Synchronous changes in length at maturity across four species of Lake Erie fish with different harvest histories

Decreases in size at maturation in harvested fish populations can reduce productivity and resilience. Delineating the causes for these changes in maturation is challenging. We assessed harvest and large-scale ecosystem variability as causes for changes in maturation in four Lake Erie fishes. Regulated harvests of Yellow Perch (Perca flavescens) and Walleye (Sander vitreus) are greater than unregulated harvests of White Perch (Morone americana) and White Bass (Morone chrysops). Our assessment considered cohort data from 1991-2012 for each species. We used a conceptual model of harvest-induced plasticity to show that changes in female length at 50% maturity (L50) were unrelated to harvest intensity in all species. We then demonstrated that changes in female L50 among cohorts were synchronous across species. Post-hoc analysis of variables capturing year-to-year variation in climatic and lake conditions suggested L50 was larger when water levels were near the norm for the study period and smaller at low and high levels. We conclude that changes in L50 were most strongly related to ecosystem changes unrelated to harvest intensity.

Status, trends, and population demographics of selected sportfish species in the La Grange Reach of the Illinois River

Sportfish species, specifically Yellow Bass Morone mississippiensis, White Bass Morone chrysops, Largemouth Bass Micropterus salmoides, Bluegill Lepomis macrochirus, Black Crappie Pomoxis nigromaculatus, and White Crappie P. annularis, often drive economically valuable fisheries in large river systems, including the Upper Mississippi River System (UMRS). Within the Illinois River, part of the UMRS, these species are routinely sampled by an ongoing long-term fisheries monitoring program. Through this program, we investigated long-term trends (1993-2017) in catch rates and relative weights and quantified demographic rates from 2012-2016. We found all six species, with the exception of Yellow Bass, to have declining catch rates with this decline being most stark in larger, older fishes. Population demographics for Yellow Bass, White Bass, Bluegill, and Black Crappie suggest populations are dominated by younger individuals, with only Black Crappie regularly living to age 3 and older, which may be driving population declines. There are many environmental stressors acting on the Illinois River that could be contributing to the lack of older and larger fishes, including, but not limited to, navigation efforts, altered hydrology, pollution, sedimentation, lack of overwintering habitat, and introduction of invasive species. Results of this study demonstrate that additional research to understand mechanisms driving reduced abundance and stunted age structure are needed to identify effective management actions that would benefit populations of recreationally valuable sportfish species.

MOLECULAR AND QUALITY MEAT CHARACTERISTICS OF NEW FISH SPECIES INTRODUCED TO THE EU MARKET

Global consumption steadily increases due to development of aquaculture but also more efficient fisheries sector. Therefore, fish processing plants and ultimately consumers face products from new fish species which significantly differ in case of their nutritional values, technological or culinary properties. The aim of the study was to randomly collect specimens of bigeye sea perch, Helicolenus barathri; New Zealand sole, Peltorhamphus novaezeelandiae; white bass, Morone chrysops; thicklip grey mullet, Chelon labrosus and ridge scaled rattail, Macrourus carinatus and provide multidimensional characteristics i.e. species authentication, proximate assessment, structure and texture analysis as well sensory evaluation. Study confirmed authenticity of all fish samples and new DNA barcodes were introduced into database of fish profiles. Chemical composition of fillets differed significantly among species, and the unfavourable nutritional values had ridge scaled rattail, bigeye sea perch and New Zealand sole which had unfavorable fatty acid profile, high atherogenic (AI) and thrombogenic (TI) indexes, and low hypocholesterolemic to hypercholesterolemic acids ratio. On the other hand, fillets of freshwater white bass had the best PUFA:SFA ratio, and favourable TI and AI indexes from the consumer’s health point of view. Moreover, fillet of the white bass was selected by panellists as the most desirable. Structural analysis also revealed different degree of undesirable changes in fillets observed as breakdown of myofibrils and connective tissue. Multidimensional analysis characterized randomly selected sample and provided a set of useful information both for customers and fish processing sector.

Population Characteristics of Co-Managed White Bass and Hybrid Striped Bass in Lake McConaughy, Nebraska

White Bass (Morone chrysops) and Hybrid Striped Bass (M. saxatillis × M. chrysops) populations often coexist in the same waterbody and are known to achieve different lengths, have differing reproductive success, and provide different opportunities for anglers. However, comparative population dynamics from systems where Moronids are managed with the same regulation is often lacking. This study aimed to assess the recruitment, mortality, and growth of these species from seasonal samples collected at Lake McConaughy in 2015 and fall 2016. White Bass demonstrated highly variable recruitment in Lake McConaughy despite stocking efforts (mean recruitment variability index = 0.157). Hybrid Striped Bass year class strength was also variable, but RVI was not calculated as the number of missing year classes exceed the number of present year classes. Total annual mortality estimates for Hybrid Striped Bass (39.7%) and White Bass (41.4%) were consistent with values reported in other populations, but both species were observed to achieve uncommon longevity. Both species exhibited sexual size dimorphism, and growth was moderate and consistent with average values presented for North American populations. This study provides insight into the population dynamics of two species with trophy potential managed by the same regulation in Lake McConaughy. Differences in growth patterns indicate the current regulation affects each species differently, and managers may be able to utilize this to inform decisions about management of coexisting Moronid populations.

Failure to detect ecological and evolutionary effects of harvest on exploited fish populations in a managed fisheries ecosystem

Overexploitation and collapse of major fisheries raises important concerns about effects of harvest on fish populations. We tested for ecological and evolutionary mechanisms by which harvest could affect exploited fish populations in Lake Erie over the last four decades, over most of which intensive fisheries management was implemented. We did not detect evidence of long-term negative effects of harvest on yellow perch (Perca flavescens), walleye (Sander vitreus), white perch (Morone americana), or white bass (Morone chrysops) populations, either through recruitment success or through alteration of maturation schedules. Current fisheries management in Lake Erie has been relatively successful with respect to minimizing negative harvest effects, such that the dynamics of exploited fish populations in Lake Erie were more strongly affected by environment than harvest. Our study adds to the evidence that effective fisheries management is capable of rebuilding depleted fisheries and (or) maintaining healthy fisheries. Nevertheless, fisheries management needs to move beyond the ecological dimension to incorporate economic, social, and institutional aspects for society to be better assured of the sustainability of fisheries in rapidly changing ecosystems.