Factors related to age-0 native fish catch per unit effort in the South Dakota Missouri River reservoirs.

The Missouri River in South Dakota was dammed in the 1950s and 1960s, altering the biotic and abiotic factors that potentially affect native species in the mainstem reservoirs. Little research has been conducted regarding what factors regulate age-0 CPUE (catch per unit effort) of native fish species since the damming occurred. Thus, we examined age-0 CPUE for thirteen native fish species in the four Missouri River mainstem reservoirs. We analyzed data from 1995-2015 in Lake Oahe, 2002-2016 in Lake Sharpe, 1998-2008 in Lake Francis Case, and 2000-2013 in Lewis and Clark Lake. Not all species were sampled in all reservoirs. We evaluated potential environmental (inflow, gauge height, peak flow, precipitation, air temperature) and biological (CPUE of other native species, non-native CPUE, predator CPUE) factors that have documented impacts on age-0 native fish CPUE. Significant relationships existed between age-0 native fish CPUE and both biotic and abiotic factors in all four reservoirs, but specific factors related to native fish CPUE were species and reservoir dependent. For all species examined in all reservoirs except age-0 Emerald Shiner Notropis atherinoides CPUE in Lewis and Clark Lake, age-0 CPUE was either stable or increasing. Age-0 Emerald Shiner CPUE in Lewis and Clark Lake was most supported by total age-0 non-native CPUE and adult White Bass Morone chrysops CPUE, and a positive relationship existed between age-0 Emerald Shiner CPUE and both factors. We believe our findings provide valuable insight into successful management of native fish populations.

Length-weight relationships of the Emerald Shiner (Notropis atherinoides - Rafinesque, 1818) in the Western Basin of Lake Erie

Total length and standard length (mm) were compared to weight (mg) in the Emerald Shiner (Notropis atherinoides - Rafinesque, 1818) in the western basin of Lake Erie. Length and weight relationship (n = 400), length-frequency distribution, and sex ratios were evaluated for coastal and tributary habitats and compared to open water habitats. A strong positive correlation was observed between length and weight for both males and females. For males (n = 195) there was a significant positive relationship between standard length (SL) and weight (F = 935.64, d.f = 195; R2 = 0.989) and between total length (TL) and weight (F = 918.75, d.f. = 195; R2 = 0.991). In females (n = 205), there was also a strong positive correlation between SL and weight (F = 1108.18, d.f. = 204; R2 = 0.976) and between TL and weight (F = 1208.86, d.f. = 204; R2 = 0.983). This same positive relationship between SL and weight (F = 1909.58, d.f. = 399; R2 = 0.984,) and between TL and weight (F = 1960.07, d.f. = 399; R2 = 0.988) that was found for the individual sexes was present in the combined data for the two sexes. Length-weight relationship patterns in Emerald Shiner were significantly influenced by sex (ANCOVA, F= 313.03, p < 0.01) and habitat (ANCOVA, F = 6.693, p = 0.013). Three separate age classes were distinguished in the data. Age 0 males ranged from 15-33 mm TL, while age 0 females ranged from 18-30 mm TL. Age I males ranged from 39-78 mm TL and Age I females ranged from 42-78 mm TL. Age II+ males ranged from 78-111 mm TL and Age II+ females ranged from 81-108 mm TL. Emerald Shiner exhibit indeterminate growth and sex influenced growth patterns based on the von Bertalanffy growth model.

Lake Ontario: food web dynamics in a changing ecosystem (1970–2000)

We examined stressors that have led to profound ecological changes in the Lake Ontario ecosystem and its fish community since 1970. The most notable changes have been reductions in phosphorus loading, invasion by Dreissena spp., fisheries management through stocking of exotic salmonids and control of sea lamprey (Petromyzon marinus), and fish harvest by anglers and double-crested cormorants (Phalacrocorax auritus). The response to these stressors has led to (i) declines in both algal photosynthesis and epilimnetic zooplankton production, (ii) decreases in alewife (Alosa pseudoharengus) abundance, (iii) declines in native Diporeia and lake whitefish (Coregonus clupeaformis), (iv) behavioral shifts in alewife spatial distribution benefitting native lake trout (Salvelinus namaycush), threespine stickleback (Gasterosteus aculeatus), and emerald shiner (Notropis atherinoides) populations, (v) dramatic increases in water clarity, (vi) predation impacts by cormorants on select fish species, and (vii) lake trout recruitment bottlenecks associated with alewife-induced thiamine deficiency. We expect stressor responses associated with anthropogenic forces like exotic species invasions and global climate warming to continue to impact the Lake Ontario ecosystem in the future and recommend continuous long-term ecological studies to enhance scientific understanding and management of this important resource.

Distribution, density, and growth of young-of-the-year fishes in Mitchell Bay, Lake St. Clair

Thirty-eight taxa of young-of-the-year fishes were collected with a beach seine and plankton nets in Mitchell Bay, a shallow, densely vegetated embayment on Lake St. Clair, from April to October, 1983, 1984, and 1990. The ecosystem of the bay and adjacent land has been altered by agricultural, industrial, and recreational development for more than a century. Although taxa were numerous, most species were rare or uncommon in collections. The assemblage of larval fish consisted primarily of brook silverside (Labidesthes sicculus), pumpkinseed (Lepomis gibbosus), spottail shiner (Notropis hudsonius), emerald shiner (Notropis atherinoides), alewife (Alosa pseudoharengus), and gizzard shad (Dorosoma cepedianum). Many species were distributed in or near submerged macrophytes at the shore. The species most abundant were pumpkinseed, which reached peak density (11 931 young of the year/100 m3) in late June 1990, and brook silverside (1363 young of the year/100 m3) in late June 1984.

Recent Changes in Lake Michigan's Fish Community and Their Probable Causes, With Emphasis on the Role of the Alewife (Alosa pseudoharengus)

Major changes in fish populations occurred in Lake Michigan between the early 1970s and 1984. The abundance of lake trout (Salvelinus namaycush) and several nonnative species of salmonines increased greatly as a result of intensive stocking. The exotic alewife (Alosa pseudoharengus), which had proliferated to extremely high levels of abundance in the mid-1960s, declined, particularly in the early 1980s. We believe that the sharp decline in alewives in the 1980s was caused primarily by poor recruitment during the colder than normal years of 1976–82. Several of Lake Michigan's endemic species of fish appeared to be adversely affected by alewives: bloater (Coregonus hoyi), lake herring (C. artedii), emerald shiner (Notropis atherinoides), yellow perch (Perca flavescens), and deepwater sculpin (Myoxocephalus thompsoni), and possibly spoonhead sculpin (Cottus ricei). All declined when alewives were abundant, and those that did not become rare, i.e. the bloater, perch, and deepwater sculpin recovered when alewives declined. We present evidence suggesting that the mechanism by which alewives affect native species is not by competition for food, as has often been hypothesized, and discuss the possibility that it is predation on early life stages. Despite the decreased availability of alewives in the early 1980s, salmonines continued to eat mainly alewives. The highly abundant alternate prey species were eaten only sparingly, but alewives still may have been abundant enough to meet the forage requirements of salmonines. Two new exotics, the pink salmon (Oncorhynchus gorbuscha) and threespine stickleback (Gasterosteus aculeatus), increased in abundance in the 1980s, and could become detrimental (particularly the salmon) to other species.