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Length-based analyses were conducted to assess the stock of the green tiger shrimp Penaeus semisulcatus. Monthly carapace length frequency data were collected from commercial catches at two main landing sites on the Yemeni Red Sea coast for eight months. Growth parameters, mortalities, exploitation rate and yield per recruit were estimated for this species in this area. The estimated growth parameters were CL∞ = 44.65 mm, K = 1.2 yr^-1 and to = -0.15 for males and CL∞ = 58.8 mm, K = 1.4 yr^-1 and to = -0.12 for females. The natural mortality coefficient (M) was estimated as 2.19 yr^-1 and 2.27 yr^-1 for males and females respectively. The total mortality coefficient (Z) was 6.55 yr^-1 for males and 5.63 yr^-1 for females. The exploitation rate was 0.67 and 0.60 for males and females, respectively. Yield per recruit analysis showed that the current exploitation rate will result in higher stock biomass than the maximum exploitation rate.

Fish stock assessment makes Widespread use of Virtual Population Analysis (VPA) and long-term equilibrium prediction models. Although there have been some statistical investigations about the properties of VPA results, apparently there are no complete analyse about predictions statistical and numerical behaviour. However, management decisions generally rely upon production forecasts. This paper compares stability properties of VPA and the yield per recruit model with regard to various errors concerning all the input parameters. Robustness fis assessed by means of first-ordo sensitivities whereas variances are inferred from delta-method estimators. Sensitivity of yield per recruit appears to be mainly due to terminal mortality rate and age-specific weights, and to a lesser extent, to catches and natural mortality. Mean values of the input parameters were also found to influence the model's behaviour. A complete estimation of variances would require a variance-covariance matrix for weights at age and terminal fishing mortality rates. Sensitivities and variances are complementary in that the first quantify the absolute robustness of the models whereas the second show model robustness in relation to the dimensioned interval of variation of each input parameter. If variances were available for all parameters, yield per recruit estimates could be taken into account for fisheries management decisions., L'analyse de population virtuelle (APV) ainsi que les modèles de prévision à l'équilibre sont souvent utilisés pour l'évaluation des stocks de poisson exploités. Bien que plusieurs études statistiques aient été entreprises quant aux propriétés des résultats des APV, il semble qu'aucune analyse approfondie du comportement numérique et statistique des modèles prévisionnels n'ait été réalisée. Ces prévisions de production orientent pourtant les décisions de gestion des pêcheries. Cet article compare les propriétés respectives des modèles d'APV et de rendement par recrue en ce qui concerne les incertitudes sur les paramètres d'entrée. Les sensibilités du premier ordre permettent d'évaluer la robustesse de chaque modèle tandis que les variances des résultats sont estimées grâce à la méthode Delta. Le rendement par recrue apparaît essentiellement sensible au coefficient terminal de mortalité par pêche et aux poids, et dans une moindre mesure, aux captures et à la mortalité naturelle. Le comportement des modèles dépend également de la valeur moyenne des paramètres d'entrée. Une estimation complète des variances nécessiterait une matrice de variance-covariance pour les poids aux âges ainsi que pour les mortalités par pêche terminales. Sensibilités et variances sont complémentaires en ce sens que les premières quantifient la robustesse absolue des modèles alors que les secondes rapportent cette robustesse à l'intervalle dimensionné de variation de chaque paramètre. Si l'on disposait de variances pour tous les paramètres d'entrée, les estimations des rendements par recrue ainsi obtenues pourraient être prises en compte lors des décisions de gestion des pêcheries.

Os parâmetros de crescimento e mortalidade estimados a partir da estrutura em comprimento foram utilizados para avaliar o estado de explotação dos estoques de quatro espécies de grandes bagres da bacia do rio Cuiabá, Pantanal norte. As espécies estudadas foram o barbado, o cachara, o jaú e o pintado. As avaliações foram realizadas por meio do modelo de rendimento por recruta, considerando os Pontos de Referência Biológicos Fmax, F0,1, F = M e F BDR. As análises indicam que os estoques do pintado e do jaú estão bem conservados. Os estoques do cachara e, menos fortemente, o do barbado estão em iminente ameaça de sobrepesca na bacia do rio Cuiabá. The growth and mortality parameters estimated from length structure were used to evaluate the state of explotation of the stocks of four large catfish species from Cuiabá River basin, north Pantanal. The species studied were the Flatwhiskered catfish, the Jaú, the Barred sorubim, and the Spotted sorubim. The assessment were conducted with the yield per recruit model, and the Biological Reference Points Fmax, F0.1, F = M, and F BDR. The analysis indicates that the stocks of the Spotted sorubim, and of the Jaú are not overexploited. However, the stocks of the Barred sorubim, and, in lower degree, of the Flatwhiskered catfish of the Cuiabá River basin are in imminent threat of overfishing.

Diplotaxodon limnothrissa is a widely distributed species occurring throughout Lake Malawi and is probably the most abundant cichlid in the pelagic zone of the lake. The species is exploited commercially in the south-east arm of the lake, but since the fishery's inception the resource has never been assessed. Per-recruit analysis indicated that the resource is under-exploited, with current spawner biomass per-recruit between 55% and 74% of pristine levels.Keywords: Cichlidae, management advice, Lake Malawi, spawner biomass per recruit, stock assessment, yield per recruit African Journal of Aquatic Science 2005, 30(2): 141–145

Submitted by Guilherme Lemeszenski (guilherme@nead.unesp.br) on 2013-08-22T18:42:22Z No. of bitstreams: 1 S1519-69842007000300023.pdf: 234887 bytes, checksum: 7b07c9ed5941092a7fa49319129df8c0 (MD5) Made available in DSpace on 2013-08-22T18:42:22Z (GMT). No. of bitstreams: 1 S1519-69842007000300023.pdf: 234887 bytes, checksum: 7b07c9ed5941092a7fa49319129df8c0 (MD5) Previous issue date: 2007-08-01 Made available in DSpace on 2013-09-30T19:29:32Z (GMT). No. of bitstreams: 2 S1519-69842007000300023.pdf: 234887 bytes, checksum: 7b07c9ed5941092a7fa49319129df8c0 (MD5) S1519-69842007000300023.pdf.txt: 34179 bytes, checksum: 332331ee8b82508632fea5f44cf7d9cb (MD5) Previous issue date: 2007-08-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T15:08:07Z No. of bitstreams: 2 S1519-69842007000300023.pdf: 234887 bytes, checksum: 7b07c9ed5941092a7fa49319129df8c0 (MD5) S1519-69842007000300023.pdf.txt: 34179 bytes, checksum: 332331ee8b82508632fea5f44cf7d9cb (MD5) Made available in DSpace on 2014-05-20T15:08:07Z (GMT). No. of bitstreams: 2 S1519-69842007000300023.pdf: 234887 bytes, checksum: 7b07c9ed5941092a7fa49319129df8c0 (MD5) S1519-69842007000300023.pdf.txt: 34179 bytes, checksum: 332331ee8b82508632fea5f44cf7d9cb (MD5) Previous issue date: 2007-08-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) O pacu (Piaractus mesopotamicus) é uma das espécies mais capturadas no Pantanal de Mato Grosso do Sul, e para manejá-lo adequadamente são necessárias informações a respeito do seu nível de explotação. Nos anos de 1996 e 1997 foram coletadas amostras mensais de comprimentos de pacu capturados por pescadores profissionais e esportivos desembarcados em Corumbá, Pantanal de Mato Grosso do Sul (MS), com o objetivo de estimar os parâmetros de crescimento e o seu nível de explotação. Para a determinação do nível de explotação foi utilizado o modelo de rendimento por recruta de Beverton e Holt. Através da análise de freqüência de comprimento, pelo pacote FISAT (ELEFAN), foram estimados os parâmetros de crescimento, com os seguintes valores: 1996: L¥ = 87,20 cm; K = 0,34 ano-1; fi´= 3,41; C = 0,74; WP = 0,81; Longevidade = 8,40 anos; e 1997: L¥ = 86,50 cm; K = 0,34 ano-1; fi´= 3,40; C = 0,60; WP = 0,80; Longevidade = 8,40 anos. O valor de t0 é -0,363 para os valores médios de L¥ e k. A relação peso-comprimento foi determinada através de dados de pescarias experimentais em 1999 e 2000, e foi a seguinte: W = 0,048 LF2.835. As taxas de mortalidade estimadas e a taxa de sobrevivência foram: 1996: Z = 1,51 ano-1; M = 0,62 ano-1; F = 0,89 ano-1; S = 21,9%; e 1997: Z = 1,65 ano-1; M = 0,63 ano-1; F = 1,02 ano-1; S = 19,1%. A análise de rendimento por recruta apresentou os seguintes resultados: Fatual = 0,96 ano-1; Fmáx= 0,67 ano-1 ; F0,1 = 0,51 ano-1 (quando Lc = 26,7 cm). Este resultado indica que o pacu está sobreexplotado, e assim há necessidade de se estabelecer medidas restritivas para sua pescaria. Among the several fish species comercially exploited at the Pantanal of Mato Grosso do Sul, the pacu (Piaractus mesopotamicus) stands as one of the most important. Information regarding its exploitation level is necessary for the proper management of its stocks. Between 1996 and 1997 data on total length of the pacu were collected on a monthly basis from specimens caught by professional and sport fishers in the municipality of Corumbá. These data were used to estimate growth parameters and to assess the exploitation level for this species, applying the Beverton and Holt yield per recruit model. Length frequency analysis, carried out with the software FISAT (ELEFAN), was used to estimate growth parameters: 1996: L¥ = 87.20 cm; K = 0.34 year-1; phi´=3.41; C = 0.74; WP = 0.81; Longevity = 8.40 years; and 1997: L¥ = 86.50 cm; K = 0.34 year-1; phi´=3.40; C = 0.60; WP = 0.80; Longevity = 8.40 years. The value for t0is -0.363 years for mean values of L¥ and k. The weight-length relationship, calculated from data derived from experimental fisheries carried out in 1999 and 2000, is described by the equation: W = 0.048LF2.835. Estimated mortalities and survival rates were: 1996: Z = 1.51 year-1; M = 0.62 year-1; F = 0.89 year-1; S = 21.9%; and 1997: Z = 1.65 year-1; M = 0.63 year-1; F = 1.02 year-1; S = 19.1%. The yield per recruit analysis showed the following values: F Present= 0.96 year-1; Fmax = 0.67 year-1 ; F0.1 = 0.51 year-1 (for Lc = 26.7 cm). These results suggest that the pacu is overexploited in the area, so that restrictive measures are in need to manage the pacu fisheries. UNESP Departamento de Ecologia Empresa Brasileira de Pesquisa Agropecuária (EMBRAPA) Pantanal UNESP Departamento de Ecologia

Fork length measurements of individuals of Brycon microlepis landed and commercialized at the Porto Market in Cuiabá, MT, from May-October 1996 to May-October 1997 were used to estimate growth and mortality parameters for this species. The average estimated populational parameters were: L¥ = 705 mm, k = 0.275 year--1, C = 0.775, WP = 0.465, Lc = 164 mm, M = 0.585 year--1, Z = 0.822 year--1, with F = 0.237 year--1. Yield per recruit analysis suggests that the stock is not yet overexploited. Medidas de comprimento furcal obtidas de exemplares de Brycon microlepis desembarcados e comercializados no Mercado do Porto em Cuiabá, MT, no período de maio a outubro de 1996 e de maio a outubro de 1997, foram utilizadas para a obtenção de estimativas dos parâmetros de crescimento e mortalidade da espécie. Os parâmetros populacionais médios estimados foram: L¥ = 705 mm; k = 0,275 ano--1; C = 0,775; WP = 0,465; Lc = 164 mm; M = 0,585 ano--1; Z = 0,822 ano--1, sendo F = 0,237 ano--1. A análise do rendimento por recruta e a taxa de explotação indicam que o rendimento máximo sustentável não foi alcançado. Portanto, o estoque ainda não está sobreexplotado.

Flemish Cap es un banco de pesca situado entre las latitudes 46° y 49° N y las longitudes 44° y 46º 30' O. Un estrecho cañón de unos 1.100 m de profundidad, denominado Flemish Pass, lo separa del resto de los caladeros de Terranova. El Consejo Científico de la Organización de Pesquerías del Noroeste Atlántico (NAFO) viene considerando aislada la población de bacalao que habita en este banco. La decisión de considerar aislada esta población se tomó, aparte de por razones de aislamiento geográfico del banco, como resultado de una serie de trabajos científicos que podríamos clasificar en los siguientes grupos: 1) estudios de genética molecular, en los que se analizó la distribución geográfica del polimorfismo de la transferrina y de la fosfoglucosa isomerasa en los bancos de Terranova; 2) estudios de los caracteres merísticos, en los que se analizaron las variaciones geográficas de las medias vertebrales y de radios espinosos de las aletas; 3) estudios de los marcadores biológicos, en los que se analizaron las distribuciones geográficas de las parasitosis producidas por Lernaeocera branchialis y Phoconema decipiens, y 4) experiencias de marcado rusas y canadienses en el área de Terranova. Sin embargo, un seguimiento histórico de la estructura de tallas de los bacalaos de Flemish Cap pone de manifiesto que allí siempre han sido escasos los ejemplares grandes y que la proporción de inmaturos viene siendo muy superior a la de los otros caladeros vecinos, incluso en épocas de muy escasa actividad pesquera. Si tenemos en cuenta que el crecimiento de esta especie, en Flemish Cap, no es inferior al que se produce en otros bancos de Terranova, la falta de grandes ejemplares podría estar poniendo de manifiesto la existencia de una migración de bacalaos adultos hacia los bancos vecinos, que lógicamente debería verse compensada por la llegada de alevines provenientes de estos bancos. [Ver Resumen completo en pdf]., Flemish Cap is a fishing bank between latitudes 46° and 49°N and longitudes 44° and 46º 36'W. A narrow canyon some 1100 m deep, called Flemish Pass, separates it from the rest of the Newfoundland fishing-grounds. The Scientific Council of the Northwest Atlantic Fisheries Organization (NAFO) has long considered the cod population which inhabits this bank to be an isolated one. The decision to consider this population to be isolated was based, apart from the bank's geographic isolation , on the results of a series of research projects, which we could classify into the following groups: 1) molecular genetics studies, in which the geographic distribution of transferrin and skeletal muscle phosphoglucose isomerase (PGI-2) polymorphism was analysed on the Newfoundland banks; 2) studies of meristic characteristics, in which geographic variations in vertebral averages and spiny radii of the fins were analyzed; 3) studies of biological markers, in which the geographic distribution of parasitosis produced by Lernaeocera branchialis and Phoconema decipiens was analyzed, and 4) Russian and Canadian tagging projects in the Newfoundland area. However , historical analysis of the size structure of Flemish Cap cod made it clear that large specimens had always been scarce, and that the proportion of immature specimens had been much higher than that of neighbouring fishing-grounds, even when the level of fishing activity was very low. Bearing in mind that the growth rate of this species, on Flernish Cap, is no lower than that of other Newfoundland banks, the lack of large specimens could be evidence of the existence of a migration of adult cod to the neighbouring banks, which logically would be compensated for by the arrival of fry from these banks. [See full Summary pdf]., Instituto Español de Oceanografía, SI

The population dynamics is developed upon data on the age-composition of catches collected since 1974 by a sampling technic at two levels (fishing day, vessel). A temporally stratified sampling is carried out. A cohort analysis is realized through these data ; assumptions for the coefficients of natural and indirect fishing mortality are set up. Catchability models for all age groups are fitted. Catchability of the most abundant age groups (2 and 3) is an increasing function of their abundance and of the fishing fleet mean horse power. These functions present a maximum asymptotical value. Their adequation is explained by the adaptations of dredges and by the population sedentary life allowing the concentration of fishing fleet on the most abundant areas. A structural model of production based on an equilibrium state is carried out. The most likely translations of required parameters are tested by reconstitution of yields per recruit or annual landings. Low values of instantaneous coefficient of natural mortality (0,15 and 0,20) and high values of terminal rate of exploitation (0,50) optimize the reconstitution. Isopleths of yield and fecundity per recruit are presented for different values of the recruitment abundance and the fishing fleet mean horse power. At present, parameters of fishing pattern control (nominal fishing effort, age at first catch) give an equilibrated production near to optimum as well as an acceptable fecundity. The present decrease of the stock is explained by interannual variability of the recruitment and by coexistence of several métiers* which causes a constant increase of vessels horse power. The sampling technic used since 1986 for directed stock assessment is analysed. These prospections are necessary for the annual determination of total allowed catches. The bay of Saint-Brieuc is divided into six spatial strata ; sampling rate for each stratum is defined by the corresponding commercial landings. The estimation of abundances needs calculation of the dredge efficiency through diving. Relative precision of abundance and biomass for each age group is 25 to 30 %. An increase of the samples number would give a small gain of precision. On the other hand, an increase of the diving number would allow a significant decrease of bias, due to the definition of efficiency as a rate estimator. Probable existence of high values of natural mortality between 1986 and 1988 is studied. Natural mortality was perhaps higher during last winter period of these years. Nevertheless, it is impossible to dissociate natural mortality from components due to the exploitation (not declared landings). It is not demonstrated that this eventuality would have provoked a fishing intensification. The annual management through short terms projections is limited. Spatial variability of growth and interannual variability of recruitment should be taken into account in the roodclization system in order to take advantage of the knowledge of the equilibrated structural analysis. Growth shows a spatial variability higher than the temporal one. No used method of comparison of growth curves is really perfect, but growth seems quicker in southern bay. Estimations of the gTowth parameters are different from those obtained by prcsious studies. Spatial variability of growth should be taken into account when a rotation of fished areas is considered or when an extensive aquaculture is developed. Study upon the recruitment is realized through an empirical model which explains its interannual fluctuations as a function of spawning biomass of the stock, of temperature and of fishing effort developed during first winter of the cohort life. An incorporation of the model to a management system with mean terms projections is carried on. Temperature seems to be the most important factor if spawning biomass reaches an adequately high level for a good reproduction., La dynamique du stock est étudiée à partir de la structure démographique des captures commerciales depuis 1974, estimée selon un plan d'échantillonnage à deux niveaux (jour de sortie en mer, bateau). Un plan d'échantillonnage à stratification temporelle est proposé. Une analyse des cohortes est conduite sur ces données ; des hypothèses sur les coefficients de mortalité naturelle et indirectement induite par la pêche sont formulées. Des modèles de capturabilité par groupe d'âge sont ensuite construits. Pour les groupes d'âge 2 et 3, qui constituent l'essentiel de la ressource, la capturabilité est une fonction croissante de l'abondance du groupe d'âge et de la puissance motrice moyenne des navires de pêche ; elle présente une valeur asymptotique maximale. Son allure est expliquée par : les caractéristiques de la drague et par la sédentarité de la ressource qui permet la concentration de l'effort de pêche sur les secteurs les plus riches. Un modèle structural de production à l'équilibre est construit. Les scénarios les plus plausibles des paramètres de départ sont testés, par reconstitution des rendements par recrue ou des débarquements annuels. Les faibles valeurs du coefficient instantané de mortalité naturelle (0,15 et 0,20) et celles, fortes, du taux d'exploitation terminal (0,50) optimisent la reconstitution. Des isoplètes de rendement et de fécondité par recrue sont présentées pour différentes valeurs de l'abondance du recrutement et de la puissance motrice moyenne de la flottille. Les paramètres actuels de contrôle du régime d'exploitation (effort de pêche nominal, âge de première capture) assurent à l'équilibre une production proche de l'optimale et une fécondité acceptable. Le fléchissement actuel de la ressource s'explique par la variabilité interannuelle du recrutement et la coexistence de plusieurs métiers dans la baie qui provoque un accroissement constant de la puissance motrice des navires. La stratégie d'échantillonnage utilisée depuis 1986 lors des campagnes annuelles d'évaluation directe, indispensables en raison du système de gestion en vigueur, est analysée. La baie est subdivisée en six strates spatiales ; le taux d'échantillonnage dans chacune est défini en fonction des débarquements commerciaux correspondant. L'estimation des abondances nécessite le calcul de l'efficacité de la drague par groupe d'âge à l'aide de plongées sousmarines. La précision relative de l'abondance et de la biomasse par groupe d'âge est de 25 à 30 %. Une augmentation du nombre total de coups de drague améliorerait de peu la précision. Par contre, une augmentation du nombre de plongées permettrait de réduire sensiblement les biais dus à la définition de l'efficacité selon un estimateur rapport. L'apparition des valeurs de mortalité naturelle probablement élevées entre 1986 et 1988 est étudiée. Bien qu'il soit impossible de dissocier la mortalité naturelle des composantes liées à l'exploitation (fraude), il est probable que la mortalité naturelle était plus forte en fin d'hiver au cours de ces années. Il n'est pas démontré que cette éventualité aurait dû encourager une intensification de l'exploitation. La gestion annuelle par projection à court terme connaît actuellement ses limites. La variabilité spatiale de la croissance et la variabilité inlcrannucllc du recrutement devraient être intégrées au système de modélisation afin de mieux bénéficier des acquis de l'analyse structurale à l'équilibre. La croissance présente une variabilité plus forte sur le plan spatial que temporel. Bien qu'aucune des méthodes de comparaison des courbes de croissance employée ne soit réellement exempte de défaut, la croissance paraît plus forte dans le sud de la baie. Les estimations des paramètres de croissance semblent différentes de celles obtenues dans des études antérieures. La variabilité spatiale de la croissance pourrait être prise en compte si une rotation des zones exploitées était envisagée ou si une aquaculture extensive se développait. L'étude du recrutement est développée à partir d'un modèle empirique expliquant ses variations interannucllcs en fonction de la biomassc féconde du stock parental, de la température et de l'cfTort de pêche exercé au cours du premier hiver de la vie d'une cohorte. Une intégration de ce modèle dans un système de gestion à moyen terme est tentée. Le rôle de la température s'avère prépondérant si la biomassc féconde se trouve à un niveau suffisamment élevé pour assurer une bonne reproduction.

There have been recent changes in the Caspian Sea ecosystem, such as those due to changes in sea level or those caused by the invasive ctenophore, Mnemiopsis leidyi. It is believed that these changes had significant impacts on the absolute and relative abundance of the commercially important anchovy kilka (Clupeonella engrauliformis) and common kilka (C. cultriventris caspia) leading to decline in the former and increase in the latter species in the Iranian waters. Consequently, more rigorous management is required. The mixed-species yield-per-recruit was applied to the Iranian conical lift-net. This study showed that the pooled fishing mortality at F40% was 0.70 yr-1 which is higher than fishing mortality of main species of anchovy kilka, but lower than the pooled fishing mortality at F0.1 (0.75 yr-1). The ABC under the best information available, at pooled species reference points for two species of anchovy and common kilkas, was estimated to be 8260mt. An analogous goal in a multispecies situation would be fishing at a fishing level, denoted Fws, such that the fishing rate for the weakest stock (in this case; anchovy kilka) does not exceed its F40% rate. Under this harvest strategy at F40% for anchovy kilka, it is suggested that the ABC of pooled species of anchovy and common kilkas was estimated 7920mt to be selected in kilka fishery in Iranian waters.