Fish production in the Jarama River, Central Spain (original) (raw)
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Limnetica, 2012
Brown trout is an important angling species worldwide, and its morphology, population structure and genetics can be highly variable from one location to another. In this study, we provide data for the establishment of reference range values for several population and growth parameters of brown trout in the Cantabrian-Atlantic siliceous rivers of Galicia (NW Spain). Additionally, this study tests the hypothesis that the population and growth parameters differ among sections of rivers with different exploitation statuses (unexploited, exploited-regulated and exploited-open sections). Our study revealed that such population parameters as biomass and production were higher in unexploited sections, but the differences in growth among the sections with different angling regulations were not consistent. The findings of this study are discussed in light of the present knowledge on the status of trout fisheries, as it is essential for the development of management plans. Additional studies are needed to clarify whether the differences in growth can be correlated to the angling regulations. Directive.
Italian Journal of Zoology, 1998
The brown trout population of the River Gallo (central Spain) was monitored every two months during 1996 to determine the current impact of angling, To evaluate the influence of additional parameters, physical habitat and food availability were also studied, To assess fishing pressure, trout harvest and angling exploitation, a partial creel census was conducted during the 1996 fishing season. Differences were found in densities and biomass between exploited (1182.4 fish ha-1, 68.3 kg ha-1) and unexploited areas, the lalter being markedly higher (3135,1 fish ha-1, 208.2 kg ha-1). Production was quite superior in the unexploited area and decreased (from 144.5 kg ha-1 yr-1 to 37.2 kg ha-1 yr-1) as fishing pressure increased. However, no consistent differences were observed in growth, condition factor, age diversity, mortality, recruitment age and turnover ratio. Sport fishing seems to be the main negative factor influencing the balance within population of brown trout in the River Gallo and therefore management should be focused on more restrictive angling measures.
Hydrobiologia, 1986
In the River Lobos-Ucero and its tributary the River Avion-Milanos (Duero basin, Old Castile, Central Spain), two limestone streams fed by aquifers, the population of brown trout, as compared with the populations of other European streams, shows a high growth rate, high condition coefficients, short life-span and early age at first maturity. Gonad cycle was also studied. Size distributions of unshed eggs exhibit a dynamic activity with a bimodal distribution from June onwards, spawning occurred in the last days of November. Fecundity (F) can be predicted from trout length (L, mm) according to the equation: F = -646.47 + 5.6167 .L. Numbers and standing crop of trout range from 18 to 3903 ind. ha-' and 3.6 to 452.9 Kg ha-', reaching higher values in the sites close to the aquifers. Egg production had values of 22.4 and 18.0 eggs m-2 in the Rivers Ucero and Avion-Milanos respectively. Some factors suggested as regulators of these demographical characteristics are discussed in the light of recent literature. I J l~l~l~l~l~l~l~l~l~ NONTH . Average monthly variations of water discharge (--) and water supplies (---)measured in the period 1970-1982 in the lower most part of the River Ucero after its confluence with the River Avion. J F M A M J J A S O N D Fig. 7. Monthly variations in the condition of 0+ and 2 1 + trouts (sexes combined) of the Rivers Ucero and Avion-Milanos. Parameter Localities
Fish stocks of the Âncora River, northern Portugal: production
Fisheries Research, 1999
The mean biomass (" B) and production (P) of four ®sh populations (brown trout, Salmo trutta m. fario (L.)), Iberian roach, Rutilus arcasii (Steindach.), Iberian nase, Chondrostoma polylepis (Steindach., ssp. duriensis (Coelho)), and eel, Anguilla anguilla (L.)) were assessed in the A Ã ncora River, north Portugal. At four sites located along the course of the A Ã ncora River and one site on its tributary " B and P were in the range 36.5±283.9 kg ha À1 and 34.0±608.5 kg ha À1 yr À1 , respectively. Lowest values were recorded at sites in the middle course of the main river, isolated by numerous dams and waterfalls. Greatest values were recorded in the natural tributary (Gondar Creek) and in the out¯ow section of the main river.
Angling impact on conservation of Spanish stream-dwelling brown trout Salmo trutta
Fisheries Management and Ecology, 2004
Spanish brown trout, Salmo trutta L., populations are currently overexploited as a result of unsuitable management activities, and their genetic uniqueness is threatened by introgression of foreign genes because of stocking. In this study, the status and management of trout fisheries were reviewed and the effects of fishery management on abundance, production and life history of trout in Spain assessed. Angling exploitation has reduced the mean age, the age diversity and number of trout exceeding the minimum size in exploited sections. Likewise, exploited areas show a general decrease in overall abundance parameters and production, as well as a depletion of the breeding stock and population fecundity. Current minimum size limit control reduces the spawning chances in fast-growing populations because of higher susceptibility to angling harvest. The effects of fishery management on population dynamics, production and life-history characteristics exhibit different patterns among Spanish rivers, and seem to depend on the environmental and biological characteristics of the populations. The current declining trend of brown trout could be reduced by river-specific management and alternative fishing regulations.
Freshwater Biology, 2002
1. Reproductive traits were studied in seven wild populations of resident brown trout in Spain. We examined whether growth, and certain environmental conditions such as water temperature or food abundance, could explain interpopulation variation in the reproductive characters. 2. The results indicated that nearby populations subjected to a wide variation in environmental conditions exhibited a similar reproductive performance. 3. Age distributions and sex ratios were not significantly different among populations. Age ranged from 0+ to 4+ years but the populations were dominated by the 0+ to 2+ groups. In all rivers females matured at age 2+ as opposed to age 1+ and 2+ for males. Mean length at the end of the growth period differed significantly among populations. However, annual growth rate was similar among rivers and was not significantly correlated with either biomass of the benthos or water temperature during the growth season. 4. Reproductive effort, body condition, fecundity and egg size did not correlate significantly with either the abundance of benthic invertebrates or water temperature. Once the effect of body length on both egg size and number was removed, a significant negative correlation was found between these two traits among populations.
Fish stocks in the Âncora River, north Portugal
Fisheries Research, 2000
In the 19 km long A Ã ncora River, divided by 20 waterfalls and dams and emptying to the Atlantic Ocean in north Portugal, ®sh were sampled for the bioenergetics study. Average monthly water temperature during the year at sites along the river course was in the range 8.5±218C. The four ®sh populations' consumption, both in energy and mass units, was lower at sites in the middle course of the river, which was isolated from upstream sites by numerous waterfalls and dams. The gross (K 1) and net (K 2) ecological ef®ciencies of brown trout, roach and nase were very low, but detritus was their dominant food item. Eel, which ate animal food only had two to three times higher growth ef®ciencies than other ®sh. High mean monthly water temperatures from May to August and the isolation effect were probably the causes of a low utilisation of consumed food for growth in the populations investigated.
1992
Effects of angling exploitation on brown trout populations were assessed by comparing fished sections with close ones unfished for at least 20 years, in mountain streams of Asturias (Northern Spain). Both the fish size and age structure significantly differed among sections in the expected direction according to their exploitation status. The main effects were a significant decrease in age structure complexity (diversity), life span, and percent individuals above the legal limit size in the exploited stocks versus the unexploited ones. Trout above the minimum length limit for fishing (18 cm) averaged 19 .47% of the fish caught in the unfished sections (sd = 4.01 ; n = 5), and 4 .72% (sd = 3.46 ; n = 4) in those subjected to angling. Furthermore, fish older than 4 years represented 39.84% (sd = 8 .53) and 1 .19% (sd = 1 .60) of the catch, respectively. Effects on recruitment (density of young fishes) and growth rates (length at age 1 + to 3 +) were not absolutely consistent, though maximum values were associated with fished sections .