Browsing by Author "Hansen, J.E."
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- ItemAspectos generales de la pesca del bonito (Sarda sarda) en la Argentina(Mar del Plata: Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP), 1987) Hansen, J.E.Basic aspects of the fising of Bonito in Argentina such as: catch statistics, fleet and gears, season and fishing grounds, and catch per unit effort (CPUE) are analized. FAO World Catch Statistics show that none of the different populations of Sarda sarda or other species of the Genus may support a highly productive fishery Exceptions are Sarda chilensis and S.sarda from the Black Sea, which us exploited by Turkey. On the basis of available information it may be inferred that the Bonito of Argentina has more competitors and a narrower thophic spectrum than that from the Black Sea.
- ItemCaracterísticas poblacionales de la anchoíta (Engraulis anchoita) del Mar Argentino. Parte I. El largo medio al primer año de vida, crecimiento y mortalidad(Mar del Plata: Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP), 1984) Hansen, J.E.; Cousseau, M.B.; Gru, D.L.A total of 7263 otoliths were collected from anchovy samples taken during two pelagic cruises which were carried out in the Spring of 1978. An statistical analysis of back calculated length distributions of one-year-old fish (L1) was made. The L1 mean values taken by geographical latitude form a cline, with higher values in the northern samples, and decreasing Southwards. Within this latitudinal gradient two main anchovy populations can be identified, one in the region of Buenos Aires Province and the other in Patagonian waters. The L1 of the females is significatively larger than that of the males for the former population, whereas in the Patagonian area differences between sexes are not significant. The parameters of the von Bertalanffy Growth curves, as well as the instantaneous total mortality rates (Z), were estimated for both populations by each cruise.
- ItemEstudios de distribución de la anchoíta (Engraulis anchoita) en un área de extensión reducida. I. Densidades mínimas de muestreo para la estimación de algunos parámetros poblacionales(Mar del Plata: Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP), 1986) Gru, D.L.; Hansen, J.E.Results of a research cruise carried out to estimate some biological parameters of anchovy (Engraulis anchoita), during the major spawning season, were analyzed in order to determine the minimum number of samples required to obtain unbiased values. Twelve samples of fishes were taken within an area of 607 nm². Size (total length)distributions, slope of the length-weight relationship, sex ratio and age population structure were considered. Results suggest that those parameters should be estimated by eight or more samples (corresponding to 76 nm² each).
- ItemEvaluación de merluza de cola (Macruronus magellanicus) en el Atlántico Sudoccidental. Período 1985-2001(Mar del Plata: Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP), 2007) Wöhler, O.C.; Hansen, J.E.; Giussi, A.R.; Cordo, H.D.Period 1985-2001. A stock assessment of Patagonian hoki of the Southwest Atlantic was carried out by using data from the years 1985-2001. A cohort analysis, fitted with some survey abundance indices was used in an adaptive conceptual framework. Simulation trials were performed to project the evolution of the fishery, to evaluate the risk of over-fish the stock under different exploitation levels, and to estimate Biologically Acceptable Catches (BAC). Both total biomass and spawning stock biomass showed increasing trends resulting from four strong year classes (1993, 1995, 1996 and 1998). Total biomass at the beginning of 2001 was estimated to be 2.5 million tons, and spawning stock biomass at the spawning time (August) was estimated to be around 1.28 million tons. The exploitation rate was low (0.19) and showed a decreasing trend in relation to previous years. The fishing mortality rate producing sustainable total catches in the long term, i.e., BAC corresponded to yields between 160 and 306 thousand tons during 2002, depending on future levels of recruitment
- ItemEvaluación de polaca (Micromesistius australis) en el Atlántico Sudoccidental. Período 1987-2001(Mar del Plata: Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP), 2007) Wöhler, O.C.; Hansen, J.E.; Cassia, M.C.; Cordo, H.D.Period 1987-2001. A diagnosis of the current state of Southern blue whiting (Micromesistius australis) stock in the Southwest Atlantic was carried out on the basis of catches corresponding to the period 1987-2001 as reported by the Argentine fleet and also by vessels operating around Malvinas Islands. Abundance and current fishing mortality rates were estimated, and the biomass evolution in the long term resulting from some possible exploitation strategies based on different management strategies were projected. A sequential population analysis calibrated under a conceptual adjustable framework with five independent abundance indices was carried out. The effects on the biomass estimates were analysed by adopting different selection patterns and calibration indices as well as taking into account the under-declaration and discard of catches. Results indicated that the declining trend of Southern Blue Whiting observed in previous studies has continued, but it has been less marked than in preceding years. Total biomass estimates at the beginning of 2001 ranged between 566 and 622 thousand tonnes, whether the under-reporting or discards of catches by the Argentine fleet were taken into account or not. Accordingly, the spawning biomass at the onset of spawning ranged between 403 and 442 thousand tonnes. These values would correspond to 27-29% of the virgin biomass. Current fishing mortality was estimated as 0.27, corresponding to a relatively high exploitation rate (0.56). Projections aimed at four possible management objectives showed that biologically acceptable catches would range 22-84 thousand tonnes in 2002. Catches in the Southwest Atlantic should not exceed 50 thousand tonnes during 2002 in order to stop the declining trend of Southern blue whiting biomass.
- ItemParámetros biológicos relevantes para las pesquerías de anchoíta argentina (Engraulis anchoita). Estimaciones resultantes de reunir datos de campañas de investigación (1993 a 2008) y de muestras de capturas comerciales (1986 a 2009)(INIDEP, 2011) Hansen, J.E.The aim of this paper was to accurately estimate population parameters of northern (“bonaerensis”, latitude < 41° S) and southern (“patagonic”, latitude 41° S) Argentine anchovy stocks and to describe some aspects of their behaviour. The research surveys allowed to obtain data on length, total weight, sex, maturity and age of 27,853 specimens of the northern and 12,787 of the southern stocks. Besides, 20,717 age determinations stemmed from commercial landing samplings of the northern stock were established. Sex proportion in the northern population was 0.50 : 0.50; the southern showed a slight predominance of males (0.52 : 0.48). Data derived from cruises and commercial landings showed statistical differences in the growth ratio of the northern stock where mean size at ages 0-2 proved to be slightly higher in landings; the opposite was observed about ages 5-6. On the other hand, research data showed similarity in mean size at age of both stocks, used to fit a unique von Bertalanffy growth function (L = 194.62; K = 0.456; t0 = -0.86). In the October surveys on the northern anchovy stock higher mean weight at size and age than in December cruises on the southern stock were observed, which resulted in significant differences between both length (mm)-weight (g) relations described, respectively, by equations W = 1.867 * 10-6 * L3.254 and W = 1,467 * 10-6 * L3,290; likewise, a higher asymptotic weight was calculated for specimens of the first group (53.36 g vs 47.47 g). Estimates of natural instantaneous mortality rates, carried out using different methods available in the literature, allow to suggest values M = 1.01 for the northern and M = 0.98 for the southern populations. A marked discrepancy between both stocks was observed in their capacity to reach sexual maturity, the northern group being precocious (L50% = 98,0 mm; t50% = 0,58 years vs 119,2 mm and 1,14 years). The size of specimens in the shoals of both populations, mainly in the southern, was homogeneous whether at day or night time. The preferential spawning period, that ranged 4-10 pm, was common to both stocks; nevertheless, females with hydrated oocytes were more frequent in the samples taken from the northen population, which indicates shorter periods between batch spawning.
- ItemPrecisión en las evaluaciones por área barrida de algunos peces demersales costeros entre los 34º S Y 42º S, Atlántico Sudoccidental(Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP), Mar del Plata, 2010) Hansen, J.E.; Hozbor, Natalia M.; Lagos, A. Nerina; Martos, PatriciaTo estimate the biomass of six species, the stratified design used at present for demersal coastal fish stocks is compared against other design alternatives. Density data (t mn-2 between 34ºS and 42ºS, from the coast line to 50m depth, corresponding to whitemouth croaker (Micropogonias furnieri), patagonian smoothhound (Mustelus schmitti), stripped) weakfish (Cynoscion guatucupa), angular angel shark (Squatina guggenheim), brazilian flathead (Percophis brasiliensis) and skate (Sympterygia bonapartii) collected in surveys carried out in spring and winter in the Argentine Sea (SW Atlantic), were analyzed. The spatial distribution of the species was strongly contagious and influenced by bottom salinity. Different marine zones that showed special salinity features for a long time were defined to test bounded strata accordingly. The simple random design caused, in general, greater uncertainty than any of the stratified designs when using the 17 fixed strata surveyed during the last cruises or when two ‘new designs’ that included 7 strata, different for spring and winter, were adopted. Although no stratified scheme showed superiority to assess all and every species, their comparative advantages are discussed. Assessments made with the design used at present seem to be less efficient in winter thus suggesting that, in the future, surveys should be carried out in spring. No great differences among designs were found when the efficiency gain-sample size relation was studied and that resulted very low above 150 trawls if compared to the cost of using the research vessel.
- ItemResultados de una campaña de investigación sobre la anchoíta (Engraulis anchoita) del sector bonaerense en el otoño de 1983. Distribución, abundancia y algunos aspectos biológico-pesqueros(Mar del Plata: Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP), 1986) Hansen, J.E.; Gru, D.L.; Perrotta, R.G.An extensive area of the continental shelf -between 37°20' and 34°40'S - was reviewed through hidroacoustical methods in order to evaluate the anchovy biomass. Within the area of highest concentration, further data on anchovy abundance were recorded, and fish samples were taken. Large anchovy shoals were located at about 170 nm from Mar del Plata, mainly in zones with sharp changes in oceanographic conditions. The distribution of the species was not uniform, but "contagious", and the log-normal distribution provided the best fit for the echo-integrator recorded data. The biomass was estimated at 1,061,727 tons (Confidence limits in between 921,010 and 1,223,930 tons). Some parameters of the population were estimated, such as: lenght-weight relationship, von Bertalanffy growth curve constants, sex ratio, maturity, and age composition. Taking into account a calculated naturaly mortality rate of M= 0.85, a Maximum Sustainable Yield at about 451,000 tons was estimated (Confidence limits at about 520,000 and 390,000 tons).