Consumption Dynamics of the Adult Piscivorous Fish Community in Spirit Lake, Iowa

At Spirit Lake, one of Iowa’s most important fisheries, walleye Sander vitreus (formerly Stizostedion vitreum) is one of the most popular species with anglers. Despite a century of walleye stocking and management in Spirit Lake, walleye growth rate, size structure, and angler harvest continue to decline. Our purpose was to determine the magnitude and dynamics of walleye population consumption relative to those of other piscivorous species in Spirit Lake, which would allow managers to judge the feasibility of increasing the abundance, growth rate, and size structure of the walleye population.We quantified food consumption by the adult piscivorous fish community in Spirit Lake over a 3-year period. Data on population dynamics, diet, energy density, and water temperature from 1995 to 1997 were used in bioenergetics models to estimate total consumption by walleye, yellow perch Perca flavescens, smallmouth bass Micropterus dolomieu, largemouth bass Micropterus salmoides, black crappie Pomoxis nigromaculatus, and northern pike Esox lucius. Estimated annual consumption by the piscivorous community varied roughly fourfold, ranging from 154,752 kg in 1995 to 662,776 kg in 1997. Walleyes dominated total consumption, accounting for 68, 73, and 90% (1995–1997, respectively) of total food consumption. Walleyes were also the dominant consumers of fish, accounting for 76, 86, and 97% of piscivorous consumption; yellow perch followed, accounting for 16% of piscivorous consumption in 1995 and 12% in 1996. Yellow perch were the predominant fish prey species in all 3 years, accounting for 68, 52, and 36% of the total prey consumed. Natural reproduction is weak, so high walleye densities are maintained by intensive stocking. Walleye stocking drives piscivorous consumption in Spirit Lake, and yearly variation in the cannibalism of stocked walleye fry may be an important determinant of walleye year-class strength and angler success. Reducing walleye stocking intensity, varying stocking intensity from year to year, and attempting to match stocking intensity with the abundance of prey species other than walleye may improve the walleye fishery in Spirit Lake

Citrus juices technology

Citrus fruits are widely grown throughout the world and contain various bioactive compounds with antioxidant activities including vitamin C, carotenoids, and phenolic compounds. These components are very important for human health and provide protection against harmful free radicals. Citrus fruits are mostly consumed as fresh fruits or fruit juices. To obtain high quality and safe citrus juice, certain critical points (oil extraction from peel, juice extraction, pulp removing, pasteurization, evaporation, and aseptic filling) need to be taken into consideration during citrus juice processing. Firstly, oil extraction from the peel is a necessary step to limit the level of peel oil components in the juice. Secondly, selected juice extraction techniques and process conditions are very important for the yield and total quality of the juice. Thirdly, the pulp removal is an important step to remove most of pectinmethylesterase (PME) and its heat resistance isoenzymes. Further inactivation of remaining PME enzymes and pathogenic or spoilage microorganisms is also obtained with the pasteurization step. Finally, equipment used for the juice production and the concentration conditions have various effects on the sensory properties of the citrus juices. As a result, minimal processing would be applied to citrus juices if the processing steps detailed above are optimized. Obtaining clarified citrus juices from the citruses which have lower carotenoid content including lemon and lime juice is a new trend these days. It is needed to be focused on enzymation (depectinization), clarification assistance agents, and filtration conditions during the clarified juices production. Citrus peel (flavedo) and layer of albedo are the main byproducts of the citrus juice industry. Citrus peel oil is obtained from flavedo layer which has a significant commercial value. Recently, promising nonthermal food preservation technologies were developed including pulsed electric fields (PEF), high pressure processing (HPP), and ultrasonication process (US). These technologies are highly appreciated for their ability to extend the shelf life of food products without the application of heat, thus also preserving the quality attributes such as sensory quality and nutritional value, as well as controlling the microbiological safety of food products. © 2014, Springer Science+Business Media New York