Effects of variable discharge on the velocity use and shoaling behaviour of Phoxinus phoxinus

The swimming and shoaling behaviour of Phoxinus phoxinus was investigated in four identical channels connected to the River Frome, U.K. Minnows (mean length 29.5 mm) were stocked at an initial density of 100 fish per channel (22.2 fish m⁻²). The position of all visible fish in the channels was recorded at basal and elevated discharges, and use of velocity habitats inferred. Although a range of velocities (including zero) was present at both discharges, the fish selected higher mean velocities at elevated discharges than at basal discharges. Habitat suitability was significantly different between periods, emphasizing the effect of habitat availability and past experience upon habitat use. This appeared to result from the fish holding position at points with variable flow conditions, rather than moving to points with more suitable conditions. Shoal size tended to be reduced during and after elevated discharge, although variability between replicates was high. Small groups of fish tended to break off during the high flow events.     

Responses of the northern anchovy to the dynamics of the pelagic environment: identification of fish behaviours that may leave the population under risk of overexploitation

Northern anchovy Engraulis mordax , in an upwelling area off the west coast of Baja California, Mexico, had several strategies in response to chlorophyll a distribution and availability. When the pigment was scarce, northern anchovies practically disappeared from the area and they returned to coastal waters when it was abundant. The fish gathered in specific areas where low turbulence mixing and high concentrations of chlorophyll a existed. The northern anchovies, responding to food concentration in a stable environment, were probably vulnerable to overexploitation because they were highly concentrated. More than 80% of the total fish density, estimated by acoustics, was recorded in a reduced area. Northern anchovies may have been vulnerable to the purse‐seiner fleet because they were swimming at shallow depth; they were close to shore not far from the fleet's base and they were concentrated in an area where several fishing boats could catch them. Studying the responses of shoaling fishes to fluctuation in the pelagic environment, with the intention of identifying behaviours that may leave the stock highly vulnerable to fishing, may help guide their management.     

房室海绵化石的微机研究:性状演化

利用微机对房室海绵进行了１）属的清理工作，２）标准化术语的建立与属的标准化术语描述，３）建数据库，４）性状的统计分析。并发现了房室海绵出水管类型、房室排列方式、房室充填物类型、孔和管、体型和房室形态方面的六大演化趋向。     

Impact of flood on distribution of bathypelagic perch fry layer along the longitudinal profile of large canyon-shaped reservoir

Previous studies have shown that under normal spring conditions, the layer of bathypelagic perch Perca fluviatilis fry (BPF) is equally distributed along most of the longitudinal profile of reservoirs. In the first half of June 2004, local flooding entering the large canyon‐shaped Orlík Reservoir (Czech Republic) completely flushed out the existing fry community from the 31 km long riverine part of the reservoir. The pelagic zone in this reach was then recolonized by cyprinid (mainly roach Rutilus rutilus and bream Abramis brama) fry being of either littoral or riverine origin. Subsequently, the BPF layer was recorded only in the 22 km long lacustrine part of the reservoir. In the upper reach of this part where, due to the sudden increase in volume, the water current slowed down rapidly and fry originating from both riverine and central parts of the reservoir gathered in high numbers, two distinct BPF layers were observed. During mid‐day, the upper BPF layer, created predominantly by shoaling fishes (abundance >126 000 individuals ha^?1), occurred between 6 and 10 m. A second, lower BPF layer, created by non‐shoaling fishes exclusively (30 000 individuals ha^?1), was recorded between 12 and 17 m depth. Both upper and lower BPF layer were composed of perch (69·6 and 66·8% in abundance respectively) and zander Sander lucioperca (29·8 and 28·6% in abundance respectively). In the lower BPF layer, ruffe Gymnocephalus cernuus also contributed considerably to the fry assemblage (4·0% in abundance). Perch from the upper BPF layer (mean 25·1 mm total length, L_T) did not differ in size from perch from the lower BPF layer (mean 25·0 mm L_T). Similarly, zander from the upper BPF layer (mean 27·2 mm L_T) were almost the same size as those from the lower BPF layer (mean 26·9 mm L_T). Perch from both BPF layers, however, were noticeably smaller than zander. The results from acoustic survey and complementary net catches suggest that no epipelagic perch fry were found in the reservoir where thermal stratification had been destroyed by flooding and windy weather.     

Home range of the Japanese fluvial sculpin, Cottus pollux, in relation to nocturnal activity patterns

Patterns of space use related to the activity of individual Japanese fluvial sculpins, Cottus pollux, were examined during the non-breeding season, in the upper reaches of the Inabe River, central Japan. Sculpins appeared more frequently at night than in daytime. Among 31 recaptured sculpins, 30 (96.8%) showed nocturnal activity patterns, there being no fish which exhibited an entirely diurnal activity pattern. Of 21 sculpins captured both in daytime and at night, the most common pattern of space use (n = 14, 66.7%) was that in which the nocturnal home range entirely encompassed the diurnal range. Overall, nocturnal home ranges were significantly larger than diurnal ranges. Active sculpins were rarely found on sand-associated substrata in daytime, but were seen more frequently on such substrata at night.     

Using unmanned aerial vehicle (UAV) surveys and image analysis in the study of large surface‐associated marine species: a case study on reef sharks Carcharhinus melanopterus shoaling behaviour

A novel image analysis‐based technique applied to unmanned aerial vehicle (UAV) survey data is described to detect and locate individual free‐ranging sharks within aggregations. The method allows rapid collection of data and quantification of fine‐scale swimming and collective patterns of sharks. We demonstrate the usefulness of this technique in a small‐scale case study exploring the shoaling tendencies of blacktip reef sharks Carcharhinus melanopterus in a large lagoon within Moorea, French Polynesia. Using our approach, we found that C. melanopterus displayed increased alignment with shoal companions when distributed over a sandflat where they are regularly fed for ecotourism purposes as compared with when they shoaled in a deeper adjacent channel. Our case study highlights the potential of a relatively low‐cost method that combines UAV survey data and image analysis to detect differences in shoaling patterns of free‐ranging sharks in shallow habitats. This approach offers an alternative to current techniques commonly used in controlled settings that require time‐consuming post‐processing effort.     

The effect of sex and shoal size on shoaling behaviour in Danio rerio

Male and female zebra fish Danio rerio were given choices of shoals that differed in sex and size. Male zebra fish preferred to associate with female shoals over male shoals, but had no preference when given a choice between a mixed‐sex shoal and either a male or female shoal. Female zebra fish showed no significant preference when given a choice between male and females shoals, nor between mixed‐sex shoals and either male or female shoals. When given choices between shoals of differing size, females preferred to associate with the larger shoal, whether or not they were composed of males or females. Males, however, had no preference for larger shoals over smaller shoals, whether or not they were composed of males or females. These results showed that male zebra fish were capable of distinguishing between males and females solely on the basis of visual cues. Furthermore, these results demonstrated a significant difference between the shoaling choices of male and female zebra fish, which may indicate a difference in the function of shoaling for the two sexes.     

Scents and scents-ability: pollution disrupts chemical social recognition and shoaling in fish

Chemical cues are of enormous importance in mediating the behaviour of animals, enabling them to navigate throughout their habitats, to detect the presence of predators or prey and for social recognition-identifying and discriminating between conspecifics. In many species of freshwater fish, social recognition is known to be based primarily on chemical cues. Such recognition mechanisms are vulnerable to disruption by the presence of anthropogenic contaminants in the aquatic environment. Here we show that acute exposure to low, environmentally relevant dosages of the ubiquitous contaminant, 4-nonylphenol, can seriously affect social recognition and ultimately social organization in fishes. A 1 hour 0.5 microgl-1 dose was sufficient to alter the response of members of a shoaling fish species (juvenile banded killifish, Fundulus diaphanus) to conspecific chemical cues. Dosages of 1-2 microgl-1 caused killifish to orient away from dosed conspecifics, in both a flow channel and an arena. Given the overall importance of shoaling as an adaptive strategy against predators and for locating food, it is likely that its disruption by anthropogenic contaminants would have serious implications for fishes' fitness.     

蛹虫草菌丝生长研究

通过对 4种不同来源的蛹虫草菌种 ,在 5种不同配方培养基上菌丝生长情况进行了比较研究。结果表明 ,不同培养基配方对不同来源的蛹虫草菌种培养菌丝的长速和长势存在较大的差异。     

Migratory decisions in birds: extent of genetic versus environmental control

Migration is one of the most spectacular of animal behaviors and is prevalent across a broad array of taxa. In birds, we know much about the physiological basis of how birds migrate, but less about the relative contribution of genetic versus environmental factors in controlling migratory tendency. To evaluate the extent to which migratory decisions are genetically determined, we examined whether individual western burrowing owls (Athene cunicularia hypugaea) change their migratory tendency from one year to the next at two sites in southern Arizona. We also evaluated the heritability of migratory decisions by using logistic regression to examine the association between the migratory tendency of burrowing owl parents and their offspring. The probability of migrating decreased with age in both sexes and adult males were less migratory than females. Individual owls sometimes changed their migratory tendency from one year to the next, but changes were one-directional: adults that were residents during winter 2004–2005 remained residents the following winter, but 47% of adults that were migrants in winter 2004–2005 became residents the following winter. We found no evidence for an association between the migratory tendency of hatch-year owls and their male or female parents. Migratory tendency of hatch-year owls did not differ between years, study sites or sexes or vary by hatching date. Experimental provision of supplemental food did not affect these relationships. All of our results suggest that heritability of migratory tendency in burrowing owls is low, and that intraspecific variation in migratory tendency is likely due to: (1) environmental factors, or (2) a combination of environmental factors and non-additive genetic variation. The fact that an individual’s migratory tendency can change across years implies that widespread anthropogenic changes (i.e., climate change or changes in land use) could potentially cause widespread changes in the migratory tendency of birds.