Biodiversiteit onder glas : Voedsel voor luizenbestrijders

In het praktijknetwerk biodiversiteit onder glas is door glastuinders geëxperimenteerd met bloemen in en rond de kas . Al dan niet in combinatie met bankerplanten zoals granen. Deze brochure is gemaakt om kennis over bloemen en biologische bestrijders te geven en specifiek het nut van biodiversiteit . Biodiversiteit geeft ondersteuning aan meerdere natuurlijke bestrijders van bladluizen. Vooral in de paprikateelt vormen bladluizen soms een ware plaag. Het praktijknetwerk heeft kennis opgeleverd die helpt het agro-eco systeem te versterken

Condition and survival of discards in tickler chain beam trawl fisheries

Dutch demersal fisheries in the North Sea is a mixed fishery that mainly targets Dover sole (Solea solea) with plaice (Pleuronectes platessa), turbot (Scophthalmus maximus), brill (Scophthalmus rhombus) and other species as valuable bycatches. The fleet currently uses two gear types: pulse beam trawls and conventional tickler chain beam trawls. Pulse beam trawlers operate with a temporary exemption from the EU prohibition to use electric stimulation in fishing gears, of which the last exemptions will expire in June 2021.To assess the consequences of transitions between pulse and tickler chain beam trawling for discards mortality, knowledge on the discards survival probabilities as well as the amount of discards is required for both gear types. The objective of the current study was to estimate discards survival probabilities for undersized plaice, sole, turbot, brill and thornback ray discarded by tickler chain beam trawl fisheries using fish condition as a proxy for survival probability. To this end the condition and reflex impairment of undersized fish in the catches of tickler chain beam trawlers were assessed and compared to similar data collected from pulse trawl fisheries. For spotted ray we assessed fish condition in tickler chain beam trawling but could not estimate its discards survival probability because a relation between survival probability and fish condition is lacking for this species. In this study direct mortality imposed by the tickler chain beam trawling ranged between 10 and 32% in flatfish species and was between 2-4 times higher than in pulse beam trawling. Direct mortality in ray species was lowest among the investigated species (2-8%) and did not differ between the two gear types. Differences in direct mortality were reflected in the condition scores. Direct mortality of sole was higher in tickler chain beam trawling (17%) than in pulse beam trawling (8%). Brill, turbot and plaice discarded by pulse beam trawling are in better condition than when discarded by tickler chain beam trawl fisheries. For sole no effect of gear type on fish condition could be detected. We consider the lower fish condition scores of brill, plaice and turbot from tickler chain beam trawling a direct reflection of the higher mechanical impact of this gear on the fish. For thornback ray and spotted ray no effect of gear type on fish condition could be detected. The predicted survival of plaice, brill and turbot discards indicate that discards survival could indeed be lower in tickler chain beam trawl fisheries compared to pulse beam trawl fisheries. For sole and thornback ray discards we found no evidence for such difference between gear types. The discards survival probabilities for tickler chain beam trawling as presented in this study should be considered as predictions based on the currently best available information instead of definite values. Actual measurements of discards survival at sea are needed to confirm and quantify survival probabilities in tickler chain beam trawling

Quantifying behavioural and muscle activation thresholds of non-target fishes for pulsed electric fields as used in flatfish electrotrawling

Electrical pulse trawling is an alternative to conventional beam trawling for common sole (Solea solea), with substantially less discards, lower fuel consumption, and reduced impact on the benthic ecosystem. Pulsed electric fields between electrode arrays induce a muscle cramp, immobilising the fishes on the sea bottom, making them easier to catch. Concerns exist, however, that the electric fields extend well beyond the netting, potentially affecting fishes outside the trawl track. Here, we address these concerns by measuring amplitude thresholds for involuntary muscle contractions and for behavioural responses, and compare these response thresholds to the field strengths around the fishing gear. For behavioural threshold measurements, both electro-receptive and non-electro-receptive fish were placed in a large circular tank with seven, individually controllable, evenly spaced electrode pairs, spanning the tank’s diameter. Responses were assessed from high-speed camera recordings for different pulse amplitudes and for different positions of the fish relative to the stimulating electrodes. Computer simulations of the electric field, verified with measurements in the experimental setup, were subsequently used to determine the threshold electric field strength at the location of the animal. For measurements of involuntary muscle contractions, fish were anaesthetised and placed in a tank with electrode pairs at different locations along the anteroposterior axis of the fish. Thresholds were established by increasing the pulse amplitude until a visible muscle twitch was observed. Threshold field strengths for both behavioural responses and for involuntary muscle activations were subsequently compared to the electric fields around commercial fishing gears. Preliminary results show that behavioural thresholds were not substantially lower in electro-receptive fish than in non-electro-receptive fish. Moreover, the behavioural field strength thresholds were similar to those for involuntary muscle activations. By modelling the field strengths around commercial electrode arrays, we show that both behavioural and muscle activation responses will be limited to distances less than 1 metre from the fishing gear. These findings suggest that electrical pulses as used in pulse trawling are unlikely to substantially affect the investigated fish species outside the trawl track

Quantifying behavioural and muscle activation thresholds of non-target fishes for pulsed electric fields as used in flatfish electrotrawling

Electrical pulse trawling is an alternative to conventional beam trawling for common sole (Solea solea), with substantially less discards, lower fuel consumption, and reduced impact on the benthic ecosystem. Pulsed electric fields between electrode arrays induce a muscle cramp, immobilising the fishes on the sea bottom, making them easier to catch. Concerns exist, however, that the electric fields extend well beyond the netting, potentially affecting fishes outside the trawl track. Here, we address these concerns by measuring amplitude thresholds for involuntary muscle contractions and for behavioural responses, and compare these response thresholds to the field strengths around the fishing gear. For behavioural threshold measurements, both electro-receptive and non-electro-receptive fish were placed in a large circular tank with seven, individually controllable, evenly spaced electrode pairs, spanning the tank’s diameter. Responses were assessed from high-speed camera recordings for different pulse amplitudes and for different positions of the fish relative to the stimulating electrodes. Computer simulations of the electric field, verified with measurements in the experimental setup, were subsequently used to determine the threshold electric field strength at the location of the animal. For measurements of involuntary muscle contractions, fish were anaesthetised and placed in a tank with electrode pairs at different locations along the anteroposterior axis of the fish. Thresholds were established by increasing the pulse amplitude until a visible muscle twitch was observed. Threshold field strengths for both behavioural responses and for involuntary muscle activations were subsequently compared to the electric fields around commercial fishing gears. Preliminary results show that behavioural thresholds were not substantially lower in electro-receptive fish than in non-electro-receptive fish. Moreover, the behavioural field strength thresholds were similar to those for involuntary muscle activations. By modelling the field strengths around commercial electrode arrays, we show that both behavioural and muscle activation responses will be limited to distances less than 1 metre from the fishing gear. These findings suggest that electrical pulses as used in pulse trawling are unlikely to substantially affect the investigated fish species outside the trawl track