Age and growth determination of blackspotted smooth-hound (Mustelus punctulatus Risso, 1827) in the northern Adriatic Sea

Abstract

Pas mekuš (Mustelus punctulatus Risso, 1827) pripada skupini mezopredatorskih morskih pasa koji se komercijalno izlovljavaju u Jadranu. Prema IUCN Crvenom popisu mekuš je nedovoljno poznata vrsta, te se malo zna o biologiji ove vrste uključujući i podatke o starosti, koji nedostaju za čitavo Jadransko i Sredozemno more. Stoga je cilj ovog rada odrediti starost i brzinu somatskog rasta, kako bi se ovi podaci mogli koristiti pri planiranju i odrţivom upravljanju vrste. Primjenom skeletokronološke metode i morfometrijskih mjerenja na tijelima kralješaka određena je starost 94 ţenke (46,8 - 136,2 cm ukupne duţine tijela, DT) i 93 muţjaka (44,6 - 126,5 cm DT). Analiza rubnog prirasta, koja pokazuje vremensku periodičnost nastanka znakova rasta, potvrdila je primjerenost upotrijebljene metode za određivanje starosti. Najstarija procijenjena dob za ţenke i muţjake iznosila je 20 i 15 godina, a u analiziranom uzorku su prevladavale jedinke s 3+ i 4+ godine ţivota. Podaci o duljinama tijela i starosti su korišteni za određivanje parametara von Bertalanffyeve funkcije rasta: k = 0,05 god-1, Linf = 193,00 cm i to = -4,72 za ţenke, te k = 0,08 god-1, Linf = 144,00 cm i to = -3,95 za muţjake. Prema dobivenim vrijednostima pas mekuš je spororastuća vrsta, koja je izrazito osjetljiva na izlov.Blackspotted smooth-hound (Mustelus punctulatus Risso, 1827) belongs to a group of meso-predator sharks which are commercially exploited in the Adriatic Sea. According to the IUCN Red List blackspotted smooth-hound is classified as data deficient species, and very little is known about important aspects of its biology, including data on age and growth rate, which are missing for the Adriatic and Mediterranean Sea. Therefore, the aim of this study was to estimate the age and somatic growth rate, important for planning and sustainable management of this species. Age was estimated on sectioned vertebrae of 94 females (46.8 to 136.2 cm total body length, DT) and 93 males (44.6 to 126.5 cm DT), by applying skeletochronological method and morphometric measurements of vertebrae. Marginal increment analysis was conducted to assess patterns in seasonal growth, which justified the use of vertebrae for ageing of these sharks. Age-length data were used to estimate parameters for the von Bertalanffy growth function: k = 0.05/yr, Linf = 193.00 cm and to = -4.72 for females, and k = 0.08/yr, Linf = 144.00 cm and to = -3.95 for males. The oldest female was aged 20 years and male 15 years, while in the collected sample prevailed animals with age 3+ and 4+. According to these results, blackspotted smooth-hound is a slow-growing species, extremely vulnerable to exploitation