Effects of predator-induced visual and olfactory cues on 0+ perch (Perca fluviatilis L.) foraging behaviour

Abstract –  Foraging juvenile fish with relatively high food demands are usually vulnerable to various aquatic and avian predators. To compromise between foraging and antipredator activity, they need exact and reliable information about current predation risk. Among direct predator-induced cues, visual and olfactory signals are considered to be most important. Food intake rates and prey-size selectivity of laboratory-reared, naive young-of-the-year (YOY) perch, Perca fluviatilis , were studied in experiments with Daphnia magna of two size classes: 2.8 and 1.3 mm as prey and northern pike, Esox lucius , as predator. Neither total intake rate nor prey-size selectivity was modified by predator kairomones alone (water from an aquarium with a pike was pumped into the test aquaria) under daylight conditions. Visual presentation of pike reduced total food intake by perch. This effect was significantly more pronounced (synergistic) when visual and olfactory cues were presented simultaneously to foraging perch. Moreover, the combination of cues caused a significant shift in prey-size selection, expressed as a reduced proportion of large prey in the diet. Our observations demonstrate that predator-induced olfactory cues alone are less important modifiers of the feeding behaviour of naive YOY perch than visual cues under daylight conditions. However, pike odour acts as a modulatory stimulus enhancing the effects of visual cues, which trigger an innate response in perch.     

Evaluation of a simple means to reduce discard in the Kattegat-Skagerrak Nephrops (Nephrops norvegicus) fishery: Commercial testing of different codends and square-mesh panels

Discarding of fish species in the Kattegat-Skagerrak Nephrops directed fisheries remains at high levels. In this work we have tested four sets of codends pair-wise with the catch comparison technique under full commercial conditions to assess their potential in reducing the catch of undersized commercial species, in particular cod. We investigate the position of a 90 mm square-mesh panel (SMP), the effect of increasing the mesh size from 90 to 120 mm in the SMP, the effect of inserting a 90 mm SMP in an 80 mm codend and the effect of increasing the codend mesh size from 90 to 120 mm in a total of 89 hauls. Inserting the SMP 3–6 m from the codline compared to 6–9 m from the codline, reduced catches of cod above the minimum landing size (MLS) and Nephrops above and below the MLS. Increasing the mesh size in the SMP from 90 to 120 mm increased the catch of cod above the MLS in weight with an overall increase of 12% in the revenue. The effect of installing a 90 mm SMP 6–9 m from the codline in a nominal 80 mm codend had no effect on the catch of cod. Increasing the nominal codend mesh size from 90 to 120 mm reduced the catch of all species below the MLS, except monkfish. Catches of Nephrops above the MLS were, however, reduced by approximately one third and the total loss in revenue was 21%.     

Non-commercial invertebrate discards in an experimental trammel net fishery

Abstract  Non-commercial invertebrate discards in an experimental trammel net fishery were studied in relation to selectivity of the gear, depth, soak time and season. Forty experimental fishing trials were carried out over a 1-year period with six combinations of small mesh (100, 120 and 140 mm) inner and large mesh (600 and 800 mm) outer panels. On average, 43.8 ± 12.2 (SD) (individuals 1000 m⁻¹ of net) of non-commercial invertebrates were discarded, accounting for 48% and 65% of the total catch and total discards by numbers, respectively. Within non-commercial invertebrates discards, the six most abundant species by number were Phallusia mammillata (Cuvier) (27.5%), Cymbium olla (L.) (13.0%), Sphaerechinus granularis (Lamarck) (11.3%), Paracentrotus lividus (Lamarck) (10.9%), Astropartus mediterraneus (Risso) (8.2%) and Astropecten aranciacus (L.) (8.1%); Echinoderms (43.1%) particularly important. The highest and lowest discard ratios were found in autumn and winter, respectively. Discards generally decreased with depth, varied considerably in relation to soak time and were not related to mesh size combinations. Trammel nets seem to be the most important gear in terms of ecological impacts on benthic invertebrates compared with other coastal fishing gears and at the depths studied (15–60 m).     

南海北部拖网35．2与30．3mm方目网囊渔获选择性比较

根据1997年10月和2000年11~12月的拖网网囊网目选择性试验资料,对网目内径35.2mm方目和30.3mm方目网囊的渔获选择性进行了比较和分析。对比试验结果表明,35.2mm方目网囊渔获尾数总逃逸率为39.28%、重量总逃逸率为16.18%,高于30.3mm方目网囊的28.40%和7.47%,35.2mm方目网囊的渔获选择性有所提高;2种规格方目网囊及其套网中出现的渔获种类较为相似,具有释放鱼类种类少、数量低的共同特点,且在渔获选择性能上的差别还不明显,对渔获种类数量的释放效果都相当有限;作为优势释放种类,大头狗母鱼、条尾绯鲤和多齿蛇鲻在2种规格方目网囊中的尾数逃逸率和重量逃逸率分别在42.9%~65.8%和24.2%~45.0%之间;其中条尾绯鲤和多齿蛇鲻的50%选择体长均未达到最低可捕标准。总体来看,2种规格方目网囊对渔获的总体释放效果还不理想,要实现负责任捕鱼,需进一步放大拖网方目网囊的网目尺寸。     

捕虾桁拖网网囊网目的选择性研究

当网囊网目分别为４０ｍｍ,４５ｍｍ和５０ｍｍ时,哈氏仿对虾的５０％选择体长分别为８５．８８,９０．２６,９５．３２ｍｍ;中华管鞭虾的３０％选择体长为８７．５８,８８．０９,９２．５６ｍｍ;鹰爪虾的５０％选择丛长为８５．０４,８５．９６％,８８．３２ｍｍ。三种虾类的５０％选择体长和网囊网目内径的线性回归方程为,哈氏仿对虾Ｌ０．５－４８．０３＋０．９４Ｍｅ中华管鞭虾;Ｌ０．５＝６７．０＋０．４９８Ｍｅ     

Evaluation of codends with sorting grids, exit windows, and diamond meshes: Size selection and fish behaviour

This paper presents the results of an experiment aimed at improving the size selection of cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) in the Nordic bottom trawl fishery. Three systems simulating commercial conditions were tested: a 135 mm diamond-mesh codend fitted with a 55 mm sorting grid (Sort-V); a 135 mm diamond-mesh codend fitted with two lateral exit windows; and a codend built entirely of 155 mm diamond mesh. The selectivity curves showed similar selection ranges (SR) for the three systems. For cod, the mean SRs were around 8 cm, while for haddock, they were around 6 cm. All the estimated l₅₀ values were far above the minimum landing sizes (MLS). For cod, the mean l₅₀s were 56.1, 53.9, and 60.7 cm for the sorting grid, exit windows, and diamond-mesh configurations, respectively, while for haddock, they were 50.2, 50.6, and 49.9 cm, respectively. Underwater observations revealed that most of the fish escaped from the grid and exit-window codends as soon as they reached the vicinity of the sorting device. In contrast, fish remained inside the diamond-mesh codend for a longer time, and consequently were more exposed to physical damage before escape. In addition, many fish escaped from this codend during haul back and these fish were not likely to survive due to the rapid changes in pressure. Thus, the selectivity results obtained with this type of codend should be interpreted carefully.     

基于结构方程模型的绿色蔬菜消费者购买意愿研究

了解消费者对绿色蔬菜的认知水平及购买意愿,对促成消费者绿色蔬菜的实际购买行为、推动绿色蔬菜产业的发展、提升涉农企业及农户的收入水平都具有积极的现实意义。以计划行为基础构建绿色蔬菜购买意愿影响因素理论模型,在哈尔滨收集了900份有效问卷,利用SPSS及AMOS软件对收集的数据进行分析。结果表明:消费者对绿色蔬菜的认知水平、健康环保意识、行为态度、主观规范、感知行为控制显著正向影响绿色蔬菜的购买意愿。其中,主观规范、行为态度对购买意愿的影响最大。以人口学变量为调节变量进行的多群组分析显示,家庭年收入、性别、年龄、教育程度、家里是否有老人或小孩同住等人口学变量在不同群组间的效应存在显著差异。     

盐胁迫对苗期湖南稷子K+、Na+含量与分布的影响

以湖南稷子(Echinochloa frumentacea)为材料,设置不同浓度(0、25、50、75、100、125、150、200 mmol·L-1)的NaCl和Na2 SO4作为胁迫处理,探讨盐胁迫对湖南稷子苗期K+、Na+吸收与分布特性的影响.结果表明,随着NaCl和Na2 SO4浓度的增加,湖南稷子叶片、茎鞘...