New Biological Studies Planned to Improve Stock Assessments of Billfish

PIFSC scientists in the Fishery Biology and Stock Assessment Division are engaged in several research projects to strengthen stock assessments that support international conservation and management of billfish. In July 2008, they participated in a Biological Research Needs workshop involving scientists from the U.S., Japan, Taiwan, China, and other partners. The meeting was part of the 8th Plenary Session of the International Scientific Committee for Tuna and Tuna-like Species in the North Pacific Ocean (ISC) held in Takamatsu, Japan.

Under a comprehensive Billfish Biological Research Plan, swordfish and other billfish will be caught and dissected to learn more about their reproductive maturity, age, and growth.

The workshop reviewed a Billfish Biological Research Plan. The plan addressed the need to improve international collaborations to leverage available assets toward the common objective of collecting data and biological samples needed to advance billfish life history research and improve stock assessment. The research will improve knowledge of age and growth, reproductive maturity, trophic dynamics, early life history, movement, and behavior of billfishes.

Age and growth and reproductive maturity are the two aspects of life history most in need of attention to improve ISC stock assessments of swordfish Xiphias gladius, striped marlin Kajikia audax, and blue marlin Makaira nigricans. Stock assessments require sex-specific length-at-age growth curves, estimates of longevity, and estimates of length at 50% reproductive maturity for three regions of the North Pacific: western, central, and eastern. The research plan provides detailed protocols for sample collection and analysis to accomplish these objectives. A group of potential collaborators for these studies have been identified as the PIFSC (U.S.A.); Fisheries Research Institute and National Taiwan University (Taiwan); National Research Institute of Far Seas Fisheries (Japan); Centro Interdisciplinario de Ciencias Marinas (B.C., Mexico); Shanghai Ocean University (China); and Charles Sturt University (Australia).

In addition to the billfish studies, the ISC created a task force to plan more biological research on tunas, particularly on age and growth, maturity schedules, and sex ratios. A report on the ISC Biological Research Seminar, including the 16-page billfish research plan (as Appendix 1), can be found at: on Biological Research Needs.pdf.

For more information contact: Robert Humphreys