Age estimation and back-calculation of fish length of the European hake, Merluccius merluccius (Linnaeus, 1758) in Sardinian waters

Aim of the present study is to evaluate the growth parameters for the European hake, Merluccius merluccius, in Sardinian waters by means of otolith annual ring analysis, providing also an indirect validation through the use of back-calculation. A total of 283 individuals (of which 150 males, ranging from 8.5 to 42.1 cm TL, and 133 females, that ranged from 11.2 to 83.3 cm TL), collected during the MEDITS survey in 2012 and 2013, were selected for the age reading. The determination of the age was carried out on the whole otolith for fish with total length smaller than 20 cm while for the others a transversal section across the core was prepared. Hyaline rings count was performed twice by two different readers, showing good reproducibility (%CV= 13.9; IAPE= 10.69). The estimated von Bertalanffy parameters (± s.e.) were Linf= 53.26 ± 10.15, k= 0.17 ± 0.06, t0= -1.73 ± 0.26 and Linf= 102.77 ± 13.67, k= 0.09 ± 0.02, t0= -1.46 ± 0.13 respectively for males and females. Back-calculation, carried out on otolith sections through the measurement of the ventral radius of each annulus, has provided an estimation of fish size at each year. Mean length at each age class (1-6 for females, 1-4 for males) obtained with the two methods was compared individually showing no statistically significant differences (t-Student, p-value> 0.05), except for age class 1 for both sexes. This result is probably due to the difficulty, well-known in literature for the European hake, in the identification of the first year annulus, which could be confused with one of the false rings around the nucleus. Nevertheless, this procedure certainly offers a valuable mean for corroboration of the age determination when other validation analysis are not achievable

Morphological descriptions of the eggcases of skates (Rajidae) from the central-western Mediterranean, with notes on their distribution

Eggcases of eight rajiform skates (Dipturus nidarosiensis, D. oxyrinchus, Leucoraja melitensis, Raja asterias, R. brachyura, R. clavata, R. miraletus and R. polystigma) present in the central-western Mediterranean are described, based on speci- mens obtained from shery surveys. Eggcase features such as dimensions, horns and apron lengths, and presence/ absence of lateral keels were crucial to discriminate the eggcases of the various species. Morphological and morpho- metric data, con rmed by the multivariate analysis, indicated that the eggcase of R. miraletus and L. melitensis were distinct from those of the other species for being unkeeled. Within the species having keeled eggcases, those of the genus Dipturus and R. brachyura were discriminated from the remaining group by having the largest dimensions and aprons. Sandy bottoms (<100–150 m depth) were identi ed as egg-laying sites (i.e. sites with females bearing eggcases in uteri) for many species belonging to genus Raja Raja asterias, R. brachyura, R. miraletus and R. polystigma). The nding of R. asterias and R. miraletus carrying eggcases yearly on the same sites, seems to con rm the theory that many rajid species demonstrate site delity, returning to the same depositional area on an annual basis. Some remarks on reproductive biology of these skates are also provided. The eggcase identi cation key reported here repre- sents the rst for the Mediterranean and may be useful, in the future, to identify egg-laying grounds of skates with a nonlethal method