Monitoring Energetic Status of Lake Michigan Chinook Salmon Using Water Content as a Predictor of Whole-fish Lipid Content

Monitoring health indicators of fish populations can be an expensive and time consuming process. This study analyzed energy dynamics of Lake Michigan Chinook salmon using proximate composition analysis with the goal of determining an efficient method for monitoring the nutritional status of the population. Condition factor performed poorly as an indicator of whole-fish lipids (r² = 0.07). Water content in a dorsal muscle plug was found to be correlated with whole-fish lipids (r² = 0.50) for all samples. For the subset of samples that included small fish collected in the spring, the strength of the relationship between water content in a dorsal muscle plug and whole-fish lipids increased (r² = 0.70). The metric of water content in a dorsal muscle plug was determined to provide an adequate surrogate of whole-fish lipid content and, therefore, overall nutritional status. We propose a monitoring program that involves collecting small individuals in the spring and reporting the proportion of samples with over 78% water content in muscle tissue. Small individuals collected in the spring had the lowest whole-fish lipid levels of any segment of the population and would be the most prone to nutritional stress; therefore we recommend focusing on them for monitoring.     

Fatty Acid and Hydrocarbon Content of Settling Sediments in Lake Michigan

Fatty acid and aliphatic hydrocarbon contents have been examined in sediment collected in traps suspended at three depths at a location in Lake Michigan. Fatty acid distributions are similar at all depths and suggest an authochtonous origin of these materials. Concentrations of acids decrease with greater depths of traps and indicate a combination of active microbial reworking and of dilution by resuspended sedimentary materials. Hydrocarbons in the metalimnion trap contain mostly algal and bacterial components, whereas near-bottom hydrocarbons contain a large land plant contribution, presumably from resuspension of bottom sediments. Comparison of trap contents with fatty acid and hydrocarbons obtained from faunal debris and with published diatom compositions indicates that a mixture of such sources is combined in the organic matter settling in Lake Michigan. Estimated fluxes to the bottom of this part of the lake are 6.5 g/m²/yr for organic carbon, 1.8 g/m²/yr for fatty acids, and 27 mg/m²/yr for aliphatic hydrocarbons.     

Relationships Between Chlorinated Hydrocarbon Concentrations and Rearing Mortality of Chinook Salmon (Oncorhynchus Tshawytscha) Eggs from Lake Michigan

A study was conducted to investigate a possible correlation between chlorinated hydrocarbon concentrations and rearing mortality of chinook salmon. Eggs, collected from adult Lake Michigan chinook salmon in October, 1982, were analyzed for chlorinated hydrocarbon concentrations and rearing mortality. Polychlorinated biphenyls, toxaphene, and fifteen other chlorinated hydrocarbons were quantified. Also, concentrations of individual PCB congeners were quantified. We found 78 quantifiable PCB congeners, only three of which were non-ortho substituted. Mean concentrations of Arocloi^® 1242, 1254 and 1260 were 1.7, 5.4, and 1.1 μg/g, respectively. The concentration of toxaphene-like material was 3.3 μg/g, and the mean concentration of the total DDT complex was 1.0 μg/g. Concentrations of chlorinated hydrocarbons ranged approximately 10-fold among individual fish. An analysis of variance components demonstrated that this variability represented among-fish variation and was not due to errors in sampling or quantification. Duplicate studies of egg viability and fry mortality, conducted at 10, 11, and 15°C, correlated with residue concentrations. While some residue concentrations were significantly negatively correlated with egg viability and survival of fry, others were positively correlated. Thus, we observed no consistent trends in Pearson, pairwise-correlations between either egg viability or survival of fry to swim-up stage and individual residue concentrations. When the residues were classified into four principal components, two of the principal components which contained primarily the toxaphene and PCB concentrations were negatively correlated with survival of fry to the swim-up stage.     

Lake whitefish (Coregonus clupeaformis) energy and nutrient partitioning in lakes Michigan,Erie and Superior

A concurrent decrease in lake whitefish (Coregonus clupeaformis) condition and Diporeia spp. abundance in Lake Michigan has spurred investigations into possible links between the two phenomena. We examined female lake whitefish δ¹³C and δ¹⁵N stable isotopes, growth, reproductive investment, dorsal muscle total lipid and docosahexaenoic acid (DHA) contents from lakes Erie, Michigan and Superior to determine whether differences in food source were correlated with measures of stock success. Stocks with higher somatic growth rates and mean reproductive potential had higher energy stores in terms of percent total lipid. Stocks with low muscle lipid concentration also had smaller egg sizes as egg number increased. Diet varied among stocks as evidenced by δ¹³C and δ¹⁵N stable isotope analyses; however, muscle total lipid and DHA were not correlated to apparent Diporeia spp. prey use. When compared to stocks from lakes Erie and Superior, Lake Michigan stocks had lower growth, reproduction, and lipid stores. While stocks in Lake Michigan with access to declining Diporeia spp. populations may still feed on the amphipod, it appears that they are unable to consume the quantities necessary to maintain historical growth and reproduction. Stable isotope analyses of lakes Erie and Superior stocks, with higher growth rates and lipid values, indicated different feeding strategies with no indication of reliance on Diporeia spp. While differences in prey resources may have an effect on lake whitefish stocks, differences in Diporeia spp. abundance alone cannot explain differences in lake whitefish condition observed among the Great Lakes included in this study.     

Diet Composition and Feeding Periodicity of Wild and Hatchery Subyearling Chinook Salmon in Lake Ontario

Diel feeding periodicity, daily ration, and diet composition of wild and hatchery subyearling Chinook salmon Oncorhynchus tshawytscha were examined in Lake Ontario and the Salmon River, New York. The diet of wild riverine salmon was composed mainly of aquatic invertebrates (63.4%), mostly ephemeropterans (25.8%), chiromomids (15.8%), and trichopterans (8.3%). The diet of riverine Chinook was more closely associated with the composition of drift samples rather than bottom samples, suggesting mid-water feeding. In Lake Ontario terrestrial invertebrates were more important in the diet of hatchery Chinook (49.0%) than wild salmon (30.5%) and diet overlap between hatchery and wild salmon was low (0.46%). The diet of both hatchery and wild Chinook salmon was more closely associated with the composition of mid-water invertebrate samples rather than benthic core samples, indicating mid-water and surface feeding. Hatchery Chinook salmon consumed significantly less food (P < 0.05) than wild Chinook salmon in the lake and in the river, and wild salmon from Lake Ontario consumed more food than wild salmon in the Salmon River. Peak feeding of wild Chinook salmon occurred between 1200–1600 hours in Lake Ontario and between 1600–2000 hours in the Salmon River; there was no discernable feeding peak for the hatchery Chinook in Lake Ontario. Hatchery Chinook salmon also had the least diverse diet over the 24-hour sample period. These results suggest that at 7 days post-stocking hatchery Chinook salmon had not yet fully adapted to their new environment.     

Comparison of thiaminase activity in fish using the radiometric and 4-nitrothiophenol colorimetric methods

Thiaminase induced thiamine deficiency occurs in fish, humans, livestock and wild animals. A non-radioactive thiaminase assay was described in 2007, but a direct comparison with the radioactive ¹⁴C-thiamine method which has been in use for more than 30 years has not been reported. The objective was to measure thiaminase activity in forage fish (alewife Alosa pseudoharengus, rainbow smelt Osmerus mordax, and slimy sculpin Cottus cognatus) consumed by predators that manifest thiamine deficiency using both methods. Modifications were made to the colorimetric assay to improve repeatability. Modification included a change in assay pH, enhanced sample clean-up, constant assay temperature (37 °C), increase in the concentration of 4-nitrothiophenol (4NTP) and use of a spectrophotometer fitted with a 0.2 cm cell. A strong relationship between the two assays was found for 51 alewife (R² = 0.85), 36 smelt (R² = 0.87) and 20 sculpin (R² = 0.82). Thiaminase activity in the colorimetric assay was about 1000 times higher than activity measured by the radioactive method. Application of the assay to fish species from which no thiaminase activity has previously been reported resulted in no 4NTP thiaminase activity being found in bloater Coregonus hoyi, lake trout Salvelinus namaycusch, steelhead trout Oncorhynchus mykiss or Chinook salmon Oncorhynchus tshawytscha. In species previously reported to contain thiaminase, 4NTP thiaminase activity was measured in bacteria Paenibacillus thiaminolyticus, gizzard shad Dorosoma cepedianum, bracken fern Pteridium aquilinum, quagga mussel Dreissena bugensis and zebra mussels D. polymorpha.     

Fatty Acid Profiles Distinguish Channel Catfish from Three Reaches of the Lower Kaskaskia River and its Floodplain Lakes

Despite the increasing use of fatty acids (FAs) as biomarkers in aquatic food web analysis, little information is available regarding differences in FA profiles of fish among habitat types in river–floodplain ecosystems. The objectives of this study were to (i) test whether the FA profiles of channel catfish (Ictalurus punctatus) differed among three reaches of the lower Kaskaskia River and its floodplain lakes, and (ii) to compare FA profiles among muscle, liver, and adipose fin tissues collected from these fish. Profiles differed significantly among sites, especially between upper and lower river sites, and between river channel and oxbow lake sites, suggesting differences in FA availability for channel catfish occupying different habitats and river reaches in the Kaskaskia River system. Specifically, the essential FAs 18:2n‐6 and 18:3n‐3 increased in catfish tissues from upstream to downstream reaches, which could reflect increased floodplain connectivity and decreasing impoundment effects downstream. Ratios of n‐3 to n‐6 FAs were higher in fish from oxbow lakes, perhaps suggesting increased use of autochthonous production in the floodplain relative to the main river channel. Muscle and adipose fin FA profiles exhibited similar location‐related trends, whereas liver FA profiles were markedly different from the other tissue types. These results suggest that adipose fin tissue samples may be a viable, less‐invasive alternative to muscle tissue for analysis of FA profiles in channel catfish. Our study supports the use of tissue FA profiles in identifying habitat utilization by channel catfish, and perhaps habitat‐specific energy contributions to riverine consumers. Furthermore, our work highlights floodplain habitat as a potential source of essential n‐3 FA and the associated importance of maintaining river–floodplain connectivity to support aquatic food webs. Copyright © 2014 John Wiley & Sons, Ltd.     

Stimulation of Lake Michigan Plankton Metabolism by Sediment Resuspension and River Runoff

Previous work during a major sediment resuspension event (March 1988) in southern Lake Michigan demonstrated that nutrients and carbon derived from resuspended sediment stimulated intense winter heterotrophic production while simultaneously decreasing light availability and autotrophic biomass. However, the role of riverine inputs on plankton metabolism remained unclear. Here we present results from a simulated enrichment experiment (March 2000) designed to examine the influence of resuspended sediments and riverine inputs on Lake Michigan plankton dynamics. Lake water amended with realistic levels of river water, coastal resuspended sediment and river water + sediment all showed enhanced heterotrophic bacterial production and plankton respiration rates, relative to the lake water control. Bacterial production increased by approximately 4× in river water treatments and by a factor of 2.5× for the sediment only treatment compared to lake water controls. Rates of net primary production were stimulated by river water (8.5×) and resuspended sediment (3×), but most by a combination of river water + sediments (11×). Community respiration showed a similar response with rates approximately 8x higher in river water amendment treatments and 3.5× higher in the sediment treatment. Extrapolating experimentally determined production rates to the southern Lake Michigan basin indicated that heterotrophic and autotrophic production in this nearshore region may be enhanced by as much as 3× and 5.2× due to these source inputs. Indeed, field measurements throughout southern Lake Michigan from 1998–2000 support these experimental results. Experimental and field observations suggest that both seasonal riverine inputs and episodic resuspended sediments influence the regional scale ecosystem metabolism and biogeochemistry in Lake Michigan.     

Content and Chemical Form of Mercury and Selenium in Lake Ontario Salmon and Trout

The content and chemical form of mercury and selenium were determined in the edible tissue of salmon (coho, chinook) and trout (lake, brown) taken offshore from Lake Ontario near Rochester, New York. For all fish species, total mercury content ranged from 0.3 to 0.8 μg/g (fresh-weight), which is similar to concentrations commonly found in canned tuna. Most of the total mercury (63 to 79 percent) was present as methylmercury, the remainder being divalent inorganic mercury. For all species, 6 to 45 percent of the total selenium content was present as selenate (SeVI), the remainder being selenite (SeIV) and selenide (Se-11). On a molar basis, total selenium content usually exceeded that of total mercury. Samples of smoked and unsmoked brown trout fillets were also examined. Based on the results of this study there is no immediate human health hazard from mercury and selenium. However, there is a need to report specific chemical forms of these metals in Lake Ontario salmonid fishes so that elevated concentrations can be better evaluated.     

Thiamine concentrations in lake trout and Atlantic salmon eggs during 14 years following the invasion of alewife in Lake Champlain

Thiamine (vitamin B₁) deficiency in Great Lakes salmonines has been linked to consumption of alewife Alosa pseudoharengus. Thiamine deficiency has been recognized as a possible impediment to lake trout Salvelinus namaycush recruitment in the Great Lakes and Atlantic salmon Salmo salar recruitment in the Finger Lakes and Baltic Sea. Alewife invaded Lake Champlain in 2003 which provided an opportunity to investigate changes in thiamine concentrations in salmonine predators during an alewife invasion. We monitored egg unphosphorylated and total thiamine concentrations in lake trout and Atlantic salmon in 2004 and 2007–2019, assessed whether concentrations were associated with mortality, and examined thiaminase activity in alewife. Total thiamine concentrations in lake trout and Atlantic salmon were significantly lower than in 2004 for seven of the ten collection years for lake trout and for nine of the 12 collection years for Atlantic salmon. Mortality and signs of thiamine deficiency were observed in laboratory-reared Atlantic salmon free embryos but not in lake trout. Average thiaminase activity in adult alewife declined from 5200 pmol/g/min in 2006 to 1500 pmol/g/min in 2012. Our results provide further evidence that a diet that includes alewife reduces egg thiamine concentrations in salmonines. This effect was observed within four years of the invasion of alewife.     

Asymmetric Hybridization of Pink (Oncorhynchus gorbuscha) and Chinook (O. tshawytscha) Salmon in the St. Marys River,Michigan

Natural hybridization between pink salmon (Oncorhynchus gorbuscha) and Chinook salmon (O. tshawytscha) has been observed only in the Great Lakes, where both species have been introduced. The direction of hybridization between these species is poorly understood, thus the present study analyzed mitochondrial DNA (mtDNA) to determine whether the maternal parents were pink or Chinook salmon. During annual salmon population surveys on the St. Marys River (1998–2002), fifty putative hybrids of pink salmon and Chinook salmon were identified from meristic, morphometric and color characters. We designed primers to amplify a fragment of the mitochondrial D-loop control region that included both a variable and a control restriction site (BstNI). Polymerase chain reaction, restriction endonuclease digestion and capillary electrophoresis of mtDNA were used in order to identify the maternal parent of each hybrid salmon. In addition, the amplified fragments from the three fish species were sequenced to further verify the results. All hybrid salmon specimens were found to possess Chinook salmon mtDNA, indicating that hybridization between Chinook salmon and pink salmon is asymmetrical and likely unidirectional, occurring only between male pink salmon and female Chinook salmon. Influences contributing to the hybridization of these salmonid species could include limited spatial and temporal segregation of spawners, sexual selection, a limiting number of Chinook males, and/or physiological factors.     

Diet predictions of Lake Ontario salmonines based on fatty acids and correlations between their fat content and thiamine concentrations

Thiamine Deficiency Complex (TDC) limits early life stage survival of salmonines. Consuming fatty prey has been hypothesized as a cause of thiamine deficiency; however, this relationship has not been evaluated in the Laurentian Great Lakes where TDC occurs. We found that alewife (Alosa pseudoharengus) have higher lipid content than other common Lake Ontario prey fish. In addition, alewife were predicted as the most consumed prey for brown trout (Salmo trutta), Chinook salmon (Oncorhynchus tshawytscha), coho salmon (O. kisutch), lake trout (Salvelinus namaycush), and steelhead trout (O. mykiss); however, the relative importance of alewife in diet composition varied within and among species. Overall, species with greater predicted consumption of alewife had lower egg and muscle thiamine concentrations. Negative correlations between thiamine concentrations and both lipid content and fatty acid concentrations (mg/mg of wet tissue) were limited to brown trout. Similarly, negative correlations between fatty acid proportions (i.e., cumulative proportions of polyunsaturated fatty acids [PUFA] and monounsaturated fatty acids [MUFA]) and thiamine concentrations were only observed for brown and lake trout. Combining data from all species produced curvilinear correlations between thiamine concentrations (egg and muscle) and fatty acid composition (eggs and belly flap). Proportions of PUFAs had negative correlations with thiamine concentrations while proportions of MUFAs had positive correlations. These results provide evidence that, in some cases, salmonine fatty acid composition negatively correlates with thiamine concentrations in Lake Ontario; however, additional research is needed to confirm that this mechanism causes TDC in salmonines, and to understand additional factors potentially associated with TDC.