Search

We used the bycatch of Caspian sturgeon to quantify the species composition, length structure, spatial and temporal distribution, temporal dynamics of relative abundance (indexed as catch‐per‐unit‐effort, CPUE), effects of fingerlings released, and to forecast future sturgeon stock status. Dynamic factor analysis of temporal changes in species CPUE was used to quantify relationships to environmental variables (sea surface temperature, chlorophyll‐a, sea surface level, and river discharge) during 2006–2022. We found that the Guilan subarea had the lowest relative abundance and differed from all other subareas. Fish abundance was highest in October and November, particularly in Mazandaran and Golestan coastal waters. Relative fish abundance declined significantly over time. Acipenser persicus was the most abundant species, followed by Aciperser gueldenstaedtii, Aciperser stellatus, Aciperser nudiventris, and Huso huso. The annual number of fingerlings released decreased during 2000–2021. Over the years, environmental variables such as sea surface level, sea surface temperature, and chlorophyll‐a showed different trends, with sea surface temperature generally increasing, chlorophyll‐a generally decreasing, sea surface level decreasing nearly linearly, and river discharge varying erratically without a trend in the southern Caspian Sea during 2006–2022. The relative abundance of all species decreased and was significantly related to sea surface level. Fish abundance was forecasted to decline by 2025, as sea surface temperature increases and sea surface level decreases. Illegal, unreported, and unregulated (IUU) harvest of sturgeon must be effectively regulated to ensure the survival and recovery of sturgeon populations in the Caspian Sea. [ABSTRACT FROM AUTHOR]

Keywords: commercial fish species; catch assemblage; temporal patterns; community structure; environmental parameters; Caspian Sea EN commercial fish species catch assemblage temporal patterns community structure environmental parameters Caspian Sea 90 99 10 04/28/22 20220301 NES 220301 1 Introduction The Caspian Sea (CS), the largest lake in the world, is a unique ecosystem known for its rich and diverse aquatic fauna (Karpinsky et al. 2005). Despite the commercial importance of bony fish, no study has been carried out on the species composition of these fish assemblages in relation to environmental parameters in the CS. 2.2 Environmental data Global variables with large-scale influence - the global temperature anomaly (GTA), the East Atlantic-West Russian pattern (EAWR), the North Atlantic Oscillation (NAO), and two regional environmental variables - sea surface temperature (SST) and sea surface level (SSL) were investigated to assess the potential effects on fish species assemblages between 1996 and 2017 (Table 1). Table 4 Relationship between environmental variables and diversity index, most abundant fish species (species with a percentage value higher than 1%) in the Caspian Sea. [Extracted from the article]

Climate change affects the ecology of reef fish through changing their habitat, community and their feeding and territorial behavior. The corals and their associated reef fish in the Persian Gulf as the world's warmest sea suffer from the increasing frequency and severity of mass bleaching events. Yet, the effects of climate-induced coral bleaching events on reef fish in this sea are poorly understood. Using a time series fish count data, this study evaluated the response of reef fish to multiple severe coral bleaching events in Kish Island located in the central Persian Gulf. The results showed a decline in species richness and diversity of reef fish after bleaching events which reduced mean coral cover by 85% following the 2007 bleaching event and by 95% following the 2017 bleaching event. Besides a drop in the number of fish species, the total density, and density of trophic groups changed as the results of coral loss. The variation in density of different trophic groups indicated an overall increase in the abundance of benthic invertebrate feeders (21.2–136.3%), omnivores (32.4–163.4%) and plankton feeders (218.5–488%). In contrast, the abundance of coral polyp feeders (−6.9 to −50%) and piscivores (−4.9 to −38.9%) significantly decreased after bleaching events. The density of herbivorous fish significantly increased by 97.1% after the bleaching event in 2007 and decreased by 10.5% after the bleaching event in 2017. In the present study, we demonstrated how the impact of the multiple bleaching events on associated reef fish assemblages sustained for about 6 years after the disturbance. These results have significant implications for our understanding of the response of reef fish to global warming and highlight the growing concern about the future of coral reef ecosystems and their associated reef fish in the region as the warmest sea in the world. [ABSTRACT FROM AUTHOR]

Longtail tuna (Thunnus tonggol) is a neritic species that supports commercial, artisanal and recreational fisheries throughout the Indo-Pacific region. Historically receiving little attention by commercial fisheries, the global annual catch of longtail tuna has steadily risen from around 30,000 t in the early 1980s to exceeding 200,000 t since 2004, reaching a peak of 291,264 t in 2007, and was 281,613 t in 2017. Catches of longtail tuna in the Indian Ocean now exceed catches of principal commercial target species, such as albacore and bigeye tunas. A sequence of stock assessments undertaken throughout the species' range since the late 1980s persistently indicated that at least three of the four stocks defined in this paper are likely to have been, and most likely are currently, subject to overfishing and overfished as a result of excess fishing effort on this relatively slow-growing and long-lived tuna species. As the spawning biomass of principal tuna target species continue to decline in both the Indian and western and central Pacific Oceans, the increasing catches of longtail tuna, other neritic tunas, and seerfishes is worrisome. Few conservation and management measures (CMMs) are currently in place specifically for longtail tuna, although in recent years some coastal States, Regional Fishery Bodies, and tuna Regional Fisheries Management Organisations have begun to develop initiatives to improve the catch and biological data quality for longtail tuna and sympatric species of neritic tunas and tuna-like species. This paper provides a global review of biological, ecological and fishery information to provide researchers, fishery managers and policy makers with the most current information from which to begin to guide future stock assessment and the development of CMMs for longtail tuna. [ABSTRACT FROM AUTHOR]

Narrow-barred Spanish mackerel, Scomberomorus commerson, is an epipelagic and migratory species of family Scombridae which have a significant role in terms of ecology and fishery. 100 samples were collected from the Persian Gulf, Oman Sea and Arabian Sea. Part of their dorsal fins was snipped and transferred to micro-tubes containing ethanol; then, DNAs were extracted and HRM-Real Time PCR was performed to designate representative specimens for sequencing. Phylogenetic relationships of S. commerson from Persian Gulf, Oman Sea and Arabian Sea were investigated using sequence data of mitochondrial DNA D-loop region. None clustered Neighbor Joining tree indicated the proximity amid S. commerson in four sites. As numbers demonstrated in sequence analyses of mitochondrial DNA D-Loop region a sublimely high degree of genetic similarity among S. commerson from the Persian Gulf and Oman Sea were perceived, thereafter, having one stock structure of S. commerson in four regions were proved, and this approximation can be merely justified by their migration process along the coasts of Oman Sea and Persian Gulf. Therefore, the assessment of distribution patterns of 20 haplotypes in the constructed phylogenetic tree using mtDNA D-Loop sequences ascertained that no significant clustering according to the sampling sites was concluded. [ABSTRACT FROM AUTHOR]