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Developing Tools to assess Sex and Maturational Stage of Bigeye Tuna (Thunnus obesus) and Swordfish (Xiphias gladius)

Progress Reports (PDF): FY 2003, FY 2002, FY 2001, FY 2000

Project Overview
The highly migratory nature of the tuna and billfish makes conservation and management of this expansive fishery a challenging task. Tuna and billfish travel thousands of miles on extensive migrations, transcending economic and geopolitical boundaries set by world nations. Technological advances and international collaborative efforts have greatly increased our understanding of the oceanographic environment of pelagic fish and its influence on fishery performance. However, a comprehensive understanding of the reproductive biology and spawning activity of a species is also needed to understand that species' population dynamics. Knowledge of the reproductive biology is fundamental for constructing reliable models for effective stock assessment. This includes obtaining accurate information on age at maturity, fecundity and sex ratio of a population. This type of information helps fisheries scientists detemine size of the standing stock and proportion of mature adults of each gender in the stock (maturity schedule).

At present, the sex and maturity of most teleost species cannot be identified by their physical appearance or by examining their gonads. Current methods for assessing maturity schedules of tunas and billfishes is based on the standard approach of collecting gonads for detailed histological examination under a microscope. While this has proven to be an accurate method, providing valuable information, it is labor-intensive, expensive and lethal for the fish. In addition, gonadal samples are often unavailable since tuna are often sold intact at the auction block and swordfish are gutted at sea. The most formidable feature of this coventional method is that it is time-consuming, thus making it impractical to reevaluate the population annually. As a result, management models are static and fail to reflect "real-time" effects of fishing pressure or environmental pertubations.

The central aim of this project is to develop accurate, simple to use and economical tests to determine sex and maturational stage so that populations can be monitored on a regular basis and at low cost. These methods are being used extensively in biomedical and human genetics research. Project researchers plan to adapt these methods for direct application to fisheries management through the following objectives:

  1. Develop and modify the technology to identify the sex and maturational status of individual fish in two species: bigeye tuna (Thunnus obesus) and swordfish (Xiphias gladius). This approach will focus on developing genetic and immunoassays to detect sex and maturational specific compounds present in blood and muscle tissue samples.

  2. Validate the accuracy of this approach by "ground truthing" the results with the standard method of staging maturity based on histological examination of the gonads.

  3. Transfer the technologies to fishery biologists throughout the Pacific for use in constructing and monitoring maturity schedules for bigeye tuna and swordfish.

Funding for this project awarded in November 1999.

Principal Investigators:
Dr. M. Malia Chow
Hawaii Institute of Marine Biology
University of Hawaii at Manoa
Coconut Island, P.O. Box 1346
Kaneohe, Hawaii 96744 USA
Phone (808) 236-7419
FAX (808) 236-7443
email: mchow@iniki.soest.hawaii.edu

 

Dr. E. Gordon Grau, Interim Director
Hawaii Institute of Marine Biology
University of Hawaii at Manoa
Coconut Island, P.O. Box 1346
Kaneohe, Hawaii 96744 USA
Phone (808) 236-7406
FAX (808) 236-7443

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This page updated August 14, 2006