Carbon content and nutritional condition of sardine larvae (Sardina pilchardus) off the Atlantic coast of Spain

As part of a “European Sardine/Anchovy Recruitment Program” (SARP), sardine larvae (Sardina pilchardus) were sampled off the Atlantic coast of Spain through the spawning season from March to June. The larvae were analysed for carbon and nitrogen content as a measure of nutritional condition and survival potential. There was no significant diel variation in larval carbon content, but there was a small significant diel variation in nitrogen; the absence of a strong diel signal in elemental composition was ascribed to the overnight retention of the gut contents. There was an increase in carbon content with increase in body length which reached an asymptote at ∼40% carbon content at a larval length of 20 mm. It is argued that larvae with a carbon content of <25% of body weight were nutritionally stressed, with the smaller larvae (<10 mm in length) appearing to be more vulnerable to food limitation. Although larvae with the lowest age-specific carbon content (poorest condition) occurred on the cruise with the lowest food availability, there was no consistent relationship between carbon content and food availability. While the successive monthly estimates of carbon content revealed differences in potential recruitment between months, these were not related to the birth-date distribution of the surviving juveniles. Received: 23 November 1998 / Accepted: 3 March 1999     

Biological factors affecting the swimbladder volume of sardine (Sardina pilchardus)

Variations in the absolute and relative swimbladder volume of sardine (Sardina pilchardus W.), were examined in relation to fish length, gonads and stomach volume, and lipid content. Fifty specimens were frozen in liquid nitrogen and sliced with a cryo-microtome. From the slices, volume estimates of the organs were obtained through computer reconstruction. Variations in absolute and relative swimbladder volume in relation to fish length and the aforementioned organs' volume and lipid contents were estimated by means of multiple regression analysis. The relative importance of these variables in the calculations of the swimbladder volume for different physiological conditions of the fish was also assessed. The results revealed that the volume can be estimated from two distinct models: the first for the reproductive and the second for the non-reproductive period. The non-reproductive period model is in agreement with the well-known positive correlation of target strength with fish log length. However, during the reproductive period the relative size of gonads and relative lipid content gradually become more important than length.     

Dynamic analysis of commercial fishing model

We investigate a quadratic commercial fishing model in this paper. The results imply that fishing capital investment is nonexplosive, the fishery resources are nonextinctive, and the solution of the bionomic system is globally stable within an invariant region.     

An analysis of beach management framework in Spain. Study case: the Catalonian coast

In the present paper, the current beach management framework in the North-Western Mediterranean coast (Catalonia, Spain) was revised. Beach management was analyzed using the concepts of Integrated Coastal Zone Management (ICZM). The history of beach management in the second half of the 20 century and the new developments in the academic field and in the practical beach management sector during the last decade were studied. The revision of legal texts and strategies in the Catalan coast allowed synthesizing all scattered information affecting beach management. A SWOT analysis was performed. The main strengths of the beach management framework in Catalonia are the public ownership of beaches, which allows the government to carry out a comprehensive management and the recent data and analysis provided by the adopted National and Autonomous ICZM strategies. The weaknesses found were related to the functioning of traditional existing institutions. New opportunities are related to the possibility of establishing new institutions that conduct a more inclusive and proactive management. The main threat is that although the possibility for a fundamental change in beach management organization exists, resources available are not fully exploited.     

An empirical analysis of economic strategies for controlling air pollution

In evaluating current environmental protection policy, economists often note that current regulations are more costly than necessary to meet environmental quality standards. While the a priori case is strong that current regulatory approaches are resulting in higher-than-necessary costs to attain environmental standards, there is relatively little empirical evidence to support this claim. The purpose of this paper is to supply some of the missing evidence by presenting the results of one study that assesses some of the potential savings associated with implementing economic, rather than command-and-control, regulatory approaches to abate one type of air pollution in one region of the country. Specifically, the paper examines the costs of meeting a prospective short-term standard for nitrogen dioxide under a range of alternative emissions control strategies for stationary sources of nitrogen oxide emissions in the Chicago Air Quality Control Region. The alternative strategies that are considered range from those that might result under current regulatory policy to those that economic policy approaches (such as emissions charges or marketable permits) are designed to implement. The analysis shows that the most efficient program of emissions controls may be more than an order of magnitude less costly than current regulatory strategies, and that economic approaches have additional advantages over more conventional regulatory approaches.     

An economic analysis of air pollution from coal-fired power plants

The benefits of air pollution control techniques on a coal-fired power plant are Simulated with a scientifically based environmental model. Air pollution abatement techniques are assessed in terms of their resource cost (measured in dollars) and their effectiveness in reducing environmental damage (measured in dollars and healthy days lost). Which air pollution techniques are most efficient depend upon how much a day of health should be valued. Other factors of potential interest such as uncertainty and equity are also simulated through the model. The paper demonstrates that scientific evidence can be organized around economic principles in order to develop more rational and effective environmental policies.     

A simulation model for Japanese sardine (Sardinops melanostictus) migrations in the western North Pacific

A two-dimensional individual-based model coupled with fish bioenergetics was developed to simulate migration and growth of Japanese sardine (Sardinops melanostictus) in the western North Pacific. In the model, fish movement is controlled by feeding and spawning migrations with passive transport by simulated ocean current. Feeding migration was assumed to be governed by search for local optimal habitats, which is estimated by the spatial distribution of net growth rate of a sardine bioenergetics model. The forage density is one of the most important factors which determines the geographical distributions of Japanese sardine during their feeding migrations. Spawning migration was modeled by an artificial neural network (ANN) with an input layer composed of five neurons that receive environmental information (surface temperature, temperature change experienced, current speed, day length and distance from land). Once the weight of the ANN was determined, the fish movement was solved by combining with the feeding migration model. To obtain the weights of the ANN, three experiments were conducted in which (1) the ANN was trained with back propagation (BP) method with optimum training data, (2) genetic algorithm (GA) was used to adjust the weights and (3) the weights of the ANN were decided by the GA with BP, respectively. BP is a supervised learning technique for training ANNs. GA is a search technique used in computing to find approximate solutions, such as optimization of parameters. Condition factor of sardine in the model is used as a factor of optimization in the GA works. The methods using only BP or GA did not work to search the appropriate weights in the ANN for spawning migration. In the third method, which is a combined approach of GA with BP, the model reproduced the most realistic spawning migration of Japanese sardine. The changes in temperature and day length are important factors for the orientation cues of Japanese sardine according to the sensitivity analysis of the weights of the ANN.     

Genetic variability in bloodworm (Glycera dibranchiata) populations in the Gulf of Maine

Genetic structure of eight Northwest Atlantic populations of the marine polychaeteGlycera dibranchiata Ehlers was examined with starch gel electrophoresis. Samples were collected during summer and fall 1981, and seven polymorphic and four monomorphic loci were consistently scored. Average heterozygosity (0.126) and percent polymorphic loci (59.3) were comparable to the averages reported for marine invertebrates. Minimum genetic distances between populations ranged from 0.003 to 0.093, levels typically associated with local populations of the same species in other taxa. Based on these data, inter- and intra-estuarine migration and gene flow appear to be low. Only two populations, separated by 13 km along the same river in New Brunswick, Canada, were not genetically different from each other. These findings may have relevance for management strategies in bloodworms.     

An assessment of heavy-metal contamination in surface sediments of the Suez Gulf using geoaccumulation indexes and statistical analysis

An assessment of marine pollution due to metals was made in the Suez Gulf based on surface costal sediment collected from 18 locations along the Gulf. The samples were dried and acid-digested, and the metal contents (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) were determined using a flame atomic absorption spectrophotometer (air-acetylene) with deuterium background correction. An evaluation of the heavy-metal pollution status of the Gulf was carried out using enrichment factors (EF) and geo-accumulation Indexes (I_geo). Also, heavy-metal concentrations in Suez Gulf sediments were evaluated using the Effect Range-Low (ERL) and the Effect Range-Median (ERM). The results of a Spearman correlation and factor and cluster analysis of the heavy metals analysed in the collected sediment were discussed. The main source of contamination is offshore oil field and industrial wastes, which arise due to the ineffective and inefficient operation equipments, illegal discharge and lack of supervision, and prosecution of offenders.     

Ecological and economic considerations on fishing and rearing of Tapes phillipinarum in the lagoon of Venice

A population dynamic model for Tapes philippinarum has been developed, using experimental data for the estimation of mortality, and literature information for recruitment. The population dynamic model has been coupled to a eco-physiological model of T. philippinarum previously developed, in order to simulate the evolution of individual size and number of individuals in each age class.The resulting age-size class model has been used to analyse the implication of different scenarios of fishing/harvesting of the bivalve in the lagoons of the Northern Adriatic Sea, where fishery and aquaculture represent important economic activities.Ten years long simulations have been performed, in which initial density, harvesting efficiency, minimum harvested size, were varied. Comparisons between the different strategies are made in term of total yields and bio-economic income. The model gives suggestions on the optimal fishing effort, in case of fishery, and on optimal seeding size and seeding moment, in case of aquaculture.A discussion of model results provides indications on harvesting policies which are appropriate from ecological-economical point of view. The final result is that economically more profitable strategies coincide with ecologically more conservative policies.     

Management and exploitation dynamics of small-scale fisheries in the Bay of Biafra: An integrative analysis of purse seine fishing activity

For many decades, fisheries research has focused on stock assessment and the impact of the fishery effort on resources. Although this knowledge remains necessary, a more integrated analysis of the joint dynamics of resource and operational activities is needed to provide more useful advice for the management of fishery systems. Since 1994 a new approach to fishery science has been carried out for Cameroonian small-scale fisheries, the aim being the incorporation into fishery science of research on fishery management, fishing processes and fishermen's behaviour. This paper presents a more systemic data approach which combines biological parameters and operational factor analyses with the goal of sustainable development. From two years of data collected on the purse seine fishing units operating in the Bay of Biafra (2002 and 2003), a set of three correspondence analyses is applied: (1) to the length frequency distribution of Ethmalosa fimbriata, (2) to the number of visits per fishing ground, and (3) to the species appearance frequency in the landings. These three analyses were plotted per month-year period. The results are presented in the form of an annual exploitation cycle, linking fishing grounds, the main species caught, and corresponding fishing period.     

Application of cluster analysis to the geochemistry zonation of the estuary waters in the Tinto and Odiel rivers (Huelva,Spain)

The combination of acid water from mines, industrial effluents and sea water plays a determining role in the evolutionary process of the chemical makeup of the water in the estuary of the Tinto and Odiel rivers. This estuary is in the southwest of the Iberian Peninsula and is one of the estuarine systems on the northwest coast of the Gulf of Cádiz. From the statistical treatment of data obtained by analyzing samples of water from this system, which is affected by industrial and mining pollution processes, we can see how the sampling points studied form two large groups depending on whether they receive tidal or fluvial influences. Fluvial input contributes acid water with high concentrations of heavy metal, whereas industrial effluents are responsible for the presence of phosphates, silica and other nutrients. The estuarine system of the Tinto and Odiel Rivers can be divided into three areas – the Tinto estuary, the Odiel estuary and the area of confluence – based on the physical – chemical characteristics of the water.     

Sardine (Sardina pilchardus) stress reactions to purse seine fishing

Observations from the purse seine fishery off northern Portugal are used to describe the early dynamics of sardine (Sardina pilchardus) stress reactions and identify likely stressors during the commercial fishing operation. Sardine blood and muscle were sampled from the onset of fishing (school identification and encircling) to the end of fish transfer onboard (90–120 min later). The evolution of haematocrit, haemoglobin, cortisol, glucose, ionic concentrations, ATP and its catabolites were modelled using linear mixed models as a function of time spent in the net, biological (sex, reproductive state and condition) and operational variables (catch, light level and phase of fishing operation). Significant linear trends with time were detected for most stress variables and mean concentrations after 2 h in the net were similar to literature values corresponding to acute stress reactions for teleosts. Biological variables were rarely significant and explained a small proportion of variation, while operational variables were never significant. For each stress variable, levels varied considerably between trips but the temporal evolution was common across trips. Random trip effects were uncorrelated among most biochemical variables, suggesting that distinct factors affected each stress variable during the sampled trips. However, the linear trend with time spent in the net observed for most stress variables indicates that the duration of the fishing operation is an important stressor in purse seine fishing due to the progressive water volume restriction, crowding and manipulation associated to the fishing method.     

Succession and growth limitation of phytoplankton in the Gulf of Bothnia (Baltic Sea)

A one year field study of four stations in the Gulf of Bothnia during 1991 showed that the biomass was ca. two times, and primary productivity ca. four times, lower in the north (Bothnian Bay) than in the south (Bothnian Sea) during the summer. Nutrient addition experiments indicated phosphorus limitation of phytoplankton in the Bothanian Bay and the coastal areas in the northern Bothnian Sea, but nitrogen limitation in the open Bothanian Sea. A positive correlation between the phosphate concentration and the production/biomass ratio of phytoplankton was demonstrated, which partly explained the differences in the specific growth rate of the phytoplankton during the summer. Differences in photosynthetic active radiation between the stations also showed a covariation with the primary productivity. The relative importance of nutrient or light limitation for photosynthetic carbon fixation could not, however, the conclusively determined from this study. Marked differences in phytoplankton species composition from north to south were also observed. The number of dominating species was higher in the Bothnian Sea than in the Bothnian Bay. The distribution of some species could be explained as due to nutrient availability (e.g. Nodularia spumigena, Aphanizomenon sp.), while salinity probably limits the distribution of some limnic as well as marine species. The potentially toxic phytoplankton N. spumigena, Dinophysis acuminata and Chrysochromulina spp. were common in the Bothnian Sea but not in the Bothnian Bay. The pico- and nanoplankton biomass during late summer was higher than previously reported due to a revised carbon/volume ratio.     

Quantitative distribution of herbivorous reef fishes in the Gulf of Aqaba (Red Sea)

The distribution of the main herbivorous fishes (Acanthuridae, Scaridae, Siganidae) was studied across a coral reef of the Jordanian coast in the Gulf of Aqaba (Red Sea). Visual counts were realized by diving along transects (200 m long and 5 m wide), parallel to the shore, at 10 stations located from the lagoon to 40 m deep on the outer reef slope. Herbivorous reef fishes reach their highest abundance on the reef front, where 234 fishes were counted per 1,000 m². Their density decreases on the reef flat, with an average of 150 fish 1,000 m^-2, and is lowest on the outer reef slope (69 fish 1,000 m^-2). Surgeonfishes form 63% of the herbivorous ichthyofauna, parrotfishes 35%, and rabbitfishes 2%. Families and species display different distributions according to biota. The Acanthuridae dominate on the reef flat, whereas the Scaridae are more numerous on the outer reef slope. The evolution of the social structure of the main species was observed: the adults generally school in the lagoon and on the reef flat, but are mainly solitary on the reef slope. The distribution of juvenile individuals is more restricted: they are concentrated on the reef front and on the upper part of the reef slope.This study is part of a cooperation programme between the University of Nice (France) and the University of Jordan, to study the ecology of the coral reefs and the surrounding waters of the Jordanian coast (Gulf of Aqaba, Red Sea)     

Length-structured analysis of the reproductive season of anchovy and common sardine off central southern Chile

The anchovy (Engraulis ringens) and common sardine (Strangomera bentincki) are two small pelagic fish which have a similar reproductive strategy off central southern Chile. The seasonal reproductive dynamics of both the species was investigated by taking into account the gonadosomatic index (GSI) and visual maturity data as a function of female size for the period 1993–1999, and also the seasonal pattern in condition factor per size classes. Larger females of common sardine (repeat spawners) have a reproductive peak earlier in the season than younger females at first maturity, while larger anchovy have a reproductive peak delayed as compared with first-time spawners. The condition factor of females exhibited an inverse cycle with the seasonal pattern of GSI, and delayed by approximately 6 months. Although larger females tend to present better and wider condition than smaller females, the condition of females seems to be delayed in larger females probably mediated by the seasonal pattern in food availability. This “energy storage strategy” in spring and summer time seems to be size-dependent and past energetic reserves could also affect the egg production and timing of reproduction. We concluded that the reproductive season of anchovy and common sardine is different and mediated by the length structure in the seasonal upwelling system off central southern Chile.     

Arsenic in the top predators sailfish (Istiophorus platypterus) and dolphinfish (Coryphaena hippurus) off the southeastern Gulf of California

Environmental Geochemistry and Health - Distribution of arsenic (As) in tissues and gonads of the Indo-Pacific sailfish Istiophorus platypterus and the dolphinfish Coryphaena hippurus from the SE...     

Winter diet shift of long-beaked common dolphins (Delphinus capensis) feeding in the sardine run off KwaZulu-Natal, South Africa

Unpredictable inter-annual variations in the timing, spatial extent and intensity of the sardine run (Sardinops sagax) have been documented in recent years along the coastline of KwaZulu-Natal, South Africa. This study aimed to determine whether variations in the availability of sardine were reflected in the diet and condition of common dolphins (Delphinus capensis) over the past three decades. Stomach contents from 95 common dolphins incidentally caught between 2000 and 2009 were analysed and compared to historical data collected between 1972 and 1992. A shift in the principal prey species consumed by the dolphins was observed over the past 30 years. Prior to 1992, sardine comprised up to 49 % of the total stomach contents by mass, whilst chub mackerel (Scomber japonicus) was the dominant prey recorded in the stomach contents between 2000 and 2009 (66 %). As common dolphins prey on locally abundant fish species, this dietary shift may indicate changes in the availability of the most abundant fish prey. Stable isotope analyses of tooth tissue revealed no significant changes in the δ¹⁵N and δ¹³C isotopic ratios over the past three decades (P = 0.283 for N and P = 0.922 for C). Blubber thickness as a percentage of body length and blubber weight as a percentage of total body weight were assessed as indicators of animal condition. No significant changes in proportional blubber weight or blubber thickness were seen over the last 40 years (1970–2009) for all age cohorts. This species appears to be well adapted to cope with changes in prey species availability, without impacting on body condition.