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Salmonid sport fishery management in Argentinian Patagonia is usually guided by stakeholder perceptions, which do not consider the biological and ecological constraints acting upon aquatic resources. An example of this are management policies for Traful Lake, where Atlantic salmon, Salmo salar L., was actively stocked during the last decade in an attempt to change the fish assemblage structure and to create a highly valuable sport fishery. This study assesses the likelihood of these policies achieving such assemblage structure changes through the study of affluent-stream suitability as spawning and breeding grounds, lake fish assemblage parameters, trophic diversity and possible competition due to diet overlap. This study also assesses alternative management practices through population simulations and bioenergetic modelling under diverse catch-size limit scenarios. This study concludes that it is not advisable to try to generate a unique and distinctive sport fishery by stocking Atlantic salmon in an already renowned fishery in Northern Patagonia. Instead, a more comprehensive framework for decision-making is suggested, involving short-term studies that go beyond the specific problem of the target species and incorporate the whole fish assemblage using diverse approaches and modelling strategies. [ABSTRACT FROM AUTHOR]

This paper examines some effects of exploitation on a simple ecosystem containing two interacting fish species, with life histories similar to mackerel ( Scomber scombrus) and cod ( Gadus morhua), using a dynamic, size-spectrum model. Such models internalize body growth and mortality from predation, allowing bookkeeping of biomass at a detailed level of individual predation and growth and enabling scaling up to the mass balance of the ecosystem. Exploitation set independently for each species with knife-edge, size-at-entry fishing can lead to collapse of cod. Exploitation to achieve a fixed ratio of yield to productivity across species can also lead to collapse of cod. However, harvesting balanced to the overall productivity of species in the exploited ecosystem exerts a strong force countering such collapse. If balancing across species is applied to a fishery with knife-edge selection, size distributions are truncated, changing the structure of the system and reducing its resilience to perturbations. If balancing is applied on the basis of productivity at each body size as well as across species, there is less disruption to size-structure, resilience is increased, and substantially greater biomass yields are possible. We note an identity between the body size at which productivity is maximized and the age at which cohort biomass is maximized. In our numerical results based on detailed bookkeeping of biomass, cohort biomass reaches its maximum at body masses <1 g, unlike standard yield-per-recruit models, where body growth and mortality are independent externalities, and cohort biomass is maximized at larger body sizes. [ABSTRACT FROM AUTHOR]

The study explores the impacts of varying gillnet mesh size and fishing level on yield per recruit (Y/R), escapement spawning stock (ESS) and mega-spawners (MS) of three widely distributed freshwater fishery target species. Y/R is maximised when the optimal length of capture (Lcap) is above the size of maturity (L50). However, the unimodal shape of gillnet selectivity results in lower impacts to ESS and MS with both smaller and larger mesh sizes. Under conditions of moderate exploitation, the fraction of MS was significantly larger if small meshed gillnets were used. This is due to the relatively smaller cumulative vulnerability from small mesh sizes through time, as they target a smaller size range of fish, which also grow more quickly through the vulnerable window due to higher growth rates. Therefore, unlike trawls and beach seines, which select all size classes beyond the minimum length of capture (Lc), small meshed gillnets are not necessarily destructive and may rather promote sustained production by allowing a higher proportion of the spawning biomass to remain in the stock. The work also helps to explain the observation of sustained fish production in many developing countries despite the persistent use of gillnets of small mesh size that target small, under-sized individuals. [ABSTRACT FROM AUTHOR]

The daggertooth pike conger, Muraenesox cinereus ( Forsskål), has become an important fish resource in the western Seto Inland Sea, Japan, since the 1990s. However, introducing sustainable fisheries resource management for this species is difficult in this region because stock assessments have not been performed, and official fisheries statistics for this stock were discontinued after 2007. This study used existing limited data sets to compile the first report for fisheries resource management for this M. cinereus stock. Yield-per-recruit analyses showed that increasing fishing pressure above current levels would provide only a minimal increase in expected catch levels. Hence, the current harvest level is considered to represent the upper limit of fishing pressure. Age composition in a given year could potentially be used to forecast landing abundance for the following 2 years. This study provides a basis for establishing effective fisheries resource management strategies for M. cinereus. [ABSTRACT FROM AUTHOR]

The middle stretch of the Madeira River has supported an intensive commercial fishery for several decades. Developed in an area of rapids and waterfalls, this fishery focuses primarily on catfish stocks, mainly pimelodids. Data from fish landings collected in the years immediately prior to the start in operations of two large hydroelectric dams were used to estimate growth and mortality rates for Pirinampus pirinampu (Spix & Agassiz) and Brachyplatystoma platynemum Boulenger. In addition, stock assessment was carried out for both species, and the results used to evaluate the status of the fishery. Mean population parameters were L∞ = 80.85 cm (total length), k = 0.52 year-1, ɸ = 3.53, A0.95 = 6 year, M = 0.87, F = 1.41-1.64 and Z = 2.28-2.51 for P. pirinampu; and L∞ = 95.55 cm (total length), k = 0.28 year-1, ɸ = 3.40, winter point = 0.41, A0.95 = 11 year, M = 0.55, F = 0.16-0.35 and Z = 0.71-0.90 for B. platynemum. Yield-per-recruit analysis indicated P. pirinampu was overfished and that the stock of B. platynemum was under-exploited. Moreover, overfishing of the P. pirinampu stock and the effects of fragmentation caused by the construction of the dam should be monitored. [ABSTRACT FROM AUTHOR]

Age and growth of Rachycentron canadum (L.) was studied in northern and eastern Australia to provide data for a preliminary assessment of the stock and to explore possible fisheries management strategies using minimum legal lengths. Fish collected from commercial and recreational fisheries ranged in size and weight from 125 to 1633 mm fork length (FL) and 0.031 to 55 kg respectively. Annual growth increments in sectioned otoliths formed by November–December. Estimated ages ranged from 0 to 7 yr for both genders. Longevity was estimated to be at least 13 yr. Von Bertalanffy growth function parameters were L ∞ = 1160 mm FL, K = 0.63 yr−1 and t0 = −0.21 yr−1. Rachycentron canadum reach 600 mm FL in their first year and over 1000 mm FL in 3 years. Natural and total mortalities were estimated at 0.35 yr−1 and 0.85 yr−1, respectively. Populations of R. canadum may be vulnerable to growth overfishing under the current minimum legal length of 750 mm total length (TL) in Queensland waters. An increase in minimum legal length to 850 mm TL is recommended. [ABSTRACT FROM AUTHOR]

Abstract The Thai river sprat, Clupeichthys aesarnensis Wongratana, is a clupeid with a short life span, and supports artisanal fisheries in a number of reservoirs in the Mekong Basin. The growth parameters, mortality rates and the status of the Thai river sprat in Sirinthorn Reservoir (28 800 ha), NE Thailand (15°N; 105°E), are presented. The fishery is based on lured lift-nets, operated 7–14 days in the new moon period, September to April each year. It was shown that the von Bertalanffy growth function (VBGF) model was L t (mm) = 78.43[1 - exp{-0.211[t - (-0.7996)]}] and its growth conformed to an isometric pattern. Natural mortality rate (month-1 ) was 0.13 month-1 . Total mortality rates ranged from 0.69 to 1.53 month-1 depending on the weather and the fishing season. Recruitment was continuous throughout the year but peaked in June and July. The yield per recruit model indicated that the exploitation rate of this fishery is probably too high. [ABSTRACT FROM AUTHOR]

The article discusses a retrospective and prospective synthesis of results from population models of marine reserves to identify key theoretical issues that appear to be well understood, and issues in need of further exploration. The models focus primarily on questions concerning fishery management at the expense of other objectives such as conservation, scientific understanding, recreation, education, and tourism. Some models remain an aspect of reserve design in need of further analysis.