Lake Whitefish and Lake Herring Population Structure and Niche in Ten South-Central Ontario Lakes

Synopsis This study compares simple fish communities of ten oligotrophic lakes in south-central Ontario. Species densities and population size structure vary significantly among these lake communities depending on fish species present beyond the littoral zone. Lake whitefish are fewer and larger in the presence of lake herring than in their absence. Diet analysis indicates that lake whitefish shift from feeding on both plankton and benthic prey when lake herring are absent to a primarily benthic feeding niche in the presence of lake herring. When benthic round whitefish are present, lake whitefish size and density decline and they move lower in the lake compared to round whitefish. Burbot are also fewer and larger in lakes with lake herring than in lakes without herring. Burbot, in turn, appear to influence the population structure of benthic coregonine species. Lower densities of benthic lake whitefish and round whitefish are found in lakes containing large benthic burbot than in lakes with either small burbot or where burbot are absent. Predation on the pelagic larvae of burbot and lake whitefish by planktivorous lake herring alters the size and age structure of these populations. As life history theory predicts, those species with poor larval survival appear to adopt a bet-hedging life history strategy of long-lived individuals as a reproductive reserve.     

Predicting variability in catch-per-effort in Atlantic cod, Gadus morhua, trap and gillnet fisheries

The relationships between catch rates and fish abundance, hydrographic conditions and fishing effort, for Atlantic cod caught by trapnets (fixed gear) and gillnets (non-fixed gear) in the northern Gulf of St Lawrence have been quantified. Daily changes in trap catch rates were accounted for by changes in salinity, currents and mean local cod densities in 1985 ( R ²= 0.78), and predicted 1986 trap catch rate changes (by 1985 model) were correlated significantly with those observed ( r = 0.60, P < 0.05). In contrast, the daily changes in 1985 gillnet catch rates were determined by currents, maximum (not mean) local cod densities, and fishing effort (negative) ( R ²= 0.68), while predicted 1986 gillnet catch rates (by 1985 model) were significantly correlated with those observed ( r = 0.35, P < 0.05). Seasonal catchability coefficients of the traps were similar in 1985 and 1986, but for gillnets this index was an order of magnitude higher in 1986 than in 1985.     

The Relationship between Red Cod, Pseudophycis Bachus, Recruitment and Environmental Variables in New Zealand

This paper examines the relationship between red cod, Pseudophycis bachus, recruitment and selected environmental variables. Commercial catch data of red cod were used as indices of relative recruitment strength for New Zealand fish stocks (east coast South Island, RCO 3; west coast South Island, RCO 7). Analysis of catch per unit effort (CPUE) supports the assumption that fluctuations in commercial catches reflect changes in abundance resulting from variable recruitment. Catch was assessed against 34 environmental variables that included the Southern Oscillation index, sea surface temperature, weather types, wind speed and direction, and river flows. Lagged correlations were calculated between annual commercial catch and averaged environmental data. Variables most strongly correlated with commercial catch were included in regression analyses. Regression models were calculated using all available data in its raw form, and after application of a logarithmic transformation. Robustness, and forecast skill was tested using a repeated leave-one-out procedure. The strongest correlations between commercial catch and explanatory variables for both RCO 3 and RCO 7 were consistently with sea surface temperature over a wide range of time lags followed by frequencies of southwest and northeast flow patterns. The correlations generally operated in the sense that colder is better: negative correlations (–0.75) with sea surface temperature, positive with the occurrence of cool southwest weather types, negative with the occurrence of warm northeast weather types. The maximum magnitude of the correlation occurs at 14-month lag for both fisheries, corresponding to the late spring/summer of the year prior to the catch year. There were often secondary maxima in the magnitude of the correlations two or three years prior to the catch year. The commercial fishery is made up largely of two and three-year-old fish, implying that juvenile fish (age one year) are most sensitive to environmental conditions, but egg, embryo and larva periods may also be affected. Regression analyses suggest that two-predictor regressions were unstable, with often large decreases in explained variance when applied to the independent years, however, at the lags when relationships are strongest (around 14 months), the explained variance on the left-out years remains high. Fluctuations in red cod landings are dependent on sea surface temperature, controlled largely by climatic variability, including El Niño and La Niña events. For short-lived species such as red cod, fluctuations in annual landings are commonplace and analyses of environmental data may be useful in predicting catches in subsequent years.     

Time series analysis of climate‐related factors and their impact on a red‐listed noble crayfish population in northern Sweden

1. Global climate change is predicted to raise water temperatures and alter flow regimes in northern river systems. Climate‐related factors might have profound impacts on survival, reproduction and distribution of freshwater species such as red‐listed noble crayfish (Astacus astacus) in its northern limit of distribution. 2. In this study, noble crayfish capture data over 27 years from the River Ljungan, Sweden, were examined. Time series of catch per unit effort (CPUE) were analysed in relation to the North Atlantic Oscillation (NAO) index, regional weather factors and water flow. CPUE was assumed to reflect differences in population size. Two models were constructed to explore the relative impact of different climate factors and density dependence on variability of catch sizes. 3. The most parsimonious model for CPUE time series, explaining 72% of the variance in CPUE, included density‐dependent population dynamics of the crayfish and climate or weather factors. The specific effect from density dependence in the model was 37%, while climate/weather factors contributed with 35% of the variation. The most important climate/weather factors are variations in NAO index and water flow. Temperature did not improve the model fit to capture data. 4. The best model was evaluated using independent data sets that gave correlations between model predictions and data ranging from 0.44 to 0.53. The density dependence shows a time lag of 1 year, while climate variables show time lags from 2 to 6 years in relation to CPUE, indicating effects on different cohorts of the crayfish population. 5. Both density dependence and climatic factors play a significant role in population fluctuations of noble crayfish. A 6‐year time lag for NAO index is puzzling but indicates that some as yet unidentified factors related to NAO might act on the juvenile stages of the population. Water flow shows a 2‐year lag to the CPUE, and high flow in the river may affect adult survival. The reasons for fluctuation of crayfish catches in response to climate need to be identified, and fishing quotas should consider the different cohort sizes because of variation in environment. Reintroduction programmes for crayfish need to consider effects of climate change when designing management strategies.     

两性具有不同出生率和死亡率的种群动态

以往的种群动力学模型均隐含假设性比为1：1,而实际上并非总如此,不同性别的出生和死亡是不完全相同的。文中就考虑了两性具有不同出生率和死亡率的种群动态问题。可以知道种群动态只是受雌性控制,与雄性无关。     

Exploring the structure of genetic variation and the influences of demography on effective population size in the gag grouper Mycteroperca microlepi (Goode & Bean)

Using 11 microsatellite markers, genetic analyses of three successive year-classes of gag Mycteroperca microlepis juveniles across the north-eastern Gulf of Mexico revealed a lack of spatial structure and very little temporal variation between year-classes. These results are consistent with long-term effective population sizes on the order of 30 000 adults. The importance of reproductive-style and sex-ratio variation is discussed as an important influence on long-term effective sizes.     

An analysis of the distribution of fish species in a large prairie lake

The distribution of fishes in Dauphin Lake, a large, shallow, turbid, prairie lake in west-central Manitoba, was examined using gillnets. Catch per unit effort was used to assess differences in distribution thai may be attributed lo year, season, lake zone (inshore, offshore), substratum, water depth, water temperature, turbidity and presence of other fish species. Although 13 species were caught, only the distributions of the six most abundant was analysed. Variation in number of species caught was attributed mainly to lake zone, water depth and water temperature. White sucker (Catastomus commersoni) distribution can be explained by zone and temperature. Shorthead redhorse (Moxostoma macrolepidotum) catches were related to depth and temperature. Cisco (Coregonus artedii) catches varied with year, zone and temperature. Variances in northern pike (Esox Indus) distribution reflected year and zone. Walleye (Stizostedkm vitreum) varied with year, depth and temperature and differences in the catches of yellow perch (Pertaflurescens) were attributed to year, depth, temperature and turbidity. They were also positively correlated to the numbers of northern pike caught.     

THE INFLUENCE OF MATING SYSTEM AND OVERLAPPING GENERATIONS ON EFFECTIVE POPULATION SIZE

The effective population size (N_e) depends strongly on mating system and generation time. These two factors interact such that, under many circumstances, N_e is close to N/2, where N is the number of adults. This is shown to be the case for both simple and highly polygynous mating systems. The random union of gametes (RUG) and monogamy are two simple systems previously used in estimating N_e, and here a third, lottery polygyny, is added. Lottery polygyny, in which all males compete equally for females, results in a lower N_e than either RUG or monogamy! Given nonoverlapping generations the reduction is 33% for autosomal loci and 25% for sex-linked loci. The highly polygynous mating systems, harem polygyny and dominance polygyny, can give very low values of N_e/N when the generation time (T) is short. However, as T is lengthened, N_e approaches N/2. The influence of a biased sex ratio depends on the mating system and, in general, is not symmetrical. Biases can occur because of sex differences in either survival or recruitment of adults, and the potential for a sex-ratio bias to change N_e is much reduced given a survival bias. The number of juveniles present also has some influence: as the maturation time is lengthened, N_e increases.     

炔雌醚对长爪沙鼠种群数量和性比的影响

: 炔雌醚是一种激素类新型鼠类不育剂,已有研究表明,炔雌醚对某些鼠类种群繁殖具有良好的控制成效。为检验新型不育剂对长爪沙鼠种群的控制效果,2006年5月在内蒙古锡林郭勒盟锡林浩特市农牧交错带开展了炔雌醚对野外长爪沙鼠种群的控制实验,本次实验设投药区和对照区2个组别,5-8月开展逐月的夹线调查以及四分之一圆洞口计数法,对样地内长爪沙鼠进行系统的追踪调查,分析炔雌醚对长爪沙鼠种群数量以及种群性比的作用。结果显示:投药1个月之后,投药区雌鼠比例(16.3%)不及对照组雌鼠比例(51.9%)的三分之一,投药区的雌鼠比例(16.3%)仅为雄鼠比例(83.7%)的五分之一;与对照区相比,投药区长爪沙鼠的密度下降达60%以上。这表明:炔雌醚对野外长爪沙鼠种群的不育控制具有良好效果,且炔雌醚对长爪沙鼠的种群性比影响很大,过量投放炔雌醚可造成雌鼠死亡,单独使用炔雌醚可降低野外不育剂的药物成本。     

Reproductive strategy of Labeo senegalensis Valenciennes 1842 (Teleostei: Cyprinidae) in the Ouémé basin,Benin

Aspects of the reproductive biology and population structure of Labeo senegalensis were investigated in the Ouémé River between April 2005 and March 2006. Reproductive strategy was investigated using gonadosomatic index, ovarian structure and fecundity. Average size-at-first-maturity (L ₅₀) was estimated at 29 cm TL for females and 25.7 cm TL for males. The average sex ratio (1:0.96) was not significantly different from unity. Oocyte diameter frequency distribution suggests synchronous development with a single total spawning. Absolute fecundity ranged between 12 948 and 74 832 eggs. Labeo senegalensisis a highly fecund fish that presents a seasonal cycle of reproduction from May to October during the rainy season.