It has been speculated that some deep-sea fishes can display large vertical migrations and likely doing so to explore the full suite of benthopelagic food resources, especially the pelagic organisms of the deep scattering layer (DSL). This would help explain the success of fishes residing at seamounts and the increased biodiversity found in these features of the open ocean. We combined active plus passive acoustic telemetry of blackspot seabream with in situ environmental and biological (backscattering) data collection at a seamount to verify if its behaviour is dominated by vertical movements as a response to temporal changes in environmental conditions and pelagic prey availability. We found that seabream extensively migrate up and down the water column, that these patterns are cyclic both in short-term (tidal, diel) as well as long-term (seasonal) scales, and that they partially match the availability of potential DSL prey components. Furthermore, the emerging pattern points to a more complex spatial behaviour than previously anticipated, suggesting a seasonal switch in the diel behaviour mode (benthic vs. pelagic) of seabream, which may reflect an adaptation to differences in prey availability. This study is the first to document the fine scale three-dimensional behaviour of a deep-sea fish residing at seamounts.
. 1998. Effects of trawl sampling variability on precision of acoustic abundance estimates of gadoids from the Barents Sea and the Gulf of Alaska. -ICES Journal of Marine Science, 55: 86-94.The quality of acoustic estimates of fish abundance is dependent on the quality of the biological information that provides the basis for determining target size, species composition and acoustic target strength distribution. Information on biological characteristics of acoustic targets is usually obtained from trawl samples. In this paper we analyse the effects of trawl sampling variability on estimates of gadoid stock abundance in two areas where behavioural characeristics of the target species differ. The analyses demonstrate the sensitivity of abundance estimates to trawl sampling. Improved procedures for allocation of trawl sample information to acoustic survey results are discussed.1998 International Council for the Exploration of the Sea
Totland, A., Johansen, G. O., Godø, O. R., Ona, E., and Torkelsen, T. 2009. Quantifying and reducing the surface blind zone and the seabed dead zone using new technology. – ICES Journal of Marine Science, 66: 1370–1376. The surface blind zone and the seabed dead zone are unobservable with hull-mounted acoustic systems. These constraints may seriously limit the effectiveness of acoustic observations in studies of ecosystem dynamics. In this paper, new technologies are used to make observations in these boundary zones, by augmenting conventional acoustic observations from transducers mounted in a retractable keel with simultaneous observations from two autonomous acoustic systems, one sampling the surface blind zone and the other the seabed dead zone. These observations to some extent overlap in depth, which allows comparisons between data collected with the vessel and the corresponding data from the two autonomous systems. The main targets of the investigation were young-of-the-year gadoids in the surface blind zone and older cod at least partly in the seabed dead zone. Species and their sizes were identified from trawl samples. The advantages and limitations of using new autonomous equipment for quantifying the acoustic backscattering within otherwise unobservable zones are discussed. The magnitudes of potential measurement biases in acoustic data collected with the vessel are also estimated for this survey.
Scientists across the globe conduct survey programs to monitor and characterize abundance, population structure, biodiversity and geographical distributions. To assess the state of marine fish and zooplankton, population surveys are often repeated annually using standardized sampling protocols and analysis techniques to establish trustworthy stock status. However, although transparency and repeatability are recognised as important principles of this process, it is often difficult to obtain comprehensive documentation of metadata and data processing steps. This is particularly challenging for workflows that include manual processing steps. StoX was principally built to process research‐vessel survey data, and we have included several standard survey estimation models. The software was developed to be robust and versatile and aimed at the open source community, such that users could easily build their own models. StoX is fully integrated with R to utilize the large number of R‐packages and enable any StoX function and stock estimation model to be controlled using R. There has been a large need for a freely available software for research–vessel survey estimation, and StoX is tested in surveys carried out in four continents and is the official tool for many important fish stock surveys. The basic workflow and transparency principles of StoX, together with a customizable GUI, makes StoX applicable for any geographically coded surveys. Future versions of StoX will include statistical models to estimate the catch composition in commercial fisheries. In fields such as conservation management, there is also a need to document the estimation methods, and additional estimation and analyses models, including biodiversity indices are currently implemented. In parallel, we envision a closer web service integration with existing international and national data centres.
Advancements in technologies have led to a rapid development of unmanned surface vehicles (USV) for marine ecosystem monitoring. The design, size, and scientific payload of the USVs differ as they are built for different purposes. Here, we present the design criteria and detailed technical solutions of a prototype USV which has been built to fulfill the following experimental and operational needs; the USV should be used for inshore and shallow water acoustic monitoring, offshore comparison of echo sounder recordings from the USV and research vessels, monitor natural fish schooling behavior and seabird-fish behavioral interactions. The prototype has been built over a period of 5 years with steadily quality improvements. As the hull is based on an expedition double kayak, the USV is named Kayak Drone, and we aimed at building the Kayak Drone using of-the-shelf hardware and existing open-source software. This allowed for the development of a modular and well-functioning USV at a relatively low cost. The Kayak Drone produces very little noise and in situ experiments show that the Kayak Drone can record echo sounder data of fish near the surface without disturbing their natural distribution and behavior. One in situ study shows that the Kayak Drone could navigate within a couple of meters from swimming puffin and other seabirds without triggering escape. These results demonstrate that the Kayak Drone can be utilized to produce unbiased survey estimates for fish distributed in shallow waters and near the surface, which is very important for many fish stock assessments and managements. Furthermore, it can also be used as a tool to observe the predation by seabirds on fish schools without interfering with their natural interspecific behavior, which traditionally has been very difficult. The use of the Kayak Drone is not restricted to these tasks, and we foresee that the Kayak Drone can be utilized in many different experiments where a silent platform is needed.
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