Introduction. Timing of management practices requires an understanding of pest population dynamics in given cropping systems. Our study was designed to establish the population trends of B. invadens in mango orchards and to determine if population fluctuations were reflected in fruit infestation levels during changes in mango phenology. Materials and methods. Bactrocera invadens flies were trapped weekly from February 2011 to November 2012, using methyl eugenol and DDVP (dichlorvos) insecticidal strips. Trapping was done in three mango orchards in the Luweero district of Uganda’s Lake Victoria Crescent. Mango fruit samples were incubated for the retrieval of puparia to calculate positivity (proportion of fruits infested) and fruit infestation indices (number of puparia per kg of fruit) for each stage of fruit maturity. Results. Mean trap catches of adult B. invadens varied significantly over the months (range : ~11 flies per trap per day (FTD) to over 590 FTD; P £ 0.0001). During each year, infestations peaked during June-July and January-February. Trap catches were higher in the major fruiting season compared with the minor fruiting season and were the highest when mango was at the physiological maturity and ripe stages. Fruit infestation and positivity were highest for fruit at the physiological maturity and ripe stages and lowest at the fruit set stage. Discussion. Our findings show that B. invadens is present year-round and all stages of mango fruit development are susceptible to attack. Thus, control measures should be implemented throughout the year and preferably started at fruit set to lessen fruit fly population build-up and damage to fruits.

Introduction. Various whitefly species attack sweet oranges in Nigeria. The economic importance of these whiteflies varies from one area to another depending on prevailing environmental conditions. Trials were established to assess the relative susceptibility of sweet orange varieties to woolly whitefly Aleurothrixus floccosus (Maskell) attack, its population dynamics and the impact of its entomopathogenic fungi Aschersonia spp.in population management. Materials and methods. Four sweet orange varieties were used for the trials: Agege, Bende, Pineapple and Valencia. The population dynamics of A. floccosus and its fungi-colonised nymphs were monitored in 2006 and 2007 by sampling 24 leaves per tree at 14-day intervals. Average monthly precipitation, relative humidity and temperature were collated for the period of our study. Results and discussion. No significant difference was observed among the populations of A. floccosus nymphs or the level of nymphal infection by Aschersonia spp. in the sweet orange varieties. Higher numbers of woolly whitefly eggs and adults were observed on the Agege and Bende varieties in 2006 and 2007, but the results were only significantly different in 2007. In both years, the populations of eggs, nymphs and adults of A. floccosus and its entomopathogenic fungi Aschersonia spp. were relatively high in the dry season months of January to March, dropped during the rainy seasons and rose again from October. Evaluation of Aschersonia spp impact showed active colonisation of whiteflies. Generally, our results showed that weather factors such as rainfall and relative humidity negatively influenced the woolly whitefly population. Conclusion. The association between the woolly whitefly population and fungi was beneficial and suggests that Aschersonia spp. could be considered as a potential biological control agent for A. floccosus

Introduction In Morocco the olive growers rely totally on pesticides to control the black scale Saissetia oleae, although this technique has adverse effects on natural enemies, on product quality and on the environment. However, the pesticides are not used efficiently because of ignorance of the developmental cycle of the insect, and of the periods of vulnerable instar presence. We studied these two parameters. Next, we tested the efficacy of the pesticide and we studied the effect of pruning on the scales as an alternative to chemicals. Materials and methods The seasonal trend of the black scale was studied in two olive orchards near Essaouira, in the west of Morocco, during 2005 and 2006. One of these orchards was subject to chemical treatment in 2007, while two new orchards were selected to study the effect of pruning on the scales. The evolution of crawler and nymph density on different olive tree organs was followed in order to discover their preferences for these different organs. Results and discussion The seasonal trend study showed the presence of one generation of S. oleae per year and the tendency to colonise young organs rather than old ones. The optimum of mobile instar population coincided with the beginning and the end of July. On the organs of the chemically-treated samples, numbers of crawlers and nymphs were highly reduced. The results showed a small-scale infestation in pruned trees compared with the unpruned trees (control). Conclusion. Though the chemical control has good results, pruning remains very efficient and can help improve the control of the black scale populations without harming the environment

Introduction. In Mali, mango annual production is estimated at 100 000 t. Because of structural and plant sanitary problems mainly related to the actions of fruit fly, seldom more than 1% of this production is exported. The principal aim of this study was to develop an integrated control of the Tephritidae using spot treatments. One of the preconditions was to identify the species responsible for the damage in the three principal Mali production zones (Sikasso, Bougouni and Bamako). Materials and methods. Mangos belonging to the principal exported varieties were collected from the beginning of April up to the beginning of October 2000 and were observed to identify the Tephritidae species present in the fruits. The installation of sex attractant or of foodstuff attractant traps allowed us to follow the evolution and constitution of the fruit fly population in the orchards of the three selected sites. The effectiveness of a spot treatment to control Ceratitis sp. was tested. Results and discussion. Starting from adult observations and determination, six species of Tephritidae were identified. Among them, Ceratitis cosyra (Walker), C. quinaria (Bezzi) and C. silvestrii Bezzi were earliest and are thus most prejudicial. C. cosyra represented 86% of the total recovered flies. The species C. anonae, C. quinaria, C. fasciventris and C. ditissima were identified for the first time in Mali. The damage due to Tephritidae in the middle of the harvest period bordered on 50% of the crop for the varieties Kent and Keitt and exceeded 60% for that of Brooks. The 180 traps installed on the three studied sites allowed us to capture 128 998 Tephritidae adults belonging to thirteen species; the six species linked to the mango tree represented 99% of this total. The spot treatments carried out on the three experimental sites gave encouraging results, with a reduction in damage of approximately 50% in the treated orchards compared with the control orchards. Conclusions. To prolong the action undertaken, it will be interesting to confirm and look for further results obtained during the years to come. The installation of a regional project for controlling mango tree Tephritidae in West Africa would be fundamental in the medium term to limit such an insect pest which itself prevails on the sub-region scale.

To characterize the population dynamics of Erionota thrax Linnaeus and its major parasitoids, biweekly samplings were carried out in a commercial Cavendish banana plantation and a subsistence farm of local varieties, from April 2004 to November 2005. Five primary endoparasitoids were recorded: Ooencyrtus erionotae Ferriere, Cotesia erionotae Wilkinson, Brachymeria albotibialis Hoffmann, Elasmus sp. and Melaloncha sp. Ooencyrtus erionotaeC. erionotae, and B. albotibialis were, respectively, the major egg, larval and pupal parasitoids. In 2004, there was no significant difference in the E. thrax population densities and parasitism of immature life stages in both farms. In 2005, the pest population densities were significantly different, while only egg and larvae parasitism rates were significantly different. In the commercial plantation, peaks of E. thrax population densities per banana mat were recorded in April, June, July, and October–December and highest values for eggs, larvae and pupae were 4.66, 2.76 and 1.7, respectively. Percentage parasitism peaked in August, October, and February with peak values ranging from 60 to 100%. In the subsistence farm, peak E. thrax population densities were observed between May–July and September–December. Percentage parasitism peaked in January, February, July, August, October and November, with peak values ranging from 24 to 100%. Correlations between population densities of E. thrax and the numbers of parasitized insects showed strong positive relationships. There was evidence of a delayed density dependence of the parasitoids as most peaks of parasitism appeared 1 or 2 months after those of the host stages. Parasitism rates in the commercial plantation were substantial in spite of the frequent use of insecticides, and activities of the parasitoids were more favoured in the subsistence farm compared with the commercial plantation.

Introduction. Tephritidae have a major economic importance in the tropical areas. In Benin, we had only very little information available on the mango fruit fly species, except the demonstration of their damage. We therefore carried out the first investigations in Northern Benin during the mango season in 2005. Our objectives were to study fluctuations of tephritid populations in orchards and to assess mango fruit fly infestations and mango losses due to tephritid species. Materials and methods. Experiments were carried out in the Parakou area (Borgou department, Northern Benin). Fruit fly males were captured on mango trees, in two different orchards, with parapheromone traps. To sample and characterize fruit fly species involved in mango infestations, fruits of 17 cultivars were collected in mango orchards from February to June 2005; then, they were brought to the laboratory for emerging species identification. To assess the loss of fruits, sampling of different mango cultivars was achieved in the same orchards. Infested fruits were counted and eliminated; potentially infested fruits were dissected. Results and discussion. Among eight mango fruit fly species found in Benin, four can be considered as species of economic significance: Ceratitis cosyra, C. quinaria, C. silvestrii and Bactrocera invadens. During the dry season, C. cosyra was the most abundant, whereas B. invadens was the most numerous during the rainy season (abiotic factor), in phenological accordance with the ripening of the different mango varieties (biotic factor). From and after mid-May, B. invadens was found more frequently than C. cosyra in the traps and from emergence of infested mangos. Loss averages varied globally from 12% at the beginning of April to 50% in June. Conclusions. Most of the tephritid species found on mangos during our experiments had already been observed previously in other West African countries except B. invadens, an invasive species lately described. Ecological and behavioral studies will be necessary in order to plan and to apply optimal methods for controlling this new pest of major economic importance in West Africa.

Introduction. Au Mali, la production annuelle de mangues est estimée à 100 000 t. Du fait de problèmes structurels et phytosanitaires principalement liés à l'action des mouches des fruits, rarement plus de 1 % de cette production est exporté. L'objectif principal de cette étude a été de mettre au point une lutte raisonnée contre les Tephritidae du manguier au Mali à l'aide de traitements par taches. L'un des préalables a été d'identifier les espèces responsables des dégâts dans les trois zones principales de production (Sikasso, Bougouni, Bamako). Matériel et méthodes. Des mangues appartenant aux principales variétés exportées ont été collectées de début avril à début octobre 2000 et mises en observation afin d'identifier les espèces de Tephritidae présentes dans les fruits. La pose de pièges à attractifs sexuels ou alimentaires a permis de suivre l'évolution et la constitution des populations de mouches des fruits dans les vergers des trois sites choisis. L'efficacité d'une méthode de traitement par taches pour lutter contre les cératites a été testée. Résultats et discussion. À partir des observations et de la détermination des adultes, six espèces de Tephritidae ont été mises en évidence. Parmi elles, Ceratitis cosyra (Walker), C. quinaria (Bezzi) et C. silvestrii Bezzi ont été les plus précoces et sont donc les plus préjudiciables. C. cosyra a représenté 86 % de l'effectif total des mouches. Les espèces C. anonae, C. quinaria, C. fasciventris et C. ditissima ont été identifiées pour la première fois au Mali. Les dégâts dus aux Tephritidae en milieu de campagne ont avoisiné 50 % de la production des variétés Kent et Keitt et dépassé 60 % de celle de Brooks. Les 180 pièges mis en place sur les trois sites suivis ont permis de capturer un total de 128 998 Tephritidae adultes appartenant à treize espèces ; les six espèces inféodées au manguier ont représenté 99 % de cet effectif. Les traitements par taches effectués sur les trois sites expérimentaux ont donné des résultats encourageants, avec une réduction des dégâts d'environ 50 % sur les parcelles traitées par rapport aux parcelles témoins. Conclusions. Pour prolonger l'action entreprise, il sera intéressant de confirmer et approfondir les résultats obtenus au cours des années à venir. La mise en place d'un projet régional de lutte contre les Tephritidae du manguier pour l'Afrique de l'Ouest serait fondamentale à moyen terme pour limiter un tel ravageur qui sévit lui-même à l'échelle de la sous-région.

The population dynamics of busseola fusca (Fuller) was studied from 1997 to 1999 at Halhale and Halhal Begos, located at altitudes of 1960 and 1850 m above sea level respectively in the highlands of Eritrea. Sowing was done in early April in Halhale and late June in Halhal Begos throughout the study period. All agronomic practices recommended for sorghum production in the two areas were followed to ensure good crop stand, except for application of pesticides. A total of 15 generations, nine in Halhale and six in Halhal Begos were observed during the study periods. Busseola fusca had three and two generations per year in Halhale and Halhal Begos, respectively. Peak egg laying at Halhale was in early May, July and early September, while at Halhal Begos it was in July and early September. The study revealed that stage-specific mortalities of B. fusca were caused by infertility, disappearance (predation by ants and earwigs, lack of suitable host, abiotic factors), residuals and parasitoids. The key mortality factor was disappearance of small larvae (35–66 % mortality). The mortality of the other stages was low but had a composite effect on the overall generation mortality. The mortality of small larvae was density-dependent and density-independent at Halhale and Halhal Begos, respectively. The changes in population between generations were due to small larval mortality of B. fusca from one generation to the next. The life table study showed that mortality due to natural factors did not reduce B. fusca population below the damage level. Integrated management strategies are discussed to reduce the damage caused by B. fusca on sorghum.

The influence of banana weevil, Cosmopolites sordidus (Germar)(Coleoptera: Curculionidae), population density on oviposition rates and larval survivorship was studied in the laboratory at the Kawanda Agricultural Research Institute in Uganda. This study was undertaken to elucidate the relationship between density-dependent factors and rates of banana weevil increase in the field. Oviposition substrates (corm pieces) were offered to a range of densities of weevils maintained in buckets. Mean oviposition rates per female at densities of 10, 20 and 40 females per bucket were 29, 37 and 53%, respectively, lower than that at a density of 5 females. Nevertheless, total oviposition for the same groups was 1.4, 2.5 and 3.7 times higher than that of the 5-female group. Providing fresh corms daily instead of every five days did not increase oviposition. Larval survivorship was slightly higher at lower densities of immatures following insertion of different densities of eggs or first instars into banana corms. The results suggest that density-dependent factors can influence oviposition rates of individual weevils and survivorship of immatures, but appear to exert only modest influence in reducing banana weevil population growth. More likely, high mortality of weevil immatures under field conditions and/or higher rates of adult mortality and emigration than previously postulated contribute to the slow population build-up of this pest.

Once a minor pest, the pea aphid, Acyrthosiphon pisum (Harris) has recently become a major pest of field pea (Pisum sativum L.) in Ethiopia, particularly in the northwestern region. To determine the population dynamics of the pest, field experiments were carried out at Adet and Zema in northwestern Ethiopia in 1994, 1995 and 1996. Treatments were planting dates at 15-day intervals in May, June and July and sampling was carried out weekly until crop maturity. Combined ANOVA, over seasons and locations, showed significant effects of sowing dates, seasons and locations. Pea aphid populations increased and decreased with delay in planting at Adet and Zema, respectively. At Adet, peaks of weekly counts of aphid numbers were observed in August and seasonal totals of aphids on individual planting dates increased as planting was delayed. At Zema, peaks of weekly counts of aphid numbers were observed in mid-July (1996), late August and early September (1995) and mid-September (1994); peas planted on June 16 gave the lowest seasonal totals of aphids. Natural enemies (predators and parasitoids) appeared in considerable numbers in 1996 and these tended to increase as planting date was delayed. For most planting dates and years, weekly aphid populations showed positive correlation with maximum temperature, and negative correlation with minimum temperature and relative humidity. Increasing maximum temperature promoted the buildup of aphid populations while increased minimum temperature, rainfall and relative humidity suppressed it. Grain yield increased and decreased as planting date was delayed at Adet and Zema, respectively. From these results, it is recommended that planting of field peas should take place from mid- to late June at Adet and during the first week of June at Zema to obtain higher yields; by doing so a mean of 0.32 t/ha and 0.50 t/ha higher yield was obtained, respectively.

The population dynamics of the coconut mite, Aceria guerreronis Keifer (Acari: Eriophyidae) infesting the coconut fruits was studied during September 1999-May 2000 in Tamil Nadu, India where the mite is a new pest. The densities of active mites and eggs were not significantly correlated with weather factors. Mites were more abundant on the post-fertilisation bunch 3 drupes (fruits) (6.0 mites/7 mm2) than on the other drupes. They were most crowded on the fourth (outer to inner) tepal (bract) of the bunch 3 perianth (2.6 mites/7 mm2). No significant difference was evident between populations of A. guerreronis from the drupe and tepal surfaces. However, eggs were more numerous on the tepal surface (4.9 eggs /tepal) than on the drupe surface (2.5 eggs /drupe). Egg density was highest on bunch 5 drupes (8.6 eggs/tepal) than on the drupes of other bunches. The inner tepals (4–6) carried more eggs (4.6–5.6/tepal) than the outer (1–3) ones (1.2–3.8/tepal). Mite population declined by 62.6 % when the tepal area decreased by 24.3 % due to mealybug (Pseudococcus cocotis Mask.) infestation which caused the tepals to deform. The predatory mites Amblyseius sp. and mealybugs were most abundant on tepals 5 and 6 (2.5–2.6 predatory mites; 4.6–4.7 mealybugs/ tepal). Eggs of A. guerreronis could be stored in the freezer at 3.9 ± 0.3 °C for one month although hatchability decreased from 98 % one day after storage to 54.7 % one month after storage. Loss of the eriophyid mites from sample drupes after five days was minimal (54.7 %) when the drupes were stored in a thermocool box containing ice at 23.7 ± 0.4 CC. Most mites (75.8 %) died when the drupes were stored in the open at room temperature (35.3 ± 0.9 °C).

Surveys for population densities of the maize borer Sesamia eretica Led. (Lepidoptera: Noctuidae) were conducted for three consecutive years (1997–1999) in several localities of the Nile delta in Egypt, in order to get a better insight into the population dynamics of the pest and to propose rational basis for its biocontrol using a recently isolated granulovirus. High population densities (more than one borer per plant) were observed only in the first plantings after winter (first fortnight of April). After this peak, populations almost vanished until the end of the crop season (September-October) when a slight increase was observed (0.1 borer per plant). The drastic decrease in population densities in plantings from the end of April occurs because most final instars of the borer leave the plant to pupate in the soil. This behaviour, uncommon in maize borers, results in a very high mortality rate due mainly to pupal parasitism. Only the few larvae pupating in the stem, which are much less parasitised, give rise to adults. Spatial distribution was studied using Taylor's power laws which enabled the elaboration of enumerative sampling plans for eggs, small larvae (1st and 2nd instars) and older ones. Fixed optimal sample size and sequential sampling plans for different precision levels were developed. The precision of the estimated sample size was checked using resampling of some of the data that were not used to build the models. The validation study showed that the plans were suitable for the entire Nile delta region.

Introduction. Jusqu'à présent, les recherches entreprises en Algérie pour contrôler P. citrella Stainton ou mineuse des agrumes, parasite responsable de nombreux dégâts sur agrumes, ont été très limitées. Une étude sur la dynamique des populations du parasite et l'impact de son complexe parasitaire a été entreprise pendant trois années, dans l'Est de la Mitidja en Algérie. Matériel et méthodes. Des échantillonnages ont été effectués, de 1996 à 1998, deux fois par mois sur deux vergers, l'un de citronniers, l'autre d'orangers. Des dénombrements aléatoires ont été faits sur 500 feuilles par prélèvement. Au laboratoire, les différents stades de développement de la mineuse et leur état (vivants, morts ou parasités) ont été notés par face foliaire et par orientation des rameaux échantillonnés. Résultats et discussion. Une forte contamination par P. citrella a été observée en été et au début de l'automne. Les pousses printanières ont été partiellement contaminées en 1996 et 1997 et pratiquement indemnes en 1998. Le taux de mortalité des populations a été très important en 1997 : 53 % sur orangers et 46,48 % sur citronniers. Quelle que soit l'année, le deuxième stade larvaire a été le plus affecté. Les sex-ratios ont été de 0,12 (citronniers) et 0,11 (orangers). Trois parasitoïdes locaux ont été identifiés : Cirrospilus pictus, C. vittatus et Pnigalio mediterraneus. En 1996, ils ont donné lieu à des taux de parasitisme maximaux de 22 % à 29 % sur citronniers et 26 % et 30 % sur orangers. Ces taux ont augmenté en 1997 et 1998, du fait de l'introduction de Semielacher petiolatus. Conclusion. Pour renforcer l'activité des auxiliaires locaux, il faudrait tout d'abord procéder à des élevages et des lâchers importants de S. petiolatus, tenter à nouveau d'élever et de lâcher l'espèce A. citricola, enfin d'introduire d'autres parasitoïdes performants.

Studies on the population dynamics of Aphis gossypii Glover carried out on cotton in the Tadla area over a 3-year period showed two periods of rapid resurgence: June-July and September, with the highest density reached in the latter month accompanied by considerable indirect economic loss. The resurgence of Aphis gossypii populations on cotton depends mainly on the date and the density of contamination flights. The evolution and other factors responsible for the variations in the population dynamics are discussed.

Aphis gossypii is one of the major pests of cucumber grown in greenhouses in the coastal areas of Morocco. A population dynamics study showed that A. gossypii populations might reach very high levels in June, causing economic damage to cucumber. The proliferation of A. gossypii on cucumber arises mainly from infestations by flying winged adults. Factors regulating the fluctuation of population of the species are discussed.

We monitored abundance, population dynamics and damage impacts of the leucaena psyllid Heteropsylla cubana Crawford (Homoptera: Psyllidae) in a maize-leucaena agroforestry system. The abundance of local ladybird beetle predator populations were also evaluated. The studies were conducted between June 1993 and November 1995 at Mtwapa and Amoyo in coastal and western Kenya respectively. Alley-cropping leucaena with maize had no effect on the abundance of the leucaena psyllid or its coccinellid predators. Therefore, neither the ‘resource concentration’ hypothesis nor the ‘enemies’ hypothesis corroborated for the psyllid-leucaena system within the spatial scale of this study. Psyllid populations were generally much higher at Mtwapa than at Amoyo, suggesting possible environmental effects on population growth. Psyllid populations were influenced by weather (mainly rainfall) and availability of suitable shoots. New growth of young shoots following rainfall encouraged psyllid abundance as long as weather conditions were not extreme. Though population of the generalist ladybird beetles was correlated with that of its psyllid prey, beetles did not appear to have significant effect on prey populations.

The present study presents a method of assessing and fitting a stock-recruitment relationship. The method is based on a combination of an equilibrium production model and a yield per recruit model. It does not use recruitment data which are, in general, highly dispersed, but production data. Thus, the relationship obtained is not of the parametric form of classical stock-recruitment relationship such as those of the Beverton and Holt (1957) and Ricker (1954), however, in some cases, the resulting stock-recruitment curve resembles models currently used in fisheries science. It is interpreted as an expectation of the recruitment conditionally to stock spawning biomass and stock demographic structure. However, for some realistic values of the parameters, the curve thus obtained describes a loop which suggests that two different recruitment levels may be expected from the same stock spawning biomass level. This theoretical property is illustrated with simulations. As an illustrative example, the method is applied to North-West Atlantic gadoid stocks. The significance of the method, its originality, the validity of the underlying assumptions and their conceptual consequences are discussed.

Populations of larvae and pupae of the African rice gall midge, Orseolia oryzivora Harris & Gagne (Diptera: Cecidomyiidae), and two parasitoids, Platygaster diplosisae Risbec and Aprostocetus procerae (Risbec)[= Tetrastichus pachy diplosisae Risbec], were recorded in replicated experiments on farmers' fields at Karfiguéla, Burkina Faso in the 1992 wet season and the 1993 dry season. In each season, four plantings were made at 14-day intervals and samples taken at weekly intervals for 10 weeks. Gall midge populations in the wet season developed through three distinct phases: an initial slow increase, followed by a period of rapid increase coinciding with maximum tillering, and then a final decline. On average, the highest midge populations and highest levels of parasitism developed in the later plantings. During the dry season midge infestations were low and no parasites were detected.

The struggle to control populations of organisms that feed on agricultural crops, livestock, and directly on humans is as old as recorded history, and will continue into the perceivable future. Only 30 years ago, the availability of relatively cheap and highly effective synthetic organic pesticides was thought to be the ultimate solution to pest populations. However, our naïveté regarding the ability of pest populations to rapidly adapt to simplistic man-induced selection pressures has become increasingly apparent, as have the detrimental impacts of pesticides on the environment. The evolution of the integrated pest management paradigm can be traced to these concerns, and it is now accepted that sustainable solutions to the management of pest populations will only be borne out of an increased understanding of the functioning of ecosystems. Knowledge of the population dynamics, and underlying causes of density changes in pest populations, behavioural ecology, and population genetics of pests and natural enemies, are essential elements for designing appropriate biologically intensive strategies for pest management. Progress is being made, and several examples of innovative strategies and promising areas of research, are discussed. Future work must continue to be based on a solid foundation of ecological understanding, to avoid the pitfalls of simple opportunistic solutions.

This study concerns the dynamics and management of the hairtail fishery (Trichiurus haumela) in the East China Sea. Virtual population analysis was used to assess the historical pattern of stock size and an age-structured production model was developed to simulate the historical and future changes of catch and stock of hairtail under different fishing strategies. The results show that the stock of hairtail has been declining in general since the beginning of the 1960s. In 1981, it was 275.103 metric tons, overfished but not very seriously. Subsequent management measures brought some positive effects to stock and catches and slowed down the decline, but they cannot change the status of overfishing of the stock. The current fishing regime will inevitably lead to more severe depletion of the stock and also decrease the catch in the end. To prevent further deterioration of the stock and maintain catches, any further expansion of fishing effort must be stopped. Alternatively, a longer closed season should be introduced or the age at first capture should be raised.