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1.
《Fisheries Research》2006,82(2-3):276-282
The role of bioluminescence stimulated by moving fishing gear was investigated using an ISIT video camera mounted inside a pelagic and demersal trawl. Data presented here show that trawling is responsible for generating bioluminescent light. In two Norwegian fjords, the mean number of bioluminescent events per metre of head rope per second were 5.14 ± 2.17 and 2.39 ± 1.0 for a pelagic trawl at ∼270 m depth and a demersal trawl at ∼500 m depth, respectively, travelling at 2–4 knots. By extrapolation of these data, thousands of point-source flashes occur over the entire mouth of a trawl every second during a tow, considerably increasing its visual presence to fish. The occurrence of stimulated bioluminescent flashes on a trawl in deep-water may provide sufficient illumination to permit herding in the absence of ambient space light. The aim of this study is to bring to the attention these preliminary observations of mechanically stimulated bioluminescence by mobile trawl gear as possible visual detection stimulus for fish and its potential to affect catch rates by altering herding, escapement and avoidance behaviour. 相似文献
2.
《Fisheries Research》2006,77(3):417-429
Pecten jacobaeus is an exploitable bivalve, whose populations have greatly declined in the main Mediterranean fisheries since the mid-1980s. A substantial population of the species was studied in the marine Lake Vouliagmeni (Korinthiakos Gulf, Greece). The population density and the spatial distribution of P. jacobaeus were estimated in the lake with line transect sampling by SCUBA diving, a method not previously used for scallop density estimations. Individuals of the first size class (small) were mainly restricted to shallow waters (4–8 m), while individuals of the second size class (large) were mainly restricted to deeper waters (>12 m). Possible reasons for this size-separation were: (1) the most appropriate settlement substrate for pediveligers was in shallow waters, (2) the strong summer thermocline in the lake may have induced the selection of the shallow and warm bottoms of the lake as settlement areas, (3) intraspecific competition between adults and pediveligers, and (4) the high fishing mortality of large individuals in shallow waters. On the hypothesis that successful recruitment of P. jacobaeus occurred mostly in the shallow areas of the lake, it was deduced that P. jacobaeus gradually migrated, as they grew, from the shallow settlement fields of the lake to the deeper areas. The density of large individuals was associated with depth and the degree of scatter (QDφ) of the granule size frequencies. Higher densities of large individuals were found deeper and in poorly sorted sediments (QDφ > 1.0). The size of large individuals was positively correlated with depth. The size of P. jacobaeus population in Lake Vouliagmeni was estimated. 相似文献
3.
Condition and recruitment of Aristeus antennatus at great depths (to 2,300 m) in the Mediterranean: Relationship with environmental factors 
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下载免费PDF全文 Depth and seasonal trends in the biological condition and recruitment of the red shrimp (Aristeus antennatus) have been analyzed over the slope to 2,233 m in the western Mediterranean. The best biological condition of A. antennatus (gonadosomatic index [GSI]) for mating and spawning occurred at 800–1,300 m in summer, in areas deeper than the fishing grounds distributed between 500 and 800 m. Females moved shallower to feed on the upper slope during periods of water‐mass homogeneity (autumn–winter), increasing their hepatic gland weight (hepatosomatic index [HSI]). Females moved downslope (800–1,100 m) to spawn (high GSI) during periods of water mass stratification (late spring–summer). The HSI of females decreased with depth down the slope in autumn, after the reproductive period. Small juveniles were distributed deeper than 1,000 m, associated with high near‐bottom O2 levels, low turbidity and high C:N in sediments, implying favorable trophic conditions. This confirms the importance in studying the biology of deep‐sea species over their entire depth range. The progressive warming and increasing salinity of deep Mediterranean waters could provoke a decrease of dissolved O2 that would affect the life cycle of A. antennatus. 相似文献
4.
《Fisheries Research》2007,83(1-3):19-29
Data on Antimora rostrata are presented from 42°N on the mid-Atlantic Ridge to approximately 65°N on the slope off West and East Greenland, a north–south range of approximately 1400 nm (∼2600 km). The species occurred in the depth interval 669–3059 m in trawl and longline experiments that sampled the depth range 450–4300 m. Length frequencies indicated both latitudinal and depth-related variation. Around Greenland small specimens occurred at shallower depths (<1000 m) while larger specimens were more frequent deeper than 1000 m. Abundance peaked between 1200 and 2700 m with generally low or no catches shallower and deeper. Sagittal otoliths were examined for 302 specimens, and zonation patterns in transverse sections suggested the existence of annuli. Counts of presumed annuli indicated a maximum age of 25 years, and length-at-age indicated linear growth within the age range sampled. Females grow larger than males and seem to live longer. Estimates of natural mortality varied from 0.11 to 0.25. Estimates of growth and mortality rates correspond to those that might be expected in virgin populations. 相似文献
5.
《Fisheries Research》2006,77(3):401-416
We identified environmental associations (depth, bottom temperature and bottom salinity) of the shortfin squid Illex argentinus in the Northern Patagonian Shelf. Data are from 15 research bottom trawl surveys conducted in the Argentine–Uruguayan Common Fishing Zone (AUCFZ) between 1985 and 1998. Squid distribution in the surveyed area showed significant associations (p < 0.05) mostly with depth and bottom temperature. Bathymetric associations of squid detected in March–April, May–June and July–August cruises revealed a preference of squid for deep depths (80–280 m, intermediate and external shelf) and cool bottom temperatures (4–10 °C, subantarctic water) within the survey area. In contrast, the results observed during November–December cruises showed a preference of squid for shallower depths (70–90 m) and warmer bottom temperatures. The majority of two-way environmental analyses showed significant associations, suggesting the existence of a strong correlation between the environmental factors used in our analyses. The identification of significant associations between squid distribution and bottom temperature seem to be related to the presence of strong thermal gradients within the study area. This could be supporting the existence of an association between I. argentinus with the Brazil–Malvinas confluence front and also with the shelf break front. 相似文献
6.
《Fisheries Research》2007,87(2-3):129-135
The percentage of Pacific cod available to Alaskan bottom trawl surveys was estimated from the proximity of tagged cod to the seafloor. Archival tags recorded time and depth data at 15- or 30-min intervals. The distance of a cod above the bottom was computed by subtracting tag depth from bottom depth, estimated as the maximum depth recorded during each 24-h day. These estimates of bottom depth are based on the assumption that cod approach the seafloor at least once a day, and do not undergo migrations up or down bottom gradients. To ensure that migrations over variable bottom gradients did not confound our estimates of bottom depth, we narrowed our analysis to 11 tagged cod that were recaptured in areas of flat bathymetry, and only analyzed data recorded within one month prior to recapture (N = 29,462 depth recordings). Pacific cod maintained short distances above the seafloor that often differed between day and night. Over 95% of the daytime tag recordings occurred within 10 m of the seafloor. Average effective headrope heights for survey bottom trawls currently used in the eastern Bering Sea and Alaska Gulf/Aleutian Islands groundfish surveys are approximately 2.5 and 7 m, respectively. In the absence of any behavior responses to an approaching trawl, we would expect 47.3% of the cod within the water column are available to the trawl used on the eastern Bering Sea survey and 91.6% are available to the trawl used on the Gulf/Aleutian Islands surveys. This study demonstrated that Pacific cod are highly demersal, and current values of trawl survey catchability (Q) used in current stock assessments are consistent with estimates of cod availability to the trawl gear. 相似文献
7.
The primary gear type used to harvest coastal sharks in the U.S. Atlantic shark fishery is bottom longline. Recent stock assessments have found several species of coastal sharks in U.S. Atlantic Ocean waters have declined from 60% to 80% of virgin levels. To aid in stock rebuilding, alternative gear restriction measures such as reduced soak time, restrictions on the length of gear, and fishing depth restrictions have been considered but not implemented. In order to evaluate the effectiveness of some of these management measures, controlled experiments were performed using hook timers and time depth recorders, assessing the factors affecting mortality during longline capture for the four most abundant species that incurred at-vessel mortality: sandbar (Carcharhinus plumbeus), blacktip (Carcharhinus limbatus), bull (Carcharhinus leucas), and blacknose (Carcharhinus acronotus). Our results indicate that as hook time and shark size increased mortality rates for the sandbar and blacktip sharks increased. Predicted models indicated mortality rates increased steadily for the three species but appeared to increase the most after 10, 6, and 1 h on the hook for sandbar, blacktip and blacknose shark, respectively. Sandbar sharks larger than approximately 170 cm FL are more susceptible to hooking mortality. Blacknose shark mortality rates increased as hook time increased but bull shark mortality rates were not affected by any factor. The probability of a hook being bitten increased the most between 5 and 12 h after the fishing gear had been set and the mean amount of time hooks were in the water prior to being bitten was 4, 5 and 9 h for sandbar and blacknose sharks, blacktip, and bull sharks, respectively. A significant difference was found between these means for sandbar and bull sharks and between blacknose and bull sharks. Shark species were commonly caught at different temperature and depth ranges. These results could be used by fisheries management to implement restrictions of fishing depth and soak time to aid in the recovery of coastal sharks species. 相似文献
8.
《Fisheries Research》2007,84(2-3):228-237
We tested the hypothesis that cellular-type composition of eastern king prawn (Melicertus plebejus) ovaries varies in space and time along the coast of New South Wales (NSW), Australia. The ‘point count technique’ commonly used in ecological studies but rarely in studies of reproductive biology was used to describe the oocyte composition of ovaries. Within Times there were differences in the cellular-type composition between Locations (Global R = 0.357 and 1% significance). Most dissimilarity was in pairwise comparisons between the southern most and each of the other locations (R values 0.2–0.6, P = 0.001). Within Locations there were differences in similarity between Times (Global R = 0.214 and 0.1% significance). Most dissimilarity occurred in pairwise comparisons between winter and summer (R values 0.36–0.45, P = 0.001). Females capable of spawning are found across the latitudinal range of the main offshore prawn fishing grounds but the main spawning area is in the north and whilst these females occur year around, we did not detect evidence of winter spawning in waters off NSW. As part of the sampling strategy, we were able to show that macro-staging of ovaries is satisfactory for distinguishing between yolked and unyolked eggs in eastern king prawns and for identifying females capable of spawning. 相似文献
9.
《Fisheries Research》2007,84(3):358-367
This paper profiles the reproductive biology of and investigates the resilience of Tasmanian striped trumpeter under different levels of fishing pressure and size at entry to the fishery using per-recruit analysis. The spawning season around Tasmania occurs in the austral spring, with peak spawning activity in September and October. Size at 50% maturity was estimated at 543 mm fork length (FL) for females (estimated age = 6.8 years) and 529 mm FL for males (estimated age = 6.2 years). Striped trumpeter is a multiple spawner with batch fecundity estimates ranging from 205,054 for a 2 kg fish (540 mm FL) to 2,351,029 for a 9.5 kg fish (800 mm FL). At the current minimum legal size limit of 450 mm total length (equivalent to approximately 425 mm FL), yield-per-recruit was estimated to be close to maximum, and spawning biomass-per-recruit (SPR) ranged from 35 to 52% of virgin stock, depending on the mortality estimates used. Although these SPR are at a level considered sustainable, this methodology does not incorporate temporal variability, specifically recruitment variability. Therefore, conservative management measures are recommended until a dynamic model is applied to the striped trumpeter population. 相似文献
10.
《Fisheries Research》2006,77(2):173-183
Temperature-depth recorders (TDRs) were attached to pelagic longline gear in the Hawaii-based commercial fishery to obtain actual fishing depths and to test the accuracy of catenary algorithms for predicting fishing depths. Swordfish gear was set shallow by typically deploying four hooks between successive floats. The observed depth of the settled deepest hook had a median value of 60 m for 333 swordfish sets. Tuna longline gear deployed more hooks between floats (mean = 26.8), and the observed median depth of the deepest hook was 248 m (n = 266 sets). Maximum gear depth was predicted from estimates of the longline sag ratio and catenary algorithms; however, depth was not predicted for all TDR-monitored sets because estimating sag ratios proved problematic. Swordfish sets had less slack in the main line and correspondingly smaller catenary angles (median = 54.2°) than tuna sets (median = 63.7°). Median values of the predicted catenary depth were 123 m for swordfish sets (n = 203) and 307 m for tuna sets (n = 198). Shallow swordfish sets reached only ∼50% of their predicted depth, while deeper tuna sets reached about 70%. These values indicated that capture depths using traditional catenary equations may be biased without the benefit of TDRs affixed to longlines. Generalized linear models (GLMs) and generalized additive models (GAMs) were developed to explain the percentage of longline shoaling as a function of predicted catenary depth and environmental effects of wind stress, surface current velocity, and current shear. The GAM explained 67.2% of the deviance in shoaling for tuna sets and 41.3% for swordfish sets. Predicted catenary depth was always the initial variable included in the stepwise process, and the inclusion of environmental information in the GAM approach explained an additional 10–17% of the deviance compared to the GLMs. The explanatory ability of the environmental data may have been limited by the scale of the observations (1° in space; weekly or monthly in time) or the geometric (transverse versus in-line) forcing between the environment and longline set. Longline gear models with environmental forcing affecting shoaling may be improved in future studies by incorporating contemporaneous environmental information, although this may restrict analyses to fine-scale experimental longlines. 相似文献
11.
《Fisheries Research》2007,85(3):285-290
Avoidance reactions of young-of-the-year fish assemblages were investigated in the offshore zone of three reservoirs in the Czech Republic during late summer. Pikeperch (Stizostedion lucioperca) strongly dominated in the Lipno Reservoir in 2003, bream (Abramis brama) and bleak (Alburnus alburnus) were the most abundant species in the Slapy Reservoir in 2004 and roach (Rutilus rutilus) and bleak dominated in the Želivka Reservoir in 2004 and 2005. Densities of fry ranged between 1.09 ind./100 m3 in the Lipno Reservoir and 2.95 ind./100 m3 in the Slapy Reservoir. In each reservoir, three trawl nets of different widths (dimensions 1.5 m × 3 m, 3 m × 3 m, 6 m × 3 m) were used in the pelagic area at night. For each trawl the estimated fish density was determined as the catch per 100 m3 of water and was compared between all three trawls. The fish length–frequency distribution was also compared between all the trawls. Day catches were much lower compared with those taken at night. Adult fish showed very clear avoidance of fry trawls. At night, no important differences in estimated fry density, obtained by these trawls, were observed in any locality for any fish species, nor in the length distribution of important species between trawls. According to these results, the avoidance reactions of fry in the late summer (August, September), at night, are unimportant. At this time of year, nighttime pelagic trawling appears to be an effective method for quantitative fry sampling. We recommend the 3 m × 3 m trawl for quantitative night sampling of the fry community as a good compromise between assured efficiency and relatively easy handling. 相似文献
12.
《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
13.
《Fisheries Research》2007,83(1-3):56-64
The pelagic thresher shark, Alopias pelagicus, is a cosmopolitan species and abundant in Taiwan waters. Some of its biological information has been documented yet its population dynamics are poorly known. The purpose of this study is to assess the pelagic thresher shark stock status in the eastern Taiwan waters. The whole weights (W) of 51,748 individuals of the pelagic thresher shark landed at Nanfanao and Chengkung fish markets, eastern Taiwan from 1990 to 2004 were converted to precaudal length (PCL) based on the W–PCL relationship (W = 2.25 × 10−4 × PCL2.533, n = 2165). The sexes combined VBGE Lt = 189.5 × (1 − e−0.10(t+6.47)) was used to estimate the age for each length group. Total mortality rates (Z) obtained with length-converted catch curves ranged from 0.208 to 0.277 year−1. Natural mortality rate (M) estimated from Hoenig method was 0.132 year−1, and exploitation rate (E) ranged from 0.069 to 0.127 for 1990–2004. Annual abundance was estimated to range from 97,551 in 2000 to 153,331 in 2003 from virtual population analysis, and the highest fishing mortality occurred in ages 8–18 years. There were four different scenarios being simulated in this study. Scenario 1 indicated that spawning per recruit (SPR) ranged from 23.07% in 2001 to 47.71% in 1990 with a mean of 36.41% for the period of 1990–2004. The mean SPR of pelagic thresher for 1990–2004 was below the BRP of SPR = 35% in scenarios 2–4 suggesting that this stock was slightly overexploited. Therefore, to ensure sustainable utilization of this stock, reduction of fishing effort and close monitoring on A. pelagicus are needed. 相似文献
14.
The east Atlantic-Mediterranean penaeid Melicertus kerathurus constitutes a valuable resource for Mediterranean fisheries. In recent years, its world production is almost totally based on the yields from Greece and Tunisia. A two-year study of prawn stock in Thermaikos Gulf (NW Aegean Sea) provided information on age, growth and mortality of the species. M. kerathurus exhibits a marked sexual growth dimorphism, with females showing an overall wider size range and greater size than males. Mean monthly size, CLmax were also in favor of females. Monthly age classes varied from one to four for females and from one to three for males, and corresponded to three generations (0+, 1+, 2+). New generation (0+) cohorts recruited into fishery in waves, from late summer to February. According to the von Bertalanffy growth curve, females grow larger than males, but there is a prominent seasonal growth oscillation in both sexes (females: CL∞ = 62.48, K = 1.15, C = 0.87, WP = 0.16, Rn = 0.170; males: CL∞ = 47.78, K = 1.28, C = 0.97, WP = 0.12, Rn = 0.205). Growth performance indices (φ′, φ) and longevity were in favor of females. K values for both sexes in Thermaikos Gulf are the highest reported for the species, suggesting a higher growth rate and a lower longevity. Estimated values for total, natural and fishery mortality were greater in males. In both sexes, an exploitation rate E > 0.5 was found, implying an intense fishing impact on M. kerathurus stock in Thermaikos Gulf. Intense exploitation in other parts of the Mediterranean and eastern Atlantic, along with the replacement of the species by Eritrean penaeid prawns in the eastern Mediterranean, has resulted in a severe reduction in catches, in most countries. Thus, existing stocks of M. kerathurus should be considered as potentially endangered, and species-specific initiatives towards sustainable management of this resource should be implemented. 相似文献
15.
《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
16.
For control and enforcement purposes, all fishing vessels operating in European waters are equipped with satellite-based Vessel Monitoring by Satellite systems (VMS) recording their position at regular time intervals. VMS data are increasingly used by scientists to study spatial and temporal patterns of fishing activity and thus fishing impact (e.g. surface of sea bed trawled during a fishing trip). However, due to their low resolution (2 h basis), these data may provide a biased perception of fishing impact. We present here a method aiming at interpolating vessel trajectories from VMS data points to obtain higher-resolution data on vessel trajectories which in turn should provide improved estimates of the spatial and temporal patterns of fishing activity and hence fishing impact. This method is based on a spline interpolation technique, the cubic Hermite spline (cHs), using position, heading and speed to interpolate the trawl track of a vessel between two succeeding VMS data points. To take uncertainty of the interpolated track into account, the method also determines a confidence interval, which represents the spatial distribution of vessel presence probability between two successive VMS positions. The cHs method was compared to the straight line interpolation technique using a reference data set with intervals of 6 min which was assumed to represent the real trawl tracks. The results showed that the cHs method approximates the real trawl track markedly better than a straight line interpolation. The cHs method should therefore be preferred to the conventional straight line approach to interpolate vessel tracks in studies aiming at estimating fishing impact from VMS data. 相似文献
17.
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
18.
《Fisheries Research》2006,79(2-3):211-217
The aim of the present study was to provide an estimation of growth of juvenile European hake, Merluccius merluccius (L., 1758) (OSTEICHTHYES; MERLUCCIIDAE), by means of the analysis of otolith daily increments. Hake specimens were collected during trawl surveys carried out in the northern Tyrrhenian Sea (NW Mediterranean). The sagittae were removed from hakes ≤20 cm total length. Left otoliths were ground and polished to obtain thin frontal sections. Otolith microstructure was analysed under a compound green light-polarising microscope. A power curve with intercept was fitted to the length-age data to describe the growth of M. merluccius. According to the growth curve, a mean length of 18 cm was reached at the end of the first year of life. The validation of the otolith increment periodicity was performed by means of two indirect methods. 相似文献
19.
Most commercial catfish farms use multiple-batch production systems that contain fish sizes ranging from recently stocked fingerlings to fish weighing more than 1.5 kg. Currently, there are no accurate and cost-effective techniques to estimate pond inventories of catfish. Three trials were conducted in earthen catfish ponds with a 12 m × 8 m trawl (bar mesh at mouth of 3.8-cm; 2.54-cm at cod end). The first two trials included trawling with and without feed as bait in 4-ha commercial catfish ponds (Trial 1) and in 1.6-ha experimental ponds (Trial 2). In Trial 3, the trawl was pulled three times without feeding in 1.6-ha experimental ponds. Mean individual weights and size distributions of catfish caught by the trawl were statistically similar to those of catfish caught by the seine (Trial 1) and to stocking data (Trial 2). Single pulls with the trawl resulted in 73% error in estimated fish inventories in Trial 3. However, if pulled two times, the estimated catfish inventory error dropped to 7%, more accurate than other inventory methods, but was variable (coefficient of variation = 186%). The trawl appears to have potential as a means to sample commercial catfish ponds to estimate means and frequency distributions of fish size, but additional refinement and correction would be needed for it to be used reliably to estimate total pond inventory. 相似文献
20.
《Fisheries Research》2007,84(2-3):263-275
Gulf menhaden, Brevoortia patronus, plays a key ecological role in the northern Gulf of Mexico and supports the second largest commercial fishery by weight in the United States. Here we describe that fishery and propose biological reference points (BRPs) for its management. The BRPs represent targets and limits of both fishing mortality rate (F) and population fecundity (Ψ), where target is defined as the management goal, and limit, a value to be avoided (F < FLimit and Ψ > ΨLimit). We assess stock status relative to the BRPs by fitting a statistical catch-age model to fishery-dependent and fishery-independent data spanning 1964–2004. Results indicate that in the terminal year neither limit reference point is exceeded (F2004/FLimit = 0.75 and Ψ2004/ΨLimit = 1.86). Of possible concern, however, is a recent increase in fishing mortality and decrease in population fecundity. With these trends, terminal values exceed their targets (F2004/FTarget = 1.16 and Ψ2004/ΨTarget = 0.93), although by little relative to uncertainty in the estimates. Sensitivity analyses show these results are robust to model assumptions. 相似文献