Training fish for restocking: refuge and predator training in the hatchery has limited benefits for a marine fish

Large numbers of hatchery-reared fish are released in stocking programmes; however, success is limited by high mortality. Predation is seen as the main cause of deaths but might be reduced by training fish before release to avoid predators and/or use refuge. In this study on a potential restocking species, yellowfin bream Acanthopagrus australis, the effects of predator training and refuge on the behaviour of fish in the hatchery were tested. In the first experiment, juvenile bream were exposed to predatory mangrove jack (Lutjanus argentimaculatus) fed exclusively on bream flesh while housed in tanks with and without refuge. Predator training altered fish behaviour when fish were re-exposed to predators, but the effects were subtle and varied between groups of fish. In contrast, refuge created strong and consistent changes in behaviour, significantly slowing down the amount of time that fish took to consume food. A second experiment focused on the effects of refuge. Bream were trained to use artificial seagrass or house bricks as refuge and then exposed to mangrove jacks in a laboratory predation experiment. When refuge was available, fish significantly slowed down their feeding rate. There was a small, transient increase in survival for fish given seagrass refuges, but this was irrespective of whether the bream were trained to use refuge. The results of this study indicate that the use of refuge may be innate and the benefits of refuge may be available to naive hatchery-reared fish or fish trained to use refuge shortly before release. This suggests that there is potential to improve post-release survival of fingerlings without time-consuming and expensive hatchery training.     

Primates are an important food resource for leopards (Panthera pardus) in Mahale,Tanzania

Leopard diets in the Kasoje area of the Mahale Mountains National Park, Tanzania, were analysed by inspecting prey remains in 256 scats. This area is unique as leopard density is high despite a relatively low density of medium-sized ungulates, regarded as the most preferred prey of leopards. At least eleven prey mammal species were confirmed in the scats. Small prey mammals up to 10 kg comprised 91.4% of the relative biomass consumed; the mean prey biomass in each scat was 7.6 kg. Blue duiker (31.2%) was the most dominant prey species, followed by the red colobus (29.2%), semi-terrestrial Cercopithecinae (the vervet monkey and yellow baboon combined) (10.5%) and the red-tailed monkey (9.9%). At the order level, the most consumed prey taxon was Primates (53.8%), followed by Cetartiodactyla (39.6%) and Rodentia (5.8%). Among primates, the blue monkey was the most preferred prey species, followed by the red colobus and semi-terrestrial Cercopithecinae. High consumption of primates is a unique characteristic of the leopards in Mahale. This trend exemplifies the flexibility of leopards in their choices of prey, and such flexibility may be one of the underlying reasons for leopards exhibiting the broadest global distribution among all wild felid species.     

Informing management decisions for ecological networks,using dynamic models calibrated to noisy time‐series data

Well‐intentioned environmental management can backfire, causing unforeseen damage. To avoid this, managers and ecologists seek accurate predictions of the ecosystem‐wide impacts of interventions, given small and imprecise datasets, which is an incredibly difficult task. We generated and analysed thousands of ecosystem population time series to investigate whether fitted models can aid decision‐makers to select interventions. Using these time‐series data (sparse and noisy datasets drawn from deterministic Lotka‐Volterra systems with two to nine species, of known network structure), dynamic model forecasts of whether a species’ future population will be positively or negatively affected by rapid eradication of another species were correct > 70% of the time. Although 70% correct classifications is only slightly better than an uninformative prediction (50%), this classification accuracy can be feasibly improved by increasing monitoring accuracy and frequency. Our findings suggest that models may not need to produce well‐constrained predictions before they can inform decisions that improve environmental outcomes.     

Habitat preferences and habitat restoration options for small‐bodied and juvenile fish species in the northern Murray–Darling Basin

Degradation of instream habitats in the northern Murray–Darling Basin has occurred through numerous stressors, including siltation, clearing of bankside vegetation, intrusion of livestock and impacts of pest species. A better understanding of habitat preferences of native fish species could help guide future instream habitat restoration actions. The habitat choices of seven native fish species, juvenile Murray Cod (Maccullochella peelii), juvenile Golden Perch (Macquaria ambigua ambigua), juvenile Silver Perch (Bidyanus bidyanus), adult Murray–Darling Rainbowfish (Melanotaenia fluviatilis), adult Olive Perchlet (Ambassis agassizii), adult Un‐specked Hardyhead (Craterocephalus stercusmuscarum fulvus) and adult carp gudgeons (Hypseleotris spp.) were tested in preference troughs to help inform potential habitat restoration actions in the Condamine catchment. Each species was given a choice between pair combinations of open sandy habitat, submerged macrophytes, emergent plants and rocky rubble. Habitat preferences varied between species. Murray Cod, Golden Perch, carp gudgeons and Olive Perchlets preferred structure over open sandy habitat, whilst juvenile Silver Perch, Un‐specked Hardyhead and Murray–Darling Rainbowfish did not avoid open sandy habitats. Juvenile Murray Cod preferred rocky rubble habitat over all other habitat choices. Use of complex rock piles to provide nursery habitat for Murray Cod populations is a potential restoration option. Introduction of rock could also benefit Golden Perch and carp gudgeons. Use of emergent plants, submerged macrophytes and rocky rubble for habitat restoration all appear to have merit for one or more species of small‐bodied fishes or juvenile stages of larger sized fishes. Rocky rubble or floating attached macrophytes could be viable restoration options in areas too turbid to establish submerged macrophytes. These habitat interventions would complement existing actions such as re‐snagging and provision of fish passage to assist with sustainable management of native fish populations.     

Colony composition,queen behavior,specialized predation on millipedes,and exocrine glands in the ponerine ant Myopias conicara Xu, 1998 (Hymenoptera: Formicidae)

We collected a queenright colony of the very rare Myopias conicara Xu in Vietnam (1 dealate queen, 41 workers and 38 larvae). Both the queen and workers fed on xystodesmid millipedes. After paralyzing a millipede, its head was first removed by the workers, and then the larvae were put on the opening of the collum (anteriormost ring of the trunk). After the inner tissue of the collum was consumed, the exoskeleton of the collum was discarded. The feeding sequence was then repeated on the following rings of the trunk, until the entire prey was consumed. The ring‐shaped exoskeletons of the prey were deposited next to the nest entrance. The exocrine system of the workers (excluding the legs) contains 15 glands of which the structural features are similar to these of other ponerine ants. The presence of an oblong plate gland is interesting, as this gland had only been found previously in Myopias hollandi (Forel). However, none of the novel thoracic glands that were recently described in M. hollandi occur in M. conicara, which illustrates the variation within the genus Myopias. A unique characteristic of the class‐3 glands of Myopias ants is the gradual widening of the ducts, which has never been found in other insects, although the functional significance remains unknown.     

Differences in regional oceanography and prey biomass influence the presence of foraging odontocetes at two Atlantic seamounts

The importance of seamounts as foraging hotspots for cetaceans depends on interactions between ocean flow and topographical features that concentrate prey. However, the oceanographic processes driving these aggregations are still unclear. Here, we analyzed two months of passive acoustic recordings from two remote seamounts in the Northeast Atlantic, Atlantis and Irving, in relation to regional oceanography and estimates of prey biomass. Delphinids and sperm whales were detected in both seamounts with higher foraging activity at night, indicating feeding on diel migrating prey. There were more detections of delphinids and sperm whales at Atlantis than at Irving. These two seamounts lie in different oceanographic settings created by the Azores Current that separates colder and less saline water masses in the north (Atlantis seamount) from warmer and more saline waters in the south (Irving seamount). Irving seamount is only affected by transient features like eddies that enhance productivity for short time periods. These conditions translate into more productive waters at Atlantis seamount than at Irving, as shown by predicted prey biomasses that ultimately attract top predators. Comparative studies such as this one can help to explain the main drivers of presence of top predators at seamounts.     

The difference between generalist and specialist: the effects of wide fluctuations in main food abundance on numbers and reproduction of two co-existing predators

Specialist individuals within animal populations have shown to be more efficient foragers and/or to have higher reproductive success than generalist individuals, but interspecific reproductive consequences of the degree of diet specialisation in vertebrate predators have remained unstudied. Eurasian pygmy owls (hereafter POs) have less vole-specialised diets than Tengmalm's owls (TOs), both of which mainly subsist on temporally fluctuating food resources (voles). To test whether the specialist TO is more limited by the main prey abundance than the generalist PO, we studied breeding densities and reproductive traits of co-existing POs and TOs in central-western Finland during 2002–2019. Breeding densities of POs increased with augmenting densities of voles in the previous autumn, whereas breeding densities of TOs increased with higher vole densities in both the previous autumn and the current spring. In years of vole scarcity, PO females started egg-laying earlier than TOs, whereas in years of vole abundance TO females laid eggs substantially earlier than PO females. The yearly mean clutch size and number of fledglings produced of both POs and TOs increased with abundance of voles in the current spring. POs laid large clutches and produced large broods in years of both high and low vole abundance, whereas TOs were able to do so only in years of high vole abundance. POs were able to raise on average 73% of the eggs to fledglings whereas TOs only 44%. The generalist foraging strategy of POs including flexible switching from main prey to alternative prey (small birds) appeared to be more productive than the strictly vole-specialized foraging strategy of TOs. In contrast to earlier studies at the individual-level, specialist predators at the species level (in this case TOs) appear to be less effective than generalists (POs), but diet specialisation was particularly costly under conditions when scarcity of main foods limited offspring production.