Influence of hydrologic attributes on brown trout recruitment in low-latitude range margins

Abstract

Factors controlling brown trout Salmo trutta recruitment in Mediterranean areas are largely unknown, despite the relevance this may have for fisheries management. The effect of hydrological variability on survival of young brown trout was studied during seven consecutive years in five resident populations from the southern range of the species distribution. Recruit density at the end of summer varied markedly among year-classes and rivers during the study period. Previous work showed that egg density the previous fall did not account for more than 50% of the observed variation in recruitment density. Thus, we expected that climatic patterns, as determinants of discharge and water temperature, would play a role in the control of young trout abundance. We tested this by analyzing the effects of flow variation and predictability on young trout survival during the spawning to emergence and the summer drought periods. Both hatching and emergence times and length of hatching and emergence periods were similar between years within each river but varied considerably among populations, due to differences in water temperature. Interannual variation in flow attributes during spawning to emergence and summer drought affected juvenile survival in all populations, once the effect of endogenous factors was removed. Survival rate was significantly related to the timing, magnitude and duration of extreme water conditions, and to the rate of change in discharge during hatching and emergence times in most rivers. The magnitude and duration of low flows during summer drought appeared to be a critical factor for survival of young trout. Our findings suggest that density-independent factors, i.e., hydrological variability, play a central role in the population dynamics of brown trout in populations from low-latitude range margins. Reported effects of hydrologic attributes on trout survival are likely to be increasingly important if, as predicted, climate change leads to greater extremes and variability of flow regimes.

Unravelling the effects of water temperature and density dependence on the spatial variation of brown trout (Salmo trutta) body size

“…Water temperature had a higher impact on the length of age-0 trout when compared with older trout. Incubation temperature could have influenced the date of emergence from the stream bed and may have caused interpopulation differences in emergence time (Elliott and Hurley 1998;Ojanguren and Braña 2003;Nicola et al 2009), which would lead to variations in the length of trout after the first growing period (Ojanguren and Braña 2003;Nicola and Almodóvar 2004). Water temperature may also influence the physiology of fish, causing differences in enzymes related to food conversion efficiency (Rungruangsak-Torrissen et al 1998) as discussed by Jonsson et al (2005) for Atlantic salmon.…”

Thermal Carrying Capacity for a Thermally-Sensitive Species at the Warmest Edge of Its Range

“…Strong flow events during emergence depressed summer recruitment. Such disturbance events drastically reduce the quantity and quality of suitable physical habitat, which results in high YOY mortality through both direct downstream displacement of subordinate individuals without shelter (e.g., [52]) and delayed carry-over effects on individuals occupying low-quality habitats that affect their performance in the following season (see [53]). We also observed that juvenile physical habitat can limit subsequent adult abundance.…”

Effects of environmental factors and predation on benthic communities in headwater streams

“…Moreover, the effects of fish on invertebrates should be strongest in streams with high densities of fish and low densities of invertebrates (Reice 1991). In the study streams fish species are currently exploited by angling (Nicola et al 2009) and probably populations do not reach densities high enough to control benthic communities.…”