Post-stocking survival of 0+ year pike in ponds as a function of water transparency, habitat complexity, prey availability and size heterogeneity

Survival of 0+ year pike Esox lucius (20–31 mm L _T) was evaluated over the first week following stocking in ponds (16 m²) depending on water transparencies (low and high), habitat complexity (low and high) and food availability (zooplankton). A multiple regression analysis showed that survival, essentially as a result of cannibalism, decreased with increasing size heterogeneity of pike, and the decrease was steeper when no food was available. Survival was equal in clear water and water containing copper chlorophyllin (chlorophyll), and slightly higher in complex than in simple habitats, but only when alternative prey availability was low. Conversely, growth in water containing chlorophyll was slightly faster than in clear water. This suggests that initial size heterogeneity is the prevailing factor controlling mortality when stocking 0+ year pike almost irrespective of the stocking environment.     

Growth and mortality of introduced fish larvae in a newly restored urban river

The potential of a newly restored river as a nursery for endangered rheophilic fish species was estimated by introducing a population of individually marked larvae of nase Chondrostoma nasus into two river sections differing in river morphology and hydrological conditions. After 12 months, clear differences in fish abundance and fish size were observed: in the braided floodplain section C. nasus were more abundant and larger in size than in the straight river channel section. Total mortality rates over the whole investigation period did not differ between the two sections.     

Stocking experiments with 0 + and 1 + trout parr, Salmo trutta L., of wild and hatchery origin: 1. Post-stocking mortality and smolt yield

Wild and hatchery-reared 8–12-month-old (5–8 cm) trout, Salmo frurta L., were stocked in tributaries of the River Gudenb. Mortality was examined by means of electrofishing. Repeated electrofishing and handling caused a small increase in mortality. The daily instantaneous mortality rate Z was high during the first 2 months after stocking, ranging from 0.0070 for wild trout to 0.0326 for domestic trout at a stocking density of one trout per m² and from 0.0206 (wild trout) to 0.0888 (domestic trout) at a stocking density of two trout per m². Two months after stocking, Z decreased drastically ranging from 0.0007 (wild trout) to 0.0067 (domestic trout). When stocked, first-generation hatchery trout showed Z equal to domestic trout. Wild trout resident in the experimental stream were negatively affected by the introduction of domestic trout and wild trout from another stream. at a stocking density above the carrying capacity. It is concluded that the higher mortality of domestic trout was caused by changes in food, feeding and exercise, possibly combined with the lack of selection in the hatchery. Smolt yield at age 2+ was 3.2% (0+ trout stocked in the fall)-7.0% (1 + trout stocked in the spring) of the domestic trout stocked (approx. one-sixth to one-third of natural populations) and 65.2–68.7% of the domestic trout present before the smolt run. For first generation hatchery trout of wild origin the corresponding figures were 7.3% (age 0 +) and 93.4%, and for wild trout introduced to the experimental stream they were 11.1% (age0 +)and39.8%.     

Winter diet and condition of two 0+ year cyprinid fish species in the lower River Trent, England

The winter diets of 0+ year juvenile dace Leuciscus leuciscus and roach Rutilus rutilus in the lower River Trent, England, were dominated by aufwuchs. There were no significant changes in the relative condition of either fish species over the winter.     

Overwinter body condition,mortality and parasite infection in two size classes of 0+ year juvenile European bitterling Rhodeus amarus

Body condition and parasite abundance were examined in two size classes of European bitterling Rhodeus amarus during the first overwintering period in two seasons (2007–2008 and 2009–2010). Body condition of large fish did not change during winter, and increased significantly in March. From November to February, small fish showed a decreasing trend in condition. Despite a significant increase in March condition of small fish only reached the same level as before winter. Total parasite abundance increased significantly in winter in both fish size classes, reflecting a seasonal increase in monogenean infection. Large fish were parasitized significantly more than small fish during winter, but only in small fish was a negative correlation between parasite infection and condition found and a significant decrease in parasite abundance recorded after wintering, indicating mortality of heavily infected individuals with low condition during the winter. A trend for higher overwinter mortality in small fish was found under semi‐experimental conditions. The decrease in condition during the winter period in small fish may reflect faster energy depletion generally expected in smaller individuals. The results indicate that parasite infection may contribute to the overwinter mortality of 0+ year R. amarus, with a stronger effect in smaller individuals.     

Sex,growth rate,rank order after brood reduction,and hatching date affect first‐year survival of long‐lived Herring Gulls

Among most species of birds, survival from hatching throughout the first year of life is generally lower than subsequent survival rates. Survival of young birds during their first year may depend on a combination of selection, learning, unpredictable resources, and environmental events (i.e., post‐fledging factors). However, knowledge about post‐fledging development in long‐lived species is usually limited due to a lengthy immature stage when individuals are generally unobservable. Therefore, pre‐fledging characteristics are often used to predict the survival of young birds. We assessed effects of nestling growth rates, hatching date, hatching asynchrony, brood size and rank order after brood reduction, and sex on first‐year survival of 137 fledglings using a mark‐resighting analysis. We found that the survival probability (Φ_1yr = 0.39) of first‐year Herring Gulls (Larus argentatus) in our study colony located at the outer port of Zeebrugge (Belgium) was lower than that of older individuals (Φ_>1yr = 0.75). All 10 models best supported by our data included nestling growth rate, suggesting that variability in first‐year survival may be linked primarily to individual variation in growth. First‐year survival was negatively correlated with hatching date and rank order after brood reduction. Hence, carry‐over effects of breeding season events such as timing of breeding, early development, and social status had an influence on survival of Herring Gulls after fledging. Furthermore, we found sex‐biased mortality in first‐year Herring Gulls, with females (Φ_1yr = 0.45) surviving better than males (Φ_1yr = 0.38). Although adult survival is generally regarded as the key parameter driving population trajectories in long‐lived species, juvenile survival has recently been acknowledged as an important source of variability in population growth rates. Thus, increasing our knowledge of factors affecting age‐specific survival rates is necessary to improve our understanding of population dynamics and ultimately life‐history variation.