scholarly journals Risks to Fish Populations in Dryland Rivers From the Combined Threats of Drought and Instream Barriers

2021 ◽  
Vol 9 ◽  
Author(s):  
Jonathan C. Marshall ◽  
Jaye S. Lobegeiger ◽  
Alisa Starkey
Keyword(s):  
Drought Resistance ◽  
Fish Population ◽  
Fish Populations ◽  
Mitigation Measures ◽  
Fish Movement ◽  
Channel Network ◽  
Murray Darling Basin ◽  
Flow Intermittency ◽  
Almost All ◽  
Dryland Rivers

In dryland rivers, flow intermittency means fish populations are often subjected to drought disturbance. The viability of these fish populations depends on the availability of waterhole refuges for individuals to survive drought (resistance) and the ability of surviving fish to repopulate the rivers by recruitment and dispersal once flow returns (resilience). In this study we combined remote-sensed mapping of the locations of waterholes that lasted through an extreme drought in the northern Murray Darling Basin, Australia, with an assessment of the impacts of in-stream barriers on limiting the opportunities for fish to move and repopulate after drought. We found that at the peak of this 2018–2020 drought, the worst on record for some rivers and the most spatially synchronous recorded across the region, waterholes were few and generally small – representing only 11% of the total river channel network. All the fish in the region that survived the drought were concentrated into this limited waterhole refuge habitat. Even small instream structures, such as minor weirs, caused large reductions in the opportunities for fish to move between river segments when there is flow. Almost all the 104 instream structures assessed reduced long-term fish movement opportunities, measured as days with discharge greater than calculated barrier drown out thresholds, by more than 70% and up to 100%, when compared to opportunities for movement if the barrier was not present. This large impact from small instream barriers is a consequence of flow intermittency and is likely to reduce fish population resilience and impact the capacity of fish populations to recover after drought. Combining information on the risks posed by limited refuge habitat availability during drought and from reduced movement opportunity following drought allowed us to identify river segments where these combined threats are the greatest risk to viability of local fish populations. Considering the spatial arrangements of these risks provides a means to systematically prioritize mitigation measures such as weir removal to improve fish movement opportunities and local management of key waterholes to increase drought resistance. The approach used here provides a guide for assessing and prioritizing the management of fish population viability risks from drought and fragmentation by barriers in any non-perennial river setting.

Freshwater, Fish and the Future: Proceedings of the Global Cross-Sectoral Conference

2016 ◽  
Keyword(s):  
Fish Populations ◽  
Native Fish ◽  
Partnership Model ◽  
European Settlement ◽  
Southeastern Australia ◽  
Murray Darling Basin ◽  
Wide Range ◽  
Funding Opportunities ◽  
Funding Cuts

<em>Abstract</em> .—The Murray–Darling basin (MDB) in southeastern Australia, covers 1.1 million km<sup>2</sup>, involves six partner jurisdictions with a myriad of different government agencies, and, hence, provides an excellent example of the complexities of multijurisdictional management across a range of social and political tiers. In the MDB, fish and fisheries compete for water with agriculture, which is the traditional water user and is driven by national economics. Murray–Darling basin rivers are now highly regulated and generally in poor health, with native fish populations estimated to be at only about 10% of their pre-European settlement abundances. All native commercial fisheries are now closed, and the only harvest is by a recreational fishery. The six partner jurisdictions developed a Native Fish Strategy (NFS) to rehabilitate native fish populations to 60% of pre-European settlement levels after 50 years of implementation by addressing priority threats through a coordinated, long-term, whole-of-fish-community (all native fishes) approach. As there are a wide range of stakeholders, broad engagement was needed at a broad range of government and community levels. The NFS funding was discontinued after 10 years, not because of its lack of successes or project governance, but due to jurisdictional political changes and funding cuts that resulted in a failure of the collaborative funding structure. The withdrawal of considerable funding by one jurisdiction led to collective decline in monetary contributions and posed a threat to the multijurisdictional structures for both water and natural resource management (NRM) within the MDB. As a consequence, there was a review and reduction in NRM programs and a subsequent reduction in focus to the core business of water delivery. Reflection on the NFS, however, provides some useful insights as to the successes (many) and failures (funding) of this partnership model. Overall, the strategy and its structure was effective, as exhibited by an audit of outputs, outcomes, and networks; by the evident ongoing advocacy by NRM practitioners and the community; and by the continuation of ideas under other funding opportunities. This has provided a powerful legacy for future management of fishes in the MDB.

STRUCTURE OF FISH POPULATION OF THE BAIDARATAYAHA RIVER'S BASIN

2017 ◽  
pp. 33-44 ◽  
Author(s):  
Vladimir Dmitrievich Bogdanov ◽  
Elena Nikolaevna Bogdanova ◽  
Yan Albertovich Kizhevatov ◽  
Irina Pavlovna Melnichenko
Keyword(s):  
Species Diversity ◽  
Pink Salmon ◽  
Fish Population ◽  
Kara Sea ◽  
Arctic Char ◽  
The Other ◽  
Fish Populations ◽  
Deep Lakes ◽  
First Time ◽  
Fish Productivity

The data of studies of fish populations in the basin of the Baidaratayakha river, received in 1998, 2002, 2013, 2014 are summarized for the first time. 18 species of fish are noted. Most of them belong to commercial and valuable species. The greatest species diversity is characteristic of the lower reaches of the river. In deep lakes and sections of the river near these lakes the density of fishes is higher. Scantiness of the fish population of river sites is due to the fact that most of the riverbeds in winter freeze. For this reason, there is no common minnow in the rivers. In most of the tundra non-riverine lakes that dominate among the waterbodies of the basin, there are no fish due to their shallow water and freezing. Some lakes of the lower reaches of the Baidaratayakha river are inhabited by fish only in summer (Asian smelt for breeding and whitefish for feeding). In some lakes, residential groupings (whitefish and pike) are formed. The estuary is used for feeding of whitefish from the Yuribey river and migrants from various regions of the Kara Sea (Arctic char, pink salmon, omul). The omul remains for the wintering in the estuary, most of the other whitefish return to the Yuribey river. The number of populations of residential forms of fish in most lakes is low due to low fish productivity and poaching. To preserve the resources of valuable fish species, it is proposed to include into the existing reserve Gornohadatinsky section of the upper and middle course of the Baidaratayakha river, where there are lakes that provide a reserve of grayling, and spawning grounds for the reproduction of arctic char and pink salmon.

scholarly journals Evolutionary response to size-selective mortality in an exploited fish population

2007 ◽  
Vol 274 (1613) ◽  
pp. 1015-1022 ◽  
Author(s):  
Douglas P Swain ◽  
Alan F Sinclair ◽  
J Mark Hanson
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Fish Population ◽  
Fish Populations ◽  
Selective Mortality ◽  
Genetic Changes ◽  
Evolutionary Response ◽  
In The Wild ◽  
Size At Age ◽  
Change In Mean

Many collapsed fish populations have failed to recover after a decade or more with little fishing. This may reflect evolutionary change in response to the highly selective mortality imposed by fisheries. Recent experimental work has demonstrated a rapid genetic change in growth rate in response to size-selective harvesting of laboratory fish populations. Here, we use a 30-year time-series of back-calculated lengths-at-age to test for a genetic response to size-selective mortality in the wild in a heavily exploited population of Atlantic cod ( Gadus morhua ). Controlling for the effects of density- and temperature-dependent growth, the change in mean length of 4-year-old cod between offspring and their parental cohorts was positively correlated with the estimated selection differential experienced by the parental cohorts between this age and spawning. This result supports the hypothesis that there have been genetic changes in growth in this population in response to size-selective fishing. Such changes may account for the continued small size-at-age in this population despite good conditions for growth and little fishing for over a decade. This study highlights the need for management regimes that take into account the evolutionary consequences of fishing.

The monitoring of biological effects: the separation of natural changes from those induced by pollution

1979 ◽  
Vol 286 (1015) ◽  
pp. 597-609 ◽  
Keyword(s):  
Biological Effects ◽  
Total Mortality ◽  
Fish Population ◽  
Maximum Sustainable Yield ◽  
The Self ◽  
Fish Populations ◽  
Sustainable Yield ◽  
Density Dependent Mortality ◽  
Unknown Risk ◽  
Dependent Mortality

An added mortality rate of eggs, larvae and juveniles of fish populations, or impact, is assumed to be density independent. The total mortality from hatching to recruitment is represented by the fecundity, and any increment in density independent mortality implies a decrement in density dependent mortality. At high stock the consequence is an increase in stock towards a position of less resilience: at low stock less resilience is found with a decrease in stock. In general impact generates a shift of K -strategy, the self-stabilizing strategy, to r -strategy, an opportunistic one. In a fish population very little impact should be tolerated at low stock because it would prevent recovery to a management objective such as maximum sustainable yield. At high stock, impact may generate more stock at an unknown risk.

scholarly journals Climate Variability, Fish, and Fisheries

2006 ◽  
Vol 19 (20) ◽  
pp. 5009-5030 ◽  
Author(s):  
P. Lehodey ◽  
J. Alheit ◽  
M. Barange ◽  
T. Baumgartner ◽  
G. Beaugrand ◽  
...  
Keyword(s):  
Climate Variability ◽  
Time Scales ◽  
Large Scale ◽  
Southern Oscillation ◽  
Low Frequency ◽  
Fish Population ◽  
Marine Ecology ◽  
Fish Populations ◽  
Global Ocean ◽  
Close Link

Abstract Fish population variability and fisheries activities are closely linked to weather and climate dynamics. While weather at sea directly affects fishing, environmental variability determines the distribution, migration, and abundance of fish. Fishery science grew up during the last century by integrating knowledge from oceanography, fish biology, marine ecology, and fish population dynamics, largely focused on the great Northern Hemisphere fisheries. During this period, understanding and explaining interannual fish recruitment variability became a major focus for fisheries oceanographers. Yet, the close link between climate and fisheries is best illustrated by the effect of “unexpected” events—that is, nonseasonal, and sometimes catastrophic—on fish exploitation, such as those associated with the El Niño–Southern Oscillation (ENSO). The observation that fish populations fluctuate at decadal time scales and show patterns of synchrony while being geographically separated drew attention to oceanographic processes driven by low-frequency signals, as reflected by indices tracking large-scale climate patterns such as the Pacific decadal oscillation (PDO) and the North Atlantic Oscillation (NAO). This low-frequency variability was first observed in catch fluctuations of small pelagic fish (anchovies and sardines), but similar effects soon emerged for larger fish such as salmon, various groundfish species, and some tuna species. Today, the availability of long time series of observations combined with major scientific advances in sampling and modeling the oceans’ ecosystems allows fisheries science to investigate processes generating variability in abundance, distribution, and dynamics of fish species at daily, decadal, and even centennial scales. These studies are central to the research program of Global Ocean Ecosystems Dynamics (GLOBEC). This review presents examples of relationships between climate variability and fisheries at these different time scales for species covering various marine ecosystems ranging from equatorial to subarctic regions. Some of the known mechanisms linking climate variability and exploited fish populations are described, as well as some leading hypotheses, and their implications for their management and for the modeling of their dynamics. It is concluded with recommendations for collaborative work between climatologists, oceanographers, and fisheries scientists to resolve some of the outstanding problems in the development of sustainable fisheries.

Fish movement patterns in a Neotropical free-flowing tributary located downstream from a large dam

2018 ◽  
Vol 69 (10) ◽  
pp. 1626 ◽  
Author(s):  
Ruanny Casarim ◽  
Ivo Gavião Prado ◽  
Raquel Coelho Loures ◽  
Paulo Santos Pompeu
Keyword(s):  
Fish Movement ◽  
Migration Route ◽  
Negative Effects ◽  
Main River ◽  
Active Fish ◽  
Samples And Sampling ◽  
Almost All ◽  
Large Dam ◽  
Dammed River ◽  
Reproductive Migration

In dammed rivers, the conservation of free-flowing tributaries is considered an important strategy to mitigate the negative effects of the dam on fish communities. In this study, we evaluated the importance of a free-flowing tributary of a dammed river as a reproductive migration route. From August 2012 to July 2013, hydroacoustics data were collected alongside active fish sampling using cast nets and ichthyoplankton nets in the São Francisco and Abaeté rivers. Cast net sampling captured 738 individuals and hydroacoustics detected 42196 fishes. In almost all samples and sampling sites, preferential movements to the Abaeté River and the main São Francisco River were observed. The increase in the flow rate of the Abaeté coincided with a greater incidence of fish movements to upstream areas of the tributary. A higher density and proportion of larger fishes, as well as a higher density of ichthyoplankton, were observed in the Abaeté River compared with the main river. Because this tributary is an alternative route for migratory fishes, its protection is essential for fish conservation and therefore maintenance of local fisheries

scholarly journals Landscape-scale social and ecological outcomes of dynamic angler and fish behaviours: processes, data, and patterns

2019 ◽  
Vol 76 (6) ◽  
pp. 970-988 ◽  
Author(s):  
Thomas R. Carruthers ◽  
Kornelia Dabrowska ◽  
Wolfgang Haider ◽  
Eric A. Parkinson ◽  
Divya A. Varkey ◽  
...  
Keyword(s):  
Fish Population ◽  
Landscape Scale ◽  
Fish Populations ◽  
Current Management ◽  
Social Ecological ◽  
Recreational Fishery ◽  
Spatial Redistribution ◽  
Behavioural Interactions ◽  
Management Policies ◽  
Lake Fisheries

The first relatively complete landscape-scale social–ecological system (SES) model of a recreational fishery was developed and ground-truthed with independent angling effort data. Based on the British Columbia multistock recreational fishery for rainbow trout (Oncorynchus mykiss), the model includes hundreds of individual lake fisheries, hundreds of thousands of anglers, originating from tens of communities, connected by complex road and trail networks, all distributed over a landscape of approximately half a million square kilometres. The approach is unique in that it incorporates realistic and empirically derived behavioural interactions within and among the three key components of the SES: angler communities, fish populations, and management policies. Current management policies were characterized and alternate policies assessed by simulation. We examined spatial patterns in ecological and social properties of the SES and used simulations to investigate the impacts of alternate management policies on these patterns. Simulation outcomes strongly depended on the spatial redistribution of anglers across the landscape, existing road networks, heterogeneity in angler behaviours, and the spatial pattern of fish population productivity.

scholarly journals Alien pathogens and parasites impacting native freshwater fish of southern Australia: a scientific and historical review

2020 ◽  
Author(s):  
Simon Kaminskas
Keyword(s):  
Freshwater Fish ◽  
Fish Species ◽  
Fish Populations ◽  
Native Fish ◽  
Freshwater Species ◽  
Trade Offs ◽  
Murray Darling Basin ◽  
General Decline ◽  
Alien Fish ◽  
The Impact

ABSTRACT Native freshwater fish of Australia have a diverse but largely undescribed endemic pathogen and parasite fauna. However, due to long-shared evolutionary histories and virulence/transmissibility trade-offs, effects of these endemic pathogens and parasites appear to be subtle: significant impacts are rarely observed and epizootics have not been recorded. In contrast, a number of alien pathogens and parasites are now established across southern Australia, causing manifestly harmful effects to native fish species and known or suspected epizootics in native fish populations. Undetected and/or undescribed alien viral pathogens are also suspected of being present. Alien pathogens and parasites were introduced to Australia with imports of live alien fish or their fertilised eggs. A review of the scientific and historical evidence indicates that they have had, and continue to have, greater impacts on native fish species than previously realised—especially for freshwater species. This review also documents a previously unknown, Murray-Darling-Basin-wide epizootic of Murray cod Maccullochella peelii in 1929–30, which may have contributed to strong declines in the related eastern freshwater cod Maccullochella ikei. A serious Chilodonella epizootic of M. peelii in 1982 is also examined. In addition, a possible role for alien viruses of the family Iridoviridae (Ranavirus and Megalocytivirus) in the general decline of the critically endangered silver perch Bidyanus bidyanus, and the rapid collapse of two specific native fish populations—upper Murrumbidgee River B. bidyanus and Shoalhaven River Macquarie perch Macquaria australasica—is suggested. It is argued that the severity of the impact of the virulent alien oomycete Saprolegnia parasitica, both historical and present day, has been underestimated. Finally, action is recommended against emerging new pathogen and parasite threats, and the extreme risk current alien fish importations pose in introducing them. These will further threaten already stressed native fish populations in southern Australia, particularly across the Murray-Darling Basin.

Hydrology and water temperature influence recruitment dynamics of the threatened silver perch Bidyanus bidyanus in a regulated lowland river

2019 ◽  
Vol 70 (9) ◽  
pp. 1333 ◽  
Author(s):  
Zeb Tonkin ◽  
Ivor Stuart ◽  
Adrian Kitchingman ◽  
Jason D. Thiem ◽  
Brenton Zampatti ◽  
...  
Keyword(s):  
Juvenile Fish ◽  
High Water ◽  
River Regulation ◽  
Fish Populations ◽  
Extrinsic Factors ◽  
Spawning Period ◽  
Murray Darling Basin ◽  
Class Strength ◽  
Age Structured ◽  
Key Aspects

Understanding the influence of extrinsic factors such as hydrology and hydraulics on recruitment provides essential insight to inform management of fish populations. The critically endangered silver perch Bidyanus bidyanus is a long-lived, potamodromous pelagophil endemic to Australia’s Murray–Darling Basin. Declines of this species are often attributed to river regulation, although quantitative studies linking hydrology and hydraulics to key aspects of its life cycle are sparse. We used a multidecadal age-structured dataset collected from a locally abundant population of silver perch to quantify the relative importance of different abiotic drivers on year-class strength (recruitment). Silver perch recruited across highly variable hydrological conditions. The strongest year classes were associated with a combination of low to average river discharge (i.e. within channel) and high water temperatures over the peak spawning period, followed in the next year by extended high flows and widespread flooding that promoted survival of age-1+ juvenile fish. We suggest that conditions affecting the growth and dispersal of juvenile fish, in addition to the spawning period, are critical in governing recruitment dynamics. This highlights the need for multiyear flow plans for freshwater fish populations.

Spatial structuring within a reservoir fish population: implications for management

2015 ◽  
Vol 66 (3) ◽  
pp. 202 ◽  
Author(s):  
David R. Stewart ◽  
James M. Long ◽  
Daniel E. Shoup
Keyword(s):  
Environmental Gradients ◽  
Additive Model ◽  
Fish Population ◽  
Fishing Effort ◽  
Fish Populations ◽  
Older Individuals ◽  
Population Modelling ◽  
White Crappie ◽  
Spatial Structuring ◽  
Unprotected Area

Spatial structuring in reservoir fish populations can exist because of environmental gradients, species-specific behaviour, or even localised fishing effort. The present study investigated whether white crappie exhibited evidence of improved population structure where the northern more productive half of a lake is closed to fishing to provide waterfowl hunting opportunities. Population response to angling was modelled for each substock of white crappie (north (protected) and south (unprotected) areas), the entire lake (single-stock model) and by combining simulations of the two independent substock models (additive model). White crappie in the protected area were more abundant, consisting of larger, older individuals, and exhibited a lower total annual mortality rate than in the unprotected area. Population modelling found that fishing mortality rates between 0.1 and 0.3 resulted in sustainable populations (spawning potential ratios (SPR) >0.30). The population in the unprotected area appeared to be more resilient (SPR>0.30) at the higher fishing intensities (0.35–0.55). Considered additively, the whole-lake fishery appeared more resilient than when modelled as a single-panmictic stock. These results provided evidence of spatial structuring in reservoir fish populations, and we recommend model assessments used to guide management decisions should consider those spatial differences in other populations where they exist.

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