Morphometric measurements of newborn blue shark Prionace glauca (Linnaeus, 1758) and characteristics of its potential parturition areas in coastal waters of Montenegro (Southeastern Adriatic)

Abstract

The blue shark belongs to the group of the most widespread pelagic sharks in the world. It inha-bits the pelagic zone of almost all warm and temperate seas and oceans. As it is one of the most abundant shark species, it is frequently caught in different types of fishing gear operated in the pela-gic zone. This study provides the first data on the reproduction of this species in Montenegrin waters (in the Southeastern Adriatic Sea). Six newborn blue sharks were found during our field excursions. For three of them, detailed morphometric measurements are presented. Alongside the newborns, a gravid female was also recorded. The data was collected in the period from April to October 2017. According to the published literature and the data presented in this paper, species reproduction is likely to be seasonal. A review of the areas where the specimens were recorded was carried out in order to infer if the adult females choose them specifically as their parturition grounds

Data‐mining social media platforms highlights conservation action for the Mediterranean Critically Endangered blue shark Prionace glauca

“…From each record, the following information was collected: (i) date and location; (ii) type of record, which included four standard categories – sightings of blue sharks swimming in inshore waters, swimming in confined areas (tourist hotspots, commercial ports, and artificial and/or natural lagoons), stranding, and by‐catch; (iii) number of individuals for each record; (iv) sex of each shark, determined, when possible, by visually examining the pelvic fins for the presence of claspers in males or their absence in females; (v) life stage, classed according to Leone et al (2017) as juvenile, with an estimated total length (ETL) of ≤120 cm, subadult, with an ETL of 120–180 cm, and adult, with an ETL of >180 cm (within the juvenile life stage, a subcategory was used to identify smaller individuals with an ETL of <80 cm, based on TL < 81.7 cm (Megalofonou, Damalas & De Metrio, 2005a), considered to be young‐of‐the‐year (YOY) (Ćetković et al, 2019; Nosal et al, 2019), and identified with an asterisk in Table S1); and (vi) biological and/or ecological observations, including pregnancy, wounds, presence of fishing gear, professional rescue operations, etc.…”

“…between the intertidal zone and an arbitrary cutoff set at approximately 100 m offshore. (Toivonen et al, 2019) dedicated to marine biodiversity, conservation, recreational diving and recreational fishery or specifically focused on elasmobranch sightings (Bargnesi, Lucrezi & Ferretti, 2020) Leone et al (2017) as juvenile, with an estimated total length (ETL) of ≤120 cm, subadult, with an ETL of 120-180 cm, and adult, with an ETL of >180 cm (within the juvenile life stage, a subcategory was used to identify smaller individuals with an ETL of <80 cm, based on TL < 81.7 cm (Megalofonou, Damalas & De Metrio, 2005a), considered to be young-of-the-year (YOY) ( Cetkovi c et al, 2019;Nosal et al, 2019), and identified with an asterisk in Table S1); and (vi) biological and/or ecological observations, including pregnancy, wounds, presence of fishing gear, professional rescue operations, etc.…”

“…However, the blue shark is still threatened by direct fishing pressure, and it suffers high mortality as it also constitutes a major fishery by-catch in the Mediterranean Sea (Megalofonou, Damalas & Yannopoulos, 2005b;Biton-PorSmoguer & Lloret, 2018). At present, information on its ecology and biology mainly comes from pelagic areas where commercial fisheries operate (Garibaldi & Orsi Relini, 2000;Hemida & Capapé, 2003;Megalofonou, Damalas & De Metrio, 2009;Damalas & Megalofonou, 2010;Leone et al, 2017;Bernardini et al, 2018;Cetkovi c et al, 2019), leaving a gap in knowledge concerning its occurrence in coastal habitats. Thus far, observations on blue sharks in coastal waters have been documented only sporadically, and their spatio-temporal distribution and habitat use remain poorly understood (Mejuto et al, 2014;Bañ on, Maño & Mucientes, 2016).…”