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Introduction
The reproductive biology of a species is a central aspect of providing sound scientific advice for fisheries management and it plays an important role in determining productivity (Morgan 2008). Estimation of fecundity and GSI of a fish is essential for evaluating the commercial potentialities of its stock, life history, practical culture and actual management of the fishery (Rahimibashar et al. 2012).
Saros Bay, which is situated in the Northeastern Aegean Sea, is connected to the North Aegean with a depth of approximately 600 m to the west. The shelf extends at a water depth of 90-120 m. The length of the bay is about 61 km and the width at the opening to the Aegean Sea is about 36 km (Eronat & Sayın 2014). As Saros Bay had been closed to bottom trawl fishing since 2000 (Cengiz et al. 2011) and no industrial activity was prevalent in the area (Sarı & Çağatay 2001), the bay can be considered as a pristine environment (Cengiz et al. 2013).
Blotched picarel Spicara maena (Linnaeus, 1758) is a commercial species inhabiting the Mediterranean Sea, the Black Sea, and the European and African coasts of the Atlantic Ocean, from Morocco to Portugal and the Canary Islands. This species mostly occurs over Posidonia beds and sandy or muddy bottoms, and distributes up to 100 m depth. S. maena feeds on mainly zooplankton and is a protogynous hermaphrodite (Froese & Pauly 2019).
There are various studies on S. maena all over the world. Arculeo et al. (1996) studied the protein differences among the Mediterranean species of the genus Spicara. Matić-Skoko et al. (2004) gave first information on its fecundity. The feeding habits of the blotched picarel were studied by Karachle & Konstantinos (2014) in the North Aegean Sea. While Dulčić et al. (2000) published the age, growth, and mortality of this species in the Adriatic, Çiçek et al. (2007), Soykan et al. (2010) and Saygılı et al. (2016) from the Turkey Seas presented its growth and reproduction. In addition, Moutopoulos & Stergiou (2002) reported data on the length-weight relationship in the Greek waters, as did Valle et al. (2003) in the western Mediterranean Sea, Dulčić & Glamuzina (2006) for the eastern Adriatic estuarine systems, Karakulak et al. (2006) from the Gökçeada Island, İşmen et al. (2007) in the Saros Bay.
Information on the reproduction of this species in the Aegean Sea is extremely scarce and incomplete (Soykan et al. 2010, Cengiz et al. 2014). For this reason, the objectives of the present study were: (1) to provide the preliminary information on the spawning period of the blotched picarel in the Saros Bay (Northern Aegean Sea, Turkey); (2) to contribute to the reproductive biology of S. maena by reporting the first data about the fecundity of the species for the Aegean Sea; and (3) to compare these results with those of the previous studies.
Materials and methods
Sampling
This study was carried out, monthly, in the Saros Bay between January 2015 and December 2015. The samples were collected with the handlines and gill nets at depths ranging from 0 m to 40 m by the commercial fishermen (Fig. 1).
Laboratory actıvıtıes
A total of 620 individuals were measured to the nearest 1 mm (total length, TL), weighed to the nearest 0.01 g (total weight, TW). The chi-square (χ 2) test was used to detect the differences in the sex ratio. The Student’s t-test was used to analyze the differences in the mean length and weight of the sexes. Following removal, the sagittal otoliths were first soaked in 5% HCL and 3% NaOH solutions, respectively, and washed in distilled water and subsequently dried. The sagittal otoliths, placed in watch glass filled with the water, were read using a stereoscopic zoom microscope under reflected light against a black background. Opaque and transparent zones were counted; one opaque zone plus one transparent zone was assumed to be one year (Cengiz et al. 2013).
Sex was determined by examining the gonads macroscopically. Maturity stages were assessed according to Gunderson’s (1993) scale: stage I immature, stage II resting, stage III developing, stage IV ripe, and stage V spent. The spawning period was estimated by analysing, monthly, the changes of the gonadosomatic index (GSI) using the equation:
GSI= (Wg × (W - Wg)-1) × 100
where Wg is the gonad weight (g) and W is the total weight (g) of fish (Avşar 2005).
Gravimetric method was used for fecundity estimates (Bagenal & Braum 1978). In order to calculate fecundity, the ovaries of mature females (prior to the reproductive period) were weighed the nearest 0.0001 g (total weight), three sub-samples were taken from the front, middle and rear sections of each ovary, weighed and then immersed separately in Gilson’s fluid. These ovaries were frequently shaken to ensure the separation of oocytes from ovarian tissues. All oocytes were counted directly under stereoscopic zoom microscope. The total number of eggs in each ovary sub-sample was then estimated by using the equation provided by Yeldan & Avşar (2000):
F1= (Wg × N) × Ws -1
where F1 is the total number of eggs in ovary sub-sample 1, Wg is the gonad weight, N is the number of eggs in the sub-sample, and Ws is sub-sample weight. Later, by taking the mean number of three sub-sample fecundities (F1, F2, and F3), the absolute fecundity (Fa) for each female fish was estimated as:
Fa= (F1 + F2 + F3)-3
Hereby, the relations between absolute fecundity (Fa) and total length (TL), absolute fecundity (Fa) and total weight (TW), as well as absolute fecundity (Fa) and age (A) were estimated as Fa= a × TLb, Fa= a + b × TW and Fa= a + b × A, respectively, where a (intercept) and b (slope) are the parameters of the equation (Avşar 2005).
Results
From 620 specimens examined, 500 (80.6%) were females, and 120 (19.4%) males. The sex ratio (F:M) was 1:0.24, which is significantly different from equipartition (χ 2 test: P < 0.05). The mean ± standard error (and range) of total length were 12.9 ± 0.11 (8.7-18.1) cm TL for females 14.9 ± 0.15 (9.6-18.6) cm TL for males (Fig. 2) and total weight were 41.78 ± 2.16 (11.19-86.83) g for females and 27.83 ± 0.56 (5.39-87.01) g for males. The student’s t-test showed significant differences between the mean lengths and weights of the both sexes (all P < 0.05).
Figure 2 The length-frequency distribution for females and males of blotched picarel Spicara maena from Saros Bay, Turkey / Distribución de frecuencia de longitud de hembras y machos del trompero Spicara maena de Bahía Saros, Turquía
The reproductive cycles of female and male individuals was synchronized. The variations in GSI values throughout the study period presented a pronounced peak in April for both sexes. While GSI values ranged between 0.21 and 5.80 for females, these ones were between 0.12 and 2.09 for males. The GSI values suggested the spawning period was from April to end of May (Fig. 3).
Figure 3 The mean gonadosomatic index (%) values for females and males of blotched picarel Spicara maena from Saros Bay, Turkey / Media de los valores del índice gonadosomático (%) de hembras y machos del trompero Spicara maena de Bahía Saros, Turquía
The absolute fecundity (Fa) was estimated for 72 ripe fe males (age 1 to 5) caught in March. A maximum value of 19,123 eggs was recorded in 5 year-old fish weighing 82.23 g (17.8 cm TL) and a minimum value of 6,389 eggs for 1 year-old fish weighing 11.32 g (9.6 cm TL). The mean value ± standard error of absolute fecundity was 12,039 ± 431. The relations between the absolute fecundity and total length, total weight and age of the blotched picarel females were estimated as Fa= 287.52TL1.40, Fa= 153.33TW + 6,680.9 and Fa= 2,407.5A + 5,289.6, respectively (Fig. 4).
Figure 4 The relations between the absolute fecundity and total length, total weight and age of the blotched picarel females Spicara maena from Saros Bay, Turkey / Relación entre la fecundidad absoluta y la longitud total, peso y edad de las hembras del trompero Spicara maena de Bahía Saros, Turquía
Discussion
The spawning period has long been a central issue in fisheries biology, ecology, and management because of its importance for the recruitment (Beaugrand et al. 2003), survival (Garvey et al. 2002), and stock biomass, and thus the fishery yield (Kjesbu & Witthames 2007). Therefore, the reproductive studies may be used for quantification of the reproductive capacity of fish (Murua et al. 2003). The reproductive biology of S. maena has been in vestigated for the first time in the Saros Bay. Matić-Skoko et al. (2004) and Dulčić et al. (2000) reported that the breeding was from September to October for the eastern central Adriatic (Crotia). While Çiçek et al. (2007) suggested that spawning period occured between March and May in Babadillimani Bight (Turkey), Soykan et al. (2010) observed it was between March and June in Izmir Bay (Turkey). In addition, Cengiz et al. (2014) stated that the breeding season occured between April and June for Gallipoli Peninsula (Turkey). The spawning period has a close relationship to the ecological characteristics of the water system in which the species live (İlkyaz et al. 2010) and apparently varies from area to area because of the differences in hydrographic and climatic conditions (İlhan et al. 2010).
The published data on fecundity of this species are extremely scarce and the fecundity results in this study represent the first data of S. maena for the Aegean Sea. Matić-Skoko et al. (2004) from eastern central Adriatic Sea reported the absolute fecundity (Fa) varied from a minimum of 42,140 eggs for a 2 year-olds to a maximum of 80,509 eggs for 3 year-olds and the relations between the absolute fecundity-total length, the absolute fecundity-total weight and the absolute fecundity-age were Fa= 33.4TL2.60, Fa= 560.2W + 15,874 and Fa= 4,100A0.43, respectively. The knowledge of fecundity is useful in investigating the population dynamics of a fish species (Dulčić et al. 1998) and the marked differences in fecundity among species often reflect different reproductive strategies (Murua & Saborido-Rey 2003). Within a given species, fecundity may vary as a result of different adaptations to environmental habitats (Witthames et al. 1995). Even within a stock, fecundity is known to vary annually, undergo long-term changes (Rijnsdorp 1991). For a given size, females in better condition exhibit higher fecundity (Kjesbu et al. 1991). Fish size and condition are, thus, key parameters to properly assess fecundity at the population level. However, the fecundity-size relations has been used principally as a rapid means of predicting the fecundity of fish (Dulčić et al. 1998).
Efficient fisheries management and enforcement regulations are known to be necessary to protect natural resources and provide their sustainability. Regular monitoring of the stock status is vital for optimal fishing and stock management, both related to sustainable fisheries (Kara & Bayhan 2015). If some legal regulations are not implemented (determination of minimum landing size, selectivity studies, catching quote, fishing effort control, efficacious monitoring and surveillance systems, etc.), the sustainability of stock can be at risk as time goes by. Consequently, the present study provides preliminary information on the spawning period of S. maena for the Saros Bay, however, it presents the first data about the fecundity of the species for the Aegean Sea, which will thus be useful for fish biologists and fisheries managers in future.
