Publications (34)27.04 Total impact
- [Show abstract] [Hide abstract] ABSTRACT: Size-selective fishing operation types and skippers’ fishing strategies in operation type combinations were analyzed using fishing data from Thai tuna purse seiners in the Western Indian Ocean during 2005–2007. Catch species and size compositions of tropical tuna, i.e., skipjack, yellowfin and bigeye tunas, were compared among operation types, including free school (FS), fish aggregating device, natural log, and other floating objects operations. FS operation was found to be the most size-selective technique, and caught the fewest small-sized individuals, while the associated operations were less size-selective. Fishing strategy analysis showed that success rates and differences between optimistic and actual values represent economic risk. FS operation holds the highest risk; however, it represents potentially high-revenue fishing because of its ability to catch large-sized individuals and high-priced species. Skipper skills are believed to affect a skipper’s fishing strategy, and specialist and generalist skippers were both identified in this analysis. The specialists achieved high revenue by overcoming the risks of FS operation via their skills, while generalists distributed fishing efforts over operation types to avoid risks. Simulation results suggested that high- and moderate- skilled skippers can shift to FS operations with no revenue decline to respond to the policies of the Tuna Regional Fishery Management Organizations, which increasingly promote FS operation.
- [Show abstract] [Hide abstract] ABSTRACT: A series of purse seine survey fishing was conducted in the Eastern Indian Ocean from 1995 to 2003 by M. V. SEAFDEC in order to assess the degree of selective capture in tropical tuna purse seining around drift fish aggregating devices. A new model of size selectivity of a purse seine net was developed as an analytical tool. The model considered retention probabilities on fish encountering a net. The feasibility of selective capture was evaluated by comparing size distributions of skipjack, yellowfin, and bigeye tunas in the catches and selectivity curves for the three species estimated on the model. Size distributions were affected by the selectivity, and sizes at 50 % selectivity were larger than industrially marketable size. Most catch in the three species were commercial sizes, which were selectively retained; however, large proportions of immature yellowfin and bigeye tunas were included in the catch. The exclusion of immature tunas by size selectivity is difficult in multi-species tuna purse seine fishery for commercial purposes. The size selectivity of a net is insufficient as a tool for tuna resource management in multi-species tuna purse seine fishery. The selective capture by other fishing techniques should be pursued for resource management.
- [Show abstract] [Hide abstract] ABSTRACT: The 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.
- [Show abstract] [Hide abstract] ABSTRACT: In this study, the susceptibility of crustacean antennular mechanosensitivity to a pesticide was examined. We investigated the sensitivity of crayfish Procambarus clarkia Girard antennules to sinusoidal stimuli during a short-term exposure to different concentrations of diazinon. Electrophysiological recordings from the antennules showed that neural activities in the crayfish antennules were still present 2 h after exposure to diazinon, although at decreased rates. In addition, responses to hydrodynamic stimuli indicated that the mechanosensitivity of crayfish antennules was reduced after exposure to concentrations of as low as 0.5 mg/L. The reduction in mechanosensitivity was larger and more rapid in the lateral flagellum than the medial flagellum. Observations from dye experiments showed that ambient water was more readily absorbed at the lateral flagellum than the medial flagellum probably because of differences in the setal structures of the 2 flagella. We discuss the results in relation to the possible immediate sublethal effects of diazinon on the ability of animals to search for and detect chemical and hydrodynamic cues that are important in feeding, mating, and prey/predator detection. Such information is important considering the rapid degradation of diazinon in the natural environment.
- [Show abstract] [Hide abstract] ABSTRACT: 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.
- [Show abstract] [Hide abstract] ABSTRACT: Following the oil spill accident of the Solar I tanker in 2006 off the coast of Guimaras Island in the Philippines, polycyclic aromatic hydrocarbons (PAHs) and alkylated PAHs in some aquatic organisms were investigated at Luzaran in Guimaras and Taklong Islands, which were heavily polluted with spilled oil, immediately and 1 month after the accident. The concentrations of total PAHs were 11.9-52.3 ng/g dry weight in fish. Meanwhile, total PAH concentrations in shellfish were 38.0-3,102 ng/g dry weight in Luzaran and 128-236 ng/g dry weight in Taklong. Pyrene, phenanthrene, and fluoranthene were dominant in most fish and chrysene in all shellfish. Significantly higher concentrations of all alkylated homologs were detected in shellfish than in fish. These differences had two possible causes, that is, the differences between fish and shellfish could be attributed to the uptake routes and/or their metabolizing abilities.
- [Show abstract] [Hide abstract] ABSTRACT: 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.
- [Show abstract] [Hide abstract] ABSTRACT: The effects of pollution on ﬁshing activities were evaluated. Using a prepared questionnaire, ﬁshers, village heads and ﬁshery ofﬁcers in three study sites in Panay Island, Philippines were interviewed. Respondents identiﬁed sources of pollution in their area and described how these affected their ﬁshing activities. Effects of pollution with reference to several indices in capture ﬁsheries, e.g., catch volume, ﬁshing frequency and duration, operation costs, and catch composition, were determined.
- [Show abstract] [Hide abstract] ABSTRACT: The food intake and prey composition of payao-associated Brama orcini were compared with individuals captured in open waters from February to May 2005 in Panay Gulf. An experimental multi-hooked handline was used to catch fish at the two sites. The food items of payao-associated and free-swimming fish in this fishing ground overlap; however, the total frequency of occurrence and abundance of all prey items were both higher in free-swimming fish than in payao-associated individuals. Invertebrates seemed to be preferred by this fish, and the ratio of prey weight to its body weight was significantly higher in unassociated fish than in fish caught near payaos. In open waters, B. orcini feeds predominantly on the sergestid shrimp Acetes sp., but it alters its diet by feeding on the small finfish that also aggregates near the payaos when the fish is associated with the floating structures. These results should be verified since they may be useful in managing the fishery resources aggregating near payao.
- [Show abstract] [Hide abstract] ABSTRACT: 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.
- [Show abstract] [Hide abstract] ABSTRACT: Hydrodynamic static pressures on the body surface of fish generated by conspecifics parallely swimming were measured in a flume tank, and they were compared with those generated by changing the position of two individuals under different flow velocities. Two dead common carp (BL=20 cm), fixed in 20% of formalin, were used. Pressure was measured by a manometer connected to the ends of three aluminum pipes (inner diameter=3 mm), which were inserted perpendicularly to the body axis from right to left in the control fish. The openings of the pipes were located on head, trunk, and caudal regions, and each was on the infraorbital or trunk canal lateral lines. The target fish was moved on the horizontal XY plane using a traverse device. Although pressures changed depending on the regions measured, changes of pressure according to position and current velocity were relatively low in the caudal region. The absolute values of the pressure increased as flow velocity increased, and decreased with an increase in the distance between individuals. Relative positions when the maximum pressure changes were observed at each flow velocity did not change, indicating that pressures were largest when the maximum body width of the conspecific is closest.
- [Show abstract] [Hide abstract] ABSTRACT: 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.
- [Show abstract] [Hide abstract] ABSTRACT: Two small experimental fish aggregation devices (FAD) of the same design were deployed separately from each other on a sandy seabed. One FAD was tangled with a bottom gillnet and the other left intact. Fishes enmeshed on the tangled gillnet and those aggregated around two FADs were monitored for the period of 1,149 days since entanglement of the gillnet. The observable days for enmeshed fish of each species were investigated independently. A model was created according to the binomial distribution based on the probability of observing one enmeshed fish. With this model, the ghost-fishing mortality was estimated from the number of observed fish enmeshed on the tangled gillnet. Mainly crimson sea bream, Evynnis japonica, and threadsail filefish, Stephanolepis cirrhifer, were enmeshed. There was no clear declining trend in ghost fishing during the experimental period. The ghost-fishing mortality per year by the tangled gillnet was estimated as 191 fish. The number of all fish aggregated around the gillnet-tangled FAD was greater than that around the control FAD, however, the numbers of aggregated individuals of the ghost-fished species were not significantly different between the two FADs. It was hypothesized that the lack of a difference was due to ghost-fishing of those fishes aggregated by the gillnet-tangled FAD.
- [Show abstract] [Hide abstract] ABSTRACT: The ghost-fishing ability descending over time and ghost-fishing mortality were quantitatively evaluated for a lost bottom-gillnet. Three experiments were conducted for a maximum period of 1,689 days since deployment of a net. The number of ghost-fishing mortalities per day per net was determined by underwater observation of enmeshed fish on two consecutive days. Mortalities were recorded continuously around the start of experiments and intermittently during the following period. The consistent faunal character around the net was confirmed and the number of mortalities was assumed to reflect the change in the ghost-fishing ability of the net. The decline in ghost-fishing ability over time was represented by a sum of two formulae, which reflect two ghost-fishing factors effective respectively for short and long periods of time. From this analysis, the effective ghost-fishing duration which was defined as the time elapsed to the day when the value of the equation declines to 5 percent of the original fishing ability of the net was 142 days during which the total number of ghost-fishing mortalities was 455 fish. Ghost fishing for red sea bream, Pagrus major and jack, Decapterus sp. occurred in the first short period and for filefish Stephanolepis cirrhifer, over a longer period.
- [Show abstract] [Hide abstract] ABSTRACT: Age and growth of the yellowbelly threadfin bream Nemipterus bathybius in Kagoshima Bay, southern Japan were examined using sectioned otoliths of 1359 fishes collected from April 1998 to November 2000. Monthly changes in marginal growth increments indicated that ring marks (outer edge of opaque zone) were formed once a year between May and August. Assuming a birth date of 1 July from the monthly change of gonadosomatic index, ages ware assigned to every individual according to the number of ring marks. Length-at-age and weight-at-age data were best fitted to the von Bertalanffy among the three growth models. Equations obtained were FLt = 274.7(1 − exp(−0.341(t + 0.762))) for males and FLt = 231.0(1 − exp(−0.161(t + 4.405))) for females, where t is age (year) and FLt is the fork length (mm) at age t, and they were significantly different (i.e. males grew faster than females). Maximum age observed was approximately 8 years for males and approximately 10 years for females.
- [Show abstract] [Hide abstract] ABSTRACT: Sinking motions of tuna longlines at the surface layer, 0-30 m depth, were studied at sea by using depth loggers attached to the bases (main lines) and tips (hooks) of branch lines. Characteristic sinking patterns and changes in sinking velocity were compared between main lines and hooks. Initially, main lines and hooks sank at different velocities; the main lines sank at 7.7 +/- 1.5 cm/s and hooks at 18.7 +/- 3.6 cm/s. There was no significant relationship between the velocities and the duration of the initial sinking. Deceleration for hooks started 36 to 112 s after shooting. Consequently, their sinking velocities became identical to those of the main lines. The sequence of sinking motions of a main line and a hook can be modeled as three stages: independent free fall at their own velocities where a hook sinks faster (initial motion), deceleration of a hook after the branch line is stretched (transitional motion) and simultaneous sinking of a main line and a hook which is suspended from the main line (final motion). The above model suggests that casting of stretched branch lines results in a prolonged sinking time to the critical depth for a hook.
Kagosima, Kagoshima, Japan
- Faculty of Fisheries