Anadromous Fish Species Research Articles

Identification and typing of fish pathogenic species of the genus Tenacibaculum.

Tenacibaculosis is a major bacterial disease that causes severe fish outbreaks and losses and limits the culture of a variety of commercially valuable anadromous and marine fish species in Europe, America, Asia and Oceania. Fish affected by tenacibaculosis have external lesions and necrosis that affect different areas of the body surface, reducing their commercial value. Several species of Tenacibaculum have been identified as the causal agent of tenacibaculosis in fish, including Tenacibaculum maritimum, Tenacibaculum soleae, Tenacibaculum discolor, Tenacibaculum gallaicum, Tenacibaculum dicentrarchi and "Tenacibaculum finnmarkense" (quotations marks denote species that have not been validly published). Diagnosis of tenacibaculosis is usually based on culture-dependent detection and identification techniques which are time-consuming and do not allow to differentiate closely related species. The development of reliable techniques for studying the relationships between members of the genus Tenacibaculum and for distinguishing fish-pathogenic species of Tenacibaculum genus is, therefore, a key step in understanding the diversity and incidence of tenacibaculosis in global aquaculture, designing effective prevention strategies and early implementation of infection control measures. In this review, recent advances in molecular, serological, proteomic and chemotaxonomic techniques developed for the identification and differentiation of Tenacibaculum species, as well as for the analysis of their genetic and epidemiological relationships are discussed. Key features of current diagnostic methods likely to facilitate control and prevention of tenacibaculosis and to avoid the spread of its aetiological agents are also outlined.

Biology and fisheries of Hilsa shad in Bay of Bengal

Hilsa (Tenualosa ilisha) or river shad is an anadromous fish species widely distributed in the North Indian Ocean, mainly in the Bay of Bengal (BoB). Hilsa is the national fish of Bangladesh and it contributes 10% of the total fish production of the country, with a market value of $1.74 billion. Hilsa also holds a very important place in the economics of West Bengal of India with 12.5% of the catch and also tops the marine capture in Myanmar. During the last two decades Hilsa production from inland waters has been stable, whereas marine yields in the BoB increased substantially. In order to sustainably manage the trans-boundary stock of Hilsa, the taxonomy, distribution, habitat, migration patterns, population dynamics, fisheries and socio-economics aspects of the fishery have been reviewed here. To achieve a successful trans-boundary management for the Hilsa stock, complete ban on undersize fishing, well-targeted temporal and spatial bans, creation of protected areas in strategic points, incentive for Hilsa fishers and ecological restoration of Hilsa habitats and more work on technological development of Hilsa aquaculture are recommended.

Comparative transcriptomics analysis of the river pufferfish (Takifugu obscurus) by tributyltin exposure: Clues for revealing its toxic injury mechanism

TBT residual in water had become a noticeable ecological problem for aquatic ecosystems. The river pufferfish (Takifugu obscurus) is a kind of an anadromous fish species and widely distributed in the East China Sea and the Yellow Sea. Because of the water contamination, the pufferfish wild resource had a sudden decline in recent years. Therefore, the study on the response of pufferfish to the TBT exposure may contribute to reveal toxic injury mechanism of T. obscurus under TBT exposure. In this study, the transcriptional library of T. obscurus liver and gill was constructed and sequenced by an improved Illumina HiseqX10 high-throughput sequencing platform under different concentrations of TBT acute stress. The blood cell numbers distinctly decreased after TBT exposure, showing the adverse effects of TBT invasion and self-adjusting ability of the pufferfish. The production of reactive oxygen species increased, demonstrating the oxidation resistance of T. obscurus when exposed to TBT. The obtained data were compared with the genome data of Takifugu rubripes and transcriptional resource database. On this basis, gene function annotation, analysis and classification were carried out by bioinformatics method, and differential genes related to toxic injury function were screened out. Meanwhile, new toxic related genes and related signal pathways were sought to provide new theoretical guidance for the pathogenesis of T. obscurus exposed to TBT. This study not only enriched the transcriptome data of T. obscurus under environmental stress, but also provided a new research method for the response mechanism of T. obscurus under the stimulation of environmental factors.

Long-term effect of a tidal, hydroelectric propeller turbine on the populations of three anadromous fish species.

Tidal hydroelectric power has been proposed as one potential solution for sustainable energy sources. The first tidal turbine in North America began continuous operation in the Annapolis River estuary (44 °45'N; 65° 29'W) in June, 1985. The machine is an axial-flow, hydraulic-lift propeller turbine, a type known to cause fish mortality. Anadromous populations of American shad Alosa sapidissima, striped bass Morone saxatilis and Atlantic sturgeon Acipenser oxyrinchus utilize the Annapolis River for spawning and other life history phases. After power generation commenced obvious turbine mortalities of these fishes began appearing downstream of the turbine. Assessments of the A. sapidissima adult spawning runs during 1981-1982 (pre-operation) and 1989-1996 (operational) indicated significant changes in population characteristics after power generation began. Adult length, mass, age and per cent repeat spawners declined and total instantaneous mortality (Z) increased from 0.30 to 0.55. The pre-turbine spawning runs had older fish with numerous adult cohorts whereas by 12 years after operation began runs consisted of younger fish with fewer adult cohorts. During 1972-1987 numerous studies indicated the Annapolis River had an important angling fishery for M. saxatilis, but detailed annual records kept by a fishing contest during 1983-1987 and an elite angler family during the period 1976-2008 demonstrated a rapid decline in the number of fish >4.0 kg after turbine operation began. Pre-turbine catch by the angling family of fish >4.0 kg accounted for 84.1% of total catch, but declined significantly to 39.6% of total catch from 1986-1999, and to none from 2000-2008. The existence of an A. oxyrinchus stock in the Annapolis River was unknown before turbine operation, but during 1985-2017, 21 mortalities were recovered by chance seaward of the turbine. Mechanical strike and cavitation mortalities consisted of juveniles, mature males and gravid and spent females of ages 10 to 53 years found during June to October, the period when this anadromous species returns to its natal river to spawn. The results of the long-term studies at Annapolis indicate managers should realize substantial risks exist for the fish resources of the world's oceans from deployment of instream propeller turbines.

Species composition and habitat preferences of the nearshore fish fauna of Bonne Bay, Newfoundland

BackgroundDetermining biodiversity baseline is the first step toward establishing species monitoring and conservation programs. In this study we report on a 10-year survey of the fish fauna of Bonne Bay, a fjord surrounded by the Gros Morne National Park on the west coast of Newfoundland, Canada. The objectives of our study were: 1) to determine the fish fauna of Bonne Bay using standardized sampling methods; 2) to gather information on the habitats of fishes of conservation concern; and 3) to provide baseline information on Bonne Bay as a potential candidate for a National Marine Conservation Area (NMCA).MethodsA survey of the fish fauna of the inner Bonne Bay was conducted each summer from 2002 to 2011 at multiple sites representing a range of fish habitats within the fjord. Sampling gears included two types of beach seine, gillnets with various mesh sizes and a bottom trawl. Species composition was statistically compared across sites within the fjord.ResultsWe collected and identified 29 fish species from 17 families. Fish assemblages comprised anadromous, estuarine, and marine fish species, including a late-maturing type of winter skate (Leucoraja ocellata) that is rarely found in the adjacent waters of the northern Gulf of St. Lawrence. Similarity in species composition across sites reflected salinity, substrate composition, and presence of eelgrass (Zostera marina), but not the geographic distance between sites.ConclusionsBonne Bay’s adjacency to a United Nations Educational, Scientific, and Cultural Organization (UNESCO) World Heritage Site, its diverse fish fauna that includes several species of conservation concern, its potential for education and enjoyment, and its stewardship by local people are suggestive of the future candidacy as a NMCA. The data presented here will help managers assess the potential of Bonne Bay as a National Marine Conservation Area.

Evaluating the potential for prezygotic isolation and hybridization between landlocked and anadromous alewife (Alosa pseudoharengus) following secondary contact.

The recent increase in river restoration projects is altering habitat connectivity for many aquatic species, increasing the chance that previously isolated populations will come into secondary contact. Anadromous and landlocked alewife (Alosa pseudoharengus) are currently undergoing secondary contact as a result of a fishway installation at Rogers Lake in Old Lyme, Connecticut. To determine the degree of prezygotic isolation and potential for hybridization between alewife life history forms, we constructed spawning time distributions for two anadromous and three landlocked alewife populations using otolith‐derived age estimates. In addition, we analyzed long‐term data from anadromous alewife migratory spawning runs to look for trends in arrival date and spawning time. Our results indicated that anadromous alewife spawned earlier and over a shorter duration than landlocked alewife, but 3%–13% of landlocked alewife spawning overlapped with the anadromous alewife spawning period. The degree of spawning time overlap was primarily driven by annual and population‐level variation in the timing of spawning by landlocked alewife, whereas the timing and duration of spawning for anadromous alewife were found to be relatively invariant among years in our study system. For alewife and many other anadromous fish species, the increase in fish passage river restoration projects in the coming decades will re‐establish habitat connectivity and may bring isolated populations into contact. Hybridization between life history forms may occur when prezygotic isolating mechanisms are minimal, leading to potentially rapid ecological and evolutionary changes in restored habitats.

Impact of the Alien Species Mnemiopsis leidyi A. Agassiz, 1865 on Fish of the Caspian Sea

The data of long-term ecological studies (1999–2014) are used for assessing the impact of a new Caspian invader Mnemiopsis leidyi A. Agassiz, 1865 on marine and anadromous fish species. The introduction of the ctenophore and its massive development in the Caspian Sea have mainly affected planktophagous fish, especially the most abundant species anchovy sprat (Clupeonella engrauliformis Borodin, 1904) and sturgeons (Family Acipenseridae). Mnemiopsis leidyi is one of the main negative factors preventing the restoration of the populations of Caspian fishes, especially anchovy tyulka. The critical state of the resources of the spawning parts of sturgeon populations (Family Acipenseridae) has been reinforced as a result of the massive development of M. leidyi.

Relationship between marine growth and sea survival of two anadromous salmonid fish species

This study found empirical evidence supporting the “growth–survival” paradigm in the marine phase of Arctic char (Salvelinus alpinus) and brown trout (Salmo trutta). The paradigm postulates that larger or faster-growing individuals are more likely to survive than smaller or slower-growing conspecifics. The study employed long-term (25 year) capture data from a trap in the River Halselva in Norway during annual migration between marine and freshwater environments. Similar results were found for both species. Growth during the sea sojourn and return rates were positively correlated, linking increased survival with growth. Specific growth rate, survival, and duration of the sea sojourn of first-time migrants were correlated, suggesting that common environmental conditions at sea influence annual fish productivity. Freshwater and sea temperatures affected migration timing, whereas annual variation in marine growth and survival did not correlate with temperatures. This suggests that other factors such as variation in energy intake were the main source of annual growth variations. Moreover, the marine growth rate of the two species may signal annual overall fjord ecosystem production, especially related to their main prey.

RESOURCES OF FISH IN BOTTOM BIOTOPES ON THE SHELF AND THE UPPER CONTINENTAL SLOPE IN THE NORTHWESTERN BERING SEA

Stock of demersal fish species at the depths of 20–386 m in the northwestern Bering Sea, as well as pelagic and anadromous fishes in the bottom biotopes, are considered on the data of the bottom trawl survey conducted within the West-Bering and Chukchi fishery districts in the summer of 2017. The total accounted biomass of demersal fish was 1756,870 t, including 1578,430 t in the West-Bering and 178,440 t in the Chukchi district. The mean distribution density was similar in both districts: 11331.8 and 10748.0 kg/km 2 , respectively. Pacific cod formed the bulk of the demersal fish biomass — 1227,300 t. Among other species, the stocks were considerable for flathead sole — 96,310 t, great sculpin — 79,160 t, alaska plaice — 71,200 t, and arrowtooth flounder — 40,630 t, and the summary biomass of all others was 242,270 t. The total biomass of pelagic and anadromous fish species presented in the bottom biotopes was estimated as 3884,150 t, including 3555,930 t in the West-Bering and 328,220 t in the Chukchi district. They had higher distribution density in the West-Bering district — 25527.9 kg/km 2 vs 19769.9 kg/km2 in the Chukchi district. Walleye pollock prevailed among these species with the total biomass 3884,150 t (assessed with the catchability coefficient for adults k = 0.4), including 36,080 t of accounted yearlings (k = 0.1). Biomasses of other pelagic fishes in the bottom biotopes were 415,380 t for pacific herring, 18,680 t for arctic cod, 920 t for capelin, and 260 t for all others in sum. Comparing these new assessments with the data of analogous survey in 2015, the stocks of pacific herring, rock sole, alaska plaice, and ray Bathyraja parmifera have decreased and the stocks of arctic cod, saffron cod, pacific cod, walleye pollock (both adults and yearlings), flathead sole, and yellowfin sole have increased. Positive and negative anomalies from the standard curves of size composition for some species could be considered as a basement for forecasting of their stocks tendencies in the nearest future.

ВЛИЯНИЕ НОВОГО ВСЕЛЕНЦА ГРЕБНЕВИКА MNEMIOPSIS LEIDYI (А. AGASSIS, 1865) НА ОСНОВНЫЕ ЗВЕНЬЯ ЭКОСИСТЕМЫ КАСПИЙСКОГО МОРЯ

The article presents annual data (1999-2016) of ecological surveillance on the influence of newish for the Caspian Sea invader Mnemiopsis leidyi (A. Agassis, 1865) on marine and anadromous fish species. There has been given the analysis of unfavourable effect of invader Mnemiopsis leidyi (A. Agassis, 1865) on the abundance of marine, anadromous, semi-anadromous fishes and Caspian seal. There have been considered mechanisms, sequence and degree of impact of ctenophoran on ichthyophauna and marine mammals via a nutritive base. It has been stated that mnemiopsis distribution corresponds to seasonal distribution of zooplankton and meroplankton, whereas ctenoforan being an organism with aggressive "r-strategy" of development influences ichthyophauna both directly (eating pelagic roe and larvae of sea fish) and indirectly (via nutritive base). Drastic reduction of catches of the Caspian sprat, in particular anchovy sprat and big-eyed sprat, is stipulated by nutritional competence between these fish species and ctenoforan Mnemiopsis leidyi. In turn, decrease in number of the Caspian sprat resulted in change of the nutrient budget of the sturgeon (Russian sturgeon, stellate sturgeon, beluga) and in decrease of their number and commercial stocks. There have been offered the solutions to the ecological problem and measures to restore sturgeon stocks. Results of the research can be used in forecasting commercial fish species stocks in the Caspian Sea and in determining the damage from annual invasions of Mnemiopsis ( Memiopsis leidyi (A. Agassis, 1865)) in the northern part of the Caspian Sea.

Downstream fish passage guide walls: A hydraulic scale model analysis

Partial-depth guide walls are used to improve passage efficiency and reduce the delay of out-migrating anadromous fish species by guiding fish to a bypass route (i.e. weir, pipe, sluice gate) that circumvents the turbine intakes, where survival is usually lower. Evaluation and monitoring studies, however, indicate a high propensity for some fish to pass underneath, rather than along, the guide walls, compromising their effectiveness. In the present study we evaluated a range of guide wall structures to identify where/if the flow field shifts from sweeping (i.e. flow direction primarily along the wall and towards the bypass) to downward-dominant. Many migratory fish species, particularly juveniles, are known to drift with the flow and/or exhibit rheotactic behaviour during their migration. When these behaviours are present, fish follow the path of the flow field. Hence, maintaining a strong sweeping velocity in relation to the downward velocity along a guide wall is essential to successful fish guidance. Nine experiments were conducted to measure the three-dimensional velocity components upstream of a scale model guide wall set at a wide range of depths and angles to flow. Results demonstrated how each guide wall configuration affected the three-dimensional velocity components, and hence the downward and sweeping velocity, along the full length of the guide wall. In general, the velocities produced in the scale model were sweeping dominant near the water surface and either downward dominant or close to the transitional depth near the bottom of the guide wall. The primary exception to this shift from sweeping do downward flow was for the minimum guide wall angle tested in this study (15°). At 15° the flow pattern was fully sweeping dominant for every cross-section, indicating that a guide wall with a relatively small angle may be more likely to produce conditions favorable to efficient guidance. A critical next step is to evaluate the behaviour of migratory fish as they approach and swim along a guide wall in a controlled laboratory environment.

ЧИСЛЕННОСТЬ И КАЧЕСТВЕННЫЕ ХАРАКТЕРИСТИКИ МАЛЬКОВ РЫБ НА МЕЛКОВОДНОМ УСТЬЕВОМ ВЗМОРЬЕ РЕКИ ВОЛГИ В ЛЕТНЕ-ОСЕННИЙ ПЕРИОД 2012 ГОДА

Shallow coastal waters of the Volga river is a flooded feeding area for fish juveniles of nonmigratory fish species. There takes place annual downstream migration of fluvial anadromous fish species from spawning grounds of the Volga river to the Northern Caspian Sea. The most important factors determining the number and qualitative characteristics of fry fishes are the level of the Caspian Sea (currently having a tendency to the lowering), hydrological and thermal regimes of the Volga river. Researches were carried out in definite periods of time. In the summer-autumn period of 2012 fry fishes were presented by 19 species (13 of them were commercial species), which belonged to 9 families. The article gives data on all the commercial fish species. In the first decade of July the maximum number of fry fish was registered in the western part of the Volga outfall offshore - in box 247 (19.86 mln specimens/km2), in the eastern part - in box 142 (20.4 mln specimens/km2). The most populous were roach, red-eye, silver bream and bream; size-weight characteristics were better in the areas remoted from the Volga delta. In the third decade of July the quantitative indicators of fry fish on these areas decreased, size-weight characteristics greatly increased. In the second decade of October in the western part of the seaside there were registered increased pre-wintering concentrations of fish juveniles, their qualitative indicators increased, which is evidence to favorable feeding conditions in 2012.

Confronting challenges to integrating Pacific salmon into ecosystem-based management policies

Ecosystem-based management is an increasingly prominent paradigm for the management of living marine resources with a focus on maintaining ecosystem level properties and processes. Although highly migratory marine and anadromous fish species often disproportionately contribute to the structure and function of ecosystems, incorporating these species into ecosystem-based management policies remains difficult because they spend a considerable portion of time outside the boundaries that define a particular management area. In this paper, two case studies are used to examine how the challenges of ecosystem openness, imperfect information, and ecosystem complexity can impede efforts to integrate highly migratory Pacific salmon into ecosystem-based management policies. This analysis highlights three main factors that hinder more effective integration: (1) uncertainties about impacts of human activities and ecological processes that occur in geographically distant jurisdictional areas or at spatial scales larger than the ecosystem-based management area, (2) spatial asymmetries in the distribution of costs and benefits associated with management decisions (i.e., positive or negative externalities), and (3) static management policies that prevent updating management decisions in a timely manner when ecosystem conditions change or new information becomes available. Given these factors, two potential strategies to address migratory challenges are suggested. First, the creation of an international ecosystem synthesis group is recommended to facilitate the collection, analysis, and dissemination of ecological, social, and policy information across national and other jurisdictional boundaries. Second, the expanded use of dynamic in-season management policies is recommended, which allow for rapid updating of management decisions based on evolving information about ecosystem conditions.

Flow Restoration in the Columbia River Basin: An Evaluation of a Flow Restoration Accounting Framework.

Securing environmental flows in support of freshwater biodiversity is an evolving field of practice. An example of a large-scale program dedicated to restoring environmental flows is the Columbia Basin Water Transactions Program in the Pacific Northwest region of North America, which has been restoring flows in dewatered tributary habitats for imperiled salmon species over the past decade. This paper discusses a four-tiered flow restoration accounting framework for tracking the implementation and impacts of water transactions as an effective tool for adaptive management. The flow restoration accounting framework provides compliance and flow accounting information to monitor transaction efficacy. We review the implementation of the flow restoration accounting framework monitoring framework to demonstrate (a) the extent of water transactions that have been implemented over the past decade, (b) the volumes of restored flow in meeting flow targets for restoring habitat for anadromous fish species, and (c) an example of aquatic habitat enhancement that resulted from Columbia Basin Water Transactions Program investments. Project results show that from 2002 to 2015, the Columbia Basin Water Transactions Program has completed more than 450 water rights transactions, restoring approximately 1.59 million megaliters to date, with an additional 10.98 million megaliters of flow protected for use over the next 100 years. This has resulted in the watering of over 2414 stream kilometers within the Columbia Basin. We conclude with a discussion of the insights gained through the implementation of the flow restoration accounting framework. Understanding the approach and efficacy of a monitoring framework applied across a large river basin can be informative to emerging flow-restoration and adaptive management efforts in areas of conservation concern.

Discovery and characterization of single nucleotide polymorphisms in two anadromous alosine fishes of conservation concern.

Freshwater habitat alteration and marine fisheries can affect anadromous fish species, and populations fluctuating in size elicit conservation concern and coordinated management. We describe the development and characterization of two sets of 96 single nucleotide polymorphism (SNP) assays for two species of anadromous alosine fishes, alewife and blueback herring (collectively known as river herring), that are native to the Atlantic coast of North America. We used data from high‐throughput DNA sequencing to discover SNPs and then developed molecular genetic assays for genotyping sets of 96 individual loci in each species. The two sets of assays were validated with multiple populations that encompass both the geographic range and the known regional genetic stocks of both species. The SNP panels developed herein accurately resolved the genetic stock structure for alewife and blueback herring that was previously identified using microsatellites and assigned individuals to regional stock of origin with high accuracy. These genetic markers, which generate data that are easily shared and combined, will greatly facilitate ongoing conservation and management of river herring including genetic assignment of marine caught individuals to stock of origin.

ОПЫТ ОЦЕНКИ НЕУЧТЕННОГО ИЗЪЯТИЯ ПОЛУПРОХОДНЫХ И РЕЧНЫХ ВИДОВ РЫБ В АСТРАХАНСКОЙ ОБЛАСТИ

The work presents the assessment of unaccounted withdrawal of fluvial anadromous and river fish species in the inland fisheries of the Astrakhan region, which is composed of despoliations of commercial catches, poaching and amateur fishing. Methodology decisions that are developed at the CaspNIRKh were the calculation basis of the unaccounted fishing withdrawal and assessment of the impact of amateur fishing on the aquatic bio-resources. The article shows the evaluation method of volumes of poaching fish withdrawal. It is found that the main objects of the unaccounted withdrawal were more valuable fishing species (roach, pike perch, catfish, carp, bream, and pike). The despoliation of commercial catches made 28% on the average. One year minimum poaching fish withdrawal in the region, using the example of 2015, was 7.94 thousands of tones and 19% from commercial catch, and 20-30% of fish catching, harvested by the amateur fishing. The work presents the pressing of unaccounted withdrawal of fluvial anadromous and river fish species on stocks. On the back of decrease of stocks and commercial catches of fluvial anadromous and river fish species, development scales of all directions of unaccounted withdrawal in the Astrakhan region disturb all preconditions for reconstruction and growth of fish number.

Application of DNA metabarcoding on faeces to identify European catfish Silurus glanis diet.

In this study, the results of conventional stomach-content analysis are compared with the recent DNA metabarcoding approach on faeces to identify fish species consumed by non-native European catfish Silurus glanis in the Garonne River (south-western France), with a special emphasis on anadromous prey. Fourteen prey species were identified in the stomach contents or faeces, including four anadromous fish species. Despite higher intestine than stomach emptiness, more species were identified through faecal analysis (11 of 14) than through stomach-content analysis (five of 14) suggesting that DNA metabarcoding on faeces is an efficient, non-intrusive technique to study the diet of predatory fishes.

Navigating Critical Thresholds in Natural Resource Management: A Case Study of Olympic National Park

As global climate change brings an increasing number of ecosystems closer to critical thresholds, land managers face new challenges regarding how to avoid and/or adapt to these dramatic changes. This paper focuses on park management for wildlife species in Olympic National Park, United States. The Olympic Marmot (Marmota olympus) and anadromous fish species are of specific concern, as ecosystems near thresholds due to warming temperatures, change in species interactions, and the loss or degradation of critical habitat. Interviews with 30 park managers and government agency staff indicate that there are many barriers to successfully navigating ecological thresholds. Park managers have limited resources for monitoring and priorities still focus on current conditions rather than anticipating future ecosystem change. In addition, many drivers of ecological change take place outside of park boundaries and require larger-scale approaches. In order to proactively navigate thresholds and protect wildlife species, park managers will need more resources, flexibility, and cooperation outside of park boundaries.

Wanted dead or alive: a state-space mark–recapture–recovery model incorporating multiple recovery types and state uncertainty

We developed a state-space mark–recapture–recovery model that incorporates multiple recovery types and state uncertainty to estimate survival of an anadromous fish species. We apply the model to a dataset of outmigrating juvenile steelhead trout (Oncorhynchus mykiss (Walbaum, 1792)) tagged with passive integrated transponders, recaptured during outmigration, and recovered on bird colonies in the Columbia River basin (2008–2014). Recoveries on bird colonies are often ignored in survival studies because the river reach of mortality is often unknown, which we model as a form of state uncertainty. Median outmigration survival from release to the lower river (river kilometre 729 to 75) ranged from 0.27 to 0.35, depending on year. Recovery probabilities were frequently ≥0.20 in the first river reach following tagging, indicating that one out of five fish that died in that reach was recovered on a bird colony. Integrating dead recovery data provided increased parameter precision, estimation of where birds consumed fish, and survival estimates across larger spatial scales. More generally, these modeling approaches provide a flexible framework to integrate multiple sources of tag recovery data into mark–recapture studies.

Network analyses reveal intra‐ and interspecific differences in behaviour when passing a complex migration obstacle

Summary Network theory offers new perspective on movement data by evaluating the relationships between animal movements (links) and detection locations (nodes) in spatially complex systems, including human‐altered landscapes. We applied network analyses to intra‐ and interspecific movement patterns in the migration behaviour and dam passage success of two anadromous fish species, Pacific lamprey Entosphenus tridentatus Gairdner and Chinook salmon Oncorhynchus tshawytscha Walbaum, when moving through a large multifishway hydroelectric project (Bonneville Dam, USA). Network analyses revealed greater variation in movement for Pacific lamprey compared with Chinook salmon. Salmon that passed the dam had networks consisting of more direct passage routes with fewer overall movements compared with lamprey that passed the dam. Lamprey that did not pass the dam exhibited a wide range of behaviours, from approaching only one fishway site to testing all possible passage routes. Accounting for the time spent in the network improved the ability to detect biological differences in network structure for lamprey that did and did not pass the dam. The movement patterns likely resulted from different behavioural responses to complex environmental and internal factors affecting a philopatric species (Chinook salmon) vs. a non‐philopatric species (Pacific lamprey) when moving through an engineered environment designed primarily for salmon. Synthesis and applications. Our case study highlights the potential for network analyses to link questions of basic movement ecology with monitoring of movement and behaviour in human‐altered landscapes. Network analyses can thus serve as a valuable tool for describing movement and behaviour in the face of environmental change and assessing the effectiveness of mitigation efforts at spatially complex obstacles to animal movement.