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4th Angler age reading Workshop.pdf (5.66 MB)

4th International Ageing Workshop on European Anglerfish

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posted on 2022-12-14, 11:59 authored by J. Landa, R. Duarte, I. Quincoces, H. Dupouy, E. Bilbao, J. Dimeet, P. Lucio, A. Marçal, H. McCormick, G. Ni Chonchuir

White (Lophius piscatorius) and black anglerfish (Lophius budegassa) are two important species of groundfish fisheries in the North East Atlantic. Both black and white anglerfish are typical bottom living species, the former having a depth range between 70 m and 800 m and the latter extending to depths >1000 m (Dardignac, 1988; Azevedo and Pereda, 1994). Black anglerfish have a more southern distribution (Mediterranean and Eastern North Atlantic from British Isles to Senegal) 2 compared to white anglerfish (Mediterranean, Black Sea and Eastern North Atlantic from Barents Sea to the Straits of Gibraltar), but there is considerable overlap. In the last two decades several studies on reproduction, age reading and growth have been carried out. The spawning season of L. piscatorius is poorly described in the literature, but is generally from late winter to summer (Afonso-Dias and Hislop, 1996; Quincoces et al., 1998a; Duarte et al., 2001). For L. budegassa the spawning period is described from October to March for the Iberian coast (Azevedo, 1996 and Duarte et al. 2001) and between May and July in the Cantabrian Sea (Quincoces et al., 1998b). The growth of L. piscatorius and L. budegassa has been studied based on sagitae otoliths (Crozier, 1989 and Tsimenidis, 1984) and illicia (Dupouy et al., 1986; Duarte et al., 1997; Landa and Pereda, 1997 and Landa et al., 2001). Studies comparing the two structures showed that age estimates based on illicia readings resulted in higher agreement between readers. (Dupouy pers. com.; IFREMER, 1991; Staalasen, 1995). Age readings based on illicia have been applied for stock assessment of both species. In spite of recent ageing studies, there are still some doubts concerning age validation and ageing precision between readers. The three previous workshops were carried out with different objectives and in different situations concerning biological knowledge of the growth of both species. The first ageing workshop for anglerfish was carried out in 1991 (IFREMER, 1991) involving readers from France and Spain. The main objective was to define clearly an ageing structure to perform ageing for stock assessment purposes. Best results were obtained with the illicium, which was adopted. The second workshop held in 1997 (IFREMER, 1997) was conducted with additional participation by Portugal and the main objective was to increase ageing precision between readers. The third workshop was carried out in 1999 (Anon., 1999) with additional participation by Ireland and the main objective was to establish and describe ageing criteria in order to increase the ageing precision between experienced readers. The present and fourth workshop is undertaken as part of the EU Study Contract No.99/013 (“Genetic characterization and stock structure of the two species of anglerfish (Lophius piscatorius and L. budegassa) of the Northeast Atlantic” - GESSAN). Prior to the workshop an Illicia Exchange was performed with the main objectives as follows: • To analyse and to compare the age readings mainly by means of precision (CV), accuracy (bias), agreement and mean length at age. • To analyse the measurement of the first ring. • To analyse the new age readings from samples of younger and older fish. This exchange program included digitised images where each reader identified the annual rings. The main objectives of the fourth Ageing Workshop were: • To analyse and discuss the results of the illicia exchange, in order to clarify the main problems of anglerfish age reading: - To discuss disagreements in age readings, based on statistical analysis of exchange results, - To analyse and discuss the digitised images that were obtained from the illicia exchange. • To review work developed for Age Validation, namely, the analysis of length distributions from surveys and the analysis of results, obtained so far, from the mark-recapture study. • To elaborate an ageing guide including images with highest agreement between readers. The present report was structured in order to cover the objectives shown above. Therefore, section 2 contains a list of the participants of the workshop, section 3 contains the statistical analysis of the illicia exchange results, section 4 contains a summary of the illicia image analysis and discussions, with a list of the illicia with the highest ring identification agreement, and section 5 contains a review of the developed work on age validation and the main results are presented.  

Funding

EU Study Contract No.99/013 “Genetic characterization and stock structure of the two species of anglerfish (Lophius piscatorius and L. budegassa) of the Northeast Atlantic” - GESSAN

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