Cyclic fluctuations of blue whiting (Micromesistius poutassou) linked to open‐sea convection processes in the northwestern Mediterranean

Abstract

In the Mediterranean, blue whiting, Micromesistius poutassou, constitutes a traditional fisheries resource. Over several decades, blue whiting landings in the Catalan coast (northwestern Mediterranean) have displayed cyclical variations, of c. 6 yrs, slightly decreased to five in the last two decades, as shown through wavelet analysis. These fluctuations have persisted under very different levels of fishing effort. This study evaluates the hypothesis that deep-water formation in the adjacent Gulf of Lions, and the enhanced primary productivity related to it, determines recruitment strength in blue whiting that results ultimately in the observed periodicity of the blue whiting landings. The link between landings and environmental drivers was explored using lagged cross-correlations, with 0-and 1-yr lag. The variables considered included large-scale indices [North Atlantic Oscillation (NAO) and the Atlantic Multi-decadal Oscillation (AMO)], Mediterranean climate indices [MO and Western Mediterranean Oscillation (WeMO)], and variables defining the local environmental conditions in the northwestern Mediterranean (sea-air heat flux, winter air temperature anomaly and Rhône river runoff). Significant correlations were only found between landings (1961-2011) and sea-air heat flux, which is generally taken as an indicator of processes of deep water convection, at 0 and 1-yr lag. These results suggest that the observed fluctuations in blue whiting landings respond to oceanographic processes taking place in the Gulf of Lions.

Growth, reproduction and their interplay in blue whiting (Micromesistius poutassou, Risso, 1827) from the NW Mediterranean

“…In the most recent years, the total catch of blue whiting in the study area remained at very low levels. Since 2012 landings remained at ≤ 500 t (Generalitat de Catalunya, 2019) lower than the minimum values reported by Martin et al (2016Martin et al ( ) over a period 1961Martin et al ( -2011 suggests that the stock would not show sign of recovery. The length of blue whiting individuals captured by bottom trawl ranged between 3 and 39 cm TL, and differences related with sex were found, with females reaching larger sizes than males.…”

“…Blue whiting, Micromesistius poutassou (Risso, 1827), is a pelagic gadoid widely distributed in the North Atlantic and the Mediterranean Sea, inhabiting over the shelf edge and continental slope (Bailey, 1982;Heino et al, 2008). There is large amount of information on its biology, behavior and fisheries for the Northeast Atlantic (Bailey and Heath, 2001;Bailey, 1982;Gonçalves et al, 2017;Hátún et al, 2009;Payne et al, 2012), but less is known for the species in the Mediterranean despite it has an important commercial interest, particularly in the northern part (Bas, 1963;Bas and Calderon-Aguilera, 1989;Martin et al, 2016;Orsi-Relini and Peirano 1985;Serrat et al, 2019).…”

“…In the North Atlantic, major migrations of the species were reported linked to reproduction (Bailey, 1982;Hátún et al, 2007), however, within the Mediterranean such migrations have not been described (Martin et al, 2016). In the Atlantic the spawning of the species takes place a temperature around 11ºC (Seaton and Bailey, 1971) and starts in January-February in its southern distribution area extending northwards with a time-lag in relation to the latitudinal temperature gradient (Bailey, 1982).…”

Trade‐offs between life‐history traits in a coldwater fish in the Mediterranean Sea: the case of blue whiting Micromesistius poutassou

“…Indeed, during the past two decades, landings of M. poutassou in the Mediterranean Sea have fallen from almost 30,000 t to just 2000 t in 2016 (GFCM, ). It has been shown that variation in M. poutassou population parameters is linked to fluctuations in environmental and hydrodynamic factors (Martin et al, ; Trenkel et al, ) as well as overfishing (Bas & Calderon‐Aguilera, ; Rueda et al, ). For these reasons, we need to assess the life‐history traits and the trade‐offs among them, for species such as these inhabiting the Mediterranean Sea.…”

Assessment of the Skill of Coupled Physical–Biogeochemical Models in the NW Mediterranean

“…The winter-spring bloom is the main contributor to the overall phytoplankton biomass and primary production in the northwestern basin (Bosc et al, 2004;Estrada et al, 2014) and fuels energy to micro and mesozooplankton that support key ecosystem components, from pelagic fish (e.g., Martin et al, 2016) to marine birds (Ramírez et al, 2016). Fluctuations in the intensity of vertical mixing result in interannual variations in the extent of the winter-spring phytoplankton bloom and zooplanktonic biomass (Vandromme et al, 2011;Severin et al, 2014) and have been related with the recruitment success of pelagic species that reproduce in winter, such as blue whiting, Micromesistius poutassou, and sardine, Sardina pilchardus (Lloret et al, 2004;Martin et al, 2016). Section "Interannual Variability" discusses the range of interannual variability represented by the models.…”