Abstract
Length-weight relationships (LWR) of the most landed pelagic fish species Sardina pilchardus Walbaum, 1792 and Engraulis encrasicolus Linnaeus, 1758 in the Izmir Bay purse seine fishery were determined to reveal latest situation. Purse seine is a non-selective fishing gear compare to the other fishing gear such as gillnet or trammel net. For this reason, sampling all size individuals is very important to calculate mean length and other LWR parameters. In this study, seasonal LWR coefficient and minimum-maximum lengths were established as monthly basis. LWR of S. pilchardus and E. encrasicolus were W = 0.0059L2.7930 (r² = 0.94) and W = 0.0019L3.4207, (r² = 0.87), respectively. Growth type of the S. pilchardus was found negative allometric whereas E. encrasicolus was positive allometric. A decrease of the mean total length of S. pilchardus has been considerable variable from 1994 to 2014 in Izmir Bay but with this study, it is observed that mean length of the sardine found near of 2006 value related to seasonal fishing pressure.
Highlights
The length-weight relationship (LWR) is an important tool in fish biology, physiology, ecology and fisheries assessment (Oscoz et al, 2005) and provide invaluable information on stock assessment studies (Moutopoulos and Stergiou, 2002; Gonzalez Acosta et al, 2004) for conversion of length observations into weight estimates to provide some measurements of biomass (Froese, 1998; Gonzalez Acosta et al, 2004).Purse seine fishery is especially important for the Turkish fishery since it is the most important gear that targets small pelagic species especially anchovy and sardines as well as big pelagic species such as tunas
A decrease of the mean total length of S. pilchardus has been considerable variable from 1994 to 2014 in Izmir Bay but with this study, it is observed that mean length of the sardine found near of 2006 value related to seasonal fishing pressure
Overall results of S. pilchardus and E. encrasicolus showed dissimilarities in total length (TL) and mean length based on sampling sites (Table 3 and Table 4)
Summary
The length-weight relationship (LWR) is an important tool in fish biology, physiology, ecology and fisheries assessment (Oscoz et al, 2005) and provide invaluable information on stock assessment studies (Moutopoulos and Stergiou, 2002; Gonzalez Acosta et al, 2004) for conversion of length observations into weight estimates to provide some measurements of biomass (Froese, 1998; Gonzalez Acosta et al, 2004).Purse seine fishery is especially important for the Turkish fishery since it is the most important gear that targets small pelagic species especially anchovy and sardines as well as big pelagic species such as tunas. Once a fish school has been detected and surrounded by the purse seine net, there is no selectivity for individual size, species or catch quantity (Handegard et al, 2017). The catch quantity of a purse seiner is too much to compare with other fishing gears (e.g. trawls, seines). According to the official catch records, anchovy is the most landed fish species in Turkey with 96452 tons (43%). Sardine landing is only 8.5% in Turkey, this value is substantially higher for the Aegean Sea (67%). Anchovy (12969 tons) and sardine (12654 tons) are the most landed pelagic fish species in the Aegean Sea (TurkStat, 2019). Anchovy landing was the first time recorded higher than the sardine’s in 2018 in the Aegean Sea
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