Adaptation of fisheries sonar for monitoring schools of large pelagic fish / Erwan Josse

Public ISBD Faire une suggestion d'achat Titre : Adaptation of fisheries sonar for monitoring schools of large pelagic fish : dependence of schooling behaviour on fish finding efficiency Type de document : texte imprimé Auteurs : Erwan Josse, Auteur Importance : pp. 377-383 Langues : Anglais (eng) Index. décimale : 578 Histoire naturelle des organismes vivants Résumé : Multibeam omnidirectional sonars are tools currently used by fishers, but also allow the monitoring of pelagic fish schools surrounding a platform. Multibeam processing methods now offer improved capacities for raw data storage. The Simrad SP90 sonar was used for the detection of fish schools associated with drifting fish aggregating devices (FADs), and digital systems developed for the acquisition and processing of volume backscattering echoes and position data. Data sampling methods were defined based on two modes: one for periods searching for FADs and associated schools, and one for school monitoring in drifting mode. Validation of the detection of several FAD-associated schooling species was made by simultaneous visual observations or/and cross-checking with echosounder recordings. The characteristics of schooling behaviour in the targeted fish species are fundamental for the correct interpretation of acoustic data. Sonar detection threshold is the result of a compromise between fish number, size, species and the nearest neighbour distance (NND) of individuals per dynamic structure (school or shoal). Tuna schooling dynamics mean that NND can sometimes be too large to allow the presence of these fish to be detected, despite their number. Sonar data should be analysed and interpreted in a holistic manner, in combination with behaviour pattern and dynamics of all species around the drifting FADs. An autonomous sonar buoy prototype equipped with 360° scanning sonar coupled to video cameras will increase our understanding of tuna behaviour around drifting or anchored objects. A similar methodology can be applied to different kinds of platforms, either anchored or in permanent positions. This would improve the monitoring of fish schools around artificial reefs, open sea aquaculture farms, and across estuaries, channels or straits; applications which are undoubtedly essential for progressive fisheries management. Adaptation of fisheries sonar for monitoring schools of large pelagic fish : dependence of schooling behaviour on fish finding efficiency [texte imprimé] / Erwan Josse, Auteur . - [s.d.] . - pp. 377-383. Langues : Anglais (eng) Index. décimale : 578 Histoire naturelle des organismes vivants Résumé : Multibeam omnidirectional sonars are tools currently used by fishers, but also allow the monitoring of pelagic fish schools surrounding a platform. Multibeam processing methods now offer improved capacities for raw data storage. The Simrad SP90 sonar was used for the detection of fish schools associated with drifting fish aggregating devices (FADs), and digital systems developed for the acquisition and processing of volume backscattering echoes and position data. Data sampling methods were defined based on two modes: one for periods searching for FADs and associated schools, and one for school monitoring in drifting mode. Validation of the detection of several FAD-associated schooling species was made by simultaneous visual observations or/and cross-checking with echosounder recordings. The characteristics of schooling behaviour in the targeted fish species are fundamental for the correct interpretation of acoustic data. Sonar detection threshold is the result of a compromise between fish number, size, species and the nearest neighbour distance (NND) of individuals per dynamic structure (school or shoal). Tuna schooling dynamics mean that NND can sometimes be too large to allow the presence of these fish to be detected, despite their number. Sonar data should be analysed and interpreted in a holistic manner, in combination with behaviour pattern and dynamics of all species around the drifting FADs. An autonomous sonar buoy prototype equipped with 360° scanning sonar coupled to video cameras will increase our understanding of tuna behaviour around drifting or anchored objects. A similar methodology can be applied to different kinds of platforms, either anchored or in permanent positions. This would improve the monitoring of fish schools around artificial reefs, open sea aquaculture farms, and across estuaries, channels or straits; applications which are undoubtedly essential for progressive fisheries management.

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Echotrace classification and spatial distribution of pelagic fish aggregations around drifting fish aggregating devices (DFAD) / Erwan Josse

Public ISBD Faire une suggestion d'achat Titre : Echotrace classification and spatial distribution of pelagic fish aggregations around drifting fish aggregating devices (DFAD) Type de document : texte imprimé Auteurs : Erwan Josse, Auteur Importance : pp. 343-355 Langues : Anglais (eng) Index. décimale : 578 Histoire naturelle des organismes vivants Résumé : This work presents a method to observe pelagic fish around drifting fish aggregating devices (DFADs). A triple-frequency vertical echosounder was employed to observe fish distributions in the vicinity of DFADs. Surveys were conducted in a star pattern that was centred at the DFADs. The objective of the study was to define a methodology for future acoustic studies. This goal was pursued by (i) studying the spatial distribution of fish aggregations, (ii) developing concepts for the grouping of observed aggregations and (iii) developing specifications for future autonomous acoustic tools. For this purpose 5 cruises were carried out in the western Indian Ocean. The multi-frequency approach proved useful as a means of separating acoustic detections into sound-scattering layers (e.g. plankton and micronekton), fish aggregations and individual fish. Fish target strength (TS) was measured. Four types of aggregations were found near DFADs: (i) dense structure (ii) medium structure (iii) loose structure and (iv) structure consisting of separated targets. More than 90% of these structures were found within a radius of 400 m and about 75% within 200 m of the DFADs. The spatial configuration of DFAD fish aggregations appeared to be more dynamic compared to aggregations near moored FADs. The spatial distribution and structure of DFAD aggregations have direct implications for their catchability by tuna purse-seiner. We have carried out the first quantitative acoustic recordings around DFADs, and obtained a better understanding of the spatiotemporal dynamics of fish aggregations around DFADs in the Indian Ocean. Based on this knowledge we are now working on specifications for instrumented buoys that are intended as autonomous data recording observatories for such pelagic environments. Echotrace classification and spatial distribution of pelagic fish aggregations around drifting fish aggregating devices (DFAD) [texte imprimé] / Erwan Josse, Auteur . - [s.d.] . - pp. 343-355. Langues : Anglais (eng) Index. décimale : 578 Histoire naturelle des organismes vivants Résumé : This work presents a method to observe pelagic fish around drifting fish aggregating devices (DFADs). A triple-frequency vertical echosounder was employed to observe fish distributions in the vicinity of DFADs. Surveys were conducted in a star pattern that was centred at the DFADs. The objective of the study was to define a methodology for future acoustic studies. This goal was pursued by (i) studying the spatial distribution of fish aggregations, (ii) developing concepts for the grouping of observed aggregations and (iii) developing specifications for future autonomous acoustic tools. For this purpose 5 cruises were carried out in the western Indian Ocean. The multi-frequency approach proved useful as a means of separating acoustic detections into sound-scattering layers (e.g. plankton and micronekton), fish aggregations and individual fish. Fish target strength (TS) was measured. Four types of aggregations were found near DFADs: (i) dense structure (ii) medium structure (iii) loose structure and (iv) structure consisting of separated targets. More than 90% of these structures were found within a radius of 400 m and about 75% within 200 m of the DFADs. The spatial configuration of DFAD fish aggregations appeared to be more dynamic compared to aggregations near moored FADs. The spatial distribution and structure of DFAD aggregations have direct implications for their catchability by tuna purse-seiner. We have carried out the first quantitative acoustic recordings around DFADs, and obtained a better understanding of the spatiotemporal dynamics of fish aggregations around DFADs in the Indian Ocean. Based on this knowledge we are now working on specifications for instrumented buoys that are intended as autonomous data recording observatories for such pelagic environments.

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Joint use of echosounding, fishing and video techniques to assess the structure of fish aggregations around moored Fish Aggregating Devices in Martinique (Lesser Antilles) / Erwan Josse

Public ISBD Faire une suggestion d'achat Titre : Joint use of echosounding, fishing and video techniques to assess the structure of fish aggregations around moored Fish Aggregating Devices in Martinique (Lesser Antilles) Type de document : texte imprimé Auteurs : Erwan Josse, Auteur Importance : pp. 357-366 Langues : Anglais (eng) Index. décimale : 578 Histoire naturelle des organismes vivants Résumé : From April 2003 to April 2004 monthly sea surveys were conducted around 2 fish aggregating déviées (FADs) moored at 2000 and 2500 m depth in Martinique (Lesser Antilles). The use of a dual frequency splitbeam echosounder combined with an underwater caméra and fishing methods allowed assessment of average space and time distribution of pelagic fish aggregated beneath the FADs, as well as identification of their overall size and species composition. At daytime, 4 fish aggregations were identified at each FAD, representing 4 distinct types: i) an aggregation of small juvenile tuna (mean fork length, FL: 30 cm) observed very close to thé surface in 25% of daytime periods; ii) a small surface aggregation dominated by carangids, Caranx crysos, present in 65% of daytime periods; iii) a large subsurface aggregation observed during ail daytime periods: this aggregation appeared to be primarily comprised of 58 cm FL blackfin tuna (Thunnus atlanticus), mixed with yellowfin (Thunnus albacares) and skipjack (Katsuwonus pelamis) tunas of the same size; and iv) sub-surface scattered large predators (mainly blue marlin, Makaira nigricans) présent in 10% of daytime periods. A smaller sub-surface aggregation comprised of médium tuna mixed with "extranatants" (fishes which remain within 10 to 50 m of a FAD) was observed in 75% of night-time periods, whereas unidentified scattered fishes were detected from 70 to 400 m depth. The low daytime vulnerability of medium sub-surface tunas to applied Une techniques leads us to assume that their feeding motivation was low during daytime. Thèse tunas could pref- , erentially feed on mesopelagic organisms during night-time and transition periods around Martinican moored FADs. Local fishermen mainly targeted thé large scattered predators using very small tunas as living bail. The sub-surface tuna aggregation hence appeared to be currently unexploited by local fisheries, though it represented thé large majority of . the pelagic biomass around the moored FADs. Joint use of echosounding, fishing and video techniques to assess the structure of fish aggregations around moored Fish Aggregating Devices in Martinique (Lesser Antilles) [texte imprimé] / Erwan Josse, Auteur . - [s.d.] . - pp. 357-366. Langues : Anglais (eng) Index. décimale : 578 Histoire naturelle des organismes vivants Résumé : From April 2003 to April 2004 monthly sea surveys were conducted around 2 fish aggregating déviées (FADs) moored at 2000 and 2500 m depth in Martinique (Lesser Antilles). The use of a dual frequency splitbeam echosounder combined with an underwater caméra and fishing methods allowed assessment of average space and time distribution of pelagic fish aggregated beneath the FADs, as well as identification of their overall size and species composition. At daytime, 4 fish aggregations were identified at each FAD, representing 4 distinct types: i) an aggregation of small juvenile tuna (mean fork length, FL: 30 cm) observed very close to thé surface in 25% of daytime periods; ii) a small surface aggregation dominated by carangids, Caranx crysos, present in 65% of daytime periods; iii) a large subsurface aggregation observed during ail daytime periods: this aggregation appeared to be primarily comprised of 58 cm FL blackfin tuna (Thunnus atlanticus), mixed with yellowfin (Thunnus albacares) and skipjack (Katsuwonus pelamis) tunas of the same size; and iv) sub-surface scattered large predators (mainly blue marlin, Makaira nigricans) présent in 10% of daytime periods. A smaller sub-surface aggregation comprised of médium tuna mixed with "extranatants" (fishes which remain within 10 to 50 m of a FAD) was observed in 75% of night-time periods, whereas unidentified scattered fishes were detected from 70 to 400 m depth. The low daytime vulnerability of medium sub-surface tunas to applied Une techniques leads us to assume that their feeding motivation was low during daytime. Thèse tunas could pref- , erentially feed on mesopelagic organisms during night-time and transition periods around Martinican moored FADs. Local fishermen mainly targeted thé large scattered predators using very small tunas as living bail. The sub-surface tuna aggregation hence appeared to be currently unexploited by local fisheries, though it represented thé large majority of . the pelagic biomass around the moored FADs.

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