Tatsuro Matsuoka

A review of ghost fishing: scientific approaches to evaluation and solutions

Research on ghost fishing became active in the late 1980s. Ghost fishing has been confirmed for traps, gillnets, trammel-nets and small seine nets. Some lost traps are functional for a long period of time, even in shallow waters. Consequences for gillnets after loss depend on seabed conditions. The ghost fishing function of gillnets remaining on flat seabeds declines rapidly with decreasing heights and increasing visibility. Gillnets left tangled around an artificial reef, for example, three-dimensionally maintain the initial magnitude of ghost fishing for a long period of time, even after badly fouled. There are increasing numbers of researches working on the total number of mortality per gear after gear loss for gillnets and trammel-nets. It has become also possible to estimate the total number of mortality for a unit period of time in a certain fishing sector. This paper reviews research which has provided evidence and quantitative data on ghost fishing, and proposes five items important for future studies on ghost fishing.

Assessment of pesticide residues in freshwater areas affected by rice paddy effluents in southern Japan.

Pesticide residues in five freshwater areas that are directly affected by rice paddy effluents in southern Japan were measured to determine their maximum concentrations and temporal variations. Water samples were collected every week during the 2005 rice planting season in Kagoshima Prefecture and stations were established in Amori River, Sudo River, Nagaida River (that drains into the bigger Kotsuki River), rice paddy drainage canal, and wastewater reservoir (that collects effluents from rice paddy fields). Of the 14 target pesticides examined, a total of 11 were detected in all stations. Mefenacet, fenobucarb, and flutolanil were the three pesticides with the highest maximum concentrations and were also detected frequently. Analysis of temporal variations of pesticides showed that herbicides had relatively higher concentrations in the earlier stages of the rice planting season, while insecticides and fungicides had relatively higher concentrations at the later stages. There was no significant difference among stations with regards to the temporal patterns of the top three pesticides. The calculated toxic units were less than 1 in all stations, implying low or negligible environmental risk of pesticides detected to freshwater organisms.

Response properties of crayfish antennules to hydrodynamic stimuli: functional differences in the lateral and medial flagella

SUMMARY Antennules have been reported to influence localization of distant food odors, sex discrimination, and agonistic and social behaviors of decapod crustaceans. Although olfaction by the antennules is largely recognized, information on the sensitivity of antennules to hydrodynamic stimuli has been scant. In red swamp crayfish Procambarus clarkii antennules, mechanosensory setae outnumber the chemosensory setae. We studied the mechanosensitivity of crayfish antennules by recording neural activities from isolated antennules in response to sinusoidal dipole stimuli. Both the lateral and the medial flagellum of the antennules responded to hydrodynamic stimuli, although the medial flagellum showed more sensitivity at frequencies higher than 60 Hz. The most dominant setae present on the stimulated site were the simple setal type. Although both lateral and medial flagella are capable of detecting chemical and hydrodynamic cues, results from neural responses, morphological observations and antennular behavior observations indicate that the lateral flagellum of P. clarkii functions as an olfactory organ whereas the medial flagellum complements as a hydrodynamic receptor. It appears that in crayfish antennular sensory processing, crayfish simultaneously use chemical and hydrodynamic information. We have compared our data with the threshold of fish lateral line to the same stimuli and we discuss probable similarities in response properties.

Blue and green fish aggregation devices are more attractive to fish

Abstract To examine the attractiveness of coloured fish aggregation devices (FADs), six sets of four to six FADs of the kite type were deployed in coastal waters and dive observations were carried out for 15 months. The FADs had the same dimensions but different kite colours: white, black, blue, green, yellow and red. Fish abundance and aggregation patterns around the FADs were scored and statistically analysed. Fish tended to be most abundant near the blue and green FADs, least abundant near the black and white FADs, and intermediate near the yellow and red FADs. Aggregations stayed closer to green and blue FADs than to white, yellow, black or red FADs. The more attractive FADs were the less visible ones. Thus, fish were attracted to blue and green FADs on the basis of hue rather than contrast.

Effectiveness of a sugarcane-fish combination as bait in trapping swimming crabs

Abstract Swimming crabs are known to be highly sensitive to saccharides, in response to which they show strong food searching behaviour. This study was done to examine the possibility of using sugarcane as an attractant in basket traps for Portunus pelagicus and Charybdis japonica during their reproductive season. A bait combination of sugarcane and fish was found more effective than fish bait alone, whereas sugarcane alone was ineffective. The use of the sugarcane-fish combination resulted in an extremely male-biased catch of P. pelagicus, one result of which would be the conservation of the population of this crab.

Sound generated by a payao and comparison with auditory sensitivity of jack mackerel Trachurus japonicus

Sound generated by a payao, an anchored bamboo fish aggregating device, is believed to be attractive to fish; but until now, there is no available record of payao-generated sound. This study presents payao-generated sound recorded by a hydrophone at water depths of 5, 10 and 15 m from a fixed distance of 3 m relative to the payao, and compares the sound with the auditory sensitivity of jack mackerel Trachurus japonicus measured at discrete frequencies from 100 to 2000 Hz using the auditory brainstem response protocol. A consistent peak appeared in the sound spectrum at 49 Hz and showed an increasing sound pressure level with depth, which suggests that payao sound may come from the anchor rope. However, the contribution of the bamboo raft can not yet be discounted. The hearing threshold curve indicated that the most sensitive frequency range in jack mackerel is from 92.1 dB at 800 Hz to 111.0 dB at 200 Hz. These results show that the dominant frequency range of payao sound does not correspond with the high sensitivity frequency range of fish hearing.

Sustainability of fishers’ communities in tropical island fisheries from the perspectives of resource use and management: a comparative study of Pohnpei (Micronesia), Mafia (Tanzania), and Guimaras (Philippines)

AbstractThe fisheries structure, fishing gear, fishing vessels and their ownership, landing sites and markets, as well as fisheries management and fishers’ participation were surveyed in three tropical islands: Pohnpei (Micronesia), Mafia (Tanzania), and Guimaras (Philippines), covering 127 fishers. Labour-intensive gear, including purse seines and ring nets, characterised Mafia fisheries. Fibre-reinforced plastic (FRP) boats characterised Pohnpei fisheries, and canoes with nonmarine engines were characteristic of Guimaras fisheries. Wooden plank boats with large crews were only seen in Mafia. From a gear/vessel ownership perspective, the fisher categories present were gear fishers, gear-vessel fishers, employers, and casual labour fishers. Casual labour fishers and employers were only apparent in Mafia. The fisheries in Pohnpei had a relatively early age of entry, which was attributed to the urban markets available and family cohesion, while community organisation-based management of these fisheries was weak. Mafia and rural Guimaras fishers depended on middlemen, due to the distance of the market. Deteriorating subsistence-related fishery dependency means that the Guimaras fishers’ community is at risk. The high shared gear/vessel ownership rates and levels of affiliation to community organisations in Mafia reflect government’s timely community sustainability enhancement initiative. Based on our analyses, we propose the “fishers’ community sustainability” concept. The sustainability of a fisher’s community can be judged on (1) the age of entry to the fisheries, (2) the monetary profits made at fish markets and through marketing, (3) the cohesion among the fishers, and (4) the level of subsistence-related dependency on the fishery. The fishery is key to community sustainability, thus ensuring fishery-dependent life. It is essential to consider the above indicators of fishers’ community sustainability during fisheries development.

.ZETA.-point against Tactile Stimulation and Its Effect to Forward Motion of Fish upon Contact with a Mesh.

触刺激に対するζポイント, ζtが網地に遭遇した魚の前進行動の継続に与える影響を調べるため, 失明させたコイ, ニジマス, ティラピア, ブルーギルを用いた水槽実験を行った。供試種では, 魚体の長さ方向での接触位置により前進後退行動が入れ替わり, ζtポイントの存在を確認できた。ζtポイントの位置は種固有で種間で異なる。網地に遭遇した魚の前進継続率は, 目合い, 縮結によって異なり, ζtポイントに基づく前進後退行動の分岐モデルに基づいて計算した前進継続確率でよく説明できた。刺網の漁獲過程で網地に遭遇した魚が網目に進入する確率は, ζtポイントの位置, 魚体の大きさと形状, 目合いと縮結に影響されると結論した。

Differences in olfactory system between wild and cultured red sea bream, Pagrus major (Teleostei)

A four-month market survey revealed that at some mariculture centers in Japan, over 90% of red sea bream reared in captivity possess a deformed single nasal opening as compared with normal fish with anterior and posterior nasal openings at each olfactory organ. The deformity occurred at day 32-40 after hatching when the medial and lateral epidermal lips failed to form the septum that separates both olfactory nares. The authors also demonstrated that the fish reared in captivity have no problems feeding on pelleted diet but their wild counterparts do not accept non-living food even under a long period of starvation. Differences in olfactory system between wild and cultured fish are discussed especially in reference to the olfactory system and fish behavior.

COMPARISON OF AUDITORY SENSITIVITY OF PELAGIC FISH WITH THE SOUND GENERATED BY A FISH AGGREGATION DEVICE

Anchored bamboo fish-aggregating devices (FADs) are used to catch tuna and small pelagic fish. Several hypotheses had been advanced previously to explain the association of fish with FADs (Castro et al. 2002; Freon & Misund 1999), but the processes responsible for fish attraction and aggregation remain unknown. There is no previous research on fish behaviour related to sound near FADs (Dempster & Tarquet 2004) or actual records of sound from FADs.