Sharks face a number of obstacles for surviving their first several years of life and many specie... more Sharks face a number of obstacles for surviving their first several years of life and many species occupy nursery areas. Although estimates of survival, particularly for young age classes, are essential for assessing, monitoring and effectively managing animal populations, there have been relatively few calculations of survival within shark populations and even fewer estimates based on direct methods for sharks on their nursery grounds. We used tag-recapture methods to estimate the population size and survival of juvenile lemon sharks (Negaprion brevirostris) on their nursery grounds at Atol das Rocas, a marine protected area in Brazil. Sharks were sampled from1999 to 2003. Population size estimates ranged from 12 to 100 juvenile sharks and survival estimates ranged between 24-54% with a mean of 44.6% over the most robust sampling periods. The population of juvenile lemon sharks declined over the course of our study, whereas survival rates may have increased over the same time period. Even a modest level of fishing and removal of mature females in adjacent areas may dramatically affect small populations of sharks within a small and isolated nursery such as Atol das Rocas. The lower survival rates and population size at Atol das Rocas could be the result of differences in physical characteristics of this nursery in comparison to others used by lemon sharks in the northwestern Atlantic. Such comparatively lower populational parameters suggest that the population of young lemon sharks is fragile at the Atol das Rocas nursery.
We expand the use of eye darkening (ED) to indicate non-social stress in the fish Nile tilapia Or... more We expand the use of eye darkening (ED) to indicate non-social stress in the fish Nile tilapia Oreochromis niloticus (L.). ED is easily estimated, not requiring any sophisticated equipment, and is non-invasive, facilitating the collection of several measures of stress over time. In the current study, we showed the following: (i) high- and low-ED occur spontaneously, indicating different fish reactions to adjustments to a novel environment; (ii) fish confinement or air exposure clearly increases ED (air exposure is a stronger stressor than confinement), and the time to restore basal values indicates the severity of the impact of the stressor on the fish (this response is not affected by period of the day, e.g., morning or afternoon); and (iii) in adults, females were more responsive (slower recovery) to 2-min air exposure than to 30-min confinement.
Nile tilapia fish were individually reared under similar light levels for 8 weeks under five colo... more Nile tilapia fish were individually reared under similar light levels for 8 weeks under five colored light spectra (maximum wavelength absorbance): white (full light spectrum), blue (,452 nm), green (,516 nm), yellow (,520 nm) or red (,628 nm). The effects of light on feeding, latency to begin feeding, growth and feed conversion were measured during the last 4 weeks of the study (i.e., after acclimation). We found that red light stimulates feeding, as in humans, most likely by affecting central control centers, but the extra feeding is not converted into growth.
Sharks face a number of obstacles for surviving their first several years of life and many specie... more Sharks face a number of obstacles for surviving their first several years of life and many species occupy nursery areas. Although estimates of survival, particularly for young age classes, are essential for assessing, monitoring and effectively managing animal populations, there have been relatively few calculations of survival within shark populations and even fewer estimates based on direct methods for sharks on their nursery grounds. We used tag-recapture methods to estimate the population size and survival of juvenile lemon sharks (Negaprion brevirostris) on their nursery grounds at Atol das Rocas, a marine protected area in Brazil. Sharks were sampled from1999 to 2003. Population size estimates ranged from 12 to 100 juvenile sharks and survival estimates ranged between 24-54% with a mean of 44.6% over the most robust sampling periods. The population of juvenile lemon sharks declined over the course of our study, whereas survival rates may have increased over the same time period. Even a modest level of fishing and removal of mature females in adjacent areas may dramatically affect small populations of sharks within a small and isolated nursery such as Atol das Rocas. The lower survival rates and population size at Atol das Rocas could be the result of differences in physical characteristics of this nursery in comparison to others used by lemon sharks in the northwestern Atlantic. Such comparatively lower populational parameters suggest that the population of young lemon sharks is fragile at the Atol das Rocas nursery.
We expand the use of eye darkening (ED) to indicate non-social stress in the fish Nile tilapia Or... more We expand the use of eye darkening (ED) to indicate non-social stress in the fish Nile tilapia Oreochromis niloticus (L.). ED is easily estimated, not requiring any sophisticated equipment, and is non-invasive, facilitating the collection of several measures of stress over time. In the current study, we showed the following: (i) high- and low-ED occur spontaneously, indicating different fish reactions to adjustments to a novel environment; (ii) fish confinement or air exposure clearly increases ED (air exposure is a stronger stressor than confinement), and the time to restore basal values indicates the severity of the impact of the stressor on the fish (this response is not affected by period of the day, e.g., morning or afternoon); and (iii) in adults, females were more responsive (slower recovery) to 2-min air exposure than to 30-min confinement.
Nile tilapia fish were individually reared under similar light levels for 8 weeks under five colo... more Nile tilapia fish were individually reared under similar light levels for 8 weeks under five colored light spectra (maximum wavelength absorbance): white (full light spectrum), blue (,452 nm), green (,516 nm), yellow (,520 nm) or red (,628 nm). The effects of light on feeding, latency to begin feeding, growth and feed conversion were measured during the last 4 weeks of the study (i.e., after acclimation). We found that red light stimulates feeding, as in humans, most likely by affecting central control centers, but the extra feeding is not converted into growth.
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Papers by Renato Freitas
Although estimates of survival, particularly for young age classes, are essential for assessing, monitoring and effectively
managing animal populations, there have been relatively few calculations of survival within shark populations and even fewer
estimates based on direct methods for sharks on their nursery grounds. We used tag-recapture methods to estimate the
population size and survival of juvenile lemon sharks (Negaprion brevirostris) on their nursery grounds at Atol das Rocas, a
marine protected area in Brazil. Sharks were sampled from1999 to 2003. Population size estimates ranged from 12 to 100 juvenile
sharks and survival estimates ranged between 24-54% with a mean of 44.6% over the most robust sampling periods. The
population of juvenile lemon sharks declined over the course of our study, whereas survival rates may have increased over the
same time period. Even a modest level of fishing and removal of mature females in adjacent areas may dramatically affect small
populations of sharks within a small and isolated nursery such as Atol das Rocas. The lower survival rates and population size
at Atol das Rocas could be the result of differences in physical characteristics of this nursery in comparison to others used by
lemon sharks in the northwestern Atlantic. Such comparatively lower populational parameters suggest that the population of
young lemon sharks is fragile at the Atol das Rocas nursery.
Although estimates of survival, particularly for young age classes, are essential for assessing, monitoring and effectively
managing animal populations, there have been relatively few calculations of survival within shark populations and even fewer
estimates based on direct methods for sharks on their nursery grounds. We used tag-recapture methods to estimate the
population size and survival of juvenile lemon sharks (Negaprion brevirostris) on their nursery grounds at Atol das Rocas, a
marine protected area in Brazil. Sharks were sampled from1999 to 2003. Population size estimates ranged from 12 to 100 juvenile
sharks and survival estimates ranged between 24-54% with a mean of 44.6% over the most robust sampling periods. The
population of juvenile lemon sharks declined over the course of our study, whereas survival rates may have increased over the
same time period. Even a modest level of fishing and removal of mature females in adjacent areas may dramatically affect small
populations of sharks within a small and isolated nursery such as Atol das Rocas. The lower survival rates and population size
at Atol das Rocas could be the result of differences in physical characteristics of this nursery in comparison to others used by
lemon sharks in the northwestern Atlantic. Such comparatively lower populational parameters suggest that the population of
young lemon sharks is fragile at the Atol das Rocas nursery.