Fisheries Science最新文献

Understanding the connectivity in estuarine waters is important for sustainable fisheries management and safeguarding of estuarine ecological environments. Knowledge regarding the functional connectivity for some “estuarine opportunist” fish species between the Yangtze River estuary (YRE) and its adjacent coastal waters is still scarce. We investigated the connectivity for an exploited sciaenid, the small yellow croaker (Larimichthys polyactis), using otolith elemental composition. In 2020, 115 juveniles were collected in four putative habitat patches, and elemental fingerprints (strontium, barium, magnesium, manganese) of the otolith margin were used to determine spatial differentiation. The results indicated that multi-elemental fingerprints had limited efficacy in identifying habitat patches at a fine spatial scale. However, an elevated Ba/Ca ratio proved to be effective in identifying the presence of L. polyactis in the YRE, which was found to be 12.5 ± 0.7 µmol/mol. In 2021, 51 adult fish were collected from the Lvsi fishing grounds, and the core-to-edge Ba/Ca profiles of the adult fish were analyzed to evaluate the connectivity in the YRE and its adjacent waters. Among the specimens examined, 41% exhibited a life history associated with estuarine habitats. In addition, among the fish with estuarine life history, 72% of the estuarine life history occurred during the juvenile stage, and almost none at the larval stage. The functional connectivity of L. polyactis in estuarine habitats is conspicuous and closely linked to ontogeny. This study emphasizes the need to incorporate the concept of functional connectivity for a more comprehensive understanding of estuarine ecosystems. Furthermore, it highlights the significance of estuaries for “estuarine opportunist” fish, warranting increased attention and research.

Maximum sustainable yield reference points (MSY-RPs) are usually calculated assuming spawner-recruitment relationships (SRR) and population dynamics of the stock. However, due to the difficulty of estimating SRR, the uncertainty in MSY-RPs is often too large to be put into practice. Therefore, based on the concept of maximum–minimum yield (MMY), fishing mortality (F) that gives %SPR (spawner biomass per recruitment [SPR] at a given F relative to SPR in the absence of fishing) of 30–50% (F_30-50%SPR) is often used as a proxy of F_MSY (F that maximizes the long-term catch). In this study, we estimated ({F}_{%{mathrm{SPR}}_{{text{MMY}}}}) (F expected to produce %SPR at MMY) for 30 stocks of Japanese fishery resources based on the life-history parameters of the stocks and steepness assumptions derived from meta-analysis. Our results showed that %SPR_MMY ranged from 23% to 62% (excluding 86% of Scomberomorus niphonius), depending on the stock and the assumed steepness scenario. If the fish were caught under ({F}_{%{mathrm{SPR}}_{{text{MMY}}}}), at least 70% of the MSY could be expected in Japanese fishery resources. When compared with the %SPR_MSY for the 15 stocks estimated through Japanese fishery stock assessment, %SPR_MMY were similar, or often larger. %SPR_MMY can be considered a precautionary value, reflecting the uncertainty of SRR.

The objective of this study was to examine the effectiveness of using ultrasonography for sex determination in young carp. Ultrasound images were obtained from anesthetized captive carp aged 11 to 13 months. After sacrifice, the body length and weight, gonadal sex and weight, and gonad-somatic index were measured. Well-developed testes and ovaries filled with granulated eggs were easily distinguishable on ultrasound imaging, based on their visible characteristic morphological features. In contrast, immature, small-sized testes and ovaries lacking granulated eggs were difficult to distinguish. The mean longitudinal thickness of gonads was technically the easiest to scan for measuring gonadal size, and it correlated well with gonadal weight (r = 0.91) and gonad-somatic index (r = 0.89). Based on the area under the curve of the receiver operating characteristic curve, we determined that 6.2 mm was the cutoff value for mean longitudinal gonadal thickness at which sex could be positively determined by ultrasonography, with a sensitivity of 82.6% and specificity of 100%. Ultrasonography therefore represents an effective and non-invasive diagnostic tool for determining sex and maturity in Japanese ornamental carp.