Otolith chemistry indicates walleye movement and entrainment in a large serial reservoir system

Understanding fish movement in impounded river systems is important for fisheries management. Otolith chemistry was used to examine walleye Sander vitreus (Mitchill) intra‐ and inter‐reservoir movement in four Missouri River impoundments. Age‐0 individuals were reclassified with 75%–93% accuracy to known natal sites, allowing for reliable evaluation of movement patterns of age‐1 and older fish. Nearly half of walleye occupied the same location annually (i.e. site residency) between 2009 and 2010. In 2011, during the largest flood on record since 1898, downstream movement (49% of age‐1 and older fish) exceeded upstream movement (7%) and site residency (33%) across the study area. After the flood, most walleye moved downstream within reservoirs (45%) or were site residents (37%). Entrainment occurred most frequently during the flood year and was proportionally greatest in downstream reservoirs. Otolith chemistry is useful for understanding walleye movement and entrainment and is a tool for fisheries management with applications such as informing reservoir water releases, harvest regulations and habitat protection and rehabilitation within and outside the Missouri River reservoir system.     

Otolith elemental characteristics of whitefish (Coregonus lavaretus) from brackish waters of the Gulf of Bothnia,Baltic Sea

To investigate whether European whitefish (Coregonus lavaretus) groups in the brackish (≤7%) Gulf of Bothnia (Baltic Sea) express specific otolith elemental characteristics, concentrations of elements (Ca, Ba, Sr, Zn, Mn, Fe) in whole otoliths were studied by inductively coupled plasma‐optical emission spectrometry. Whitefish (N = 67) were sampled from six different latitudinal sites; four in the sea and two in rivers along the west coast of Finland, and from a fresh water lake for comparison. The concentration of several elements showed significant differences among sampling sites. Otolith Ba concentrations were higher at the northern sampling sites compared to the southern ones, thereby showing negative association to capture‐habitat salinity. In contrast, otolith Sr and Zn concentrations were lower at the northern sampling sites, thereby associating positively to capture‐habitat salinity. Otolith Mn concentrations did not associate with latitude or salinity but markedly varied between sampling sites. Elevated Fe concentrations occurred in fish otoliths from the two northernmost sites. Ca concentrations were at the same levels in otoliths from all whitefish samples. Otoliths of whitefish from the lake had very high Ba and low Sr concentrations compared to concentrations in otoliths from whitefish in the sea and rivers. Our results show that otolith elemental characteristics of whitefish vary considerably at various geographic scales showing high potential for population identification using elemental fingerprints. Analysis of otolith elemental characteristics may therefore provide an efficient tool for the identification of main areas of residence, spawning locations, and migration routes, thus contributing towards the sustainable management of whitefish stocks.     

Variability in the performance of juvenile Chinook salmon is explained primarily by when and where they resided in estuarine habitats

Estuarine habitats provide rearing opportunities for the juvenile life stage of anadromous fishes. Because survival is positively correlated with juvenile performance, these estuarine habitats play an important role in population abundance and productivity. To provide information for the recovery of several depressed stocks of Chinook salmon in the Columbia River Basin, we sought to identify the factors that explain variability in performance. Using otolith‐derived estimates of juvenile somatic growth rate as an index of recent performance, we observed a negative nonlinear relationship between growth rate and day of year, and a decreasing and increasing trend of growth rate over the 8 years of this study and distance from the river mouth respectively. Using a generalised linear modelling approach, we found that variability in juvenile somatic growth rate was best explained by where and when individuals were collected, their body size, contaminant loads, stock of origin, and whether a fish was hatchery produced or unmarked. Lastly, we argue that a considerable improvement to the growth rate of juveniles in estuarine habitats is physiologically possible. The results of this 8‐year study provide a baseline of the performance of juvenile Chinook salmon to evaluate habitat restoration programs and to compare against future anthropogenic conditions.     

长江口及邻近海域4个不同地理群体凤鲚矢耳石形态差异

为探明相邻海域凤鲚（Coilia mystus）群体间的差异性，分别采集江苏吕四（吕四群体）、上海崇明（崇明群体）、浙江舟山（舟山群体）和浙江温州（温州群体）邻近海域的凤鲚共240尾。以凤鲚矢耳石为研究对象，利用耳石测量法和耳石框架法获得21个测量参数，通过公式转化为20个形态指标数据，并进行多元统计分析。非参数检验显示4个群体间14个形态指标具有显著性差异（P<0.05）；应用主成分分析构建了7个反映耳石形态特征的主成分，累计贡献率为81.79%，结果显示不同群体耳石的整体形态相似，各群体间的耳石形态差异主要体现在局部的框架形态指标；利用贡献率最大的9个形态指标构建了4个群体的判别方程，温州群体的判别准确率最高，为96.7%，其次是崇明群体（66.7%）、吕四群体（60.0%）和舟山群体（58.3%）；聚类分析表明崇明和舟山群体距离最近，其次为吕四群体，与温州群体距离最远。结果表明，崇明、舟山和吕四群体间矢耳石形态差异较小，而温州群体与这3个群体的差异最大，可单独确立为一个生态群体。可见，短距离洄游性凤鲚不同群体间耳石形态差异大小与群体地理阻隔程度相关。     

An additional life-history tactic of masu salmon: Migration of parr to coastal habitats

Alternative life-history tactics of masu salmon Oncorhynchus masou are well documented. Subsequent to the freshwater parr stage (age ≥ 1 + years), an anadromous form migrates to the sea after smolting, while a resident form matures without seaward migration. In addition to this typical migratory dimorphism, anecdotal reports based on field observations have indicated that some underyearling masu salmon use estuarine waters. However, no empirical evidence indicates saltwater utilisation and subsequent survival in the early parr stage. Here, we used otolith microchemistry to examine whether a portion of masu salmon parr in northern Japan enters coastal habitats. The otolith Sr:Ca ratios of most juveniles collected from six rivers had consistently low values, indicating that masu salmon parr inhabiting these rivers stay only in freshwater. In contrast, in individuals from a steep-gradient river the Sr:Ca ratios increased at about a 200-µm distance from the otolith core. These results suggest that some masu salmon parr might use brackish water or sea water temporarily. In addition, three masu salmon parr were found in another steep river where a culvert located only ten metres from the river mouth completely blocked upstream migration for spawning. The Sr:Ca ratios in these fish increased at about >200 µm from the otolith core, indicating the parr had immigrated to the non-natal river from the sea. Such flexible behaviour at an early life stage may contribute to the spatial expansion of masu salmon, and the movement could moreover help to stabilise its population dynamics.     

Parallelism in thermal growth response in otoliths and scales of brown trout (Salmo trutta L.) from alpine lakes independent of genetic background

Low density in natural populations of salmonids has predominantly been managed by stocking of non‐native conspecifics. Due partly to domestication, introduced non‐native fish may be maladapted under natural conditions. Interbreeding between introduced and wild individuals may therefore impair local adaptation and potentially population viability. Brown trout (Salmo trutta L.) from three headwaters (with stocked fish) and three interconnected lakes (with native fish) on the Hardangervidda mountain plateau, southern Norway, were tested for differences in thermal effects on scale and otolith growth. Otolith and scale annuli widths from immature brown trout showed positive correlation with mean annual summer temperature for all six sampled populations. In mature individuals, a similar positive thermal correlation was evident for the otoliths only. Interannuli width measurements from scales indicate a halt in somatic growth for brown trout in this alpine environment when reaching ages between 7 and 9 winters, coinciding with age at maturity. Our study indicates that otolith growth follows summer temperature even when individuals do not respond with somatic growth in these populations and that introduced brown trout and introgressed populations have similar thermal growth responses. Due to the continued otolith growth after stagnation in somatic growth and the impact of fluctuations in summer temperature, the utilisation of otolith annuli widths for back calculation of length at age should be treated with caution.     

To sea or not to sea? Multiple lines of evidence reveal the contribution of non‐diadromous recruitment for supporting endemic fish populations within New Zealand's longest river

1. Otolith microchemistry was used to identify marine‐ versus freshwater‐derived recruitment of three native freshwater fish species belonging to the southern hemisphere family Galaxiidae, in New Zealand's longest river system, the Waikato River.
2. Water chemistry data for trace elements and ⁸⁷Sr/⁸⁶Sr isotope ratios were collected from five lentic and 10 lotic water bodies throughout the lower river floodplain. Potential spawning sites for galaxiids were compared with values obtained by laser ablation inductively coupled mass spectrometry (LA‐ICPMS) depth profiling of young‐of‐the‐year otoliths sampled from fish in nine lower river catchment sites.
3. Otolith chemical signatures from the larval rearing period indicated that catchment‐scale recruitment for two species, Galaxias argenteus (Gmelin, 1789) and Galaxias fasciatus Gray, 1842, was driven predominantly by non‐diadromous recruitment from one lake (Lake Waahi). In contrast, diadromous recruitment appeared to be more common for Galaxias maculatus (Jenyns, 1842); however, non‐diadromous specimens were also identified for the first time from a New Zealand river.
4. Reversing lake outlet flows linked to river stage appears be important in facilitating the dispersal of rheotactic larvae out of lakes, suggesting that lake outflow management at key times could be used to sustain this ecologically important function.
5. This study highlights that some water bodies can supply a disproportionately large number of recruits to support fish populations within the wider riverscape. Identifying these water bodies and managing them to sustain recruitment is key to the conservation of non‐diadromous Galaxiidae in this modified lowland environment

     

Understanding the life histories of amphidromous fish by integrating otolith‐derived growth reconstructions,post‐larval migrations and reproductive traits

1. Amphidromy is the most prevalent type of diadromous migration. Despite this, the conservation and management of amphidromous species is exceptionally challenging because this life history type, with larval development in a pelagic habitat (usually marine) and adult development in fresh water, is poorly resolved.
2. The chronological properties of otoliths, together with a spatial and temporal analysis of post‐larval migration traits and adult reproductive traits, were used to reconstruct the life history of a widespread, yet declining amphidromous galaxiid, Galaxias maculatus, and to explore relationships between marine and freshwater life phases.
3. A wide range of post‐larval migration traits were observed over the peak migratory period. Post‐larvae were smaller and younger at inward migration late in the migration season (November) and were derived from winter spawning events. Earlier migrants (September) were larger, older and derived from autumn spawning events.
4. Age estimates confirmed that G. maculatus is largely an annual species, but back‐calculated hatch dates showed that spawning times are more extensive than previously known.
5. Growth reconstructions revealed that winter‐hatched larvae were faster growing during marine and freshwater life and attained sexual maturity at a younger age than autumn‐hatched fish. However, no differences in body size or reproductive investment were detected between autumn‐ and winter‐hatched larvae.
6. The first 50 days of marine growth were inter‐dependent, indicating that early larval growth may be the critical link to understanding intra‐ and inter‐annual recruitment variations of inward migrating post‐larvae. Furthermore, growth after 60 days of larval life propagated through to adult freshwater development, highlighting linkages between late marine and adult freshwater life.
7. This study highlights the value of studying the marine and freshwater life phases of amphidromous species in tandem. This interconnected understanding must ultimately be achieved for the conservation and management of species with this poorly understood life history type.

     

Using otolith increment widths to infer spatial,temporal and gender variation in the growth of sand whiting Sillago ciliata

Abstract Two methods of otolith increment analysis were used to describe spatial, temporal and gender variation in growth of sand whiting, Sillago ciliata (Cuvier), in four south‐east Australian estuaries. Mean annual standardised otolith increment widths were used as indices of individual lifetime growth rates, while raw otolith increment widths were used to describe variation in growth throughout the life of S. ciliata. Temporal variation in growth was observed at an annual scale, while spatial variation in growth was observed between estuaries. Growth rates increased significantly with decreasing latitude and greater mean sea surface temperatures. A divergence in growth rates between sexes was detected, with females growing faster than males after sexual maturity. This study highlights how otolith increment analyses can: (1) be used to analyse temporal trends in growth from a single sample and (2) provide insight into juvenile growth when samples have an absence of undersized fish.     

Evidence of diadromy in the French Polynesian Kuhlia malo (Teleostei: Percoidei) inferred from otolith microchemistry analysis

Abstract – Strontium/Calcium (Sr/Ca) and Barium/Calcium (Ba/Ca) ratios were measured in 60 otoliths of the French Polynesian flagtail Kuhlia malo. Both elemental ratios were needed to correctly distinguish residence in marine, brackish and fresh water. High Sr/Ca and low Ba/Ca around the nucleus of all otoliths provided evidence of marine residency during the early life of all individuals. At about 0.5 mm from the core, Ba/Ca increased rapidly and remained high in all otoliths. High and unstable Sr/Ca ratios were attributed to estuarine residency, whereas low and stable Sr/Ca ratios were attributed to freshwater residency. These chemical signatures inferred that following recruitment to rivers, some fish remained in the estuary, while others moved upstream. Some individuals shared their time between fresh and brackish waters later in life. The findings of this study have important implications for the protection of nearshore, brackish and freshwater environments for the conservation of this French Polynesian diadromous species.