Bayesian modelling suggests that the sterlet (Acipenser ruthenus, Linnaeus 1758) population is ageing in the middle Danube River

Abstract

In the past, sturgeons played an important role in commercial and recreational fisheries in the Danube River and its tributaries. Human impacts in the Danube River Basin coupled with exploitation of sturgeon stocks led to all species being either locally extinct, critically endangered or of unknown status. Sterlet (Acipenser ruthenus, Linnaeus 1758) is the last known sturgeon species occurring in the upper and middle Danube; however, the population of this species is considered unbalanced and decreasing since the beginning of the twenty‐first century. The decline of sturgeon stocks has been noted before owing to their economic importance. With commercial fisheries being forbidden in the Slovak section of the Danube River, there is generally no information available about the status of what is considered a local population. Databases containing recreational catch of sterlet (2003–2018) and historical records of commercial harvest (1961–1990) were used to describe the trend in the weight and number of sterlet caught over the following years. Modelling indicated that the number of fish caught each year appears to be lower, while the average weight of each individual is increasing. This might suggest that the population is ageing. Although older individuals can contribute a great deal more to spawning because they produce a greater number of eggs, several problems are apparent. The number of spawners might be decreasing as a result of bycatch or fishing, their ability to spawn might be obstructed, or annual recruitment may fail owing to unpredictable events. Although restocking programmes are in place to help maintain the sterlet population in the Danube River, their efficiency seems to be drastically low. In fact, restocking could be of little value unless studies on the availability of key habitats are conducted and their protection and restoration are ensured.

Sturgeons in large rivers: detecting the near-extinct needles in a haystack via eDNA metabarcoding from water samples

“…However, despite being of a certain economic value in the Middle and Lower Danube catchments (Guti 2008;Vassilev and Pehlivanov 2003), the current status of the population remains almost completely unknown, although the consensus among most authors is that stocks are declining (e.g. Bacalbasa-Dobrovici 1991;Paraschiv et al 2006) and aging (Kubala et al 2021). In the present study, approximately half of the samples collected from the Danube yielded a positive signal for the sterlet, and notably, we identified 3 areas with higher densities of this species, as indicated by a high frequency of detection and a high number of reads (namely, the Danube Delta, Iron Gate to Belgrade, and Budapest to Gabčíkovo sections of the river).…”

Assessing large‐scale movement of an endangered fish: Dispersal of stocked age‐0 pallid sturgeon in the lower Missouri River

“…For example, a recent study of multiple acipenseriform species highlighted the need to extend monitoring and management activities beyond pre‐established jurisdictional boundaries (Tripp et al, 2019). Kubala et al (2021) also called for the collaborative planning of monitoring efforts, given the propensity of sturgeon species to cross jurisdictional boundaries. This could also be important for early life stages, as Lechner, Keckeis & Humphries (2016) suggested that understanding drift dynamics of eggs, free embryos, and larvae is critical for managing a variety of river fishes, including both common and rare species.…”

“…country borders or state lines) that have different management priorities, monitoring plans, and species protections. This is often the case for acipenseriform species such as sturgeons, and can lead to varying designations of species status, depending on location (Kubala et al, 2021). Recent work has highlighted the importance of inter‐jurisdictional management and collaboration to better account for the large‐scale movement of river fishes.…”