Insight into environments that contribute recruits to adult fish stocks in riverine systems is vital for effective population management and conservation. Catfish are an important recreational species in the Mississippi River and are commercially harvested. However, contributions of main channel and tributary habitats to catfish recruitment in large rivers are unknown. Stable isotope and trace elemental signatures in otoliths are useful for determining environmental history of fishes in a variety of aquatic systems, including the Mississippi River. The objectives of this study were to identify the principal natal environments of channel catfish Ictalurus punctatus and blue catfish I. furcatus in the middle Mississippi River (MMR) using otolith stable oxygen isotopic composition (δ 18 O) and strontium:calcium ratios (Sr:Ca). Catfishes were sampled during July-October 2013-2014 and lapilli otoliths were analyzed for δ 18 O and Sr:Ca. Water samples from the MMR and tributaries were collected seasonally from 2006-2014 to characterize sitespecific signatures. Persistent differences in water δ 18 O and Sr:Ca among the MMR and tributaries (including the upper Mississippi, Illinois, and Missouri rivers as well as smaller tributaries) were evident, enabling identification of natal environment for individual fish. Blue and channel catfish stocks in the MMR primarily recruited from the large rivers (Missouri and Mississippi) in our study area, with minimal contributions from smaller tributaries. Recruitment and year class strength investigations and efforts to enhance spawning and nursery habitats should be focused in the large rivers with less emphasis in smaller tributaries.
Dams are a conservation threat because they function as barriers to native fish movement; however, they may prevent the spread of invasive species. Invasive bigheaded carps (Hypophthalmichthys spp.) threaten the Great Lakes ecosystem and are advancing towards Lake Michigan via the Illinois River. Navigation dams on the Illinois River may deter bigheaded carps' upstream movement. We investigated the permeability of the Starved Rock Lock and Dam (SRLD), the most downstream gated Illinois River dam, to bigheaded carps' migration by examining the timing of individuals approaching and passing through SRLD in relation to gate openness, tailwater elevation, and water temperature. Using acoustic telemetry of (N =~104 per year) tagged fish, 13 upstream passages of bigheaded carps occurred through SRLD between 2013 and 2016. Eleven passages occurred through the dam gates and 2 through the lock chamber, indicating deterrents (e.g., CO 2 ) placed in SRLD lock chamber may only limit passage of a small proportion of all fish passing through the lock-and-dam structure. Passages were documented only in 2013 and 2015. Most of the dam gate passages occurred during high water when gates were completely out of the water. Timing of bigheaded carps approaching SRLD was positively correlated with rising water temperature and high tailwater elevation, and all fish approached during late March through mid-September. Movement through dams is rare; modifying gate operations to reduce gate openness during late spring and summer could further reduce the permeability of gated dams such as SRLD to bigheaded carps, slowing their upstream advance.
Understanding spatial patterns in population characteristics and the principal natal environments supporting riverine fish populations are important for fisheries management. Fin ray microchemistry was used to identify natal environment, and age estimates from sectioned fin rays were used to estimate growth and mortality rates for spotted bass, Micropterus punctulatus (Rafinesque), in a segment of the Ohio River (Smithland Pool) and three tributaries. Differences in water Sr:Ca and Ba:Ca among the Ohio River and tributaries were reflected in fin ray edge Sr:Ca and Ba:Ca. Fourteen percent of spotted bass ≥ age 2 captured in the Ohio River originated in tributaries, whereas 10% captured in tributaries originated in the Ohio River. Spotted bass in the Ohio River reached larger maximum size (L∞ = 448.7) than conspecifics in tributaries (L∞ = 324.4), although mortality rates were not different. Although 86% of spotted bass were collected in their inferred natal environment, small tributaries may be a supplemental source of recruitment for the spotted bass stock in Smithland Pool.
The occurrence of problematic pest organisms is an increasing global phenomenon, adversely affecting a range of environments and associated values. In marine systems, the efficacy of pest control has to date been constrained by a lack of tools that are not only highly effective, but also applicable across broad spatial scales. Here we consider the extent to which biological control (biocontrol) has the potential to fulfil these needs. We describe different biocontrol approaches and potential ecological mechanisms (e.g. consumption, space competition, habitat modification) through which problematic species could be supressed. We also discuss the ideal traits of marine control agents within the context of the selection criteria commonly applied in terrestrial systems. Classical biocontrol based on the deliberate introduction of non-indigenous agents has a high risk of leading to adverse non-target effects in marine environments, and cannot be justified. By contrast, approaches that use indigenous species have a low risk of unacceptable non-target effects, and could be used as part of pest eradication, as a means of containing spread, or for the control of established pest populations to mitigate adverse effects. While biocontrol based on indigenous species can be highly effective for such purposes, it is unlikely that it could be feasibly applied at broad spatial scales, except in specific circumstances (e.g. in some types of aquaculture). There is clearly a need to develop new approaches to manage marine pests. Biocontrol when used in conjunction with traditional approaches can provide a valuable tool for pest eradication, containment and mitigation of adverse effects.
Sauger Sander canadensis are a popular sport fish native to large turbid midwestern rivers and are in decline across much of their range due to habitat loss and exploitation. Specifically, within the lower Kaskaskia and Ohio rivers, Sauger are managed under different harvest regulations and a knowledge gap exists regarding the current status of both populations as well as the effects of the harvest regulations on the size and age structures of both populations. We collected Sauger by nighttime boat electrofishing during early winter 2014-2016 and used otoliths to age all fish. Sauger stocks in both rivers exhibited fast growth rates and high annual mortality rates. Yield-per-recruit modeling indicated that the current 356-mm minimum size limit for Sauger in the Kaskaskia River is sufficient to prevent growth overfishing and likely explains the consistently larger size structure (greater proportion of fish !356-mm total length) of Sauger sampled from the Kaskaskia River compared with the Ohio River. Modeling suggested that growth and recruitment overfishing of Sauger are likely occurring in the Ohio River with no minimum length limit based on available exploitation estimates for Sauger in the lower Ohio River. Implementing a 356-mm minimum length limit for Sauger in the lower Ohio River is predicted to prevent growth and recruitment overfishing based on available exploitation rate estimates and would be consistent with the statewide minimum length limit for Sauger in Illinois and minimum length limits on two major tributaries (Tennessee and Cumberland rivers downstream of Kentucky and Barkley lakes, respectively).
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