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doi: 10.1093/icesjms/41.3.211pmid: N/A
Techniques of fish population dynamics, model building, and optimal control theory are applied to the problem of managing the Spencer Gulf prawn fishery in South Australia which involves the annual exploitation of a single year class of prawnsworth about A$ 6 million.Twelve years of catch and effort statistics, information on the growth and behaviour of prawns, and the economics of fishing are available. These data are used to build a model of the fishery which then is subjected to optimization techniques to derive optimal management strategies. These strategies take into account the interdependence of fisheries data availability and ill-conditioning, parameter uncertainty, and the robustness of prescribed controls.A combination of factors (continuous recruitment, seasonal vulnerability, large environmental fluctuations) makes the estimation of the non-linear parameters and the prescription of optimal controls impossible by previously published methods alone.Consequently, the Beverton-Holt model first is extended to incorporate the above effects; statistical model building techniques (least squares minimization and Monte Carlo simulation) are then used to estimate the population dynamics parameters and the random characteristics of the system.The model is then optimized within an economic framework. Dynamic programming is used to derive optimal fishery closures for a given number of vessels. The derived controls take into account the major source of variation (variable recruitment). Their sensitivity to the uncertain parameters and to possible changes in costs is lso considered, and the best number of vessels is determined taking into account parameter uncertainty, expected total profits, returns to capital, and the statistical distribution of returns.
Pieper, R. E.; Holliday, D. V.
doi: 10.1093/icesjms/41.3.226pmid: N/A
Acoustic volume-scattering strengths were recorded at frequencies of 0·54, 1·16, 1·80, and 3·08 MHz from the upper 100 m of the water column off southern California. Concurrent pump samples of zooplankton were collected from discrete depths at the time of the acoustic recordings. Three predictive scattering models were used to calculate the volume-scattering strengths of these samples. Positive correlations between the calculated values from the pump samples and in situ field measurements were produced from all three scattering models. Correlations produced with the truncated fluid-sphere model values were slightly higher than correlations generated by data from the other two models, especially at a frequency of 1·80 MHz. Acoustic scattering at 1·80 MHz appeared to result primarily from organisms in the 0·4 to 0·6 mm equivalent spherical radius size class which included the copepods Calanus pacificus and Rhincalanus nasutus (2·5 to 3·5 mm in length). Correlations between calculated and measured volume-scattering strengths were highest at 3·08 MHz and decreased with decreasing frequency. A similar trend occurred when comparing measured volume-scattering strengths with the volume of zooplankton collected. Positive correlations between the measured acoustic values and both the results of the predictive models and the zooplankton volumes indicated that the acoustic values reflected the distribution of zooplankton in the water column.
Mauchline, J.; Gordon, J. D. M.
doi: 10.1093/icesjms/41.3.239pmid: N/A
Some 17 species of berycomorphid and percomorphid teleost fish occurred in pelagic and demersal samples taken in the Rockall Trough during the period 1973 to 1981. Demersal trawls were deployed at approximately 250 m bathymetric intervals between 400 and 2900 m depth. Pelagic rectangular midwater trawls were fished open to depths of approximately 2500 m. The most common species caught were Hoplostethus atlanticus, a subdominant among the species caught in the 1000 to 1250 m bathymetric zones, and Epigonus telescopus and Aphanopus carbo, subdominants among the species caught in the 500 to 750 m zones. The majority of the other species were rare in the samples. Hoplostethus atlanticus and Epigonus telescopus, whose distributions do not overlap bathymetrically, both exploit the benthopelagic fauna. Aphanopus carbo prey primarily on other fish. The exploiters of the epibenthos are Beryx decadactylus, Lycodes spp., Cataetyx laticeps, and Spectrunculus grandis. The rare Nesiarchus nasutus may exploit benthopelagic prey while the remaining eight species are primarily meso- and bathypelagic. Three of them, however, also exploit benthopelagic prey to varying degrees; they are Scopelogadus beanii, Poromitra crassiceps, and possibly Melanostigma atlanticum.
doi: 10.1093/icesjms/41.3.248pmid: N/A
This paper uses random length values simulated around a von Bertalanffy growth function to test the efficiency of three methods (Gulland and Holt, 1959; Fabens, 1965; Munro, 1982) for estimating the parameters K and L∞. It is concluded that Fabens' method gives the most accurate estimates and it is recommended that this method be used in preference to the other two.
doi: 10.1093/icesjms/41.3.259pmid: N/A
Windermere is a lake in the English Lake District. Perch, Perca fluviatilis L., were heavily exploited in the 1940s, and since then they have been monitored each spring by trapping. Pike, Esox lucius L., have been gill netted each winter since 1944, removing each year about one third of the population over 55 cm in length. Perch are the main food of pike. Major changes have been observed in several population characteristics, including numbers, year-class strengths, and growth. These changes were not always similar in the north and south basins of the lake. Three periods, 1942 to 1959, 1960 to 1968, and 1969 to 1975, have been identified, with summer temperatures variable, cool, and warm respectively. Temperature, predation, and cannibalism are suggested as the most important factors and their relative importance has varied in the different periods. Fishing policy has remained almost constant since the late 1940s, and the changes haveoccurred as a result of natural events.
Lockwood, Stephen J.; Lucassen, Werner
doi: 10.1093/icesjms/41.3.268pmid: N/A
Between 1969 and 1972, 2282 juvenile plaice were tagged and released in Filey Bay, Yorkshire. Up to 1982, 458 valid returns were made. The overwhelming majority of these returns were made from fishing grounds within the area occupied by the Flamborough spawning stock. The conclusion drawn from the results was that when plaice approach sexual maturity they emigrate from the nursery area in which they settle as 0-groups, and recruit to their parent spawning stock. Estimates of vectors and dispersion coefficients support the hypothesis that the mean position of the population of mature fish moves very little from year to year.
doi: 10.1093/icesjms/41.3.276pmid: N/A
An attempt has been made to construct a stock and recruitment curve for the plaice stock in the southern North Sea with the use of average estimates of recruitment and of stock. The slope at the origin, which represents the fractional survival under conditions of optional feeding, may be characteristic of species or families. Some indication of the data needed to establish the magnitude of the slope at the origin is given.
doi: 10.1093/icesjms/41.3.280pmid: N/A
The mechanisms used by physiologists and fishery biologists to explain why fish become mature are shown to be wanting. The hypothesis is presented that diminishing oxygen supply per unit weight serves in growing fish as the master factor in inducing the transition from juvenile to adult.
Williamson, Neal J.; Traynor, Jimmie J.
doi: 10.1093/icesjms/41.3.285pmid: N/A
Pacific whiting (Merluccius productus) biomass estimates determined from echointegrator surveys depend on target-strength values used to scale the echo-integrator data. During August 1980, a 38 kHz, dual-beam system was used to collect targetstrength data on Pacific whiting off the Oregon-Washington coast. Estimates derived from these data indicate that at night the target strength of whiting with a mean length of 50 to 55 cm is -36 dB/kg. Results of other research emphasize the need to obtain additional data for Pacific whiting, particularly the target-strength size relationship and the variation between day and night target-strength estimates.
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