No abstract

We have evaluated the fatty acid composition of the livers from two cartilaginous fish species Raja clavata (thornback ray) and Mustelus mustelus (common smooth-hound) caught off the Northern Aegean Sea. While there was generally little variation between species, Mustelus mustelus indicated low saturated (SFA) in summer (29.61%), in spring (32.57%), in autumn (30.07%) and in winter (31.81%) and high polyunsaturated fatty acid (PUFA) in summer (40.35%), in spring (36.50%), in autumn (30.21%) and in winter (27.26%) levels. The dominant fatty acids were palmitic acid (C16:0), oleic acid (C18:1 (n-9)), eicosapentaenoic acid (EPA; C20:5 (n-3)), and docosahexaenoic acid (DHA; C22:6 (n-3)) in both cartilaginous fish species in all seasons. The ratio of DHA/EPA with respect to the total of fatty acids in livers oils was ranged from 2.66% to 4.44% for Mustelus mustelus and 2.89% to 4.46% for Raja clavata. The n:3/n:6 ratio of thornback ray was higher compared to smooth-hound shark in all seasons. The liver oil of R. clavata and M. mustelus represent a valuable source of omega-3 PUFA that can be used for human and animal nutrition.

The study deals with aspects of the population dynamics in the thornback ray (Raja clavata L., 1758), one of the most abundant cartilaginous fish caught in the North Aegean Sea. Females accounted for 73.08% and males 26.92% of all individuals. Total length of females and males ranged between 50.2 and 89.9 cm (disc width: 33.4–62.0 cm), and between 43.1 cm and 82.7 cm (disc width: 30.7–64.2 cm), respectively. Relationships between total length (TL) and total weight (TW), and between disc width (DW) and total weight (TW) were described by the equations: TW = 0.0041 TL3.10 and TW = 0.0178 DW3.03, respectively. Age data derived from vertebrae readings were used to estimate growth parameters using the von Bertalanffy function: L∞ = 101.71 cm, K = 0.18 y−1, t0 = −0.07 y for males and L∞ = 106.54 cm, K = 0.16 y−1, t0 = −0.28 y for females. The maximum age was 8 years for males and females. Total length at first maturity of males and females was 70.9 cm and 81.2 cm, respectively. Based on the gonadosomatic index and gonadal macroscopic observations, it was determined that the spawning period lasted throughout the year. Stomach content analysis showed that crustaceans (53.03% IRI) and teleosts (14.70% IRI) were the most preferred prey.

No abstract

No abstract

No abstract

This study determines the length distribution, length– weight relationship, age, growth parameters, mortality rate, sex ratios, length at first maturity and reproduction of saddled seabream (Oblada melanura) collected monthly by fishermen around the Northern Aegean Sea between November 2017 and October 2018. The length–weight relationship was calculated as W=0.0091×L3.11 (R2=0.95) and positive allometric growth was found. The condition factor and GSI varied between 0.81–1.58 and 0.01–9.61, respectively. The spawning season extended from May to July and peaked in June. Total lengths at 50% maturity were 18.97 cm for males and 18.83 cm for females. Parameters of the von Bertalanffy growth equation were: L∞ =29.91 cm, K =0.27 per year, t0 =−0.82 year and age varied between 1 and 8. The instantaneous rates of total mortality (Z) and natural mortality (M) were 1.36 and 0.58 per year, respectively. Rates for fishing mortality F and exploitation E were 0.78 and 0.57 per year, respectively. The mean absolute fecundity (F) was 117 075±23 243 oocytes, ranging from 19130 to 470 132.

2021 yılı içerisinde Marmara Denizi ve Türk Boğazlar Sistemlerinde, su sıcaklığına bağlı olarak birincil üretimde önemli rol oynayan mikro alglerin aşırı çoğalması sonucunda hücre dışı polisakkaritlerden oluşan Müsilaj adı verilen bir olay meydana gelmiştir. Gerçekleştiği alanın büyüklüğü ve etkilenen canlı topluluklarının sayısı dikkate alındığında ülkemiz denizel alanlarında gerçekleşen en büyük çevre felaketi olarak tarihte yerini almıştır. Bu nedenle Çanakkale Boğazı’nda dağılım gösteren deniz çayırlarının bu olaydan sonra durum tespiti önem taşımaktadır. Çalışma kapsamında Çanakkale Boğazı, Dardanos mevkiinde dağılım gösteren P. oceanica çayırlarının mevcut durumu belirlenerek, fenolojik ve lepidokronolojik çalışmaları yapılmış ve BiPo indeksine göre “Ekolojik Kalite oranları” belirlenmiştir. Çalışma sonucunda son sekiz yılda Dardanos bölgesinde dağılım gösteren deniz çayırı alt limitinin yaklaşık 1,4 m gerileyerek 15,6 m derinliğe kadar dağılım gösterdiği tespit edilmiştir. Ayrıca 2014 yılında deniz çayırlarının alt limit sınırlarında yeşil alglerden Caulerpa racemosa yoğun olarak dağılım gösterirken gerçekleştirdiğimiz çalışmada alt limit sınırlarında Ceremiales takımına ait kırmızı alglerin varlığı dikkat çekmiştir. BiPo indeksine göre elde edilen ekolojik kalite oranları 0,30- 0,20 arasında değişim göstermiştir. Çalışma sonucunda, bu indekse dayanarak Dardanos bölgesindeki P. oceanica çayırlarının müsilaj olayından sonra durumu "kötü" olarak belirlenmiş olup bu bölgedeki çayırların korunması yönelik eylem planlarının oluşturulması önem arz etmektedir.