Workshop 3 on age estimation of European anchovy (Engraulis encrasicolus) (WKARA3; outputs from 2021 meeting).

Type Article
Date 2023
Language English
Author(s) ICES
Contributor(s) Bled--Defruit Geoffrey
Source ICES Scientific Reports/Rapports scientifiques du CIEM (2618-1371) (ICES), 2023 , Vol. 5 , N. 46 , P. 59pp.
DOI 10.17895/

The Working Group on Biological Parameters (WGBIOP) approved the realization of a new workshop on age reading of European anchovy to discuss the results of the exchange conducted in 2018 and the development of validation studies in this species. Particularly, the workshop previously scheduled for 2020 has been proposed for 2021 (ICES, 2020). The third Workshop on Age Reading of European Anchovy (WKARA3), chaired by Gualtiero Basilone (Italy) and held from 23 to 25 November 2021, was an online meeting due to the persistence of the pandemic situation. Six countries took part in this workshop (Spain, Italy, Croatia, Greece, Portugal and France), with a total of 26 participants from 12 laboratories [(IEO (Santander, Palma de Mallorca, Cádiz and Malaga), AZTI, CNR-IAS, CNR-IRBIM, CIBM, COISPA, UNIPARTENOPE, UNICA, IOF, HCMR, IPMA, and Ifremer]. Fourteen of the participants in this workshop are readers for the assessment of anchovy. In total 16 areas/stocks were considered for evaluation, particularly 4 from the Atlantic Ocean and 12 from the Mediterranean Sea.

The workshop was focused on the review of information on anchovy age estimations, otolith exchanges, workshops and validation studies done the information on age determination; on analysis and discussion of the results of the previous exchange (2018); on the review of the validation methods existing for the target species (Engraulis encrasicolus); and update the age reading protocol.

This workshop was preceded by an otolith exchange (2018), as well as a Workshop on Age estimation of Small Pelagic (WKGESP 2019) in Italy supported by the Italian national fishery data collection plan (Basilone et al., 2019). The main conclusions achieved by both meetings have been presented during the WKARA3. 

The otolith exchange programme was focused on two areas (Bay of Biscay and Strait of Sicily) and produced comparable results in both study places. Particularly, the overall agreement between readers and areas is lower than in the previous exchange held in 2014. Moreover, in both areas results from the stock readers group are better than the other groups of readers (including advanced and expert groups) Finally, the growth pattern is commonly identified in both Bay of Biscay and the Strait of Sicily.

The main results of the WKGESP were a new otoliths reference collection (on a national basis) and standardizing age assignments to improve the coherence of age estimation among the participant laboratories. Finally, the WKAGESP group adopted 1 January as the conventional birthdate for anchovy, since the main discrepancy between labs was represented by the adoption of 1 January or 1 July as the species birthdate. 

During the second day of the workshop, a new otolith exchange program was set up to integrate and complete the old database. The proposal suggests sharing about 200 otoliths, stratified by area (i.e. the Atlantic Ocean and the Mediterranean Sea) as well as for embedding medium (i.e. water or resin). 

As recommended by WKARA2 (ICES, 2017) as well as the last exchange program, age validation studies should be conducted for all anchovy stocks, especially those that are assessed analytically, since the validation of the annual deposition of seasonal zones and the checks in the otolith allow to improve the aging precision. For such reasons, some validation studies have been conducted on anchovy stocks in both Atlantic and Mediterranean waters. Particularly, an age validation study was conducted in the Gulf of Cádiz with the objectives to validate the periodicity of the otolith increment formation through the otolith marginal increment (MIA) and the otolith edge analysis (EA), and to evaluate the temporal link between the reproductive cycle and the somatic conditions with the otolith edge formation and the patterns of monthly increments. For the Strait of Sicily, the results of published research were presented (Basilone et al., 2020). A statistical modelling approach has been here adopted to assess the coherence of two well-known methods, namely Edge Analysis and Marginal Increment Analysis, to validate the first annulus formation in European anchovy. Both methodologies in two different yearly cycles converged toward the same result, thus confirming the annulus identification for the first-year class. In addition, the completion dates of the checks and the first annulus were computed to gain a better insight into otolith growth dynamic. The obtained results corroborated temporally coherent patterns providing a better insight into the otolith growth dynamic as well as a more robust validation of the first annulus formation in the European anchovy. Finally, a preliminary validation on anchovy stock inhabiting the South Tyrrhenian Sea was presented during the WKARA3, according to the experience the researcher already obtained by validation on Mullus barbatus (Carbonara et al., 2018). The work done assigning the age according to the criteria by Carbonara and Follesa (2019), then the growth parameter of the von Bertalanffy curve (VBGC) was estimated for males and females, later VBGC parameters for each sex were compared to identify a possible sexual dimorphism.

On the last day, the workshop proceeded with a detailed and joint discussion on the growth patterns shown by otoliths from the different areas, proposed by attendees to the meeting. This common examination and discussion of otoliths by areas allowed finding out the major reasons for discrepancies in age determination among readers and a better understanding of the pattern of otolith growth increments by areas to improve the guidelines for their interpretation (ToR b). Such an exercise served to enhance the collections of agreed-aged otoliths (ToR d), as well as to highlight the importance of a new exchange program. 

The discussions on examples among the set of otoliths which generated the discrepancies in the age determination led to conclude that mainly source of disagreement is linked to a divergent otolith interpretation. Particularly, different interpretations of the marks, growth bands and edges through their conformity with the expected growth pattern of the anchovies, seasonal formation of the otolith by age and most common checks.

The importance of technical advice on storage was also highlighted. In fact, before embedding them in resin or before placing them in cuvettes, readers should be ensured that the otolith is completely dry. Moreover, this discussion strongly encouraged each lab area to conduct validation studies by different techniques as reported in Basilone et al. (2020). 

In conclusion of the former statements, a new exchange exercise has been planned for after 2022, also suggesting two new chairs who will join the coordination with Gualtiero Basilone. Similarly, to improve the coherence of the age estimates among Atlantic and Mediterranean areas and corroborate the kindly suggested studies of validation, the group recommend a new WKARA in 2023, which will be chaired by new coordinators together with the former one (G. Basilone). 

Full Text
File Pages Size Access
Publisher's official version 67 3 MB Open access
Top of the page