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2.
《Fisheries Research》2007,86(1):15-30
Observers aboard commercial trawlers collected data on the total catch composition of 614 and 479 hauls made by vessels operating off the south and west coasts of South Africa, respectively. On the south coast, four fishing areas were identified on the basis of target species and fishing depth. On the west coast, hauls were separated into those targeting hake Merluccius spp. in four depth ranges (0–300, 301–400, 401–500, and >500 m) and those targeting monkfish Lophius vomerinus. For each area, the catch composition was calculated and the species assemblages were investigated using cluster analysis and multi-dimensional scaling. Finally, for each coast, the weight of fish discarded annually was estimated. On the south coast, although hake dominated, between 21% and 47% of the catch was not hake, depending on the fishing area. In comparison, hake dominated west coast catches, the proportion of hake increasing with depth. For each fishery investigated, approximately 90% of the catch was processed and landed. However, estimates of annual discards indicate that the south and west coast fisheries may annually discard 9000 or 10,000 t and 17,000 or 25,000 t, of undersized and unutilizable fish and offal, respectively, depending on the estimation method used. When developing strategies to limit or enhance utilization of bycatch, cognisance should be taken of the differences in catch composition between the south and west coasts and of the importance of bycatch revenue to south coast fishing companies. 相似文献
3.
J.C. Pacheco D.W. Kerstetter F.H. Hazin Humberto Hazin R.S.S.L. Segundo J.E. Graves F. Carvalho P.E. Travassos 《Fisheries Research》2011,107(1-3):39-45
Catch composition, catch rates, hooking location, and status at release at haulback were monitored during 81 experimental sets (launches and hauling fishing per day) in a commercial pelagic longline fishery targeting tuna in the equatorial South Atlantic Ocean. Circle hooks (size 18/0, 0° offset) and J-style hooks (size 9/0, 10° offset) with squid baits were deployed in an alternating fashion. The catch composition was not significantly different for most species between the two types of hooks, except for bigeye tuna, which showed a significantly higher proportion of catches on the circle hook (p ? 0.001) and for sailfish, pelagic stingray, and leatherback sea turtle, which had higher catch rates on the J-style hook (p = 0.018, p ? 0.001, and p = 0.044, respectively). Bigeye and yellowfin tuna showed significantly higher rates of survival at the time of gear retrieval with circle hooks, and circle hooks hooked bigeye tuna, yellowfin tuna, swordfish, and sailfish significantly more often externally than internally. Our results suggest that the use of size 18/0, 0° offset circle hooks in the equatorial pelagic longline fishery may increase the survival of bycatch species at the time of gear retrieval with minimal effects on the catches of target species. 相似文献
4.
Kimberly T. Murray 《Fisheries Research》2011,107(1-3):137-146
Since 2006, the National Marine Fisheries Service (NMFS) has mandated gear modifications (“chain mats”) and fishing effort reductions in the U.S. Mid-Atlantic sea scallop dredge fishery to alleviate or minimize interactions with sea turtles. Turtle interactions with gear can be defined as those that are “observable” based on standard fishery observer protocols, plus unobserved interactions, which include both quantifiable and unquantifiable interactions. Once a gear modification is in place, a turtle interaction that was once observable may become unobservable, because the gear modification successfully prevented the turtle from being captured. This paper describes turtle interactions in scallop dredge gear from 2001 to 2008, identifies gear and environmental correlates with observable interaction rates, and reports the average annual number of interactions and adult-equivalent interactions before and after chain mats were mandated in the fishery. Fisheries observer data were used to develop a Generalized Additive Model (GAM) to estimate rates of observable interactions of hard-shelled turtles. These rates were applied to commercial dredge fishing effort to estimate the total number of observable interactions, and to infer the number of unobservable, yet quantifiable interactions after chain mats were implemented. Interaction rates of hard-shelled turtles were correlated with sea surface temperature, depth, and use of a chain mat. The average number of annual observable interactions of hard-shelled turtles in the Mid-Atlantic scallop dredge fishery prior to the implementation of chain mats (1 January 2001 through 25 September 2006) was estimated to be 288 turtles (CV = 0.14, 95% CI: 209–363), which is equivalent to 49 adults. After implementation of chain mats, the average annual number of observable interactions was estimated to be 20 turtles (CV = 0.48, 95% CI: 3–42), equivalent to 4 adults. If the rate of observable interactions from dredges without chain mats had been applied to trips with chain mats, the estimated number of observable and inferred interactions of hard-shelled species after chain mats were implemented would have been 125 turtles per year (CV = 0.15, 95% CI: 88–163). Results from this analysis suggest that chain mats and fishing effort reductions contributed to the decline in estimated turtle interactions after 2006. 相似文献
5.
Little is known about the size selectivity of cod in static fishing gears such as pots and traps. In this field study, floating fishing pots were equipped with 40, 45 and 50 mm square mesh escape windows in order to estimate the size selectivity of cod at different mesh sizes. Relationships between selectivity parameters and mesh size, as well as an optimal mesh size for the escape window with respect to current minimum landing size of cod in the Baltic Sea were sought. The results show that the floating pot is not only species selective when used in the Baltic Sea cod fishery, the implementation of an escape window reduced the proportion of undersized bycatch in the pots by more than 90%. The estimated length at 50% retention was found to be a direct function of fish body length (girth) and mesh size of the escape window, while the estimated selection range remained unchanged regardless of mesh size. Optimal mesh size, with respect to the length at 50% retention and current minimal landing size of 38 cm in the Baltic, was determined to be 45 mm. Strong indications (significant on the 0.01 probability level in the case of 50 and 40 mm escape windows) suggested that the relative fishing power of the pots increased with the implementation of an escape window. This result could be explained as a “saturation effect”, i.e. the probability of cod entering the pot is likely to be negatively dependent on cod density in the pot. The high species selectivity and the low catch rate of undersized fish have consolidated the floating pots position as a highly benign fishing method and the foremost alternative gear for the future coastal cod fishery in the Baltic Sea. 相似文献
6.
To develop ways to catch fewer undersized specimens of Jasus frontalis in the traps of the rock lobster fishery off the Juan Fernández Archipelago (Chile), we studied the use of lobster traps with different-sized escape vents (circular windows of 80, 85, or 90 mm diameter). The traps used in the present fishery served as controls. Selection curves were fit to each of the vent sizes examined in the study. The method of alternating hauls was used for this purpose in a manner similar to that employed with trawl nets. We compared the size–frequency distributions obtained for each vent size with those determined for the control traps. We monitored 2437 traps and obtained a total catch of 13,444 specimens. Undersized individuals decreased in the catch as the diameter of the openings increased. The selection curves fit a logistic-type model adequately. A direct relationship was established between the vent size and the length corresponding of the first catch (L50). The CPUE for legal-sized rock lobster increased in traps having up to 85-mm vents, but this yield dropped in traps fitted with 90-mm vents. The CPUE for undersized rock lobster, however, was inversely proportional to the size of the vents. Unlike typical selectivity literature that relies on the L50, the objective of this study was to maximize the number of legal (≥98 mm Lc) specimens retained in the traps while simultaneously minimizing the retention of undersized specimens. To achieve this, we used a model relating vent size to L50 and the slope of the selection ogives. The optimal diameter for vents in this fishery was determined to be 83 mm. Furthermore, underwater recordings were used to register the escape behavior of the lobsters. These recordings contributed new data on the way in which the lobsters detect, confront, and escape through the vents. 相似文献
7.
《Fisheries Research》2007,83(1-3):304-318
In 1986 a motorised, commercial gillnet fishery was introduced in Lake Tana, Ethiopia's largest lake (3050 km2) in addition to the artisanal, predominantly subsistence fishery conducted from reedboats. The three main species groups targeted by this fishery are a species flock of endemic, large Labeobarbus spp., African catfish (Clarias gariepinus) and Nile tilapia (Oreochromis niloticus). The commercial gillnet fisheries was monitored during 1991–1993 and in 2001 (CPUE, effort allocation, catch composition, yield) and the development of the stocks of the three species groups was determined using an experimental trawl program during 1991–1993 and 1999–2001.In 1991–1993 the vast majority of fishing activities took place in the southern Bahar Dar Gulf (71%). Each species group contributed roughly one third to the total catch. In 2001, 41% of the effort was allocated to the north-eastern shores of Lake Tana. Both the CPUE and the contribution of O. niloticus to the total catch had doubled. However, the proportion of large specimen (>50 cm TL C. gariepinus; >20 cm FL O. niloticus) in the trawl surveys decreased significantly. A three-fold decline in abundance of the anadromous Labeobarbus species occurred. The 15 large labeobarb species are long-lived, ecologically specialised endemics. The seven riverine spawning Labeobarbus species form aggregations in the river mouths in August–September, during which period they are targeted by the commercial gillnet fishery.A sharp decrease in abundance by ca. 75% of the migratory riverine spawning Labeobarbus species in the sublittoral and pelagic zones of the lake, areas where no fishing takes place and the collapse of juvenile Labeobarbus (between 5 and 18 cm FL: by 90%) during the 1990s suggest recruitment-overfishing. To prevent the possible extinction of the unique Labeobarbus species flock all fishing effort should be severely restricted near the river mouths and on the upstream spawning areas during August–September (peak breeding period) to protect the vulnerable spawning aggregations. 相似文献
8.
《Aquacultural Engineering》2007,36(3):271-282
In a commercial scallop hatchery spat production depends on a culture system which ensures high survival and good growth. Reuse of water with algae may increase the food exploitation and hence reduce the costs. Post-larvae of great scallop (Pecten maximus) were studied in a commercial hatchery using a partial open and continuous feeding tank system. Three different water recirculation rates (67, 83 and 92%) were tried out in two experiments with post-larvae originating from three spawning groups of ages between 43 and 57 days post-spawn, 316–886 μm shell-height and 1.1–9.6 μg ash-free dry weight. The post-larvae were held in sieves in tanks of 2500 l where a downwelling flow was maintained by airlifts. New water with a mix of monocultured algae was continuously added to the tanks at algal concentrations of 10 and 15 cells μl−1 in experiment 1 (groups 1 and 2) and 2 (group 3), respectively. The algal supply to each sieve was reduced along with increased recirculation rate, but was kept between 6 and 13 cells μl−1. Generally no significant differences in survival, growth or chemical content were found between the three recirculation rates, while few differences were found between and within groups. Large variation in survival was found between and within groups (1–81%). Highest survival was found in experiment 1, and where post-larvae from two settlements were used, the first settlement survived better than the second. The daily growth ranged from 15 to 62 μm shell-height and from 0.3 to 2.6 μg ash-free dry weight. The scallop post-larvae could well be reared at all three recirculation rates studied as an increase from 67 to 92% did not seem to affect the post-larval performance seriously. The algal supply, however, had to be compensated by an increasing number of cells (>10 cells μl−1) when increasing the recirculation rate. 相似文献
9.
《Aquaculture (Amsterdam, Netherlands)》2006,251(2-4):306-313
Shell strength development of the scallop Pecten maximus collected from wild stocks and from suspended cultures was described over the culture period when most of the growth takes place (20–110 mm shell height). Shell strength, shell height and shell thickness were determined in scallops of age groups 2–5 years. Wild and cultured scallops showed a strong divergence in shell strength development in scallops older than age group 3, which was not reflected in the concurrent development of shell height and thickness, indicating that factors other than shell height and shell thickness explain the differences in observed shell strength. In wild scallops, shell height, shell thickness and age accounted for about 65% of the variation in shell strength, while the same variables accounted for about 30% in cultured scallops. Wild scallops had stronger shells than the cultured scallops of the same size (53–68 mm shell height) grown at the same site, suggesting that factors related to suspended culture could explain the weak shells in cultured scallops. The results indicate that conditions related to suspended culture can have a negative impact on shell strength development in P. maximus. As the shell is the primary protection against decapod predation in scallops, a better understanding of what affects the shell strength is of importance for the development of release strategies in bottom culture of P. maximus. 相似文献
10.
Eduardo Grimaldo Ira Leifer Svein Helge Gjøsund Roger B. Larsen Henrik Jeuthe Sünnje Basedow 《Fisheries Research》2011,107(1-3):147-158
This paper presents the field testing of a new technology to harvest marine copepods (Calanus sp.) by bubble-induced upwelling. Two large-scale bubble rafts, a 21 m2 and a flexible 75 m2 bubble raft with tow-parallel and tow-perpendicular sparger elements, respectively, were tested in the sea with high Calanus densities in the upper 25 m. Bubble-driven upwelling velocities (Vup) measured with different air flows (Q) and source depths (z0), gave Vup ～ Q0.27 with stratified water, and were in agreement with other results for stratified conditions. Bubble trawls significantly enhanced Calanus concentrations in the upper water column: up to 1416%, with the best results for the transverse sparger raft, which also was tested with weak stratification. Bubble trawl performance also was affected by the stratification, with the highest enhancement for the lowest stratification. Catch species analysis showed reduced bycatch. Thus, this new harvesting technology showed a potential to develop an economically robust, environmentally benign, and sustainable fishery on a renewable resource at lower trophic levels in the food web, within the context of ecosystem-based management. 相似文献
11.
Murray cod Maccullochella peelii peelii is one of the world’s largest freshwater fish and supports popular fisheries in southeast Australia, but no previous modelling efforts have evaluated the effects of fisheries regulations or attempted to develop sustainable harvest policies. We compiled existing population metrics and constructed an age-structured model to evaluate the effects of minimum length limits (MLLs) and fishing mortality rates on Murray cod fisheries. The model incorporated a Beverton and Holt stock recruit curve, age-specific survivorship and vulnerability schedules, and discard (catch and release) mortality for fish caught and released. Output metrics included yield (kg), spawning potential ratio (SPR), total angler catch, total harvest, and the proportion of angler trips that would be influenced by each regulation based on recent creel survey data. The model suggested that annual exploitation (U) should be held to less than 0.15 under the current MLL of 500 mm total length to achieve an SPR > 0.3, a target usually considered to prevent recruitment overfishing. Exploitation rates at or exceeding 0.3 would cause SPR values to drop below typical management targets unless the MLL was set at or above 700 mm. Regulations that protected Murray cod from overfishing created higher angler catches and higher catch of trophy fish, but at a cost of reducing the proportion of angler trips resulting in a harvested fish. Expressing model output on a per-angler trip basis may help fishery managers explain regulation trade offs to anglers. 相似文献
12.
Germán Merino Eduardo Uribe Gaspar Soria Elisabeth von Brand 《Aquacultural Engineering》2009,40(2):95-103
Northern scallop Argopecten purpuratus aquaculture relies on an efficient all year-round larval supply. Larvae are generally produced in closed aquaculture systems (CAS) using the batch techniques with periodical water changes. For instance, survival rates are greatly variable and can range from 0 to 80% making production of scallop larvae uncertain. The main goal of this study was to determine the feasibility of rearing scallop larvae in a recirculating aquacultural system (RAS), and secondarily to compare scallop larval growth rate and time length to reach the settling stage when reared with a traditional Chilean CAS technique and in a novel RAS technique in an industrial-like approach.Several batches of larvae were cultured in CAS and RAS. Larvae were fed on Isochrysis galbana cultured in 35-L tubular photobioreactors. Growth rates were significantly different (F11,2840 = 274.66; p < 0.001). All scallop larvae cultured in CAS showed lower growth rates ranging within 4.49 and 7.30 μm day?1 and protracted period of culture until settlement (at least 10 more culture days) than those reared in RAS (growth rates between 9.56 and 13.15 μm day?1). However, final survival (from D-larvae until settlement) of larvae reared in CAS showed higher values than those values recorded for larvae cultured on RAS. Higher growth rates observed in RAS could be attributed to a reduction in daily manipulation of the animals and/or more feed availability as well as higher temperatures and a steady state conditions in water quality. Even though, the reduction in time for rearing larvae until settlement in RAS was high, the comparison between systems is more significant in view of the reduction in make up seawater from 100% of system volume (CAS) to less than 10% of system volume (RAS). Therefore, RAS was independent from daily water quality variation from natural seawater by increasing water retention time, and with that improve water quality steady state conditions. Results of this research show that a more efficient use of water and heating systems than generally used in the Chilean hatchery industry is achievable. This is an important result since it could lead to significant reductions in the cost of operating a scallop hatchery, however further work is required to accurately compare the two systems (CAS and RAS). The main result from this research is that scallop larvae can be cultivated using recirculating aquaculture systems (RAS) as a method to increase production. The information reported in this paper will be useful for the improvement of scallop larvae culture techniques under controlled conditions. 相似文献
13.
Hae-Hoon Park Russell B. Millar Bong-Seong Bae Heui-Chun An Young Yull Chun Jae Hyeong Yang Sang Chul Yoon 《Fisheries Research》2011,107(1-3):196-200
In 2008, Korean flounder (Glyptocephalus stelleri) was designated by the Korean Ministry for Food, Agriculture, Forestry and Fisheries as a species for restoration in the coastal waters of Korea. However, there are currently no regulations regarding the minimum landed size of flounder, or the minimum legal mesh size used by the coastal gillnet and trammel net fisheries. Selectivity experiments for gillnets and trammel nets were conducted using commercial vessels in several areas off the eastern coast of Korea between October 2006 and June 2009. The selectivity analysis required an adaption of the SELECT method because trammel net mesh sizes were altered part-way through the experiment. Gillnet and trammel net selectivity was best described using a bi-modal selection curve. The two gears were found to have different selection curves for a given mesh size. The length of maximum retention was similar for the two gears, but the selection curve of the trammel net was substantially wider than that of the gillnet. For the largest size of mesh used in the commercial fishery (8.5 cm stretched), 50% relative retention was estimated to occur at a length of 20.4 cm for the trammel net, and 22.5 cm for the gillnet. In comparison, the length of 50% maturity for this species is approximately 26 cm. As there are currently no size restrictions on landings of Korean flounder, these results suggest that use of these gears may pose a serious threat to local stocks of this species. 相似文献
14.
Neon flying squid (Ommastrephes bartramii) plays an important role in the pelagic ecosystem and is an international fishery resource with high commercial value in the North Pacific Ocean. The west stock of winter–spring cohort of this species is an important target for the squid-jigging vessels of Japan, Korea and China (including Taiwan). The squid has a life span of less than 12 months, and its population dynamics is heavily influenced by its environment. Thus, a good understanding of its interactions with the habitats, often quantified with a habitat suitability index (HSI) model, is critical in developing a sustainable fishery. In this study, using the Chinese commercial squid-jigger fishery data and corresponding environmental variables we conducted HSI modeling to evaluate the habitat of the west stock of winter–spring cohort of neon flying squid in the northwestern Pacific Ocean. We compared catch per unit effort (CPUE) and fishing effort data in HSI modeling. This study suggests that the CPUE-based HSI model tends to overestimate the ranges of optimal habitats and under-estimate monthly variations in the spatial distribution of optimal habitats. We conclude that a fishing effort-based HSI model performs better in defining optimal habitats for neon flying squid. According to the fishing-effort-based HSI model, the optimal ranges of the following key habitat variables are defined: from 16.6 to 19.6 °C for SST, from 5.8 to 12 °C for temperature at depths of 35 m, from 3.4 to 4.8 °C for temperature at depth of 317 m, from 33.10 to 33.55 psu for SSS and from ?20 cm to ?4 cm for SLH. 相似文献
15.
M. J. KAISER A. S. HILL K. RAMSAY B. E. SPENCER A. R. BRAND L. O. VEALE K. PRUDDEN E. I. S. REES B. W. MUNDAY B. BALL S. J. HAWKINS 《水产资源保护:海洋与淡水生态系统》1996,6(4):269-285
1. The distribution of effort for the most frequently used mobile demersal gears in the Irish Sea was examined and their potential to disturb different benthic communities calculated. Fishing effort data, expressed as the number of days fished, was collated for all fleets operating in the Irish Sea in 1994. For each gear, the percentage of the seabed swept by those parts of the gear that penetrate the seabed was calculated. 2. For all gears, the majority of fishing effort was concentrated in the northern Irish Sea. Effort was concentrated in three main locations: on the muddy sediments between Northern Ireland and the Isle of Man (otter and Nephrops trawling); off the north Wales, Lancashire and Cumbrian coast (beam trawling); the area surrounding the Isle of Man (scallop dredging). 3. In some areas, e.g. between Anglesey and the Isle of Man, the use of scallop dredges and beam trawls was coincident. A comparative experimental study revealed that scallop dredges caught much less by-catch than beam trawls. Multivariate analysis revealed that both gears modified the benthic community in a similar manner, causing a reduction in the abundance of most epifaunal species. 4. Although beam trawling disturbed the greatest area of seabed in 1994, the majority of effort occurred on grounds which supported communities that are exposed to high levels of natural disturbance. Scallop dredging, Nephrops and otter trawling were concentrated in areas that either have long-lived or poorly studied communities. The latter highlights the need for more detailed knowledge of the distribution of sublittoral communities that are vulnerable to fishing disturbance. ©British Crown Copyright 1996. 相似文献
16.
In the coastal zone of the Sea of Okhotsk off Hokkaido, Japan, the giant ezo scallop ( Patinopecten yessoensis ) is widely cultivated on the sea bed, making its fishery a major industry. However, the area experiences intense cyclones, including typhoons, about once a decade and the scallop resources appear to have received severe damage from the storms. Such an event occurred on 29 October 1988. The storm caused 12-m-high wind waves, which appeared to be fully developed sea waves. The water above the sea bed repeatedly moved back and forth at speeds of 1∼2 m s-1 causing damage to the scallops due to collisions and rubbing with gravel and other scallops. From a comparison of wind data with the annual catch of scallops, intense cyclones seem to play an important role on the year-to-year fluctuations in the scallop fishery. 相似文献
17.
《Fisheries Research》2007,84(3):338-344
The black bream Acanthopagrus butcheri recreational fishery is the largest estuarine fishery in Victoria. This fishery is managed through legal-minimum length and daily bag limits. The success of this management strategy requires a high survival rate for released fish. Deep-hooking is known to reduce the chance of fish survival after recreational capture and release. This study investigated the potential to reduce deep-hooking and the number of under-size A. butcheri caught by varying angling gear and techniques. Three sizes of long shank hook (small [size 8], medium [size 4] and large [size 1/0]) and two angling techniques (slack line and tight line) were tested for their deep-hooking rates and selectivity characteristics. Increasing the hook size from small to large decreased the likelihood of deep-hooking by 6.6 times (95% CI 2.3–16.3 times). Fishing with a tight line instead of a slack line decreased the chance of deep-hooking by almost 100% (95% CI 0.8–3.6). Fishing with a large hook instead of a small hook significantly (F = 6.71, df = 2, P = <0.001) increased the mean A. butcheri length, although this mean size increase was less than 1 cm. This study was able to identify angling gear and angling technique manipulations that reduced the rate of deep-hooking when targeting A. butcheri in Victorian estuaries. 相似文献
18.
《Fisheries Research》2007,88(2-3):181-195
This investigation reconstructs the development of major fisheries for herring, eel and whitefish in the Limfjord estuary, Denmark ca. 1667–1860, and then evaluates how their long-term dynamics have been influenced by some key fishery and environmental developments. The commercially most important fishery was for herring, Clupea harengus, which spawned in the Limfjord. This fishery underwent large changes in these centuries. High landings occurred in two periods in the early 18th and again in the early 19th centuries, when 4000–8000 metric tonnes were caught annually. In 1830, the fishery collapsed and landings were <1000 tonnes until the 1910s. Even during the 20th century using modern fishing techniques, the herring fishery never exceeded 7000 tonnes. The collapse was most likely due to unsustainable fishing practices (direct impacts on adults, juveniles, larvae and eggs). The second most important fishery of the Limfjord was the eel fishery. Eel, Anguilla anguilla, seems to have fled the fjord after a winter storm in 1825 broke the narrow Agger Tange isthmus which used to separate the Limfjord from the North Sea, and permanently increased the salinity in the western part of the Limfjord from 8 psu to 33 psu. The, so-called pulse seine fishery for eel declined rapidly following the salt water intrusion, and the population needed at least one to two generations to even partly recover. One possible technological reason for the recovery of the fishery was the 1848 invention of a new type of gear in the Limfjord which today is known as the Danish seine. However, the commercial eel fishery in Limfjord ceased by the 1980s coincident with the overall decline in European eel populations. The third fishery analyzed is the fishery for common whitefish, Coregonus lavaretus. A local population formed the basis of a substantial seasonal fishery, but the whitefish did not survive the salinity obstacle presented by the salt water intrusion in 1825. This study documents both the effects of fishing and environmental variability on collapses of different Limfjord fish species. 相似文献
19.
Pelagic fishes are typically considered mobile and wide-ranging open ocean foragers. However, many species have also been recorded in association with nearshore topographic structures. The relative abundance of four pelagic species at and away from topographic features on the continental shelf, as inferred from fine-scale catch data collected over a 7-year period, was examined for southern Western Australia. A total of 1056 captures were recorded from 890 h of trolling over 102 days: the top four species accounted for 97.5% of all captures. Eight distinct topographic features received 13.7% of the total trolling effort and produced 43.8% of captures. The percentage of all captures within 1 km of these features were 80% for yellowtail kingfish (Seriola lalandi, YTK), 50% for bonito (Sarda australia, BON), 27% for southern bluefin tuna (Thunnus maccoyii, SBT), and less than 5% for skipjack tuna (Katsuwonus pelamis, SKJ). Catch rates were 26, 6.59, and 2.47 times higher than catch rates away from the topographic features for YTK, BON, and SBT, respectively. In contrast, SKJ catch rates were 1/3rd lower at topographic features, indicating avoidance rather than preference. The mean distance at which species were captured from the center of each feature differed significantly, with YTK closest (303 m), followed by SBT (442 m), BON (493 m), and SKJ (539 m). These findings indicate habitat partitioning in pelagic fishes at topographic features and offer a way to increase catch of a targeted species, or reduce the capture of unwanted or quota-limited species. 相似文献
