Tagged tuna graphic by Nancy Hulbirt, SOEST Illustration.

PFRP Biology Projects

Age and Growth of Striped Marlin, Kajikia audax, Caught in the Hawaii-based Longline Fishery

Progress Reports: FY 2012, FY 2011

Project Summary

Striped marlin are an important component of commercial longline fisheries in the Indian and Pacific Oceans and are a vital ecological resource as a top predator in the open ocean ecosystem. Approximately 4000 mt are harvested each year from the US Western and Central Pacific Ocean but the sustainability of these catches are uncertain due to a lack of biological information pertaining to this species. We propose a study of the key age and growth characteristics of the population of striped marlin caught in the Hawaiian-based longline fishery in order to support stock assessment in this region. This research aims to develop a sex-specific age and growth model for striped marlin in the north-central Pacific Ocean based on previously developed and validated aging methods (Kopf and Davie 2009; Kopf et al. 2010; Kopf 2010). The study will take advantage of previous collections of biological hardparts (dorsal fin spines and sagittal otoliths) provided by collaboration with the Pacific Islands Fisheries Science Center (Humphreys) as well as current and on-going collections of these hardparts through Pacific Islands Regional Office (PIRO) Observer Program. The expected outcomes from this research are to provide length-at-age and growth rate information in support of stock assessment models for striped marlin in the North Pacific Ocean.


  1. Determine the periodicity of annulus formation in fin spine sections using Marginal Increment Analysis.
  2. Evaluate presumed daily periodicity of micro-increments formed in sagittal otoliths by comparing back-calculated hatch dates with the spawning season.
  3. Corroborate the location of the first yearly annulus formed in fin spine sections using otolith micro-increment counts.
  4. Model daily and annual growth and length-at-age of male and female striped marlin (pending indirect validation).

Expected Outcomes

This research is expected to provide length-at-age and annual growth rate information on striped marlin in the north-central Pacific Ocean. This information will be made available for use in regional stock assessment models for striped marlin and is therefore intended to benefit management of sustainable fisheries in the region. The results will also be published in scientific peer-reviewed journals.

Funding for this project to be available late 2010.

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Kopf, R.K. 2010. Age, growth, and reproductive dynamics of striped marlin, Kajikia audax in the southwest Pacific Ocean. PhD Thesis. Charles Sturt University, Australia, 1-235pp.

Kopf R.K., Drew K., and. Humphreys R.L Jr. 2010. Age estimation of billfishes (Kajikia spp.) using fin spinecross-sections: the need for an international code of practice. Aqua. Liv. Res. 23(1): 13-23.

Kopf R.K. and Davie P.S. 2009. Population biology and habitat preferences of striped marlin, Kajikia audax in eastern Australia and southwest Pacific Ocean. Australian Fisheries Management Authority and Fisheries Research and Development Corporation, Final Report. Project number 2006/816.

Principal Investigator

Dr. R. Keller Kopf
Charles Sturt University
Institute for Land Water & Society
School of Environmental Sciences
PO Box 789
Albury, NSW 2640
Phone (61) 2 60265227/4 04265690
FAX (61) 2 6051 9897
email: rkopf@csu.edu.au

Dr. Robert Humphreys, Jr. (Collaborator)
NOAA Fisheries
Pacific Islands Fisheries Science Center
Fish BIology & Stock Assessment Division
2570 Dole Street
Honolulu, HI 96822, USA
Phone (808) 983-5377
FAX (808) 983-2980
email: Robert.Humphreys@noaa.gov


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