Longline-caught blue shark (Prionace glauca): factors affecting the numbers available for live release
The blue shark (Prionace glauca) is an oceanic species that occurs in temperate and tropical waters around the globe (Robins and Ray, 1986). This species is a major bycatch of pelagic longline fleets that operate to supply the world's growing demand for tunas and swordfish (Xiphias gladius) (Stevens, 1992; Bailey et al., 1996; Francis, 1998; Francis et al., 2001; Macias and de la Serna, 2002); numerically, the blue shark is the top nontarget species captured by the U.S. longline pelagic Atlantic fleet (Beerkircher et al.1). Ward et al. (2004) examined the effect of longline soak time (set duration) on the catch rate of several target and bycatch species, including the blue shark. However, they did not investigate the effects of fish size, set duration, and water temperature on shark survival, and, therefore, numbers potentially available for live release (Francis et al., 2001; Campana et al.2). Knowledge of such relationships may be of value: 1) for minimizing bycatch mortality on this and other highly vulnerable pelagic species through modification of fishing strategy; and 2) for blue shark stock assessments that are based on commercial longline catch data.