Population ecological parameters and stock assessment of Russian sturgeonAcipenser gueldenstaedtiBrandt & Ratzeburg, 1833 in the Southern Caspian Sea

Abstract

Russian sturgeon (Acipenser gueldenstaedti Brandt & Ratzeburg, 1833) is one of the major commercial sturgeon species, but there is no adequate information and previous‐published about population dynamics and stock assessment of this species in the southern Caspian Sea. This paper examines the age structure, growth parameters, maturity, age at first capture, optimum length, natural and fishing mortality and amount of biomass in the southern Caspian Sea (Iranian waters), during a two decades time series period from 1990–1991 to 2008–2009. For a pooled data, the growth parameters were estimated as L∞ = 214.0 cm, K = 0.054, t0 = −4.5 year. Size at fifty percent sexual maturity was at FL = 118 cm for females and 113 cm for males. The age at first capture (tc) estimated to be 12.1 years. In the catch composition, bulk of the catch (75%) belonged to 13–17 years old. The instantaneous coefficient of natural mortality (M) was estimated as 0.120 year−1 and the instantaneous coefficient of fishing mortality (F) varied during the 19‐year period between 0.130 to 0.505 year−1. The biomass showed a descending trend from 1,941.2 mt in 1990–1991 collapsed to about 55 mt in 2004–2005, and then decreased to the lowest level and represented 18.5 mt in 2008–2009. The result revealed that, the stock of Russian sturgeon is being over‐fished. We concluded that to manage the sturgeons stocks, a coordinated regional and international effort are needed to provide immediate implementation of stock enhancement and management in the Caspian Sea.

Spatial and temporal trends in the relative abundance of Caspian sturgeon during 2006–2022

“…The CPUE of all adult sturgeons has been decreasing in the Caspian Sea from 1990 to 2014 (Fazli, Khoshghalb, & Abdolmaleki, 2022). Our results showed that the decreasing trend in CPUE continued from the mid‐2000s to the 2010s, which is consistent with previous studies that have shown declining sturgeon populations in the Caspian Sea (Fazli et al., 2020, 2021; Fazli, Kaymaram, & Daryanabard, 2022; Fazli, Khoshghalb, & Abdolmaleki, 2022; Khodorevskaya et al., 2014; Ruban & Khodorevskaya, 2011; Tavakoli et al., 2019). Based on our forecasting, the CPUE of all species will continue into the future and be close to zero in 2025.…”

“…Bycatch of juvenile and young A. persicus sharply increased on the eastern coasts of the Caspian Sea from 2000 to 2004, and was expected to increase into the 2010s with effective regulation in the whole Caspian Sea (Moghim et al (2006). However, stocks of all five species declined sharply and were critically endangered (Fazli et al, 2020(Fazli et al, , 2021Fazli, Kaymaram, & Daryanabard, 2022;Khodorevskaya et al, 2014;Ruban & Khodorevskaya, 2011;Tavakoli et al, 2019). In the present study, a bycatch of juvenile and young sturgeon since 2006 was used to assess the status of these species' populations.…”

“…These fish are currently categorized as “critically endangered” (IUCN, 2022). In the 1990s and 2000s, the catch and stocks of sturgeon in the Caspian Sea greatly decreased (Fazli et al., 2020, 2021; Fazli, Kaymaram, & Daryanabard, 2022; Khodorevskaya et al., 2014; Ruban & Khodorevskaya, 2011; Tavakoli et al., 2019) due to overexploitation, illegal, unreported and unregulated (IUU) fishing, poaching, habitat destruction, decreased sea surface level (SSL), increased sea surface temperature (SST), and dissolution of the Ex‐Soviet Union in 1991. Following this decrease, the Commission of Aquatic Living Sea Resources of the Caspian Sea decided to ban fishing in 2012 to restore stocks of these fishes, which have continued until 2023.…”

“…(2006). However, stocks of all five species declined sharply and were critically endangered (Fazli et al., 2020, 2021; Fazli, Kaymaram, & Daryanabard, 2022; Khodorevskaya et al., 2014; Ruban & Khodorevskaya, 2011; Tavakoli et al., 2019). In the present study, a bycatch of juvenile and young sturgeon since 2006 was used to assess the status of these species' populations.…”

Spatial distribution and diversity of commercial demersal fish species in the shelf waters of the Caspian Sea

“…Several studies have been conducted to assess the state of the most valuable commercial demersal fish stocks of the CS such as sturgeon, Acipenser gueldenstadtii (Tavakoli et al, 2019), Rutilus kutum (Fazli et al, 2012), and mullet (Fazli et al, 2013). However, no study was conducted on the diversity and community composition of demersal fish species in the Iranian shelf waters of the CS.…”