Classification of fish schools based on evaluation of acoustic descriptor characteristics

Charef, Aymen; Ohshimo, Seiji; Aoki, Ichiro; Absi, Natheer Al

doi:10.1007/s12562-009-0186-x

Cited by 29 publications

(16 citation statements)

References 41 publications

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“…Significant differences among species were identified for all the parameters selected during the stepwise procedure of the DFA. �athymetric descriptors (School Depth, Altitude) were among the ones contributing the most to the discrimination both in the analysis of the pooled data and in the separate analyses of each research cruise (results not shown) in line with other similar studies (Lawson et al, 2001;Charef et al, 2010;Robotham et al, 2010;D'Elia et al, 2014). School Depth and the distance from the bottom (Altitude) reveal species-specific behaviours that may be related to micro-habitat preferences (e.g.…”

Section: Discussionsupporting

confidence: 86%

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

et al. 2015

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Reliable biomass estimates by means of hydroacoustics largely depend on the correct identification of acoustic targets. Data collected during five summer acoustic surveys (2004)(2005)(2006)(2007)(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.

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Section: Discussionsupporting

confidence: 86%

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

et al. 2015

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“…The thermal stratification at the depth of the thermocline provides physical means to vertically aggregate food for prey species (Gray 2003;Crocker et al 2006). Indeed, evidence suggests that Japanese anchovy aggregate at the upper layers of the thermocline Charef et al 2010). The ability to adapt to the variability of prey abundance in the vertical dimension is essential to dolphinfish as a pelagic predator.…”

Section: Discussionmentioning

confidence: 99%

Vertical movement of dolphinfish Coryphaena hippurus as recorded by acceleration data-loggers in the northern East China Sea

et al. 2011

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Environmental changes influence foraging behavior for most animals. Dolphinfish, Coryphaena hippurus, are epipelagic predators and have a cosmopolitan tropical to warm-temperate (>20°C) distribution. We simultaneously obtained the ambient temperature and the foraging behavior (i.e., swimming speed, depth and tailbeat acceleration) of dolphinfish, using an acceleration data-individuals. Although the dolphinfish spent a mean ± standard deviation of 43.4±27.7% of their time at the surface (0-5 m), dive excursions from the surface (DES) were observed in all individuals and maximum DES depths ranged from 50.1 to 95.4 m. DES events resulted dives below the thermocline for these dolphinfish, and there was a significantly positive relationship between the isothermal layer depth (ILD) and DES depth. Our results demonstrate that dolphinfish avoided the rapid thermal change beyond the thermocline, and their prey is most likely found in the upper layers of the thermocline. Gliding behavior during the DES phase was also observed and dolphinfish gradually descended to deeper waters with gliding. The gliding time was longer when the ILD was deeper, and fish tended to dive deeper. We suggest that dolphinfish adopt gliding behavior to search a broader range of depths for prey, while minimizing energy use.

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“…In particular, myctophids are difficult to identify to species level using underwater acoustics and further studies are required to gain new insight into the TS relationships and acoustic backscattering properties of myctophid species. New approaches, such as acoustic morphometric descriptors/classification (Charef et al, 2010;Korneliussen and Ona, 2003), in situ TS probes and theoretical TS modelling (Yasuma et al, 2003;Yasuma et al, 2010), together with continued acoustic surveys and scientific netting, are likely to develop the field of myctophid acoustics. However, there is clearly a pressing need to acquire basic data on these fish and their schooling behaviour in these high latitude regions that are experiencing rapid environmental change.…”

Section: Discussionmentioning

confidence: 99%

School characteristics of mesopelagic fish at South Georgia

Saunders

Fielding

Thorpe

et al. 2013

Deep Sea Research Part I: Oceanographic Research Papers

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In this paper, we describe the variation in myctophid schools characteristics at South Georgia using multi-frequency acoustic data collected annually between November 2007 and January 2012. We studied the relationship between the proximity of land and the distribution and schooling characteristics of myctophid fish. We also examined patterns in schooling behaviour in relation to oceanographic data. Fish schools were identified using a dualfrequency dB identification method (S v120-38 kHz ), where negative S v120-38 kHz is indicative of gas-bearing organisms, such as swimbladdered fish. Available net data were used to provide information on the meosopelagic fish community in the region. School morphometrics (e.g. length, thickness, area) data were extracted and pooled according to their distance from the shore (0-30 km, 30-60 km, 60-90 km, 90-120 km). A total of 578 schools were detected in the survey region and there was high variation in school backscattering strength (NASC), length, height, perimeter, depth and horizontal distribution between surveys, including distinct inter-annual variation in these parameters when surveys were conducted in the same season (2009)(2010)(2011)(2012). Schools were distributed predominantly on-shelf (0-500 m isobaths) during some summer surveys (2007 and 2012) and predominantly off-shelf on others (>500 2 m isobaths; 2009, 2010 and 2011). There was also evidence of bathymetric separation in the horizontal distribution of schools. Schools observed in the late-season in 2008 had the greatest NASC, largest height and the deepest depth distribution. Most schools occurred at depths between ~60-300 m, but they did not occupy the same water masses during each survey. Schools became progressively thinner, shallower and acoustically weaker with increasing distance to land, whilst school length and perimeter increased correspondingly.The change in fish schooling behaviour between environments could be a response to a combination of local predatory threats over short spatial/temporal scales and differences in oceanographic conditions, such as current velocity. The trend could also be evidence of spatial habitat partitioning of myctophids, with different schooling species, or different lifestages, orientating along a bathymetric gradient at South Georgia.

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Classification of fish schools based on evaluation of acoustic descriptor characteristics

Cited by 29 publications

References 41 publications

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

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

Vertical movement of dolphinfish Coryphaena hippurus as recorded by acceleration data-loggers in the northern East China Sea

School characteristics of mesopelagic fish at South Georgia

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