Effect of nursery ground variability on condition of age 0+ year Merluccius hubbsi

Abstract

This study examined the southern or Patagonian (41°–55° S) stock of Argentine hake Merluccius hubbsi, the more abundant of the two stocks on the Argentinean continental shelf. Pre‐recruits (age 0+ year individuals) of this stock settle and grow in the San Jorge Gulf (45°–47° S, 65° 30′ W), a complex habitat with large spatial variability in environmental features. Relative condition factor, hepatosomatic index, lipid content and fatty‐acid composition of muscle and liver, and diet information were combined with physical and biological data to evaluate: how nutritional status of age 0+ year hake varies spatially within the nursery ground; whether changes in condition are related to environmental factors and feeding; whether the indices are interchangeable metrics of condition. Both morphometric and biochemical indices showed dissimilar spatial trends; enhanced liver‐based condition coincided with low salinity nutrient rich waters, higher chlorophyll‐a values and abundances of Euphausia spp., the preferred prey at most stations, suggesting a bottom‐up effect on age 0+ year hake condition. Diminished condition at stations where Thermisto gaudichaudii was the main prey could derive from lower prey quality in terms of energy density and essential fatty acids content. Coastal waters of the gulf would be essential habitats for M. hubbsi pre‐recruits. Future monitoring of condition with liver‐based indices is encouraged in the gulf, where interannual increasing trends of satellite‐derived chlorophyll‐a values have been observed, which could have implications for recruitment of the species.

Seasonal and spatial variability in condition of age‐0+ Argentine hake Merluccius hubbsi Marini, 1933, in the San Jorge Gulf (Argentina): A bottom‐up perspective

“…For instance, HSI and % L revealed clear seasonal trends that K n did not. Liver‐based indices exhibited similar trends, reinforcing their accuracy to reveal seasonal and spatial shifts in condition, as previously suggested for prerecruits (Temperoni, Derisio, et al, 2018; Temperoni, Massa, et al, 2018) and adults (Leonarduzzi et al., 2014) of M. hubbsi , and for other gadoids (e.g., juvenile pollock; Kooka et al., 2009). It is also worth mentioning that these indices were not significantly correlated with total length, suggesting a very weak effect of M. hubbsi size on the condition estimates within the size range used.…”

“…This paper examines the seasonal and spatial variability in age‐0+ M. hubbsi condition within their main nursery ground in the north Patagonian shelf, in relation to environmental features and by means of different indices. Results represent an improvement with respect to previous studies on the Patagonian stock (Temperoni, Massa, et al, 2018), which only explored spatial patterns of age‐0+ condition during austral summer. Here, further exploration of the seasonal dynamics on the nutritional well‐being of the individuals, as well as the spatial variability during winter and spring periods, was carried out.…”

“…These euphausiids are mainly herbivorous species (Gurney, Froneman, Pakhomov, & Mc Quaid, 2002; Stuart, 1989) that can benefit from nutrient resuspension and elevated chl‐ a values to sustain their populations and build energetic reserves, especially during spring and summer. In this sense, the bottom‐up effect upon age‐0+ hake condition that was suggested for the summer by Temperoni, Massa, et al (2018), in which the available phytoplankton energy was transferred to the prerecruits through consumption of herbivorous euphausiids, would also be occurring in spring and winter, modulated by prey abundance. Corroborating our hypothesis, the bottom‐up effect was manifested as a poorer condition, in winter, when local productive and feeding conditions were less favorable.…”

“…In recent years, studies on age‐0+ hake condition using morphometric, physiological and biochemical indicators have intensified in the main nursery areas of both stocks in the ACS (Temperoni, Derisio, Massa, & Viñas, 2018; Temperoni, Massa, et al, 2018). For the Patagonian population, results evidenced a strong spatial coupling between nutritional status of the individuals and phytoplankton biomass in the SJG during summer.…”

Morphological and biochemical approaches to assess the nutritional condition of the Argentine hake Merluccius hubbsi larvae from two different nursery areas

“…Temperoni et al . (2018) have analysed the nutritional status of M. hubbsi juveniles from the Patagonian stock within different areas of their main nursery ground, by a combination of different indexes (relative condition factor, hepato‐somatic index, lipid content and fatty acid composition in liver and muscle) combined with physical and biological information, and have found significant differences in the nutritional condition according to the predominant prey in the area. On the contrary, in M. hubbsi larvae, the histology and histochemistry of the digestive system have also been analysed, and no differences have been observed between both stocks (Cohen, 2019; Cohen et al ., 2020).…”