Fisheries Research 60 (2003) 405–414 Gillnet selectivity of small coastal sharks off the southeastern United States John K. Carlson ∗ , Enric Cortés 1 NOAA/National Marine Fisheries Service, Southeast Fisheries Science Center, 3500 Delwood Beach Road, Panama City, FL 32408, USA Received 6 February 2002; received in revised form 31 May 2002; accepted 12 June 2002 Abstract Gillnet selectivity parameters for the Atlantic sharpnose, Rhizoprionodon terraenovae, blacknose, Carcharhinus acronotus, finetooth, Carcharhinus isodon, and bonnethead, Sphyrna tiburo, sharks were estimated from fishery-independent catches in multi-panel gillnets with stretched mesh sizes ranging from 8.9 to 14.0 cm in steps of 1.3 cm, with an additional size of 20.3 cm. Mesh selectivities were estimated using a maximum-likelihood model, which fits a gamma distribution to length data for each mesh size using the log-likelihood function. The Atlantic sharpnose and finetooth shark exhibited the broadest selection curves. Peak selectivities for the Atlantic sharpnose were reached from 750 mm FL for the 8.9 cm mesh to 1150 mm FL for the 14.0 cm mesh in 50 mm FL increments per mesh. Peak selectivity for the finetooth shark was reached at 550 mm FL for the 8.9 and 10.2 cm meshes, increased to 650 mm FL for the 11.4 mesh, and 750 mm FL for the 12.7 and 14.0 cm meshes. Selectivity was highest at 1150 mm FL for the 20.3 cm mesh. The bonnethead and blacknose shark exhibited narrower selection curves, with peak selectivity occurring at 450 mm FL for the 8.9 cm mesh, 750 mm for the 12.7 cm mesh in 100 mm FL increments per mesh. Maximum selectivity for the 20.3 cm mesh was 950 and 1050 mm FL for bonnethead and blacknose shark, respectively. The θ 1 values for blacknose and finetooth shark were most similar (140.58 and 141.25), whereas the value calculated for Atlantic sharpnose was the highest (211.95) and that for the bonnethead (131.77) was the lowest. Values calculated for θ 2 ,a parameter that describes the variance of sizes by mesh, ranged from 27,259 for the bonnethead to 189,873 for the finetooth shark. Although gillnets used in this study were not directly constructed for use in estimation of gillnet selectivities, information on mesh selectivities estimated herein has direct applicability to commercial gillnets with meshes of similar sizes. Published by Elsevier Science B.V. Keywords: Shark; Gillnet; Selectivity; Mesh size; Fishery 1. Introduction Gillnets are widely used for the harvest of fish. Be- cause gillnets are highly selective for fish of certain ∗ Corresponding author. Tel.: +1-850-234-6541x221; fax: +1-850-235-3559. E-mail addresses: john.carlson@noaa.gov (J.K. Carlson), enric.cortes@noaa.gov (E. Cort´ es). 1 Tel.: +1-850-234-6541x220; fax: +1-850-235-3559. size, knowledge of the size selection of gillnets is nec- essary to effectively regulate their use and for popu- lation assessment (Regier and Robson, 1966; Hamley, 1975). Using various indirect methods (see review in Millar and Fryer, 1999; Millar, 2000), gillnet selectiv- ity models have been developed and applied to a wide variety of species, such as Spanish mackerel, Scomber- morus maculatus (Ehrhardt and Die, 1988); spotted seatrout, Cynoscion nebulosus (Helser et al., 1991); lake trout, Salvelinus namaycush (Hansen et al., 1997); 0165-7836/02/$ – see front matter. Published by Elsevier Science B.V. PII:S0165-7836(02)00135-2 SEDAR 13-DW-07