Larval Fish Assemblages and Distribution Patterns in the Zhongsha Atoll (Macclesfield Bank, South China Sea)

The remote coral reef in the deep sea is one of the most important nursery grounds for many marine fishes in the South China Sea. Diversity studies on larval fishes in this area are few, and the fish information on the coral reefs ecosystem is lacking. In this study, larval fishes were sampled during the summer of 2019 from the Zhongsha Atoll in the South China Sea and identified using DNA barcodes for the first time. Ninety-five larval fish species were recognized, belonging to 37 families and 12 orders based on morphological classification and DNA barcoding identification. The larval fish collected could be assigned to three categories as reef-associated, deep-sea, and pelagic. Most of the species were small fish with low commercial value but would play an essential role in the coral reef ecosystem. Some commercial fishes, including Auxis thazard, Euthynnus affinis, Sarda orientalis, Decapterus macarellus, Lutjanus viridis, and Centropyge vrolikii, were the dominant species higher than 2% total catch. The larval fish assemblage showed distinct spatial differences responding well with the geographical conditions. The most reef-associated fish occurred inside the Atoll, and the abyssal fish presented near the edge. In addition, larval fish spread over from the southwest to northeast may reflect the oceanography effect.

Design and Operation of “Siklob”, a Mechanised Falling Gear Operated in Northern Iloilo, Philippines

Fisheries in the Philippines is multispecies, and this is seen with the wide variety of fishing gears used in major and minor fishing grounds in the country. These gears constantly face modification and development to improve catch quality, quantity, and overall efficiency. This study investigated the features of “siklob”, a mechanised falling gear operated along the municipal waters of Northern Iloilo, Philippines. Some coastal residents claimed that fishers use fine mesh nets for this gear, and this was because of some incidences of the capture of very small fish. Results of this study, however, indicate that the mesh size of nettings used for “siklob” is 4.35 cm, which is above the minimum set by the national law (3 cm). The gear is operated offshore, in a fishing vessel, with lights and fish-finding devices. The catch included an array of pelagic to benthic species, with Sardinella gibbosa (Bleeker, 1849) as the top species. The catch per unit effort values for two fishing operations were 17.40 kg.cast-1 and 16.5 kg.cast-1, respectively. If a management plan for the gear is to be implemented in the area, it would be necessary first to study the spawning seasons of commercially important species and impose closed fishing seasons. Before any attempt to ban or control the use of the gear, it is necessary first to understand the gear design, performance, and selectivity.

Aquatic bioresources of artificial water bodies in Republic of Mordovia (case of Turgenev Reservoir)

On the territory of the Republic of Mordovia there are found more than 220 multi-purpose ponds and water reservoirs built on the watercourses. The Turgenev Reservoir on the Alatyr River is a typical channel artificial reservoir. The results of comprehensive fisheries research for the period of 2009–2015 are presented. Analysis of the fod der base showed a significant underutilization of zoobenthos and phytoplankton. Using the average indicators of the fodder base over the above period, the production capacity of the reservoir fodder base was calculated, which amounted to 39.69 tons or 405 kg/ha. According to the results of research fishing with fry seine, the ichthyomass of small fish species and juveniles under the age of two years is estimated by years at the level of 8 tons or 73–91 kg/ha. According to the results of net catches, the ichthyomass of the commercial fish fauna is at the level of 6.3 t or 64 kg/ha; the total ichthyomass is 146 kg/ha. The possible catch of mainly small fish in the Turgenev Reservoir can make 5–7 tons, and in total in the Republic of Mordovia in the multi-purpose water reservoirs - about 260 tons. Due to the reconstruction of ichthyofauna at the expense of a free food base, reproduction, fish- and water protecting measures the catches of marketable fish in ponds and water bodies of Mordovia can reach 1000 tons. The artificial reservoirs of the republic have a significant regulated potential of the aquatic biological resources for the low-water regions of Central Russia both providing the population with freshwater fish and creating the conditions for active and useful recreation on the territory near the water reservoirs: developing facilities for sport and amateur fishing and tourism.

Hydraulic flow rate increase maneuver for ichthyofauna repulsion in bulb-type generating units – Jirau Hydroelectric Power Plant

Several repulsion systems have been developed to minimize the confinement of ichthyofauna in draft tubes. In this perspective, this study intends to analyze the efficiency of the hydraulic flow rate increase maneuver, using a hydroacoustic system for real-time monitoring of the movement of the ichthyofauna confined within the draft tube of the generating units of Jirau Hydroelectric Power Plant. It is located on the Madeira River, in Rondônia, Brazil. We analyzed footage of 105 machine shutdowns taken between 2019 and 2020 at Jirau Hydroelectric Power Plant that used the hydraulic flow rate increase maneuver as a strategy to repulse ichthyofauna. Also, the footage of 7 two-stage shutdowns in the year 2020 was analyzed, the first stage without the maneuver and the second with the maneuver. The follow-up of 105 shutdowns demonstrate that approximately 85% of the footage showed little or no movement of ichthyofauna in the draft tube, with images of movements showing patterns characteristic of small fish (~97%). Furthermore, the quantitative evaluation of the two-stage maneuver indicated a reduction of approximately 91% in the movement of ichthyofauna after the hydraulic flow rate increase maneuver. Thus, the increase in the rate of the hydraulic flow procedure, developed by Jirau Energia, proved to be an innovative and efficient strategy in reducing extensive social and environmental impacts and in favoring positive economic impacts.

Struktur, Perilaku dan Kinerja Pemasaran Ikan Cakalang di Kabupaten Halmahera Selatan

Skipjack tuna is the result of the main capture fisheries in the South Halmahera district which experienced significant growth of 4,2 percent during the 2016-2018 period, but increased production experienced constraints in the marketing system and caused income uncertainty for fishermen and traders. The purpose of this study was to determine the marketing system of skipjack tuna in the South Halmahera Regency using a structural, behavioural, and performance (SCP) approach. The sampling method uses snowball sampling which started with 68 fishermen. The results showed that the market structure formed was an oligopsonistic market structure and there was a barrier to market entry of 14 percent. Meanwhile, market behaviour shows that fishermen only act as price takers. Based on the marketing margin analysis, there are 10 (ten) skipjack fish marketing channels. Judging from the value of large skipjack fish, marketing channel 7 has the highest margin value of 70,4 percent and the lowest is channel 8 of 53,9 percent. Meanwhile, the marketing channel of small fish the highest margin value is marketing channel 9 of 73,9 and the lowest is channel 9 of 65,1 percent. While the value of farmer share, channel 1 has the highest value of 70 percent and the lowest is channel 7 of 36 percent. Overall, skipjack tuna marketing channels have not been efficient.

An experimental evaluation of the effect of escape gaps on the quantity, diversity, and size of fish caught in traps in Montserrat

Coral reef fisheries are vital to the livelihoods of millions of people worldwide but are challenging to manage due to the high diversity of fish species that are harvested and the multiple types of fishing gear that are used. Fish traps are a commonly used gear in reef fisheries in the Caribbean and other regions, but they have poor selectivity and frequently capture juvenile fish, impacting the sustainability of the fishery. One option for managing trap fisheries is the addition of escape gaps, which allow small fish to escape. We compared catches of traps with and without two 2.5 cm (1 inch) escape gaps on the Caribbean island of Montserrat. No significant differences were found in the mean fish length, total fish biomass, number of fish, fish species richness, and Shannon diversity index between hauls of the two trap designs, though traps with escape gaps did catch larger proportions of wider-bodied fish and smaller proportions of narrow-bodied fish. Furthermore, traps with gaps caught a smaller proportion of small-sized fish and fewer immature fish (though differences were not statistically significant). Linear mixed effect models predict that soak time (the length of time between trap hauls) increases the mean catch length, total catch biomass and total number of species in the catch. The relatively modest evidence for the effect of the gaps on catch may be explained by the long soak times used, which could have allowed most smaller-sized fish to escape or be consumed by larger individuals before hauling in both traps with and without escape gaps. Despite the small differences detected in this study, escape gaps may still offer one of the best options for improving sustainability of catches from fish traps, but larger escape gaps should be tested with varying soak times to determine optimum escape gap size.

Determination of arsenic, cadmium, selenium, zinc and other trace elements in Bangladeshi fish and arsenic speciation study of Hilsa fish flesh and eggs: Implications for dietary intake

Exposure to As from drinking water and its impact on the health of the Bangladeshi population has received much attention. However, very little information is available regarding As exposure through consumption of fish, which is the main source of animal protein for the majority of Bangladeshis. In this study, concentrations of As, Cd, Pb, Mn Se and Zn in different types of fish, consumed by Bangladeshis, were determined using Inductively Coupled Plasma Mass Spectrometry. Daily intakes of the toxic elements As, Cd and Pb through fish consumption were estimated to be 31.8, 0.4 and 4.8 μg/day, respectively. Hilsa (Tenualosa ilisha) contained the highest concentrations of total As (mean ± SD was 2.55 ± 1.3 mg/kg; n = 15) among the fish analysed. However, toxic inorganic As species were not detected. The dominant As species in Hilsa fish were: dimethylarsenic acid, arsenobetaine and arsenosugars, at 69, 11 and 20% of total As, respectively. The high concentration of Cd detected in Hilsa eggs (average 278 ± 518 μg/kg; range 7.4–1725 μg/kg; n = 10) is of concern since this may have harmful effects on the development of embryos and lead to a decline in the Hilsa population or the quality of the fish. It can also be harmful to those who consume Hilsa eggs on a regular basis. Selenium was found to be highest in Shoal (Micropterus cataractae) fish and a type of small fish, and lowest in Mrigal (Cirrhinus cirrhosis). Small fish species contained Mn and Zn at 7.1- and 4.3-fold higher concentrations, respectively, compared to big fish species. Keski (Corica soborna), a small fish species, contained by far the highest concentrations of Mn (52 mg/kg) and Zn (140 mg/kg), although the concentration of As (1.4 mg/kg) in this fish was lower than that of several other fish species. Small fish species are often consumed whole, including the bones, and therefore the essential trace elements present are potentially bioavailable for cellular metabolism. Our study shows that the Bangladeshi population can easily meet their daily requirement of Se and Zn from consumption of fish such as Shoal fish (Se and Zn), Hilsa fish (Se and Zn) and Keski fish (Se and Zn). Consumption of small fish (such as Keski) and big fish (such as Hilsa) from Bangladesh can provide valuable sources of essential trace elements as part of a balanced diet and thus negate the need for supplements and biofortification of certain foods. Ours is a small study and a detailed total dietary intake and human biomonitoring studies, that includes coverage of different socio-economic groups, are needed in Bangladesh before giving people supplements or biofortified foods.

Controlling effort, catch and biomass in models of the global marine fisheries

The starting point is the reduced model of global marine fisheries designated by W-3. The main variables of an ordinary differential equation are: the stock of bioresource, its net natural increase, as well as the catch value, which linearly depends on exogenous effort and nonlinearly on available biomass. In W-4, the effort became endogenous as a result of its positive feedback from biomass. In both models, there are values of control parameters in the catch equations, in which the value of the latter can be maintained for a long time at the maximum stable level, with the exception of transition sections. The principle of necessary precaution is fulfilled for small fish stocks more reliably in W-4 than in W-3, thanks to the transformation of the saddle into an unstable node with a common stable node. For these one-dimensional models, the author proposed an original generalization - the R-1 model of two nonlinear ordinary differential equations. In the latter effort, a new phase variable appears, subordinated to proportional control and derivative regulation. Biomass serves as a “prey”, and the effort appears as a “predator”. For two key control parameters, areas of change were identified for which the target stationary state is a locally asymptotically stable node or focus in R-1. A policy has been proposed for the restoration of depleted fish stocks and a transition to a long-term maximum sustainable harvest has been determined. Optimization over a wide time frame (from 40 to 400 years) allows us to calculate the values of the selected control parameters for which the integral catch volume in R-1 is higher than in W-4 for the same initial values of stock, effort and catch. Social constraints from below on the magnitude of the effort, as well as the desired nature of the transition to the target stationary state, are taken into account. The danger of biomass collapse is overcome, unlike previous models.

Pulsed supplies of small fish facilitate short-term intraguild predation in salmon stocked streams

Pulsed supplies of prey organisms generally increase predator food intake. However, whether this holds true when predators and pulsed prey are in same guild (i.e., intraguild [IG] predators and prey) is unclear. IG prey may increase IG-predator food intake by providing a food source, but they may decrease food intake through competition. To test these hypotheses, we compared the food intake of white-spotted charr (Salvelinus leucomaenis) (IG predator) in streams that were stocked or unstocked with hatchery-reared masu salmon (Oncorhynchus masou) fry (IG prey) in streams in Hokkaido, Japan. One day after stocking, masu salmon fry occupied nearly 60% of the stomach contents by wet weight of white-spotted charr in stocked streams, and mean stomach content weight was six-times higher than in unstocked streams. However, predation of white-spotted charr on stocked fry was rare on other days. Acquisition of predator-avoidance behavior by stocked fry and/or a lack of accommodation by white-spotted charr to the sudden emergence of a new prey source (e.g., the charr in study sites were basically insectivorous, and their foraging behavior might have been ineffective for piscivory) may explain this time-limited intraguild predation. In days other than the first day post-stocking, food intake by white-spotted charr did not differ between stocked and unstocked streams. No effects of interspecific competition on white-spotted charr food intake were observed; this may be due to the body-size advantage of white-spotted charr and/or the low density of stocked masu-salmon fry.