Use of otolith chemistry to discriminate juvenile Chinook salmon (Oncorhynchus tshawytscha) from different wild populations and hatcheries in Lake Huron

Chinook salmon (Oncorhynchus tshawytscha) in Lake Huron consist of wild and hatchery-reared fish distributed among several populations. This study tested whether otolith chemistry can be used to identify the natal origin of Chinook salmon in this system. Concentrations of nine elements (Mg, K, Mn, Fe, Zn, Rb, Sr, Ba, and Pb) in the otoliths of Chinook salmon juveniles from 24 collection sites (17 streams and 7 hatcheries) around Lake Huron were analyzed using laser-ablation inductively-coupled mass spectrometry. Differences in otolith chemistry were found between rearing environments (wild and hatchery), among geological regions (Precambrian, Ordovician, Silurian, Devonian, and Carboniferous), and among collection sites. Discriminant function analysis showed high classification accuracies of juveniles to their rearing environment (wild versus hatchery, 82%), geological region (84%), and collection site (87%) of origin. With these values, there is excellent potential for otolith chemistry to be used to predict the natal origin of adults, and thus inform research and management of Chinook salmon in Lake Huron.     

Dispelling common beliefs about angler opposition to lake trout (Salvelinus namaycush) rehabilitation efforts in Lake Huron

Rehabilitating native fish species in the Laurentian Great Lakes and elsewhere remains a challenge for fisheries managers. One factor that often makes rehabilitation a challenge is presumed opposition to rehabilitation programs. We examined the extent and variability in support and opposition for lake trout (Salvelinus namaycush) management and proposed rehabilitation activities for the Ontario waters of Lake Huron, principally amongst anglers. Specifically, we compared four common beliefs (hypotheses) that should affect angler opposition to lake trout rehabilitation. Through a questionnaire sent to a random sample of local licensed anglers, we found very high support for lake trout rehabilitation. As hypothesized, this support was lower among a sample of individuals who actively sought opportunities to complete the questionnaire (who were termed the convenience sample). However, even within this convenience sample, about an equal percentage of respondents supported and opposed lake trout rehabilitation. For the sample of local licensed anglers, we found little support for the remaining three hypotheses. Within this sample, very few differences in support for lake trout rehabilitation existed between respondents who did or did not fish Lake Huron, who were or were not participants in past public involvement opportunities for managing Lake Huron's fisheries, and who were and were not knowledgeable about the proposed rehabilitation plan. These results question common beliefs that anglers are unsupportive of lake trout rehabilitation in Lake Huron and that support for rehabilitation varies widely among anglers with different characteristics and experiences.     

Comparative Diets of Subyearling Chinook Salmon (Oncorhynchus tshawytscha) and Steelhead (O. mykiss) in the Salmon River,New York

Chinook salmon (Oncorhynchus tshawytscha) and steelhead (O. mykiss) have established naturalized populations throughout the Great Lakes. Young-of-year of these species occur sympatrically for about one month in Lake Ontario tributaries. This study examined the diets of subyearling Chinook salmon and steelhead relative to available food in the Salmon River, New York. Terrestrial invertebrates and trichopterans were the major prey of Chinook salmon, whereas steelhead fed primarily on baetid nymphs and chironomid larvae. Diet overlap was low (0.45) between the species. The diet of Chinook was closely associated to the composition of the drift (0.88). Steelhead diet drew equally from the drift and benthos during the first year of the study, but more closely matched the benthos during the second year. Differences in prey selection, perhaps associated with differences in fish size, in addition to apparent differences in feeding mode (drift versus benthic), likely reduce competitive interactions between these species.     

Progress Toward the Rehabilitation of Lake Trout (Salvelinus namaycush) in South Bay,Lake Huron

Our objective was to evaluate the status of lake trout Salvelinus namaycush rehabilitation in South Bay, Lake Huron. Standardized surveys were conducted to quantify natural recruitment, annual mortality, and the contribution of wild-versus hatchery-origin lake trout. Some indicators suggest a high level of natural recruitment. The spawning population was comprised of multiple ages, and the mean age of spawners (8.4 years for females, 7.9 years for males) was at least 1 year older than the age at 50% maturity (5.8 years). Estimated annual total mortality rates (0.20–0.25) and sea-lamprey induced mortality rates (0.02) were less than maximum allowable values. The proportion of wild-origin fish captured was high among spawners but varied among sampling programs (42% in fall trap nets, 70% in fall gill nets, and 88% in summer gill nets). A strong year class (1997) could be tracked from 2001 to 2005. Few fish were captured from early (< 1996) or later (1999–2002) year classes. Possible explanations for low natural recruitment during these later years include declining spawning habitat quality caused by low water levels and/or invasion of non-native mussels (Dreissena spp.) and/or direct or indirect effects of alewife (Alosa pseudoharengus).     

Majority of age-3 Chinook salmon (Oncorhynchus tshawytscha) in Lake Ontario were wild from 1992 to 2005, based on scale pattern analysis

Stocking of hatchery-raised Chinook salmon has been the principal tool utilized by fishery managers for controlling alewives in Lake Ontario and elsewhere in the Great Lakes. Stocked Chinook salmon are also often viewed by anglers as the principal source of maintaining catch rates. Stocking levels are often controversial and set with limited information about the relative contribution of wild fish to lake-wide populations. Recent research documenting large numbers of age-0 fish in tributaries suggested that wild reproduction was increasing and greater than previously thought. Estimating the contribution of wild Chinook salmon is imperative for successful management of this economically important recreational fishery. To differentiate wild from hatchery-derived Chinook salmon, we developed and validated a classification rule from scale pattern analysis of known-origin fish that was based on the area of the scale focus and the distance between the scale focus and the first circulus. We used this technique to determine the annual proportion of angler-caught, age-3 wild Chinook salmon in Lake Ontario from 1992 to 2005. On average over 14 years, the annual proportion of wild age-3 Chinook salmon was 62% (± 13.6%, 95% CI), but has varied between 24% (± 9.4%) and 82% (± 11.2%). Wild fish have been a high proportion of the Chinook salmon population in Lake Ontario since the late 1980s throughout a period when the lake underwent considerable changes, suggesting that wild and hatchery-origin Chinook salmon are both important components for managing the predator–prey dynamics in Lake Ontario and maintaining angler catch rates.     

Evaluating the growth potential of sea lampreys (Petromyzon marinus) feeding on siscowet lake trout (Salvelinus namaycush) in Lake Superior

Differences in the preferred thermal habitat of Lake Superior lake trout morphotypes create alternative growth scenarios for parasitic sea lamprey (Petromyzon marinus) attached to lake trout hosts. Siscowet lake trout (Salvelinus namaycush) inhabit deep, consistently cold water (4-6 °C) and are more abundant than lean lake trout (Salvelinus namaycush) which occupy temperatures between 8 and 12 °C during summer thermal stratification. Using bioenergetics models we contrasted the growth potential of sea lampreys attached to siscowet and lean lake trout to determine how host temperature influences the growth and ultimate size of adult sea lamprey. Sea lampreys simulated under the thermal regime of siscowets are capable of reaching sizes within the range of adult sea lamprey sizes observed in Lake Superior tributaries. High lamprey wounding rates on siscowets suggest siscowets are important lamprey hosts. In addition, siscowets have higher survival rates from lamprey attacks than those observed for lean lake trout which raises the prospect that siscowets serve as a buffer to predation on more commercially desirable hosts such as lean lake trout, and could serve to subsidize lamprey growth.     

Fall diet and bathymetric distribution of deepwater sculpin (Myoxocephalus thompsonii) in Lake Huron

Deepwater sculpin Myoxocephalus thompsonii are an important component of Great Lake's offshore benthic food webs. Recent declines in deepwater sculpin abundance and changes in bathymetric distribution may be associated with changes in the deepwater food web of Lake Huron, particularly, decreased abundance of benthic invertebrates such as Diporeia. To assess how deepwater sculpins have responded to recent changes, we examined a fifteen-year time series of spatial and temporal patterns in abundance as well as the diets of fish collected in bottom trawls during fall of 2003, 2004, and 2005. During 1992–2007, deepwater sculpin abundance declined on a lake-wide scale but the decline in abundance at shallower depths and in the southern portion of Lake Huron was more pronounced. Of the 534 fish examined for diet analysis, 97% had food in the stomach. Mysis, Diporeia, and Chironomidae were consumed frequently, while sphaerid clams, ostracods, fish eggs, and small fish were found in only low numbers. We found an inverse relationship between prevalence of Mysis and Diporeia in diets that reflected geographic and temporal trends in abundance of these invertebrates in Lake Huron. Because deepwater sculpins are an important trophic link in offshore benthic food webs, declines in population abundance and changes in distribution may cascade throughout the food web and impede fish community restoration goals.     

The extent of cage aquaculture,adherence to best practices and reflections for sustainable aquaculture on African inland waters

Cage aquaculture is expanding on African inland waters and has potential to close the fish supply deficit in the region and provide other social benefits such as employment and income. However, if not appropriately guided and regulated, cage aquaculture could become unsustainable, causing conflicts with other water uses, environmental degradation and economic losses to aquaculture enterprises. To enhance sustainability of cage aquaculture on the African inland waters, we developed an inventory of cage aquaculture installations and used it to investigate the distribution and magnitude of cage aquaculture and adherence to best practices for sustainable aquaculture. Our results show evidence of spatial expansion of cage aquaculture on the African inland waters, of varying magnitude across and within water bodies and partial adherence to best practices. Cage aquaculture was confirmed on 18 water bodies which together share 263 installations with more than 20,000 cages. Lakes Victoria, Kariba, Volta and River Volta host 82.9% of cage aquaculture installations on the African inland waters and are major areas for cage aquaculture. Contrary to best practices, evidence shows cage aquaculture installations entirely or in close proximity to protected areas, in eutrophic and hypertrophic waters, shallow water bodies and sites (≥5 m average depth) and close to the shoreline. Cage aquaculture is qualified as an additional stressor to the African inland waters and because it is expected to continue expanding, adherence to best practices should be promoted for sustainability.     

Seasonal distribution of bloater (Coregonus hoyi) in the waters of Lake Huron surrounding the Bruce Peninsula

Information about bloater (Coregonus hoyi) habitat in Lake Huron was limited to correlations between commercial yield and fishing depth, despite available information from other Great Lakes. We identified seasonal patterns of bloater habitat use in hypolimnetic waters surrounding the Bruce Peninsula, Lake Huron. We applied a delta-lognormal model to fisheries-independent survey data to evaluate whether bloater catch-per-unit-effort was related to depth, temperature, and bathymetric slope. A Bayesian variable selection technique indicated that bloater distribution was most strongly related to bottom depth and water temperature. Our study also reconfirmed a previously-described pattern of seasonal inshore movement during warmer months followed by a return to deeper offshore waters during cooler months. By focusing our sampling within the hypolimnion, we characterized intra-annual patterns of bloater habitat use with respect to a temperature gradient near the minimum thermal requirements reported for this species. Bloater distribution under these thermal conditions has not been previously reported.     

Phytoplankton community composition of Saginaw Bay,Lake Huron,during the zebra mussel (Dreissena polymorpha) invasion: A multivariate analysis

The colonization of the zebra mussel (Dreissena polymorpha) in Saginaw Bay dramatically altered the phytoplankton community composition resulting in exclusion of light sensitive species and dominance of species with oligotrophic preferences and light resistance. In 1990, the NOAA Great Lakes Environmental Research Laboratory initiated a 7-year survey program to monitor changes in the lower food web of Saginaw Bay, where zebra mussels became established in the fall of 1991. To investigate shifts in the phytoplankton community composition over the 7-year period from 1990 to 1996 we searched for clusters of similar composition using multivariate principal component analysis (PCA) on proportions of 22 taxonomic groupings of the total phytoplankton density (cells per milliliter). We then used an agglomerative hierarchical clustering analysis of the PCA scores. We identified five characteristic phytoplankton communities in configurations that allowed recognizing four distinct periods in Saginaw Bay linked to the zebra mussel invasion. Significant changes were indicative of increased water clarity and eutrophic conditions being replaced by more oligotrophic conditions as clusters dominated by light sensitive species, such as the cyanobacteria Oscillatoria redekii, became immediately rare and clusters dominated by diatoms such as Cyclotella spp. became common. Microcystis spp., a light tolerant cyanobacteria not grazed by zebra mussel, dominated assemblages after 1994. The shifts in phytoplankton composition confirm that zebra mussels effects on phytoplankton communities are mediated by both direct (filtration) and indirect (nutrient cycling) mechanisms and also suggests that increased light penetration is an important mechanism behind some changes.     

Using Microfossil Remains in Lake Sediments to Examine the Invasion of Eubosmina coregoni (Cladocera,Bosminidae) in Lake of the Woods,Ontario, Canada

Many nonindigenous species (NIS) present in the Laurentian Great Lakes are expanding their ranges to inland lakes and streams. This study used cladoceran microfossils to examine the invasion history of Eubosmina coregoni, the first known nonindigenous zooplankter to invade Lake of the Woods (LOW), Ontario, Canada. Sediment cores from 16 sites in LOW were used to analyze broad-scale presence/absence of E. coregoni prior to human development (bottom sediment samples) in comparison with present-day distribution (top sediment samples). E. coregoni had the highest relative abundance in the northern and eastern regions of LOW and the abundance of all cladoceran remains was low in the southern region of the lake. A long core (time core) from Clearwater Bay provided a more detailed historical account of E. coregoni's abundance in the northern region of LOW, indicating that E. coregoni was first detected in the lake in the early 1990s, approximately 25 years after it was discovered in the Laurentian Great Lakes. Results obtained in this study have illuminated temporal and spatial patterns of colonization of this inland water body. Study of the early invasion dynamics of NIS in these inland lakes may aid in the prevention of future invasions of taxa that have already altered the food web dynamics in the Laurentian Great Lakes.     

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.     

Evidence of lake trout (Salvelinus namaycush) spawning and spawning habitat use in the Dog River,Lake Superior

Lake trout spawn primarily in lakes, and the few river-spawning populations that were known in Lake Superior were believed to be extirpated. We confirmed spawning by lake trout in the Dog River, Ontario, during 2013–2016 by the collection of and genetic identification of eggs, and we describe spawning meso- and microhabitat use by spawning fish. Between 2013 and 2016, a total of 277 lake trout eggs were collected from 39 of 137 sampling locations in the river. The majority of eggs (220) were collected at the transition between the estuary and the river channel crossing the beach. Lake trout eggs were most often located near the downstream end of pools in areas characterized by rapid changes in depth or slope, coarse substrates, and increased water velocities, where interstitial flows may occur. Depths in wadeable areas where eggs were found averaged 0.9?m (range: 0.4 to 1.3?m) and substrate sizes consisted of large gravel, cobble, and boulder; comparable to spawning characteristics noted in lakes. Water velocities averaged 0.66?m·s^?1 (range: 0.33 to 1.7?m³·s^?1) at mid-depth. This information on spawning habitat could be used to help locate other remnant river-spawning populations and to restore river-spawning lake trout and their habitat in rivers that previously supported lake trout in Lake Superior. The Dog River population offers a unique opportunity to understand the ecology of a river spawning lake trout population.     

Genetic variation at the mtDNA ND-1 locus among North American wild and hatchery brown trout (Salmo trutta)

Despite extensive knowledge of mitochondrial DNA (mtDNA) variation in European brown trout (Salmo trutta) populations, little is known about their nucleotide sequence variation in North America. The objective of this study was to quantify single nucleotide polymorphisms (SNPs) at the ND-1 mtDNA locus of 62 brown trout from hatcheries in Michigan and Wisconsin as well as Michigan streams and Lake Michigan. We identified 25 SNPs that characterized nine distinct mtDNA haplotypes in the Wild Rose, Gilchrist and Seeforellen brown trout strains. Although most SNPs were represented by synonymous nucleotide substitutions, three individuals of the Seeforellen strain had non-synonymous nucleotide changes. MtDNA haplotypes identified in North American brown trout in this study showed nucleotide similarity at the ND-1 locus to brown trout from northern Europe.     

Statistical Analysis of the Spatial and Temporal Variability of the Ratio Chlorophyll A to Phytoplankton Cell Volume in Saginaw Bay,Lake Huron

Chlorophyll a has traditionally been used as an indicator of phytoplankton concentration in natural waters. This parameter has also been widely used by phytoplankton modelers for the purpose of comparing model output with field data. Examination of 1974 field data from Saginaw Bay indicated that chlorophyll a concentrations were inconsistent with phytoplankton cell volume concentrations. Statistical procedures were employed to determine the significance and source of the observed variability in the ratio of chlorophyll a to cell volume concentrations.The procedures employed included t-tests, analysis of variance and polynomial regression. The hypothesis that the natural log of the ratio of chlorophyll a to cell volume was constant in time was tested on six different sampling station groupings representing various spatial divisions of Saginaw Bay. In all cases, this ratio was found to vary significantly at the 95% confidence level. The variability of the ratio decreased when only data from the outer portion of Saginaw Bay were used. Greater than 60% of the variability of the ratio can be removed by using a linear correlation of the natural log chlorophyll a to cell volume ratio with the fraction of diatom cell volume.     

Differences in pyloric caeca counts between lean and siscowet lake trout (Salvelinus namaycush) in southern Lake Superior

There are four documented morphotypes of lake trout (Salvelinus namaycush) in Lake Superior, with the two dominant forms being the shallow water lean and the deep water siscowet. These morphotypes are differentiated externally by morphometrics and meristics. Pyloric caeca counts have been used to distinguish closely related fish species including the Salvelinus genus. From samples collected in 2009, 2011–2013, and 2017, we counted and measured pyloric caeca from 116 lean and 119 siscowet lake trout from southern Lake Superior. For a subset of 22 leans and 19 siscowets between 575 and 625 mm, we measured individual pyloric caecum basal diameter, length, and estimated individual caecum and total caeca surface areas. Siscowets had significantly fewer and thicker pyloric caeca than leans, but caecum length did not differ between the morphotypes. Mean pyloric caeca count for siscowets and leans was 131 and 153, respectively. Mean individual caecum surface area was 31% higher in siscowets than in leans. When adjusted for mean total number of pyloric caeca, total caecum surface area for siscowets was 12% greater than leans. We postulate that greater pyloric caecum surface area in siscowets may be an adaption for greater lipid uptake because they have substantially higher lipid content than leans. Based on our findings, pyloric caeca counts can be used in addition to other meristic and morphometric characteristics to help distinguish lean and siscowet lake trout.     

Movement and growth indicators in resident and adfluvial coaster brook trout (Salvelinus fontinalis) in the Hurricane River,Lake Superior,Michigan, USA

Brook trout (Salvelinus fontinalis) are found throughout Lake Superior, Lake Nipigon, and their tributaries. Lacustrine and adfluvial life history variants were historically popular with anglers and were called coasters; coaster brook trout populations are now severely reduced and are of conservation concern. Coasters were known to grow larger and mature later than their stream resident counterparts. This study compared movement patterns, age, size, condition, and relative weight of wild coaster and resident brook trout from the Hurricane River, Pictured Rocks National Lakeshore, Michigan. Wild brook trout ≥ 100 mm from the Hurricane River downstream from Hurricane Falls were tagged with passive integrated transponder tags and monitored for stream-lake movement behavior from May 2003 to November 2007. During 2006 and 2007, brook trout were scale sampled and aged to construct a regression that was then used to calculate the age of all brook trout tagged from 2003 to 2007. Most brook trout movement took place in the fall with October the peak month of emigration with a secondary peak in late spring/early summer and some activity nearly year round. There were no differences found in age structure, size or condition between coasters and residents while in the stream. Our data suggest that a priori growth differences are not determining the expression of coaster outmigration and that stream-lake movements made by coasters, likely driven by habitat requirements, may be highly flexible and facultative.     

Genetic assessment of straying rates of wild and hatchery reared lake sturgeon (Acipenser fulvescens) in Lake Superior tributaries

Natal philopatry in lake sturgeon (Acipenser fulvescens) has been hypothesized to be an important factor that has lead to genetically distinct Great Lakes populations. Due to declining abundance, population extirpation, and restricted distribution, hatchery supplementation is being used to augment natural recruitment and to reestablish populations. If hatchery-reared lake sturgeon are more likely to stray than naturally produced individuals, as documented in other well-studied species, outbreeding could potentially jeopardize beneficial site-specific phenotypic and genotypic adaptations. From 1983 to 1994, lake sturgeon propagated using eggs taken from Lake Winnebago adults (Lake Michigan basin) were released in the St. Louis River estuary in western Lake Superior. Our objective was to determine whether these introduced individuals have strayed into annual spawning runs in the Sturgeon River, Michigan. Additionally, we estimated a natural migration rate between the Sturgeon River and Bad River, Wisconsin populations. Presumed primiparous lake sturgeon sampled during Sturgeon River spawning runs from 2003 to 2008 were genotyped at 12 microsatellite loci. Genotypic baselines established for the Sturgeon River (n = 101), Bad River (n = 40), and Lake Winnebago river system (n = 73) revealed a relatively high level of genetic divergence among populations (mean F_ST = 0.103; mean R_ST = 0.124). Likelihood-based assignment tests indicated no straying of stocked Lake Winnebago strain lake sturgeon from the St. Louis River into the Sturgeon River spawning population. One presumed primiparous Sturgeon River individual likely originated from the Bad River population. Four first-generation migrants were detected in the Sturgeon River baseline, indicating an estimated 3.5% natural migration rate for the system.