Decapod crustacean larval communities in the Balearic Sea (western Mediterranean): Seasonal composition, horizontal and vertical distribution patterns

Decapod crustaceans are the main target species of deepwater bottomtrawl fisheries in the Balearic Sea but little is known about their larval stages. This work focuses on the species composition of the decapod larval community, describing the main spatio-temporal assemblages and assessing their vertical distribution. Mesozooplankton sampling was carried out using depth-stratified sampling devices at two stations located over the shelf break and themid slope, in the north-western and southern Mallorca in late autumn 2009 and summer 2010. Differences among decapod larvae communities, in terms of composition, adult's habitat such as pelagic or benthic, and distribution patternswere observed between seasons, areas and station. Results showed that for both seasonsmost species and developmental stages aggregatedwithin the upperwater column (above 75 mdepth) and showed higher biodiversity in summer compared to late autumn. Most abundant species were pelagic prawns (e.g., Sergestidae) occurring in both seasons and areas. The larval assemblages' distributions were different between seasonal hydrographic scenarios and during situations of stratified and non-stratified water column. The vertical distribution patterns of different larval developmental stages in respect to the adult's habitat were analyzed in relation to environmental variables. Fluorescence had the highest explanatory power. Four clearly different vertical patterns were identified: two corresponding to late autumn, which were common for all the main larval groups and other two in summer, one corresponding to larvae of coastal benthic and the second to pelagic species larvae.Versión del editor2,655

Size dependent predation in piscivorous larval stages of three tuna species

The bluefin tuna (Thunnus thynnus) is a heavily fished temperate tuna that spawns in the Mediterranean Sea; the area off the Balearic Islands is a key spawning area. Other abundant tunas, including albacore (Thunnus alalunga) and the small bullet tuna (Auxis rochei) spawn in the same area. The three species temporally overlap during the summer spawning period of the adults. Because they are clearly piscivorous already at very early larval stages, we expect strong interactions both in terms of a direct predator–prey relationship and as competitors for food resources. In this study, we focus on understanding the size dependent trophic interactions among the three species at the different developmental larval stages. First, we describe the environmental and biological scenarios where different size stages of the three species co-occur through the application of generalized additive model (GAM) analyses to field data collected during cruise surveys in 2004–2005. We then develop an individual_based model (IBM) to evaluate inter- and intraspecific predation rates considering size structured prey and predator fields in the framework of piscivorous behaviour. The results demonstrate how predation mortality rates influence the spawning location of the three speci

RETROCALCULATED LARVAL ABUNDANCE INDEX OF ATLANTIC BLUEFIN TUNA IN THE WESTERN MEDITERRANEAN SEA, 2001-2020

This document presents the update of the bluefin tuna retrocalculated larval abundance indices from the Balearic archipelago (western Mediterranean). The index has been calculated following methods presented in 2020 (SCRS/2020/067) and 2021 (SCRS/2021/033). The abundance index shows an increasing trend with a maximum value in 2020. A previous version of the index (SCRS/P/2019/055) is also provided for comparison.En prensa

First record of Palaemon macrodactylus Rathbun, 1902 (Decapoda, Palaemonidae) in the western Mediterranean

The Mediterranean Sea is one of the world’s hotspots for marine bio-invasions. Most invasions are first documented based on an initial record of occasional adult captures. However, reports of larval stages could indicate that there is an adult population that is reproducing and therefore well established in the area. The spread of the oriental shrimp, Palaemon macrodactylus, from its native estuarine waters of southeast Asia to new regions worldwide is well documented. We report the first record of this species in the Mediterranean based on the presence of its larval stages in plankton samples. Decapod larvae were collected in five offshore plankton surveys performed off the Balearic Islands (western Mediterranean), and zoeae III and VI of the oriental shrimp were found among them. Taking into account the duration of the successive developmental stages, and the hydrodynamic characteristics of the study area, these larvae were most probably spawned by adult populations not yet documented. The larvae were found in marine waters despite the fact that adults usually inhabit brackish waters. Our study is a good example of how plankton studies can help to detect larval stages of invasive species before the adult populations are detectedPublicado

Climate effects on swordfish early-life habitats: the western Mediterranean open-ocean observatory

Trabajo presentado en ICES Annual Science Conference (2023), celebrada en Bilbao (España), entre el 11 y el 14 de septiembre de 2023.The Balearic Sea, in the western Mediterranean, is a remarkable reproductive area for many marine species, among which large oceanic migrants stand out. This region presents unique oceanic features with fronts and eddies, favouring the early-life stages of these species. We take advantage of already existing biological and oceanographic data and know how to advance in the understanding of the open-ocean pelagic ecosystem. We purpose indicators to monitor the environmental variability of the pelagic habitat, such as temperature anomalies that affect the survival of tuna larvae. The indicators are designed to inform climate aspects of the ecosystem approach to fisheries management for tunas and other related species in the framework of the International Commission for the Conservation of Atlantic Tuna, the organisation in charge of the fisheries management of these species. We take swordfish (Xiphias gladius) as a case study. Swordfish is a highly migratory species that, in the Mediterranean, reproduces at several locations and has the Balearic Islands as one of the main breeding areas. We investigate if climate change has already affected the suitability of this potential spawning ground. For that, we analyse how the variability of ocean characteristics and features affects the presence of swordfish larvae collected in ichthyoplanktonic surveys and identify their preferential habitat. Results of this work show that, during reproductive season and early developmental time of this species, significant heatwaves impact the pelagic realm in the Balearic Sea, a prominent hydrodynamic retention area of the western Mediterranean, with direct effects on the distribution of the swordfish larval habitat.Peer reviewe

The Deep-Water Red Shrimp Fishery in the Spanish Mediterranean Sea

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First attempt to assess the viability of bluefin tuna spawning events in offshore cages located in an a priori favourable larval habitat

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