Role of sea surface temperature and rainfall in determining the stock and fishery of the common octopus (Octopus vulgaris,Mollusca, Cephalopoda) in Tunisia

Octopus (Octopus vulgaris, Mollusca, Cephalopoda) is an important and valuable fishery resource on the eastern and southern coasts of Tunisia, but its landings are highly variable. This paper explores the effect of environment on octopus catch per unit effort (CPUE) during a 12‐year period, through correlation analyses and the incorporation into surplus production models of sea surface temperature (SST) and rainfall data collected during cold (January–May) and hot (August–October) seasons. CLIMPROD software was used to select the appropriate model and fit it to the fishery and environment data. In both seasons, SST significantly contributed to CPUE variability; fishery production was influenced positively by cold season SST but negatively by hot season SST. Due to a poor fit with cold season data, the impact of rainfall was analysed only for the hot season, during which it has a positive effect on production. Results are discussed in view of the life‐cycle of octopus and the dynamics of the Tunisian fishery. This first study of octopus variability in Tunisia highlights the necessity to incorporate environmental influence into stock assessment and management advice.     

利用南极走航观测评估卫星遥感海表面温度

利用1989-2005年间南极走航观测的海表面温度,对目前3个主要的卫星反演的SST产品AVHRR(Advanced Very High Resolution Radiometer),TMI(TRMM Microwave Imager)和AMSR-E(Advanced Microwave Scanning Radiometer for the Earth Observing System)进行了较为系统的评估,并着重检验了它们在南大洋的准确性.结果表明,AVHRR SST比观测数据偏冷,白天的偏差为-0.12℃,夜晚的偏差为-0.04℃,而且南大洋的冷偏差更为显著.TMI SST比观测数据明显偏暖,白天的偏差为0.48℃,夜晚的偏差为0.57℃,其温差ΔT受37GHz风速影响,在强风速(>6m/s)下这种影响仍然存在.AMSR-ESST比观测数据偏暖,白天的偏差为0.34℃,夜晚的偏差为0.27℃,而且南大洋的暖偏差相对较大.AMSR-E SST温差受水汽影响,并在南大洋随着水汽的增加而增加.通过进一步比较微波(AMSR-E和TMI)和红外(AVHRR)遥感的SST在2004年北半球冬季(即南半球夏季)的差别,发现微波遥感在热带(15°S-15°N)和南大洋区域(45°S以南)比红外遥感偏暖,而且在南大洋区域的偏差相对较大,相反在北半球中纬度区域(15°~40°N)偏冷.AMSR-E与AVHRR SST的温差,从白天到夜晚有减小的趋势,而TMI与AVHRR SST的温差无明显的变化.     

高频电力线信息传输的电机模型与仿真

研究在电机驱动系统中,电力线通信的建模问题,着重讨论在高频时电机输入阻抗的特性下,电机模型的建立.通过实验测量得到电机和电力线在频率100 kHz～40 MHz的输入阻抗特性曲线,并分析高频输入阻抗的谐振特点.在Matlab中,提出基于阻抗公式的分析法、最小均方值误差估计法以及最优化方法进行模型的参数识别,将得到的参数代入模型中可以得到电机的阻抗模型.电机模型的精确度可以通过仿真曲线和测量曲线的逼近程度看出,从结果看仿真得到的阻抗曲线跟实际测量的阻抗曲线走向基本一致.     

Climate driven changes in subtidal kelp forest communities in NW Spain

Reconstructions suggest a massive decline of nearly 1400 ha of kelp forest in North Western Spain in 2007. In line with global rising temperatures, we hypothesized that Sea Surface Temperature (SST) surpassed a lethal threshold for kelp. We examined whether changes in SST correlated to the proposed decline in kelp forest. All investigated SST characteristics suggested to affect kelp abundance increased significantly during the past thirty years, reaching extreme values during the last decade. In addition over the past two decades, the landscape formerly dominated by both cold and warm temperate canopy forming and understory species changed to one dominated by warm temperate understory species, resulting in a loss of vertical community structure. Fisheries landing data of kelp associated species was used to support the suggested change in kelp abundance. Subsequent recovery of the kelp appears to be occurring in deeper waters.     

A mass mortality of subtropical intertidal populations of the sea urchin Paracentrotus lividus: analysis of potential links with environmental conditions

An outbreak of bald sea urchin disease was detected affecting intertidal populations of the edible temperate species Paracentrotus lividus at its southernmost geographical limit. The mortality event was detected in three sites (Güímar, Palmar and Alcalá) off Tenerife, Canary Islands (Northeastern Atlantic), in October 2003, coinciding with the highest sea surface temperatures (SST) and the lowest wave heights of the year. The prevalence of infection reached 100% but did not affect equally all studied sites or the different size classes. The disease was more prevalent in large sea urchins (>40 mm). The prevalence appeared to be positively correlated with the environmental variable SST and negatively correlated with wave height. In October 2004, only two infected urchins were found (prevalence 1%) at one of the studied sites. However, during 2004 no such extreme values of temperature and wave height were observed. We conclude that high SSTs and low wave heights such as those observed during 2003 are conditions that may trigger outbreaks of urchin disease.     

Role of mean circulation,tides, and waves in the transport of bottom sediment on the New Zealand continental shelf

Evaluation of velocity data on water movements over the New Zealand continental shelf has revealed that the mean circulation by itself is too slow to induce transport of bottom sediments. Tides generally have higher velocities, but are still not the main transporting agent except in the tide‐dominated Cook and Foveaux. Straits. Waves have the potential to stir sediments on the inner and middle shelf (less than about 70 m deep) during annual storms, and probably down to 130 m depth during the maximum 25‐y storm.

For sediment transport to take place, energies of at least two of the major water movements would have to complement one another. Optimum conditions for transport probably occur during storm periods when wave‐suspended sediment is readily moved by tides and the mean circulation.

The direction of transport is mainly along the continental shelf and is largely in response to prevailing weather patterns coincident with the direction of the mean circulation and strongly reinforced by the appropriate phase of the tide.     

Reproductive cues in Panulirus ornatus

Two experiments were performed to assess the effect of photoperiod and temperature on spawning of Panulirus ornatus. In experiment 1, sexually mature lobsters taken from the wild during summer were held at one of two photoperiods, winter (13 Light: 11 Dark) and summer (14.5 Light:9.5 Dark). Additionally, lobsters were also exposed to either summer (29°C) or winter (24°C) average water temperatures. Spawning was significantly greater when animals were exposed to summer photoperiod than to winter photoperiod, irrespective of temperature. Although a higher percentage of lobsters spawned when placed under a higher temperature, this trend was not statistically significant. In experiment 2, sexually mature lobsters were taken from the wild during winter and exposed to the same two photoperiods as in experiment 1, at a summer equivalent temperature of 29°C. Breeding started earlier and was more successful at the summer photoperiod. Time to first breeding was 17 weeks after exposure to summer photoperiod, compared with less than 1 week in experiment 1, and did not occur until individuals had moulted. Moulting occurred in 81% of lobsters, primarily after an increase in temperature to 29°C. The time between moulting and mating was varied and there was no significant difference in moult frequency between the two experimental photoperiods. After the lobsters had moulted, breeding success was reached earlier if photoperiod was lengthened. Results suggest photoperiod is the primary cue for the onset of gonad maturity and mating activity, with temperature playing a less important role. Physiological rest and possibly a moult may be required between breeding seasons before spawning can occur. Furthermore, temperature may be an important cue for pre‐reproduction moulting.