Fishery dynamics of blue whiting, Micromesistius poutassou, a highly discarded bycatch species in the NW Mediterranean Sea

Abstract

This study characterized the fishery dynamics of blue whiting, a bycatch species of the bottom trawl Norway lobster fishery, in the NW Mediterranean. Landings and effort data over the last two decades were combined with current information on the spatial distribution of effort and catch, and with the size and age structure of blue whiting over the year. Recruitment to the demersal habitat occurred from 5 cm total length (TL) over the shelf break in spring (April-May), when discards showed the highest values (>95% of the catch). Adults were located over the upper slope, and large individuals (≥26 cm TL) were abundant during the reproductive period (January-March). A decline in landings has been observed in the last decade, probably related to the absence of intense deep convection processes in winter since 2013, which favour recruitment of the species. The effect of exploitation on the decrease in landings cannot be disregarded considering that the bulk of the catch is made up of immature (age 0) individuals, and the presence of old individuals is very low.

Nursery areas of Micromesistius poutassou and Sardina pilchardus unveil their reproductive strategies in the northwestern Mediterranean Sea

“…Unlike the north Atlantic, where major migrations of blue whiting between feeding areas, in the Norwegian Sea, and the spawning areas west of the British Isles have been reported (Bailey, 1982; Hátún et al, 2007), within the Mediterranean such large‐scale migrations had not been described (Martín et al, 2016). However, recent studies based on the fishery dynamics of the species, showed that the largest individuals only appeared in the catches in winter, their reproductive period, being practically absent during the rest of the year (Mir‐Arguimbau et al, 2022). In light of these observations, the authors suggested migration movements of large individuals from offshore waters to the upper slope (between 200 and 600 m) for reproduction.…”

“…Blue whiting larvae at more advanced developmental stages were found close to the coast, in the more productive shelf waters and near the recruitment zones that are located over the shelf (Mir‐Arguimbau et al, 2022). Interestingly, they were mainly located in the canyons head.…”

“…In the NW Mediterranean, historical landings of both species have shown fluctuations in population size linked to environmental conditions (Lloret et al, 2004; Martín et al, 2012, 2016; Quattrocchi & Maynou, 2017). However, since mid‐2000s, landings have displayed a decreasing trend and remained at low levels in the most recent years (Coll et al, 2019; Mir‐Arguimbau et al, 2022). As pelagic species, their recruitment is controlled to a large extent by egg and larval survival, which in turn is dependent on suitable oceanographic conditions influencing the larval distribution, retention and transport (e.g., Bakun, 1996; Hare et al, 2002; Houde, 2008; Raya et al, 2020).…”

Life history traits and historical comparison of blue whiting (Micromesistius poutassou) growth performance from the western Pomo/Jabuka Pits area (central Adriatic Sea)

“…Indeed, the adaptive phenotypic plasticity may determine changes in population life history traits even on a short-term scale, depending on the environmental context (Hidalgo et al, 2014). Such natural oscillations occur not only in biological parameters but also in abundance as a result of environmental variations and fishing exploitation (Martin et al, 2016;Mir-Arguimbau et al, 2022). Another limitation of this study is represented by the small sample size of the 1985-86 sample (not fully representative of the population) and the different methodologies used in the two periods.…”

“…Another limitation of this study is represented by the small sample size of the 1985-86 sample (not fully representative of the population) and the different methodologies used in the two periods. The different selectivity of the net due to different mesh sizes represents a limit to properly compare the LFDs and size structure of the samples, even if we can assume a comparable selectivity on adult specimens since it was reported that juveniles smaller than 20 cm TL account for a large proportion of catches in otter bottom trawler deploying a 40 mm mesh size at the codend (Mir-Arguimbau et al, 2022).…”