Diurnal variation in bottom trawl survey catches: does it pay to adjust?

Hjellvik, Vidar; Godø, Olav Rune; Tjøstheim, Dag

doi:10.1139/f01-193

Cited by 34 publications

(33 citation statements)

References 18 publications

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“…In the Barents Sea, however, there is ample evidence that vertical zonation of gadoid fish can vary throughout the day or year (Hjellvik et al 2002). In the present analysis, this would not be expected to have a major impact.…”

Section: Time Of Day Considerationsmentioning

confidence: 56%

Acoustic data collected during and between bottom trawl stations: consistency and common trends

Bez¹,

Reid²,

Neville³

et al. 2007

Can. J. Fish. Aquat. Sci.

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Acoustic data are often collected during bottom trawl surveys. Their use can potentially improve the precision and accuracy of fish abundance estimates if acoustic data collected between trawl stations are consistent with those collected during trawling operations. This question is addressed here through the analysis of 20 bottom trawl surveys (three survey areas and five different survey series) with coincident acoustic measurements during and between trawl stations. Firstly, on-station and underway acoustic data were compared using statistics computed globally over each survey (average vertical profiles, global indices of collocations, and spatial structures) for various combinations of depth layers. Secondly, we focussed on underway acoustic data recorded in the vicinity of stations, distinguishing between data recorded before and after the tows. On-station and underway acoustic data were highly consistent, and no systematic perturbation of the acoustic sign due to the presence of the gear a few hundred metres behind the vessel was observed.Résumé : On récolte souvent des données acoustiques durant les inventaires faits au chalut de fond. Leur utilisation peut potentiellement améliorer la précision et la justesse des estimations d'abondance des poissons, si les données acoustiques récoltées entre les stations de chalutage sont compatibles avec celles récoltées durant les opérations de pêche. Nous examinons la question en analysant 20 inventaires faits au chalut de fond (trois zones d'inventaire et cinq séries différentes d'inventaires) pour lesquels il existe des mesures acoustiques coïncidentes obtenues dans et entre les stations de chalutage. Nous avons d'abord comparé les données acoustiques obtenues en route et dans les stations à l'aide de statistiques calculées globalement pour chaque inventaire (profils verticaux moyens, indices globaux de collocation et structures spatiales) selon diverses combinaisons de couches de profondeur. Ensuite, nous nous sommes intéressés aux données acoustiques obtenues en route près des stations, en distinguant entre les données enregistrées avant et après le chalutage. Il existe un excellent accord entre les données acoustiques obtenues dans les stations et celles enregistrées en route; on n'observe pas de perturbation systématique du signal acoustique due à la présence des engins de pêche à quelques centaines de mètres derrière le navire.[Traduit par la Rédaction] Bez et al. 180

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Section: Time Of Day Considerationsmentioning

confidence: 56%

Acoustic data collected during and between bottom trawl stations: consistency and common trends

Bez¹,

Reid²,

Neville³

et al. 2007

Can. J. Fish. Aquat. Sci.

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“…Finally, if fish were go- ing into and out of the dead zone at dusk and dawn, one would expect a higher density just above the dead zone at these times, whereas the opposite is the case. An all-out dead zone explanation also conflicts with the fact that many studies report higher trawl catches by day than by night (Engås and Soldal 1992;Hjellvik et al 2001Hjellvik et al , 2002. This may partly be explained by a higher catchability in daytime because of more effective herding.…”

Section: Why Do We See Less In the Dark?mentioning

confidence: 97%

“…However, it is easy to construct global test statistics. We followed the ideas in Hjellvik et al (2001Hjellvik et al ( , 2002 to construct two test statistics, one of which takes a possible symmetric pattern into account. In both cases, we test several null hypotheses: H 0 T , there is no diurnal pattern in the total echo abundance, and H q 0 , there is no diurnal pattern in the quantile q of the vertical density profile.…”

Section: Test Statisticsmentioning

confidence: 99%

“…Diurnal variations in the results of bottom-trawl surveys (Casey and Myers 1998;Korsbrekke and Nakken 1999;Hjellvik et al 2002) and acoustic surveys (Engås and Godø 1986;Michalsen et al 1996;Stensholt et al 2002) are well known. The causes of these variations and the relationship between them, however, are poorly understood and hence difficult to treat in survey assessments.…”

Section: Introductionmentioning

confidence: 99%

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Diurnal variation in acoustic densities: why do we see less in the dark?

Hjellvik¹,

Godø²,

Tjøstheim³

2004

Can. J. Fish. Aquat. Sci.

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Diurnal fluctuations in total integrated echo abundance and in vertical density profiles were examined using data from the Norwegian combined acoustic and bottom-trawl survey for demersal fish during winter in the Barents Sea. The total echo abundance was about 40%-50% higher at day than at night. An unknown amount of fish was lost close to the seabed in the acoustic dead zone, but the systematic changes in the near-bottom vertical density profiles did not indicate that migration in and out of the dead zone was the major reason for the large diurnal differences in echo abundance. A more plausible explanation could be that diurnal changes in fish behaviour affect the mean acoustic target strength. Based on the present study, we recommend that the time series of acoustic surveys should be reanalysed, taking the diurnal bias into account. Any comparison of the fish densities indicated by trawl and acoustic surveys will suffer if this bias is not corrected. We believe that model development utilizing this type of information is crucial for future ecosystem-based monitoring.Résumé : Nous avons examiné les fluctuations journalières des abondances totales intégrées basées sur l'écho et des profils verticaux de densité; nous avons utilisé une combinaison de données norvégiennes provenant d'inventaires acoustiques et d'inventaires au chalut de fond de poissons démersaux durant l'hiver dans la mer de Barents. L'abondance totale déterminée à l'écho est d'environ 40-50 % plus élevée le jour que la nuit. Une quantité inconnue de poissons est perdue près du fond dans la zone acoustique morte; cependant, les changements systématiques qui se produisent dans les profils verticaux de densité près du fond n'indiquent pas que l'immigration ou l'émigration dans la zone morte est la raison majeure des importantes différences journalières dans les abondances déterminées à l'écho. Une explication plus plausible est que les changements diurnes de comportement des poissons affecte la force moyenne des cibles acoustiques. Sur la base de notre étude, nous recommandons une nouvelle analyse des séries chronologiques des inventaires acoustiques qui tienne compte des sources d'erreur journalières. Toute comparaison entre les densités de poissons déterminées par les inventaires au chalut et celles données par les inventaires acoustiques sera affectée si cette erreur n'est pas corrigée. Nous croyons que la mise au point de modèles qui utilisent ce genre d'information est essentielle pour la surveillance future à l'échelle de l'écosystème.[Traduit par la Rédaction] Hjellvik et al. 2254

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“…One possible cause of this result is gear avoidance. Several trawling studies have reported catch increases in trawls during nighttime hours that are thought to occur because of reduced visual detection of the trawl (Walsh 1988;Casey and Myers 1998;Hjellvik et al 2002). However, it is also possible that the fishes we studied changed their distribution in response to frontal passages.…”

Section: Discussionmentioning

confidence: 99%

The Effects of Front‐Associated Wind Events and Resultant Sediment Resuspension on Dietary Habits and Caloric Intake of Bay Anchovy and Age‐0 Atlantic Croaker in Mobile Bay, Alabama

Jackson

Cowan

2013

Mar Coast Fish

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We examined the effects of wind‐driven sediment resuspension on the stomach fullness, prey composition, and caloric intake of Bay Anchovy Anchoa mitchilli, a particulate planktivore, and age‐0 Atlantic Croaker Micropogonias undulatus, a benthic omnivore, in Mobile Bay, Alabama. Mobile Bay is a shallow estuary in the northern Gulf of Mexico with substrates ranging from silt to small sand. High‐wind events were associated with cold fronts and were characterized by wind velocities ≥4.0 m/s. Bay Anchovy stomachs were less full during such events and gut contents contained greater contributions by low‐calorie items. Atlantic Croaker stomach fullness did not differ significantly with wind speed. However, prey composition during high‐wind events shifted toward high‐calorie items. These scenarios imply that high‐wind events in Mobile Bay could have an adverse effect on energy uptake by resident Bay Anchovy but may benefit energy uptake by Atlantic Croaker.Received December 14, 2012; accepted March 23, 2013

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Diurnal variation in bottom trawl survey catches: does it pay to adjust?

Cited by 34 publications

References 18 publications

Acoustic data collected during and between bottom trawl stations: consistency and common trends

Acoustic data collected during and between bottom trawl stations: consistency and common trends

Diurnal variation in acoustic densities: why do we see less in the dark?

The Effects of Front‐Associated Wind Events and Resultant Sediment Resuspension on Dietary Habits and Caloric Intake of Bay Anchovy and Age‐0 Atlantic Croaker in Mobile Bay, Alabama

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