Age and growth of the Norway lobster (Nephrops norvegicus) in Icelandic waters

• Main Author: Sigurvin Bjarnason 1989-
• Other Authors: Háskóli Íslands
• Format: Thesis
• Language: English
• Published: 2016
• Subjects: Líffræði; Leturhumar; Aldursgreiningar; Stofnstærð (vistfræði); Eldey; Norway; Iceland
• Online Access: http://hdl.handle.net/1946/24865

A lack of extensive age information can lead to a poor understanding of life history and population dynamics. As with most crustaceans, Nephrops norvegicus (Linnaeus, 1758) was thought to shed all calcified body parts that could be used to determine age, during periodic moulting. Number of indirect ageing methods have therefore been developed to estimate age. Recently, a direct method to determine the age of crustaceans was developed using growth bands that are deposited in the eyestalk and/or the gastric mill ossicles as age indicator. In this study both indirect length-based methods (ELEFAN I) and new direct method were used to inspect temporal changes in growth of Nephrops in Icelandic waters. Two fishing grounds in Iceland were chosen for comparison (Eldey and Breiðamerkurdýpi sites). In recent years the mean size has increased considerably and small animals are almost absent in Icelandic waters. The estimated von Bertalanffy growth parameters from the length-based method varied between time periods and sites (L∞ = 83–104 mm CL and K = 0.04 – 0.15). Consistent bands were observed with the novel direct age determination method in the zygocardiac ossicle of the gastric mill which were found superior to other ageing structures. Nephrops have a long life span and the oldest observed Nephrops in this study was estimated to be 22 years old at carapace length (CL) of 86 mm. Site-specific estimated age-at-size curves were developed using growth band counts which suggest a higher growth rate at Eldey site. Comparison between band counts and size-at-age interpretation determined from older length-frequency analysis differ slightly with increased variations for larger animals. The novel direct age determination method has the potential to be immensely valuable for future stock assessment for Icelandic Nephrops. Upplýsingar um aldur lífvera eru mikilvægar til að skilja lífsögu þeirra og fyrir flest stofnstærðarlíkön. Leturhumarinn, Nephrops norvegicus (Linnaeus, 1758), líkt og önnur krabbadýr tapar svo til öllum ...