Causes of mortality of Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) smolts in a restored river and its estuary

During October 2000 to August 2002, the River Skjern Nature Project was implemented by removing dykes and re‐meandering 20.5 km of the lower canalized river. As a consequence the length of the river stretch increased to 23 km. A lake of 250 ha developed in the river valley 5 km upstream from the river mouth because of subsiding soils caused by reclamation and drainage since the 1960s. Using radiotelemetry, the mortality of wild Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) smolts in the River Skjern and its estuary was investigated prior to and after the implementation of the project. Altogether, 77 Atlantic salmon and 66 brown trout smolts were caught, tagged and released in the river upstream of the restoration project during the spring of 2000 and 2002. The in‐river smolt mortality was more than double in 2002 for both Atlantic salmon and brown trout compared with 2000. This was primarily due to bird predation in 2002 which was not observed in 2000. The in‐river bird predation in 2002 was mediated by the new lake, which quickly became an important bird rest area. Estuarine mortality mainly caused by cormorants (Phalacrocorax carbo sinensis) differed significantly between species, but was high for both Atlantic salmon (39%) and brown trout (12%) in both years of investigation. The aggregated smolt mortality in the river and in the estuary (48%) may threaten an indigenous self‐sustaining Atlantic salmon population in the River Skjern. When planning river restoration projects, caution should be used, especially where permanently flooded floodplains (lakes) develop due to subsiding soil. In situations where rivers pass directly through newly developed lakes, migratory species such as Atlantic salmon and brown trout may be severely affected due to increased exposure to predation from predatory fish and birds. Copyright © 2006 John Wiley & Sons, Ltd.     

Growth and population parameters of Nile tilapia,Oreochromis niloticus (L.) in the open waters of Lake Victoria,Kenya

The Nile tilapia (Oreochromis niloticus) was introduced into Lake Victoria in the early 1950s and 1960s and has since become the dominant tilapiine in the lake. This study investigated the growth and population parameters of O. niloticus in Lake Victoria on the basis of length–frequency data collected during the period June 2014 and June 2015. The asymptotic length (L_∞) had a mean (±SE) value of 46.24 ± 0.04 cm TL, growth curvature (K) of 0.69 ± 0.25 year^?1, total mortality (Z) of 2.18 ± 0.80 year^?1, a natural mortality (M) of 1.14 ± 0.28 year^?1, a fishing mortality (F) of 1.05 ± 0.53 year^?1, an exploitation rate (E) of 0.46 ± 0.08, a growth performance index (?) of 3.14 ± 0.17 and a length at first capture (L_C50) of 20.31 ± 0.40 cm TL. Comparing the results of this study with previous studies indicates the parameters K, Z and M have increased, whereas ?, F, E and L_C50 have decreased. Changes in these parameters could be attributed to the existing high fishing capacity, and changing lake conditions. Thus, management measures should include continued restriction on illegal fishing methods and gears, such as the use of undersized gillnets (<5 in. mesh size) and beach seines. More attention also should be directed to the implementation of measures to control pollution of the lake from its various sources.     

Use of a fishery model (FAST) to explain declines in the stocked barramundi (Lates calcarifer) (Bloch) fishery in Lake Tinaroo, Australia

Electrofishing, a fishery‐independent technique, was used to determine the size structure of a stocked impoundment barramundi (Lates calcarifer) fishery in Australia, in order to determine their size and age structure. Along with known recruitment values (stockings), this information was used to back‐calculate the mortality on each successive age class of fish. Using the fisher model, Fishery Analysis Simulation Tool (FAST), it was found that the fishery biomass reached a peak in the 1990s, and has since fallen rapidly because of the lack of successful recruitment until 2003. The fishery sampled in 2002 was dominated by older age fish classes (10⁺ to 14⁺ years old), which is opposite to that naturally found in wild fisheries. Although no juvenile L. calcarifer was found in the gut contents, cannibalism is suggested as an overriding cause for recent recruitment failure. Possible future management options for stocking apex piscivorous fish species into closed water systems also are suggested.     

Life satisfaction shows terminal decline in old age: Longitudinal evidence from the German Socio-Economic Panel Study (SOEP).

Longitudinal data spanning 22 years, obtained from deceased participants of the German Socio-Economic Panel Study (SOEP; N = 1,637; 70- to 100-year-olds), were used to examine if and how life satisfaction exhibits terminal decline at the end of life. Changes in life satisfaction were more strongly associated with distance to death than with distance from birth (chronological age). Multiphase growth models were used to identify a transition point about 4 years prior to death where the prototypical rate of decline in life satisfaction tripled from -0.64 to -1.94 T-score units per year. Further individual-level analyses suggest that individuals dying at older ages spend more years in the terminal periods of life satisfaction decline than individuals dying at earlier ages. Overall, the evidence suggests that late-life changes in aspects of well-being are driven by mortality-related mechanisms and characterized by terminal decline. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mortality problem and affine automata

The mortality problem for 2×2 matrices is treated from the automata theory viewpoint. This problem is shown to be closely related to the reachability problem for linear and affine automata of low dimensions. The decidability of the reachability problem is proved for some subclasses of one-dimensional affine automata. __________ Translated from Kibernetika i Sistemnyi Analiz, No. 2, pp. 24–29, March–April 2008.