Size-biased Mortality Due to Predation in a Nesting Freshwater Turtle, Trachemys scripta

Tucker, John K.; Filoramo, Nirvana I.; Janzen, Fredric J.

doi:10.1674/0003-0031(1999)141[0198:sbmdtp]2.0.co;2

Cited by 47 publications

(29 citation statements)

References 17 publications

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“…Early maturation is advantageous for males because it allows males to obtain more matings over their lifetime. Large size at maturity is advantageous for females because growth slows significantly at maturity, and both reproductive output and survivorship of nesting females are positively correlated with size (Congdon and Gibbons 1983;Tucker et al 1999). Clark and Gibbons (1969) hypothesized that juvenile turtles may be carnivorous in order to obtain sufficient calcium for shell hardening after hatching.…”

Section: Juvenile Growth and Compositionmentioning

confidence: 99%

Ontogenetic Diet Shifts and Digestive Constraints in the Omnivorous Freshwater Turtle Trachemys scripta

Bouchard

Bjorndal

2006

Physiological and Biochemical Zoology

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Many reptiles undergo an ontogenetic diet shift from carnivory to herbivory. In this study, we used the yellow-bellied slider turtle, Trachemys scripta, as a model to evaluate whether juvenile turtles are carnivorous because physiological constraints preclude herbivory. We conducted feeding trials in which we fed juvenile and adult turtles a duckweed plant, Lemna valdiviana, or a freshwater grass shrimp, Palaemontes paludosus, for 5 wk. During the trials, we measured mass-specific intake, digestibility, and digestible intake for both size classes, as well as juvenile growth. At the end of the trials, we measured the nutrient composition of the juvenile turtles. Juveniles fed shrimp grew 3.2 times faster than those fed duckweed and had equivalent lipid stores. Digestive processing in juveniles was extremely efficient on the shrimp diet, with higher mass-specific intakes than adults and very high digestibilities (97%). Juveniles digested duckweed as well as adults did; however, their intake of this diet was limited, possibly by the time required for fermentation. We concluded that although juveniles can process plant material, an animal diet allows for greater juvenile growth, which in turtles is linked to higher survivorship and increased future reproductive success.

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Section: Juvenile Growth and Compositionmentioning

confidence: 99%

Ontogenetic Diet Shifts and Digestive Constraints in the Omnivorous Freshwater Turtle Trachemys scripta

Bouchard

Bjorndal

2006

Physiological and Biochemical Zoology

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“…Thus, we predicted that larger turtles should spend longer times hidden before they decide to re-emerge from the shell to reduce the probability that the predator still remains in the surroundings and could easily detect or capture them. Likewise, smaller hatchling turtles have a higher predation rate than larger ones (Tucker et al 1999;Janzen et al 2000). Similarly, prey vulnerability increased as size decreased in juvenile fish (Scharf et al 1998).…”

Section: Introductionmentioning

confidence: 98%

Inter‐individual Variation in Antipredator Hiding Behavior of Spanish Terrapins Depends on Sex, Size, and Coloration

2014

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Behavioral responses to predation risk are critical for survival but as antipredator behavior is costly, prey animals should flexibly modulate their optimum defensive responses by considering both costs and benefits, which are partly influenced by the individual characteristics of the prey. Turtles have the shell as a morphological structure that may provide partial protection against predators, but hiding into the shell may entail some high costs, and turtles should decide when to switch to an active escape strategy to safe refuges. Here, we examined how gender, body size, and sexual coloration influence inter‐individual variability of antipredatory hiding behavior into the shell of Spanish terrapins (Mauremys leprosa). We simulated predatory attacks under different conditions and measured the time that the turtles spent hidden entirely inside the shell (i.e., appearance times) and from then until the turtle started to flee actively (i.e., waiting times). Our results showed that when risk increased, appearance times increased but waiting times decreased. When turtles were in a prone position, their hiding behavior was related with their body weight with heavier turtles having longer appearance times. Also, the conspicuousness of limb coloration was important for the appearance times of males, but not for females. Thus, males with brighter coloration of the limb stripes had longer appearance times than duller ones. In addition, when turtles were overturned, males appeared out of the shell earlier than females and heavier turtles started to right sooner, but only when risk was low. However, when turtles were overturned and risk was high, they should assume that they have already been detected, making inter‐individual differences in size and coloration apparently unimportant for deciding hiding behavior.

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“…The pattern of survival in freshwater turtles is characterized by high natural mortality at the egg, hatchling and juvenile life-history stages, but with low natural mortality and high survival (often exceeding 90%) in the adult stage (Shine and Iverson, 1995). The survival strategy appears to rely on rapid growth over the first year to a size at which predation pressures are reduced (Tucker et al, 1999). It is possible, therefore, that even low levels of fishing-related mortality may have a significant impact on the adult population, emphasizing the importance of effective bycatch minimization measures.…”

Section: Discussionmentioning

confidence: 99%

Reducing the mortality of freshwater turtles in commercial fish traps

Lowry

Pease

Graham

et al. 2005

Aquatic Conserv: Mar. Freshw. Ecosyst.

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ABSTRACT1. Mortality of air-breathing vertebrates has been recognized for some time as a significant risk in Australian inland fisheries. There has often been conflict between the desires of fishers to maximize catches of their target species and the implementation of effective methods to reduce nontarget bycatch.2. Two trials were conducted to evaluate the effectiveness of modifications to fish traps designed to prevent the capture of freshwater turtles (Emydura macquarii) and to facilitate their release. The first study evaluated the use of 100 mm exclusion rings to prevent turtles entering eel traps. The second study assessed two configurations of a carp trap designed to release the accidental catch of turtles.3. Eel traps fitted with 100 mm exclusion rings significantly reduced the turtle bycatch, with no significant difference being observed between mean size of eels captured in traps fitted with exclusion rings and traps without rings.4. The trials on the modified carp trap confirmed that they effectively retained carp and released a majority (77%) of turtles over a 4 h period. Turtles retained in the carp traps were significantly longer than those that found their way out of the trap.5. This study demonstrates the different approaches that can be taken to achieve a reduction in non-target bycatch associated with traps, and illustrates the importance of exploiting both the physical and behavioural differences of the target and non-target species in order to develop appropriate gear designs that effectively restrict the entry, or facilitate the release, of bycatch species.

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Size-biased Mortality Due to Predation in a Nesting Freshwater Turtle, Trachemys scripta

Cited by 47 publications

References 17 publications

Ontogenetic Diet Shifts and Digestive Constraints in the Omnivorous Freshwater Turtle Trachemys scripta

Ontogenetic Diet Shifts and Digestive Constraints in the Omnivorous Freshwater Turtle Trachemys scripta

Inter‐individual Variation in Antipredator Hiding Behavior of Spanish Terrapins Depends on Sex, Size, and Coloration

Reducing the mortality of freshwater turtles in commercial fish traps

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