Daily Mortality Rates of Larval and Juvenile American Shad (Alosa sapidissima) in the Connecticut River with Changes in Year-Class Strength

1983 ◽  
Vol 40 (10) ◽  
pp. 1719-1728 ◽  
Author(s):  
V. Crecco ◽  
T. Savoy ◽  
L. Gunn
Keyword(s):  
Survival Rates ◽  
Mortality Rates ◽  
American Shad ◽  
Connecticut River ◽  
Alosa Sapidissima ◽  
Growth And Survival ◽  
Juvenile Mortality ◽  
First Feeding ◽  
Gompertz Equation ◽  
Class Strength

Age-specific growth and survival rates were estimated for larval and juvenile American shad (Alosa sapidissima) from the Connecticut River from 1979 to 1982. Relative indices (CPE) of year-class strength of juveniles determined from seine sampling in 1978–82 and 1966–73 are compared with resulting levels of adult recruitment. Length–age data for larval and juvenile American shad were determined from sagittal otoliths. Length increments among larval and juvenile shad followed an asymptotic pattern with age, both life stages being well described by the Gompertz equation. Larval survivorship curves from 1979 to 1982 were age specific, with mortality rates of 19.8–25.6%/d for first feeding larvae and 4.3–8.7%/d for larvae approaching metamorphosis. By contrast, juvenile mortality rates were much lower (1.8–2.0%/d) and more consistent among years. Juvenile indices of year-class strength from 1966 to 1973 were positively correlated (r = +0.92, df 7, P < 0.001) with recruitment levels of adult females 4–6 yr later, suggesting that year-class strength of shad is established prior to the juvenile stage.

Effects of Biotic and Abiotic Factors on Growth and Relative Survival of Young American Shad, Alosa sapidissima, in the Connecticut River

1985 ◽  
Vol 42 (10) ◽  
pp. 1640-1648 ◽  
Author(s):  
Victor A. Crecco ◽  
Thomas F. Savoy
Keyword(s):  
Growth Rates ◽  
Abiotic Factors ◽  
Survival Rates ◽  
Relative Survival ◽  
American Shad ◽  
Zooplankton Abundance ◽  
Connecticut River ◽  
River Flows ◽  
Alosa Sapidissima ◽  
Specific Growth Rates

We examined the hypothesis that temporal oscillations in zooplankton abundance, river flows, and temperatures in the Connecticut River affect the survival and growth rates of larval and juvenile American shad, Alosa sapidissima, among 5-d cohorts. The relative survival rates between newly hatched shad larvae and juveniles were low among early cohorts (May 21 – June 15), but rose rapidly among later cohorts (June 21 – July 6) when river flows were low and temperatures and zooplankton densities were high. Age of larval and juvenile shad was estimated by counting daily rings on sagittal otoliths and age-specific length increments determined by backcalculation techniques. Cohort-specific growth rates of larval shad increased linearly with rising zooplankton densities, and asymptotically with rising river temperatures and declining flows. By contrast, juvenile growth rates among 5-d cohorts showed no significant linear or nonlinear relationships to water temperatures and flows.

Effects of Fluctuations in Hydrographic Conditions on Year-Class Strength of American Shad (Alosa sapidissima) in the Connecticut River

1984 ◽  
Vol 41 (8) ◽  
pp. 1216-1223 ◽  
Author(s):  
Victor A. Crecco ◽  
Thomas F. Savoy
Keyword(s):  
Environmental Variables ◽  
River Flow ◽  
Abiotic Factors ◽  
American Shad ◽  
Larval Feeding ◽  
Monthly Precipitation ◽  
Connecticut River ◽  
Alosa Sapidissima ◽  
Hydrographic Conditions ◽  
Class Strength

We evaluated a parent–progeny relationship for Connecticut River shad, Alosa sapidissima, with population data from 1966 through 1982. The hypothesis that shad year-class strength is established during larval development mainly by abiotic factors was assessed by correlation analysis between environmental variables, year-class strength, weekly zooplankton densities, hydrographic conditions, and larval feeding success among the 1979 through 1982 year-classes. No significant parent–progeny relationship was found for American shad even after recruitment variations due to river flow and water temperatures were removed. All three environmental variables (mean river discharge, water temperatures, and total monthly precipitation) were significantly correlated with shad year-class strength for the month of June, the period when most American shad larvae emerge.

Effects of Density-Dependent and Climatic Factors on American shad, Alosa sapidissima, Recruitment: A Predictive Approach

1986 ◽  
Vol 43 (2) ◽  
pp. 457-463 ◽  
Author(s):  
Victor Crecco ◽  
Thomas Savoy ◽  
Walter Whitworth
Keyword(s):  
River Flow ◽  
Climatic Factors ◽  
American Shad ◽  
Connecticut River ◽  
Alosa Sapidissima ◽  
Density Dependent ◽  
Class Strength ◽  
Stock Recruitment ◽  
Parent Stock ◽  
Recruitment Variability

We developed environment-dependent stock–recruitment models for American shad, Alosa sapidissima, in the Connecticut River to forecast recruitment variability and measure density-dependent effects. These models were fitted to the 1966–78 stock–recruitment estimates and to May and June river flow, water temperature, and rainfall data shown previously to affect American shad year-class strength. We also attempted to validate the models by forecasting the 1979–84 year-classes based on juvenile indices, parent stock size, and hydrographic data for these years. The stock–recruitment models without environmental factors explained less than 3% of the recruitment variability, and none of the density-dependent exponents were statistically different from 0. The predictive capability of the Ricker stock–recruitment model improved dramatically (r2 = 0.90) when combined with mean May flows, June flows, and the number of American shad lifted over the Holyoke Dam. The density-dependent exponents of these multiple regression models were highly significant, indicating that density-dependent processes are hidden by climatically induced variability in recruitment. Two environment-dependent stock–recruitment models predicted 80–90% of the American shad recruitment variability from 1979–84.

Effect of Prey Density and Prey Size on Growth and Survival of Juvenile Walleye (Stizostedion vitreum vitreum)

1989 ◽  
Vol 46 (8) ◽  
pp. 1323-1328 ◽  
Author(s):  
Michael G. Fox
Keyword(s):  
Prey Density ◽  
Prey Availability ◽  
Food Limitation ◽  
Survival Rates ◽  
Stizostedion Vitreum ◽  
Growth And Survival ◽  
First Feeding ◽  
Length Increase ◽  
Prey Length ◽  
Chironomid Biomass

I investigated the influence of food availability on growth and survival of walleye (Stizostedion vitreum vitreum) fry stocked in six fertilized experimental ponds (density 40 fish∙m−3) and reared for 8 wk. Walleye fed largely on chironomid larvae and cyclopoid copepods in weeks 1 and 2, and chironomids thereafter. Prey choice and consumption were strongly influenced by chironomid biomass in the benthos, and to a lesser extent by zoo-plankton density. Weekly length increase of the populations and mean length in week 7 were significantly correlated with chironomid benthic biomass and mean prey length. Chironomid biomass and density of large zoo-plankton together explained 56% of the variation in the weekly population growth rate. Despite obvious food limitation in the second half of the experiment, pond survival rate was not significantly correlated with mean prey density, mean stomach fullness, or percentage of fish with empty stomachs. The results indicate that juvenile walleye growth can be regulated by the density and size of available prey. Prey availability apparently does not regulate short term juvenile walleye survival rates after the period around first feeding.

Food Availability and Consumption by Young Connecticut River Shad Alosa sapidissima

1972 ◽  
Vol 29 (10) ◽  
pp. 1495-1499 ◽  
Author(s):  
Raymond C. Levesque ◽  
Roger J. Reed
Keyword(s):  
Stomach Content ◽  
Food Habits ◽  
Negative Selection ◽  
Content Volume ◽  
American Shad ◽  
Initial Time ◽  
Connecticut River ◽  
Alosa Sapidissima ◽  
Selection For ◽  
Selection Of

Food habits of young American shad (Alosa sapidissima) were studied in the Connecticut River above Holyoke, Massachusetts, 1969. Diurnal feeding data revealed a peak in stomach content volume at 8:00 PM during midsummer. Larval shad fed mainly on aquatic crustaceans and tendipedid larvae and pupae. Juveniles ingested the most abundant organisms: crustaceans, tendipedid larvae and pupae, hydropsychid larvae and adult insects. Electivity data indicated positive selection for tendipedid pupae and crustaceans and negative selection for hydropsychid larvae and tendipedid larvae. Selection of Trichoptera larvae by young shad in significant amounts was documented for the initial time.

Behavior of Adult American Shad (Alosa sapidissima) Homing to the Connecticut River from Long Island Sound

1973 ◽  
Vol 30 (12) ◽  
pp. 1847-1860 ◽  
Author(s):  
Julian J. Dodson ◽  
William C. Leggett
Keyword(s):  
Tidal Current ◽  
Open Water ◽  
American Shad ◽  
Behavior Patterns ◽  
Connecticut River ◽  
Directed Movement ◽  
Alosa Sapidissima ◽  
Preferred Direction ◽  
Tidal Current Velocity ◽  
Ultrasonic Tracking

The migratory behavior of American shad (Alosa sapidissima) approaching their natal river during the final saltwater stage of the spawning migration was studied using ultrasonic tracking and conventional tagging procedures. Initial displacement of most sonic-tagged shad released without displacement adjacent to and 10 km west of the Connecticut River was not in the direction of the home river. These fish, however, homed successfully to the Connecticut River as did dart-tagged shad released in the same areas.Shad exhibited two major behavior patterns; countercurrent orientation in response to the reversing tidal current and adjustment of swimming speed to changes in tidal velocity. Countercurrent orientation was equally significant during daylight and darkness, whereas the adjustment of swimming speeds to tidal current velocity was more significant during daylight than darkness.Shad tracked to the west exhibited a westerly bias inherent in the basic open water behavior patterns. Shad exhibited a greater degree of directed movement when oriented against the ebb tide and adjusted their swimming speeds to exceed the ebb tide velocity and to approximately equal the flood tide velocity. Shad tracked to the east exhibited the same major behavior patterns but with the opposite directional bias.A hypothesis is presented suggesting that the location of the home river is achieved by means of a nonrandom search. Environmental clues indicative of the Connecticut River act to establish a preferred direction of displacement while the actual unidirectional displacement is achieved by reference to the rate and direction of tidal currents.

Comparison of Logistic Regression and Discriminant Analyses for Stock Identification of Anadromous Fish, with Application to Striped Bass (Morone saxatilis) and American Shad (Alosa sapidissima)

1990 ◽  
Vol 47 (8) ◽  
pp. 1570-1577 ◽  
Author(s):  
Michael H. Prager ◽  
Mary C. Fabrizio
Keyword(s):  
Logistic Regression ◽  
Striped Bass ◽  
Logistic Model ◽  
Morone Saxatilis ◽  
Hudson River ◽  
American Shad ◽  
Stock Identification ◽  
Connecticut River ◽  
Alosa Sapidissima ◽  
Discriminant Analyses

We examined the applicability of logistic regression to stock identification studies and compared its performance on two data sets to that of linear and quadratic discriminant functions. Logistic regression can be used to model a categorical dependent variable associated with continuous or discrete independent variables, and is preferred to discriminant analyses when the explanatory variables are not multivariate normal. Our examples were American shad (Alosa sapidissima) from the Connecticut River and Hudson River estuaries, and striped bass (Morone Saxatilis) from the Hudson River, Chesapeake Bay, and Roanoke River estuaries. In the examples we used a resampling method to assess classification and allocation errors of the two methods on new data. For the shad data, the logistic model classified significantly more fish correctly, and provided a significantly better estimate of stock composition. For the striped bass data, the two methods classified about the same proportion of fish correctly, but the logistic model gave a significantly better estimate of stock composition.

Spatiotemporal variations in juvenile mortality and cohort strength of Atlantic cod (Gadus morhua) off Newfoundland and Labrador

2020 ◽  
Vol 77 (3) ◽  
pp. 625-635
Author(s):  
Fan Zhang ◽  
Rick M. Rideout ◽  
Noel G. Cadigan
Keyword(s):  
Newfoundland And Labrador ◽  
Large Scale ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Survival Rates ◽  
Mortality Rates ◽  
Spatiotemporal Variations ◽  
Juvenile Mortality ◽  
Modelling Framework ◽  
Fish Recruitment

Juvenile mortality is an important factor affecting the spatiotemporal dynamics of fish recruitment, but estimation of the spatiotemporal variations in juvenile mortality rates remains challenging. We developed a state-space metapopulation dynamics model to simultaneously estimate spatiotemporal variations in juvenile mortality rates and cohort strength and applied this general modelling framework to data from multiple surveys for juvenile (ages 2–5) Atlantic cod (Gadus morhua) stocks off Newfoundland and Labrador (NL). We found large-scale synchronized dynamics of decreasing juvenile mortality rates and increasing cohort strength from offshore surveys off eastern and southeastern NL, suggesting improving reproduction and survival rates for juvenile cod. No synchronized patterns of juvenile mortality rates and cohort strength were detected for cod stocks off southern and western NL, indicating more complex cod population spatial structures in those areas. Our study demonstrates the potential of juvenile mortality to cause temporally variable and spatially synchronized dynamics of fish recruitment, and the spatial patterns of juvenile mortality and cohort strength indicate some potential mismatch between cod population structure and current management units off NL.

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