Predictive Model of Habitat Suitability for the Marbled Murrelet in Western Washington

Abstract: The marbled murrelet (Brachyramphus marmoratus) is a small Pacific seabird with a breeding range that extends from the Aleutian Islands to central California. Throughout most of its breeding range, it uses mature and old-growth coniferous forests as nesting habitat. Although most murrelets seem to nest within 60 km of the coast, occupied nesting habitat has been identified as far as 84 km from the ocean in Washington state. Due to the extensive inland distances within which birds are known to breed, the area requiring surveys to identify breeding sites can be enormous. Therefore, the standard 2-year survey protocol can be expensive and time-consuming for forest management agencies and companies to administer. We developed a logistic regression model to determine whether a suite of forest structural characteristics could be used to reliably predict occupancy of a forest patch by marbled murrelets. We tested the performance of the final model using cross-validation procedures and a sample of independent sites. We used 50 sites surveyed for marbled murrelets to estimate the model, and 48 independent sites were available to test model performance. All 50 sites were on private forestland owned by Rayonier located in the western lowlands of Olympic Peninsula within the Sitka spruce and western hemlock transition zones. We sampled forest habitat at each site, and we collected information on 15 explanatory variables. The best-fitting logistic regression model contained variables that measured number of canopy layers (P<0.001, approx. F test) and mistletoe (Arceuthobium sp.) abundance (P = 0.031, approx. F test). The model misclassified 2 of 33 (94% correct) unoccupied sites as occupied using a classification cut-off (c) of c=0.25. In the other direction, under cross-validation the final model misclassified 2 of 17 (88% correct) occupied sites as unoccupied. On a test of the model against an independent sample, using a classification cut-off value of c = 0.25, the final model correctly classified 36 of 48 sites (75% correct). The final model misclassified 3 of 31 occupied sites as unoccupied (90% correct). Use of predictive models could greatly reduce the amount of forest that requires surveys by screening out those sites with little probability of use and by focusing remaining effort on higher probability sites, resulting in a higher likelihood of identifying occupied sites and thereby more efficiently conserving marbled murrelet nesting habitat.     

Abundance and Production of Riparian Trees in the Lowland Floodplain of the Queets River, Washington

Riparian zones associated with alluvial rivers are spatially dynamic, forming distinct vegetative mosaics that exhibit sharp contrasts in structure and processes related to the underlying biophysical template. The productivity of riparian plants, especially trees, influences streamside community characteristics as well as the forms and fluxes of organic matter to adjacent streams – thereby strongly impacting patterns of channel morphology, water flow, sedimentation, and habitat in rivers. As part of a comprehensive investigation of riparian dynamics in coastal rain forest rivers of the Pacific Northwest (USA), we examined riparian tree abundance (density, basal area, and biomass) and rates of production (basal area growth [BAI] and bole wood biomass increase [P]) of seven common species – red alder (Alnus rubra), Sitka spruce (Picea sitchensis), bigleaf maple (Acer macrophyllum), western hemlock (Tsuga heterophylla), black cottonwood (Populus trichocarpa), vine maple (Acer circinatum) and willow (Salix spp.) – in the lowland floodplain of the Queets River (Olympic National Park), Washington. Measurements were made annually for three years (1999 – 2001) in 16 permanent plots on three biophysical templates that formed a toposequence – active floodplain, young terrace and mature terrace. Stem density was highest in the active floodplain (∼27,000 stems/ ha), decreasing in the young terrace (∼2,700 stems /ha) and the mature terrace (∼500 stems/ha). Basal area and total stem biomass were lowest in the active floodplain (∼16 m2/ha and ∼18 Mg dry weight/ha, respectively) and higher on the young terrace (∼32 m2/ha and ∼134 Mg dry weight/ha) and on the mature terrace (∼69 m2/ha and ∼540 Mg dry weight /ha). Total plot-scale BAI was not significantly different among the physical templates with mean values ranging from approximately 1.4 (low terrace) to approximately 2.8 m2/ha/y (active floodplain). In contrast, P was significantly higher on the mature terrace (10.3 Mg/ha) than the active floodplain (3.2 Mg/ha) but there was no significant difference between young terrace (6.5 Mg/ha) and mature terrace. For the entire Queets River floodplain (57 km² over 77 km of river length), the mature terrace contributed 81% of the total annual production (28,764 Mg) whereas the active floodplain and young terrace accounted only for 5 and 14%, respectively. Overall, we show that riparian trees grow quickly in this coastal Pacific Northwest system and that the older riparian forests on mature terraces are the main contributors to stem production at the plot and floodplain scales for at least 350 years after stand initiation. This suggests that, in combination with the rapid lateral migrations of many alluvial rivers, the older riparian forests on those terraces are important and sustained sources of organic matter (especially large woody debris, LWD) that, over decades to centuries, shape the character of coastal rivers in the Pacific Northwest.     

Unusually high‐quality soil seed banks in a Midwestern U.S. oak savanna region: variation with land use history,habitat restoration,and soil properties

An overarching conclusion in the literature is that soil seed banks rarely contain many restoration‐target species and are often liabilities rather than assets to restoration. Our objective was to evaluate composition and spatial variation of seed banks and their potential contributions to restoration, including restoration‐target species such as rare species and those characterizing historical habitats. On 64 sites in a Midwestern U.S. oak savanna landscape, we sampled soil seed banks in seven habitat types (restored oak savannas, oak woodlands, and mesic prairies; unmanaged upland oak and mesic forests; and unmanaged and managed pine plantations). The germinable seed bank was exceptionally rich in restoration‐target species. In total for the 64 sites, seedlings of 127 species emerged from seed bank samples. Of the 101 native species, 56 were restoration‐target species, an unusually high number among seed bank studies. Restoration‐target species in seed banks included 13 threatened or endangered species, in addition to 43 other specialist species associated with high‐quality native habitats or on a floral list thought to characterize historical ecosystems. When analyzed across the 64‐site gradient, seed banks differed among the seven habitat types and varied with historical (1939) land use, recent management activities that restored open‐structured habitats, and biophysical gradients of tree density, soil drainage, and soil texture. While not all restoration‐target species were detected in the seed bank, the unusually high‐quality seed bank is a potential asset to restoration and was partly structured along environmental gradients across the landscape.     

Identifying a surrogate metric for monitoring the population status of a secretive habitat specialist,the heath skink Liopholis multiscutata,in south‐eastern Australia

Threatened species that exist in small isolated populations are vulnerable to extinction processes, so effectively monitoring the trajectory of such populations will help determine the most appropriate management actions to combat extinction threats. In this study, we aimed to track the population status of the fossorial heath skink Liopholis multiscutata that is listed as threatened in Victoria, south‐eastern Australia, and exists there as a few small and highly disjunct populations, by using an appropriate surrogate population monitoring metric. This secretive lizard is a habitat specialist, is highly localised in Victoria and lives in warrens in semi‐arid heathland or mallee on large dunes. Survey data, which included every warren and their constituent burrows, as well as an assessment of whether each burrow was ‘active’, were collected for the four known Victorian populations in 2007 and annually during 2014–2018 inclusive. We compared five population indices per monitoring site: number of active warrens (NAW), number of active burrows (NAB), population area for 80% of active warrens (PA80), percentage of warrens that were active (PAW) and average number of active burrows per active warren. The heath skink currently occurs in small populations (8–46 active warrens) and these populations have typically declined over recent years. NAW was the most robust metric; NAB and PA80 did not reveal strong temporal trends. PAW indicated that inactive warrens and burrows persist less than a year and hence may provide information about recent (within months) population changes. It is imperative to establish a material link between the effective monitoring of small, vulnerable populations and the implementation of management actions that benefit such populations. Here, NAW could be used as a long‐term monitoring tool to provide an estimate of the minimum population size of the heath skink at a site. Its use would also ensure continuity in monitoring approaches for the Victorian populations.     

Composition of mixed‐species flocks and shifts in foraging location of flocking species on Hainan Island,China

A total of 134 bird species were recorded at Jianfengling, Hainan Island, in China from May 2000 to September 2004, of which 44 participated in one or more of 134 mixed‐species flocks. These flocks averaged 3.8 ± 0.2 species and 20.3 ± 1.2 individuals. Flocking propensity in a given species ranged from 1.5 to 100%. For flocking species, frequency of flocking and number of individuals in flocks was positively correlated with frequency and number in point counts. Among all species pairs with flocking frequency above 5%, cluster and correlation analysis indicated there were two principal groups of flocking birds – canopy species and understorey species: associations were positive within a group, but negative between groups. Canopy birds had a higher flocking propensity than understorey birds. They also made significantly less use of inner branches and trunks and greater use of middle branches, and foraged at a significantly greater height when in mixed‐species flocks than when solitary. For understorey bird species, there were no significant differences in foraging locations between solitary and mixed‐species flocks. Higher flocking frequency occurred in the wet season for canopy birds, but in the dry season for understorey birds. Overall patterns were consistent with the explanation that flocking enables an expansion of foraging niche by reducing the risk of predation.     

Landscape context affects the success of habitat restoration: large‐scale colonization patterns of saproxylic and fire‐associated species in boreal forests

Aim Restoration of habitats may be used as a conservation tool when ecosystems have lost their natural structure, dynamics or functioning over large areas. Controlled and planned use of fire could be an effective way to restore habitats of many threatened species in boreal forests where fire suppression has been effective. We asked whether the large‐scale landscape context affects the occurrence of rare and threatened species in forest habitats that have been burned to restore their fire‐related structures. Location Boreal forests in southern Finland. Methods We designed a large‐scale field experiment that included nine Pinus sylvestris forests (5–10 ha each) in southern Finland. Sites were located in two regions: (1) in eastern region with shorter management history and (2) in western region where intensive forestry has continued longer. We evaluated whether restoration of dead/burned wood is beneficial for rare and conservation‐dependent species and measured the recovery of pyrophilous and red‐listed insects (beetles and flatbugs) in burned forests, using standardized sampling effort. Altogether, 956 individuals of 29 red‐listed and pyrophilous species were sampled. Results Rare species colonized areas quickly, but there was a clear difference in species richness between the regions. The eastern forests harboured higher species richness after restoration. In these sites, the average species richness was 13.7 species per site, whereas in western forests it was 5.0 species per site. Similar pattern was also observed in subgroups: the corresponding numbers for pyrophilous species were 9.7 vs. 3.8, for red‐listed 8.7 vs. 2.3 and for red‐listed pyrophiles 4.7 vs. 1.2. Main conclusions Introducing fire back to boreal forests can aid in the recovery of rare species, but the landscape context considerably affects the success of restoring species. If restored habitats are located in landscapes that have lost their natural properties long ago, the success of restoration seems to be more challenging than in landscapes where habitats have been modified more recently.     

Linking radial growth patterns and moderate‐severity disturbance dynamics in boreal old‐growth forests driven by recurrent insect outbreaks: A tale of opportunities,successes, and failures

In boreal landscapes, emphasis is currently placed on close‐to‐nature management strategies, which aim to maintain the biodiversity and ecosystem services related to old‐growth forests. The success of these strategies, however, depends on an accurate understanding of the dynamics within these forests. While moderate‐severity disturbances have recently been recognized as important drivers of boreal forests, little is known about their effects on stand structure and growth. This study therefore aimed to reconstruct the disturbance and postdisturbance dynamics in boreal old‐growth forests that are driven by recurrent moderate‐severity disturbances. We studied eight primary old‐growth forests in Québec, Canada, that have recorded recurrent and moderately severe spruce budworm (Choristoneura fumiferana [Clem.]) outbreaks over the 20th century. We applied an innovative dendrochronological approach based on the combined study of growth patterns and releases to reconstruct stand disturbance and postdisturbance dynamics. We identified nine growth patterns; they represented trees differing in age, size, and canopy layer. These patterns highlighted the ability of suppressed trees to rapidly fill gaps created by moderate‐severity disturbances through a single and significant increase in radial growth and height. Trees that are unable to attain the canopy following the disturbance tend to remain in the lower canopy layers, even if subsequent disturbances create new gaps. This combination of a low stand height typical of boreal forests, periodic disturbances, and rapid canopy closure often resulted in stands constituted mainly of dominant and codominant trees, similar to even‐aged forests. Overall, this study underscored the resistance of boreal old‐growth forests owing to their capacity to withstand repeated moderate‐severity disturbances. Moreover, the combined study of growth patterns and growth release demonstrated the efficacy of such an approach for improving the understanding of the fine‐scale dynamics of natural forests. The results of this research will thus help develop silvicultural practices that approximate the moderate‐severity disturbance dynamics observed in primary and old‐growth boreal forests.     

Length‐weight relationships of three freshwater fish species from the Nandu River and Changhua River in Hainan Island,China

Length‐weight relationships (LRWs) were determined for three fish species from the Hainan Island, China. Fish specimens were sampled across the Nandu River and Changhua River from May 2017 to June 2018 with benthic fyke‐nets (stretched mesh size: 0.4 cm), multi‐mesh gillnets (stretched mesh size ranging from 1.0 to 12.5 cm) and electrofishing. Relationships between length and weight were fitted very well for all species (all R²>0.95). The b values of the LRW equations ranging from 2.938 for Liniparhomaloptera qiongzhongensis to 3.259 for Toxabramis houdemeri.     

Spatially variable response of native fish assemblages to discharge,predators and habitat characteristics in an arid‐land river

1. Fish assemblages and habitats were sampled annually at fixed sites in three tributaries of the Gila River catchment over a 21‐year span that included prolonged low‐ and high‐flow periods. Model selection was used to evaluate responses of seven native fishes with variable ecological traits (four small‐bodied cyprinids, one large‐bodied cyprinid, and two large‐bodied catostomids) to mean annual discharge and predacious non‐native fishes across the three sites. We also compared habitat use and overlap of native and non‐native fishes to identify potential for negative interactions among species. 2. Assemblage structure (species abundance and richness) and recruitment of native species was strongly and primarily affected by mean annual discharge and secondarily by location and densities of non‐native predators (mainly the centrarchid Micropterus dolomieui). 3. Densities of age‐0 catostomids and small‐bodied cyprinids were positively associated with discharge, and this pattern was strongest in the tributary with the lowest densities of non‐native predators. Absence or extreme low abundance of natives during low‐flow years was most pronounced at the sites where non‐native predators were comparatively common. Densities of adults of large‐bodied native species also varied by site, but often were positively associated with densities of non‐native predators. 4. Spatially variable responses of native fish assemblages indicated that the persistence of native fishes could be jeopardized if key habitats were lost or flow regimes unnaturally altered, particularly during low‐flow conditions when recruitment of native fishes is low and predation by non‐natives is high. Large‐bodied species may be less vulnerable to multiple years of poor conditions because adults are able to avoid predation by non‐natives and thus can rely on occasional high discharge years for successful recruitment. 5. As in other arid‐land streams, native fish assemblages of the Gila River Basin continue to decline. Our results indicate that conservation requires specific knowledge and consideration of physical influences as well as life‐history attributes of native and non‐native fishes.     

Stand characteristics and biodiversity indicators along the productivity gradient in boreal forests: Defining a critical set of indicators for the monitoring of habitat nature quality

Abstract

We quantified the effects of anthropogenic disturbances on the structure and biodiversity of boreal forests on acidic soils and created a statistically supported rational set of indicators to monitor the stand “naturalness”. For that, we surveyed various traits of tree layer, understory, herb layer, forest floor and several widely accepted biodiversity epiphytic indicators in 252 old‐aged boreal stands in Estonia, mostly dominated by Scots pine or Norway spruce. Multifactorial general linear model analyses showed that many forest characteristics and potential indicators were confounded by the gradient of soil productivity (reflected by the forest site type), local biogeographic gradients and also by stand age. Considering confounding effects, boreal forests in a near‐natural state have more large‐diameter trees (diameter at breast height >40 cm) and larger variety of diameter classes, higher proportion of spruce or deciduous trees, a larger amount of coarse woody debris in various stages, a more closed tree canopy and denser understory than managed mature forests. By increasing light availability above the field layer, forest management indirectly increases the coverage of herbs and lichens on the forest floor but reduces the alpha‐ and beta‐diversity of herbs and the proportion of graminoids. Human disturbances reduce the relative incidence of many commonly accepted biodiversity indicators such as indicator lichens, woodpeckers, wood‐dwelling insects or fungi on trees. The test for the predictive power of characteristics reacting on disturbance revealed that only a fraction of them appeared to be included in a diagnostic easy‐to‐apply set of indicators to assess the nature quality of boreal forest: the amount of dead wood, the proportion of deciduous trees, the presence of specially shaped trees and woodpeckers and, as an indicator of disturbances, the forest herb Melampyrum pratensis. Many of these indicators have already been implemented in practice.     

Predicting the impacts of climate change on the distribution of threatened forest‐restricted birds in Madagascar

The greatest common threat to birds in Madagascar has historically been from anthropogenic deforestation. During recent decades, global climate change is now also regarded as a significant threat to biodiversity. This study uses Maximum Entropy species distribution modeling to explore how potential climate change could affect the distribution of 17 threatened forest endemic bird species, using a range of climate variables from the Hadley Center's HadCM3 climate change model, for IPCC scenario B2a, for 2050. We explore the importance of forest cover as a modeling variable and we test the use of pseudo‐presences drawn from extent of occurrence distributions. Inclusion of the forest cover variable improves the models and models derived from real‐presence data with forest layer are better predictors than those from pseudo‐presence data. Using real‐presence data, we analyzed the impacts of climate change on the distribution of nine species. We could not predict the impact of climate change on eight species because of low numbers of occurrences. All nine species were predicted to experience reductions in their total range areas, and their maximum modeled probabilities of occurrence. In general, species range and altitudinal contractions follow the reductive trend of the Maximum presence probability. Only two species (Tyto soumagnei and Newtonia fanovanae) are expected to expand their altitude range. These results indicate that future availability of suitable habitat at different elevations is likely to be critical for species persistence through climate change. Five species (Eutriorchis astur, Neodrepanis hypoxantha, Mesitornis unicolor, Euryceros prevostii, and Oriola bernieri) are probably the most vulnerable to climate change. Four of them (E. astur, M. unicolor, E. prevostii, and O. bernieri) were found vulnerable to the forest fragmentation during previous research. Combination of these two threats in the future could negatively affect these species in a drastic way. Climate change is expected to act differently on each species and it is important to incorporate complex ecological variables into species distribution models.     

Phylogeographic structure in long‐tailed voles (Rodentia: Arvicolinae) belies the complex Pleistocene history of isolation,divergence, and recolonization of Northwest North America's fauna

Quaternary climate fluctuations restructured biodiversity across North American high latitudes through repeated episodes of range contraction, population isolation and divergence, and subsequent expansion. Identifying how species responded to changing environmental conditions not only allows us to explore the mode and tempo of evolution in northern taxa, but also provides a basis for forecasting future biotic response across the highly variable topography of western North America. Using a multilocus approach under a Bayesian coalescent framework, we investigated the phylogeography of a wide‐ranging mammal, the long‐tailed vole, Microtus longicaudus. We focused on populations along the North Pacific Coast to refine our understanding of diversification by exploring the potentially compounding roles of multiple glacial refugia and more recent fragmentation of an extensive coastal archipelago. Through a combination of genetic data and species distribution models (SDMs), we found that historical climate variability influenced contemporary genetic structure, with multiple isolated locations of persistence (refugia) producing multiple divergent lineages (Beringian or northern, southeast Alaska or coastal, and southern or continental) during glacial advances. These vole lineages all occur along the North Pacific Coast where the confluence of numerous independent lineages in other species has produced overlapping zones of secondary contact, collectively a suture zone. Finally, we detected high levels of neoendemism due to complex island geography that developed in the last 10,000 years with the rising sea levels of the Holocene.     

Breeding ecology of Red‐faced Cormorants in the Pribilof Islands,Alaska

ABSTRACT Red‐faced Cormorants (Phalacrocorax urile) are North Pacific endemics recognized as a vulnerable species, but little is known about their breeding ecology. We studied Red‐faced Cormorants on St. Paul Island, Alaska, from 1975 to 2009, with more detailed data collected in 2004 and 2005. Mean clutch sizes in 2004 (3.2 ± 0.8 [SD] eggs) and 2005 (3.1 ± 0.8 eggs) were similar to the long‐term average (2.9 ± 0.3 eggs from 1976 to 2009). The mean laying interval in 2004 and 2005 was 2.15 ± 0.80 d (N= 407), and the mean egg period (number of days between laying of an egg and hatching) was 31.1 ± 1.4 d (N= 158). Approximately 64 ± 17% of eggs hatched during the period from 1975 to 2009. The mean number of chicks per nest in 2004 and 2005 was 2.8 ± 0.8 (N= 232), and the mean number of fledglings per initiated nest in all years was 1.22 ± 0.52. Chicks fledged 46 to 66 d posthatching. In 2004 and 2005, the primary causes of egg loss were predation by Arctic foxes (Vulpes lagopus) and destruction of eggs and abandonment of nests due to storms. Starvation was the primary cause of nestling mortality in both years. Because chicks are dependent on parents to provide food for over 45 d, consistent near‐shore foraging opportunities must be available. From 1975 to 2009, Red‐faced Cormorants experienced only 1 yr of complete reproductive failure (1984). The consistent reproductive success of Red‐faced Cormorants suggests that conditions may be relatively stable for this species on St. Paul Island, or that the variability in their breeding ecology (e.g., phenology, clutch sizes, and incubation strategies) provides the flexibility needed to successfully fledge some chicks nearly every year.     

Canopy disturbance and gap partitioning promote the persistence of a pioneer tree population in a near‐climax temperate forest of the Qinling Mountains,China

An unresolved question of temperate forests is how pioneer tree species persist in mature forests. In order to understand the responsible mechanisms, we investigated a near‐climax mixed temperate forest dominated by Betula albosinensis in the Qinling Mountains of China. Through establishing four 50 m × 50 m plots, we examined the canopy disturbance characteristics and its effects on tree recruitments. We further test the intra‐ and interspecific effects on the recruitment of B. albosinensis. The obtained data demonstrated canopy disturbance was frequent but most small‐sized. The canopy gaps are caused mainly by adult B. albosinensis by snapping. The regeneration of coexistent tree species shows a distinct preference for gap size. B. albosinensis were clumped at the juvenile stage and small scales. B. albosinensis juveniles were positively associated with B. utilis juveniles and negatively associated with the conspecific and B. utilis large trees. In addition, B. albosinensis juveniles showed negative associations with contemporary other tree species. Our results suggested that canopy disturbance caused by canopy trees and gap partitioning among the coexistent tree species are important for the persistence of the mixed forest. As a main gapmaker, B. albosinensis appear to develop a self‐perpetuating life‐history trait and allow them to persist.     

Changing gull diet in a changing world: A 150‐year stable isotope (δ13C, δ15N) record from feathers collected in the Pacific Northwest of North America

The world's oceans have undergone significant ecological changes following European colonial expansion and associated industrialization. Seabirds are useful indicators of marine food web structure and can be used to track multidecadal environmental change, potentially reflecting long‐term human impacts. We used stable isotope (δ¹³C, δ¹⁵N) analysis of feathers from glaucous‐winged gulls (Larus glaucescens) in a heavily disturbed region of the northeast Pacific to ask whether diets of this generalist forager changed in response to shifts in food availability over 150 years, and whether any detected change might explain long‐term trends in gull abundance. Sampled feathers came from birds collected between 1860 and 2009 at nesting colonies in the Salish Sea, a transboundary marine system adjacent to Washington, USA and British Columbia, Canada. To determine whether temporal trends in stable isotope ratios might simply reflect changes to baseline environmental values, we also analysed muscle tissue from forage fishes collected in the same region over a multidecadal timeframe. Values of δ¹³C and δ¹⁵N declined since 1860 in both subadult and adult gulls (δ¹³C, ~ 2–6‰; δ¹⁵N, ~4–5‰), indicating that their diet has become less marine over time, and that birds now feed at a lower trophic level than previously. Conversely, forage fish δ¹³C and δ¹⁵N values showed no trends, supporting our conclusion that gull feather values were indicative of declines in marine food availability rather than of baseline environmental change. Gradual declines in feather isotope values are consistent with trends predicted had gulls consumed less fish over time, but were equivocal with respect to whether gulls had switched to a more garbage‐based diet, or one comprising marine invertebrates. Nevertheless, our results suggest a long‐term decrease in diet quality linked to declining fish abundance or other anthropogenic influences, and may help to explain regional population declines in this species and other piscivores.     

Recent status and life history traits of endangered soft‐mouth trout,Salmo obtusirostris in the River Neretva catchment (Bosnia and Herzegovina) as a consequence of river alteration

Soft‐mouth trout, Salmo obtusirostris has disappeared from most of its historical distribution range in the River Neretva catchment. Remnant groups are highly fragmented and distribution of the species is restricted to only 15% of it's historical area. The most abundant length range of remnant individuals is between 20 and 40 cm; with a significant decrease of the bigger individuals. Age population structure is dominated by younger fish aged 2, 3 and 4 years, however, age class 4⁺ and 6⁺ predominated in the lower river part. Specimens older than 8 years were not observed, and estimated fishing mortality (F) was high, particularly in the upper part of the river (0.786). The River Neretva soft‐mouth trout population is under heavy pressure including anthropogenic habitat changes and illegal fishery, leading to disappearance in number of formerly inhabited areas. The Upper and Lower Neretva are the only areas where the species is still abundant. However, the collapse of the number of old individuals increases the risk of extinction of the remaining wild subpopulations.