Reproductive biology of Oreochromis mossambicus populations of man-made lakes in Sri Lanka: a comparative study

Abstract. The sex ratio, mean size at maturity (L_m), gonosomatic index (GSI), frequency of distribution of egg diameter of the mature ovaries and fecundity of Oreochromis mossambicus (Peters) populations of 12 man-made lakes were studied using commercial landings from the gill-net fishery. The overall sex ratio was 1·0:0·88 of females to males and that of the individual populations varied from 1·0:0·54 to 1·0:1·34. The L_m ranged from 16·0 to 21·0 cm (TL) and was found to be correlated to the size of the water-body. The GSI of the females in stage V, the stage prior to spawning, did not differ from each other, except in one reservoir. The variations in the mean egg size (μ) of different populations were negatively correlated to the fecundity of a Ash of standard weight (FW₂₀₀) of the different populations and the relationship was, y =3487·4– 1·14FW₂₀₀(df = 10; r= -0·64; P < 0·05) The overall fecundity ranged from 318 to 3169 in fish ranging in body length (TL) and body weight from 16·5 to 32·0 cm and 80 to 651 g respectively. Fecundity was linearly related to body weight and curvilinearly to body length. The exponent b of the fecundity (F) length (1) regressions (F = aL^b) of the different populations varied between 1·20 and 3·83. The overall relationship of fecundity to body weight (W) and body length (1) for O. mossambicus reservoir populations in Sri Lanka were: F = 3·23W + 357·8 (df = 203; r= 0·73; P < 0·001) F = l·52L^2·11(df = 203; r= 0·68; P < 0·001) The variations in the theoretical fecundity calculated for a standard size individual of 200 g in weight (FW₂₀₀) of the reservoir populations were correlated to the mean fishing pressure (X) exerted on each population according to the equations. (a) FW₂₀₀= 10–24X+ 896·8 (df 9; r= 0·58; P < 0·05) (b) FW₂₀₀= 1200 – 422·76e^?0·102X (df 9; P < 0·05)     

Effect of chloride concentration on the acute toxicity of nitrite to common carp, Cyprinus carpio L., fry

Abstract. Duplicate static bioassays were conducted for 168 h each to determine the median lelhal concentration (LC50) of nitrite (NO^?₂) for common carp, Cyprinus carpio L., fry at five different chloride (Cl^?) levels. The acute toxicity of nilrite ceased towards the end of 96 h at all levels of chloride concentration. There was a highly significant positive correlation between the chloride concentration tested and the 96-h LC50. The 96-h LC50 values are 2·55, 5·77, 14·41 27·26 and 48·70 mgl^?1 NO^?₂-N at chloride concentration of 1·0. 5·0, 10·5, 27·3 and 45·0 mgl^?1 Cl^? respectively. The linear relationship between chloride concentration and 96-h LC50 is best described by the equation: y= 1·03x+ 1·49 (r=+ 0·996; d.f. = 3;P <0·001), where y= 96 h LC50 of NO^?₂-N and x= concentration of Cl^?. A NO^?₂-N to Cl^? ratio of about 1:1·5–3·0 prevented complete mortality over the 168-h experimental period. A NO^?₂-N to Cl^? ratio of 1:5 is recommended for protection of carp fry against nilrite mortality in fish farms.     

Effects of environmental factors and food availability in Northern Aegean sea on the cultivation of Mediterranean Mussels (Mytilus galloprovincialis)

This study used two different collectors made of polypropylene (PP) rope and polyethylene (PE) fishing net to determine Mediterranean mussel's settlement, growth, condition index (CI), meat yield (MY) and shell thickness index (STI) during the period spent between June 2017 and November 2018. With this regard, chlorophyll a, water temperature, salinity, pH and particulate matter were defined through water samples that were collected on monthly basis triplicate. The mean chlorophyll a level was recorded as 0.32 ± 0.31 μg/L, while water temperature was 19.73 ± 5.14°C, salinity was 35 ± 2.070‰, pH was 8.12 ± 0.04, and TPM was 14.91 ± 10.48 mg/L. As a result of the cultivation period of 8 months spent following the first intense grip, the length of the mussels is measured as 31.79 ± 6.20 mm. Based on the Pearson correlation analysis results, the most important environmental parameter affecting Mediterranean mussels growth in length on PP rope collectors is the temperature (p < .05). The STI and CI were determined to be related with environmental temperature parameters, while no determinations could be obtained concerning the correlation of MY with environmental parameters. Assessment of Mediterranean mussels’ growth rate in PP rope collectors proved significant differences (p < .05) between March and November 2018. As no Mediterranean mussels are observed on PE fishing nets during the samplings performed throughout the study period, it is determined that PE fishing nets are not suitable collector types for Mediterranean mussel cultivation.     

Density dependence of herbivorous central stoneroller Campostoma anomalum in stream mesocosms

Herbivorous fish can have strong effects on stream ecosystem function by consuming primary producers and excreting limiting nutrients, but it is unclear whether they are resource limited. Thus, understanding factors regulating abundance of these fish might help predict ecosystem function. We used stream mesocosms to test whether populations of central stoneroller Campostoma anomalum exhibit density dependence across a range of typical densities and resource abundance found in Great Plains streams. We predicted that incrementally increasing stocking biomass from 3·7 to 24·9 g·m^?2 would reduce standing stocks of resources resulting in lower growth of stocked fish. Fish growth (over 41 days) was compared to initial stocking biomass and primary production as well as standing stocks of algae and invertebrates using regression analysis. Mean growth of individuals was negatively associated with stocking biomass ( = 0·55; P = 0·02), as predicted. Contrary to our prediction, increases in fish biomass led to increased primary productivity ( = 0·31, P = 0·07), but resulted in no relationship among algal filament lengths ( = 0·00; P = 0·34), algal biomass ( = 0·12; P = 0·19) or invertebrate biomass ( = 0·03; P = 0·30). Thus, density dependence occurred without an apparent reduction in food resources. We hypothesised that stoneroller growth was possibly limited by competition for high‐quality algae or invertebrates, or behavioural interactions causing interference competition.     

Dynamics of floodplain fisheries in Bangladesh, results of 8 years fisheries monitoring in the Compartmentalization Pilot Project

Floodplain fisheries were monitored from 1992 until 2000 in the Compartmentalization Pilot Project in Tangail, Bangladesh. In permanent floodplains about 165 ± 28 kg ha^?1 of fish was caught annually. For seasonal floodplains, this figure was 83 ± 23 kg ha^?1 yr^?1. The fish catch exhibited a strong seasonal variation, with the highest catch in October, when the floodwater recedes towards the river, and the lowest catch during the dry season in April/May. The annual catch varied with the extent of flooding, with high catches in wet years and low catches in dry years. The extent of flooding was quantified through a Flood Index. Plotting the annual yields against this Flood Index provided a significant relation (P < 0.05), confirming the existence of a flood pulse. The fishing effort (f) and the catch‐per‐unit‐effort (CPUE) were significantly related (P < 0.05), whereby the fishing effort increased with increasing CPUE. The results are discussed within the frame of fisheries management in Bangladesh and highlight the need for long‐term data for proper evaluation of fisheries projects and the development of management schemes, and the difficulty of applying standard surplus production models in floodplain fisheries.     

Modification of tissue fatty acid composition in Murray cod (Maccullochella peelii peelii, Mitchell) resulting from a shift from vegetable oil diets to a fish oil diet

The dynamics of fatty acid composition modifications were examined in tissues of Murray cod fed diets containing fish oil (FO), canola oil (CO) and linseed oil (LO) for a 25‐week period and subsequently transferred to a FO (finishing/wash‐out) diet for a further 16 weeks. At the commencement of the wash‐out period, following 25 weeks of vegetable oil substitution diets, the fatty acid compositions of Murray cod fillets were reflective of the respective diets. After transfer to the FO diet, differences decreased in quantity and in numerousness, resulting in a revert to the FO fatty acid composition. Changes in percentages of the fatty acids and total accumulation in the fillet could be described by exponential equations and demonstrated that major modifications occurred in the first days of the finishing period. A dilution model was tested to predict fatty acid composition. In spite of a general reliability of the model (Y=0.9234X+0.4260, R²=0.957, P<0.001, where X is the predicted percentage of fatty acid; Y the observed percentage of fatty acid), in some instances the regression comparing observed and predicted values was markedly different from the line of equity, indicating that the rate of change was higher than predicted (i.e. Y=0.4205X+1.191, R²=0.974, P<0.001, where X is the predicted percentage of α‐linolenic acid; Y the observed percentage of α‐linolenic acid). Ultimately, using the coefficient of distance (D), it was shown that the fatty acid composition of fish previously fed the vegetable oil diets returned to the average variability of the fillet fatty acid composition of Murray cod after 70 or 97 days (LO and CO respectively).     

Food consumption, moulting and survival of Penaeus semisulcatus during over-wintering

Over‐wintering of Penaeus semisulcatus (20.61 g) at three different temperatures (14, 18 and 22°C) was carried out in a greenhouse in three different closed recirculating systems. Temperature significantly influenced specific growth rate (SGR) and moulting interval (MI) (P<0.05). The SGR was 15‐fold higher and the MI was 2.7‐fold shorter at 22°C in comparison with 14°C. The relationship between SGR and temperature (T) was: Y=?0.053+0.070T (R²=0.97). Shrimps over‐wintered at 14°C consumed almost three times less food (0.43% body weight) than those at 22°C (1.28%) (P<0.05). A positive relationship (FR=0.426T–0.020, R²=0.99) was observed between feeding rate (FR) and temperature. The survival rate achieved at 14, 18 and 22°C over the experimental period of 70 days was 87%, 67% and 73% respectively. Our data indicate that it is possible to over‐winter this shrimp species in the sub‐tropical regions by maintaining water temperature at around 14°C and 39 ppt salinity, in which little energy expenditure is needed, and the shrimp can survive and consume minimum amount of feed.     

Relationship of precipitation, freshwater input, and sea level height with the abundance of the white shrimp (Litopenaeus occidentalis; Street, 1871) off Buenaventura, eastern tropical Pacific

Penaeid shrimp fisheries are an important source of income for the fishing communities that live in estuarine zones around the world. Off Buenaventura, the habitat of the western white shrimp (Litopenaeus occidentalis) is subject to high precipitation associated with the intertropical convergence zone, contributions from numerous short rivers descending from the Andes Mountains, and seasonal alternations in Trade Winds directions responsible for the upwelling in the Panama Bight. This work analyzes the relationship of precipitation, the San Juan River runoff, and sea level height with Litopenaeus occidentalis abundance in fishing areas between 1968 and 1989. The results indicate that precipitation is significantly correlated (p < 0.01) with the catch per unit effort on a monthly scale with a lag of approximately 1 calendar year but the inclusion of the data in a transfer function model does not improve considerably the forecasting power of a simpler autoregressive moving average model of the catch per unit effort. On an annual scale, the catch per unit effort for white shrimp depends significantly [r² = 0.36, p (corrected for autocorrelation)  0.01] on the precipitation that fell the previous December, whereas the residuals of this regression are significantly associated with variations of mean sea level between January and March (the upwelling season in the Panama Bight) of the current year at Buenaventura (r² = 0.61, p (corrected for autocorrelation)  0.01). The inclusion of these two variables in a multiple linear regression model accounted for a substantial proportion of the total annual variance of the mean CPUE (r² = 0.54), suggesting that freshwater contributions (lower salinities) and offshore transport during the main settlement period of postlarvae in the estuaries play a significant role in determining the strength of the cohorts recruited in the fishing areas. The industrial fishing yield decreased sharply after the 1982–1983 El Niño event. However, a high percentage of this change can be explained not by invoking El Niño effects but by a decreasing tendency of precipitation and offshore advection of early life stages between December and March, which took place on a multi-annual scale since the mid 1980s     

Kinetics of Total Volatile Basic Nitrogen and Trimethylamine Formation in Stored Rohu (Labeo rohita) Fish

Fish freshness estimation has been mostly studied in terms of total volatile basic nitrogen (TVB-N) and trimethylamine nitrogen (TMA-N) determination and partially addresses the kinetics, which limits its practical utility. In this study, TVB-N and TMA-N content of Rohu stored under limited refrigerated (5 and 0°C) and frozen (?5°C) conditions for 42 days showed an increasing trend, respectively. TVB-N and TMA-N formation in stored Rohu was higher at higher temperature and their initial and final values were found 4.57 ± 0.321, 0.14 ± 0.047 mg/100g and 46.56 ± 0.994, 3.24 ± 0.112 mg/100g, respectively. The volatile formations in Rohu at ?5°C were slow, as the frozen storage arrests the enzymatic and microbial activities in comparison to 0°C and above. The kinetics of TVB-N and TMA-N were investigated using zero, first, and nth-order reaction model. First-order kinetics exhibited the best fit model for TVB-N (R² = 0.98; χ² = 0.045), whereas TMA-N formation showed nth-order kinetics (n = ?0.4608, R² = 0.96, χ² = 0.028) as best fit model. The first-order kinetic reaction contributed activation energy of 58.16 kJ/mol for TVB-N and 10.86 kJ/mol for TMA-N. TVB-N and TMA-N formations were influenced by storage temperature and duration as expected. Kinetic parameters were also significantly (P ≤ 0.05) affected by storage temperatures.     

Gillnet selectivity to pikeperch, Stizostedion lucioperca (L.), and perch, Percafluviatilis L., caught mainly wedged

Abstract. The size selectivity of gillnets to pikeperch, Stizosiedion lucioperca (L.), and perch, Perca fluviatilis L., caught mainly wedged, was estimated by the selective use of the deterministic model of Holt (1963). The selectivity characteristics for pikeperch based on samples in gillnets with 48-65-mm bar mesh were: k= 0·903 and σ= 4·93cm (fork length). When a higher efficiency of large-meshed nets is accounted for, the estimated selectivity curve shifts to the right. The condition of the pikeperch had a major influence on the position and shape o(the selectivity curve. The selectivity to perch was established with 25–35-mm gillnets in a year with a poor food supply: k= 0·723 and σ= 2·59cm (fork length). Estimates based on literature data from an exploited perch population showed a much lower k= 0σ639 (total length) (σ= 2·69cm).     

Diphasic sedimentation technique complemented by a statistical approach as a useful tool to the quantification and the determination of dynamics of eggs produced by adult monogenean parasitizing groupers,Epinephelus marginatus (Lowe, 1834), in captivity

Monogenean parasites create problems in confined fish, such as at aquaculture and aquariums facilities. Strategic timing of antihelminthic treatments should be based on the dynamics of monogenean egg production which requires egg quantification, but there is no standardized analytical method. The WHO diphasic sedimentation method for helminth quantification of eggs was applied in samples with tetrahedral and fusiform monogenean eggs from six specimens of confined groupers (Epinephelus marginatus) (31 m³ sea water tank; water temperature 21.1–14.4°C; photoperiod 9:53–15 h light; November 2011 to June 2012). Helminth eggs remain in the pellet, while most organic matter was removed forming a cap. In contrast, monogenean eggs are distributed within both the pellet and cap. The diphasic sedimentation method is suitable to quantify tetrahedral and total egg number by counting those eggs in the pellet and incorporing water temperature data to obtain a statistically significant model expression (R² = 0.943; R² = 0.809), while this approach only weakly predicted fusiform egg numbers (R² = 0.297). Fusiform egg numbers declined along November–December, and increased in February–March, until June. Tetrahedral eggs decreased in November–December, but did not increase until March. The trend of egg populations and best time for antihelminthic treatment application can be set by WHO technique with the statistical approach proposed.     

Effects of production intensity and production strategies in commercial Atlantic salmon smolt (Salmo salar L.) production on subsequent performance in the early sea stage

A data set from commercial Atlantic salmon (Salmo salar L.) producers on production intensity and production strategies in smolt tanks (N = 63–94) was obtained during 1999–2006. The effects of production intensity on subsequent fish mortality and growth during the early sea phase (90 days) were examined by principal component analysis and subsequent generalized linear model analysis. Levels of accumulated metabolites (CO₂, total ammonia nitrogen and NH₃), and information provided by producers (production density (kg fish m³⁻¹), specific water use (l kg fish⁻¹ min⁻¹) and oxygen drop (mg l⁻¹) from tank inlet to tank outlet), were used as predictor variables. In addition, several other welfare relevant variables such as disease history, temperature during freshwater and sea stage; season (S1) or off-season (S0) smolt production; and the use of seawater addition during the freshwater stage were analyzed. No strong intensity effects on mortality or growth were found. CO₂ levels alone (P < 0.001, R ² = 0.16), and in combination with specific water use (R ² = 0.20), had the strongest effect on mortality. In both cases, mortality decreased with increasing density. For growth, the intensity model with the most support (R ² = 0.17) was O₂ drop, density and their interaction effects, resulting in the best growth at low and high intensity, and poorer growth at intermediate levels. Documented viral disease outbreaks (infectious pancreatic necrosis and two cases of pancreas disease) in the sea phase resulted in significantly higher mortalities at 90 days compared with undiagnosed smolt groups, although mortalities were highly variable in both categories. The temperature difference between the freshwater stage and seawater had a small, but significant, effect on growth with the best growth in groups stocked to warmer seawater (P = 0.04, R ² = 0.06). S0 and S1 smolt groups did not differ significantly in growth, but the mortality was significantly (P = 0.02) higher in S1 groups. Seawater addition as a categorical variable had no significant effects, but when analyzed within the seawater addition group, intermediate salinities (15–25 ppt) gave the best results on growth (p = 0.04, R ² = 0.15). Production intensity had small explanatory power on subsequent seawater performance in the analyzed smolt groups. If anything, the analysis shows a beneficial effect of intensive production strategies on subsequent performance. Analysis of the various production strategies indicates better survival of S0 compared with S1 smolt groups, improved growth when stocked in seawater warmer than freshwater, and a negative effect of viral disease outbreaks on survival. The results clearly demonstrate the difficulty of extrapolating results from experimental work on fish welfare and production intensity variables to commercial production. On the other hand, the presented results may simply demonstrate that the traditional fish welfare criteria growth and mortality may not suffice to evaluate welfare consequences of suboptimal water quality or production strategies in the aquaculture industry.     

基于渔船捕捞行为特征的远洋延绳钓渔场捕捞强度计算

渔场捕捞强度信息可以为渔业资源评估和管理提供帮助。本研究结合2017年10—11月船舶自动监控系统(AutomaticIdentificationSystem,AIS)信息和同期中国中西太平洋延绳钓渔船捕捞日志数据,通过挖掘延绳钓渔船作业航速和航向特征,建立渔场作业状态识别模型,提取渔场捕捞强度信息。以3～9节为航速阈值和0°～10°及300°～360°为航向阈值,渔船作业状态识别准确率为68.29%。阈值识别和日志记录的捕捞强度信息在空间上相关性很高(0.96),基于AIS信息挖掘的渔船捕捞强度空间分布特征和实际非常相似。阈值识别和日志记录的捕捞强度信息在空间上与单位捕捞努力量渔获量(catch per unite of effort, CPUE)、渔获尾数、渔获重量和投钩数的空间相关系数均大于0.62,基于AIS信息挖掘的渔船空间捕捞强度也可替代用于渔业资源分析。     

Sperm density, seminal plasma composition and their physiological relationship in the endangered Caspian brown trout (Salmo trutta caspius)

Sperm density, mineral and organic composition of the seminal plasma and their physiological relationship were investigated in the Caspian brown trout (Salmo trutta caspius). To establish a rapid and accurate method for assessment of sperm density, three different techniques were used: sperm counting, spectrophotometry (at 480 nm) and determination of the spermatocrit. The seminal plasma contained 159.26±8.84 mM sodium (Na), 33.72±2.01 mM potassium (K), 133.04±5.96 mM chlorine (Cl), 1.68±0.2 mM calcium (Ca) and 0.988±0.13 mM magnesium (Mg). The following organic components were found: total protein 0.75±0.14 mg 100 mL⁻¹, cholesterol 2.86±0.58 mg L⁻¹ and glucose 3.81±1.04 mM L⁻¹. The mean sperm density was estimated to be 3.3 × 10⁹ spermatozoa mL⁻¹. The spermatocrit (%) ranged from 25 to 52 in sperm samples. Highly significant linear relationships were found between sperm density and spermatocrit (R²=0.703, P<0.001) and sperm density and optical density (R²=0.909, P<0.001), indicating that optical density can be used as a quick and accurate method of estimating sperm density. Significant relationships were also found between sperm density and Ca, Mg and total protein of seminal plasma. A significant correlation was also observed between the Ca and Mg concentrations (R²=0.774, P<0.01). The following correlations were observed between mineral and organic components: total protein and Ca (R²=0.462, P<0.05), total protein and Mg (R²=0.518, P<0.05) and glucose and Cl (R²=0.374, P<0.05). These parameters should be considered when developing procedures for either artificial fertilization or for cryopreservation of sperm.     

长江口日本鳗鲡苗的时空分布与捕捞生产现状

为掌握长江口日本鳗鲡的苗汛特征与捕捞生产现状,于2017—2020年在长江口开展了定点监测和走访调查,分析了长江口鳗苗的汛期规律、捕捞努力量及捕捞产量和产值。研究发现,长江口鳗苗旺发期为2-4月,主要捕捞区域分布在东旺沙、佘山岛和南汇嘴附近水域。长江口鳗苗捕捞努力量呈现下降趋势,有效网口面积从2017年的78.72万m²,下降到2020年的50.40万m²,下降了36%。长江口鳗苗汛期的单位捕捞努力量渔获量(CPUE)和总捕捞产量呈现波动变化趋势,2017和2020年较高,分别为(4 474±256)尾/100 m²和(5 220±1 063)尾/100 m²,2018和2019年较低,分别为(1 917±335)和(1 365±257)尾/100 m²。研究表明,长江口鳗苗生产值受到捕捞总产量影响,近4年来逐渐下降。建议进一步加强长江口鳗苗的资源监测和科学评估,指导规范鳗苗捕捞生产。     

Characterizing environmental and spatial variables associated with the incidental catch of olive ridley (Lepidochelys olivacea) in the Eastern Tropical Pacific purse‐seine fishery

In the Eastern Tropical Pacific (ETP), a region of high fishing activity, olive ridley (Lepidochelis olivacea) and other sea turtles are accidentally caught in fishing nets with tuna and other animals. To date, the interaction between fishing activity, ocean conditions and sea turtle incidental catch in the ETP has been described and quantified, but the factors leading to the interaction of olive ridleys and fishing activity are not well understood. This information is essential for the development of future management strategies that avoid bycatch and incidental captures of sea turtles. We used Generalized additive models (GAM) to analyze the relationship between olive ridley incidental catch per unit effort (iCPUE) in the ETP purse‐seine fisheries and environmental conditions, geographic extent and fishing set type (associated with dolphins, floating objects or in free‐swimming tuna schools). Our results suggest that water temperature, set type and geographic location (latitude, longitude and distance to nesting beaches) are the most important predictor variables to describe the probability of a capture event, with the highest iCPUE observed in sets made over floating objects. With the environmental predictors used, sea surface temperatures (SST) of 26–30°C and chlorophyll‐a (chl‐a) concentrations <0.36 mg m^?3 were associated with the highest probability of an incidental catch. Temporally, the highest probability of an incidental catch was observed in the second half of the year (June to December). Four regions were observed as high incidental catch hotspots: North and south of the equator between 0–10°N; 0–10°S and from 120 to 140°W; and along the Colombian coast and surrounding regions.     

A comparison of methods for calculating Catch Per Unit Effort (CPUE) of gill net catches in lakes

Fish constitute an important component of lake ecosystems and many different methods have been used for fish assessment. Based on gill net catches in two stratified (max depth = 14–22 m) eutrophic Danish lakes, relative fish abundance measured as Catch Per Unit Effort (CPUE) was calculated. We used three different methods of which two followed the European standard based on benthic nets (CEN (European Committee for Standardization), 2005: EN 14757. Water quality – Sampling of fish with multi-mesh gill nets. Brussels, 27 pp.), one assuming equal volumes in all depth strata and the other using calculated volumes in the depth strata. The third method followed a modified CEN standard, adopted as a new Danish (DK) standardized method based on calculated benthic and pelagic water volumes and by including both benthic nets and, compared to the CEN standard, an increased fishing effort with pelagic nets. Fish were concentrated in the littoral/benthic part of the upper two depth strata (0–6 m depth) with an up to 8 fold higher abundance than in the pelagic. Calculated CPUE is highly sensitive to the morphometry of the lakes. In lakes with extreme morphometry (unequal volumes in depth strata) it is important to use calculated water volumes for the depth strata. By including information derived from the pelagic nets, total lake CPUEs were 42–56% lower than CPUE values based on benthic nets only. We further show that the relative contribution of CPUE between habitats changes markedly with the nutrient level in 12 deep lakes. It is concluded that for deep lakes it is of key importance to include pelagic nets when comparing fish assemblages and abundances among lakes and when evaluating effects of major changes in key environmental factors, such as nutrient loading and climate.     

Relationships between CPUE fluctuation of southern bluefin tuna and ocean temperature variability in the Central Indian Ocean

In this study, catch and effort data of southern bluefin tuna (SBT) from Taiwan longliners operating in the Central Indian Ocean (CIO) during 1982 to 2003 were compiled and their catch per unit effort (CPUE) was standardized using the generalized linear model (GLM). The GLM includes factors such as year, season, by-catch, latitude, sea surface temperature (SST) and the interactive effects among factors. The standardized CPUE and its relationship with SST fluctuation were then analyzed to understand the effects of fishing ground SST variations on CPUE of SBT, as well as their connection to El Niño-Southern Oscillation (ENSO) events. The standardized CPUE in the CIO seemed to oscillate with the sea surface temperature anomalies (SSTA) between 30 and 50°S where SSTA fluctuations were prolonged and slower than the ENSO cycle. It is then very likely that fishing conditions at the CIO fishing ground were influenced by the expansion of the cold water mass from the Southern Ocean, and the colder SST is beneficial to increasing SBT catch rate.     

Predicting night time dissolved oxygen loss in prawn ponds of Hawaii: Part II. A new method

Dissolved oxygen concentration (DO), water temperature and wind speed were monitored overnight at prawn (Macrobrachium rosenbergii) ponds of Amorient Aquafarm Inc. (Kahuku, Oahu) and at Brigham Young University-Hawaii (Laie, Oahu) from June to November 1985. A new model, the whole pond respiration-diffusion (WPRD) model, was developed to predict pond DO at dawn. The two components comprising the model were whole pond respiration and diffusion. Model inputs included a measurement of pond DO and water temperature at dusk, another DO and temperature measurement made several hours after the dusk measurement, and an estimate of the average wind speed for the night. For a lag of 3 h between the dusk and second DO measurement, the mean absolute deviation of the predicted dawn DO from the observed dawn DO was 0·40 mg O₂ liter⁻¹ (standard error of mean = 0·8 mg O₂ liter⁻¹), based on 40 verification trials. The WPRD model performed equally well for both calm nights (wind speed < 0·3 m s⁻¹) and for relatively windy nights (wind speed > 7 m s⁻¹).     

Kittiwake breeding success in the southern North Sea correlates with prior sandeel fishing mortality

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