Size composition of catches of Yellowfin tuna in the Japanese long-line fishery in the eastern tropical Pacific east of 130°W

ENGLISH (pgs. 267-283): In the spring of 1963, the senior author, who is a member of the staff of the Nankai Regional Fisheries Research. Laboratory, Fisheries Agency, Japanese Government, came to the Institute of Marine Resources of the University of California as a visiting investigator, bringing with him catch statistical data from the fishery in the eastern Pacific, which had been collected at the Nankai Regional Fisheries Research Laboratory (NRFRL) through September 1962, in order to conduct studies of these data in collaboration with the junior author, and with investigators of the InterAmerican Tropical Tuna Commission. A general review of the long-line fishery, based on the catch statistics of the commercial fishing fleet has been published by Suda and Schaefer (1965). In this paper we present an analysis of data respecting the size-composition of yellowfin tuna taken on long-line gear throughout the eastern Pacific between 1958 and 1962, and make some comparisons with data on size-composition of yellowfin tuna taken in the near-surface fishery, by bait boats and purse-seiners, in waters adjacent to the American coast. As has been shown by Suda and Schaefer (1965), the long-line fishery in the eastern Pacific is primarily directed toward the capture of bigeye tuna. However, considerable quantities of yellowfin tuna are also taken on this gear, and, in addition, there are substantial catches of albacore and of several species of spearfishes in some parts of the range of this fishery. Information respecting the catch rates of yellowfin tuna, and information respecting the size-composition of the stock of yellowfin tuna being exploited by the long-line fishery, is of particular interes~" because the yellowfin tuna population of the eastern Pacific is also subject to an intensive fishery by baitboats and purse-seiners which capture this species, together with skipjack, near the surface along the coast of the Americas, and around the outlying islands, in the region of California to northern Chile. SPANISH (pgs. 311-329): En la primavera de 1963, el autor principal, quien es miembro del personal del Nankai Regional Fisheries Research Laboratory, Fisheries Agency del gobierno japonés, vino al Institute of Marine Resources de la Universidad de California en calidad de investigador visitante y trajo consigo datos estadísticos de las capturas de la pesquería en el Pacífico oriental, que habían sido recolectados en el Nankai Regional Fisheries Research Laboratory (NRFRL) hasta septiembre de 1962, con el fin de hacer estudios de esos datos en colaboración con el coautor y con investigadores de la Comisión Interamericana del Atún Tropical. Una revisión general de la pesquería con palangre, basada sobre las estadísticas de captura de la flota pesquera comercial, ha sido publicada por Suda y Schaefer (1965). En este trabajo presentamos un análisis de los datos correspondientes a la composición de tamaños del atún aleta amarilla capturado con equipo palangrero en todo el Pacífico oriental, entre 1958 y 1962, y hacemos algunas comparaciones con los datos sobre la composición de tamaños del atún aleta amarilla cogido en la pesquería superficial cercana, por barcos de carnada y rederos en aguas adyacentes a la costa americana. Como ha sido demostrado por Suda y Schaefer (1965) la pesquería con palangre en el Pacífico oriental tiene como principal objeto la captura del atún ojo grande. Sin embargo, considerables cantidades de atún aleta amarilla son capturadas también por este equipo y, además, hay también considerables capturas de albacora y de diversas especies de peces-espada en algunas partes de la región que abarca esta pesquería. La información respecto a las tasas de captura del atún aleta amarilla, y la relativa a la composición de tamaños del stock de esta especie que explota la pesquería con palangre, es de particular interés, a causa de que la población de atún aleta amarilla del Pacífico oriental es también objeto de una pesca intensiva por barcos de carnada y rederos que capturan esta especie, junto con el barrilete, cerca de la superficie a 10 largo de la costa de las Américas y alrededor de las islas mar afuera, en la región desde California hasta el norte de Chile.

Changes in the size structure of the yellowfin tuna population of the tropical eastern Pacific Ocean from 1947 to 1955

ENGLISH: Morphometric studies by Godsil (1948), Godsil and Greenhood (1951), Royce (1953) and Schaefer (1952, 1955) have indicated that the yellowfin tuna of the Eastern Pacific are distinct from those of the Central Pacific. Tagging of yellowfin tuna by the California Department of Fish and Game, and by the Inter-American Tropical Tuna Commission in the Eastern Pacific, and by the Pacific Oceanic Fishery Investigations in the Central Pacific, have not yet revealed any migrations between these areas. Shimada and Schaefer (1956) have compared changes in population abundance and fishing intensity, considering the population in the Eastern Pacific as a separate entity. They conclude " ... the amount of fishing has had a real effect upon the stock of Eastern Pacific yellowfin tuna, taken in the aggregate, over the period studied. The evidence suggests also that for this species the intensity of fishing in some recent years has reached and might have even exceeded the level corresponding to the maximum equilibrium yield." Tagging experiments by the California Department of Fish and Game and by the Inter-American Tropical Tuna Commission have yielded returns in the order of one to five percent (Roedel 1954, and unpublished data of both agencies), a level much lower than that at which fishing intensity would be expected to noticeably affect the population size. These results are probably a reflection of the inadequacies of the present tagging methods, but they could lend doubt to the conclusions of Shimada and Schaefer. It is desirable, therefore, to examine other, independent, evidence as to the effects of fishing on the population. At the high levels of fishing intensity suggested by Shimada and Schaefer, in addition to changes in quantity, measurable changes would be expected to have occurred in the quality of the yellowfin tuna stocks, because the average age and size of the fish would have been reduced by the high mortality rates accompanying high fishing intensities. A continuing regular program of sampling catches and determining their length composition, to assess changes in the size composition of the stocks, was initiated by the Commission in 1954 but direct measurements are not available for the earlier, more dynamic period of growth of the fishery. Consequently, other, more general indications of possible changes in the size composition were sought. SPANISH: Los estudios morfométricos efectudos por Godsil (1948), Godsil y Greenhood (1951), Royce (1953) y Schaefer (1952, 1955), han demostrado que el atún aleta amarilla del Pacífico Oriental es distinto del que habita el PacÍfico Central. Los experimentos del Departamento de Pesca y Caza de California y de la Comisión Interamericana del Atún Tropical en el Pacífico Oriental, así como los de las Investigaciones Pesqueras del Océano Pacífico en el Pacífico Central,consistentes en la marcación de atunes aleta amarilla, aún no han puesto de manifiesto movimientos migratorios entre dichas áreas. Shimada y Schaefer (1956) han hecho estudios comparativos sobre la abundancia de la población y la intensidad de la pesca, considerando a la población del Pacífico Oriental como una entidad separada. Su conclusión es que " ... la intensidad de la pesca ha tenido un definido efecto sobre la población del atún aleta amarilla del Pacífico Oriental, tomada en conjunto, a lo largo del período estudiado. La evidencia de que se dispone sugiere así mismo que, por lo que hace a esta especie, la intensidad de la pesca en los últimos años ha alcanzado y quizás aún sobrepasado el nivel correspondiente a la máxima pesca de equilibrio". Los experimentos de mar•cación del Departamento de Pesca y Caza de California y de la Comisión Interamericana del Atún Tropical han producido recuperaciones ,entre el uno y el cinco por ciento (Roedel 1954 y datos inéditos de ambos organismos), lo que constituye un nivel mucho más bajo de aquél en que la intensidad de la pesca podría considerarse que afectaría notablemente el tamaño de la población. Estos resultados reflejan probablemente lo inadecuados que son aún los métodos de marcación, pero ellos podrían, quizá, poner en tela de juicio las conclusiones de Shimada y Schaefer. Por lo tanto,es deseable examinar otras fuentes de evidencia independientes, relacionadas con el efecto que la pesca tiene sobre la población. En efecto, si los altos índices de pesca sugeridos por Shimada y Schaefer son correctos, es de esperar que, además de los cambios en la magnitud de la población, se hayan producido otros, concomitantes y sensibles, en la calidad de los stocks de atún aleta amarilla, puesto que tanto el promedio de edad como el de tamaño de los individuos habrían disminuído debido a las elevadas tasas de mortalidad inherentes a las altas intensidades de pesca. En 1954 la Comisión inició un programa ininterrumpido para tomar muestras y determinar en ellas las frecuencias de tallas y evaluar de este modo los cambios correlativos que tuvieran lugar en los stocks pero, infortunadamente, este sistema de evaluación directa no fué practicado en el período anterior, que fué precisamente el de rápida expansión de la pesquería. En tal virtud, hubo de ser necesario buscar indicios más generales referentes a los cambios posibles en la composición de tamaños. (PDF contains 20 pages.)

An analysis of methods of sampling to determine the size composition of commercial landings of yellowfin tuna, Neothunnus macropterus, and skipjack, Katsuwonus pelamis

ENGLISH: The staff of the Inter-American Tropical Tuna Commission is collecting and analyzing catch statistics of the Eastern Pacific fishery for yellowfin tuna (Neothunnus macropterus) and skipjack (Katsuwonus pelamis) in order to provide the factual information required for maintaining the catch of these species at maximum sustainable levels (Shimada and Schaefer, 1956). Careful, systematic and continued studies of the population structure, life history, and ecology of these species are needed for a proper and adequate interpretation of the catch statistics so that a sound conservation program may be achieved (Schaefer, 1956). SPANISH: El personal científico de la Comisión Interamericana del Atún Tropical cumple, entre sus tareas, la de reunir y analizar las estadísticas de pesca del atún aleta amarilla (Neothunnus macropterus) y del barrilete (Katsuwonus pelamis) de la pesquería del Pacífico Oriental, a fin de adquirir la información necesaria para mantener la pesca de estas especies a niveles de producción máxima sostenible (Shimada y Schaefer, 1956). Estudios cuidadosos, sistemáticos y continuos de la estructura de la población y ciclo de vida y ecología de estas especies, son necesarios para lograr una interpretación adecuada de las estadísticas de pesca, de modo que éstas, a su vez, permitan realizar un programa conservacionista serio (Schaefer, 1956). (PDF contains 73 pages.)

Shore seines for reservoirs - Part 2 - Studies on optimum mesh size

Fish landings by shore seines operated in the Hirakud reservoir were analysed species wise and their morphometrical details were recorded. Based on the above investigation proportionality coefficients in respect of important species of fish were worked out in order to detetmine the optimum mesh size as this was important from the conservation point of view. This communication discusses the significance of mesh regulation for shore seines.

Size distribution of heavy mineral grains in some modern Nile Delta coastal sands, Egypt

This study includes determination and discussion of the texture and heavy mineral compositions of some modem Nile Delta coastal sands (river, coastal dune, beach-face, and nearshore marine) in order to delineate the process and factors that regulate the size distribution of heavy mineral grains comprising these coastal sands. Textural analysis of unseparated bulk samples indicate that the examined four types of sands differ in their mean grain sizes and degree of sorting. However, analysis of size distribution curves of 10 heavy mineral species or group of species in the four environments having the same general shape and nearly similar in that general order of arrangement. However, these curves vary both in median sizes and sorting. The size distribution of a heavy mineral in the Nile Delta coastal sands appear to depend on: (1) range of grain size fractions in each sample, (2) relative availability of heavy mineral in each size grade of the sample, (3) specific gravity of minerals comprising these sands, and (4) some other unknown factor or factors. Results of size measurement of heavy minerals indicated that increasing specific gravity is accompanied by increasing fineness of the heavy minerals. This study may be useful in search for marine placers and understanding the processes of grain-sorting on the sea beaches.

The effect of hook size on the catch rate and size of the Nile perch Lates niloticus (Linne) fishery in the Napoleon Gulf, Lake Victoria, Uganda

This study was undertaken in Napoleon gulf, Lake Victoria Uganda from July – December 2009. It was conducted in four landing sites; Bukaya (0.41103N, 33.19133E), Bugungu (0.40216N, 33.2028E), Busana (0.39062N, 33.25228E) and Kikondo (0.3995N, 33.21848E) all from Buikwe district (Formerly part of Mukono district). The main aim was to determine the effect of both hook size and bait type on the catch rate (mean weight) and size composition of Nile perch (Lates niloticus) (LINNE) fishery in the Napoleon Gulf, Lake Victoria. The main hook sizes investigated during the experiment were 7, 8, 9, 10, 11 and 12 that were dominantly used in harvesting Nile perch in Napoleon Gulf, Lake Victoria. In this study length, weight and bait type data were collected on site from each boat at that particular fishing spot; since most fishermen in the Napoleon Gulf could sell their fish immediately the catch is caught there and then. The results indicated a total of 873 Nile perch fish samples collected during the study. Statistical tests, descriptive statistics, regression and correlation were all carried out using the Statistical Package for the Social Sciences (SPSS) in addition to Microsoft excel. The bait types in the Gulf ranged from 5-10 cm Total length (TL) haplochromine, 24.5-27 cm TL Mormyrus kannume and 9-24 cm TL Clarias species. The bait types had a significant effect on the catch rate and also on the size composition the fish harvested measured as Total length (ANCOVA F=8.231; P<0.05) despite the fact that bait type had no influence on mean weight of fish captured (ANCOVA F=2.898; P>0.05). Hook sizes used by the fishers had a significant effect on the both the size (TL) composition (ANCOVA F=3.847; P<0.05) and the mean weight (ANCOVA F=4.599; P<0.005) of the Nile perch captured. Investigations indicated hook sizes seven (7) and eight (8) were the ones that harvested the Nile perch above the slot size of 50 cm total length. In general hook sizes indicated to be the main drive in the harvesting of the Nile perch though bait type also contributed toward that. Generally there is need for management to put a law in place on the minimum hook size to be used on the harvesting of the Nile perch and also monitored by the Fisheries Management as a regulatory measure. In addition to that aquaculture should be encouraged to farm the fish for bait at a higher scale in the region in order to avoid depleting the wild stocks already in danger of extinction. Through this kind of venture, both biodiversity conservation and environmental sustainability will be observed in the Lake Victoria basin.