The Experts below are selected from a list of 291 Experts worldwide ranked by ideXlab platform
Josef Matěna - One of the best experts on this subject based on the ideXlab platform.
-
The influence of the Trawl mouth opening size and net colour on catch efficiency during sampling of early stages of perch (Perca fluviatilis) and pikeperch (Sander lucioperca) in the bathypelagic layer of a canyon-shaped reservoir
Fisheries Research, 2011Co-Authors: T Jůza, Jan Kubecka, Mojmir Vasek, Jiři Peterka, Martin Čech, Michal Kratochvíl, Jaroslava Frouzová, Josef MatěnaAbstract:Abstract The efficiency of different sized (0.5 m × 2 m, 1 m × 2 m, 2 m × 2 m, 4 m × 2 m) and coloured (black, white) ichthyoplankton Trawl Nets was investigated during daytime in the bathypelagic layer of the Řimov Reservoir (Czech Republic) in late May 2008. Eight to 16 mm long perch ( Perca fluviatilis ) and pikeperch ( Sander lucioperca ) fry were the dominant species in fry catches in this layer. We did not find any significant differences between the densities of either species when black and white Nets were compared or when different sized Nets were compared. Neither were there any significant differences in body lengths of the fish caught in the different Trawls. Our results indicate that both perch and pikeperch fry in the bathypelagic layer are quite passive, without observable avoidance behaviour to the ichthyoplankton Trawl Nets. This is in contrast to active avoidance of the same species and sizes previously observed in the epipelagic layer.
-
the influence of the Trawl mouth opening size and net colour on catch efficiency during sampling of early fish stages
Fisheries Research, 2010Co-Authors: T Jůza, Martin Cech, Jan Kubecka, Mojmir Vasek, Jiři Peterka, Josef MatěnaAbstract:Abstract The efficiency of different sized (0.5 m × 2 m, 1 m × 2 m, 2 m × 2 m, 4 m × 2 m) and coloured (black, white) ichthyoplankton Trawl Nets and the densities of fry between day and night were investigated in the surface stratum of the Řimov Reservoir (Czech Republic) during two surveys in mid-May and early June 2007. In mid-May, perch ( Perca fluviatilis ) was the most abundant fry species in the open water, whereas cyprinids ( Cyprinidae ) dominated 2 weeks later. Minor fry species in the Trawl catches were pikeperch ( Sander lucioperca ) and ruffe ( Gymnocephalus cernua ) in both surveys. The comparison of fry densities during day and night revealed significantly higher day densities for the dominant perch and cyprinids, whereas for pikeperch and ruffe significantly higher densities were observed during the night. No significant differences in efficiency and body lengths of the fry sampled were found for any taxa when black and white Trawl Nets were compared. Comparison of the efficiencies of different sized Trawl Nets revealed different patterns for the dominant perch and cyprinids during both day and night. For perch, the lowest efficiency was observed for the smallest Trawl, whereas the greatest efficiency was observed for the largest Trawl net. The efficiencies were significantly different between Trawls during day and night only for perch. For cyprinids, the efficiencies of different sized Trawl Nets were insignificantly different during both day and night. For pikeperch and ruffe similar trends in efficiency of different sized Trawl Nets were revealed. The lowest efficiency was reached with the smallest Trawl but during the day a significant decline in efficiency of the largest Trawl was also observed. Our results indicate that for sampling perch fry during both day and night and for sampling ruffe and pikeperch fry, especially during the day, a Trawl net with a 1 m 2 mouth is not sufficiently efficient. The density of these fry species is significantly under estimated with such small Nets. The fry body lengths sampled by different sized Trawl Nets did not differ significantly.
Sheryl Hamilton - One of the best experts on this subject based on the ideXlab platform.
-
no evidence of cryptic bycatch causing new zealand sea lion population decline
Proceedings of the National Academy of Sciences of the United States of America, 2018Co-Authors: Jim Roberts, S Childerhouse, Barry G Baker, Sheryl HamiltonAbstract:In PNAS, Meyer et al. (1) analyze whether exclusion devices in Trawl Nets contributed to New Zealand sea lion (NZSL; Phocarctos hookeri ) population decline at the Auckland Islands. We refute the primary conclusion from their correlative assessment: that annual pup production changes (as a measure of population size) were primarily driven by cryptic bycatch of adults in sub-Antarctic Trawl fisheries. We also contest their interpretation that sea lion exclusion devices (SLEDs), used throughout the Auckland Islands squid Trawl fishery since 2004, “…can obscure rather than alleviate fishery impacts on marine megafauna” (1). Meyer et al. (1) compare annual pup estimates with factors that could impact NZSL populations, reporting that when the fisheries interaction rate (IR; NZSL interactions per Trawl) was high in one year, … [↵][1]1To whom correspondence should be addressed. Email: sheryl.hamilton{at}utas.edu.au. [1]: #xref-corresp-1-1
T Jůza - One of the best experts on this subject based on the ideXlab platform.
-
The influence of the Trawl mouth opening size and net colour on catch efficiency during sampling of early stages of perch (Perca fluviatilis) and pikeperch (Sander lucioperca) in the bathypelagic layer of a canyon-shaped reservoir
Fisheries Research, 2011Co-Authors: T Jůza, Jan Kubecka, Mojmir Vasek, Jiři Peterka, Martin Čech, Michal Kratochvíl, Jaroslava Frouzová, Josef MatěnaAbstract:Abstract The efficiency of different sized (0.5 m × 2 m, 1 m × 2 m, 2 m × 2 m, 4 m × 2 m) and coloured (black, white) ichthyoplankton Trawl Nets was investigated during daytime in the bathypelagic layer of the Řimov Reservoir (Czech Republic) in late May 2008. Eight to 16 mm long perch ( Perca fluviatilis ) and pikeperch ( Sander lucioperca ) fry were the dominant species in fry catches in this layer. We did not find any significant differences between the densities of either species when black and white Nets were compared or when different sized Nets were compared. Neither were there any significant differences in body lengths of the fish caught in the different Trawls. Our results indicate that both perch and pikeperch fry in the bathypelagic layer are quite passive, without observable avoidance behaviour to the ichthyoplankton Trawl Nets. This is in contrast to active avoidance of the same species and sizes previously observed in the epipelagic layer.
-
the influence of the Trawl mouth opening size and net colour on catch efficiency during sampling of early fish stages
Fisheries Research, 2010Co-Authors: T Jůza, Martin Cech, Jan Kubecka, Mojmir Vasek, Jiři Peterka, Josef MatěnaAbstract:Abstract The efficiency of different sized (0.5 m × 2 m, 1 m × 2 m, 2 m × 2 m, 4 m × 2 m) and coloured (black, white) ichthyoplankton Trawl Nets and the densities of fry between day and night were investigated in the surface stratum of the Řimov Reservoir (Czech Republic) during two surveys in mid-May and early June 2007. In mid-May, perch ( Perca fluviatilis ) was the most abundant fry species in the open water, whereas cyprinids ( Cyprinidae ) dominated 2 weeks later. Minor fry species in the Trawl catches were pikeperch ( Sander lucioperca ) and ruffe ( Gymnocephalus cernua ) in both surveys. The comparison of fry densities during day and night revealed significantly higher day densities for the dominant perch and cyprinids, whereas for pikeperch and ruffe significantly higher densities were observed during the night. No significant differences in efficiency and body lengths of the fry sampled were found for any taxa when black and white Trawl Nets were compared. Comparison of the efficiencies of different sized Trawl Nets revealed different patterns for the dominant perch and cyprinids during both day and night. For perch, the lowest efficiency was observed for the smallest Trawl, whereas the greatest efficiency was observed for the largest Trawl net. The efficiencies were significantly different between Trawls during day and night only for perch. For cyprinids, the efficiencies of different sized Trawl Nets were insignificantly different during both day and night. For pikeperch and ruffe similar trends in efficiency of different sized Trawl Nets were revealed. The lowest efficiency was reached with the smallest Trawl but during the day a significant decline in efficiency of the largest Trawl was also observed. Our results indicate that for sampling perch fry during both day and night and for sampling ruffe and pikeperch fry, especially during the day, a Trawl net with a 1 m 2 mouth is not sufficiently efficient. The density of these fry species is significantly under estimated with such small Nets. The fry body lengths sampled by different sized Trawl Nets did not differ significantly.
Neil R. Loneragan - One of the best experts on this subject based on the ideXlab platform.
-
Subsurface behavior of bottlenose dolphins (Tursiops truncatus) interacting with fish Trawl Nets in northwestern Australia: Implications for bycatch mitigation
Marine Mammal Science, 2012Co-Authors: V. Jaiteh, Simon J. Allen, Jessica J. Meeuwig, Neil R. LoneraganAbstract:Most studies of delphinid-Trawler interactions have documented the surface behavior of dolphins feeding on discarded bycatch, but not their subsurface behavior around demersal Trawl gear. Using video cameras mounted inside Trawl Nets, we recorded the subsurface behavior of common bottlenose dolphins (Tursiops truncatus) in a demersal fish Trawl fishery in northwestern Australia. Footage from 36 Trawls across the fishery was analyzed to determine the extent of dolphin-gear interactions and the behavior of dolphins inside the Nets. Interaction rates were high, with dolphins present inside and outside the Nets during 29 and 34 Trawls, respectively, and for up to 99% of the Trawl duration. The proportion of foraging behaviors exhibited inside the Nets was higher than the proportions of traveling and socializing behaviors. Twenty-nine individuals were identified inside the net, seven of which returned repeatedly within and between Trawls and fishing trips, but were observed primarily in the same localized areas in which they were first recorded. Our results suggest that entering Trawl Nets may be a frequently occurring, yet specialized behavior exhibited by a small subset of Trawler-associated dolphins. We propose that gear modifications, not spatial or temporal adjustments to fishing effort, have the greatest potential to reduce dolphin bycatch.
-
Sub-surface behaviour of bottlenose dolphins (Tursiops truncatus) interacting with fish Trawl Nets in north-western Australia
2011Co-Authors: V. Jaiteh, Simon J. Allen, Jessica J. Meeuwig, Neil R. LoneraganAbstract:Most studies on the interactions between dolphins and Trawl fisheries have focused on the opportunistic feeding of dolphins on discards at the surface. Little is known about sub-surface associations between dolphins and actively fishing Trawl Nets. Using underwater video footage recorded inside Trawl Nets, we evaluated behavioural aspects of interactions between common bottlenose dolphins (Tursiops truncatus) and Trawl Nets in the Pilbara Trawl fishery. The interaction rates were very high; in 85 hours of footage collected from 36 Trawls, dolphins were recorded inside Trawl Nets during 29 (81%) Trawls and outside Trawl Nets in 34 (94%) Trawls, and for up to 98% and 99% of the Trawl duration, respectively. The proportion of foraging behaviours was significantly higher for dolphins inside the net (54%) than those outside the net (31%), indicating that dolphins were presented with a concentrated food source inside the net. Dolphins observed outside the net spent time ‘trampolining’ and socialising, indicating that they were motivated by several factors to approach and interact with Trawl Nets. Twenty-nine individuals were identified inside the net, some returning to the net numerous times within each Trawl and between different Trawls and fishing trips. Our results suggest that these dolphins are highly motivated to interact with Trawl Nets and that entering Nets may be a specialised behaviour exhibited only by a subset of Trawler-associated dolphins. We conclude that gear modifications, not spatial or temporal adjustments to fishing effort, have the greatest potential to reduce dolphin bycatch in this fishery.
Jim Roberts - One of the best experts on this subject based on the ideXlab platform.
-
no evidence of cryptic bycatch causing new zealand sea lion population decline
Proceedings of the National Academy of Sciences of the United States of America, 2018Co-Authors: Jim Roberts, S Childerhouse, Barry G Baker, Sheryl HamiltonAbstract:In PNAS, Meyer et al. (1) analyze whether exclusion devices in Trawl Nets contributed to New Zealand sea lion (NZSL; Phocarctos hookeri ) population decline at the Auckland Islands. We refute the primary conclusion from their correlative assessment: that annual pup production changes (as a measure of population size) were primarily driven by cryptic bycatch of adults in sub-Antarctic Trawl fisheries. We also contest their interpretation that sea lion exclusion devices (SLEDs), used throughout the Auckland Islands squid Trawl fishery since 2004, “…can obscure rather than alleviate fishery impacts on marine megafauna” (1). Meyer et al. (1) compare annual pup estimates with factors that could impact NZSL populations, reporting that when the fisheries interaction rate (IR; NZSL interactions per Trawl) was high in one year, … [↵][1]1To whom correspondence should be addressed. Email: sheryl.hamilton{at}utas.edu.au. [1]: #xref-corresp-1-1
