Population status of the Orinoco crocodile (Crocodylus intermedius) in the Cojedes river system, Venezuela

Seijas, Andrés E.; Chávez, Carlos

doi:10.1016/s0006-3207(99)00184-6

Cited by 10 publications

(9 citation statements)

References 13 publications

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“…Our results, and observations from previous studies documenting male hierarchies in Orinoco crocodiles during the breeding season [ 55 , 56 ], suggest unequal distribution of matings. In this study shared paternity across clutches revealed highly skewed contributions among identified males.…”

Section: Discussionsupporting

confidence: 83%

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Multiple Paternity in a Reintroduced Population of the Orinoco Crocodile (Crocodylus intermedius) at the El Frío Biological Station, Venezuela

et al. 2016

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The success of a reintroduction program is determined by the ability of individuals to reproduce and thrive. Hence, an understanding of the mating system and breeding strategies of reintroduced species can be critical to the success, evaluation and effective management of reintroduction programs. As one of the most threatened crocodile species in the world, the Orinoco crocodile (Crocodylus intermedius) has been reduced to only a few wild populations in the Llanos of Venezuela and Colombia. One of these populations was founded by reintroduction at Caño Macanillal and La Ramera lagoon within the El Frío Biological Station, Venezuela. Twenty egg clutches of C. intermedius were collected at the El Frío Biological Station for incubation in the lab and release of juveniles after one year. Analyzing 17 polymorphic microsatellite loci from 335 hatchlings we found multiple paternity in C. intermedius, with half of the 20 clutches fathered by two or three males. Sixteen mothers and 14 fathers were inferred by reconstruction of multilocus parental genotypes. Our findings showed skewed paternal contributions to multiple-sired clutches in four of the clutches (40%), leading to an overall unequal contribution of offspring among fathers with six of the 14 inferred males fathering 90% of the total offspring, and three of those six males fathering more than 70% of the total offspring. Our results provide the first evidence of multiple paternity occurring in the Orinoco crocodile and confirm the success of reintroduction efforts of this critically endangered species in the El Frío Biological Station, Venezuela.

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Section: Discussionsupporting

confidence: 83%

“…The occurrence of male hierarchies in Orinoco crocodiles during the breeding season was observed in previous studies [ 55 , 56 ]. However, both the extent to which males are able to monopolize breeding, and the occurrence of multiple mating, were unknown.…”

Section: Introductionsupporting

confidence: 61%

Multiple Paternity in a Reintroduced Population of the Orinoco Crocodile (Crocodylus intermedius) at the El Frío Biological Station, Venezuela

et al. 2016

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“…Messel et al (1981in Seijas et al, 1999 described this method as calculating the population structure of crocodiles using the maximum number of individuals in a particular size category, regardless of the survey in which they were observed. This is then assumed to be the best estimate for that particular size class for that year.…”

Section: Methodsmentioning

confidence: 99%

A multi-method approach for the inventory of the adult population of a critically endangered crocodilian, the Gharial (Gavialis gangeticus) at Dhikala, Corbett Tiger Reserve incorporating direct counts and trail cameras

Chowfin¹,

Leslie²

2014

Int. J. Biodivers. Conserv.

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The Corbett Tiger Reserve (CTR), a very highly rated protected area in the State of Uttarakhand, India, is home to the third largest breeding population of adult gharial globally. It contributes 20% to the estimated global population of 200 -250 adults of the taxon and it is also the only known population of the taxon which lives predominantly in a lake-like environment. CTR was surveyed for gharial in 2008 which was the first systematic survey with regard to the taxon since 1974 and the meta-population here was found distributed amongst six sub-populations in the Sarpduli, Dhikala, Kalagarh, Sonanadi, Palain and Adnala Ranges of the Reserve. This paper documents a multi-method approach for the estimation of gharial at Dhikala (Dhikala Range) namely: at the confluence of the Ramganga River with the Kalagarh Reservoir. It details the use of trail cameras combined with boat surveys along the shoreline and stationary counts for estimating the adult population of gharial at Dhikala, the site of the largest subpopulation of gharial in CTR. Using this multi-method approach to count basking animals, we estimated the adult population in the area to consist of 32 adults (inclusive of seven adult males) based on the maximum ± minimum (MM) method. We also considered the unknown proportion of adults that may have gone undetected during these surveys by subjecting the data to a Double Sampling analysis. The results are indicative that we were able to sample 88.9% of the adult gharial population at Dhikala using this Multi-Method Approach. Based on our three population estimates (n= 29, 32 and 36) we averaged the adult population at Dhikala as 32.3 ± 1.69 adults (Mean ± SE) with an encounter rate of 4.01 ± 0.33 adults km⁻¹ over 8.06 km of shoreline. Further, comparing population estimates between 2008 and 2013 based on the maximum ± minimum (MM) method, we estimated that the number of adults in Dhikala increased by 77.8% between 2008 and 2013. This increase in adult gharial numbers detected in the study area between 2008 and 2013 is primarily a result of: (1) Improved survey techniques which detected more number of animals in the area due to the cumulative effects of population growth from sub-adults to adults, in-migration and the possibility of some animals being missed during the 2008 surveys; (2) improved knowledge and familiarity with the study area; (3) effective protection measures already in place in CTR particularly in Corbett National Park (CNP), which has allowed the adult population to increase naturally without any disturbances. The ability of this multi-method approach in detecting these changes in numbers is important for monitoring the taxon and studying population trends within CNP.

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“…The technique can underestimate populations because of these difficulties and because of the cryptic nature of crocodiles (Bayliss et al, 1986;Hutton & Woolhouse, 1989). Repeated standardized spotlight surveys are the most common form of population monitoring for crocodiles (Seijas & Chavez, 2000). The real population size is often unknown as complete counts of an entire study site are rarely possible.…”

Section: Introductionmentioning

confidence: 99%

Population size and structure of the Nile crocodile Crocodylus niloticus in the lower Zambezi valley

Wallace

Leslie

Coulson

et al. 2013

Oryx

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Concern has been raised about the lack of population data for the Nile crocodile Crocodylus niloticus in the lower/middle Zambezi valley. This area is important for conservation as well as being a source of crocodile eggs and adults for the ranching industry. Two spotlight surveys, in 2006 and 2009, were used to estimate population size, structure and trends. A stage-structured matrix model was parameterized from existing literature and the expected predictions were compared to those observed. The survey data suggests a population increase since 2006. Crocodile density was greatest (3.1 km −1 ) in the areas of increased wildlife and habitat protection and lowest (1.4 km −1 ) in areas of increased human presence. The predicted population stage structure differed to that observed, suggestive of a population not at equilibrium. Data on offtakes of crocodile eggs and adults would be useful for examining why this is the case. Continued monitoring of the wild population is necessary, to evaluate the trend of an increasing crocodile population, and additional demographic data for modelling purposes would be desirable. This paper contains supplementary material that can be found online at

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Population status of the Orinoco crocodile (Crocodylus intermedius) in the Cojedes river system, Venezuela

Cited by 10 publications

References 13 publications

Multiple Paternity in a Reintroduced Population of the Orinoco Crocodile (Crocodylus intermedius) at the El Frío Biological Station, Venezuela

Multiple Paternity in a Reintroduced Population of the Orinoco Crocodile (Crocodylus intermedius) at the El Frío Biological Station, Venezuela

A multi-method approach for the inventory of the adult population of a critically endangered crocodilian, the Gharial (Gavialis gangeticus) at Dhikala, Corbett Tiger Reserve incorporating direct counts and trail cameras

Population size and structure of the Nile crocodile Crocodylus niloticus in the lower Zambezi valley

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