Phylogeography and genetic diversity of Psammophis schokari (Serpentes) in North Africa based on mitochondrial DNA sequences

The snake Psammophis schokari has a widespread distribution across North Africa, and in Morocco/Western Sahara is represented by three different morphotypes: striped, unicoloured and the Western-Sahara morph. ND4 mitochondrial DNA sequences from 28 specimens comprising 20 P. shokari, two P. aegyptius, one P. elegans, two P. sibilans, one P. condanarus and two outgroups were analysed. Within P. schokari we identified four genetic lineages (Morocco/Western Sahara, Mauritania, Algeria and Israel) with a genetic divergence ranging from 4-5%, less than that typically found between different species. Surprisingly, Moroccan/Western Sahara and Algerian lineages are the most divergent ones. This geographic substructuring may be due to severe climate changes in the Sahara desert between the Miocene and Pleistocene associated with expansion/contraction phases of this desert. Psammophis aegyptius is the sister-taxon of Psammophis schokari with a high level of genetic divergence between them (10.7%) supporting the recognition of P. aegyptius as a distinct species. The three Moroccan/Western Sahara colour morphotypes form one genetic lineage, indicating that colour pattern does not reflect a different phylogenetic history, and is probably an ecological adaptation to the local environment.     

The source of autumn and spring downstream migrating juvenile Atlantic salmon in a small lowland river

Over 3 years, 32,444 age‐0 group Atlantic salmon (Salmo salar) parr tagged with passive integrated transponder tags throughout the River Frome catchment were assigned to one of three groups, nonmigrants, autumn migrants and spring smolts, depending on the detection and the timing of detection at downstream tag readers (situated 8.6 km above the tidal limit). We examined the effect of density at the time of tagging (n·m^?2), distance upstream from the tidal limit (km), fish length (mm), Fulton condition index, habitat type (divided into two types, main river and carrier), days after 1 September that each fish was tagged and year (replication) on the proportions of fish in each of the migration groups. Distance upstream from tidal limit was strongly negatively related to the proportion of autumn migrants and positively related to the proportion of spring smolts. Nonmigrants had a lower average body size than migrants, although there were no differences in the sizes of autumn migrants and spring smolts in September prior to migration. Fish density had no effect on migration strategy. A lower proportion of fish migrated as autumn migrants from the smaller carrier habitats than the main river channel. There is some evidence that those parr destined to become autumn migrants underwent a lower mortality rate during September before tagging than those destined to become spring migrants indicating possible physiological or behavioural differences between these two groups of fish at that time. More research into the factors responsible for initiating the autumn migration is required.     

我国北方地区防治荒漠化的法律思考

荒漠化问题是当今危害全球人类最严重的问题之一。我国北方地区荒漠化土地面积为 3 2 .8万平方公里 ,约占全国国土面积的 3 .4% ,而且还在进一步发展 ,长此下去 ,令人担忧。笔者提出治理北方荒漠化的主要方面 :6项法律对策 3项政策建议。     

北部沿海人工繁殖长江蟹试验

首次在北部沿海进行了长江蟹人工繁殖试验，报告了亲蟹促产，越冬培育，饵料投喂，水质管理，幼体孵化，幼体培育等全套工艺流程，交配抱卵率达８１％，越冬成活率８４．６％，大眼幼体育成率２２．５％，认为长江蟹，黄河蟹幼体培育方法一致，培养结果，育成率无显著差异，但越冬水深应保持１．５ｍ以上，亲蟹须先进行１５￣２０天强化培育。     

A system for automatic recording of fish tagged with coded acoustic transmitters

A telemetry system designed to automatically record the presence and swimming direction of fish tagged with coded acoustic transmitters is described. The present paper presents results from an extensive mapping of signal strengths and the proportion of correctly identified codes from a transmitter at various positions outside automatic listening stations (ALS). The system is evaluated on the basis of two field seasons, during which 107 Atlantic salmon, Salmo salar L., were tagged with acoustic transmitters in a fjord system in south-western Norway. By installing one ALS (two at high water discharges) in the mouth of the River Suldalslågen and two ALSs in the Hylsfjord, the presence and swimming direction of all tagged salmon entering the river and the inner part of the 750-m-wide Hylsfjord were recorded.     

Environmental influences on melatonin secretion in Atlantic cod (Gadus morhua L.) and their relevance to commercial culture

This study investigated the effects of photoperiod and temperature on plasma melatonin secretion in Atlantic cod (Gadus morhua L.). Initial work confirmed the presence of a diel profile of melatonin synthesis, with elevated levels during the dark phase. Unusually for fish, the peak in plasma melatonin occurred towards the end of the dark phase, which is indicative of a type `A' melatonin profile. When exposed to 60 hours of continuous darkness a clear endogenous rhythm of melatonin synthesis was observed, which continued for 4 cycles with a periodicity which, approximated to 24 h. When acclimated to varying temperatures (4, 8, 12 or 16 °C) no variation in melatonin production was seen, however, body size appeared to be an important influence, with the smallest fish exhibiting significantly higher levels of dark phase melatonin. Finally, the application of additional night-time illumination to cod maintained in sea cages i.e. without blackout, did not significantly reduce dark phase plasma melatonin, suggesting that cod are less sensitive to photoperiod manipulation in cages than salmonids.     

冀北高原草资源退化的成因分析

冀北高原草资源退化的成因主要可归纳为四个方面:自然因素,经营观念和经营方式的原因,政策原因,产权制度原因。     

Laboratory and field investigations of salmon lice [Lepeophtheirus salmonis (Krøyer)] infestation on Atlantic salmon (Salmo salar L.) post-smolts

Hatchery‐reared 1‐year‐old Atlantic salmon post‐smolts (Salmo salar L.), artificially infected with salmon lice [Lepeophtheirus salmonis (Krøyer)] copepodids, were found to suffer from primary alterations (increased cortisol levels) at early lice stages. Secondary alterations, such as osmotic stress (increased chloride levels), first occurred after the preadult stages of the lice appeared. Fish with the highest salmon lice infections died throughout the experiment. Seven years of field investigation of Trondheimsfjorden showed that Atlantic salmon post‐smolts descending coastal waters can become heavily infected with salmon lice. The migrating post‐smolts were only infected with the chalimus stages, showing that the fish had only recently left the rivers. The infection level, however, varied considerably between the years, and, in 1998, the infection was higher than previous years. The experimental results have been combined with the field data to appraise the consequences of the infection.     

Interannual variability in stock abundance of the neon flying squid, Ommastrephes bartramii, in the North Pacific Ocean during 1979–1998: impact of driftnet fishing and oceanographic conditions

Variability in catch-per-unit-effort (CPUE) was examined for the autumn cohort of Ommastrephes bartramii collected with research driftnets during 1979–1998 along five longitudinal transects passing through the Subarctic, Transitional and Subtropical Domains in the North Pacific. CPUE was generally low during the period of intensive commercial driftnet fishing (1980–1992) and increased following the 1992 moratorium on the use of large-scale driftnets. However, CPUE levels were low for the cohorts hatched in 1992 and 1996 (captured in subsequent years owing to a one-year life of O. bartramii ) that experienced low sea surface temperatures from hatching to recruitment. Among similar-aged squid collected from 180° and 179°30'W in June, mantle lengths were significantly greater in 1997 than during 1995–96. These findings suggest that the driftnet fishery and sea surface temperatures from hatching to recruitment strongly affected stock abundance and possibly growth.