Allison N. Evans

Increasing Thiamine Concentrations in Lake Trout Eggs from Lakes Huron and Michigan Coincide with Low Alewife Abundance

Abstract Lake trout Salvelinus namaycush in the Laurentian Great Lakes suffer from thiamine deficiency as a result of adult lake trout consuming prey containing thiaminase, a thiamine-degrading enzyme. Sufficiently low egg thiamine concentrations result in direct mortality of or sublethal effects on newly hatched lake trout fry. To determine the prevalence and severity of low thiamine in lake trout eggs, we monitored thiamine concentrations in lake trout eggs from 15 sites in Lakes Huron and Michigan from 2001 to 2009. Lake trout egg thiamine concentrations at most sites in both lakes were initially low and increased over time at 11 of 15 sites, and the proportion of females with egg thiamine concentrations lower than the recommended management objective of 4 nmol/g decreased over time at eight sites. Egg thiamine concentrations at five of six sites in Lakes Huron and Michigan were significantly inversely related to site-specific estimates of mean abundance of alewives Alosa pseudoharengus, and successful...

Understanding the ecology of disease in Great Lakes fish populations

Disease may be an important factor affecting wild fish population dynamics in the Great Lakes, but a lack of information on the ecology of fish disease currently precludes the prediction of risks to fish populations. Here we propose a conceptual framework for conducting ecologically-oriented fish health research that addresses the inter-relationships among fish health, fish populations, and ecosystem dysfunction in the Great Lakes. The conceptual framework describes potential ways in which disease processes and the population-level impacts of disease may relate to ecosystem function, and suggests that functional ecosystems are more likely to be resilient with respect to disease events than dysfunctional ecosystems. We suggest that ecosystem- or population-level research on the ecology of fish disease is necessary to understand the relationships between ecosystem function and fish health, and to improve prediction of population-level effects of diseases on wild fish populations in the Great Lakes. Examples of how the framework can be used to generate research questions are provided using three disease models of current interest in the Great Lakes: thiamine deficiency complex, botulism, and bacterial kidney disease.

Dreissenid mussels from the Great Lakes contain elevated thiaminase activity

ABSTRACT We examined thiaminase activity in dreissenid mussels collected at different depths and seasons, and from various locations in Lakes Michigan, Ontario, and Huron. Here we present evidence that two dreissenid mussel species (Dreissena bugensis and D. polymorpha) contain thiaminase activity that is 5–100 fold greater than observed in Great Lakes fishes. Thiaminase activity in zebra mussels ranged from 10,600 to 47,900 pmol g-1·min-1 and activities in quagga mussels ranged from 19,500 to 223,800 pmol g-1 ·min-1. Activity in the mussels was greatest in spring, less in summer, and least in fall. Additionally, we observed greater thiaminase activity in dreissenid mussels collected at shallow depths compared to mussels collected at deeper depths. Dreissenids constitute a significant and previously unknown pool of thiaminase in the Great Lakes food web compared to other known sources of this thiamine (vitamin B1)-degrading enzyme. Thiaminase in forage fish of the Great Lakes has been causally linked to thiamine deficiency in salmonines. We currently do not know whether linkages exist between thiaminase activities observed in dreissenids and the thiaminase activities in higher trophic levels of the Great Lakes food web. However, the extreme thiaminase activities observed in dreissenids from the Great Lakes may represent a serious unanticipated negative effect of these exotic species on Great Lakes ecosystems.

Phylogenetic and Ecological Characteristics Associated with Thiaminase Activity in Laurentian Great Lakes Fishes

Abstract Thiamine deficiency complex (TDC) causes mortality and sublethal effects in Great Lakes salmonines and results from low concentrations of egg thiamine that are thought to be caused by thiaminolytic enzymes (i.e., thiaminase) present in the diet. This complex has the potential to undermine efforts to restore lake trout Salvelinus namaycush and severely restrict salmonid production in the Great Lakes. Although thiaminase has been found in a variety of Great Lakes fishes, the ultimate source of thiaminase in Great Lakes fishes is currently unknown. We used logistic regression analysis to investigate relationships between thiaminase activity and phylogenetic or ecological characteristics of 39 Great Lakes fish species. The taxonomically more ancestral species were more likely to show thiaminase activity than the more derived species. Species that feed at lower trophic levels and occupy benthic habitats also appeared to be more likely to show thiaminase activity; these variables were correlated with t...

Migratory Patterns of Wild Chinook Salmon Oncorhynchus tshawytscha Returning to a Large, Free-Flowing River Basin

Upriver movements were determined for Chinook salmon Oncorhynchus tshawytscha returning to the Yukon River, a large, virtually pristine river basin. These returns have declined dramatically since the late 1990s, and information is needed to better manage the run and facilitate conservation efforts. A total of 2,860 fish were radio tagged during 2002–2004. Most (97.5%) of the fish tracked upriver to spawning areas displayed continual upriver movements and strong fidelity to the terminal tributaries entered. Movement rates were substantially slower for fish spawning in lower river tributaries (28–40 km d-1) compared to upper basin stocks (52–62 km d-1). Three distinct migratory patterns were observed, including a gradual decline, pronounced decline, and substantial increase in movement rate as the fish moved upriver. Stocks destined for the same region exhibited similar migratory patterns. Individual fish within a stock showed substantial variation, but tended to reflect the regional pattern. Differences between consistently faster and slower fish explained 74% of the within-stock variation, whereas relative shifts in sequential movement rates between “hares” (faster fish becoming slower) and “tortoises” (slow but steady fish) explained 22% of the variation. Pulses of fish moving upriver were not cohesive. Fish tagged over a 4-day period took 16 days to pass a site 872 km upriver. Movement rates were substantially faster and the percentage of atypical movements considerably less than reported in more southerly drainages, but may reflect the pristine conditions within the Yukon River, wild origins of the fish, and discrete run timing of the returns. Movement data can provide numerous insights into the status and management of salmon returns, particularly in large river drainages with widely scattered fisheries where management actions in the lower river potentially impact harvests and escapement farther upstream. However, the substantial variation exhibited among individual fish within a stock can complicate these efforts.

Can humans coexist with fishes

Deciding which textbook to assign to students is often a very difficult decision. A textbook should offer more than just a synthesis of information, it should inspire curiosity, cause one to reflect, and provide a framework for making decisions. Most reviews reflect a single opinion, sometimes based on personal preferences. What is missing from most reviews is an assessment of how a book affected students. We approach this book review differently. We present separate reviews by the instructors and the students participating in a graduate seminar on Fish Conservation. The class format was a mixture of guest lecturers and group discussion. Students were required to write critical comments about each chapter of the book. They understood that they would be co-authors on this review and critical assessment was necessary. The presumption is that similarities between two reviews suggest consensus, but that differences reflect honest differences of opinion as well as differences in background and experience.

The role of maternal age and context-dependent maternal effects in the offspring provisioning of a long-lived marine teleost

Despite evidence of maternal age effects in a number of teleost species, there have been challenges to the assertion that maternal age intrinsically influences offspring quality. From an evolutionary perspective, maternal age effects result in young females paradoxically investing in less fit offspring despite a greater potential fitness benefit that might be gained by allocating this energy to individual somatic growth. Although a narrow range of conditions could lead to a maternal fitness benefit via the production of lower quality offspring, evolutionary theorists suggest these conditions are seldom met and that the reported maternal age effects are more likely products of the environmental context. Our goal was to determine if maternal effects operated on offspring provisioning in a long-lived rockfish (genus Sebastes), and to evaluate any such effects as an intrinsic function of maternal age or a context-dependent effect of the offspring release environment. We found that offspring provisioning is a function of both maternal age and the timing of offspring release; older females exhibit increased provisioning over younger females throughout the spawning season despite a decrease in provisioning across all maternal ages as the season progresses. These findings suggest a role for both maternal age effects and a potential context-dependent maternal effect in population productivity, carrying important implications when modelling population persistence and resilience.

Thiamine deficiency in fishes: Causes, consequences, and potential solutions

Thiamine deficiency complex (TDC) is a disorder resulting from the inability to acquire or retain thiamine (vitamin B1) and has been documented in organisms in aquatic ecosystems ranging from the Baltic Sea to the Laurentian Great Lakes. The biological mechanisms leading to TDC emergence may vary among systems, but in fishes, one common outcome is high mortality among early life stages. Here, we review the causes and consequences of thiamine deficiency in fishes and identify potential solutions. First, we examine the biochemical and physiological roles of thiamine in vertebrates and find that thiamine deficiency consistently results in impaired neurological function across diverse taxa. Next, we review natural producers of thiamine, which include bacteria, fungi, and plants, and suggest that thiamine is not currently limiting for most animal species inhabiting natural aquatic environments. A survey of historic occurrences of thiamine deficiency identifies consumption of a thiamine-degrading enzyme, thiaminase, as the primary explanation for low levels of thiamine in individuals and subsequent onset of TDC. Lastly, we review conservation and management strategies for TDC mitigation ranging from evolutionary rescue to managing for a diverse forage base. As recent evidence suggests occurrences of thiamine deficiency may be increasing in frequency, increased awareness and a better mechanistic understanding of the underlying causes associated with thiamine deficiency may help prevent further population declines.

Threatened fishes of the world: Deltistes luxatus (Cope 1879) (Catostomidae)

Common name: Lost River sucker, mullet, c’waam. Conservation status: Endangered: (USFWS 1988; Gimenez Dixon 1996). Identification: D 10–12, LL 82–113, gill rakers 23–37 in adults >200 mm, 44–48 post-Weberian vertebrae. Elongate body with long, narrow head, long snout, small eyes. Upper lip thin (two to five rows of large papillae). Lower lip (one to three rows of papillae) deeply notched. Adults up to 1 m TL and 4.5 kg. Maximum recorded age: 43 years. Illustration by Joe Tomelleri. Distribution: Historically widely distributed in upper Klamath and Lost River basins (Oregon/California). Limited to the following lakes/rivers and their tributaries: Upper Klamath Lake, Clear Lake, Lost River, Tule Lake, and Klamath River to Copco Reservoir. Abundance: Historically very abundant; sufficiently abundant to support a fishery. Long-term abundance data limited, but dramatic decline evident (NRC 2004). Current population size estimated in the tens of thousands (USFWS 2007). Low recruitment and low adult survival may indicate future declines (USFWS 2007). Habitat and ecology: Lakes: shallow depths, cool water (16–24°C), moderate alkalinity (pH 7.2– 9.2), DO levels of 6–10 mg/L (Moyle 2002). Feeds benthically on detritus and invertebrates. Reproduction: Spawns at shoreline lake springs and in tributaries from February–May in shallow riffle/run habitat with gravel substrate and moderate current. Matures between 5– 9 years (Scoppettone and Vinyard 1991); most mature by age 9. Iteroparous. Threats: Current threats include hyper-eutrophication of Upper Klamath Lake and mass mortality of adults; loss of aquatic marsh habitat from drainage of wetlands for agriculture; conflicting water management goals; and predation of larvae by nonnative species. Some measures addressing limited access to spawning areas by dams and entrainment by water control structures are underway. Conservation action: ESA listing prompted wetland/riparian restoration, dam removal, and fish screening/passage programs. Remarks: Recovery is complicated by the long life span, episodic recruitment, and multiple demands on water management of the upper Klamath Basin. Environ Biol Fish (2009) 86:401–402 DOI 10.1007/s10641-009-9530-3