Criteria for age estimation of anchovy otoliths in the Alborán Sea (Western Mediterranean Sea) based on the monitoring of the hyaline edge formation

Abstract This study determines the seasonality in the formation of rings in the anchovy otoliths by monitoring hyaline edge in the Alborán Sea. Monthly samples were collected between October 1989 and December 1992 from the catches of the purse seine fleet. Two hyaline zones in the otolith are deposited per year, one in winter (primary) and a minor one during the summer spawning season. The formation of hyaline rings is significantly correlated with the temperature of seawater. The highest percentage of hyaline edge formation, recorded over the four year study, periodically occurred in February, when the temperature is at its lowest. When the nutritional status of fish is better, the percentage of individuals forming hyaline edge is lower. Considering these facts, a number of criteria for interpreting the growth rings on the anchovy otolith were developed. The population is subjected to a high rate of exploitation, so with the absence of older individuals in the area, it means that growth can only be accurately described in the first year. With some variations, depending on the year, anchovy grows between 12 and 13cm in their first year of life

Biogeography of epibenthic crustaceans on the shelf and upper slope off the Iberian Peninsula Mediterranean coasts: implications for the establishment of natural management areas

Special Volume: Mediterranean marine demersal resources: the Medits international trawl survey (1994-1999)The patterns of occurrence and bathymetric distribution of epibenthic crustaceans on the continental shelf and upper slope down to a depth of 800 m are analysed based on data gathered during six demersal trawl surveys performed annually in spring along the Mediterranean coasts of the Iberian Peninsula (from the Straits of Gibraltar to Cape Creus) between 1994 and 1999. A total of 598 valid hauls has been studied providing a total of 108 species of decapods, two stomatopods, one euphausiid, one mysid and one isopod. The study area has been subdivided into seven sectors according to their geomorphological characteristics, and the patterns of occurrence and abundance by depth have been analysed separately for each of the sectors. Detailed data on bathymetric distribution are presented for each species. Two main biogeographical areas can be discerned along the study area, which can approximately be separated at Palos Cape: the Alborán Sea to the southwest, and the northwestern Mediterranean (Levantine and Catalan Seas) northwest of Palos Cape. The continental shelf in the Alborán Sea (the most western area of the Mediterranean) is extremely narrow whereas it is much wider in the northwestern Mediterranean. The influence of Atlantic waters entering the Mediterranean is particularly strong in the Alborán Sea which shows a particularly high species richness of Atlantic affinity. Within the context of the western Mediterranean Sea, the Alborán Sea region shows important faunistic characteristics such that it might be considered as a possible separate natural management area for demersal fisheriesVersión del editor1,006

Climate variability and recruitment success of European hake (Merluccius merluccius L.) in NW Africa

Recently it was stated a strong dependence of European hake abundance with climate variability in NW Africa. This relationship was explained by the North Atlantic Oscillation (NAO) driving the upwelling temporality and its geographic coverage, which could be responsible of changes in survival rate during early life stages of this species. Following this hypothesis, this work focuses on the relative importance of climate variability on recruitment dynamics of European hake. Interannual variability of recruitment success were analyzed through two types of time series: (i) from monthly and annual length distribution fishery data (1982-1999) of Spanish trawling fleet that worked under Spanish or European-Moroccan fishery agreements and (ii) recruits annual abundance from scientific Moroccan surveys (1982-2004). The time series were compared with the annual smoothed NAO index to evaluate the type of relationship, persistence and their relative contribution as a variation source of recruitment success. The recruitment to the fishery took place during all year with peaks in spring and summer, but the seasonal component was weak. The time series were in synchrony with NAO index of the previous year and showed strong positive correlation. The variation of recruitment success explained by NAO was 25 to 82 % depending on time series size. The main NAO effect in recruitment dynamics was the widening-contraction of Recruitment Window. During NAO+ phase several success cohorts were recruited by year, while in NAO- the success cohorts were scarce and weak. The climate signal in recruitment dynamics of European hake was robust, recurrent and persistent independently of fishing effort

Report of the Workshop on Age estimation of European anchovy (Engraulis encrasicolus)

Based on the results of a full-scale otolith exchange held in 2014, the Working Group on Biological Parameters (WGBIOP 2015) identified the need for an age reading workshop on European Anchovy otoliths (WKARA2). This workshop (chaired by Andres Uriarte, Spain, Begoña Villamor, Spain and Gualtiero Basilone, Italy), was held in Pasaia, Gui-puzcoa (Spain) from the 28 November to 2 December 2016. Five countries took part in this workshop (Spain, Italy, Croatia, Greece and Tunisia), with a total of 16 participants from 9 laboratories. In total 17 areas/stocks were analysed (4 from the Atlantic area and 13 from Mediterranean Sea) The aim of this workshop was to review the information on age determination, discuss the results of the previous exchange (2014), review the validation methods existing on these species, clarify the interpretation of annual rings and update the age reading pro-tocol and a reference collection of well-defined otoliths. Age validation studies, in the Bay of Biscay and preliminary validation studies in Divi-sion 9a, Alboran Sea and Strait of Sicily areas were presented, including a compilation of age validation studies of this species as well in the literature. There are several ar-eas/stocks in which validations of the anchovy annual age determination have not been done yet. Due to the poor percentage of agreement achieved in the 2014 Exchange (mean agree-ment of 66%; mean CV of 58%), the workshop proceeded with a detailed and joint dis-cussion on the growth patterns shown by otoliths from the different areas to find out the major reasons for discrepancies in age determination among readers. At the same time, the joint discussion allowed a better understanding of the pattern of otolith growth in-crements by areas to improve the guidelines for their interpretation. The discussions on examples among otoliths which generated discrepancies in the age determination led to conclude that there were two major sources of disagreements: a) Divergent otolith inter-pretation: different interpretations of the marks, growth bands and edges in terms of their conformity with the expected growth pattern of the anchovies, seasonal formation of the otolith by ages and most common checks. and b) wrong application of the age allocation Rules: it was evidenced during the workshop that for the birthdate first July (or first June) in some cases the age determination rule was not being correctly applied during the first half of the year (from January to June). Following the workshop discussions there has been a progressive change in the percep-tion of the growth pattern applicable to these anchovy otoliths in many areas which led to some revisions of the otolith interpretation and assigned ages, by which growth at ages 0 and 1 are far prominent than at older ages and the occurrence of checks became more frequently admitted. Furthermore, there have been evidences that the age determination rules have in some instances been inconsistently applied. All these evidences led to con-clude on the need to review past age determinations. Although this task should be de-layed until running an exchange in 2018 to be sure that all the readers apply the protocol and the current criteria of this workshop coherently, since current criteria would change the otoliths interpretation and the age determination in many areas. In addition, for the Mediterranean regions the convenience of midyear birthdates was put in question in comparison with the simplicity of the conventional birthdates at first of January (as these anchovies are in the northern hemisphere). As a corollary of the former statements, intercalibration exercises by areas, for the differ-ent countries taking part in the age reading of the same exploited stock, are still required. Finally, this Workshop adopted a common protocol for all areas in order to standardize the anchovy age assignments and to improve the coherence of the age estimates. An agreed collection of otoliths by areas were produced and upload to the Age Readers Fo-rum

Decapod crustacean assemblages on trawlable grounds in the northern Alboran Sea and Gulf of Vera

This study analyses the samples collected annually (2012 to 2018) on circalittoral and bathyal soft bottoms (30 to 800 m) by the MEDITS surveys in the northern Alboran Sea (including Alboran Island) and the Gulf of Vera to determine the composition, structure and distribution of decapod crustacean assemblages. A total of 94 decapod crustacean species were identified. Non-metric multidimensional scaling showed depth to be the main factor for distinguishing four main decapod assemblages: the inner shelf (30-100 m depth), outer shelf (101-200 m), upper slope (201-500 m) and middle slope (501-800 m). PERMANOVA analyses revealed further significant depth-related differences between three established geographical sectors of the study area (northern Alboran Sea, Gulf of Vera and Alboran Island). Generalized additive model analyses were used to assess the bathymetrical, geographical and environmental effects on the ecological indices of each assemblage. Results showed that depth and the geographical effect were the main drivers in all cases. Decreases in abundance and increases in species richness, Shannon-Wiener diversity and Pielou’s evenness indices with depth were detected. This study shows the primacy of depth and geographical effect on the distribution of decapod species in the study area, in alignment with findings from other parts of the Mediterranean Sea.Versión del editor1,00

Zooplankton Biomass Depletion Event Reveals the Importance of Small Pelagic Fish Top-Down Control in the Western Mediterranean Coastal Waters

The influence of hydrochemistry and trophic conditions on the coastal zooplankton community’s biomass and metabolic activities was investigated along the Spanish Mediterranean coastal waters, from Algeciras Bay to Barcelona, from autumn 2011 to autumn 2012. Two hydrographic regions were differentiated: NW Alboran (ALB) and W Mediterranean (MED). Zooplankton metabolism was assessed from measurements of the electron transport system (ETS) and aminoacyl-tRNA synthetases (AARS) activities, as proxies for potential respiration and somatic growth, respectively. Zooplankton showed three to fivefold higher biomass in ALB than in MED during autumn 2011 and spring 2012. However, in autumn 2012, a drastic decrease in biomass standing stock was observed in ALB, with no significant differences between the two regions. This biomass depletion event was not associated with environmental variables, food availability or zooplankton metabolic rates, but coincided with a twofold peak of Sardina pilchardus landings in ALB. A reduced standing stock coupled with high zooplankton growth rates suggests mortality by predation as the main cause for the low zooplankton biomass typically observed in MED, and in ALB during autumn 2012.Versión del edito

Preliminary Analysis for Identification of Priority Species of Small Pelagic Shared Stocks in GSA01 And GSA03 (Alborán Sea)

Small pelagic resources and particularly sardine (Sardina pilchardus) and anchovy (Engraulis encrasicholus) represent an important fishery activity for the countries bordering the Alboran Sea. This paper aims at contributing to the identification of priority species of small pelagic shared stocks in GSA01 and GSA03 (northern and southern Alboran Sea GFCM regions) for carrying out joint stock assessments and promoting new management measures that would allow the sustainability of the resources and its exploitation. The WG on small pelagic shared stocks met twice during 2011 progressing in analysing the available data on the stocks and its exploitation and building a common data base. Moreover a comparative analysis on sardine landings data from 2003-2010 in GSA01 and GSA03 was carried out explaining that the exploitation pattern in sub-areas (GSAs 01 and 03) is different but the total length-frequency distribution of sardine exploited by each country appears to be similar. A tentative in applying a LCA analysis of the Moroccan and Spanish data on sardine using different biological parameters and with the VIT software was unsuccessful but orientated for future works of the W

Issues related to the MEDITS reference list of species

The MEDITS survey programme started in 1994 and adopted the basic protocols by the four first partners, just before the first survey. These protocols included the design of the survey, the sampling gear, the information collected, and the management of the data as far as the production of common standardized analyses of the data (Bertrand et al., 2002). The last updating of protocols has been done in 2007 (MEDITS, 2007). According to it, for each species the total weight and number of individuals is recorded. For a reference list of 38 species of fish, crustaceans and cephalopods, the length frequency by sex must be reported, as well as the maturity stage of the gonads. However, two different things should be taken into account. On one hand, for most works performed using MEDITS data (including assessments), the length frequency distributions are used, without taking into account the sex. On the other hand, the period of the surveys is not always coincident with the spawning season for all the species in the MEDITS reference list. This document attempts to be a practical exercise in relation to these topics, using both surveys and commercial data, and gives some proposals to the reference list of specie

Spatial and temporal variability of discards indicators and fishery factors affecting otter-trawl fishery in the spanish Mediterranean sea

A set of diversity indices were studied from data of observers on board two Mediterranean trawlers from 2001 to 2009. These diversity indices comprise relationships between total catch, landing and discard fractions to explore the accuracy of the estimates and to analyse the series trends using different methods, such as ARIMA. The hypothesis tested was that diversity indicators give a good representation of the changes produced in impacted bottom‐trawl areas, providing a reasonable fit of the data. ARIMA models are useful because they handle time-correlated modelling and forecasting. These techniques can also reveal changes in total catch as well changes in catch composition, probably induced by changes in effort fishery, seasonal (time) fluctuations, and environmental or climatic processes. Contrasted trends were also compared with survey data by MEDITS Mediterranean trawl survey time‐series indicator