The distribution and dispersal of introduced fish at Thumbi West Island in Lake Malawi, Africa

The rock-dwelling cichlids, or mbuna, of Lake Malawi are exceptionally diverse. Explanations of this diversity have used limited dispersal by the mbuna as the basis for allopatric models of speciation. However, there have been no studies that have attempted to define the extent and rates of dispersal of mbuna populations in the field. The present work took advantage of some translocations in which several species of mbuna were introduced to the Cape Maclear region of Lake Malawi from elsewhere in the lake. A detailed series of transects involving observations at four depths was undertaken at Thumbi West Island to define the distribution of the introduced species. There are large differences between species in the extent to which they have spread. Some species are now present all round the island while others have dispersed only a limited distance from the site of the initial introductions. This survey provides the first comprehensive data set on the distribution of the introduced species and it raises a number of important questions regarding their dispersal ability and their likely impact on the endemic community.     

Significant range extensions for two fish species at Pitcairn Island,South Pacific

A baited videographic survey at Pitcairn Island has significantly extended the known range for two reef‐fish species: blue‐lined triggerfish Xanthichthys caeruleolineatus and greater amberjack Seriola dumerili, with an additional minor extension noted for giant trevally Caranx ignobilis. This highlights the importance of further research in this remote, poorly studied island group and provides evidence supplementing the understanding of oceanographic patterns in the South Pacific.     

Abundance,distribution, and territory areas of rock-dwelling Lake Tanganyika cichlid fish species

Lake Tanganyika, the second-oldest and second-deepest lake in the world, harbors an impressive cichlid fish fauna counting about 250 endemic species that are characterized by a great level of ecological, morphological, and behavioral specialization. This study describes and compares cichlid fish communities at two rocky shores with differential human impact in the south of Lake Tanganyika. Species inventories and depth-dependent abundances were elaborated. About 41 and 46 sympatric cichlid species were recorded in the two study sites, respectively. Variabilichromis moorii was the most abundant species (29–60% of total number of fishes), followed by Aulonocranus dewindti (3–19%), Tropheus moorii (12%), Ophthalmotilapia ventralis (4–10%), Eretmodus cyanostictus (6–11%), and Cyathopharynx furcifer (0.01–9%). All other species had abundances below 5%. It further emerged that large cichlids such as Petrochromis species, Cyathopharynx furcifer, and Lobochilotes labiatus were very rare at one location, with frequencies of 0.55% or less. Territorial sizes of three particularly abundant species, Variabilichromis moorii, Aulonocranus dewindti, and Tropheus moorii, were assessed by behavioral observations. We distinguished between territorial core areas and total defended area, yielding average core areas between 0.4 (V. moorii) and 1.6 m² (T. moorii), and total defended areas averaging for each species between 1.6 (V. moorii) and 5.0 m² (A. dewindti) with no significant differences between the two study sites. The data on individual densities are also relevant for evolutionary studies, in that they allow more accurate calculations of effective population sizes.     

Idiosyncratic responses of Pacific salmon species to land cover,fragmentation, and scale

Salmon are critical to the ecology and livelihood of the Pacific Northwest, and are declining throughout much of their range. While much of their life cycle occurs in open ocean, freshwater conditions also contribute to population trends. Because stream habitats are connected to uplands by water flow, salmon can be influenced by the characteristics of terrestrial systems. We analyzed the relationships between the population trends of Pacific salmon (1953–2006) and land cover, fragmentation, and forest age derived from remotely‐sensed, landscape level datasets. Analyses included 425 populations of all native salmon species in 156 watersheds on Vancouver Island, British Columbia, Canada. Vancouver Island salmon escapements exhibited general patterns of decline, which may be largely controlled by broad‐scale marine conditions. The spatial variation in these population trends was related to landscape variables at watershed and riparian scales with regression trees. Results were found to be species specific, but characteristics indicating a legacy of historic and current forest management (such as fragmented forests and non‐forested or early‐successional forest cover) generally had negative effects, driven by a small subset of highly fragmented watersheds. Chum and coho had strong negative relationships with fragmentation, pink had a strong positive relationship with wetland abundance, and Chinook and sockeye were most closely related to geomorphology. There was no ‘single best’ scale of analysis. Salmon trends were generally more closely related to variables estimated over the entire watershed, however, the relative importances of watershed and riparian level predictors varied by both variable and species. Efforts to restore salmon habitat will be complicated by marine and freshwater processes, terrestrial conditions throughout watersheds, and the idiosyncratic requirements of each species.     

Changes in fish species composition in Lake Naivasha,Kenya

The fish species composition in Lake Naivasha has been modified during recent years. Out of seven introduced and one indigenous species reported in 1962, only three introduced ones are found today. The elimination of species has been brought about by predation and changing ecological conditions. The most common fish species today is Sarotherodon leucosticuus. The hybridization found by previous workers between S. leucostictus x S. spilurus niger has stopped, as S. s. niger is no longer found in the lake. Most of the hybrid characters have been lost by the few surviving hybrids due to backcrossing between hybrids and between hybrids and S. leucostictus. The hybrids now mostly resemble S. leucostictus.     

Water circulation and fish larvae recruitment in papyrus wetlands,Rubondo Island,Lake Victoria

A field study was undertaken of the hydrodynamics, water quality and adult and larval fish abundance in papyrus wetlands and surrounding coastal waters at Rubondo Island, Lake Victoria. Because they were exposed to the prevailing wind, the two bays facing east had small (0.01 km²) wetlands and were well flushed, with minimal accumulation of organic detritus and little oxygen depletion. Because it faced west, the third bay, Mlaga Bay, was sheltered and poorly flushed; organic matter accumulated in a large (1.41 km²) papyrus wetland. The rises and falls of the lake level at decadal time scales, may, by drowning or drying out wetlands, contribute significantly to storing organic matter as detritus. Vegetation decay in the wetlands, as well as primary production, resulted in large diurnal fluctuations of pH and dissolved oxygen concentration. Shading in daytime and cooling at night, cooled the wetlands water sufficiently to generate a baroclinic circulation whereby cold, wetland water sank and moved offshore in the lake while warm, lake water intruded in the wetlands near the surface. This flushing prevented the occurrence of anoxic conditions in the wetlands which were used by adult and larval fish, mainly tilapia, and freshwater shrimps (Caridina nilotica). No fish larvae were found at more than 150 m from the shore in the three bays. Both larval fish and Caridina nilotica appeared to move in and out of the wetlands at night, possibly as a result of low dissolved oxygen as well as sheltering from predation. Their abundance varied with the lunar phase, with maximum near new moon and first quarter. Being the only protected wetlands in Lake Victoria, Rubondo Island may increasingly become an important source of replenishment for fisheries in the lake which elsewhere appears overfished.     

千岛湖库区岛屿面积对植物分布的影响及植物物种多样性保护研究

修建大坝形成水库蓄水是造成景观破碎化的原因和形式之一.本研究选取了浙江千岛湖库区景观破碎化的典型区域小金山林场,调查了74个大小不一的岛屿,研究了面积对植物物种分布的影响,并比较了使物种多样性最大化的几种植物物种保护方案:小岛组合、中岛组合、大岛组合、大中小组合岛.调查共记录到乔木物种56种,灌木物种79种.将岛屿按照面积由大到小排序,将相对应分布的乔木、灌木绘制成植物物种分布表.结果显示:乔木中分布不受面积影响的物种有15种,受面积影响的有11种,介于两者之间的有30种;灌木物种中不受面积影响的有24种,受面积影响的有16种,介于两者之间的有39种.将乔木、灌木和总物种数分别累加,同时将相对应的岛屿面积按不同组合累加,绘制累加物种和面积关系图,发现在特定的相同累加面积下,组合岛的累加乔木、灌木、总物种数最多,小岛组合次之,大岛组合最少.因此,建立相同面积的保护区时,组合岛有利于保护更多的物种.     

Mature and juvenile tissue models of regeneration in small fish species

The multitude of cells constituting organisms are fragile and easily damaged day by day. Therefore, maintenance of tissue morphology and function is fundamental for multicellular organisms to attain long life. For proper maintenance of tissue integrity, organisms must have mechanisms that detect the loss of tissue mass, activate the de novo production of cells, and organize those cells into functional tissues. However, these processes are only poorly understood. Here we give an overview of adult and juvenile tissue regeneration models in small fish species, such as zebrafish and medaka, and highlight recent advances at the molecular level. From these advances, we have come to realize that the epidermal and mesenchymal parts of the regenerating fish fin-that is, the wound epidermis and blastema, respectively-comprise heterogeneous populations of cells with different molecular identities that can be termed "compartments." These compartments and their mutual interactions are thought to play important roles in promoting the proper progression of tissue regeneration. We further describe the current understanding of these compartments and discuss the possible approaches to affording a better understanding of their roles and interactions during regeneration.     

The spatial distribution of temperature, oxygen, plankton and fish determined simultaneously in Lake Kinneret, Israel

Temperature and concentrations of oxygen, phytoplankton, zooplanktonand fish were measured simultaneously on the night of 28 February-1March 1991, in Lake Kinneret, Israel. High concentrations ofoxygen, up to 19.9 mg l^–1 (207% saturation), were recorded.The phytoplankton was dominated by the dinoflagellate Peridiniwngatunense, which was horizontally and vertically unevenly distributed.We hypothesize that the oxygen supersaturation was the resultof a high standing stock of Peridinium, combined with high irradianceinput and mild wind-generated turbulence. The relationship betweenthe concentration of oxygen and Peridinium density was highlysignificant, both above the thermocline (negative correlation)and below the thermocline (positive correlation). Zooplanktonbiomass was dominated by cladocerans and cyclopoid copepods.The spatial distribution of these groups was not correlatedwith other measured parameters. Rotifers and calanoid copepodswere highly abundant in the northern part of the lake, and significantlyrelated to oxygen concentrations. It is suggested that the distributionsof rotifers and calanoid copepods are affected by the JordanRiver inflow. fish abundance was not correlated with limnologicalparameters or other biological components. We conclude thatthe distribution of the dominant fish species was governed byfactors other than those measured in this study.     

Spatial distribution of limited resources and local density regulation in juvenile Atlantic salmon

1. Spatial heterogeneity of resources may influence competition among individuals and thus have a fundamental role in shaping population dynamics and carrying capacity. In the present study, we identify shelter opportunities as a limiting resource for juvenile Atlantic salmon (Salmo salar L.). Experimental and field studies are combined in order to demonstrate how the spatial distribution of shelters may influence population dynamics on both within and among population scales. 2. In closed experimental streams, fish performance scaled negatively with decreasing shelter availability and increasing densities. In contrast, the fish in open stream channels dispersed according to shelter availability and performance of fish remaining in the streams did not depend on initial density or shelters. 3. The field study confirmed that spatial variation in densities of 1-year-old juveniles was governed both by initial recruit density and shelter availability. Strength of density-dependent population regulation, measured as carrying capacity, increased with decreasing number of shelters. 4. Nine rivers were surveyed for spatial variation in shelter availability and increased shelter heterogeneity tended to decrease maximum observed population size (measured using catch statistics of adult salmon as a proxy). 5. Our studies highlight the importance of small-scale within-population spatial structure in population dynamics and demonstrate that not only the absolute amount of limiting resources but also their spatial arrangement can be an important factor influencing population carrying capacity.     

Spatial and temporal distribution of coho salmon carcasses in a stream in the Pacific Northwest,USA

During two consecutive spawning seasons, the movement and distribution of naturally occurring coho salmon (Oncorhynchus kisutch) carcasses were monitored, and the effectiveness of large woody debris (LWD) in retaining carcasses in a stream was evaluated. In both seasons studied, the proportion of carcasses trapped by LWD increased as the season progressed. Densities of salmon carcasses were higher in slow waters such as stream edges and backwaters throughout the study periods. The average distance drifted by carcasses was 19.5m in the first season and 32.1 m in the second season. These results support the notion that LWD contributes to retention of salmon carcasses and enhances availability of salmon-derived nutrients for organisms near salmon spawning grounds.     

千岛湖两栖爬行类动物群落结构嵌套分析

生境片段化是导致生物多样性降低的主要原因之一.该文采用样线法对千岛湖23个岛屿的两栖爬行类进行了调查,并结合植物种类调查数据和GIS技术提取的栖息地景观参数,使用“BINMATNEST”软件和Spearman相关性分析等方法,对这些岛屿上的两栖爬行类群落的分布格局及其影响因素进行分析.结果表明,千岛湖两栖爬行类群落整体上呈现嵌套分布格局;嵌套格局与岛屿面积和生境类型相关显著.因此,在制定千岛湖地区两栖爬行动物保护措施时,应优先考虑面积较大和生境类型多的岛屿.     

The distribution of an invasive fish species is highly affected by the presence of native fish species: evidence based on species distribution modelling

Topmouth gudgeon (Pseudorasbora parva) is one of the most invasive aquatic fish species in Europe and causes adverse effects to ecosystem structure and functioning. Knowledge and understanding of the species’ interactions with the environment and with native fish are important to stop and prevent the further spread of the species. Creating species distribution models is a useful technique to determine which factors influence the occurrence and abundance of a species. We applied three different modelling techniques: general additive models, random forests and fuzzy habitat suitability modelling (FHSM) to assess the habitat suitability of topmouth gudgeon. The former two techniques indicated that the abundance of native fish (i.e. biotic variables) was more important than environmental variables when determining the abundance of topmouth gudgeon in Flanders (Belgium). Bitterling (Rhodeus amarus), stone loach (Barbatula barbatula), three-spined stickleback (Gasterosteus aculeatus) and predator abundance were selected as the most important biotic variables and implemented in the FHSM to investigate species interactions. Depending on the preferred food source and spawning behaviour, either coexistence or interspecific competition can occur with bitterling, stone loach and three-spined stickleback. In contrast, the presence of predators clearly had a top down effect on topmouth gudgeon abundance. These findings could be applied as a biological control measure and implemented in conservation strategies in order to reduce the abundance of earlier established populations of topmouth gudgeon.     

The influence of food distribution upon the development of aggressive and competitive behaviour in juvenile chum salmon, Oncorhynchus keta

Groups of juvenile chum salmon were reared on food that was either dispersed throughout, or localized in one area of, the rearing tank. Groups receiving localized food displayed more aggression than those receiving dispersed food. This led to differences in growth, with fish reared on localized food having greater individual growth variability, i.e. growth depensation. However, after several months of rearing in these different feeding/social environments, fish reared on dispersed food were just as aggressive when first exposed to localized food as were fish reared on localized food. Furthermore, in competitive contests between fish of the two rearing histories, those reared on dispersed food were just as likely to become dominant as those reared on localized food. These results suggest that the behavioural development of aggressiveness is not amenable to alteration by manipulation of food distribution.     

Factors affecting the distribution of juvenile estuarine and inshore fish

The differential distributions of juveniles and adults of 25 species of teleost were investigated and compared from four habitat types in sub-tropical Moreton Bay, Queensland. The aim of the study was to identify factors influencing the distribution of juveniles, particularly the species which enter estuaries. The following habitats were sampled: a shallow, sheltered tidal estuary (Caboolture); a shallow, exposed bay with muddy substrates (Deception Bay); an exposed area of sandy substrates and seagrass (Toorbol Point) and a sheltered oceanic site with sandy substrates and seagrass (Kooringal). Data on diet, spawning seasons and recruitment periods of fry are presented together with measurements of salinity, temperature and turbidity. Species entering estuaries recruited mainly in summer (rainy season). The possible preference of juveniles for calm water, the roles of food and predation pressure, the effects of salinity, temperature and turbidity are discussed in relation to the biology and distribution of the fish. Salinity and temperature were probably not important to most juvenile fish. The effects of calm water, suitable food and predators vary according to species. Although all juveniles studied preferred shallow water, in the case of those entering estuaries, turbidity was the single most important factor. Juveniles of the same species occurred in both the estuary and Deception Bay where abiotic and biotic factors other than turbidity were different. During summer, turbidity gradients extended from east to west in Moreton Bay with highest turbidities in Caboolture estuary and Deception Bay. In winter, turbidities throughout Moreton Bay were low and relatively uniform. At this time many of the ‘clear water’ species occurred in Deception Bay. The influence of high turbidity on fish may be linked to reduced predation pressure and perhaps food supply in shallow water. Turbidity gradients in summer may aid fry in locating estuarine nursery grounds. It is apparent however, that juveniles of many species are probably not attracted to estuaries per se but to shallow turbid areas.     

Impact of multiple stressors on juvenile fish in estuaries of the northeast Pacific

A key step in identifying global change impacts on species and ecosystems is to quantify effects of multiple stressors. To date, the science of global change has been dominated by regional field studies, experimental manipulation, meta‐analyses, conceptual models, reviews, and studies focusing on a single stressor or species over broad spatial and temporal scales. Here, we provide one of the first studies for coastal systems examining multiple stressor effects across broad scales, focused on the nursery function of 20 estuaries spanning 1,600 km of coastline, 25 years of monitoring, and seven fish and invertebrate species along the northeast Pacific coast. We hypothesized those species most estuarine dependent and negatively impacted by human activities would have lower presence and abundances in estuaries with greater anthropogenic land cover, pollution, and water flow stress. We found significant negative relationships between juveniles of two of seven species (Chinook salmon and English sole) and estuarine stressors. Chinook salmon were less likely to occur and were less abundant in estuaries with greater pollution stress. They were also less abundant in estuaries with greater flow stress, although this relationship was marginally insignificant. English sole were less abundant in estuaries with greater land cover stress. Together, we provide new empirical evidence that effects of stressors on two fish species culminate in detectable trends along the northeast Pacific coast, elevating the need for protection from pollution, land cover, and flow stressors to their habitats. Lack of response among the other five species could be related to differing resistance to specific stressors, type and precision of the stressor metrics, and limitations in catch data across estuaries and habitats. Acquiring improved measurements of impacts to species will guide future management actions, and help predict how estuarine nursery functions can be optimized given anthropogenic stressors and climate change scenarios.     

Simultaneous patterns of temperature, oxygen, zooplankton and fish distribution in Lake Kinneret, Israel

1. Temperature, oxygen concentration and zooplankton density were measured simultaneously on 25 December 1990 at twenty-six stations during an acoustic survey of the fish population of Lake Kinneret, Israel. Data from a preliminary acoustic survey were used to establish the optimal distance between transects (4km). 2. The distribution of temperature and oxygen concentration (and their gradients), and zooplankton and fish densities were compared using three-dimensional plots and correlation analysis. Both fish and zooplankton were concentrated in frontal zones where temperature and oxygen gradients were highest. 3. In the south-eastern part of the lake, where fish abundance was highest, a minimum of zooplankton density was observed, suggesting that predation by fish reduced zooplankton concentrations.     

The survival of Pacific salmon in the North Pacific in the winter and spring

The effects of various factors (water temperature, food availability, predation, and the size of juveniles) on the survival of Pacific salmons during overwintering in open ocean waters are analyzed based on the data collected by expeditions of the Pacific Research Fisheries Center to the northwestern Pacific Ocean in the winter and spring seasons of 1986–1992 and 2009–2011, as well as in the summer seasons of 2004–2011. The temperature factor is unlikely to be a direct cause of the high salmon mortality in the ocean during the winter, as there is no clear evidence that it affects food availability for salmon. The biomass of forage zooplankton in the Subarctic Front zone in February and March is lower than that in April and June–July, but it does not decrease substantially in the winter months. Taking the fact into account that the total abundance of planktivorous nekton is also low in this area during the winter, food availability cannot be considered a crucial factor that has a serious influence on salmon mortality in this period. The difference in feeding intensity between salmon species and between their size groups in the winter and spring is determined by their life strategies. The observed variations in feeding intensity and lipid accumulation from autumn to spring are caused by cyclic seasonal changes in physiological processes in salmon rather than by the amount and availability of food resources. The low abundance of predators in subarctic waters and in the Subarctic Front zone in the winter also cannot reduce salmon abundance substantially. The probable relationship between the critical size of juveniles and their survival in the winter is considered using the example of a Sea of Okhotsk stock of pink salmon. The conclusion is that the size of juvenile pink salmon cannot always be used as a predictor of the values of its subsequent returns, because survival of salmon during the ocean period of life depends both on the initial conditions during downstream migration and on the ocean conditions that form in the winter. Thus, none of the factors above can be considered as strictly limiting the abundance of Pacific salmon in the winter. It is more probable that the survival of salmon in the ocean is influenced, to a lesser or greater extent, by the combined effects of abiotic and biotic factors.     

Assessment of exploited fish species in the Lake Edward System,East Africa

The unknown status of inland fish stocks hinders their sustainable management. Therefore, increasing stock status information is important for sustainable inland fisheries. Fisheries reference points were estimated for five exploited fish species (11 stocks) in the Lake Edward system, East Africa, which is one of the most productive inland water systems. The aim was to ascertain the status of the fisheries and establish reference points for effective management. The reference points were based on four linked stock assessment approaches for data-limited fisheries. Estimates showed poor stock status with the stocks defined as either collapsed, recruitment impaired or overfished. However, higher catches could be obtained under sustainable management. Estimates of maximum sustainable yield (MSY) and supporting biomass (B_msy) are provided for 10 of the stocks as targets for rebuilding plans. The immediate target of management should be rebuilding biomass to B_msy. Applicable measures include shifting length at first capture to the length that maximizes catch without endangering size structure and biomass, and livelihood diversification out of fisheries.