Male‐biased sex ratio of nonanadromous Oncorhynchus mykiss in a partially migratory population in California

Abstract – Differential rates of anadromy between males and females are common in partially migratory salmonid populations, but this pattern is not fully clear for Oncorhynchus mykiss (rainbow trout/steelhead) from the limited but mixed data available. In particular, there are very few data on sex ratios of juvenile and nonanadromous (resident) fish to help assess sex composition of various life stages and life‐history types. We used a recently developed Y‐chromosome genetic marker to assess sex ratio of stream‐dwelling (i.e., juvenile and nonanadromous) O. mykiss in a small coastal basin in central California, USA. We analysed 384 samples collected from three contiguous study reaches over 3 years. Sex ratio was 1:1 among juvenile‐sized O. mykiss (<150 mm) but highly male‐skewed (83%) among nonanadromous‐sized individuals (≥150 mm), and this sex ratio × size pattern did not differ among years or study reaches. Our results suggest that the rate of anadromy differs between males and females in this basin. Our study also demonstrates the application of new genetic markers to determine sex composition of immature and nonanadromous salmonids, which will help assess sex‐specific life‐history behaviour in partially migratory populations of O. mykiss and other species.     

Reliance on lakes by salmon,trout and charr (Oncorhynchus,Salmo and Salvelinus): An evaluation of spawning habitats,rearing strategies and trophic polymorphisms

Salmonid fishes may reside within or migrate between stream and lake habitats, or undergo anadromous migrations between freshwater and the ocean. While the degree of anadromy of salmonids has been thoroughly compared, no analogous review has examined the degree of lake use. To assess the extent of reliance on lake habitat in this family, we considered 16 species of salmon, trout and charr from the genera Oncorhynchus, Salmo and Salvelinus, comparing their (a) use of lakes as spawning habitat, (b) rearing strategies in lakes, and (c) occurrence and diversity of lacustrine trophic polymorphism. In identifying the primary life‐history patterns of each species and exploring the lesser‐known lacustrine behaviours, we found that the extent of reliance on lakes exhibits a negative association with the degree of anadromy. Oncorhynchus rely least on lakes, Salmo to an intermediate level and Salvelinus the most, opposite of the general prevalence of anadromy among these genera. Lakes are critical to adfluvial and lake‐resident salmonids, but they also support anadromous and fluvial life histories by providing spawning, rearing, overwintering and/or summer refuge habitat. Adfluviality, although a non‐anadromous life history, consists of similar migration‐related traits and behaviours as anadromy, including the parr–smolt transformation, sex‐biased patterns of migration and residency, and the presence of precocious males. Lakes support life‐history variants, reproductive ecotypes and trophic morphs unique to lacustrine habitat. Therefore, conservation of salmonids is dependent on maintaining the diversity and quality of their habitats, including lakes.     

Anadromy and the dispersal of an invasive fish species (Oncorhynchus mykiss) in Eastern Quebec,as revealed by otolith microchemistry

Thibault I, Hedger RD, Dodson JJ, Shiao J‐C, Iizuka Y, Tzeng W‐N. Anadromy and the dispersal of an invasive fish species (Oncorhynchus mykiss) in Eastern Quebec, as revealed by otolith microchemistry. Ecology of Freshwater Fish 2010: 19: 348–360. © 2010 John Wiley & Sons A/S Abstract – Rainbow trout (Oncorhynchus mykiss) is invading rivers bordering the St. Lawrence Estuary (Quebec, Canada). Some rivers in Eastern Quebec support self‐sustaining populations while adult vagrants are frequently captured in rivers where no reproduction has been confirmed. We hypothesised that the development of anadromy has promoted the species dispersal. Otolith Sr:Ca analyses revealed that although all fish captured in the upstream stocking region were freshwater residents, both anadromous and freshwater resident phenotypes were found downstream in Eastern Quebec. The proportion of fish exhibiting the anadromous life cycle increased with the distance from the stocking zone. Eastern Quebec steelhead migrated to sea at the same age but at a larger size than steelhead within their native range. Age at first reproduction was similar to that observed in native populations. The development of the anadromous life cycle enables this species to colonise new rivers following long‐distance migrations along the St. Lawrence Estuary corridor.     

Genetic differentiation between and within ecotypes of pike (Esox lucius) in the Baltic Sea

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Stability in reproductive timing and habitat usage of Chinook salmon across six years of varying environmental conditions and abundance

The spatial and temporal distribution of spawning activity by autumn‐run Chinook salmon Oncorhynchus tshawytscha (Walbaum) was examined across multiple years. The study period included two years of extreme drought conditions when water temperatures in the spawning reach of the Stanislaus River were considered sub‐optimal for spawning and egg incubation. Despite varying levels of superimposition, redd counts and densities remained stable and positively associated with river location, indicating that superimposition may be driven by habitat preference rather than the absence of suitable spawning locations. Spawning occurred slightly later during drought years (6–10 days later compared with wetter years). This delay was attributable to deferred migration instead of deferred spawning, and the majority of redds were constructed at water temperatures exceeding the optimal temperature range. As a consequence, estimates of juvenile production during 2014 and 2015 were among the lowest on record. These findings may be related in part to the high hatchery contribution to the population, above‐average temperatures during spawning and incubation, and superimposition rates. Management recommendations include adequate cold‐water storage in the upstream reservoir, refined spawning habitat restoration techniques in the light of superimposition rates and, on a broader system scale, actions that reduce the amount of stray hatchery Chinook salmon.     

Dispersal and tributary immigration by juvenile coho salmon contribute to spatial expansion during colonisation

Anadromous fishes are frequently restricted by artificial barriers to movement such as dams and culverts, so measuring dispersal helps identify sites where improved connectivity could promote range expansion and population viability. We used a combination of DNA‐based parentage analysis and mark–recapture techniques to evaluate dispersal by juvenile coho salmon (Oncorhynchus kisutch) in a population in the initial stages of colonisation following installation of fish passage structures at a previously impassable dam on the Cedar River, WA, USA. The spatial distribution of individuals within maternal families revealed that dispersal was common. Among the offspring of radio‐tagged mothers, 28% were collected outside the spawning reach and dispersed up to 6.3 km (median = 1.5 km). Most juveniles captured in a tributary (Rock Creek, where few adults spawned) had immigrated from the Cedar River and represented many different families. Juvenile dispersal therefore provided a secondary phase of spatial expansion following initial colonisation by adults. Consistent with the condition‐dependent dispersal hypothesis, juveniles that dispersed farther upstream in the tributary were larger than fish collected near the tributary mouth. Overall, the results demonstrated widespread dispersal in a system with low coho salmon densities, and this might increase the rate of population growth if it reduces the effects of local density dependence. By implication, juveniles can take advantage of rearing habitats reconnected through barrier removal, even when such areas are located several kilometres from adult breeding grounds.     

Spawning distribution and abundance of a northern Chinook salmon population

Chinook salmon, Oncorhynchus tshawytscha (Walbaum), is an important biological and cultural resource in Alaska, but knowledge about Chinook salmon ecology is limited in many regions. From 2009 to 2012, spawning distribution and abundance of a northern Chinook salmon population on the Togiak River in south‐west Alaska were assessed. Chinook salmon preferred deeper mainstem channel spawning habitat, with 12% (14 of 118 tags in 2009) to 21% (22 of 106 tags in 2012) of radio‐tagged fish spawning in smaller order tributaries. Tributary spawners tended to have earlier run timing than mainstem spawners. Chinook salmon exhibited extended holding and backout (entering freshwater but returning to saltwater before completing anadromous migration) behaviours near the mouth of Togiak River, potentially prolonging their exposure to fishery harvest. Mark–recapture total annual run estimates (2010–2012) ranged from 11 240 (2011) to 18 299 (2012) fish. Exploitation of Chinook salmon ranged from 36% (2012) to 55% (2011) during the study period, with incidental fishery catches near the mouth of the river comprising the largest source of harvest.     

Environmental DNA as a non‐invasive sampling tool to detect the spawning distribution of European anadromous shads (Alosa spp.)

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Water level influences migratory patterns of anadromous brown trout in small streams

Habitats modify the population ecology of species. Here, we show how low water level influences abundance and size of adult anadromous brown trout (Salmo trutta) entering a small, South Norwegian stream for spawning. After smolting, the fish appear chiefly to feed within 10 km of the home stream. In the autumn, South Norwegian streams typically flood because of heavy rainfall, when the anadromous brown trout entered from the sea. Mean annual duration of the upstream migration period was 34 days and ended when the flooding ended and the water temperature dropped to below 4°C. During most of the migration period, on average two trout ascended the river per day. The sexes entered the spawning area concurrently, and the male:female ratio of the anadromous trout was 1.27. No fish entered when the water depth just downstream of the spawning area was below 5 cm, and mean number of fish increased with increasing water depth to ca. 30 cm, but not at higher flows when the ascent gradually decreased. Mean and maximum size of the entering spawners increased with water depth between 5 and 16 cm. Among those that had been to sea, most were recaptured in the home stream, 4% in other streams, but only two of the strays were caught close to spawning time. The present results illustrate that population traits of anadromous brown trout from a small stream differ from those in larger rivers, probably because of selection associated with water flow.     

The influence of physical watercourse parameters on the degree of anadromy in different lake populations of Arctic charr (Salvelinus alpinus (L.)) in northern Norway

The influence of physical watercourse parameters on the degree of anadromy was studied in 15 lake populations of Arctic charr (Salvelinus alpinus (L.)) in northern Norway. The anadromy of the different populations was scored based on the following criteria; marine parasites. fish length and length at maturity. There were significant negative correlations between the anadromy scores and both the length of the outlet rivers of the different lakes and a migration barrier index for the different watercourses (combining migration distance and water velocity). It is hypothsized that these correlations were due to differences in energy expenditure for charr during upstream migration and/or differences in predation pressure on charr during river migration. Short rivers with relatively high water velocity seem to be the most preferable conditions for the anadromous life-history strategy. There were no correlations between the degree of anadromy and mean river slope or minimum summer water discharge.     

Do sea trout Salmo trutta parr surveys monitor the densities of anadromous or resident maternal origin parr,or both?

Brown trout Salmo trutta L. parr were sampled from 21 Estonian and three Finnish streams to investigate whether national sea trout parr surveys sample the progeny of anadromous or resident maternal parents. Otolith Sr:Ca core values were used and validated as a tool for distinguishing between the progeny of the two forms. In Estonia (n = 283), 92% of the parr were the progeny of anadromous maternal parents, and 8% were the progeny of resident maternal parents, whereas in Finland (n = 24), the respective proportions were 79% and 21%. Variation in the maximum otolith Sr:Ca core values among progeny of anadromous maternal parents indicated that some adult females may enter fresh waters several months before spawning. It was concluded that easily accessible locations situated up to 30 km from the sea largely contain progeny of sea trout, whereas sites with poor connectivity with the sea can be dominated by progeny of resident trout. This study demonstrated that the method applied provided an effective means to distinguish between the progeny of sea trout and resident brown trout.     

Evaluation of the removal of impassable barriers on anadromous salmon and steelhead in the Columbia River Basin

Despite the popularity of barrier removal as a habitat restoration technique, there are few studies that evaluate the biological effects of restored stream crossings. An extensive post‐treatment study design was used to quantify fish populations (e.g. species, life stage, abundance) and habitat attributes (e.g. gradient, geomorphic channel units) at 32 culvert removal or replacement projects to determine their effectiveness in restoring habitat access for juvenile salmon, Oncorhynchus spp., and steelhead, O. mykiss (Walbaum), in the Columbia River Basin, USA. Anadromous fish (steelhead, Chinook salmon O. tshawytscha [Walbaum]) abundance, juvenile steelhead abundance and habitat conditions were not significantly different between paired reaches (i.e. upstream and downstream of former barrier sites), suggesting these sites are no longer full barriers to movement. This suggests that barrier removal projects on small Columbia Basin streams provide adequate fish passage, increased habitat availability and increased juvenile anadromous fish abundance immediately upstream of former barriers.     

Population differentiation and temporal changes of carotenoid pigments and stable isotope ratios in the offspring of anadromous and non‐anadromous trout Salmo trutta

Trout (Salmo trutta) exhibit anadromous and non‐anadromous forms which are commonly sympatric. Offspring of the two forms can be separated by differences in characteristics such as stable isotope ratios and carotenoid pigments, which differ due to the influence of maternal resources. The rate of change in different characteristics due to freshwater feeding and the extent of differences between populations however remain unclear. Stable isotope (N and C) ratios and carotenoid pigment profiles were examined in the offspring of anadromous and non‐anadromous fish sampled at different times from six sites within the catchment of the River Tweed, UK. Both techniques were able to separate newly emerged fry successfully, with carbon isotopes distinguishing the forms better than nitrogen isotopes and zeaxanthin being the primary carotenoid pigment used to distinguish the offspring of different migratory forms. By 4 months, stable isotope ratios of the two forms were still distinct although both carbon and nitrogen ratios needed to be considered to distinguish the forms. Zeaxanthin levels were more variable and overlapped between the offspring of the two forms. There was significant variation between populations and over time in both isotope ratios and carotenoid composition. Comparison between the two techniques would suggest that stable isotopes are more effective for distinguishing between offspring of different forms as the distinctions are evident for longer. Population differences in isotope ratios could influence the extent to which the forms can be distinguished and need to be quantified more thoroughly to fully evaluate the technique.     

Assessment of potential trade‐off between maternal colouration and offspring quality in the ornamental “red cherry” shrimp Neocaridina davidi (Bouvier)

Maternal colouration based on carotenoids has been proposed to negatively affect offspring quality in several taxa, since females might trade off their limited carotenoid resources between body colouration and eggs. This study investigated in the ornamental “red cherry” shrimp (Neocaridina davidi) the relationship between maternal colouration and female reproductive performance, as well as offspring quality. Females selected displayed a broad array of body colour, from less coloured to intensely red coloured and were paired with transparent males. The first two spawning events of each female were studied and compared. The number of newly hatched juveniles was associated to maternal weight, but not to maternal colouration. Offspring quality was measured in terms of survival at the end of the 90‐day growth period, weight and length increment for 0–30 days and 30–60 days periods, and protein, lipid and glycogen contents in 30‐day‐old offspring. Yet, neither of these variables was associated to maternal colouration. These results indicate that there is no trade‐off between maternal colouration and offspring quality in this species. Furthermore, no association was found between maternal and offspring colouration, evaluated at a similar age. However, body colouration in 180‐day old females was significantly higher than in 90‐day‐old females, indicating that female colouration is strongly influenced by age.     

Upstream migration of the anadromous sea lamprey (Petromyzon marinus Linnaeus, 1758) in a highly impounded river: Impact of low‐head obstacles and fisheries

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Simulation of mackerel (Scomber scombrus) recruitment with an individual-based model and comparison with field data

An individual‐based model (IBM) for the simulation of year‐to‐year survival during the early life‐history stages of the north‐east Atlantic stock of mackerel (Scomber scombrus) was developed within the EU funded Shelf‐Edge Advection, Mortality and Recruitment (SEAMAR) programme. The IBM included transport, growth and survival and was used to track the passive movement of mackerel eggs, larvae and post‐larvae and determine their distribution and abundance after approximately 2 months of drift. One of the main outputs from the IBM, namely distributions and numbers of surviving post‐larvae, are compared with field data as recruit (age‐0/age‐1 juveniles) distribution and abundance for the years 1998, 1999 and 2000. The juvenile distributions show more inter‐annual and spatial variability than the modelled distributions of survivors; this may be due to the restriction of using the same initial egg distribution for all 3 yr of simulation. The IBM simulations indicate two main recruitment areas for the north‐east Atlantic stock of mackerel, these being Porcupine Bank and the south‐eastern Bay of Biscay. These areas correspond to areas of high juvenile catches, although the juveniles generally have a more widespread distribution than the model simulations. The best agreement between modelled data and field data for distribution (juveniles and model survivors) is for the year 1998. The juvenile catches in different representative nursery areas are totalled to give a field abundance index (FAI). This index is compared with a model survivor index (MSI) which is calculated from the total of survivors for the whole spawning season. The MSI compares favourably with the FAI for 1998 and 1999 but not for 2000; in this year, juvenile catches dropped sharply compared with the previous years but there was no equivalent drop in modelled survivors.     

Cumulative impacts of habitat fragmentation and the environmental factors affecting upstream migration in the threatened sea lamprey,Petromyzon marinus

1. River ecosystems are often fragmented by artificial structures, such as weirs. For anadromous species, these structures can impede access to upstream spawning sites and ultimately lead to severe population declines.
2. This study focused on the freshwater spawning migration of the sea lamprey, Petromyzon marinus, an anadromous species threatened by habitat fragmentation across its native range. To quantify the cumulative impacts of multiple weirs on upstream-migrating adults, and to explore the environmental factors affecting migratory movements, passive acoustic telemetry was applied to 56 individuals during their spawning migration in the heavily fragmented River Severn basin, UK.
3. While 89% of tagged sea lamprey passed the first weir upstream of the release site on the main river, only 4% passed the fifth weir. For 85% of migrants, the upstream extent of migration was immediately downstream of a weir. Individuals that passed weirs upstream of the release site (n = 50) took 21.6 ± 2.8 days to reach their most upstream location, experiencing cumulative passage times at weirs of 15.7 ± 2.8 days; these delays constituted a median of 84% of total upstream movement times.
4. Multistate models showed that the weir passage rates of sea lamprey in tidal and non-tidal areas increased significantly when downstream river level and discharge were elevated. Upstream-to-downstream changes in direction were frequent downstream of weirs, but rare in unobstructed river sections.
5. The results provided evidence for a cumulative effect of multiple weirs on sea lamprey movements, substantially delaying upstream migrants and limiting their spawning to atypical habitat. The results also demonstrated the crucial roles of high tides and elevated discharge events in enabling weir passage. Although the Severn Estuary features conservation designations for sea lamprey, this study reveals that barriers are inhibiting their upstream migration, a problem that should be addressed to assist sea lamprey conservation.

     

The effects of flow on Atlantic salmon (Salmo salar) redd distribution in a UK chalk stream between 1980 and 2015

Atlantic salmon are an ecologically and economically important migratory fish in the UK, whose stocks have been declining over the past 30 years. Future climate and water use changes have the potential to alter the reproductive behaviour and distribution of salmon within a river, by restricting times and ability to access suitable spawning areas. As the survival of emergent salmon juveniles is density dependent, understanding how climate‐driven changes in flow affect the location of salmon redds is important for future conservation efforts. This study examined how flow conditions affect the distribution of redds within a UK chalk stream, the river Frome in Dorset. Sixteen years of redd distribution and flow data between 1980 and 2015 were analysed using linear mixed‐effects modelling. Generally, highest redd densities occurred within middle reaches of the main river. Mean flow during the river Frome critical migration period (October–December) did not affect the density of redds directly but affected the relationship between redd density and distance from tidal limit: redd densities were spread more uniformly throughout the river under high flow conditions, whereas redds were more aggregated in the middle river reaches under low flow conditions. Together, these findings suggest that access to upstream spawning grounds was limited under low flow conditions, which could have negative repercussions on juvenile survival. This study has revealed the distribution of redds along the river Frome for the first time and provided a basis for further study into the effects of redd distribution on subsequent juvenile life stages.     

Drift diving: A quick and accurate method for assessment of anadromous salmonid spawning populations

The accuracy of drift diving surveys of Atlantic salmon, Salmo salar L. and sea trout, Salmo trutta L., was evaluated by comparing the abundance and size distribution with catches in a fish trap over 6 years in the River Etneelva, western Norway. The population count from drift diving accounted for on average 96.3% of the salmon in the trap after accounting for the catches during fishing. Size structure registered during drift diving corresponded with trap catches of salmon, but the number of small salmon (<3 kg) appeared to be somewhat underestimated, while large salmon (>7 kg) were overestimated in drift diving. For sea trout, the match between drift diving counts and trap registrations was poorer (average 76.3%), but may have been affected by the surveys being performed too late with regards to sea trout spawning time. The study illustrates the utility of drift counting for estimating the entire population of anadromous salmonids in a river.     

Whole otolith elemental analysis reveals feeding migration patterns causing growth rate differences in anadromous whitefish from the Baltic Sea

Impact of feeding migration pattern on growth rate of whitefish (Coregonus lavaretus L.) from River Kemijoki was investigated. River Kemijoki is located in the northernmost Gulf of Bothnia (Baltic Sea). Whitefish ascending the river to spawn show major growth rate variations. To study whether these variations are related to different feeding areas (migratory connectivity), whole otoliths from fast‐growing (FAST^G) whitefish (n = 9, age 4 years, average weight 790 g) and slowly growing (SLOWLY^G) whitefish (n = 9, age 8 years, average weight 600 g) were analysed for elemental (Ba, Sr, Mg, Zn, Mn, Ca) concentrations by inductively coupled plasma‐optical emission spectrometry. Results showed that the FAST^G whitefish had much lower otolith Ba concentration (~45%, p ≤ .01) than SLOWLY^G whitefish, revealing that FAST^G whitefish have spent more time in water of higher salinity/lower latitude, that is at feeding grounds in the southern Gulf of Bothnia. Otoliths of the FAST^G whitefish had also higher Mg (~25%, p ≤ .001) and Zn (~20%, p ≤ .05) concentrations, but lower Ca (~5%, p ≤ .01) concentrations, than the otoliths from SLOWLY^G whitefish. These results further reveal that FAST^G and SLOWLY^G whitefish have been spatially separated. In conclusion, bulk otolith elemental analysis revealed spatial separation and migration differences in river‐spawning whitefish subpopulations in the Gulf of Bothnia, which apparently lead to differences in fish growth rate. Our results increase the understanding of river‐spawning whitefish biology and its population structure and dynamics and may contribute to a sustainable management of river‐spawning whitefish stocks.