Behavioural response of farmed Atlantic salmon (Salmo salar L.) to artificial underwater lights: Wavelet analysis of acoustic telemetry data

Biological, environmental, economic and ethical issues become increasingly pertinent as the scale of the aquaculture industry expands. This study used acoustic telemetry data and wavelet analysis to investigate behavioural patterns of Atlantic salmon when exposed to artificial underwater lights in fully stocked production cages located on the Norwegian coast. Using acoustic depth sensor tags, time series of depth registrations were gathered from 21 individual salmon distributed over three cages during a five-month experimental period. Underwater lights, normally used to suppress pre-harvest sexual maturation amongst Atlantic salmon, were installed at eight-metre depth and switched on in the middle of the experimental period. Swimming depth registrations initially showed a typical diurnal swimming behaviour, manifested by registrations generally in deeper waters during day-time than during night-time. The diurnal swimming behaviour abruptly ceased after the onset of lights. The change in swimming behaviour was detected by wavelet analysis and coincided with the introduction of underwater lights. Results from this study demonstrate the utility of wavelet analysis as a timely surveillance tool when investigating behavioural patterns of a periodic nature in fish, and specifically the individual response of farmed salmon to artificial lighting in a genuine industrial setting.     

Biomonitoring using tagged sentinel fish and acoustic telemetry in commercial salmon aquaculture: A feasibility study

We tested if it is technically feasible to monitor fish in real-time in full-scale commercial fish farms using acoustic telemetry. 31 Atlantic salmon were equipped with acoustic transmitter tags containing depth sensors. Tagged fish were monitored for three months in two industrial scale sea-cages containing 180000 and 150000 fish, respectively. Each cage was fitted with two prototype acoustic receiver units designed to collect, interpret and store the information transmitted by the acoustic transmitter tags. Ten in each cage were also equipped with Data Storage Tags (DSTs) containing depth sensors to record individual-based datasets for comparison with the acoustically transmitted datasets. After compensation for sample loss caused by expected acoustic interference between the transmitter tags, the resulting dataset revealed that the receiver units collected 90–95% of the signals in both cages. Acoustic communication conditions in the sea-cages were not strongly impaired by factors such as fish density and local noise. Further, the dataset from the acoustic transmitters had comparable resolution and quality to that produced by the DSTs. However, acoustic tags provide data in real time and enable farmers to respond to the received information with farm management measures, whereas archival tags such as DSTs need to be retrieved and downloaded and hence have no real-time applications. We conclude that acoustic telemetry is feasible as a method to monitor the depth of fish in real-time commercial aquaculture.     

A case study of biofilter activation and microbial nitrification in a marine recirculation aquaculture system for rearing Atlantic salmon (Salmo salar L.)

Marine recirculation aquaculture system (RAS) is a prominent technology within fish farming. However, the nitrifying bacteria in the biofilter have low growth rates, which can make the biofilter activation a long and delicate process with periods of low nitrification rates and variations in water quality. More knowledge on the microbial development in biofilters is therefore needed in order to understand the rearing conditions that favour optimal activation of the biofilters. In this case study, we investigated the activation of two biofilters in a marine RAS for Atlantic salmon post‐smolt associated with either high or low stocking densities of fish by monitoring the microbial communities and chemical composition. The results showed that the microbial communities in both biofilters were similar during the first rearing cycle, despite variations in the water quality. Nitrifying bacteria were established in both biofilters; however, the biofilter associated with low stocking density had the highest relative abundance of ammonia‐oxidizing Nitrosococcus (1.0%) and nitrite‐oxidizing Nitrospira (2.1%) at the end of the first rearing cycle, while the relative abundance of ammonia‐oxidizing Nitrosomonas (2.3%–2.9%) was similar in both biofilters. Our study showed that low fish stocking density during the first rearing cycle provided low and steady concentrations of ammonium, nitrite and organic load, which can stimulate rapid development of a nitrifying population in new marine RAS biofilters.     

Spatial and temporal variations of sediment quality in and around fish cage farms: A case study of aquaculture in the Seto Inland Sea, Japan

ABSTRACT: Fish cage farming generates large amounts of organic waste in the form of unconsumed feed and fecal matter, resulting in sediment deterioration and a threat to its own sustainability. Field studies analysed the scale of the impact of fish cage farming on sediment quality, variability of impact and spread of sediment enrichment in the vicinity of a fish farm. Two fish culture sites near the Fukuyama area of the Seto Inland Sea of Japan were chosen for the study. There was a significant difference between the quality of the sediment in aquaculture and non-aquaculture areas. The sediment underlying the fish cage farms was found to be extremely reducing, acidic and sulfidic. Sediment ignition loss did not vary markedly with the season. However, the redox potential and acid volatile sulfide content of aquaculture areas did show some seasonal variation. Sediment encircling a 165 m radius from the center of a farm in Yokota was judged as organically enriched by fish farming. A variation in sediment quality within the two sites and also within the stations was observed. Based on sediment quality, the stations could be categorized as less affected, highly affected or moderately affected.     

Critically examining the knowledge base required to mechanistically project climate impacts: A case study of Europe's fish and shellfish

An amalgam of empirical data from laboratory and field studies is needed to build robust, theoretical models of climate impacts that can provide science‐based advice for sustainable management of fish and shellfish resources. Using a semi‐systematic literature review, Gap Analysis and multilevel meta‐analysis, we assessed the status of empirical knowledge on the direct effects of climate change on 37 high‐value species targeted by European fisheries and aquaculture sectors operating in marine and freshwater regions. Knowledge on potential climate change‐related drivers (single or combined) on several responses (vital rates) across four categories (exploitation sector, region, life stage, species), was considerably unbalanced as well as biased, including a low number of studies (a) examining the interaction of abiotic factors, (b) offering opportunities to assess local adaptation, (c) targeting lower‐value species. The meta‐analysis revealed that projected warming would increase mean growth rates in fish and mollusks and significantly elevate metabolic rates in fish. Decreased levels of dissolved oxygen depressed rates of growth and metabolism across coherent species groups (e.g., small pelagics, etc.) while expected declines in pH reduced growth in most species groups and increased mortality in bivalves. The meta‐analytical results were influenced by the study design and moderators (e.g., life stage, season). Although meta‐analytic tools have become increasingly popular, when performed on the limited available data, these analyses cannot grasp relevant population effects, even in species with a long history of study. We recommend actions to overcome these shortcomings and improve mechanistic (cause‐and‐effect) projections of climate impacts on fish and shellfish.     

A case study: Impacts of deviating from model research design to the commercial industry for split-pond aquaculture

A case study is presented to compare the results of design and management including circulation and dissolved oxygen management at a modified split-pond facility in west-central Alabama to the recommended design. Modifications included: the use of and a propeller pump instead of a slow-moving paddlewheel, lack of baffle in the waste cells, waste cell to fish cell ratio size, and improperly positioned aerators and DO sensing probes.Over a three year time period, the modified split-pond facility had net yields of hybrid catfish (Ictalurus punctatus ♀ x I. furcatus ♂) that reached up to 11,416 kg/ha/year; however, this includes several reports of fish kills. The present study experienced a minimum 15% reduction in net production compared to the recommended design values with a maximum potential loss of 54%. Ponds used an axial pump to transfer water between a 6:1 ratio of waste treatment area to fish grow-out area. Water flowed from the fish cell to the waste cell at a rate of 31.2 m³/min and from the waste cell back to the fish cell at a rate of 0.78 m³/min. Aerators used 5619–7492 kW-hr/ha which is more than the electrical use in traditional ponds (2238 kW-hr/ha). Even with the extra aeration, this study had at least one fish cell and one waste cell drop below a dissolved oxygen concentration of 2.5 mg/L. These specific modifications may lead to poor survival and production in split-pond aquaculture and are discussed with best management practices of the recommended design.     

Operational performance in aquaculture: A case study of the manual harvesting of cultivated mussels

Aquaculture is one of the fastest growing food production sectors in recent decades. Such rapid development emphasizes the need to adopt more efficient production strategies while simultaneously increasing productivity and sustainability. Monitoring of production is an important strategy to achieve process efficiency. Therefore, we conducted a time and motion study using operational performance indicators to evaluate mussel harvesting on a commercial marine farm in Southern Brazil. We analyzed the operations of mussel sea withdrawal and disaggregation, which are widely used by local farmers but demanding for workers to perform. Mussel sea withdrawal and disaggregation had standard times of 133.7 and 266.7 s, respectively, for one mussel rope; operational production capacities of 0.16 and 0.08 kg s⁻¹, respectively; operational efficiencies of 100 and 31.6%, respectively; time efficiencies of 56.1 and 34.7%, respectively, rework percentages of 0 and 65%, respectively; and percentages of damaged products of 0 and 3.4%, respectively. These parameters indicate low operational performance. The approach used in this study also allowed us to identify process wastes and propose ways to eliminate or mitigate them, with the aim of adopting more efficient work methods.     

How are the salmon lice (Lepeophtheirus salmonis Krøyer, 1837) in Atlantic salmon farming affected by different control efforts: A case study of an intensive production area with coordinated production cycles and changing delousing practices in 2013–2018

The aims of the present study were to describe the salmon lice (Lepeophtheirus salmonis Krøyer, 1837) situation in an intensive salmon production area in mid‐Norway and to consider implications of changing practices of how salmon lice infestation can be controlled. The results in this study suggest that there are steps that can be carried out to keep salmon lice under control even during years when the temperature facilitates a quick salmon lice development. The present work indicates that the use of cleaner fish can delay the time it takes adult female lice to reach 0.1 per salmon in the beginning of a production cycle. It suggests that the timing of cleaner fish deployment into salmon cages can influence its effectiveness in controlling salmon lice. It also gives caution to letting salmon lice develop unchecked, even at levels far below the current lice limit, because of the difficulties to control salmon lice when the external infection pressure is too high. This study took place during a rapid change in delousing methods, in an area with coordinated salmon production. Despite its exploratory nature, this study offers insights into the salmon lice fluctuations in relation to efforts aimed at controlling it.     

基于长度贝叶斯生物量法估算北部湾二长棘鲷种群参数

渔业数据缺乏是渔业资源评估和管理面临的难题。以2006—2018年北部湾二长棘鲷体长频率数据为例,运用基于长度频率的贝叶斯生物量方法 (LBB),估算二长棘鲷的渐近体长(L_∞)、最适开捕体长(L_copt)、相对自然死亡率(M/k)和相对捕捞死亡率(F/k)等种群参数。结果发现,2006—2018年间北部湾二长棘鲷的渐近体长平均为21.0 cm,最适开捕体长平均为12.6 cm,相对死亡率M/k、F/k、Z/k和开发率E分别为1.49、3.65、5.15和0.67。二长棘鲷的开捕体长和渐近体长的变化趋势一致,均呈下降趋势,且其生长速度有加快趋势。基于LBB估算的最适开捕体长和开发率与运用独立评估模型估算的结果基本一致。如果长度频率能代表资源开发阶段的长度组成,使用LBB估算的结果将较好地反映其真实情况。基于LBB的研究方法可为渔业数据缺乏情况下进行渔业资源评估提供借鉴。