Andrew M. Muir

Global introductions of salmon and trout in the genus Oncorhynchus: 1870-2007

The purpose of this review is to provide a global perspective on Oncorhynchus salmonine introductions and put-and-take fisheries based on modern stocking programs, with special emphasis on freshwater ecosystems. We survey the global introductions of nine selected salmonines of the genus Oncorhynchus: golden trout, cutthroat trout, pink salmon, chum salmon, coho salmon, masu/cherry salmon, rainbow trout/steelhead, sockeye salmon/kokanee, and chinook salmon. The information is organized on a geographical basis by continent, and then by species and chronology. Two different objectives and associated definitions of ‘success’ for introductions are distinguished: (a) seed introduction: release of individuals with the purpose of creating a wild-reproducing, self-sustaining population; and (b) put-and-take introduction: release of individuals with the purpose of maintaining some level of wild population abundance, regardless of wild reproduction. We identify four major phenomena regarding global salmonine introductions: (1) general inadequacy of documentation regarding introductions; (2) a fundamental disconnect between management actions and ecological consequences of introductions; (3) the importance of global climate change on success of previous and future introductions; and (4) the significance of aquaculture as a key uncertainty in accidental introductions. We conclude this review with a recognition of the need to terminate ongoing stocking programs for introduced salmonines worldwide.

Ecomorphological Diversity of Lake Trout at Isle Royale, Lake Superior

AbstractFour Lake Trout Salvelinus namaycush morphs were identified from Isle Royale, Lake Superior; the morphs differed in shape, traits linked to feeding and locomotion, buoyancy, and physical habitat use. Lean, humper, and siscowet Lake Trout generally conformed to previous descriptions, and we report, for the first time, quantitative evidence of a fourth morph, previously described anecdotally as the “redfin.” Jackknife classification of individuals to morphs based on body shape were 94% correct. High variation within and low variation among morphs led to moderately low percent agreement among visual identifications and high uncertainty in Bayesian model groupings of morphs. Eight linear measures of phenotypic traits linked to feeding (i.e., head and eyes) and locomotion (i.e., fin lengths and caudal peduncle shape) varied among morphs, consistent with specialized adaptations for trophic and physical resource use. Habitat differed among morphs with leans being most abundant in the 0–50-m depth stratum...

A Perspective on Perspectives: Methods to Reduce Variation in Shape Analysis of Digital Images

Abstract We present digital imaging methods for geometric morphometric analysis of shape, and we describe issues associated with improper image acquisition by using lake trout Salvelinus namaycush as an example. The choice of imaging equipment, the configuration of that equipment, and the orientation of the specimens with respect to the camera lens can lead to inaccurate imaging and ultimately to error in landmark placement during morphometric analysis. Lake trout that were imaged at 15-mm focal length and 0.5-m focal distance (treatment 1) were distorted in comparison with fish that were imaged at 50-mm focal length and 2-m focal distance (treatment 2). Deformation grids showed dramatic variation in the horizontal plane along the length of the fish, especially midbody, suggesting that barrel distortion was occurring at the 15-mm focal length. Partial warp scores resulting from geometric analysis of body shape differed for all fish on all 18 warps as a result of the different focal length and distance tre...

A Comparison of the Scale and Otolith Methods of Age Estimation for Lake Whitefish in Lake Huron

Abstract We compared sagittal otolith and scale age estimation methodologies for lake whitefish Coregonus clupeaformis collected in Georgian Bay and the main basin of Lake Huron between 2002 and 2004 in terms of the age, growth, and mortality estimates generated by the two methodologies. In general, otolith age estimates were higher than scale age estimates. Forty-nine percent of the fish aged by otoliths were judged to be greater than 10 years of age, compared with 5% of the fish aged by scales, and more age-classes were found when otoliths were used. Otolith and scale ages agreed for 16% (n = 60) of Georgian Bay fish and only 9% (n = 27) of main-basin fish. The overall coefficients of variation for the otolith and scale age estimation methodologies pooled across years and basins were 5.52% and 2.68%, respectively. Mean length at age based on otoliths was significantly lower than mean length at age based on scales. Variation in the mean length at age was greatest for fish age 7 and older. Otolith-based c...

An Evaluation of Age Estimation Structures for Lake Whitefish in Lake Michigan: Selecting an Aging Method Based on Precision and a Decision Analysis

Abstract Declines in growth and condition of lake whitefish Coregonus clupeaformis in Lakes Huron and Michigan have led to increased mean age in the harvest and greater difficulty in scale age interpretation. We evaluated the precision and efficiency of scale acetate impressions, transverse pectoral fin ray sections, and transverse sagittal otolith sections for three lake whitefish stocks (Baileys Harbor, Naubinway, and Saugatuck) that were sampled in Lake Michigan during 2004 and 2005. We conducted a decision matrix analysis that incorporated capital, production, and personnel costs and precision of age estimates to determine the best aging method given current management priorities. For the Baileys Harbor stock, age estimates were systematically lower based on scales (mean = 7.85 years) than based on fin rays (8.44 years) or otoliths (8.78 years); fin ray and otolith estimates did not differ significantly. Similar results were observed for both Naubinway and Saugatuck stocks. For Baileys Harbor lake ...

The adaptive capacity of lake food webs: from individuals to ecosystems

Aquatic ecosystems support size structured food webs, wherein predator-prey body sizes span orders of magnitude. As such, these food webs are replete with extremely generalized feeding strategies, especially among the larger bodied, higher trophic position taxa. The movement scale of aquatic organisms also generally increases with body size and trophic position. Together, these body size, mobility, and foraging relationships suggest that organisms lower in the food web generate relatively distinct energetic pathways by feeding over smaller spatial areas. Concurrently, the potential capacity for generalist foraging and spatial coupling of these pathways often increases, on average, moving up the food web toward higher trophic levels. We argue that these attributes make for a food web architecture that is inherently ‘adaptive’ in its response to environmental conditions. This is because variation in lower trophic level dynamics is dampened by the capacity of predators to flexibly alter their foraging behavior. We argue that empirical, theoretical, and applied research needs to embrace this inherently adaptive architecture if we are to understand the relationship between structure and function in the face of ongoing environmental change. Toward this goal, we discuss empirical patterns in the structure of lake food webs to suggest that ecosystems change consistently, from individual traits to the structure of whole food webs, under changing environmental conditions. We then explore an empirical example to reveal that explicitly unfolding the mechanisms that drive these adaptive responses offers insight into how human-driven impacts, such as climate change, invasive species, and fisheries harvest, ought to influence ecosystem structure and function (e.g., stability, secondary productivity, maintenance of major energy pathways). We end by arguing that such a directed food web research program promises a powerful across-scale framework for more effective ecosystem monitoring and management.

Spatio-Temporal Trends in the Food Habits of Age-0 Lake Whitefish

ABSTRACT We compared diets of juvenile lake whitefish among six sites in Lake Michigan and one in Lake Superior during 2005 and 2006 to assess spatial and temporal patterns in food habits and evaluate if ontogenetic diet shifts occur that may influence growth and survival. A total of 262 and 496 juveniles were captured in 2005 and 2006, the majority of which were captured during June and July. Sites in southern Lake Michigan tended to have larger juveniles, and the smallest juveniles were observed at Naubinway, northern Lake Michigan, and Whitefish Point, Lake Superior. The mean number of prey items per stomach differed among sampling sites and years. Copepods were the most prevalent prey item, and were present in greater than 70% of juvenile stomachs from most sites. However, the percent by number of copepods decreased during July as chironomids and other benthic macroinvertebrates increased in number. There was a significant positive relationship between percent of benthic prey items and mean length of juvenile lake whitefish. A substantial increase in the percent of benthic prey consumed after 40 mm (total length) was observed and likely resulted from juvenile lake whitefish crossing a size threshold for benthic feeding relating to morphological changes (i.e., transition of mouth opening from terminal to sub-terminal) in addition to a potential increase in the availability of emergent macroinvertebrates. Timing of the transition to benthic feeding is likely regulated by the number of prey per juvenile and the overlap with peak emergence of important benthic aquatic invertebrates such as chironomids. A better understanding of these factors will increase our understanding of juvenile lake whitefish growth and survival, which are necessary for improving year-class strength predictions.

Measures of Larval Lake Whitefish Length and Abundance as Early Predictors of Year-Class Strength in Lake Michigan

ABSTRACT Many lake whitefish stocks in Lake Michigan have experienced substantial declines in growth and condition since the 1990s. Reduced growth and condition could result in reduced quality or quantity of eggs produced by spawning females, which in turn could negatively impact recruitment. We evaluated the potential for reduced recruitment by measuring early life stage density and length, and we discuss the utility of these measures as early indicators of lake whitefish year-class strength. Overall, mean larval density (number per 1000 m3 ± SE) in Lake Michigan was greater in 2006 (373.7 ± 28.3) than in 2005 (16.6±24.8); whereas, mean length (mm±SE) of larval lake whitefish was smaller in 2006 (12.87±0.07) than in 2005 (14.38± 0.13). The ratio of Zooplankton to fish density did not show an expected relationship with larval fish density or length. Rather, variation in larval density was best explained by a multiple-regression model that included larval length, spring wind intensity, and adult stock density as predictor variables. Our results suggest that the density of larval lake whitefish is not directly regulated by temperature or Zooplankton density at the time of emergence, but that a potential for density-dependent regulation exists when larval emergence rates are high. We conclude that the observed declines in growth and condition of adult lake whitefish are not resulting in substantial reductions in recruitment.

Does Condition of Lake Whitefish Spawners Affect Physiological Condition of Juveniles

ABSTRACT Recent declines in growth and condition of several Great Lakes lake whitefish populations have raised concerns over potential impacts on juvenile physiological condition and ultimately recruitment. To test whether the condition of spawning adults influences juvenile condition via energy allocation dynamics, we partitioned the variation in age 0 juvenile physiological condition (i.e., growth in length and weight, whole-body moisture content, energy density, and protein content) among adult male and female (i.e., body condition, muscle moisture content, energy density, and protein content) and egg (i.e., wet and dry weight, moisture content, energy density, energy content per egg, and protein content) effects using redundancy analysis. Overall, a model that included sampling site, female condition, and egg quality explained 39% of the variation in juvenile physiological condition. After partitioning out the effects of females and eggs, site explained the most variation (23%). When other factors were accounted for, neither females (1.4%) nor eggs (2.7%) explained much variation in juvenile physiological condition. Of the variables studied, female muscle energy density, muscle moisture content, and egg moisture content were most closely associated with juvenile physiological condition. Our results suggest that parental effects, such as size, age, body condition, or body composition, may not be as important as extrinsic site-related effects or density-dependent effects in determining juvenile physiological condition.

New insight into the spawning behavior of lake trout, Salvelinus namaycush, from a recovering population in the Laurentian Great Lakes

Spawning behavior of lake trout, Salvelinus namaycush, is poorly understood, relative to stream-dwelling salmonines. Underwater video records of spawning in a recovering population from the Drummond Island Refuge (Lake Huron) represent the first reported direct observations of lake trout spawning in the Laurentian Great Lakes. These observations provide new insight into lake trout spawning behavior and expand the current conceptual model. Lake trout spawning consisted of at least four distinct behaviors: hovering, traveling, sinking, and gamete release. Hovering is a new courtship behavior that has not been previously described. The apparent concentration of hovering near the margin of the spawning grounds suggests that courtship and mate selection might be isolated from the spawning act (i.e., traveling, sinking, and gamete release). Moreover, we interpret jockeying for position displayed by males during traveling as a unique form of male-male competition that likely evolved in concert with the switch from redd-building to itinerant spawning in lake trout. Unlike previous models, which suggested that intra-sexual competition and mate selection do not occur in lake trout, our model includes both and is therefore consistent with evolutionary theory, given that the sex ratio on spawning grounds is skewed heavily towards males. The model presented in this paper is intended as a working hypothesis, and further revision may become necessary as we gain a more complete understanding of lake trout spawning behavior.