Integrating climate–hydrology–ecology for alpine river systems

• 1. High climatic sensitivity and lack of significant human impact make alpine river basins important environments for examining hydrological and ecological response to global change.
• 2. This paper is based upon previous and ongoing research within a glacierized, alpine river system (Taillon‐Gabiétous basin, French Pyrenees), which adopts an interdisciplinary approach to investigate the climate–hydrology–ecology cascade. Data are used to advance hypotheses concerning impacts of climate change/variability upon alpine river system hydrology and ecology.
• 3. The snowpacks and glaciers that are the source of Pyrenean streams are climatically sensitive, with glaciers in retreat for most of the historical period. Given anticipated changes in summer air‐mass frequencies, the volume of meltwater may decrease, the nature and rate of glacier drainage may alter, and the timing of peak snow‐ and ice‐melt may shift. However, rainfall‐runoff and groundwater may increase their relative contributions to stream flow.
• 4. The influence of changing water source contributions on physico‐chemical habitat and, in turn, on benthic communities is assessed using an alternative alpine stream classification. This model predicts more rapid downstream change in benthic communities in the future as meltwater contributions decline and, at the basin‐scale, biodiversity may be reduced owing to less spatio‐temporal heterogeneity in water sources contributions and, thus, physico‐chemical habitat. However, predictions are complicated by potential changes in biotic interactions with altered species' distributions.
• 5. Integrated, long‐term research into the climate–hydrology–ecology cascade in other alpine river basins is vital because interdisciplinary science is fundamental to predicting stream hydrology and ecology under scenarios of future climate/variability, to assessing the utility of alpine river systems as indicators of global change, and to developing conservation strategies for these fragile ecosystems.

Copyright © 2006 John Wiley & Sons, Ltd.     

A study of organic carbon,nitrogen and phosphorus budget in jellyfish–shellfish–fish–prawn polyculture ponds

A budget describing the flow of organic carbon (OC), nitrogen (N) and phosphorus (P) through two polyculture ponds (jellyfish–shellfish–fish–prawn) was constructed. The total input of OC was 3107 kg ha^?1 in pond 1 and 3358 kg ha^?1 in pond 2, while total output was 1759 kg ha^?1 in pond 1 and 1325 kg ha^?1 in pond 2. In pond 1, the total input of N was 364 kg ha^?1 and output was 359 kg ha^?1, whereas, in pond 2, the total input of N was 439 kg ha^?1 and total output was 331 kg ha^?1. The total input of P was 75 kg ha^?1 in pond 1 and 66 kg ha^?1 in pond 2, while total outputs for pond 1 and pond 2 were 74 and 65 kg ha^?1 respectively. Primary production from phytoplankton contributed the largest proportion of total OC (49–56%), while feed contributed the largest proportion of N (78–81%) and P (79–80%). Animals harvested from the aquaculture ponds accounted for the largest proportion of N (50–73%) and P (49–52%), and respiration accounted for the largest proportion of OC (43–61%) output from the system. The OC, N and P use efficiency of harvested animals was 30.30%, 70.19% and 50.14% in pond 1, respectively, and 21.03%, 46.95% and 46.47% in pond 2 respectively. In terms of nutrient use, the filter‐feeding bivalve, Sinonovacula constricta, was the most efficient species within the polyculture system.     

Oyster shell–meat sensor

Oyster processing sometimes requires determining if the shucking process has been completed. One application of this requirement is in the automated Wheaton oyster shucking machine where one oyster shell valve is removed and it is necessary to determine before the oyster proceeds through the remaining machine components whether the valve has been removed. Failure to remove the valve will cause the oyster meat to be destroyed downstream in the processing system. Thus, an automated sensor was developed to view the oyster and determine automatically if the valve was removed. The sensor is based on the difference in light absorption between the oyster meat and shell. Light reflected from the oyster passing beneath the sensor enters the sensor and passes through a beam splitter. Each light beam passes through a different narrow band filter and into a photocell. The output difference between the two photocells was used to determine if an oyster meat or shell was passing beneath the sensor. The sensor output for the 875 nm shell sensor varied from 0.143 to 0.305 mV and for the 975 nm shell sensor varied from 0.27 to 0.615 mV. When looking at meat the 875 nm sensor output varied from 0.157 to 0.305 mV and the 975 nm sensor varied from 0.307 to 0.622 mV. Results show the sensor will detect the difference between the oyster shell and the meat as long as there are readings for both sensing elements for both the meat and the shell. With the Wheaton shucking machine the design configuration will provide only a wavelength readings for either the meat or the shell but not both. Suggestions are presented to modify the system to allow the sensor to differentiate between the oyster meat and shell.

Because the study was designed to determine if the sensor would perform as designed data on the sensor speed was not available. However, the sensor was designed as part of a shucking machine with a design shucking rate of 60 oyster/min. With the electronic processing needed and the available computer processing power today the sensor should be able to meet the 60 oyster/min for which the shucking machine was designed.     

Performance evaluation of concurrent rice–fish–prawn culture with and without cull harvesting

This study was carried out in farmers' fields for three experimental culture cycles to evaluate the performance of rice–fish–prawn culture. The treatments carried out were deepwater rice mono‐cropping (R), and rice–fish–prawn culture with cull harvesting (R–FC) and without cull harvesting (R–F). Water pH and total alkalinity were significantly higher (P<0.05) in R–FC than in R–F, while the concentrations of total suspended solids, plankton and chlorophyll a were higher in R–F. Cull harvesting in R–FC had no marked influence on the concentrations of dissolved oxygen, NH₄⁺, nitrite, nitrate and phosphate compared with the R–F treatment. The significantly higher fish and prawn yields (P<0.05) and species‐wise faster individual growth performance in R–FC than in R–F were probably due to periodic cull harvesting, which minimized the competition for food and space as well as physiological stress at reduced density. The paddy yield and percentage increase in paddy yield over rice mono‐crop was significantly higher (P<0.05) in R–FC (25%), followed by R–F (16.9%), probably due to lower chlorophyll a (36.7 mg m^?3) and plankton density (1.4 × 10⁴ L^?1), which minimized the competition for nutrients with rice plants. The highest rice equivalent yield (38.5), output value–cultivation cost ratio (1.56) and enhanced net return (28%) in deepwater rice–fish culture were recorded when cull harvesting was practiced.     

Recent decline in cod stocks in the North Sea–Skagerrak–Kattegat shifts the sources of larval supply

Cod stocks in the North Sea, including the Kattegat and the Skagerrak, have declined dramatically since the 1970s. Occasionally there is a high recruitment of juveniles in Kattegat/Skagerrak, without leading to the rebuilding of adult cod stocks despite reduced fishing mortality. In a biophysical model of egg and larval drift, we examined the potential importance of extant and historical spawning grounds for recruitment of cod in the Kattegat/Skagerrak seas using data of spawning stock biomass from the 1970s and from today's reduced stocks. The results suggest that Kattegat in the 1970s relied on largely locally retained (83%) larvae with little annual variation in recruitment. Kattegat also provided a substantial proportion of larvae recruiting in Swedish Skagerrak (72%). This is in contrast to present conditions where the Kattegat spawning stock has been reduced by 94%, and Kattegat only provides 34% of locally retained larvae and 30% to Swedish Skagerrak. Instead, the protected area in the Öresund and the Belt Sea are expected today to provide most larvae recruiting in Kattegat. Also, the inflow of larvae from the North Sea to Skagerrak and Kattegat can be significant although highly variable between years, with a positive correlation to the North‐Atlantic Oscillation index (NAO). The rebuilding of healthy spawning areas in the Kattegat may be key for restoring local cod stocks in both Kattegat and along the Skagerrak coast. This poses a management challenge if cod with local ‘Kattegat’ adaptations, e.g., in terms of egg density and migration patterns, are lost or reduced to non‐resilient densities.     

Nutrient dynamics in integrated aquaculture–hydroponics systems

Changes in concentrations of dissolved Ca, Cu, Fe, K, Mg, Mn, NO₃-N, Na, P, and Zn, as a function of increasing biomass of Nile tilapia (Oreochromis niloticus) fed a commercial diet in integrated aquaculture–hydroponic systems growing romaine lettuce (Lactuca sativa longifolia cv. Jericho), were monitored over three, 28-day experimental trials. The integrated systems, 320–330 l in volume, were filled initially with a complete nutrient hydroponic solution, and were operated at a 100% recirculation rate. Treatment levels were 0 (control) 151, 377, 902, and 1804 g of fish/system and treatments were conducted in duplicate. Nutrient concentrations and mutual ratios of nutrients quickly departed from initial conditions because the relative proportion of dissolved nutrients excreted by fish and subsequently absorbed by plants differed. The removal of nutrients by lettuce, fish, and solids collection was determined as a function of treatment size. The objective of this study was to quantify both the flow of nutrients through representative integrated aquaculture–hydroponics systems and the effects of different quantities of feed nutrient input on changes in nutrient-specific concentrations.     

Linear mixed-effects models for weight–length relationships

Length and weight data are often analyzed in fisheries science to derive a parametric weight–length relationship for estimating biomass and to develop indices of condition for comparing the ‘wellness’ of different populations of fish. However, analysis of such data often ignores the inherent spatial and temporal grouping of the observations, and hence, the data hierarchy. This paper proposes the use of linear mixed-effects models as an effective means of analyzing and comparing weight–length relationships and indices of condition when there are many groups. The use of simple linear regression (where grouping is ignored), ANCOVA (where group effects are incorporated as fixed-effects), and linear mixed-effects models (where group effects are random-effects) are compared using data for Atlantic sea scallops (Placopecten magellanicus). The group means of residuals is proposed as a measure of relative weight or index of population condition. Linear mixed-effects models should be used to analyze grouped data because the variability among groups is ignored in simple linear regression and ANCOVA. Also, it is important that explanatory variables be incorporated in analyses of grouped data because their influence may mask the true differences among groups.     

Infectious salmon anaemia – pathogenesis and tropism

Infectious salmon anaemia (ISA) is a serious disease of farmed Atlantic salmon caused by the aquatic orthomyxovirus infectious salmon anaemia virus (ISAV). ISA was first detected in Norway in 1984 and was characterized by severe anaemia and circulatory disturbances. This review elucidates factors related to the pathogenesis of ISA in Atlantic salmon, the dissemination of the virus in the host and the general distribution of the 4‐O‐acetylated sialic acids ISAV receptor. The knowledge contributes to the understanding of this disease, and why, almost 30 years after the first detection, it is still causing problems for the aquaculture industry.     

The demography of Calanus pacificus during winter–spring Californian El Niño conditions, 1992–1993: implications for anchovy?

Samples from the southern California sector of the California Current System were examined to test for changes in abundance, reproduction, recruitment and naupliar survival of the planktonic copepod, Calanus pacificus, coincident with the 1993 Californian El?Niño, relative to 1992 (also El Niño conditions) and to 1989–1991 (defined as `normal'). In 1993, as in 1992, females were rare in both winter and spring, but per capita reproduction was less, food limitation was greater and biomass of chlorophyll was reduced only in winter. Recruitment was more variable than was naupliar survival. Recruitment increased in both El Niño springs, but survival of older naupliar stages decreased. The mesoscale distributions of larval anchovy, relative to eggs and nauplii of Calanus, did not result in efficient use of the reduced supply of this source of food, and the abundance of larval anchovy did not cause measurable variation in the survival of naupliar Calanus.     

A Length–Weight Relationship for Pond‐raised Hybrid Catfish Fingerlings

A length–weight relationship was developed for pond‐raised hybrid catfish fingerlings, Ictalurus punctatus × Ictalurus furcatus. A total of 4663 fish were sampled ranging from 20 to 240 mm total length. Predicted weight (g) from length (mm) is based on the equation: Y = 0.000017311X^2.868474309 (r² = 0.996) where Y is the estimated individual fish weight and X is measured total length. The predicted values generated by this model differ from, but follow the same general trends seen with channel catfish, I. punctatus, fingerlings and can be used as a baseline for the development of a length–weight table for hybrid catfish fingerling production.