Takafumi Arimoto

The condition of fish escaping from fishing gears-a review

The capture of immature fish in many commercial fisheries is controlled by restricting the use of fishing gears or elements of fishing gears that prevent the escape of immature fish. Improving the selective characteristics of fishing gear is based on the assumption that fish escaping are not seriously damaged and able to make a complete recovery. If fish escape and die as a direct result of stress and injuries or indirectly due to disease and predation associated with gear damage, then increasing the opportunity for escape by improving selectivity may result in an increased level of unaccounted fishing mortality. This paper identifies the main fishing gear types used for harvesting marine and freshwater fish, a range of injuries, stress reactions and mortalities that can occur during capture and escape. It is concluded that immediate and delayed mortalities can occur in fish escaping from fishing gears and that the high variation in mortality rates within experiments is associated with a lack of information on how fish condition is affected by various fishing stressors and the type and severity of physical damage received. Improving selectivity without reducing damage or stress incurred during capture and escape may not be the most appropriate way of protecting immature fish.

Development of a catch mortality model

Abstract The discarding of non-target species and sizes of fish by commercial fishing vessels is a common practice in many fisheries around the world. Efforts to reduce discarding in North Sea fisheries were initiated over 100 years ago, and were the precursor to development of mesh-selectivity research for many European countries. In most cases mechanical selection through fishing gear modifications has been carried out without research into the survival of fish after escape. In recent years, research into fish mortality after escape has shown that mortalities vary by gear type and species, may be immediate or delayed, and may be due to injuries or stressors associated with capture—escape trauma. Based on this information, a general model of fishing mortality has been developed. Measuring the level of catch, discards and escape mortality associated with each gear type may be one index for assessing the conservation aspects of fishing gears, and may lead to more realistic estimates of induced fishing mortality.

A comparison of the stress response and mortality of sea bream Pagrus major captured by hook and line and trammel net

Abstract Fisheries management policy to increase escapement of non-target species and sizes of fish from fishing gears is generally based on the assumption that injury and stress received during the capture-escape process do not result in a significant level of mortality after escape. However, there has been little research to validate this assumption. To investigate the stress response and mortality associated with capture-escape trauma, a series of comparative experiments were carried out using red sea bream Pagrus major captured by hook and line and trammel net. Cortisol levels in fish captured by hook and line were measured as an index of the stress associated with capture duration using commercially available plasma Cortisol RIA kits. Plasma cortisol levels of resting fish (12.21 ng ml−1, n = 12) were significantly lower than those for all fish captured. In hook and line caught fish, stress increased as capture duration was increased from 10 min to 3 h. Stress levels for capture periods of 6, 9, 12 and 18 h were lower than those for 1 and 3 h but above 10 min capture time and resting values. Fish behaviour during capture included initial flight response, successive struggles of decreasing magnitude, reverse swimming and finning to maintain position. Struggle activity reduced as time of capture increased. No mortalities occurred during capture or 38 days of post release monitoring. On the other hand, stress levels of fish after 10 min, 1.5, 3, 6, 9, 12 and 18 h captured by trammel net were significantly higher than resting fish and continued to rise with capture duration. Forty four percent of all fish captured by trammel net died, of which 28% occurred in the net in fish whose gill cover was held closed by the small mesh netting. Five percent of the fish died within 48 h post release and 11% were delayed mortalities between 8–18 days post release in fish with severe open wounds. No mortalities occurred between 19–38 days post release. We suggest that hook and line caught fish are able to exhibit an adaptive response to capture, in which a cessation of struggling resulted in the captured fish regaining their normal swimming position and allowed the fish to recover from struggling which reduces the probability of mortality. Adaptive behaviour was not possible in fish caught by trammel net in which the degree of entanglement remained constant or increased with capture duration. Ceasing or continuing to struggle did not reduce the degree of entanglement or reduce the constriction of netting around the fish body and gills. These results show that fish stress during capture may vary by gear type and that mortalities may be immediate or delayed after release from the fishing gear. Stress and injury incurred during encounter and subsequent escape may result in an unaccounted level of fishing mortality.

Fish stress become visible: a new attempt to use biosensor for real-time monitoring fish stress.

To avoid fish mortality and improve productivity, the physiological conditions including stress state of the cultured fish must be monitored. As an important indicator of stress, glucose concentrations are monitored using in vitro blood analysis. The physiological processes of fish under environmental conditions are harsher in many ways than those experienced by terrestrial animals. Moreover, the process of anaesthetizing and capturing the fish prior to analysis may produce inaccurate results. To solve these problems, we developed wireless biosensor system to monitor the physiological condition of fish. This system enables artificial stress-free and non-lethal analysis, and allows for reliable real-time monitoring of fish stress. The biosensor comprised Pt-Ir wire as the working electrode and Ag/AgCl paste as the reference electrode. Glucose oxidase was immobilized on the working electrode using glutaraldehyde. We used the eyeball interstitial sclera fluid (EISF) as the in vivo implantation site of the sensor, which component concentration correlates well with that of blood component concentration. In the present study, we investigated stress due to alterations in water chemistry, including dissolved oxygen, pH, and ammonia-nitrogen compounds. Stress perceived from behavioural interactions, including attacking behaviour and visual irritation, was also monitored. Water chemistry alterations induced increases in the glucose concentration (stress) that decreased with removal of the stimulus. For behavioural interactions, stress levels change with avoidance, sensory behaviour and activity. We believe that the proposed biosensor system could be useful for rapid, reliable, and convenient analysis of the fish physiological condition and accurately reflects the stress experienced by fish.

Design and concept of a Biointeractive Autonomous Underwater Vehicle “BA-1”

To keep the precious protein source, it is thus extremely important to conserve the biodiversity of the ocean and at the same time to make use of its limited space as much as possible without doing any environmental harm. With this broad objective in mind, Tokyo University of Marine Science and Technology (TUMSAT) and Mitsui Engineering & Shipbuilding Co., Ltd. have started a research and development project, “Pen-free Offshore Aquaculture System using Biointeractive Autonomous Underwater Vehicles.” This project is part of a more comprehensive project, “Marine Biotechnology Innovation,” which has been funded by the Japanese government since 2007. In this paper, we propose a concept of a biointeractive AUV that monitors and takes care of schools of fish just like a sheep dog in a ranch. In a future plan of this system, multiple biointeractive AUVs monitor the environment spatially and accurately, feed the fish, monitor the growth of the fish, guide them, and report the data through satellite to the land while charging their batteries by docking with buoys. A first model of the biointeractive AUV “BA-1” has launched in early 2009. The design of the biointeractive AUV “BA-1” is described in this paper. The basic test result of the interaction system for fish is also described briefly.

Visual acuity of Pacific Saury Cololabis saira for understanding capture process

To understand the mechanism of the behavioral response in the capture process of how fish recognize fishing gear and then how they can avoid the gear, the visual acuity of Pacific saury Cololabis saira was investigated by histological examination of the retina of individuals in the size range of 75–365 mm fork length (FL). The contour map of cone density distribution shows that the highest cone density is located in the temporal area of the retina, which indicated the visual axis as the forward direction. The visual acuity (VA) depends both on the focal length of the lens and the number of cones in the retina. The lens diameter increased linearly from 1.40 to 4.73 mm with fish growth, while the cone density decreased gradually from 765 to 378 cells/0.01 mm2. Our results show that the visual acuity increases proportionately from 0.057 to 0.140 for individuals ranging in FL from 75 to 365 mm as expressed by the equation VA=0.0065×FL0.5271 (r2=0.9624).

A case study of life cycle impacts of small-scale fishing techniques in Thailand

Abstract Fish provides an important source of protein, especially in developing countries, and the amounts of fish consumed are increasing worldwide (mostly from aquaculture). More than half of all marine fish are caught by small-scale fishery operations. However, no life cycle assessment (LCA) of small-scale fisheries and no LCA of marine fishery operations in Asia (Thailand) exists today. We perform LCAs to compare the impacts of three different fishing techniques: crab gill-nets, squid traps, and fish traps. Primary data sourced from four different fishers were used. We distinguished the life cycle inventories for three different seasons (northeast monsoon, southwest monsoon and pre-monsoon), since the time spent on the water and catch varied significantly between the seasons. Our results showed the largest impacts from artisanal fishing operations affect climate change, human toxicity, and fossil and metal depletion. Our results are, in terms of global warming potential, comparable with other artisanal fisheries. Between different fishing operations, impacts vary between a factor of 2 (for land transformation impacts) and up to a factor of more than 20 (fossil fuel depletion and marine eutrophication). This shows that the way in which operations are performed have a very strong influence on results. Seasonality plays a relevant role for the assessment. Our results highlight that it is important to account for seasonal aspects in LCAs. We encourage a continual effort for collecting and modeling inventory processes, as well as making them available, in order to guarantee that LCA studies outside of Europe can be performed more easily.

Laboratory study on the behavioral patterns of Japanese common squid Todarodes pacificus under light and dark conditions

1National Research Institute of Fisheries Engineering, Fisheries Research Agency, Kamisu, Ibaraki 3140408, 2Graduate Course of Applied Marine Bioscience, Tokyo University of Marine Science and Technology, Minato, Tokyo 1088477, 3Division of Marine Bioresource and Environmental Science, Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido 0418611, 4Department of Marine Biosciences, Graduate School of Marine Science and Technology, Tokyo University of Marine Science and Technology, Minato, Tokyo 1088477, Japan

Development of retinal structure and visual acuity in Japanese flounder (Paralichthys olivaceus)

The retinal structure and visual acuity in Japanese flounderParalichthys olivaceus at different stages of development were examined by light microscopy. The resolving power of the retina, the visual axis and the best visual field were estimated based on the distribution of cone cells in the retina. The visual system of the larvae appears poorly developed at hatching. The larvae with total length (TL) of less than 10 mm, have single cones only and the eyes were well pigmented. At 10–11 mm TL, most single cones fused to form double cones, with the single and double cones forming a mosaic pattern. From larvae to early juvenile the retina stretches, the cones increase in diameter and rods increase in number. Based on the highest density of the cones in the ventro-temporal region, the visual axis was orientated upforward. The resolving power of the retina in 40–530 mm TL Japanese flounder was found to range from 25.1 to 11.5 min. The results indicated continual improvements in the visual system of the growing fish towards higher resolving power, visual acuity and sensitivity.