Spawning Per Recruit Analysis of the Blue Shark (Prionace glauca) in the Coastal Waters of Taiwan

Abstract

Shark conservation and management have become issues of great concern for international conservation organizations in recent years. For Taiwan, as one of the leading shark fishing countries, the evaluation and management of shark resources are extremely important. Prionace glauca (blue shark) is the most commonly caught large shark species in small and medium-scale longline fishing in Taiwan. Three main fishing ports include Nanfangao Fishing Port in Yilan, Tungkang in Pingtung, and Chenggong in Taitung. Estimated annual yields are between 7,233-16,080 mt. Since 2001, the nominal catch per unit effort (CPUE) of blue shark caught by Taiwanese longline fisheries had an upward tendency, followed by a downward tendency. The nominal CPUE during the last three years has been lower than that in previous years. Demographic matrix assessment indicated that blue sharks in the North Pacific are characterized by population growth rate of 0.329±0.089 and generation interval of 8.67±2.12 years. This is a species with a relatively high growth rate among large sharks. As SPR at 4%, the estimated biological reference point F for Pacific blue shark is equal to 0.193 yr-1 (±0.036), and Fcur/F40% are equal to 0.57, 0.81, and 0.72 in the scenario 1-3, respectively. The results suggest the current fishing pressure is appropriate and is below the sustainable biological reference point for blue shark stock in the Pacific Ocean.