ROV Navigation in a Fish Cage with Laser-Camera Triangulation

Aquaculture net cage inspection and maintenance is a central issue in fish farming. Inspection using autonomous underwater vehicles is a promising solution. This paper proposes laser-camera triangulation for pose estimation to enable autonomous net following for an autonomous vehicle. The laser triangulation 3D data is experimentally compared to a doppler velocity log (DVL) in an active fish farm. We show that our system is comparable in performance to a DVL for distance and angular pose measurements. Laser triangulation is promising as a short distance ranging sensor for autonomous vehicles at a low cost compared to acoustic sensors.

Low Contribution Of Fishermen’s Wives To Family Income On Seafishing Industrial Sector In Indonesia (A Case Study In Rembang, Central Java, Indonesia)

Majority of the coastal community members in Indonesia still rely their life on fishing. Most of fishermen in the community are small-scale fishers, fishing workers, small-scale fish processors, and small traders. Efforts to obtain a larger income need support from family members. The role of husbands as the heads of family, responsible in earning a living, needs to be supported by their wives. The role of wives is as their husbands’ helpers in acquiring a livelihood as to raise their family income. The objective of this research is to analyze factors influencing women to enter workforce and their contribution to raising their family income. To analyze the case, theories of gender and development, women empowerment, and family economy are needed. This research used quantitative methodology. Its samples consisted of 85 fishermen’s wives from several villages that have active fish processing home industry in Rembang, Central Java. The results of research show that the income contribution of fishermen’s wives to the family income was still low, amounting to 33.13%. Factors influencing the wives to take up work were their education level and their motivation to work, while factors influencing their income were time allotted to work and types of work.

Awareness and adoption levels of improved smoking oven among fish processors in Lagos Lagoon, Nigeria

This paper investigated awareness and adoption levels of improved smoking oven among fish processors in four fishing communities along Lagos Lagoon, Nigeria. Multi-stage sampling procedure was used to select 153 respondents who were engaged in fish smoking. Data collected using structured interview guides were subjected to descriptive and inferential analyses. Results revealed that majority of the respondents were young, married women with average fish smoking experience of 22.6 years. Majority (90.8%) of them were solely engaged in fish smoking while 9.2% combined fish smoking with other income-generating activities. All the processors used traditional smoking oven (drum, box and mud ovens). More than 66.0% of the fish processors were not aware of improved fish smoking equipment. Lack of awareness, inadequate access to the technologies, low relative advantage and lack of maintenance services and high cost of procurement were responsible for low adoption levels of improved smoking oven. Irregular visits of extension agents to the study area had negative impact on the adoption of improved traditional smoking ovens. Proper dissemination of innovations developed on improved fish processing equipment to the active fish processors in Lagos State using available communication channels is hereby advocated.

Who will become dominant? Investigating the roles of individual behaviour, body size, and environmental predictability in brown trout fry hierarchies

This paper presents a study investigating performance of brown trout fry, with different behavioural characteristics, in environments differing in food predictability. Based on previous experimental findings, we hypothesised that more active individuals would be favoured by a predictable environment, as compared to an unpredictable environment, as a consequence of being more aggressive and likely to dominate the best feeding stations. This hypothesis was not supported, as more active individuals instead tended to perform better, in terms of growth and survival, in unpredictable environments. However, this effect may stem from initial size differences, as more active fish also tended to be larger. In predictable environments, no trends between activity (or size) and performance were detected. Dominant individuals could be identified based on lighter body colouration in 9 out of 10 rearing tanks, but dominance appeared not to be related to activity score. The results highlight a potential advantage of more active and/or larger fry in unpredictable environments, while performance in predictable environments is likely depending on other phenotypic characteristics. Our general experimental approach can be useful for further developments in the investigation of performance of different ethotypes of brown trout fry.

Fish movement patterns in a Neotropical free-flowing tributary located downstream from a large dam

In dammed rivers, the conservation of free-flowing tributaries is considered an important strategy to mitigate the negative effects of the dam on fish communities. In this study, we evaluated the importance of a free-flowing tributary of a dammed river as a reproductive migration route. From August 2012 to July 2013, hydroacoustics data were collected alongside active fish sampling using cast nets and ichthyoplankton nets in the São Francisco and Abaeté rivers. Cast net sampling captured 738 individuals and hydroacoustics detected 42196 fishes. In almost all samples and sampling sites, preferential movements to the Abaeté River and the main São Francisco River were observed. The increase in the flow rate of the Abaeté coincided with a greater incidence of fish movements to upstream areas of the tributary. A higher density and proportion of larger fishes, as well as a higher density of ichthyoplankton, were observed in the Abaeté River compared with the main river. Because this tributary is an alternative route for migratory fishes, its protection is essential for fish conservation and therefore maintenance of local fisheries