Hydrological manipulation to assist spawning of a threatened galaxiid fish in a highland lake system

Hydrological alterations threaten freshwater fishes globally, with infrastructure-related modification of inland waterways (e.g. dams, water diversions) having profound impacts on many species. Adapting existing water-management systems can provide opportunities for undertaking hydrological manipulations to assist management of threatened fishes. The present study conducted two hydrological manipulations in an impounded highland lake system in Tasmania, Australia, under differing hydrological conditions in 2007 and 2009, to assist recovery of an endemic species, Galaxias auratus, following a prolonged drought. Monitoring at egg, larvae, juvenile and adult life stages revealed a positive response by G. auratus in Lake Crescent (recipient of water release), with no adverse impact on the species in Lake Sorell (source of water release). In both years, reproductive constraints imposed by water level-related availability of sediment-free rocky substrata delayed spawning (~1 month) of G. auratus in Lake Crescent. Despite this, spawning and recruitment occurred in 2007 (drought year) and 2009 (drought-breaking year), and the 2007 manipulation resulted in a two-fold increase in the seasonal density of larvae in Lake Crescent and an abundant cohort of YOY fish. Given knowledge of life histories and eco-hydrological relationships, manipulating (or re-instating) hydrologic conditions is a powerful tool for assisting recovery of threatened lacustrine fishes.

Eels at the Edge: Science, Status, and Conservation Concerns

<em>Abstract.</em>—In Taiwan, there has been a shortage of local Japanese eel <em>Anguilla japonica </em>elvers for culture, so culturists have imported American eel <em>Anguilla rostrata </em>(Le Sueur) elvers from North America to meet their needs. From 1999 to 2001, six exotic adult American eels were found in the estuary of the Kaoping River of Taiwan that had escaped from aquaculture ponds as young eels and stayed in the river until silvering. This study compares growth performance and migratory behavior, using otolith strontium (Sr)/calcium (Ca) ratios of those six American eels with cohabitating Japanese eels and American eels in North America. Regardless of sex, mean age at maturity of the exotic American eels was greater and mean annual growth rate was less than that of Japanese eels in Taiwan and similar to that of American eels in the southern United States. Sr/Ca ratios at the otolith edge of the six exotic American eels, which recorded their salinity history, increased significantly. Furthermore, four of the six exotic American eels spent more than one year in the high-salinity estuary. Their extended residence in the estuary may be due to a delayed spawning migration resulting from a failure to orientate and migrate properly to their native spawning site.

The central mudminnow, Umbra limi (Kirtland), a habitat specialist and resource generalist

The central mudminnow, Umbra limi (Kirtland), successfully inhabits a variable and unpredictable environment in southern Manitoba streams. Umbra accomplishes this by specializing in habitat and generalizing in resources utilized and life history strategies displayed. Mudminnows are restricted to still waters and show a preference for a variety of cover types. They are morphologically, physiologically, and behaviourally specialized for this habitat. Umbra limi inhabits areas subjected to hypoxia and all sizes are able to use both atmospheric and aquatic respiration. Mudminnows are euryphagic carnivores that eat aquatic and terrestrial invertebrates and fish. They feed from a variety of locations (benthic, midwater, and surface) and organisms attached to vegetation are included in the diet. Activity patterns (including feeding) vary daily and seasonally. Differences in rate of growth, age at first maturity, gonadal development, and survival occur between sexes. Individual and population variability is apparent. Spawning time varies and there is evidence for delayed spawning under unfavourable conditions.