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Robust
Statistical Re-evaluation of the Effect of Pelagic Longline Fisheries
on Loggerhead Sea Turtle Stocks in the Pacific
BACKGROUND
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)
OBJECTIVES
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.
References
•
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
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