Physical and biological drivers of pelagic fish distribution at high spatial resolution in two Patagonian Gulfs

Abstract

The North Patagonian gulfs, Argentina, support an important population of small pelagic fish (SPF) that play a key role in the marine ecosystem. Here, we assessed the seasonal SPF distribution in Nuevo gulf and San Matías Gulf concerning several environmental variables and the nautical area scattering coefficient (NASC) of Munida gregaria using generalized additive models (GAMs). We collected biological data by a 38/200 kHz echosounder along zigzag transects in all four seasons. The echoes of fish were separated from other targets using a dB difference algorithm. Then, we calculated the mean NASC of pelagic fishes every 0.5 nm. Satellite‐derived data were used to characterize the environment at study sites. GAMs were built in two stages for each gulf considering all season in a single model in one hand, and each season separately in the other one. In the first stage, we modeled the probability of presence as a function of predictors. In the second stage, we used the NASC of fish as the response for presence data only. In general terms, the probability of fish presence increases with bottom depth, and the fish density was higher in cold waters and zones with higher chlorophyll‐a concentration. The relative importance of the variables was different according to the season. The formation and rupture of the thermocline and its subsequent spatial heterogeneity observed in spring and autumn could be important drivers of SPF distribution. Squat lobsters’ distributions related positively with SPF in San Matías Gulf summer and negatively in Nuevo Gulf summer.

Group dynamics and activity patterns of two dolphin species, the Common Dolphin (Delphinus delphis) and Dusky Dolphin (Lagenorhynchus obscurus) in direct sympatry

“…Seasonal variation in the activity pattern of common dolphins and the occurrence of dusky dolphins in our study area suggest that these species are responding differently to seasonal changes of the environment. There is evidence that fish density, mainly anchovy, is higher in shallow areas, cold waters, and zones with high chlorophyl “a” concentration, but the relative importance of these variables varies seasonally (Luzenti et al 2020). The formation and rupture of the thermocline and the subsequent spatial heterogeneity in sea surface temperature observed in spring and autumn seems to be a key factor in determining fish distribution (Luzenti et al 2020).…”

“…There is evidence that fish density, mainly anchovy, is higher in shallow areas, cold waters, and zones with high chlorophyl “a” concentration, but the relative importance of these variables varies seasonally (Luzenti et al 2020). The formation and rupture of the thermocline and the subsequent spatial heterogeneity in sea surface temperature observed in spring and autumn seems to be a key factor in determining fish distribution (Luzenti et al 2020). The depth and morphology of anchovy shoals, as well as their energetic density also vary seasonally (Luzenti 2022).…”

“…1a). Within this area, shoals of anchovy occur throughout the year but their abundance seems to increase from winter to autumn (Luzenti et al 2020). The seasonality of anchovy occurrence probably responds to the bimodal pattern of phytoplankton biomass described for the northwest sector of the gulf (Williams et al 2021), characterized by a peak in autumn (April–May) and another in spring (September–November), driven by water circulation in the gulf (Williams et al 2021).…”

Melting Antarctic Sea Ice Is Yielding Adverse Effects on a Short-Lived Squid Species in the Antarctic Adjacent Waters

“…The important relationship between the distribution of I. argentinus and water temperature at 200 m water layers may be related to thermocline (Yatsu and Watanabe, 1996). The formation, rupture, and spatial heterogeneity of the thermocline in different seasons had a significant impact on marine life in Patagonia Gulf in the northern Argentina of the Southwest Atlantic Ocean (Luzenti et al, 2021). Therefore, for the marine species living above the thermocline, it prevented them from entering the deeper water, which was favorable for the formation of a productive fishing ground above the thermocline.…”

“…On the contrary, for the marine species inhabiting below the thermocline, it was difficult to attract the fish to rise through the thermocline by means of lighting and other trapping methods, which might lead to lower catch (Wang et al, 2019). Thus, the water layer of the upper and lower boundary of thermocline was important for the formation of fishing grounds (Luzenti et al, 2021). At present, there were few studies on the seasonal and interannual changes on the thermocline position on the fishing ground of I. argentinus in the Southwest Atlantic Ocean.…”