Estimating some population parameters and stock assesment of spiny butterfly ray, Gymnura altavela (Linnaeus, 1758) the Levant Basin coast (Northeastern Mediterranean)

Abstract

The purpose of this study was to investigate the morphometric characteristics, growth, mortality and exploitation rate of the spiny butterfly ray (Gymnura altavela Linnaeus, 1758). The study was conducted using 284 specimens from the coastal waters of the Levant Basin (the northeastern Mediterranean). Samples were collected monthly between July 2014 and June 2015 using a bottom trawl from the following depth strata: 0-10m, 10-20m, and 20-50m. The following measurements were taken total length (TL), disc length (DL), disc width (DW) distance from nose tip to eye (NE), nose tip to mouth (NM, cm), width of mouth (MW, cm) where Y is the various dimensions (TL; W; DL; DW; NE; NM; MW, respectively) and X is the total length estimated by linear regression analysis. Length-weight and disc width-weight relationships were W = 0.097 * TL 3.2070 and W = 0.084 * DW 3.169 for total individuals. The von Bertalanffy growth function contained in DW was DW = 136.50cm K = 0.230 year -1 t 0 = -0.492year -1 for total individuals. The total mortality (Z) was 0.91year -1 , the natural mortality (M) was 0.41year -1, and the fishing mortality (F) was estimated to be 0.51year -1 . The exploitation rate (E) was calculated as 0.55 year -1 for all obtained individuals.

Indian Freshwater Elasmobranchs: Ongoing Threats along with IUCN Current Status and Conservation of Protecting Hidden Treasures: A Review

“…The freshwater elasmobranches occupy a wide range of habitats, including freshwater riverine (but not land-locked water systems) and lake systems, inshore estuaries and lagoons, coastal waters, the open sea and the deep ocean. Most elasmobranchs are mid-level or top predators and play a key role in trophic food webs (Yeldan, 2018).…”

The first record of gravid spiny butterfly ray (Gymnura altavela) in the northern Mediterranean Sea, with description of near‐term foetuses

“…This species typically inhabits sandy and muddy coastal waters up to c . 100 m deep (Özbek et al ., 2016; Yaglioglu et al ., 2015), with the majority of records shallower than 50 m (Alkusairy et al ., 2014; Yeldan, 2018). Reproduction in G. altavela has been previously described (Alkusairy et al ., 2014; Tomita et al ., 2020) with a gestation period between 6 and 12 months and a litter size range of one to eight pups (Alkusairy et al ., 2014; Capapé et al ., 1992; Taylan et al ., 2019).…”

“…The results herein indicate that the observed specimen is the largest on record for the Mediterranean. In addition, the depth of capture was the greatest on record for this species and at areas further from shore than previously identified (Brito, 1991; Alkusairy et al ., 2014; Zenetos et al ., 2015; Özbek et al ., 2016; Yeldan, 2018). Whether the observed size at capture is an anomaly for this region and whether the location of capture is a retreat of the species into deeper waters due to increased fishing pressures (Bradai et al ., 2018; Colloca, Enea, et al, 2017a; Colloca, Scarcella, & Libralato, 2017b; Fiorentino & Vitale, 2021; Michailidis et al ., 2020; Morales‐Nin et al ., 2010; Quetglas et al ., 2016) or pollution/habitat loss in the coastal waters (Consoli et al ., 2020; Gajić et al ., 2020) needs further evaluation given the critically endangered classification of this little‐known species.…”

“…The fact that the female had seven near‐term foetuses might shed new light into reproduction of the species in the Mediterranean and warrants further studies. Furthermore, the individual significantly deviates compared to almost 500 recently described specimens from the eastern and southern Mediterranean Sea (Alkusairy et al ., 2014; Capapé et al ., 1992; Zenetos et al ., 2015; Yeldan, 2018; Taylan et al ., 2019). It was caught deeper than all others, was larger than all previously described individuals, had the largest litter size and had near‐term foetuses considerably larger compared to the previously reported size at birth for the entire Mediterranean Sea.…”

“…Maximum reported size in the Mediterranean Sea is 165 cm disc width (DW) and 36 kg total weight (TW) (Özbek et al, 2016), whereas generally individuals are less than 110 cm DW and 10 kg TW (Alkusairy, 2013, Alkusairy et al, 2014Özbek et al, 2016). This species typically inhabits sandy and muddy coastal waters up to c. 100 m deep (Özbek et al, 2016;Yaglioglu et al, 2015), with the majority of records shallower than 50 m (Alkusairy et al, 2014;Yeldan, 2018). Reproduction in G. altavela has been previously described (Alkusairy et al, 2014;Tomita et al, 2020) with a gestation period between 6 and 12 months and a litter size range of one to eight pups (Alkusairy et al, 2014;Capapé et al, 1992;Taylan et al, 2019).…”