Recovery of saltwater crocodiles following unregulated hunting in tidal rivers of the Northern Territory, Australia

Yusuke Fukuda, Grahame Webb, Charlie Manolis, Robyn Delaney, Mike Letnic, Garry Lindner, Peter Whitehead

    Research output: Contribution to journalArticleResearchpeer-review

    Abstract

    Saltwater crocodiles (Crocodylus porosus) in the Northern Territory of Australia were protected in 1971, after a severe population decline resulting from 26 yr of intense commercial hunting. By that time wild saltwater crocodiles were rarely sighted anywhere and they were commercially extinct in areas where they had once been abundant. Standardized monitoring by spotlight surveys started in 1975 and provided relative density indices over time (1975-2009) as a unique record of the post-protection recovery of a wild crocodilian population. We examined the survey data for populations at 12 major tidal rivers, individually and as a single subpopulation. The pattern of recovery in the subpopulation in both abundance and biomass was approximated by logistic curves, predicting 5.26 non-hatchling crocodiles weighing 387.64 kg sighted per kilometer of river in 2010. We predicted potential carrying capacity as 5.58 non-hatchling crocodiles (5.73% higher than 2010) weighing 519.0 kg (25.31% higher than 2010). Individual rivers showed largely different abundance and biomass among rivers. The statistical model that best described the recovery in individual rivers was not always logistic. However, where it was logistic, expected carrying capacity of different rivers showed considerable variation in abundance and biomass. The variation indicates different habitat quality among the rivers. Recovery occurred despite various consumptive uses, particularly a widespread egg-harvest program, which has been an integral part of the incentive-driven conservation program for saltwater crocodiles in the Northern Territory since 1983. We suggest that the saltwater crocodile population of the Northern Territory is achieving full recovery from uncontrolled hunting in 1945-1971. Although saltwater crocodiles are considered an important natural resource, their increase in number, size, and distribution is posing management issues for public safety. Continuation of human-crocodile conflict management through public education and strategic removal of problem crocodiles will be essential.
    Original languageEnglish
    Pages (from-to)1253-1266
    Number of pages14
    JournalJournal of Wildlife Management
    Volume75
    Issue number6
    DOIs
    Publication statusPublished - Aug 2011

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    Crocodylus porosus
    Northern Territory
    hunting
    crocodiles
    rivers
    river
    carrying capacity
    logistics
    biomass
    subpopulation
    Crocodylia
    public safety
    conflict management
    spotlight survey
    conservation programs
    crocodile
    statistical models
    natural resources
    education
    population decline

    Cite this

    Fukuda, Y., Webb, G., Manolis, C., Delaney, R., Letnic, M., Lindner, G., & Whitehead, P. (2011). Recovery of saltwater crocodiles following unregulated hunting in tidal rivers of the Northern Territory, Australia. Journal of Wildlife Management, 75(6), 1253-1266. https://doi.org/10.1002/jwmg.191
    Fukuda, Yusuke ; Webb, Grahame ; Manolis, Charlie ; Delaney, Robyn ; Letnic, Mike ; Lindner, Garry ; Whitehead, Peter. / Recovery of saltwater crocodiles following unregulated hunting in tidal rivers of the Northern Territory, Australia. In: Journal of Wildlife Management. 2011 ; Vol. 75, No. 6. pp. 1253-1266.
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    abstract = "Saltwater crocodiles (Crocodylus porosus) in the Northern Territory of Australia were protected in 1971, after a severe population decline resulting from 26 yr of intense commercial hunting. By that time wild saltwater crocodiles were rarely sighted anywhere and they were commercially extinct in areas where they had once been abundant. Standardized monitoring by spotlight surveys started in 1975 and provided relative density indices over time (1975-2009) as a unique record of the post-protection recovery of a wild crocodilian population. We examined the survey data for populations at 12 major tidal rivers, individually and as a single subpopulation. The pattern of recovery in the subpopulation in both abundance and biomass was approximated by logistic curves, predicting 5.26 non-hatchling crocodiles weighing 387.64 kg sighted per kilometer of river in 2010. We predicted potential carrying capacity as 5.58 non-hatchling crocodiles (5.73{\%} higher than 2010) weighing 519.0 kg (25.31{\%} higher than 2010). Individual rivers showed largely different abundance and biomass among rivers. The statistical model that best described the recovery in individual rivers was not always logistic. However, where it was logistic, expected carrying capacity of different rivers showed considerable variation in abundance and biomass. The variation indicates different habitat quality among the rivers. Recovery occurred despite various consumptive uses, particularly a widespread egg-harvest program, which has been an integral part of the incentive-driven conservation program for saltwater crocodiles in the Northern Territory since 1983. We suggest that the saltwater crocodile population of the Northern Territory is achieving full recovery from uncontrolled hunting in 1945-1971. Although saltwater crocodiles are considered an important natural resource, their increase in number, size, and distribution is posing management issues for public safety. Continuation of human-crocodile conflict management through public education and strategic removal of problem crocodiles will be essential.",
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    Fukuda, Y, Webb, G, Manolis, C, Delaney, R, Letnic, M, Lindner, G & Whitehead, P 2011, 'Recovery of saltwater crocodiles following unregulated hunting in tidal rivers of the Northern Territory, Australia' Journal of Wildlife Management, vol. 75, no. 6, pp. 1253-1266. https://doi.org/10.1002/jwmg.191

    Recovery of saltwater crocodiles following unregulated hunting in tidal rivers of the Northern Territory, Australia. / Fukuda, Yusuke; Webb, Grahame; Manolis, Charlie; Delaney, Robyn; Letnic, Mike; Lindner, Garry; Whitehead, Peter.

    In: Journal of Wildlife Management, Vol. 75, No. 6, 08.2011, p. 1253-1266.

    Research output: Contribution to journalArticleResearchpeer-review

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    AU - Fukuda, Yusuke

    AU - Webb, Grahame

    AU - Manolis, Charlie

    AU - Delaney, Robyn

    AU - Letnic, Mike

    AU - Lindner, Garry

    AU - Whitehead, Peter

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    KW - population decline

    KW - seawater

    KW - spotlight survey

    KW - wildlife management

    KW - Australia

    KW - Northern Territory

    KW - Alligator

    KW - Crocodylidae (all crocodiles)

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