Brent A. Murry

Lakewide Estimates of Alewife Biomass and Chinook Salmon Abundance and Consumption in Lake Ontario, 1989-2005: Implications for Prey Fish Sustainability

Abstract Stocking levels of Chinook salmon Oncorhynchus tshawytscha for Lake Ontario have been highly controversial since the early 1990s, largely because of uncertainties about lakewide abundance and rates of prey consumption. Previous estimates have focused on years before 1995; since then, however, the Lake Ontario ecosystem has undergone substantial changes, and there is new evidence of extensive natural recruitment. Presented here are new abundance estimates of Chinook salmon and alewives Alosa pseudoharengus in Lake Ontario and a reevaluation of the potential risk of alewife population collapse. We found that Lake Ontario has been supporting, on average (1989–2005), 1.83 × 106 (range, 1.08 × 106 to 3.24 × 106) Chinook salmon of ages 1–4, amounting to a mean annual biomass of 11.33 × 103 metric tons (range, 5.83 × 103 to 23.04 × 103 metric tons). During the same period (1989–2005), the lake supported an alewife biomass of 173.66 × 103 metric tons (range, 62.37 × 103 to 345.49 × 103 metric tons); Chin...

Effects of dreissenid mussels, chironomids, fishes, and zooplankton on growth of round goby in experimental aquaria

There is a widely accepted paradigm supported by early field and laboratory observations that the adult round goby (Neogobius melanostomus) is highly adapted to, and primarily survives on, dreissenid mussels. However, more recent stable isotope and diet analyses indicate that the round goby may not rely on dreissenid prey to the extent that was previously believed. We conducted a feeding experiment where round gobies were provided with an excess of one of four naturally occurring diets for 25 days – dreissenid mussels, juvenile fish, chironomids, or zooplankton. Round gobies fed dreissenids had significantly lower growth (−0.04 g day−1) than individuals fed fish and chironomids (0.13 g day−1) and displayed the same weight loss as round gobies fed only zooplankton. Although dreissenids are often consumed by round gobies, this likely happens only when more profitable prey such as fish and non-dreissenid invertebrates are lacking or difficult to capture. Additionally, field observations of round goby diets that have supported the paradigm may overestimate the importance of dreissenid prey due to the longer retention time of shells in round goby guts compared to other soft-bodied prey. Our results provide direct evidence supporting recent findings that dreissenid mussels may not be as essential to round goby survival as previously considered.

Feeding Strategies and Diets of Young-of-the-Year Muskellunge from Two Large River Ecosystems

Abstract We analyzed stomach contents from 674 young-of-the-year (age-0) muskellunge Esox masquinongy sampled in New York waters of the St. Lawrence and upper Niagara rivers to (1) describe diets and document use of nonnative prey, (2) examine the feeding strategy (generalized versus specialized) and the importance of different prey types, (3) evaluate temporal patterns in feeding strategy and prey importance, and (4) determine how prey length related to muskellunge length and whether this relationship differed among prey types. Banded killifish Fundulus diaphanus, native cyprinids, and tessellated darters Etheostoma olmstedi were the most important prey numerically and by weight in the St. Lawrence River. Native cyprinids, banded killifish, and darters (Etheostoma spp. and Percina spp.) were the most important prey in the Niagara River, but nonnative cyprinids were more important by weight than darters. Muskellunge from both rivers exhibited a specialized feeding strategy, with individuals specializing o...

Shift in a large river fish assemblage: body-size and trophic structure dynamics.

As the intensity and speed of environmental change increase at both local and global scales it is imperative that we gain a better understanding of the ecological implications of community shifts. While there has been substantial progress toward understanding the drivers and subsequent responses of community change (e.g. lake trophic state), the ecological impacts of food web changes are far less understood. We analyzed Wabash River fish assemblage data collected from 1974-2008, to evaluate temporal variation in body-size structure and functional group composition. Two parameters derived from annual community size-spectra were our major response variables: (1) the regression slope is an index of ecological efficiency and predator-prey biomass ratios, and (2) spectral elevation (regression midpoint height) is a proxy for food web capacity. We detected a large assemblage shift, over at least a seven year period, defined by dramatic changes in abundance (measured as catch-per-unit-effort) of the dominant functional feeding groups among two time periods; from an assemblage dominated by planktivore-omnivores to benthic invertivores. There was a concurrent increase in ecological efficiency (slopes increased over time) following the shift associated with an increase in large-bodied low trophic level fish. Food web capacity remained relatively stable with no clear temporal trends. Thus, increased ecological efficiency occurred simultaneous to a compensatory response that shifted biomass among functional feeding groups.

Species turnover drives β-diversity patterns across multiple spatial and temporal scales in Great Lake Coastal Wetland Communities

Abstractβ dissimilarity indices have described community variation occurring from unique structuring processes: species turnover and nestedness. However, the importance of scale definition remains critical and challenging during β assessments with a need for simultaneous spatial and temporal assessment to determine ecological phenomena governing biological communities. We aim to examine the contribution of turnover and nestedness structuring processes across multiple spatial and temporal scales to demonstrate the importance of scale consideration in β assessments. Using a site-to-basin-wide spatiotemporal hierarchical design, we examined diversity patterns, testing spatial, and temporal facets of β diversity structuring Laurentian Great Lake coastal wetland fish and macroinvertebrate communities from 2000 to 2012. Both fish and macroinvertebrate communities were analyzed using β dissimilarity indices under the same hierarchical design. Results indicated strong spatial and temporal turnover structuring with increasing β diversity and community turnover as scale localized. We suggest that high turnover is the result of inhospitable winter conditions followed by random re-colonization events in the spring. With relatively unique communities across space and time, biodiversity-oriented management of coastal wetlands should consider an all-inclusive approach as biodiversity hotspots are not apparent.

Fish community size structure of small lakes: the role of lake size, biodiversity and disturbance

Aquatic community body size distributions are highly predictable with decreasing abundance and increasing body size. This basic relationship has led to significant increases in our understanding of the internal regulation processes of aquatic communities. However, most of our understanding of the patterns of community size structure is derived from large aquatic systems with little known about the dynamics of small lakes. Processes that promote predictable, or deterministic, community size structure likely differ with levels of biodiversity and disturbance patterns, both of which frequently co-vary with ecosystem size. Here we examine the influence of lake size, fish species richness, and natural disturbance regime on fish community size structure in six small lakes (<200 ha) on Beaver Island, Michigan, USA. Fish communities in three of the six lakes exhibited a deterministic size structure and it appears that disturbance regime is the most obvious barrier to developing and/or maintaining stable and predictable community size structure. In this study, lakes with less than 10 species and lakes experiencing periodic winterkills exhibited stochastic size structure. Lake size did not show any clear relation to fish community size structure. Collectively our results shed some light on the conditions that promote (or do not promote) deterministic size structure.

Application and transferability of Great Lakes coastal wetland indices of biotic integrity to high quality inland lakes of Beaver Island in northern Lake Michigan

Biological indicators or indices of biotic integrity (IBI) have been developed for land management and regulatory agencies to categorize the condition of a given ecosystem. IBIs are more widely used in lotic systems and those that can be used over wide geographic regions or multiple systems are deemed most valuable. Lacustrine wetlands have intrinsic complexity and multidimensionality making them very difficult to classify. This, in turn, greatly affects the transferability of indices created for explicit regions and wetland types. Similarly, due to scarcity, relatively pristine reference conditions are seldom included in IBI calibration and represent a critical end of the disturbance continuum. The robustness and transferability of macroinvertebrate and fish IBIs created for fringing lacustrine and drowned river mouth wetlands of the Great Lakes for use in wetlands occurring in inland-lakes on islands within the Great Lakes were tested. Islands within the Laurentian Great Lakes contain unique and critical habitats that have received little attention, but also require specialized tools for monitoring and management. Inland-lake wetlands of Beaver Island, Lake Michigan, were ranked a priori along a disturbance gradient based on adjacent land use/cover. Transferability of the pre-existing Great Lakes IBIs was determined by correlating the site-specific IBI rank with the site-specific disturbance ranks. Results indicated that the IBIs were not directly transferable and may require substantial modification.

Contribution of wild-origin chinook salmon (Oncorhynchus tshawytcha) to the spawning run in the Salmon River, New York

We examined the contribution and distribution of wild-origin chinook salmon (Oncorhynchus tshawytcha) in the Salmon River, New York, during the 2005 spawning run. To determine the origin of each fish, we used scale metrics and a recently developed discriminant function model. We estimated that approximately 32% (∼20,000 individuals) of chinook salmon were of wild-origin and that there was a greater proportion of wild fish in younger age groups than in older groups (age-1 = 48.6%, age-2 = 47.2%, and age-3 = 21.1%). We also observed spatial differences in the distribution of wild- and hatchery-derived fish, with a higher proportion of wild-origin chinook salmon in the lower section of the river (47.5%) than in the upper sections (28.2%). The lowest proportion of wild fish was found in the Salmon River hatchery (12.4%), located in the upper section of the river. These findings suggest that wild-origin fish were more evenly distributed along the river, whereas hatchery fish were more likely to reach the upper parts of the river or enter the hatchery.