Neil H. Ringler

Effects of Logging on Water Temperature, and Dissolved Oxygen in Spawning Beds

Abstract The temperature and dissolved oxygen content of intragravel water were measured in three Oregon coastal streams between June 1968 and June 1969. In 1966, the watershed of one stream had been completely clearcut, and that of a second stream partially clearcut in staggered settings. A third watershed was left unlogged. Clearcut logging resulted in increased temperature of intragravel water in salmon and trout spawning beds and decreased concentrations of dissolved oxygen. The changes were related largely to reduced forest cover over the stream surface and to deposition of fine sediment in the gravel. No serious reduction in survival to emergence of coho salmon occurred along with the observed changes in temperature or dissolved oxygen. A decrease in the resident population of cutthroat trout after logging may have been related to these changes.

Double-Crested Cormorant Predation on Yellow Perch in the Eastern Basin of Lake Ontario

Previous work indicated that the abundance of yellow perch (Perca flavescens) in the eastern basin of Lake Ontario declined from 1976 to 1999 despite production of moderate to strong year classes each year during 1991 through 1995. Adult perch stock size failed to increase because of accelerated mortality after the first fall of life. Increases in mortality coincided with a number of ecosystem changes including increased abundance of double-crested cormorants (Phalacrocorax auritus). Otoliths obtained from cormorant pellets collected on Little Galloo Island were used to examine the size and age of perch consumed by cormorants during 1993 to 1994 and 1996 to 1999. Size and age specific diet composition, combined with existing estimates of yellow perch consumed annually by cormorants were compared to perch population projections to evaluate the potential for this new form of predation to induce observed population trends. Perch stock abundance was projected using a range of standing stock estimates from the literature partitioned with age composition data from the eastern basin population. The total length of perch consumed by cormorants ranged from 59 to 236 mm, the majority of which were age-1 (48%), age-2 (20%), and age-3 (20%). Comparisons of age structured predation by cormorants and perch population projections indicated that cormorant predation reduced age-3 perch abundance most. At a high estimate of 65 kg/ha, cormorants were capable of consuming 29% of the age-3 perch stock. This analysis indicated that cormorant predation had the potential to play an important role in regulating perch population levels in the eastern basin during the 1990s.

Variation in foraging tactics of fishes

Changes in feeding tactics over short intervals and variation among individuals have often been ignored or treated as ecological ‘noise’. This paper reviews foraging variability in fishes and discusses its sources and consequences. Evidence is accumulating that individuals in many populations differ substantially in physiological, morphological, and behavioral characteristics. Short-term (within individual) variation includes changes in strike pattern with prey type, reversals in preference during feeding trials, and shifts in the extent of realization of an optimal diet. Documented cases of variation among individuals include differences in the time required to respond to new prey, the tendency to switch to abundant prey, foraging stance, feeding location, and in parameters describing the functional response. Such variation appears to be a general phenomenon, bearing directly on ecological questions such as resource partitioning, optimal foraging, population structure and community organization.

The Role of Pollution and External Refugia in Structuring the Onondaga Lake Fish Community

ABSTRACT Historical accounts of Onondaga Lake dating to the 1600s indicate that the lake once supported a coldwater fishery. By the late 1800s, severe degradation of the lake and adjacent tributary environments was accompanied by declines in the American eel (Anguilla rostrata), and extirpation of Atlantic salmon (Salmo salar) and whitefish (Coregonus sp.). Nine faunal surveys were conducted from 1927 to 1994. We used rarefaction analyses to standardize survey results by computing expected species richness values (E(Sm)) relative to the 1946 gill net catch (7 species, m=164 individuals). Linear regression applied to the expected richness values (E (S164)) over time showed a significant increase in richness from 1946 (YEAR=0) to 1994 (YEAR=47) for fish caught in gill nets [E(S164) = 0.153*YEAR + 6.785, r2=0.79, P<0.005] and trap nets [E(S164) = 0.226*YEAR + 3.723, r2=0.89, P<0.01]. Although species richness has increased, almost half of the species captured since 1989 show no evidence of juvenile recruit...

Individual and Temporal Variation in Prey Switching by Brown Trout, Salmo trutta

canum) and mealworm larvae (Tenebrio molitor) were introduced to the stream by conveyor belt and the ratio of prey species was changed over an 11 d period from 0:1-5:1. Two of five individuals appeared to switch to the most abundant prey species. Preference values based on a model of switching (Murdoch, 1969) differed among individuals and varied as much as five-fold among 5 min intervals. In some individuals diet preferences reversed during 30 min bouts; shortterm changes in feeding preference were not generally predictive of longer-term trends. Individual differences were detected in the expression of negative bias toward tent caterpillars. Some effects of exposure to relatively unpalatable prey appeared to extend over at least a 24 d period. Studies of foraging variability should contribute to an understanding of the role of switching in stabilizing prey communities and to the successful application of optimal foraging theory to stream fishes.

Experimental Manipulation of Sculpin (Cottus cognatus) Populations in a Small Stream

Abstract We examined movement and age distribution of experimentally manipulated natural populations of slimy sculpin (Cottus cognatus) in streams having open and closed vegetation canopies. Densities were estimated in three treatments: reference populations (no transfers), reductions (fish removed from the sites), and additions (fish added to the sites). Biweekly replenishment of addition sites raised sculpin densities to over 10/m2 in the open canopy, at least 3 times that of reduction and reference populations. In closed canopy habitats, densities of addition populations (6/m2) were twice as great as reference populations (3/m2), although reduction populations (41m2) did not differ from either. Addition sites showed a net increase of numbers of sculpin over four summer months, in spite of a decline in older sculpin (age III-V years). Reduction sites showed no differences from reference sites regarding sculpin numbers, indicating that recruitment of fish to reduction sites did occur. However, more than ...

Survival and Growth Responses of Juvenile Salmonines Stocked in Eastern Lake Ontario Tributaries

Abstract To evaluate the species-specific and stream-specific suitability of juvenile salmonine habitat in the southern Lake Ontario watershed, we studied the effects of multiple environmental gradients on the first-summer apparent survival and growth of various combinations of Atlantic salmon Salmo salar, rainbow trout Oncorhynchus mykiss, and coho salmon O. kisutch stocked in tributaries. Costocking of either Oncorhynchus species had no detectable effect on the apparent survival or change in cohort biomass of Atlantic salmon, but their growth rates were reduced slightly when they were stocked with rainbow trout. Generally, Atlantic salmon outperformed their putative competitors. Summer temperatures were near the physiological optimum for Atlantic salmon but may have limited the success of rainbow trout and especially coho salmon. Total salmonine biomass was maximized at sites in which only Atlantic salmon were planted. Apparent survival and biomass elaboration of Atlantic salmon varied inversely with st...

Application and Modification of an Auger Trap to Quantify Emigrating Fishes in Lake Ontario Tributaries

Abstract Assessments of natural reproduction, rates of survival, and patterns of migration by Pacific salmon Oncorhynchus spp. in Great Lakes tributaries require quantification of emigrating smolts. Auger smolt traps were modified and tested during annual downstream migrations of juvenile chinook salmon Oncorhynchus tshawytscha, coho salmon O. kisutch, and steelhead O. mykiss in three eastern Lake Ontario tributaries. The traps were scaled to fit small- to medium-sized streams (third or fourth order) that had fluctuating flows and high debris outputs. During periods of reduced discharge, up to 85% of the streamflow was sampled by one trap. The fraction of migrating smolts captured (efficiency) was determined with wild and hatchery-released fish. Site choice played a major role in determination of trapping efficiencies, which ranged from 1.3 to 17% for wild salmonids. The highest efficiencies were found for wild chinook salmon smolts (11–17%) in a tributary of the Salmon River, New York. No salmonids appea...

Lakewide Estimates of Alewife Biomass and Chinook Salmon Abundance and Consumption in Lake Ontario, 1989-2005: Implications for Prey Fish Sustainability

Abstract Stocking levels of Chinook salmon Oncorhynchus tshawytscha for Lake Ontario have been highly controversial since the early 1990s, largely because of uncertainties about lakewide abundance and rates of prey consumption. Previous estimates have focused on years before 1995; since then, however, the Lake Ontario ecosystem has undergone substantial changes, and there is new evidence of extensive natural recruitment. Presented here are new abundance estimates of Chinook salmon and alewives Alosa pseudoharengus in Lake Ontario and a reevaluation of the potential risk of alewife population collapse. We found that Lake Ontario has been supporting, on average (1989–2005), 1.83 × 106 (range, 1.08 × 106 to 3.24 × 106) Chinook salmon of ages 1–4, amounting to a mean annual biomass of 11.33 × 103 metric tons (range, 5.83 × 103 to 23.04 × 103 metric tons). During the same period (1989–2005), the lake supported an alewife biomass of 173.66 × 103 metric tons (range, 62.37 × 103 to 345.49 × 103 metric tons); Chin...

Temperature-dependent Effects of Rainbow Trout on Growth of Atlantic Salmon Parr

Abstract Temperature may influence interactions between species by regulating energy balances of individuals. We conducted a laboratory study to determine whether temperature influenced the effects exerted by large rainbow trout on the growth of Atlantic salmon parr. Bioenergetic models were used to predict maintenance rations so that food resources were limiting over a range of temperatures; equal biomasses of rainbow trout were substituted for Atlantic salmon to evaluate the relative effect of interspecific interactions on Atlantic salmon growth. In the presence of rainbow trout, salmon growth increased as temperatures increased from 15°C to 25°C; no such temperature effect occurred for salmon maintained alone. Growth differences between salmon maintained with and without trout were highly significant at 25°C but not at 15°C. We conclude that the presence of trout depressed salmon growth at 15°C but not at higher temperatures, most likely a result of differences in thermal optima between these two species. Field data show that the proportion of stocked Atlantic salmon to wild rainbow trout coexisting in natural streams is a function of mean summer temperature. As stream temperatures increased, Atlantic salmon became increasingly favored over rainbow trout, but with a concomitant decrease in total salmonine biomass. We suggest that Atlantic salmon restoration programs focus more attention on relatively warm streams in watersheds where interactions with naturalized rainbow trout may occur.