Survival Of Yearlings Research Articles

First successful head-start program of leatherback sea turtles (Dermochelys coriacea) in Thailand and proposed dietary strategy.

Leatherback sea turtle (Dermochelys coriacea) hatchlings have previously been kept alive for over a year in captive conditions but these were the few survivors of initially larger groups. In this report, newly hatched leatherback sea turtles were randomly harvested from two nests in Thailand and successfully reared before release back to the wild. In captivity, the survival of the turtles decreased sharply during the first 4 or 5 months, and then steadied until the end of the 12-month trial. The survival of yearlings from one nest was 13.3% and from the other nest 46.7%. Their growth was exponential, reaching 1.36-3.35 kg (n = 9) at the end of program. The causes of death of the reared turtles were accidents (25.0-38.5%) and infections from water and live food (61.5-75.0%). The dietary requirements of the turtles were investigated by determining the digestibility of protein and carbohydrate in vitro, using enzymes from the digestive tracts of hatchlings that had died in an accident (70.1-92.9 g body weight). The results indicated that the most suitable source of protein was wheat gluten, followed by soybean meal, nonruminant meat and bone meal, fish meal, nonruminant meat meal, pork meal, and skimmed milk, while suitable carbohydrate sources were mashed cassava, corn, wheat flour, and alpha starch, followed by cereal meal and rice flour. Findings from the current report provide a practical protocol for head-starting leatherback sea turtles, and indicate the possible basis of an effective artificial diet for this species.

Early survival of Punjab urial

There is almost no information on age-specific survival of Asiatic ungulates based on mark–recapture studies. Survival of marked Punjab urial ( Ovis vignei punjabiensis Lydekker, 1913) aged 0–2 years was studied in the Salt Range, Pakistan, in 2001–2005. Male lambs were heavier than females at birth. The relationship between litter size and birth mass varied among years, with a tendency for twins to be lighter than singletons. Birth mass had a positive but nonsignificant relation with survival to 1 year. Neither sex nor litter size affected survival to 1 year, which averaged 55% (95% CI = 41%–68%). There was no sex effect on survival of yearlings, which averaged 88% (95% CI = 4%–100%). Although survival of lambs and yearlings was similar to that reported for other ungulates, apparent survival of 2- and 3-year-olds was very low at only 47%, possibly because of emigration. Early survival in this protected area is adequate to allow population growth, but more data are required on adult survival.

Aspects of survival in juvenile polar bears

We captured, weighed, tagged, and monitored polar bear (Ursus maritimus) cubs and yearlings in western Hudson Bay to examine survival rates and correlates with survival. Cub survival between spring and autumn increased with cub mass and maternal mass, but was not related to maternal age or maternal condition. Cub survival between spring and autumn varied annually between 39.0 and 100.0% and averaged 53.2%. Whole-litter loss between spring and autumn was 30.8%, and only 38.0% of the females did not lose any cubs. Survival of spring twins was similar regardless of size, but in triplet litters, survival between spring and autumn varied according to cub size. Minimum cub survival from one autumn to the next was 34.7% and was related to cub mass, maternal mass, and maternal condition. Cub survival during autumn was estimated at 83.0%. Survival during the first year of life was no more than 44.0% but we could not estimate an annual survival rate because of the sampling regime. Possibly because harvesting was the major mortality factor for yearlings (19.4% of the yearlings were removed from the population per year), no factors examined correlated with survival of yearlings. We found no sex-related differences in survival of cubs or yearlings in any period. Relationships between survival in polar bear cubs and their condition suggest that lack of food availability, sometimes due to low maternal fat stores for lactation, leads to starvation and may be the main cause of mortality.

Survival, Growth, and Smolt Production of Atlantic Salmon Stocked as Fry in a Southern New England Stream

Abstract The performance of Atlantic salmon Salmo salar stocked as fry was assessed in a third-order stream of the lower Connecticut River system. Stocking densities of 100–150 unfed fry per 100 m2 of stream area were tested for their ability to maximize smolt production. Because the Connecticut River no longer had a natural population of Atlantic salmon, fry originating from the Penobscot River of Maine were stocked in 1982, 1984, and 1985. In 1983, the Penobscot strain was unavailable and fry originating from Iceland were used instead. Although stocking conditions were not always favorable, an average of 27% of Penobscot fry survived to the fall age-0 pan stage. In contrast, only 2% of Icelandic fry survived to this stage, The low survival of Icelandic fry may have been due to their smaller total lengths and to intraspecific competition from an abundant population of yearlings that had been stocked in 1982. However, these factors would not have influenced summer-to-fall survival of yearlings, which was ...

Life History and Demographic Variation in the Lizard Sceloporus Graciosus: A Long‐Term Study

An 11—yr study of life history and demographic variation in the sagebrush lizard Sceloporus graciosus was carried out on two study areas (Rattlesnake Ridge and Ponderosa Flat) in the Kolob Mesa Section of Zion National Park, Utah. Two primary objectives of this mark—recapture study were to: (1) quantify variation in age structure, age and size at maturity, age—specific survivorship and fecundity, and individual growth rates, and (2) conduct a series of density reduction experiments designed to elucidate the effects of density on growth rates and survival of posthatchling lizards. In addition, we examined the relationships of variation in population density and deviation from long—term average precipitation and temperature to variation in individual growth, reproduction, and demography. At both sites the active season was °160 d, extending from early April to mid—September. Reproduction occurred during a 50—d period between mid—May and early July. Mean clutch size was 3.7 eggs and most females produced their first clutch in the 2nd yr of life (their third active season) at an age of °22—24 mo and a minimum snout—vent length of °50 mm. Most mature females produced two clutches of eggs per year, and there was no statistically significant variation in either mean clutch size or body—size—adjusted clutch size among the 11 yr of study. Clutch size was significantly correlated with body size. Relative clutch mass averaged 0.247 and was not significantly correlated with body size. Since hatchlings first appeared in early to mid—August, their first growing season was °2 mo long. There was no significant sexual dimorphism in growth rate or body size in either population. There was great variation in estimates of egg—yearling survival among years. Egg—yearling survival probability varied from 0.12 to 0.59 with a mean of 0.28. At Ponderosa Flat, the survival of yearling males (0.38) was significantly lower than that of yearling females (0.47). Survival of yearling males (0.45) and females (0.43) at Rattlesnake Ridge was not significantly different. There were no other significant differences in the survival of males and females (X = 0.56 for both sexes) within any age class in any year of the study. However, the survival of yearlings was significantly lower than that of older lizards in both populations. Mean posthatchling survival over all years was 0.45, and there was significant heterogeneity in posthatchling survival among years. Average annual survival of immigrants (0.32) was significantly lower than that of residents (0.44). There was a significant negative linear relationship between yearling body size in late June and total density of posthatchling lizards. A stepwise linear regression model revealed significant effects of both rainfall (and presumably resource availability) and population density on the growth of yearlings. This model explained 78% of the annual variation in yearling growth. Rank correlation analysis revealed that survivorship of hatchlings was negatively correlated with density of conspecific lizards. The negative correlation implies direct density dependence of hatchling mortality rates and is a potentially important mechanism of population regulation. Removals of almost all yearling and older age lizards from the study sites resulted in significant increases in growth rates of hatchlings in the year of the removal and yearlings during the following year. Four results from this study combine to suggest substantial resource limitation of S. graciosus on the Kolob Mesa. (1) Snout—vent lengths attained by yearling lizards were positively correlated with deviations from long—term mean rainfall values. (2) Body sizes attained by yearlings were greatest in the years following density reductions. (3) Body size attained by yearlings was negatively correlated with density of conspecifics. And (4), in a year in which a density reduction followed a warm, wet spring, more yearling females reached maturity than in all other years of the study combined.

In-situ striped bass (Morone saxatilis) contaminant and water quality studies in the Potomac River and upper Chesapeake Bay in 1989

In-situ striped bass contaminant studies were conducted in two important Chesapeake Bay spawning areas during the spring of 1989. The objectives of this research were to: (1) conduct three 96-h in-situ striped bass prolarval survival studies and one 27-day in-situ yearling survival study at three stations in the Potomac River during a major portion of the spawning season; (2) monitor 11 water quality parameters. 11 inorganic contaminants and 14 organic contaminants during the above experiments; (3) conduct three 96-h in-situ striped bass prolarval studies, one 14-day in-situ yearling test and one 27-day in-situ yearling test at three stations in the Upper Chesapeake Bay; (4) evaluate the water quality and contaminant conditions described in Objective (2) during these Upper Bay studies and (5) conduct histological and hematological examinations on surviving yearling striped bass tested in both the Potomac River and Upper Bay. Survival of prolarvae ranged from 3 to 33% in all three 96-h tests conducted in the Potomac River. Control survival was greater than 83%. Lowest prolarval survival was reported during the first experiment (less than 8%) when low water temperatures of 10 to 11°C were reported. These temperatures are stressful to prolarvae. Stressful conditions during the second and third experiments were not documented although 12 μg/l of arsenic was reported during experiment 3. Yearling survival during the 27-day in-situ test was 5% on the Maryland side of the river, 80% in the middle of the river and 30% on the Virginia side of the river. Control survival was 100%. Potentially stressful concentrations of chromium (29 μg/l) and arsenic (12 μg/l) were reported at the Virginia station (30% survival) during the yearling study. Stressful conditions were not documented at the Maryland station where survival was low (5%) or the middle river station where survival was high (80%). Survival of prolarvae at the three stations during Upper Chesapeake Bay tests ranged from 31 to 46% for experiment 1, 28 to 52% for experiment 2, and 6 to 22% for experiment 3. Control survival was 77% or greater. Prolarval survival during experiments 1 and 2 was considered good based on natural mortality that occurs with this life stage. The low survival during experiment 3 was likely related to the low temperatures of 10–11 °C reported during these tests. Survival of striped bass yearlings during the first 14-day yearling study ranged from 10 to 35% at the three field locations: control survival was 100%. This lest was conducted before the spawning season. Low water temperatures and temperature reductions of 7°C during short time periods were likely responsible for the reduced survival. Survival of yearlings during the 27-day yearling study (representing the spawning season) was greater than 98% al all stations. Control survival was 100%-. Although the survival of striped bass prolarvae and yearlings was generally good during these tests, it is important to note that various potentially toxic concentrations of metals (cadmium, chromium, copper and lead) were reported in the Upper Bay. The following insecticides were also reported after a major storm event in the Upper Bay between prolarval experiments 1 and 2: heptachlor epoxide ( 0.008 μg/l). edosulfan l(0.006 μg/l). dieldrin (0.005 μg/l) and 4.4-DDT (0.0014 μg/l). All contaminant concentrations were reported from composite samples: therefore, maximum values were likely much higher. Histological and hematological examinations of yearling striped bass exposed to Potomac River water suggested pathology that may be associated with water-borne contaminants. The following pathology was observed in these fish. PAS-positive inclusions of variable size and distribution in the hepatocytes of the liver, dilated kidney tubules and deposits of amorphous material near the glomerular arterioles and increased erythrocyte destruction resulting in hemoglobin in the liver and excessive accumulation and hemosiderin in the spleen. Pathology of yearlings exposed to Upper Chesapeake Bay water did not provide conclusive data to suggest the presence of contaminants. The condition of the gills from these nsh suggested a possible non-specific irritant in the water.

Survival, Growth, and Prey of Esocidae in Experimental Systems

Abstract Survival (July to November) of young-of-the-year esocids stocked in 0.2-hectare experimental ponds in Missouri was: muskellunge (Esox masquinongy), 24%; northern pike (Esox lucius), 58%; and the F1 hybrid of these two species (commonly called the “tiger muskie”), 74%. Survival of yearlings from April to September was: muskellunge, 80%; northern pike, 90%; and hybrids, 85%. Growth rate of yearlings of all three forms was rapid in late spring, declined to a seasonal low in July, and then increased until the ponds were drained in September. Average weight gain of the hybrids (719 g) during their second year of life in ponds was significantly greater than that of northern pike (617 g) or muskellunge (615 g). Maintenance diets (grams of food per gram of fish) calculated for fish in tanks (1.2 × 4.8 × 1.1 m) for 28-day periods were as follows: northern pike, 0.23; muskellunge, 0.51; and hybrids, 0.62. Food conversion efficiencies in tanks were: northern pike, 29.0%; muskellunge, 25.0%; and hybrids, 22....