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Robust Statistical Re-evaluation of the Effect of Pelagic Longline Fisheries on Loggerhead Sea Turtle Stocks in the Pacific

The loggerhead sea turtle is an endangered marine species that is exposed to a range of fisheries hazards in the Pacific (Chaloupka 2003, Chaloupka et al. 2004b). There are 2 distinct genetic stocks of loggerhead in the Pacific - a Japanese stock and an east Australian stock (Chaloupka et al. 2004a). Both stocks have shown significant declines over the past few decades due mainly to egg harvesting, habitat destruction and incidental capture in coastal and pelagic fisheries (Chaloupka & Limpus 2001, Chaloupka 2003, Chaloupka et al. 2004b).

Lewison et al. (2004) have recently attempted to quantify the effects of pelagic longline fisheries on loggerhead sea turtle populations in the Pacific. This was an important attempt to undertake such a regional bycatch assessment but was seriously flawed for the following reasons:

  • inadequate fisheries bycatch data were sourced
  • incomplete fisheries effort data were sourced
  • inappropriate use of catch-effort ratio estimators
  • invalid loggerhead sea turtle demographic assumptions were used
  • invalid estimates of post-hooking sea turtle mortality were used
  • inadequate statistical modelling approach was used (linear covariate functional form assumed, uncorrelated spatial variation assumed, failed to account for sampling and structural zeroes in bycatch count data)

This project proposes to undertake a similar bycatch assessment attempted by Lewison et al. (2004) but based on:

  • more up-to-date pelagic longline fisheries catch and effort data (SPC, IATTC)
  • valid and published loggerhead demographic parameter estimates (Chaloupka & Limpus 2001, Chaloupka & Limpus 2002, Chaloupka 2003)
  • valid and published loggerhead post-hooking mortality estimates (Chaloupka et al. 2004b)
  • and a more appropriate spatial semiparametric regression modelling framework that accounts for nonlinear covariate functional form, correlated and random spatial variation, as well as overdispersion, which is characteristic of sea turtle sampling data (Chaloupka & Limpus 1998) or sea turtle bycatch count data (McCracken 2000)

The major objectives and tangible outputs from this proposed project include:

  • compilation of relevant geo-referenced pelagic longline fisheries and loggerhead bycatch data for the Pacific
  • compilation of best available scientific information on loggerhead demography in the Pacific, including up-to-date data on status and trend of the 2 Pacific stocks
  • development of a robust statistical model of temporal and spatial risk of exposure of Pacific loggerheads to pelagic longline fisheries that incorporates the best available scientific information
  • completion of a robust re-evaluation of Lewison et al. (2004) to determine the validity of their findings or if those findings were seriously flawed and not suitable for pelagic fisheries management policy
  • completion of a manuscript for publication in a major international scientific journal of the Bayesian geoadditive model of loggerhead bycatch

Funding for this project to be available mid 2006.


Chaloupka M (2003) Stochastic simulation modelling of loggerhead sea turtle population dynamics given exposure to competing mortality risks in the western south Pacific. p 274-294, In: Bolten AB, Witherington B (Eds) Loggerhead Sea Turtles. Smithsonian Institution Press, Washington, DC, USA
Chaloupka MY, Limpus CJ (1998) Modelling green sea turtle survivorship rates. In: Epperly SP, Braun J (eds) Proceedings of the 17th Annual Sea Turtle Symposium. NOAA Technical Memorandum NMFS-SEFSC-415: 24-26
Chaloupka MY, Limpus CJ (2001) Trends in the abundance of sea turtles resident in southern Great Barrier Reef waters. Biol Conserv 102: 235-249
Chaloupka MY, Limpus CJ (2002) Survival probability estimates for the endangered loggerhead sea turtle resident in southern Great Barrier Reef waters. Mar Biol 140: 267-277
Chaloupka M, Dutton P, Nakano H (2004a) Status of sea turtle stocks in the Pacific. pp 135-164. in "Papers presented at the Expert Consultation on interactions between sea turtles and fisheries within an ecosystem context". FAO, Rome 9-12 March 2004. FAO Fisheries Report No. 738, Supplement
Chaloupka M, Parker D, Balazs G (2004b) Modeling post-release mortality of pelagic loggerhead sea turtles exposed to the Hawaii-based pelagic longline fishery. Mar Ecol Prog Ser 280: 285-293
Lewison RL, Freeman SA, Crowder LB (2004) Quantifying the effects of fisheries on threatened species: the impact of pelagic longlines on loggerhead and leatherback sea turtles. Ecol Letters 7: 221-231
McCracken ML (2000) Estimation of the sea turtle take and mortality in the Hawaiian longline fisheries. Administrative Report H-00-06, Honolulu Laboratory, Southwest Fisheries Science Center, National Marine Fisheries Service, NOAA, Honolulu, Hawaii, p 1-29

Principal Investigator:

Dr. Milani Chaloupka
Ecological Modeling Services P/L
P.O. Box 6150
University of Queensland
St. Lucia, Queensland 4067
Phone (61) 7-38783229
FAX (61) 7-33657299
email: m.chaloupka@uq.edu.au

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This page updated August 9, 2006