on stereo vision, is applied to record the gradual change in the area encircled by the ropes. The experimental results from the flume tank are compared with data obtained using the simulation model. Finally, the validated simulation model is applied for predictions.

Consequences of fishing moratoria on catch and bycatch: the case of tropical tuna purse-seiners and whale and whale shark associated sets

Time–area regulations have been introduced to manage stocks of tropical tuna, given the increased use of drifting fish aggregation devices (FADs). However, the consequences in terms of changes in fishing strategies and effort reallocation may not always be as expected. For instance, in the eastern Pacific Ocean, previous studies have highlighted that the increase use of FAD-fishing following the demand for tuna caught without dolphin mortality has raised concerns about the bycatch and the capture of juvenile tuna. In the tropical eastern Atlantic and western Indian Oceans, this study aimed to (1) assess, using before–after analysis, the consequences of previous time–area regulations on FAD sets on the fishing effort allocated to megafauna associated sets, and (2) evaluate through Monte Carlo simulations the potential effect of new regulations banning whale or/and whale shark associated sets. Firstly, we showed that previous time–area regulations, which were mainly implemented during seasons with few whale and whale shark associated sets, generally had thus little effect on the number of megafauna associated sets. Secondly, some simulations, particularly when both whale and whale shark associated sets were banned, predicted consequences of changes in fishing strategy. Indeed, these types of ban could lead to an increase in the number of FAD and free school sets but no change in the tuna catch, as well as a slight decrease in bycatch. These results indicate that an ecosystem approach to fisheries, by taking into account megafauna associated sets and bycatch, should thus be adopted when implementing management or conservation measures.

Acoustic detection of larval fish aggregations in Galician waters (NW Spain)

The authors thank the crew of RV `Cornide de Saavedra' and all the participants in the Cramer 0312 cruise for their assistance. This work was supported by the project CRAMER (CTM2010-21856-CO3), funded by the Spanish Ministry of Economy and Competitiveness and by the project ECOPREGA (10MMA602021PR), funded by the Regional Government of Galicia (Xunta de Galicia). We are also grateful to the 2 anonymous referees for their constructive comments on the manuscript.

High resolution study of the spatial distributions of abyssal fishes by autonomous underwater vehicle.

On abyssal plains, demersal fish are believed to play an important role in transferring energy across the seafloor and between the pelagic and benthic realms. However, little is known about their spatial distributions, making it difficult to quantify their ecological significance. To address this, we employed an autonomous underwater vehicle to conduct an exceptionally large photographic survey of fish distributions on the Porcupine Abyssal Plain (NE Atlantic, 4850 m water depth) encompassing two spatial scales (1–10 km2) on and adjacent to a small abyssal hill (240 m elevation). The spatial distributions of the total fish fauna and that of the two dominant morphotypes (Coryphaenoides sp. 1 and C. profundicolus) appeared to be random, a result contrary to common expectation but consistent with previous predictions for these fishes. We estimated total fish density on the abyssal plain to be 723 individuals km−2 (95% CI: 601–844). This estimate is higher, and likely more precise, than prior estimates from trawl catch and baited camera techniques (152 and 188 individuals km−2 respectively). We detected no significant difference in fish density between abyssal hill and plain, nor did we detect any evidence for the existence of fish aggregations at any spatial scale assessed.

Investigating acoustic diversity of fish aggregations in coral reef ecosystems from multifrequency fishery sonar surveys

Remote species classification using fisheries acoustic techniques in coral reef ecosystems remains one of the greatest hurdles in developing informative metrics and indicators required for ecosystem management. We reviewed long-term marine ecosystem acoustic surveys that have been carried out in the US Caribbean covering various coral reef habitat types and evaluated metrics that may be helpful in classifying multifrequency acoustic signatures of fish aggregations to taxonomic groups. We found that the energetic properties across frequencies, in particular the mean and the maximum volume backscattering coefficient, provided the majority of the discriminating power in separating schools and aggregations into distinct groups. To a lesser extent, school shape and geometry helped isolate a distinctive group of reef fishes based on shoaling behaviour. Schools and aggregations were clustered into five distinct groups. The use of underwater video surveys from a Remote Operating Vehicle (ROV) conducted in the proximity of the acoustic observations allowed us to associate the clusters with broad categories of species groups such as large predators, including fishery important species to small forage fishes. The remote classification methods described here are an important step toward improving marine ecosystem acoustics for the study and management of coral reef fish communities.

A model based on data from echosounder buoys to estimate biomass of fish species associated with fish aggregating devices

Most of the drifting fish aggregating devices (DFADs) used in industrial tropical tuna purse seine fisheries are equipped with satellite linked echosounder buoys, which provide fishing crews with remote, accurate geolocation information and rough estimates of FAD-associated tuna biomass. One of the most common brands of echosounder buoys (SATLINK, Madrid, Spain) is currently calibrated for the target strength of skipjack tuna (Katsuwonus pelamis) and provides biomass data on. that species. Using that brand of echosounder buoy, we developed a new behavior-based approach to provide relative biomass estimates and a remote target classification of fish aggregations at FADs. The model is based on current knowledge of the vertical distribution of the main fish species associated with FADs, as well as on appropriate TS and weight values for different species and sizes, and is further based on parameter optimization against a set of fishing operations on DFADs. This model reduced the error variability in biomass estimates by about 60% and also reduced the ranges of underestimation. and overestimation by 55% and 75%, respectively. Similarly, the original coefficients of correlation and determination were also considerably improved from 0.50 and 0.25 to 0.90 and 0.82, respectively. We discuss how this new method opens new opportunities for scientific studies and has implications for sustainable fishing.

Documentation of Cryptobranchus alleganiensis alleganiensis (Eastern Hellbender) Predation on Nest-Associate Stream Fishes

The covert habits of Cryptobranchus alleganiensis alleganiensis (Eastern Hellbender) make direct field observations of their behavior difficult. Here I provide the first video documentation of in situ predation by a hellbender on a spawning aggregation of stream fishes. Both targeting fish and diurnal activity are behaviors rarely documented among hellbenders. The present observation, however, supports previously described patterns of elevated diurnal activity in late spring hypothesized to be associated with increased foraging-activity to meet higher energy-demands. The observation demonstrates that Eastern Hellbenders will modify behavior to exploit stream fishes when prey are easily captured.

Bioenergetics, Trophic Ecology, and Niche Separation of Tunas.

Tunas are highly specialized predators that have evolved numerous adaptations for a lifestyle that requires large amounts of energy consumption. Here we review our understanding of the bioenergetics and feeding dynamics of tunas on a global scale, with an emphasis on yellowfin, bigeye, skipjack, albacore, and Atlantic bluefin tunas. Food consumption balances bioenergetics expenditures for respiration, growth (including gonad production), specific dynamic action, egestion, and excretion. Tunas feed across the micronekton and some large zooplankton. Some tunas appear to time their life history to take advantage of ephemeral aggregations of crustacean, fish, and molluscan prey. Ontogenetic and spatial diet differences are substantial, and significant interdecadal changes in prey composition have been observed. Diet shifts from larger to smaller prey taxa highlight ecosystem-wide changes in prey availability and diversity and provide implications for changing bioenergetics requirements into the future. Where tunas overlap, we show evidence of niche separation between them; resources are divided largely by differences in diet percentages and size ranges of prey taxa. The lack of long-term data limits the ability to predict impacts of climate change on tuna feeding behaviour. We note the need for systematic collection of feeding data as part of routine monitoring of these species, and we highlight the advantages of using biochemical techniques for broad-scale analyses of trophic relations. We support the continued development of ecosystem models, which all too often lack the regional-specific trophic data needed to adequately investigate climate and fishing impacts.

Intraspecies structure of beaked redfish Sebastes mentella of the Atlantic and Arctic oceans

On the basis of the results of complex interdisciplinary investigations of the population composition and structure of the beaked redfish Sebastes mentella of the Atlantic and Arctic oceans, its three populations are discerned relatively isolated from each other by the system of permanent marine currents—North Atlantic, Flemish-Cape, and Norway-Barents Sea. The population structure of the species in the southern part of its area corresponds to the model of a local stock. Interaction of the North Atlantic and the Norway-Barents Sea populations well correspond to the model of fluctuating stocks. Redfish aggregations in different biotopes (mesobenthal and mesopelagial) are intrapopulational epigenetic groups. In the period of warm and anomalously warm years, a part of mature specimens from the pelagial of the North Irminger Sea make an irreversible migration to the southern part of the Norwegian Sea and form there mixed aggregations of fish from the North Atlantic and Norway-Barents Sea populations. With consideration of the effect of climatic–oceanological processes, a principally new scheme is elaborated describing the process of seasonal migrations of redfish in the mesobenthal and mesopelagial. The previous views on direction of return migrations of redfish of the Norway-Barents Sea population are reconsidered. Juveniles from the western part of the Barents Sea and Spitsbergen not only supplement the demersal aggregations but also migrate to the pelagial of the Norwegian Sea.

Development of a Finite-Difference Time Domain (FDTD) Model for Propagation of Transient Sounds in Very Shallow Water.

This finite-difference time domain (FDTD) model for sound propagation in very shallow water uses pressure and velocity grids with both 3-dimensional Cartesian and 2-dimensional cylindrical implementations. Parameters, including water and sediment properties, can vary in each dimension. Steady-state and transient signals from discrete and distributed sources, such as the surface of a vibrating pile, can be used. The cylindrical implementation uses less computation but requires axial symmetry. The Cartesian implementation allows asymmetry. FDTD calculations compare well with those of a split-step parabolic equation. Applications include modeling the propagation of individual fish sounds, fish aggregation sounds, and distributed sources.

2014년 동계 북부 동중국해 저층 트롤 및 음향학적 조사에 의한 저서어족 생물자원의 분포특성 비교

This study examined the spatiotemporal distribution of demersal fish aggregations in the Northern East China Sea by conducting a trawl survey with hydroacoustic devices. A bottom trawl was used for this survey and fish density was determined from the catch data. Acoustic data were collected at frequencies of 38 and 200 kHz from November to December 2014 and converted into the nautical area scattering coefficient (NASC, <TEX>$m^2/n{\cdot}mile^2$</TEX>). In the catch data analysis, the range of catch per unit area by station was <TEX>$26-8,055kg/km^2$</TEX> and for the acoustic data, that of the NASC was <TEX>$0.45-34.80m^2/n{\cdot}mile^2$</TEX>. The values were significantly correlated. The combined results of both surveys found that the density was highest at St. 5 (<TEX>$33^{\circ}$</TEX> 10.3', <TEX>$126^{\circ}$</TEX> 23.3') and lowest at St. 8 (<TEX>$33^{\circ}$</TEX> 20.7', <TEX>$127^{\circ}$</TEX> 36.3'). The application of hydroacoustic methods offers a new approach for estimating the biomass of demersal fish aggregations.

Can fish habitat restoration for rheophilic species in highly modified rivers be sustainable in the long run?

As a result of the ongoing loss of freshwater biodiversity, restoration of riverine habitats is high on the agenda. However, it remains controversial if commonly used instream fish habitat restoration techniques have sustainable effects in highly modified waterbodies.This study compared the effects of introducing four different instream structures (bank rip-rap, benched bank rip-rap, successively grown riparian wood and introduced dead wood, nine replicates each) on the fish community distribution in the river Günz in Germany. To assess the sustainability of the restoration measures, different time points (seven and two years after the restoration) and seasons were considered.Out of all measures, the introduction of dead wood had strongest effects on fish aggregation (biomass and density) as well as on species richness and diversity. Even seven years after restoration, no alterations in the density and demography of target species in conservation was detectable.These results suggest that instream habitat restoration measures are unlikely to fully mitigate deficiencies in highly modified rivers. Consequently, the investment of resources for aquatic restoration may have greater effects in systems that are closer to an optimal state, unless greater effort into restoration beyond the main channel is made.

An approach to the economic value of diving sites: artificial versus natural reefs off Sal Island, Cape Verde

Summary In the present paper there was a twofold hypothesis, i.e. that the deployment of artificial reefs adds value to natural features by diversifying diving sites and thus be a certain propensity concerning the type of added value (either of non-extractive direct or indirect use). Two vessels were used as artificial reefs off Sal Island (Cape Verde) in 2006 and 2008, with the aim of bolstering the local economy through ecotourism. The additional economic value anticipated was to: (i) enhance fish aggregation as well as other marine organisms, and (ii) mitigate human pressure on natural reefs by diverting divers. The supply-side view of diving trips was tested and analysed over a 4-year period (2008–2011) in the choice of divers between natural and artificial reefs, as well as such reef attributes as reef depth, reef distance from the main pier in Santa Maria Bay, and the year-season as well as combinations thereof. Data were also analysed to determine if the deployed reefs off Sal Island had a complementary or a substitute function. It was observed that the presence of artificial reefs created more dive users, but that divers who used these reefs were not deterred from diving at natural reefs. This resulted in a low-diversion effect (low substitutability). Thus, dive operators can offer additional options to divers (moderate to highly complementary). The distance to diving sites was the most influential factor in diving decisions (linear model results indicated 15 more divers at distances closer to Santa Maria Bay than elsewhere). From the log-linear model the number of divers would be expected to change, the distance being the most influential factor (11.7 times higher at closer sites); reef type and depth were less influential (0.2 times fewer divers at artificial reefs; 2.3 times more divers in shallower waters). Also apparent was that the depth of the reef was fundamental in the diver niche allocation throughout the seasons.

Elucidating fishing effects in a large-predator dominated system: The case of Darwin and Wolf Islands (Galápagos)

Fifty years of artisanal fishing history in Galápagos characterized by boom and bust of resources has changed the natural marine community structure close to fishing ports in the Galápagos Marine Reserve. Nonetheless, the remote Darwin and Wolf Islands are still in a “near natural state” harboring high species richness unique for the archipelago and high biomass. Marine life that aggregates to the pinnacles linked to the wider oceanic seascape makes them interesting and unique systems in terms of community structure and study of on-shore/offshore trophic interactions. Although >200km from local fishing ports the two islands also support an artisanal fishery targeting large demersal predators of high trophic levels. They are areas prioritized for conservation actions by Galápagos National Park, and local non-governmental organizations given their natural heritage importance, value to local fishers and revenue from dive tourism attracted by the promise of large marine predator aggregations such as sharks. Given that catch data upon which to base conservation recommendations is sparse it is difficult to accurately estimate present day fishing trends in Darwin and Wolf. We used a trophic steady-state model that connects benthic and pelagic communities to assess the potential effects of a change in fishing intensity in the two islands system. A predator–prey matrix was built using the Ecopath with Ecosim (EwE) software with total biomass estimated at 937tkm−2. Large fish aggregations accounted for 19%, primary producers for 9.0% and non-fish (seabirds, marine mammals and sea turtles) for less than 0.1% of the total living biomass. The total system size in terms of overall flows was 16,652tkm−2year−1, four times larger than a generic seamount model but smaller than that modeled for a Galápagos upwelling system based upon the western Bolivar Channel region. Consumption and respiration dominated the flows in the system (53.4 and 31.8% respectively). The Darwin and Wolf system shows a mature state, dominated by respiration, and top–down control via sharks and benthic predatory fish as the most important system compartments in terms of biomass. Model simulations suggest that heavy fishing pressure on top predators would greatly change the system's trophic structure. The nature of impacts depended on the types of gears simulated. Reduced natural predator densities through fishing exert strong direct and indirect influences on the system towards sea urchin-dominated benthos.

Husbandry and environmental conditions explain temporal variability of wild fish assemblages aggregated around a Mediterranean fish farm

The aggregation of wild fish around fish farms is spatially and temporally variable in terms of species composition and structure. In general, temporal variability has been less well studied than the spatial aspect of these aggregations. We analyzed temporal variability at differ- ent scales following a hierarchical sampling design, with year, season and time of day as the main factors, with the levels of the latter factor corresponding with feeding intensity at the farm. Envi- ronmental and production variables were considered, such as water temperature, photoperiod, feed supplied, number of stocked fish and stocked biomass. Dominant fish species were analyzed separately to determine possible segregation processes. The most relevant sources of variation in abundance and assemblage structure were seasonal changes among years and hourly changes with different feeding intensities between seasons. Feed supplied was the production variable that best explained the temporal pattern with respect to abundance, and this variable, combined with hours of daylight, determined the assemblage structure. Liza ramada and Sarpa salpa domi- nated the assemblage in winter and were always aggregated around the farm. Boops boops, Ob - lada melanura and Sardinella aurita dominated the assemblage in spring, summer and autumn, showing a marked seasonal pattern. These 3 species, although present around the farm most of the year, displayed periods of distinct maximum abundance corresponding to their reproductive period. This study emphasizes the importance of determining the temporal patterns in abundance of dominant species in order to better understand the interaction between fish farming and wild fish assemblages, and to ascertain the contribution of wild fish to the recycling of aquaculture- derived wastes.

Verifying FAD-association in purse seine catches on the basis of catch sampling

We investigate the potential of verifying whether individual purse seine sets were made in association with a fish aggregation device (FAD) or on an unassociated (FAD-free) tuna school, on the basis of low intensity catch sampling by onboard observers. The target tuna catch and length compositions and bycatch amounts were analyzed from more than 50,000 purse seine sets sampled by onboard observers who had, in addition to collecting sampling data on species and size composition of target tunas in the catch, and set-level estimates of total bycatch, also identified the sets as either “associated” or “unassociated”. Classification tree (CT) models were developed based on 2007–2011 observer data and tested for misclassification error rates on 2012 data. Two types of model misclassification errors (MCE) are possible: unassociated sets misclassified as associated (termed false positive or Type I) and associated sets misclassified as unassociated sets (false negative or Type II error). A third error measure, overall MCE, is a weighted average of Type I and Type II errors. The classification rules developed on the basis of observer catch sampling tended to be nearly presence/absence, e.g. greater than 99% skipjack composition or presence of 0.5kg rainbow runner, likely keyed by the modest observer sample sizes. Overall MCE rates were 21.8% for the initial tuna-only CT model and 14.4% for the bycatch-included model. The improvement in overall classification for the bycatch models derived principally from a reduction in Type I errors. The addition of auxiliary non-sampling variables (e.g., longitude, month) and use of more complex resampling extensions to CT modelling led to little to no improvement in MCE rates. We employed our methodology to analyze a particular subset of the purse seine data, i.e., sets from the FAD-closure periods of 2009–12. The intent was to determine if MCE rates of these particular sets were greater than the MCE rates found in the more general analysis. Reassuringly, the MCE rates of sets during the FAD closure period were found to be equal, or even a bit lower than MCE rates in the broader analyses based on our best performing model.