Toxic blooms of golden alga (Prymnesium parvum) have caused substantial ecological and economic harm in freshwater and marine systems throughout the world. In North America, toxic blooms have impacted freshwater systems including large reservoirs. Management of water chemistry is one proposed option for golden alga control in these systems. The main objective of this study was to assess physicochemical characteristics of water that influence golden alga presence, abundance, and toxicity in the Upper Colorado River basin (UCR) in Texas. The UCR contains reservoirs that have experienced repeated blooms and other reservoirs where golden alga is present but has not been toxic. We quantified golden alga abundance (hemocytometer counts), ichthyotoxicity (bioassay), and water chemistry (surface grab samples) at three impacted reservoirs on the Colorado River; two reference reservoirs on the Concho River; and three sites at the confluence of these rivers. Sampling occurred monthly from January 2010 to July 2011. Impacted sites were characterized by higher specific conductance, calcium and magnesium hardness, and fluoride than reference and confluence sites. At impacted sites, golden alga abundance and toxicity were positively associated with salinity-related variables and blooms peaked at~10°C and generally did not occur above 20°C. Overall, these findings suggest management of land and water use to reduce hardness or salinity could produce unfavorable conditions for golden alga. (KEY TERMS: algae; aquatic ecology; harmful algal blooms; watershed management.) VanLandeghem, Matthew M., Mukhtar Farooqi, Greg M. Southard, and Reynaldo Patiño, 2015. Associations between Water Physicochemistry and Prymnesium parvum Presence, Abundance, and Toxicity in West Texas Reservoirs.

Golden alga (Prymnesium parvum) is a harmful alga that has caused ecological and economic harm in freshwater and marine systems worldwide. In inland systems of North America, toxic blooms have nearly eliminated fish populations in some systems. Modifying nutrient profiles through alterations to land or water use may be a viable alternative for golden alga control in reservoirs. The main objective of this study was to improve our understanding of the nutrient dynamics that influence golden alga bloom formation and toxicity in west Texas reservoirs. We examined eight sites in the Upper Colorado River basin, Texas: three impacted reservoirs that have experienced repeated golden alga blooms; two reference reservoirs where golden alga is present but nontoxic; and three confluence sites downstream of the impacted and reference sites. Total, inorganic, and organic nitrogen and phosphorus and their ratios were quantified monthly along with golden alga abundance and ichthyotoxicity between December 2010 and July 2011. Blooms persisted for several months at the impacted sites, which were characterized by high organic nitrogen and low inorganic nitrogen. At impacted sites, abundance was positively associated with inorganic phosphorus and bloom termination coincided with increases in inorganic nitrogen and decreases in inorganic phosphorus in late spring. Management of both inorganic and organic forms of nutrients may create conditions in reservoirs unfavorable to golden alga. (KEY TERMS: algae; aquatic ecology; environmental impacts; nutrients.) VanLandeghem, Matthew M., Mukhtar Farooqi, Greg M. Southard, and Reynaldo Patiño, 2015. Spatiotemporal Associations of Reservoir Nutrient Characteristics and the Invasive, Harmful Alga Prymnesium parvum in West Texas.

The stocking of fish represents a major activity in current fisheries management practice. To maximise benefit to the environment in general and to fisheries in particular, optimal stocking strategies need to be developed. Examples from two studies, one involving Atlantic salmon, Salmo salar L., and the other involving three coarse fish species, are used to illustrate how such strategies might be developed. Atlantic salmon fed fry (age 0+) were stocked into eight streams in the North West of England at densities ranging from 1 to 4 m−2 over a period of up to 3 years to evaluate survival to the end of the first and second growing periods. Survival to the end of the first growing period (mean duration 108 days) varied between 1.2 and 41.3% with a mean of 20.45% and CV of 0.53. Survival from the end of the first growing period to the end of the second growing period (mean duration 384 days) ranged from 19.9 to 34.1% with a mean of 26.3% and a CV of 0.21. Hatchery‐reared roach, Rutilus rutilus (L.), chub, Leuciscus cephalus (L.) and dace, Leuciscus leuciscus (L.), were stocked into four rivers to determine the optimal age and season which would maximise survival over a 6‐month post‐stocking period. Post‐stocking persistence within the stocked reaches was generally low; the highest level of persistence was estimated at only 33.8%. However, most of the estimates of persistence were considerably lower and (in practical terms) approached zero in several instances. The analysis indicated that river‐specific factors are important in determining the success of stocking exercises. The survival estimates derived from these two studies were compared with other published estimates.

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Several reservoirs in the upper Colorado River and Brazos River basins in Texas have experienced toxic blooms of golden alga Prymnesium parvum and associated fish kills since 2001. There is a paucity of information, however, regarding the population‐level effects of such kills in large reservoirs, species‐specific resistance to or recovery from kills, or potential differences in the patterns of impacts among basins. We used multiple before–after, control–impact analysis to determine whether repeated golden alga blooms have led to declines in the relative abundance and size structure of fish populations. Sustained declines were noted for 9 of 12 fish species surveyed in the upper Colorado River, whereas only one of eight species was impacted by golden alga in the Brazos River. In the upper Colorado River, White Bass Morone chrysops, White Crappie Pomoxis annularis, Largemouth Bass Micropterus salmoides, Bluegill Lepomis macrochirus, River Carpsucker Carpiodes carpio, Freshwater Drum Aplodinotus grunniens, Channel Catfish Ictalurus punctatus, Flathead Catfish Pylodictis olivaris, and Blue Catfish I. furcatus exhibited sustained declines in relative abundance, size structure, or both; Gizzard Shad Dorosoma cepedianum, Longnose Gar Lepisosteus osseus, and Common Carp Cyprinus carpio did not exhibit those declines. In the Brazos River, only the relative abundance of Blue Catfish was impacted. Overall, toxic golden alga blooms can negatively impact fish populations over the long‐term, but the patterns of impact can vary considerably among river basins and species. In the Brazos River, populations of most fish species appear to be healthy, suggesting a positive angling outlook for this basin. In the upper Colorado River, fish populations have been severely impacted, and angling opportunities have been reduced. Basin‐specific management plans aimed at improving water quality and quantity will likely reduce bloom intensity and allow recovery of fish populations to the abundances and size structures present before golden alga.