Length-weight relationship, sex ratio and condition factor of Merlangius merlangus (Linnaeus, 1758) from the Sea of Marmara, Turkey

In this study, some biological properties of Merlangius merlangus (Linnaeus, 1758) were examined. In this context, relationship of length-weight, distribution of length-frequency, sex ratios and condition factors were examined. A total of 303 individuals were taken by random sampling from fishing vessels (beam trawl) in the Sea of Marmara. Minimum length and weight values of all sample individuals was found 10.0 cm and 6.6 g, maximum length 41.2 cm and 535 g was found. The average length was found 17.15±0.49 cm and the average weight was 47.03±7.57 g. Length-weight relationship for all samples as W=0.0044TL3.1777 regression coefficient r2=0.98 was determined. Growth type, positive allometric was determined for all samples and both sexes (b˃3; P˂0.05). The sex ratio (F:M) was calculated as 1:1.27. The mean values of condition factor (K) were calculated as 0.729±0.089, 0.733±0.091 and 0.737±0.081 for male, female and combined sex respectively. There are no significant differences between male and female (P˃0.05). Please cite this paper as follows: Bal, H. (2021). Length-weight relationship, sex ratio and condition factor of Merlangius merlangus (Linnaeus, 1758) from the Sea of Marmara, Turkey. Marine Science and Technology Bulletin, 10(1): 99-105.

M. merlangus is one of the economically important fish species in Turkey (Sağlam and Sağlam, 2012). There are many studies on this species such as biology, population characteristics, growth parameters, diet, mortality rates and biomass in Black It is necessary to carry out such studies continuously monitoring study for fisheries management and fisheries biology the conservation of economically important species aquatic ecosystems. The population parameters such as lengthweight relationship, length frequency, condition factors and biological parameters are important data sources for fisheries and fisheries management. Especially length and weight parameters gives information about the growth type of fish, whether growth is isometric or allometric (Ricker, 1975).
In this study, relationship of length-weight, distribution of length-frequency, condition factor and sex ratio of whiting were determined. It is expected that the data of the study may be source for both the fisheries of the region and fisheries science.

Material and Methods
A total of 303 samples were sampled by randomly from fishing vessels (beam trawl) and commercial fisheries in fishing season (between September and April, 2019) in the Sea of Marmara. The beam trawl had 5 m width and 50 cm mouth opening; with a cod end 32 mm mesh size. Samples, total length (cm) with 1 mm precision, weight (g) with 0.01 g accuracy recorded and macroscopically sex (female and male) was determined. W=aL b equation was used to determine the lengthweight relationship (LWR) of fishes (Ricker, 1975). Where, W indicates the weight of the fish in g, L the total length in cm, a the condition of the fish, and b to the growth type of the fish. Student t test was used to determine the growth type (if; b=3, isometric; b˂3, negative allometric; b˃3, positive allometric) (Ricker, 1975). Fulton's condition factor was calculated (Froese, 2006).

= � 3 � × 100
According to the formula given above; W indicates fish weight (g), L indicates total fish length (cm).

Length-Weight Relationships
The length-weight relationship was calculated according to all of the samples examined and gender groups, and it was found that the regression coefficient between the relationships was high. Growth types for each gender group and all samples were calculated and growth was found to be positive allometric for all. The results of the examples are given in Table 1.

Distribution of Length-Frequency
For all individuals, the minimum length 10 cm and 6.6 g. The maximum length 41.2 cm, maximum weight of 535 g was determined. The minimum, maximum, average and standard error values of the lengths and weights of the samples are given in Table 2.    It has been determined that the size distribution of the samples is generally between 14 and 18 cm. In this study, 68% of all samples are over 18 cm (Figure 1).
The length-frequency all samples and distributions according to the months were calculated and graphics were drawn ( Figure 2).

Condition Factors
The mean highest condition factor was recorded 0.849 in December for females, 0.773 in September for males. The mean low condition factor was recorded 0.668 in October for females, 0.667 in October for males. The mean values of condition factor (K) were calculated as 0.729±0.089, 0.733±0.091 and 0.737±0.081 for male, female and combined sex respectively ( Figure 3). There are no significant differences between male and female (P˃0.05).

Discussion
Length-weight relationship (LWR) is very important data sources for fisheries. It has many applications in fishery management, ecological studies such as estimating the condition, feeding and spawning (Gonçalves et al., 1997;Stergiou and Moutopoulos, 2001). Although, there are many study on whiting especially Black Sea and Aegean Sea, there is a few information on growth and biological characteristics of Merlangius merlangus in the Sea of Marmara (Göksungur, 2004;Bök et al., 2011;Demirel and Dalkara, 2012).
The growth pattern (b) typically varies between 2.0 and 3.5 (Froese and Pauly, 2010).Values of b changeable in different population of same fish species. The growth pattern (b) depends on temperature, salinity, food, conditional of environmental conditions (predation) sex and stage of maturity (Ricker, 1973;Freitas et al., 2017). In this study, the growth pattern (b) of all samples positive allometric (b˃3; P˂0.05) was found. It is similar to the Bök et al., (2011). However, Demirel and Dalkara, (2012) reported that they found the b value of this species to be negative allometric (b˂3; P˂0.05). It has been determined that this aspect is not similar to our study results.
Growth pattern (b), range from 2.77 (Çalık and Erdoğan Sağlam, 2017)-3.24 (Samsun and Erkoyuncu, 1998). It's estimated that the reason for the difference in b value between stocks in different regions and unsuitable environmental conditions due to overfishing.
The result about sex ratio in present study is also similar by Erkoyuncu, (1998) and Bilgin et al., (2012) in the Black Sea. But different from the F:M ratio found by Ak et al., (2009) as 1.00:1.95. Condition factor in previous studies, Samsun et al. (1994) 0.740, Erkoyuncu (1998) 0.740, andGöksungur (2004) 0.746 values similar to in present study (0.737). These minor differences are thought to be due to changes in the ecosystem. The parameters obtained from LWR, sex ratio and condition factor for previous study is showed in Table 3.

Conclusion
In present study, it has been determined that the size distribution of the samples is generally between 14 cm and 18 cm. The absence of specimens larger than 18 cm indicates a prey pressure on the species. The regular monitoring studies are essential to understand the dynamics of exploited whiting stocks under the pressure of environmental changes in the Sea of Marmara ecosystem. Therefore, whiting fishery needs new regulation measures and management plans for the sustainable fisheries. It is expected that the data of the study may be source for both the fisheries of the region and fisheries science.

Conflict of Interest
The authors declare that they have no competing interests.

Ethical Approval
For this type of study, formal consent is not required.