Effects of feeding conditions and size differences on aggressive behaviour and cannibalism in the Pacific bluefin tuna Thunnus orientalis (Temminck and Schlegel) larvae

We examined the effects of feeding conditions and size differences on the aggressive behaviour and cannibalism in Pacific bluefin tuna (PBT) Thunnus orientalis larvae. In a 24 h experiment, restricted feeding alone was found to remarkably increase the frequency of aggressive behaviour, which was further elevated by differences in fish size. In a 4‐day rearing experiment, while aggressive behaviour was increased by restricted feeding alone, the frequency of cannibalism did not change significantly. Although the frequency of aggressive behaviour did not increase with difference in size factor, small fish in this group gradually tended to die over 4‐day period. In the restricted feeding and size difference group, large fish were observed to bite the small fish, and almost all the small fish died on the day after the start of the experiment. These results suggest that the aggressive behaviour of PBT larvae is chiefly increased by the shortage of live food; however, deaths related to cannibalism mainly occurred in small larvae and rapidly increased with food restriction and differences in fish size.     

城市景观安全格局及其预案研究——以厦门市为例

以ArcGIS、ENVI等为主要技术平台,采用“斑块-廊道-基质”的模式分析厦门市的景观安全格局,综合考虑自然因子和社会因子,并对不同的因子赋予不同的阻力值和权重,制定低安全水平格局的城市扩张优先发展预案、中安全水平格局的协调发展预案、高安全水平格局的生态保护优先预案3种城市扩张预案,利用最小累积阻力模型(MCR)分别建立3种预案的累积阻力表面,并对3种预案进行综合评价。结果显示：（1）3种安全水平的适宜城镇用地面积分别为694.87、575.1、454.96 km²,可提供新的城镇用地面积分别为433.12、313.12、193.21 km²;（2）随着安全水平的提高,适宜生态的用地逐渐增加,适宜城镇建设的用地逐渐减少;（3）低安全水平和中安全水平下的城市扩张预案均可满足厦门市“十二五”规划预测的2020年的城镇建设用地需求,高安全水平的城市扩张在生态优先保护的前提下,建设用地需做出让步。     

Annual variation in otolith increment widths of walleye pollock (Gadus chalcogrammus) larvae in Funka Bay,Hokkaido, Japan

To clarify relationships between year‐class strength and larval growth of walleye pollock (Gadus chalcogrammus), and oceanographic conditions in the Pacific stock off Hokkaido and Tohoku, Japan, we undertook conductivity/temperature/depth (CTD) observations and investigated larval densities, larval otolith increment widths and larval prey densities (of copepod nauplii) of the 2008, 2009, 2010 and 2011 yr classes in Funka Bay. Oyashio Coastal Water (OCW) flowed into the bay in late February in 2008, 2010 and 2011, and the mean water temperatures decreased to 1.9–3.1 °C in March. OCW was not observed in 2009, and it was warm in late February (≥3.4 °C). Increment widths of lapillar otoliths during the yolk‐sac stage were wide in 2009 and 2011, medium in 2010 and narrow in 2008. Increment widths during the first‐feeding stage tended to become wider as the hatch month progressed, and the annual variation during the first‐feeding stage was larger than that of the yolk‐sac stage. The densities of the primary food for the larvae were high in 2008 when larval increment widths were narrowest, so the effect of prey abundance on larval growth appeared to be small. The ranking of the larval abundance in March was nearly coincident with that of the increment width during the larval stage. We, therefore, suggest that the larval growth rate is associated with the mortality rate and that the growth–mortality hypothesis may be applicable to walleye pollock in Funka Bay. Feeding success under warm water conditions may be an important factor that contributes towards high growth rates.     

大黄鱼耳石锶标志技术

利用六水合氯化锶进行大黄鱼(Larimichthys crocea)幼鱼耳石的标记,探讨了锶元素对大黄鱼幼鱼耳石的元素指纹标记效果,分析了锶元素标记对大黄鱼幼鱼生长和存活的影响。结果表明:(1)阶段性倍增饲养水体中锶离子浓度可使标记组个体在特定耳石区段的Sr/Ca比值显著提升,形成与对照组个体和野生个体在该耳石区段Sr/Ca比值的显著差异(P0.01),标记组、对照组和野生个体在该耳石区段的Sr/Ca比值分别为(3.58±1.09)mmol/mol、(1.73±0.08)mmol/mol和(1.09±0.35)mmol/mol。此区段形成的Sr/Ca比值峰值可视作标记组个体的耳石锶元素人工标记。(2)标志组和对照组大黄鱼幼鱼的生长速率和存活率均无显著性差异(P0.05),表明此项标记技术对受标个体的生长和存活状况不会产生显著负面影响,可用作大黄鱼增殖放流鱼苗的规模化标记手段。     

Isolation and characterization of bacteria causing mortality in early stage larvae of captive‐bred Japanese eels (Anguilla japonica Temminck & Schlegel)

Bacteria with lethal effect on eel larvae were isolated from moribund captive‐bred eel larvae and their 16S rRNA gene sequences were analysed. Nucleotide sequence of 10 isolates showed highest similarity with Lacinutrix algicola, Crocinitomix catalasitica and Pseudoalteromonas rubra. Age‐dependent changes in the susceptibility of eel larvae were observed in response to challenge by a highly lethal isolate. Compared with 10 and 11 days after hatching (DAH), larval susceptibility to the highly lethal isolate was lower at 18 DAH. We found that the bacterial isolates have lethal effect on the captive‐bred eel larvae, especially at the early developmental stage. These results will be useful to establish appropriate culture practices for eel larvae that will improve the success of mass production of glass eels for aquaculture.     

Wild boar populations up,numbers of hunters down? A review of trends and implications for Europe

Across Europe, wild boar numbers increased in the 1960s–1970s but stabilised in the 1980s; recent evidence suggests that the numbers and impact of wild boar has grown steadily since the 1980s. As hunting is the main cause of mortality for this species, we reviewed wild boar hunting bags and hunter population trends in 18 European countries from 1982 to 2012. Hunting statistics and numbers of hunters were used as indicators of animal numbers and hunting pressure. The results confirmed that wild boar increased consistently throughout Europe, while the number of hunters remained relatively stable or declined in most countries. We conclude that recreational hunting is insufficient to limit wild boar population growth and that the relative impact of hunting on wild boar mortality had decreased. Other factors, such as mild winters, reforestation, intensification of crop production, supplementary feeding and compensatory population responses of wild boar to hunting pressure might also explain population growth. As populations continue to grow, more human–wild boar conflicts are expected unless this trend is reversed. New interdisciplinary approaches are urgently required to mitigate human–wild boar conflicts, which are otherwise destined to grow further. © 2014 Crown copyright. Pest Management Science © 2014 Society of Chemical Industry     

Population dynamics and stock assessment of Colossoma macropomum caught in the Manacapuru Lake system (Amazon Basin,Brazil)

Colossoma macropomum is the second largest scaled fish in the Amazon basin. Reduced harvests in recent decades suggest that populations of this species are already overexploited in some areas. In this study, the population dynamics of C. macropomum was investigated using length and weight data for fish caught in the Manacapuru Lake system, a large ria lake located along the lower reach of the Solimões River. A total of 1270 individuals of C. macropomum with standard lengths varying from 17 to 62 cm and mean length of 31.0 ± 6.7 cm were sampled. Weights varied from 165 to 8195 g, and mean weight was 1148.3 ± 883.8 g. Maximum sustainable yield was estimated at 285.8 g recruit⁻¹, corresponding to a fishing mortality of 0.51 year⁻¹. A scenario analysis based on changes in fishing mortality and age at first capture, two parameters potentially addressed by fishing management strategies, suggested that any improvement in fishing yield depends on increases in age at first capture.     

Population characteristics of channel catfish near the northern edge of their distribution: implications for management

Channel catfish, Ictalurus punctatus (Rafinesque), populations in six lakes in northern Idaho, USA, were sampled to describe their population characteristics. During the summers of 2011 and 2012, 4864 channel catfish were sampled. Channel catfish populations had low to moderate catch rates, and length structure was dominated by fish <400 mm. Channel catfish were in good body condition. All populations were maintained by stocking age‐1 or age‐2 fish. Growth of fish reared in thermally enriched environments prior to stocking was fast compared to other North American channel catfish populations. After stocking, growth of channel catfish declined rapidly. Once stocked, cold water temperatures, prey resources and (or) genetic capabilities limited growth. Total annual mortality of age 2 and older channel catfish was generally <40%. Tag returns indicated that angler exploitation was low, varying from 0 to 43% among lakes. This research provides insight on factors regulating channel catfish population dynamics and highlights important considerations associated with their ecology and management.     

延迟初次摄食对长薄鳅仔鱼的影响

为丰富长薄鳅（Leptobotia elongata）早期生活史资料,开展了延迟投喂对长薄鳅仔鱼形态、初次摄食率、不可逆点、生长率和死亡率的影响研究。结果显示：饥饿仔鱼鱼体消瘦、头大、尾小、身体显得不匀称,器官发育停止,游动缓慢;日龄2 d 时,初次摄食率达到60％,日龄3 d 时达到了100％,不可逆点出现在15～16 d,可恢复性饥饿时间长达13 d;饥饿仔鱼体长基本维持不变,甚至出现负增长;饥饿仔鱼的死亡率高峰出现在15～16 d,与不可逆点在同一天,当天死亡率达到45．92％,瞬时死亡率为32．91％。