Lake trout (Salvelinus namaycush) otoliths indicate effects of climate and lake morphology on growth patterns in Arctic lakes

Climate change is occurring rapidly in the Arctic, and an improved understanding of the response of aquatic biota and ecosystems will be important for this data-limited region. Here, we applied biochronology techniques and mixed-effects modelling to assess relationships among growth increments found on lake trout (Salvelinus namaycush) otoliths (N = 49) captured from 13 lakes on the Arctic Coastal Plain of northern Alaska, observed and modelled climate patterns, and individual-level fish and lake characteristics. We found that annual growth varied by year, fish growth slowed significantly as individuals aged, and females grew faster than males. Lake trout had higher growth in flow-through lakes relative to lakes that were perennially or seasonally connected. Annual growth was positively correlated with observed air temperature measurements from a local weather station for the period 1998–2014, but no clear warming trend was evident for this period. Modelled August air temperatures from 1978–2014 predicted lake trout annual growth (root mean squared error = 0.045 mm) and indicated increasing temperatures and annual lake trout growth over the period 1950–2014. This study demonstrated that biochronology techniques can reconstruct recent climate patterns and provide a better understanding of trends in Arctic lake ecosystems under a changing climate.     

Baseline demographics of a non‐native lake trout population and inferences for suppression from sensitivity‐elasticity analyses

Management agencies in several western states of the United States are implementing suppression programmes to control non‐native lake trout, Salvelinus namaycush (Walbaum), for the conservation of native species. This study was implemented to ascertain the population demographics of an expanding lake trout population and use those data to construct an age‐structured model to inform suppression efforts. Population projection matrices were used to model population growth and identify age or stage classes with the greatest influence on population growth. The size and age structure of lake trout sampled was skewed towards juveniles, indicating strong recruitment and a growing population. Matrix‐model simulations corroborated the observed size and age structure, as the lake trout population was predicted to grow exponentially (λ = 1.35, 95% CL: 1.25–1.43) with no suppression efforts. Elasticity analysis of matrix models indicated the relative contribution of survival rates to population growth among immature age classes was equal from age 0 to age at first maturity, but immature survival rates contributed more than adult survival and fertility rates. These results emphasise the importance of targeting juvenile lake trout for suppression efforts during exponential growth in recently established populations.     

Suppression of invasive lake trout in an isolated backcountry lake in Glacier National Park

Fisheries managers have implemented suppression programmes to control non‐native lake trout, Salvelinus namaycush (Walbaum), in several lakes throughout the western United States. This study determined the feasibility of experimentally suppressing lake trout using gillnets in an isolated backcountry lake in Glacier National Park, Montana, USA, for the conservation of threatened bull trout, Salvelinus confluentus (Suckley). The demographics of the lake trout population during suppression (2009–2013) were described, and those data were used to assess the effects of suppression scenarios on population growth rate (λ) using an age‐structured population model. Model simulations indicated that the population was growing exponentially (λ = 1.23, 95% CI: 1.16–1.28) prior to suppression. However, suppression resulted in declining λ (0.61–0.79) for lake trout, which was concomitant with stable bull trout adult abundances. Continued suppression at or above observed exploitation levels is needed to ensure continued population declines.     

Changes in native bull trout and non‐native brook trout distributions in the upper Powder River basin after 20 years,relationships to water temperature and implications of climate change

Many bull trout populations have declined from non‐native brook trout introductions, habitat changes (e.g. water temperature) and other factors. We systematically sampled the distribution of bull trout and brook trout in the upper Powder River basin in Oregon in the 1990s and resampled it in 2013–2015, examined temperature differences in the habitats of the two species and analysed trends in temperatures in the light of possible increases associated with climate change. The species’ distributions are currently similar to those in the 1990s, except in one stream where bull trout declined. However, bull trout consisting of resident forms remain restricted to a few kilometres of habitat at the upper end of fish distribution. In streams where both species occur, the typical pattern was an intermediate zone of mixed bull trout, brook trout, and hybrids downstream of allopatric bull trout and allopatric brook trout extending farther downstream. Temperature differences between where bull trout and most brook trout occurred were small (0.5–1.0°C August mean). There were no statistical increases in water temperatures in nearby streams since the 1990s and no warming trends in air temperatures for the past 25–60 years. However, peak summer water temperatures are occurring about 3 weeks earlier than 25 years ago. Future effects of climate change, including possible increases in temperature, changes in timing and other factors (e.g. snowpack, flow and extreme events) remain a concern for the persistence of these populations. However, it is difficult to precisely predict where those changes will occur and what they will be.     

Seasonal home range estimates and habitat selection of saugeye in a small warmwater impoundment

Abstract Saugeye, a hatchery‐produced hybrid of walleye, Sander vitreus (Mitchill), × sauger, Sander canadense (Griffith & Smith), is commonly stocked by several state fishery management agencies in the United States. Saugeye is a top‐level predator that can restructure fish communities and provide supplemental angling opportunities. However, there are few published studies explaining distributions and habitat selection of saugeye. This study determined seasonal home range estimates and habitat selection of saugeye in a small warmwater impoundment using ultrasonic telemetry. Seasons for this study were defined as winter, spawn, spring, summer and autumn. Mean home range estimates were greatest during spawn when water temperature increased from 7.5 to 15 °C and lowest in winter when water temperature decreased below 7.5 °C. Saugeye selected open water and mid‐water ledge habitat during each season, but rock/gravel shoreline was increasingly selected during winter and spawn. These results corroborate previous studies that suggest saugeye exhibit seasonal variation in distribution and habitat use patterns. Managers should consider distribution and habitat selection trends of saugeye when assessing stocks or determining whether to introduce the species in a small warmwater impoundment.     

Potential impacts of non‐native channel catfish on commercially important species in a Japanese lake,as inferred from long‐term monitoring data

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Stable isotope evaluation of population‐ and individual‐level diet variability in a large,oligotrophic lake with non‐native lake trout

Non‐native piscivores can alter food web dynamics; therefore, evaluating interspecific relationships is vital for conservation and management of ecosystems with introduced fishes. Priest Lake, Idaho, supports a number of introduced species, including lake trout Salvelinus namaycush, brook trout S. fontinalis and opossum shrimp Mysis diluviana. In this study, we used stable isotopes (δ¹³C and δ¹⁵N) to describe the food web structure of Priest Lake and to test hypotheses about apparent patterns in lake trout growth. We found that isotopic niches of species using pelagic‐origin carbon did not overlap with those using more littoral‐origin carbon. Species using more littoral‐origin carbon, such as brook trout and westslope cutthroat trout Oncorhynchus clarki lewisi, exhibited a high degree of isotopic niche overlap and high intrapopulation variability in resource use. Although we hypothesised that lake trout would experience an ontogenetic diet shift, no such patterns were apparent in isotopic signatures. Lake trout growth rates were not associated with patterns in δ¹⁵N, indicating that variation in adult body composition may not be related to adult diet. Understanding trophic relationships at both the individual and species levels provides a more complete understanding of food webs altered by non‐native species.     

Seasonal migrations of adult and sub‐adult redband trout in a high desert basin of Eastern Oregon,USA

Abstract – Redband trout (Oncorhynchus mykiss gairdneri) migrations were tracked between March 2007 and June 2009 in the Donner und Blitzen River, Oregon, USA, using radio telemetry and PIT tags. We investigated the upstream extent and timing of spawning migrations for two groups of trout, considered the factors that influenced the rate of trout migration and explored the seasonal patterns of redband trout migration related to temperature and flow conditions. We found that trout made long‐distance migrations (up to 91 km) to spawn. Spawning trout from the lower river and middle river migrated to the same reaches, but lower river trout reached spawning habitats later than individuals from the middle river. Migration rate had a positive relationship with fork length and mean river discharge. We also found that redband trout made upstream spring migrations as sub‐adults and as adults. Whereas adult trout migrated to spawn, immature individuals migrated to river segments with more favourable thermal conditions. In both cases, migrations occurred where seasonally appropriate or life‐stage‐specific habitat patches for growth, survival, or reproduction were spatially segregated.     

Long‐term impacts of introduced flathead catfish on native ictalurids in a north Florida,USA, river

Introduction of flathead catfish, Pylodictis olivaris (Rafinesque), in waters of the USA has been widespread and often with negative impacts. Flathead catfish have been collected in Florida waters since the 1980s, and this study documents their impact on native fishes shortly after establishment. Four sites in the Choctawhatchee River, Florida, were sampled from 1997 to 2011, a time period spanning several years before and after the presence of flathead catfish at all sites. Flathead catfish expanded more than 91 river km in 2 years. The population increased rapidly and became the numerically dominant ictalurid at each site within 3 years of first detection at the site. Concurrent with the increases in flathead catfish was the precipitous decline of the native spotted bullhead, Ameiurus serracanthus (Yerger & Relyea). Electric fishing catch rates of flathead catfish significantly increased (P < 0.03) over time at all sites, while spotted bullhead catch rates significantly declined (P < 0.03) at three of four sites. Catch rates of flathead catfish and spotted bullhead were negatively correlated at all but the last site to be colonised by flathead catfish. This study provides evidence that introduced flathead catfish can quickly and significantly impact native ictalurids.     

Spawning salmon increase brook trout movements in a Lake Michigan tributary

Abstract – Salmon and trout have been introduced to many ecosystems worldwide, yet the ecological impacts of salmonid introductions remain poorly understood. We investigated the effects of introduced Pacific salmon on stream‐resident fish in the Great Lakes basin by monitoring the movements of passive integrative transponder (PIT)‐tagged brook trout in a Lake Michigan tributary receiving a salmon spawning run and in a nearby stream not receiving salmon. Coincident with the September arrival of salmon, an estimated 52% of resident brook trout moved >200 m, while no such movements were detected in the nonsalmon stream. After 3–4 days, however, brook trout movement patterns became similar in the two streams, suggesting that salmon effects on brook trout movements were short‐lived. Movements in the salmon stream were predominantly upstream in direction, with 50% of the tagged brook trout travelling from below to above the stationary PIT tag readers during the study. Declining water temperatures with the onset of fall coincided with low levels of brook trout movement at both sites, likely due to relocation for spawning. Increased brook trout movements coincident with the arrival of salmon spawners could be driven by a combination of interference competition and egg consumption. Using a bioenergetics model, we estimated that the energy lost to movement was likely compensated by the energy obtained from consuming salmon eggs. We conclude that salmon spawners can substantially increase brook trout movement, but in our study, these effects were short‐lived and likely negligible from a bioenergetics perspective.     

Individual movements,home ranges and habitat use by native rheophilic cyprinids and non‐native catfish in a large regulated river

The mobility patterns of two native species, barbel, Barbus barbus (L.) and chub, Squalius cephalus (L.), and of one non‐native fish species, the catfish Silurus glanis (L.), were assessed on a 35.5‐km reach of the Upper Rhône River, a strong flowing river with notable thermal regime alterations. An active acoustic tracking technique adapted to large rivers allowed (1) the identification of longitudinal home ranges, movements and preferred habitat at large scale, and (2) the analysis of the influence of discharge and water temperature on the movement patterns of the fish. The active fish‐tracking system recorded 1,572 fish localisations over 7 months on a weekly basis for 80% of the tagged fish (37 barbel, 23 chub and 13 catfish). Compared with the catfish, barbel and chub showed wider longitudinal home ranges, more movements >1 km and higher interindividual variability. The catfish preferred artificially heated habitats with less morphological diversity. The three species were more often localised in river sections with high density of woody debris. The results suggest that habitat degradation is more damaging for cyprinids in large modified rivers, while the catfish seemed less, impacted.     

Different longitudinal distribution patterns of native white-spotted charr and non-native brown trout in Monbetsu stream, Hokkaido, northern Japan

Abstract  This study focused on longitudinal distribution patterns of native white-spotted charr and non-native brown trout in a mountainous stream in Hokkaido, Japan. Brown trout ratio, which is the proportion of brown trout in the catch of salmonids, was decreasing from downstream to upstream. Brown trout ratio correlated negatively with water temperature. Thus, our results suggested that temperature may influence the possible competition between native white-spotted charr and non-native brown trout.     

Broad‐scale habitat classification variables predict maximum local abundance for native but not non‐native trout in New York streams

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Seasonal meso‐ and microhabitat selection by the northern snakehead (Channa argus) in the Potomac river system

Lapointe NWR, Thorson JT, Angermeier PL. Seasonal meso‐ and microhabitat selection by the northern snakehead (Channa argus) in the Potomac river system.
Ecology of Freshwater Fish 2010: 19: 566–577. © 2010 John Wiley & Sons A/S Abstract – The northern snakehead (Channa argus) is a large piscivorous fish that is invasive in eastern Europe and has recently been introduced in North America. We examined the seasonal habitat selection at meso‐ and microhabitat scales using radio‐telemetry to increase understanding of the ecology of this species, which will help to inform management decisions. After the spawning season (postspawn season, September–November), northern snakeheads preferred offshore Eurasian water‐milfoil (Myriophyllum spicatum) beds with shallow water (～115 cm) and soft substrate. In the winter (November–April), these fish moved to deeper water (～135 cm) with warmer temperatures, but habitat selection was weak at both scales. Northern snakeheads returned to shallower water (～95 cm) in the prespawn season (April–June) and used milfoil and other cover. Habitat selection was the strongest at both meso‐ and microhabitat scales during the spawning season (June–September), when fish preferred macrophytes and cover in shallow water (～88 cm). Our results help to identify habitats at the risk of invasion by northern snakeheads. We suggest that control efforts and future research focus on shallow waters, and take into consideration the seasonal habitat preferences.     

Comprehensive review of the records of the biota of the Indian Seas and introduction of non‐indigenous species

• 1. Comparison of the pre‐1960 faunal survey data for the Indian Seas with that for the post‐1960 period showed that 205 non‐indigenous taxa were introduced in the post‐1960 period; shipping activity is considered a plausible major vector for many of these introductions.
• 2. Of the non‐indigenous taxa, 21% were fish, followed by Polychaeta (<11%), Algae (10%), Crustacea (10%), Mollusca (10%), Ciliata (8%), Fungi (7%), Ascidians (6%) and minor invertebrates (17%).
• 3. An analysis of the data suggests a correspondence between the shipping routes between India and various regions. There were 75 species common to the Indian Seas and the coastal seas of China and Japan, 63 to the Indo‐Malaysian region, 42 to the Mediterranean, 40 and 34 to western and eastern Atlantic respectively, and 41 to Australia and New Zealand. A further 33 species were common to the Caribbean region, 32 to the eastern Pacific, 14 and 24 to the west and east coasts of Africa respectively, 18 to the Baltic, 15 to the middle Arabian Gulf and Red Sea, and 10 to the Brazilian coast.
• 4. The Indo‐Malaysian region can be identified as a centre of xenodiversity for biota from Southeast Asia, China, Japan, Philippines and Australian regions.
• 5. Of the introduced species, the bivalve Mytilopsis sallei and the serpulid Ficopomatus enigmaticus have become pests in the Indian Seas, consistent with the Williamson and Fitter ‘tens rule’. Included amongst the biota with economic impact are nine fouling and six wood‐destroying organisms.
• 6. Novel occurrences of the human pathogenic vibrios, e.g. Vibrio parahaemolyticus, non‐01 Vibrio cholerae, Vibrio vulnificus and Vibrio mimicus and the harmful algal bloom species Alexandrium spp. and Gymnodinium nagasakiense in the Indian coastal waters could be attributed to ballast water introductions.
• 7. Introductions of alien biota could pose a threat to the highly productive tropical coastal waters, estuaries and mariculture sites and could cause economic impacts and ecological surprises.
• 8. In addition to strict enforcement of a national quarantine policy on ballast water discharges, long‐term multidisciplinary research on ballast water invaders is crucial to enhance our understanding of the biodiversity and functioning of the ecosystem.

Copyright © 2005 John Wiley & Sons, Ltd.     

Seasonal residency and movement patterns of two co‐occurring catadromous percichthyids within a south‐eastern Australian river

Abstract – Understanding movement patterns and habitat utilisation is critical for the management of diadromous fishes. An acoustic telemetry array was used to monitor 33 estuary perch, Macquaria colonorum and 39 Australian bass, Macquaria novemaculeata in the freshwater and estuarine reaches on the Shoalhaven River, south‐east Australia. On average, tagged M. novemaculeata were detected for a considerably shorter period than M. colonorum, and evidence suggested that fishing pressure may have impacted on their survival. Macquaria colonorum displayed significant shifts in seasonal and size‐related habitat use, with fish predominantly residing in deep (>5 m) areas within the middle (mesohaline) reaches of the estuary during the austral spring to autumn months. In winter, M. colonorum individuals made frequent downstream migrations, often to localised areas, within the lower estuary (LE). In contrast, M. novemaculeata were distributed in shallow (<2 m) habitats throughout the year, within the upper (oligohaline) estuarine reaches of the river, as well as in fresh water. Like M. colonorum, M. novemaculeata made extensive downstream and upstream movements, often coincident with reproductive behaviour, water temperature and increased freshwater inflows. It is postulated that the high site fidelity and repetitive homing displayed by both species is influenced by ontogenetic behaviour and prey availability. Furthermore, the extent of instream distribution by both species, and the lack of observed annual spawning migrations by some M. novemaculeata individuals, indicates the once considered ‘catadromous’ life cycle of these fishes may not be obligatory. A management approach is recommended to ensure that both these species are not over‐exploited within a portion of their instream range, thus maintaining their full reproductive potential.     

Effect of an intensive mechanical removal effort on a population of non‐native rainbow trout Oncorhynchus mykiss in a South African headwater stream

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Seasonal movements with shifts in lateral and longitudinal habitat use by common bream,Abramis brama,in a heavily modified lowland river

Acoustic telemetry was used to investigate the longitudinal and lateral movements and distribution of adult common bream, Abramis brama (L.), over 43 months in a heavily modified lowland river in eastern England. A positive relationship between activity and temperature was found, with bream moving greater cumulative distances during the warmer months and distributed over a greater longitudinal proportion of the main channel. The occupancy of tributaries was related to temperature, with bream entering shallow tributaries during rising temperatures in the spring, whilst a deeper, slow‐flowing tributary was used more frequently during the cooler autumn/winter months. During the autumn, occupancy of this deeper tributary was positively related to flow rate in the main channel, suggesting that bream use this tributary for flow refuge. The functions of these behaviours are discussed along with potential management of heavily modified lowland rivers.     

Movements by wild brown trout in a boreal river: response to habitat and flow contrasts

Abstract  Radio transmitters were implanted in wild brown trout, Salmo trutta L., in the River Måna at low summer water flows ( n  = 18), higher flow in summer ( n  =   20), and variable, peaking flows in autumn ( n  =   20), and tracked two to four times day and night for 4–5 weeks. Individuals were caught and released in a 4-km uniformly channelised section, and in a 4-km natural diverse river section. Substantial individual variation in home range and total movement (924–85 818 m² and 295–7014 m) suggested flexibility to adapt to local environmental conditions. Fish were stationary most of the time (median movement 0 m), but some individuals undertook few and apparently sporadic longer movements, sometimes involving shifts in home range. No consistent diurnal pattern in movements was found. Trout in the uniform habitat section appeared to have larger home ranges and moved more than trout in the natural section. Differences were, however, not statistically significant in most comparisons, due to large individual variation. Similarly, larger home ranges and movements between trials related to higher flow were found, but differences were generally not significant. No consistent effects of sudden, extreme peaking flows on area use or movements by the brown trout were observed.     

Potential population and assemblage influences of non‐native trout on native nongame fish in Nebraska headwater streams

Non‐native trout are currently stocked to support recreational fisheries in headwater streams throughout Nebraska. The influence of non‐native trout introductions on native fish populations and their role in structuring fish assemblages in these systems is unknown. The objectives of this study were to determine (i) if the size structure or relative abundance of native fish differs in the presence and absence of non‐native trout, (ii) if native fish‐assemblage structure differs in the presence and absence of non‐native trout and (iii) if native fish‐assemblage structure differs across a gradient in abundances of non‐native trout. Longnose dace Rhinichthys cataractae were larger in the presence of brown trout Salmo trutta and smaller in the presence of rainbow trout Oncorhynchus mykiss compared to sites without trout. There was also a greater proportion of larger white suckers Catostomus commersonii in the presence of brown trout. Creek chub Semotilus atromaculatus and fathead minnow Pimephales promelas size structures were similar in the presence and absence of trout. Relative abundances of longnose dace, white sucker, creek chub and fathead minnow were similar in the presence and absence of trout, but there was greater distinction in native fish‐assemblage structure between sites with trout compared to sites without trout as trout abundances increased. These results suggest increased risk to native fish assemblages in sites with high abundances of trout. However, more research is needed to determine the role of non‐native trout in structuring native fish assemblages in streams, and the mechanisms through which introduced trout may influence native fish populations.