Zweikampf im Wattenmeer : Wird die heimische Miesmuschel verdrängt?

Since a couple of years, the introduced Pacific oyster (Crassostrea gigas) is spreading out in the Wadden Sea off the German North Sea coast where it competes with the native blue mussel (Mytilus edulis). First catches of the new species have now been observed in fishing surveys.

Fishery dynamics and present status of the yellowfin tuna population of the Eastern Pacific Ocean

ENGLISH: From morphometric data, tagging results and reaction of the stock to fishing, it is inferred that the yellowfin tuna of the Eastern Pacific form a distinct population which intermingles little, if at all, with populations to the westward. Excellent statistics of catch and effort, and records of total catch, available since 1934, during rapid growth of the fishery, have made possible application of a generalized mathematical predator-prey model to estimate the effect of fishing on the population, and the average abundance and yield corresponding to different amounts of fishing effort, and also to estimate the rate of fishing mortality per unit of effort. From serial samples of size composition of catches, and from tagging experiments, it has been possible to determine rates of growth and of total mortality. These kinds of information permit application of the catch-per-recruit model of Beverton and Holt. Combination of the results of application of the Beverton and Holt model and of the generalized predator-prey model, leads to inference of the relationship between stock size and recruitment. The form of the relationship is remarkably similar to the theoretical model developed by W. E. Ricker. These studies, based on the data of the near-surface fishery by baitboats and purse seiners, indicate clearly that the increased intensity of fishing has caused diminution of the stocks to the point where they are somewhat "overfished"-that is, incapable of supporting the maximum sustainable average harvest. SPANISH: De los datos morfométricos, de los resultados de las marcaciones y de la reacción del stock a la pesca, se infiere que el atún aleta amarilla del Pacífico oriental forma una población diferente que se mezcla poco, si es que llega a mezclarse, con las poblaciones del oeste. Las excelentes estadísticas de la captura y el esfuerzo y los registros de la pesca global disponibles desde 1934, durante el rápido crecimiento de la pesquería, han hecho posible la aplicación de un modelo matemático generalizado depredador-presa para estimar el efecto de la pesca en la población y el promedio de la abundancia y del rendimiento correspondientes a los diferentes valores del esfuerzo de pesca, y también para estimar la tasa de la mortalidad de pesca por unidad de esfuerzo. Gracias a las muestras en serie de la composición de tamaños de las capturas y a los experimentos de marcación, ha sido posible determinar las tasas del crecimiento y de la mortalidad total. Estos tipos de información permiten la aplicación del modelo de la captura-porrecluta de Beverton y Holt. La combinación de los resultados de la aplicación del modelo de Beverton y Holt y del modelo generalizado depredador-presa, conduce a la inferencia de la relación entre el tamaño del stock y el reclutamiento. La forma de la relación es notoriamente similar al modelo teórico desarrollado por W. E. Ricker. Estos estudios, basados en los datos de la pesquería cerca de la superficie efectuada por barcos de carnada y rederos, indican claramente que el aumento de la intensidad de la pesca ha causado la disminución de los stocks hasta el punto de dejarlos algo "superexplotados", o sea, incapacitados para mantener una producción máxima promedio. (PDF contains 50 pages.)

Estimating abundances of 0-group western Baltic cod by using pound net fisheries

Nearshore 0-group western Baltic cod are frequently caught as bycatch in the commercial pound net fishery. Pound net fishermen from the Danish Isle of Funen and Lolland and the German Isle of Fehmarn have recorded their catches of small cod between September and December 2008. Abundance patterns were analysed, particularly concerning the influence of abiotic factors (hydrography, meteorology) and the differences between sampling sites. Catch per unit effort (CPUE) differed by site and location, whereas CPUE were highest at Lolland. Correlation between catch and wind/currents were generally weak. However, wind directions and current speeds seem to affect the catch rates. Finally an algorithm was developed to calculate a recruitment index for western Baltic cod recruitment success based on previous analyses.

Population dynamics of the skipjack tuna (Katsuwonus pelamis) of the Eastern Pacific Ocean

ENGLISH: Catches of skipjack tuna supporting major fisheries in parts of the western, central and eastern Pacific Ocean have increased in recent years; thus, it is important to examine the dynamics of the fishery to determine man's effect on the abundance of the stocks. A general linear hypothesis model was developed to standardize fishing effort to a single vessel size and gear type. Standardized effort was then used to compute an index of abundance which accounts for seasonal variability in the fishing area. The indices of abundance were highly variable from year to year in both the northern and southern areas of the fishery but indicated a generally higher abundance in the south. Data from 438 fish tagged and recovered in the eastern Pacific Ocean were used to compute growth curves. A least-squares technique was used to estimate the parameters of the von Bertalanffy growth function. Two estimates of the parameters were made by analyzing the same data in different ways. For the first set of estimates, K= 0.819 on an annual instantaneous basis and L= 729 mm; for the second, K = 0.431 and L=881. These compared well with estimates derived using the Chapman-Richards growth function, which includes the von Bertalanffy function as a special case. It was concluded that the latter function provided an adequate empirical fit to the skipjack data since the more complicated function did not significantly improve the fit. Tagging data from three cruises involving 8852 releases and 1777 returns were used to compute mortality rates during the time the fish were in the fishery. Two models were used in the analyses. The best estimates of the catchability coefficient (q) in the north and south were 8.4 X 10- 4 and 5.0 X 10- 5 respectively. The other loss rate (X), which included losses due to emigration, natural mortality and mortality due to carrying a tag, was 0.14 on an annual instantaneous basis for both areas. To detect the possible effect of fishing on abundance and total yield, the relation between abundance and effort and between total catch and effort was examined. It was found that at levels of intensity observed in the fishery, fishing does not appear to have had any measurable effect on the stocks. It was concluded therefore that the total catch could probably be increased by substantially increasing total effort beyond the present level, and that the fluctuations in abundance are fishery-independent. The estimates of growth, mortality and fishing effort were used to compute yield-per-recruitment isopleths for skipjack in both the northern and southern areas. For a size at first entry of about 425 mm, the yield per recruitment was calculated at 3 pounds in the north and 1.5 pounds in the south. In both areas it would be possible to increase the yield per recruitment by increasing fishing effort. It was not possible to assess potential production of the skipjack stocks fished in the eastern Pacific, except to note that the fishery had not affected their abundance and that they were certainly under-exploited. It was concluded that the northern and southern stocks could support increased harvests, especially the latter. SPANISH: Las capturas de atún barrilete que sostienen las pesquerías principales de la parte occidental, central y oriental del Océano Pacífico han aumentado en los últimos años; así que es importante examinar la dinámica de la pesquería para determinar el efecto que pueda tener sobre la abundancia de los stocks. Se desarrolló un modelo hipotético, lineal para standardizar el esfuerzo de pesca a un solo tamaño de barco y tipo de arte. Luego se usó el esfuerzo standardizado para computar un índice de la abundancia que pueda dar razón de la variabilidad estacional en el área de pesca. Los índices de la abundancia variaron mucho de un año a otro tanto en el área septentrional como en el área meridional de la pesquería, pero indicaron una abundancia generalmente superior en el sur. Se emplearon los datos de 438 peces marcados y recuperados en el Océano Pacífico oriental para computar las curvas de crecimiento. Una técnica de mínimos cuadrados fue usada para estimar los parámetros de la función de crecimiento de van Bertalanffy. Se hicieron dos estimativos de los parámetros mediante el análisis de los mismos datos, de diferente manera. Para el primer juego de estimativos, K=0.819 sobre una base anual instantánea y L∞=729 mm; para el segundo, K=0.431 y L∞=881. Estos se correlacionaron bien con los estimativos obtenidos usando la función de crecimiento de Chapman-Richards, que incluye la de von Bertalanffy como un caso especial. Se decidió que la última función proveía un ajuste empírico, adecuado a los datos del barrilete, ya que la función más complicada no mejoró significativamente el ajuste. Los datos de marcación de tres cruceros incluyendo 8852 liberaciones y 1777 retornos, fueron usados para computar las tasas de mortalidad durante el tiempo en que los peces estuvieron en la pesquería. Se usaron dos modelos en los análisis. Los mejores estimativos del coeficiente de capturabilidad (q) en el norte y en el sur fueron 8.4 X 10-4 y 5.0 X 10-5 , respectivamente. La otra tasa de pérdida (X), la cual incluyó pérdidas debidas a la emigración, mortalidad natural y mortalidad debida a llevar una marca, fue 0.14 sobre una base anual instantánea para las dos áreas. Con el fin de descubrir el efecto que posiblemente pueda tener la pesca sobre la abundancia y el rendimiento total, se examinó la relación entre la abundancia y el esfuerzo y entre la captura total y el esfuerzo. Se encontró que a los niveles de la intensidad observada en la pesquería, la pesca no parece haber tenido ningún efecto perceptible en los stocks. Por lo tanto se decidió que mediante un aumento substancial del esfuerzo total, más allá del nivel actual, la captura total probablemente podría aumentarse, y que las fluctuaciones de la abundancia son independientes de la pesquería. Los estimativos del crecimiento, mortalidad y esfuerzo de pesca fueron usados para computar las isopletas del rendimiento por recluta del barrilete, tanto en las áreas del norte como del sur. Para una talla de primera entrada de unos 425 mm, el rendimiento por recluta fue calculado en 3 libras en el norte y 1.5 libras en el sur. En ambas áreas sería posible aumentar el rendimiento por recluta mediante un aumento del esfuerzo de pesca. No fue posible determinar la producción potencial de los stocks del barrilete pescado en el Pacífico oriental, excepto para observar que la pesquería no ha afectado su abundancia y que ciertamente se encuentran subexplotados. Se concluyó que los stocks norte y sur pueden soportar un aumento en el rendimiento, especialmente este último. (PDF contains 274 pages.)

The Japanese longline fishery for tunas and billfishes in the Eastern Pacific Ocean east of 130°W, 1964-1966

ENGLISH: Catch and effort statistics from the Japanese longline fishery operating in the eastern Pacific Ocean east of 130°W, from 1964 through 1966, were examined to study the geographic distribution, trends in apparent abundance, sexual maturity, and size composition of the tunas and billfishes. Yellowfin and bigeye tuna are generally most abundant in the equatorial regions of the high seas between about 10°N and 20°S, but west of 95°W. The marlins are more coastal in distribution, usually occurring to the east, and to the north and south of the heavy concentration of tropical tunas. Sailfish tend to be associated with coastal areas also, whereas shortbill spearfish are more frequently captured on the high seas. Swordfish are found most abundantly in the coastal regions off northern Mexico, and off northern Peru and southern Ecuador. The albacore, a temperate-water species of tuna, is most abundant in the high-seas area of the southeastern Pacific, Trends in apparent abundance were measured by the hook-rate (i.e. catch per 100 hooks). Hook-rates for bigeye tuna have decreased from about 3.5 fish per 100 hooks in 1958 to about 1.1 fish per 100 hooks in 1966. During the same period, effort was increased substantially and total catch has decreased since 1963. It does not appear that increased effort will result in sustained increased catches of bigeye. Hook-rates for yellowfin tuna in recent years have decreased to about one third of their initial levels. The surface fishery for yellowfin in the eastern Pacific apparently affects recruitment to the longline fishery. Assuming that present conditions in the surface fishery do not change appreciably, increased effort in the longline fishery probably would not produce sustained increased catches, but might in fact result in reduced catch rates. Unlike the situation for the other tunas of the eastern Pacific, it appears that the albacore fishery east of 130°W is not having a marked effect on their abundance. Although a high degree of variability was observed in the hookrates for striped marlin, no obvious trends are evident. Catches have decreased slightly from 13,500 tons in 1964 to about 11,000 tons in 1966. Heavy fishing for sailfish began in 1964 with a hook-rate of 10.6 fish per 100 hooks; by 1966 it had dropped to 5.8. Catches of this species in the area of major concentration dropped from 329,900 fish in 1965 to 173,600 fish in 1966. This fishery has operated for too short a period of time to enable one to determine its effect on the sustainable yield. Length-frequency measurements and gonad samples from yellowfin and bigeye tunas collected in the eastern Pacific were analyzed to determine sexual maturity and growth characteristics. The results corroborate the findings of earlier investigators. SPANISH: Las estadísticas de captura y del esfuerzo de la pesca japonesa con palangre que maniobra en el Océano Pacífico oriental al este de los 130°W, desde 1964 hasta 1966, fueron examinadas para estudiar la distribución geográfica, las tendencias de la abundancia aparente, la madurez sexual y la composición de talla de los atunes y de los peces espada. Los atunes aleta amarilla y ojo grande son generalmente más abundantes en las regiones ecuatoriales de alta entre unos 10°N y 20°S, pero al oeste de los 95°W. Los marlines son costaneros en distribución, apareciendo habitualmente hacia el y hacia el norte y sur de la densa concentración de atunes tropicales. pez vela tiende a asociarse también con las áreas costaneras, mientras el pez aguja corta es capturado con más frecuencia en alta mar. Los peces espada se encuentran más abundantemente en las regiones costaneras de México septentrional y frente al norte del Perú y del Ecuador meridional. La albacora, una especie de atún de aguas templadas, es más abundante en el área de alta mar del Pacífico sudoriental. Las tendencias en la abundancia aparente fueron evaluadas por la tasa de captura por anzuelo (i.e., captura por 100 anzuelos). Las tasas de captura por anzuelo del atún ojo grande, disminuyeron en 1958, de unos 3.5 peces por 100 anzuelos a cerca de 1.1 pez por 100 anzuelos en 1966. Durante el mismo período, el esfuerzo fue aumentado substancialmente y, desde 1963, la captura total disminuyó. No parece que el aumento del esfuerzo resultara en un aumento sostenido de las capturas del atún ojo grande. Las tasas de captura por anzuelo de atún aleta amarilla han disminuido en un tercio de los niveles iniciales, en años recientes. La pesca de superficie de esta especie en el Pacífico oriental afectó aparentemente el reclutamiento en la pesca con palangre. Suponiendo que las condiciones actuales de la pesquería no cambien apreciablemente, un aumento del esfuerzo en la pesquería palangrera probablemente no produciría un aumento sostenido de las capturas, pero en realidad podría resultar en tasas de captura reducidas. A diferencia de la situación de otros túnidos del Pacífico oriental, parece que la pesca de la albacora al este de los 130°W no ha tenido un efecto marcado en su abundancia. Aunque se observó un alto grado de variabilidad en las tasas de captura por anzuelo correspondientes al marlin rayado, no fueron evidentes tendencias obvias. Las capturas han mermado ligeramente de 13,500 toneladas en 1964 a unas 11,000 toneladas en 1966. La fuerte pesca por peces vela empezó en 1964 con una tasa por anzuelo de 10.6 peces por 100 anzuelos; en 1966 había mermado a 5.8. Las capturas de esta especie en el área de mayor concentración disminuyeron de 329,000 peces en 1965, a 173,600 peces en 1966. Esta pesquería ha maniobrado por un período demasiado corto de tiempo para que pueda determinarse su efecto en el rendimiento sostenible. Las mediciones frecuencia-longitud, y las muestras de las gónadas de los atunes aleta amarilla y ojo grande, obtenidas en el Pacífico oriental, fueron analizadas para determinar la madurez sexual y las características del crecimiento. Los resultados corroboraron los hallazgos anteriores de investigadores. (PDF contains 144 pages.)

Variations in year-class strength and estimates of the catchability coefficient of yellowfin tuna, Thunnus albacares, in the Eastern Pacific Ocean

ENGLISH: Year-class composition of catch, virtual population size and yearclass strength were determined from serial samples of size composition of catches and catch records. Murphy's Solution to the catch equation, which is free from the effects caused by changes in fishing pressure, was used to estimate year-class strength, i.e. the total population of fish age 3/4 years. The resultant estimates indicated that the X55, X56, X57, X62 and X63 year classes were above average and the X58, X59, X60, X61 and X64 year classes were below average. The year-class designation refers to the year of actual entry or presumed year of entry into the commercial fishery (at approximately 1 year of age). The strongest and poorest year classes were the X57 and X61 classes, respectively. The ratio of the strongest to the weakest year class was 2.6. This amount of variation is small compared to that found for other species of fish. It was found that the relationship between stock size and yearclass strength is of no value in predicting year-class strength. As a by-product of the analysis, estimates of the catchability coefficients (qN) of the age groups in the fishery were obtained, These estimates were found to vary with age and time. Age-two fish apparently showed the greatest vulnerability to fishing gear, followed by ages three and one, respectively. The average estimate of the catchability coefficient in weight was calculated and found to compare favorably with Schaefer's estimate. The influence of sea-surface water temperature upon year-class strength was investigated to determine whether the latter can be predicted from a knowledge of sea-surface temperatures prevailing during and following spawning. No correlation was evident. SPANISH: La composición de la clase anual en la captura, el tamaño de la población virtual y la fuerza de clase anual, fueron determinados según una serie de muestras de la composición de tamaño de las capturas y de los registros de captura. La Solución de Murphy de la ecuación de captura, que está libre de los efectos causados por los cambios de la presión de pesca, fue usada para estimar la fuerza de la clase anual, i.e. la población total de peces de 3/4 años. Las estimaciones resultantes indican que las clases anuales X55, X56, X57, X62 y X63 fueron superiores al promedio y que las clases anuales X58, X59, X60, X61 y X64 fueron inferiores al promedio. La designación de la clase anual se refiere al año actual de entrada o al año supuesto de entrada en la pesca comercial (aproximadamente a la edad de 1 año). Las clases anuales más fuertes y más pobres fueron la X57 y X61 respectivamente. La razón de la clase anual más fuerte en relación a la más débil fue 2.6. Esta cantidad de variación es pequeña comparada con la encontrada para otras especies de peces. Se encontró que la relación entre en tamaño del stock y la fuerza de la clase anual no tiene valor en predecir la fuerza de la clase anual. Se obtuvieron estimaciones de los coeficientes de capturabilidad (qN) de los grupos de edad en la pesquería como un producto derivado del análisis. Se encontraron que estas estimaciones variaron con la edad y tiempo. Los peces de edad dos aparentemente presentaron la vulnerabilidad más grande en relación al arte pesquero, seguidos por las edades tres y una, respectivamente. La estimación promedio del coeficiente de capturabilidad en peso fue calculada y se encontró que podía compararse favorablemente con la estimación de Schaefer. La influencia de la temperatura del agua superficial del mar sobre la fuerza de la clase anual fue investigada para determinar si se podía predecir esta última según el conocimíento de las temperaturas superficiales del mar prevalecientes durante el desove y después de éste. No hubo correlación evidente. (PDF contains 44 pages.)

The distribution, abundance, and ecology of larval tunas from the entrance to the Gulf of California

ENGLISH: This study is based on collections of larvae of Thunnus albacares, Euthynnus llneatus, and Auxis sp. obtained from surface and oblique net tows made during seven cruises, each along a comparable track in the entrance of the Gulf of California and each during a different month. Concomitant measurements of surface temperature, salinity, and zooplankton were made at each of the plankton stations. The catches of larval Auxis sp. were examined by analysis of variance techniques to determine which environmental features were associated with the spawning of this tuna as indicated by the distribution of larvae and to gain some insight into the behavior of the larvae themselves. The testing indicated that the spawning of Auxis sp. varied significantly among the different months of the cruises. The testing also indicated that if the larvae were capable of avoiding the sampling apparatus, this ability was not related to features associated with time of day such as light conditions. The analysis did not detect any change in the vertical distribution of the larvae among the months of the experiment. It was concluded that the larvae did not exhibit a diel vertical movement. The measurements of temperature, salinity, and zooplankton volumes were treated as covariates in the analysis. The surface temperature proved to be a highly important factor in explaining the distribution of larvae, but salinity and zooplankton volumes were not. Catches of Thunnus albaeares and Euthynnus lineatus were rare during the course of the study; these are discussed in qualitative terms with respect to the time of the year and the surface temperature. The distribution of larval tunas in the area of study was compared with the distribution of surface water masses. It appeared that these masses had no influence per se on the distribution of larvae. SPANISH: Este estudio está basado en las recolecciones de larvas de Thunnus albacares, Eutbynnus lineatus, y Auxis sp. obtenidas según los arrastres superficiales y oblicuos de la red, realizados durante siete cruceros, cada uno a la entrada del Golfo de California a lo largo de un derrotero comparable, y cada uno durante distintos meses. Las mediciones correspondientes de la temperatura superficial, salinidad y de zooplancton se realizaron en cada una de las estaciones de plancton. Las capturas de larvas Auxís sp. fueron examinadas mediante el análisis de la varianza para determinar cuales características ambientales se encontraban asociadas con el desove de este atún según lo indicaba la distribución de las larvas, y para obtener alguna idea del comportamiento de las larvas en sí mismas. Las pruebas indicaron que el desove de Auxis sp. varió significativamente entre los diferentes meses de los cruceros; indicaron también que si las larvas eran capaces de evitar el aparato de muestreo, esta habilidad no se relacionaba a las características asociadas con la hora del día de acuerdo a las condiciones de luz. El análisis no demostró ningún cambio en la distribución vertical de las larvas durante los meses del experimento. Se determinó que las larvas no exhiben un movimiento vertical diario. Las mediciones de temperatura, salinidad, y de los volúmenes de zooplancton fueron tratadas como covariables en el análisis. La temperatura superficial demostró ser un factor altamente importante en la explicación de la distribución de las larvas, pero la salinidad y los volúmenes de zooplancton no lo fueron. Las capturas de Thunnus albacares y Eutbynnus lineatus fueron pocas durante el curso de este estudio; éstas se discuten en términos cualitativos respecto a la época del año y a la temperatura superficial. La distribución de los atunes larvales en el área de estudio fue comparada con la distribución de las masas superficiales de agua. Parece que estas masas no tienen influencia per se en la distribución de las larvas. (PDF contains 40 pages.)

Geographical catch distribution of yellowfin and skipjack tuna in the Eastern Pacific Ocean, 1967-1970, and fleet and total catch statistics, 1962-1970

ENGLISH: Logbook records of tuna vessels fishing in the eastern Pacific Ocean were used to prepare charts showing the distribution of yellowfin tuna and skipjack catches by i-degree area, by quarter of the year, and by gear, for the years 1967-1970. Recent changes in the geographical distribution of yellowfin catch are illustrated. Also given are annual catch statistics and the composition of the international tuna fishing fleets which operated in the Commission's Yellowfin Regulatory Area each year, 1962-1970. SPANISH: Los registros de los cuadernos de bitácora de los barcos pesqueros de atún en el Océano Pacífico oriental se usaron para preparar gráficos que presentan para los años de 1967-1970, la distribución de captura del atún aleta amarilla y barrilete por área de 1 grado, trimestre del año y, por las artes. Se ilustran los recientes cambios en la distribución geográfica de la captura del atún aleta amarilla. Se presentan también las estadísticas de captura anual y la composición de la flota internacional de pesca, que explota cada año el Area Reglamentaria de la Comisión, 1962-1970. (PDF contains 95 pages.)

Fischereiökonomische Forschung in Deutschland – Ergebnisse zur deutschen Fischereiflotte aus einem EU-Verbundprojekt

The economic situation of the German fishing fleet, economic indicators and backgrounds have been analysed in the overall framework of the EU-Concerted Action ‘Economic Assessment of European fishing fleets’. Trends in number of vessels, employment on board and catches for main target species are decreasing. This development may clearly be related to bad fish stock conditions, missing investment op-portunities for vessels and the short-term fishing quota man-agement system. To facilitate fisheries economics research a better data collection system is needed. As a consequence economic advice may be given for the development of a long-term sustainable management system.

Maifische an der deutschen Nordseeküste - zum Auftreten von Finte (Alosa fallax) und Alse (Alosa alosa)

Quantitative data on twaite shad are collected annually in spring and autumn since 1974 by the Demersal Young Fish Survey. Results for occurrence of these anadromous species show that twaite shad has been caught in the entire Wadden Sea area despite of the poorly suited 3-m shrimp beam trawl applied in the survey. Regional differences occur: Only sporadic catches are observed in the northern part of the German Wadden Sea, while more frequent ones occurred southwards and in the East Frisian Islands region. The obvious recent increase of abundance of Alosa fallax in spring allows for a lower ranking in the Red List of Endangered Species, while Allis shad (Alosa alosa) requires the same classification, as it was the never caught during the thirty years of surveys.

Horizontale Trennblätter in Trawls zur Verringerung von Discards in der Ostsee

A primary objective of the Common Fishery Policy of the European Union is the reduction of discards and unwanted by-catches in the fishery. In principle this could be achieved if the catching methods were optimised for this. Still high numbers of undersized flatfish are caught in the bottom trawls. Although EU regulations make the use of the BACOMA codend mandatory in the Baltic Sea cod areable to escape through square mesh escape window of the BACOMA net the whereas flatfish still remain in the cod-end. Gear experiments have been carried out with the aim to better separate cod from the flatfish fraction already when entering the rear belly, making use of the natural behaviour of the fish, i. e. the preferred swimming distance from the bottom of the net in the funnel. As cod have a natural tendency to keep a relativly great distance from the bottom, flatfish tend to stay close to it. It was attempted to separate both fractions by splitting the funnel into an upper and lower part with a horizontal panel. This wastested for two different nets, a cod trawl to separate cod from flatfish, and an eel-trawl to separate cod and flatfish from eel. Cod and flatfish separation is best at a panel distance of 50 cm from the bottom. Thus, 74 % of the cod were found in the upper panel, whereas 75 % of the flounder were in the lower section. A separation of eel from cod was however not possible, since eel tend to rise to the upper part of the net, together with cod.

Einfluss der Umsetzung der ICES-Fangempfehlungen auf den Zustand der Fischbest

The implementation of the precautionary approach in the mid-1990s required commercial fish stocks to be classified into different categories. These are based on the degree to which stocks have been exploited or are threatened by fishing activities. According to current ICES terminology, stocks are classified as being either “within” or “outside safe biological limits”, or as being “harvested outside safe biological limits”. Between 1996 and 2002, the relative share of stocks in these three categories remained relatively stable (at about 20 %, 30 % and 15 %, respectively). Over the same time span, the number of stocks were insufficient data is available to quantify and thus to appropriately classify the state of the spawning stock biomass (“status unknown”) has increased. Neglecting potential impacts of fishing pressure, the combined average proportion of all stocks with sufficiently high spawning stock biomass is at about one third, while only one fifth of the stocks assessed have been managed sustainably. For some important fish stocks in the ICES environment – specifically demersal ones –, science recently had to call for rebuilding plans or even a closure of the fishery to allow recovery, in spite of the management’s agreement to manage the resources according to the precautionary approach. This obvious difference between approach and implementation has a number of potential causes: erroneous or imprecise input data (landings, discard and sampling information), insufficient assessment models, problems in the understanding of the scientific advice, and implementation errors. The latter could be either a difference between advised and implemented total allowable catches (TACs), or an excess of legal TACs. During the fifteen years covered by this analysis (1987 to 2002), the average deviation between the implemented TACs for a specific stock and that recommended by ICES for the same stock was more than 30 %. The overall average deviation (summed over all stocks) for the entire period was 34 %, excluding, however, four extreme outliers in the data, representing cases in which scientific recommendations were exceeded by as much as 1000 to 2500 %. If these were included, the overall average would be as high as 45 %. The annual deviation has substantially increased in recent years (from roughly 20 % in earlier years of the surveyed period). This recently observed high deviation also matches ICES’s estimate that the fishing mortality in the ICES convention area in the 1990s was well above recommended sustainable levels in the pelagic and demersal fishery. A direct comparison of scientifically proposed and politically implemented TACs is problematic in many case

On the climatology, oceanography and fisheries of the Panama Bight

ENGLISH: Seasonal changes in the climatology, oceanography and fisheries of the Panama Bight are determined mainly by the latitudinal movements of the ITCZ over the region. Evaporation is about 980 mm annually. Rainfall is probably much less than previous estimates because of a discontinuity in the ITCZ. Freshwater runoff from the northern watershed varies from 22 X 109 m3/mo in October-November to 11 X 109 m3/mo in February-March; from the southeastern watershed it varies from 16 X 109 m3/mo in April-June to 9 X 109 m3/mo in October-December. Total annual runoff is about 350 X 109m3. A marked salinity front is found at all seasons off the eastern shore. In the northern part of the Bight temperatures in the upper layers remained fairly constant from May to November; by February the mean temperature had decreased by 4°C and sharp gradients existed in the geographic distributions. Salinities in the upper layers decreased steadily from May to November; by February the mean salinity had increased by 2.5‰. The mean depth of the mixed layer increased from 27 m in May to 40 m in November; by February upwelling decreased it to 18 m. Between November and February upwelling had doubled the amount of P04-P and tripled that of NO3-N in the euphotic zone; surface phytoplankton production and standing crop, and zooplankton concentrations also doubled during this period. Upwelling was about 1.5 m/mo during May-November and about 9.0 m/mo during November-February, the annual total is about 48 m, Mean primary production is about 0.3 gC/m2day during May-December and about 0.6 gC/m2day during January-April; annual production is about 140 gC/m2. A thermal ridge occurred in February running from the northern to the southwestern part of the Bight. Within this ridge was a marked thermal dome coinciding with the center of the cyclonic circulation cell. Upwelling in the dome averaged 16 m/mo in November-February. The fisheries of the Panama Bight annually produce about 30,000 metric tons of food species and about 68,000 m.t. of species used for reduction. Most attempts to further the understanding of tuna ecology were unsuccessful. The apparent abundances of yellowfin and skipjack in the northern part of the Bight appear to be related to the seasonal cycle of upwelling and enrichment, as abundances are greatest in April and May when food appears to be plentiful. The life-cycle of the anchoveta in the Gulf of Panama also appears to be related to upwelling; the species mass varies from about 39,000 m.t. in December to about 169,000 m.t, in April. About 19.1 X 1012 anchoveta eggs are spawned annually. The life-cycles of shrimp in the Panama Bight appear to be related to upwelling as catches are greatest in May-July, about 3-5 months after peak upwelling, and annual catches are inversely correlated with sea level. SPANISH: Los cambios estacionales en la climatología, oceanografía y pesquerías del Panamá Bight están determinados principalmente por el movimiento latitudinal sobre la región de la Zona de Convergencia Intertropical (ZCIT). La evaporación es de unos 980 mm al año. La pluviosidad es probablemente muy inferior a las estimaciones previas a causa de la descontinuidad en la ZCIT. El drenaje de agua dulce, de la vertiente septentrional, varía de 22 x 109m3/mes en octubre-noviembre hasta 11 x 109m3/mes en febreromarzo; el de la vertiente sudeste varía de 16 x 109m3/mes en abril-junio a 9 x 109m3/mes en octubre-diciembre. El drenaje total, anual, es alrededor de 350 x 109m3. En todas las estaciones frente al litoral oriental se encuentra un frente de salinidad marcada. En la parte septentrional del Bight las temperaturas en las capas superiores permanecieron más bien constantes de mayo a noviembre; en febrero la temperatura media había disminuido en unos 4°C y existieron gradientes agudos en las distribuciones geográficas. Las salinidades en las capas superiores disminuyeron constantemente de mayo a noviembre; en febrero la salinidad media había aumentado en 2.5‰. La profundidad media de la capa mixta aumentó de 27 m en mayo a 40 m en noviembre; en febrero el afloramiento disminuyó el espesor de la capa mixta hasta 18 m. Entre noviembre y febrero el afloramiento había duplicado la cantidad de PO4-P y triplicado la de NO3-N en la zona eufótica; la producción superficial de fitoplancton y la biomasa primaria y las concentraciones de zooplancton también se duplicaron durante este período. El afloramiento era cerca de 1.5 mimes durante mayo-noviembre y de unos 9.0 mimes durante noviembre-febrero, el total anual es de unos 48 m. La producción media primaria es aproximadamente de 0.3 gC/m2 al día durante mayo-diciembre y cerca de 0.6 gC/m2 al día durante enero-abril; la producción anual es de unos 140 gC/m2. En febrero apareció una convexidad termal que se extendió de la parte norte a la parte sudoeste del Bight. Dentro de esta convexidad se encontró un domo termal marcado el cual coincidió con el centro de la circulación ciclonal de la célula. El afloramiento en el domo tuvo un promedio de 16 mimes en noviembre-febrero. Las pesquerías del Panamá Bight producen anualmente de cerca 30,000 toneladas métricas de especies alimenticias y unas 68,000 t.m. de especies usadas para la reducción. La mayoría de los esfuerzos realizados con el fin de adquirir más conocimiento sobre la ecología del atún no tuvo éxito. La abundancia aparente del atún aleta amarilla y del barrilete en la parte septentrional del Bight parece estar relacionada con el ciclo estacional del afloramiento y del enriquecimiento, ya que la abundancia mayor en abril y mayo cuando parece que hay abundancia es de alimento. El ciclo de vida de la anchoveta en el Golfo de Panamá parece también que está relacionada al afloramiento. La masa de la especie varía de unas 39,000 t.m. en diciembre a cerca de 169,000 t.m. en abril. Aproximadamente 19.1 x 1012 huevos de anchoveta son desovados anualmente. Los ciclos de vida del camarón en el Panamá Bight parecen estar relacionados con el afloramiento ya que las capturas son superiores en mayo-julio, unos 3-5 meses después del ápice del afloramiento, y las capturas anuales se correlacionan inversamente con el nivel del mar. (PDF contains 340 pages.)

A review of the Japanese longline fishery for tunas and billfishes in the Eastern Pacific Ocean, 1967-1970

ENGLISH: This report deals with the Japanese longline fishery for tunas and billfishes from 1967 through 1970, extending the studies made by Kume and Joseph (1969a, 1969b). The distribution of effort and catch is discussed and evaluated, and the changes in apparent abundance are examined. An analysis is made of the sexual maturity and size composition of the fish, and a brief comparison of the size composition of the catches from the longline and the surface fisheries is included. SPANISH: Este informe analiza la pesca palangrera japonesa de atunes y peces espada desde 1967 a 1970, ampliando los estudios hechos por Kume y Joseph (1969a, 1969b). Se discute y avalúa la distribución del esfuerzo y la captura, y los cambios en la abundancia aparente. Se hace un análisis de la madurez sexual y de la composición de talla de los peces y una breve comparación entre la composición de talla de los peces capturados en la pesca palangrera y la epípelágíca. (PDF contains 166 pages.)

Keine überdurchschnittlichen Nachwuchsjahrgänge bei den Nutzfischen der Nordsee

In January/February 2001, Germany participated with “Walther Herwig III” in the International Bottom Trawl Survey (IBTS) of ICES by contributing 70 half hour tows with the Grande Ouverture Verticale Bottom Trawl (GOV), 78 hydrographic stations, and 88 catches with the Method-Isaac-Kidd net (MIK), mostly in the central and northern North Sea. In total, 368 fishing stations by means of the GOV were covered by the international fleet. Preliminary results indicate that only indices for herring, whiting, and – to some degree – haddock are in the long-term mean. In contrast, the index for cod gives reason to serious concern. In addition, indices for both mackerel and Norway pout do not show any signs for an increasing strength of these stocks. Oceanographic data show that in comparison with the data from 1995 onwards actual temperatures and salinities are in the normal range. However, mean water temperatures of this short period are about more than a half degree above the long-term means of the period 1961 to 1990.