Length structure and weight-length relationship of the slaty-spotted guitarfish, Rhinobatos glaucostigma (Rajiformes: Rhinobatidae) from continental shelf of Sinaloa, Mexico

Abstract

We analyzed the size structure and weight-length relationship of Rhinobatos glaucostigma in the continental shelf of Sinaloa, Mexico. A total of 1129 specimens were examined, of which 491 were female and 638 were males. The sizes for females were 7.4 to 87 cm of total length (LT) with mean of 39.7 cm and males ranged 8.3 and 71.9 cm with mean of 40.3 cm. The total weight (WT) for females ranged 6 to 2256 g with mean of 332.1 g and males ranged 6 to 900 g with mean of 284.5 g. The size embryos ranged 7.4 to 11 cm (8.6 ± 1.3 cm), the neonates between 16 and 31.2 cm (21.5 ± 3.4 cm), the juvenile ranged of 17 to 61 cm (32.6 ± 10.3 cm) and the adults 26.5 to 87 cm (57.4 ± 8.4 cm). The TL-TW relationship for females were TW = 0.004(TL)2.968 and for males were TW = 0.004(TL)2.924. The sex ratio for adults was 1:1.3 (females: males) and for embryos was 1:0.95 (females : males). Catches occurred between 3.6 to 45 m depth, collecting in the first 15 m over 83% of the population. The shrimp trawl fishery had an impact on more than 63% of juvenile than other maturity stages; this can affect directly in the population of R. glaucostigma by not allowing them get to reproductive process.