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Data provided by the Southeast Area Monitoring and Assessment Program (SEAMAP) shrimp/groundfish trawl survey have long been used in assessing diverse managed taxa, including several reef fishes; however, there are rising concerns over the impacts of trawling on live‐bottom habitats. Using data collected from summer SEAMAP trawl surveys (2009–2016; N = 1,103), we examined how avoiding areas of live‐bottom habitat might affect the survey's ability to assess interannual changes in abundance of managed reef fish taxa. Trawl samples at 48% of sampling sites contained <50 kg of sponge, and 12% of sampling sites contained at least 50 kg of sponge, while 40% of sites had zero sponge bycatch. Mean number of taxa, taxonomic richness, and taxonomic diversity were significantly higher as sponge bycatch increased, while the total number of individuals remained the same. To examine interannual variability of managed reef fish taxa, annual indices of relative abundance were calculated on different subsets of data (all data, data excluding sites with sponge bycatch ≥50 kg, and data excluding all sites with sponge bycatch). For Red Snapper Lutjanus campechanus and pink shrimp Farfantepenaeus duorarum, indices and general trends were largely unaffected by excluding sites with sponge, but for most selected taxa (e.g., Gray Triggerfish Balistes capriscus and Red Grouper Epinephelus morio), overall trends were affected by excluding sites that contained sponge bycatch, and in some cases the frequency of occurrence did not meet the requirement to calculate an index of abundance (i.e., <5%) when sponge sites were excluded (e.g., Hogfish Lachnolaimus maximus). Efforts to mitigate survey interactions with live‐bottom habitats will likely alter the utility of survey data and the ability to assess managed species, so careful consideration is needed to evaluate any trade‐offs between the benefits of the trawl survey for fishery assessments and the benefits of protecting the habitat. [ABSTRACT FROM AUTHOR]

Adaptive spatial management provides a way to balance the conservation of bycatch species and the potential economic effects of bycatch‐induced closures on a fishery, but implementation can be both data and resource intensive. We present a survey exploring a novel approach to adaptively manage an intermittent bycatch issue in an inshore trawl fishery where Sciaenidae bycatch species (including juvenile Mulloway Argyrosomus japonicus, a species of conservation concern) co‐occur with large aggregations of a valuable target species (eastern school prawn Metapenaeus macleayi), following flood‐induced egression from estuarine habitats. Diurnal sampling surveys followed three flood events and targeted permanent inshore closure zones (designed to protect the normally nocturnally harvested eastern king prawn Melicertus plebejus) and adjacent inshore nonclosure areas. Sciaenidae abundance was mostly <10 fish/ha trawled, but larger catches generally corresponded with larger catches of eastern school prawn, and these relationships appeared to be steeper within nonclosure zones. There were only minor differences in the size structure of eastern school prawn between zones, and patterns were event and location specific. Negligible eastern king prawn were encountered. The results show that temporarily allowing fishers access to permanent trawl closures following floods may support the exploitation of aggregated target species with reduced interaction with bycatch species of concern. The approach presented here is relevant to the consideration of adaptive spatial management in other trawl fisheries. [ABSTRACT FROM AUTHOR]

Trawling is generally an unselective fishing method that is employed to harvest a number of species. Capture of nontarget species that are subsequently discarded is an important issue for trawl fisheries, especially penaeid trawl fisheries. While gear modifications are a common approach to manage this issue, maintaining areas that are closed to trawling may also have a positive impact on these nontarget species. This study systematically examined the diversity and abundance of nontarget species across a network of areas closed to trawling (trawl closure areas) relative to adjacent areas that were open to trawling. Analysis of nontarget species from 209 trawls and 72,787 animals (across 216 taxa) revealed some impact on both abundance and diversity within trawl closure areas. Latitude was a key variable that was driving differences in the taxonomic assemblage among locations. Within locations, there were inconsistent impacts for different nontarget species in trawl closure areas. Length distributions showed size truncation of abundant nontarget species in fished areas relative to adjacent trawl closure areas. While the impact of trawl closure areas varied among species, it was clear that the spatial management in the fishery provided some refuge for a diversity of nontarget species, observed in patterns of species richness, abundance, and population size structure. Latitudinal breadth appears to be an essential component of the trawl closure network, but localized effects may be important for maintaining reproductive capacity for nontarget species. These data highlight the broader utility of trawl closure networks as a management tool for trawl fisheries. [ABSTRACT FROM AUTHOR]

Silver Carp Hypophthalmichthys molitrix are elusive fish that can be difficult to capture with conventional management tools. New tools must be developed to help increase the capture of Silver Carp, thereby improving the understanding and management of the species. An electrified dozer trawl was developed in an attempt to increase the capture of Silver Carp while reducing the amount of sampling effort needed to successfully assess a population and inform management actions. We compared Silver Carp catch rates, sample run time, and Silver Carp length frequency distributions from the electrified dozer trawl with those from conventional boat electrofishing. Silver Carp capture was greater and sample time was shorter for the electrified dozer trawl compared to conventional boat electrofishing. Length frequency distributions were similar between gears. The electrified dozer trawl can shorten sample run times and potentially improve Silver Carp capture, thus facilitating management. Use of the electrified dozer trawl should be expanded beyond Missouri River tributaries to further understand the gear's potential for sampling Silver Carp in a diverse array of environments. [ABSTRACT FROM AUTHOR]

Abstract: Electrotrawling using electric pulse stimulation is a promising alternative to beam trawling in the brown shrimp Crangon crangon and Dover Sole Solea solea (also known as Solea vulgaris) fisheries of the North Sea. In the sole fishery, a 40–80‐Hz pulse stimulation induces tetany in the muscles, which may result in injuries. Whereas no injuries have been reported in flatfish or selachian sharks and rays, electrically induced spinal injuries have been observed in gadoids such as Atlantic Cod Gadus morhua and Whiting (also known as European Whiting) Merlangius merlangus. This may indicate that fish species with a fusiform shape are more susceptible to electric pulses. Similar variation among species in electrically induced spinal injuries has been observed in freshwater electrofishing, although large variability in vulnerability has been reported among different freshwater fusiform species. Therefore, we aimed to assess the vulnerability of another, nongadoid, fusiform osteichthyan: Sea Bass Dicentrarchus labrax (also known as European Bass Morone labrax). Two length groups of Sea Bass (31.3 ± 2.2 and 42.1 ± 2.5 cm) were exposed to electric pulses as used in commercial electrotrawls targeting Sole (80 bipolar pulses per second, 2% duty cycle). Thereafter, the fish were monitored daily and then euthanized 14 d after exposure for gross, radiographic, and histologic examination. No injuries were found in fish exposed to the electrical pulses. Differences in vertebral morphology among fusiform species may result in varying vulnerabilities to electrically induced spinal injuries. As a result, electrically induced spinal injuries and/or their variability in both marine and freshwater species may be determined by similar morphological parameters. [ABSTRACT FROM AUTHOR]

Long-term population monitoring assumes that relative abundance reflects trends in the population. Sampling efficiency and capture probability are assumed to be consistent so samples can be temporally and spatially compared. Benthic otter trawls are being used for a long-term monitoring project on the Missouri River. To estimate the capture probability of Pallid SturgeonScaphirhynchus albus, we used acoustic telemetry to locate and target tagged sturgeon with benthic otter trawls. Conditional capture probability (pi*) of a fish in a known location was only 0.08 on the first pass, increased slightly (pi* = 0.18) on the second pass, and again on the third pass (pi* = 0.26). Individual habitat parameters or their interactions did not explain when Pallid Sturgeon were successfully or unsuccessfully captured. Our study suggests that otter trawls are a highly inefficient gear for capturingScaphirhynchusspecies. Therefore, relative abundance indices based on otter trawl captures need to be assessed cautiously for juvenile and adult Pallid Sturgeon, especially in highly variable conditions. Received December 4, 2014; accepted March 19, 2015 [ABSTRACT FROM PUBLISHER]

The effect of reach length on species richness (estimated with boat-mounted electrofishing, a modified Missouri trawl, and a bag seine) was evaluated in Iowa's nonwadeable river systems. In 2007 and 2008, 21 reaches were sampled on 16 nonwadeable rivers throughout Iowa; reaches were 3 or 5 km in length, depending on stream order. A total of 21,197 fish from 83 species were sampled in this study. Electrofishing produced the highest number of species (65), followed by trawling (60) and seining (54). Forty-seven percent of all the species sampled in this study were captured by all three gears. Four species were captured only by the seine, 8 only by the trawl, and 13 only by electrofishing. Fish sampling data were used to evaluate gears and estimate the number of samples required to observe specified percentages of the total number of species in each reach. The minimum effort necessary to sample 90% of the species in a reach with 95% confidence was determined using a resampling procedure. Sampling with a seine was considered ineffective in nonwadeable rivers and did not substantially reduce the effort necessary to sample 90% of the species in a reach. In 3-km-long reaches, the minimum effort necessary to sample 90% of the species observed was fifteen 100-m electrofishing runs and twenty-four 50-m-long trawls. Twenty-five 100-m electrofishing runs and forty-two 50-m-long trawls were necessary to sample 90% of the species observed in 5-km-long reaches. [ABSTRACT FROM AUTHOR]

We compared the size structure, estimated mean total length (TL) at age, and estimated mortality of black crappie caught by otter trawl and haul seine at two Florida water bodies (Lakes Parker and Griffin) and used the capture data, estimates of gear-induced mortality, and fishing variables (i.e., fishing effort and volume sampled) to evaluate the efficacy of using haul seines in future projects. Haul seines captured a smaller size range of black crappie than did trawls, and black crappie did not appear to be recruited to the haul seines until they attained 209 mm TL. Haul seines tended to capture proportionally more large fish than did trawls, when considering individuals 210 mm or longer. Mean TL-at-age estimates tended to be larger for haul seines due to differences in gear selectivity. At Lake Parker, trawl captures produced a greater annual mortality estimate ( A), and the differences between catch curve slopes were significant. At Lake Griffin, however, haul seines produced a larger value of A, but the differences between the two catch curve slopes were not significant. Gear-induced mortality estimates of sport fish (bluegill , redear sunfish , and black crappie) captured with the haul seines ranged from 3.2% to 24.2% but varied with species, with black crappie mortality rates being the highest. Haul seines required a relatively high level of effort but provided a larger sample size of black crappie 210 mm or longer than did trawls because of extreme differences in the volume of water sampled and trawls' selectivity for smaller fish. A smaller-mesh haul seine would allow us to sample larger size ranges of fish and increase the number of age-classes captured by the gear, which may allow for more accurate estimates of the population size and age structures. However, the size selectivity patterns of black crappie captured by the haul seine are not known, and further research is recommended to evaluate haul seines with smaller mesh sizes. [ABSTRACT FROM AUTHOR]

The Northern Refuge was established in 1985 as pan of the lake trout Salvelinus namaycush rehabilitation effort for Lake Michigan. To evaluate progress toward lake trout rehabilitation in the Northern Refuge, we conducted annual (1991-2008) gill-net surveys in the tall to assess the adult population and beam trawl surveys in the spring to assess naturally reproduced age-0 lake trout. Our criteria for evaluating progress included the density of "wild" age-0 fish within the Northern Refuge, the proportion of wild fish within the adult population, density of spawners, adult survival, growth, and wounding rate by sea lampreys Petromyzon marinus. No wild age-0 lake trout were caught in the Northern Refuge during 1991-2008. Overall, wild lake trout did not recruit to the adult population to any detectable degree. The mean density of spawning lake trout decreased from 45 fish ⋅ 305 m of gill net-1 ⋅ d-1 during 1991-1999 to only 4 fish ⋅ 305 m-1 ⋅ d-1 during 2000-2008. Although the sea lamprey wounding rate more than doubled between these two time periods, catch curve analysis revealed that mortality of adult lake trout actually decreased between the two periods. Therefore, the 90% decrease in abundance of spawning lake trout between the two periods could not be attributed to increased sea lamprey predation but instead was probably due in part to the reduced lake trout stocking rate during 1995-2005. The paucity of natural reproduction in the Northern Refuge during 1991-2008 most likely resulted from alewife Alosa pseudoharengus interference with lake trout reproduction and from the relatively low lake trout spawner density during 2000-2008. Our results suggest that the annual stocking rate of lake trout yearlings should be increased to at least 250,000 fish/reef to achieve greater densities of spawners. [ABSTRACT FROM AUTHOR]

We evaluated the efficacy of three gears commonly used to sample shovelnose sturgeon Scaphirhynchus platorynchus, pallid sturgeon S. albus, and lake sturgeon Acipenser fulvescens in large rivers. We stratified habitats and randomly sampled sites with trawls, gill nets, and trotlines in the middle Mississippi River from June 2003 through May 2005 (N = 3,476 samples). A total of 3,523 shovelnose sturgeon, 31 pallid sturgeon, and 13 lake sturgeon were captured. When sample sizes were adequate (based on power analysis), we used a mixed analysis of variance (ANOVA) procedure to determine the relative impact of season and gear type on sturgeon catch per unit effort (CPUE). Kolmogorov-Smirnov tests were used to determine whether the length frequency distributions for each species differed among gears. Overall, the power analyses indicated that there were adequate sample sizes for comparing standardized CPUE for shovelnose sturgeon among seasons; however, too few pallid or lake sturgeon were collected to make statistical comparisons. Shovelnose sturgeon catch rates varied among gears and seasons; season and gear type interacted in the ANOVA model. Among gear types, 5.08-cm gill nets produced the highest standardized CPUE, and catch rates were highest during spring. The length frequency distributions of shovelnose sturgeon depended on gear type. Shovelnose sturgeon can be sampled in large rivers using stratified random sampling with this combination of gear. However, pallid sturgeon and lake sturgeon may be too rare to sample with this approach. [ABSTRACT FROM AUTHOR]

Populations of cisco Coregonus artedi in the Laurentian Great Lakes supported large-scale commercial fisheries and were the primary forage of piscivores during the first half of the 20th century. However, by 1970 populations had collapsed in all of the lakes. Since then, ciscoes have staged a recovery in Lake Superior. In this synthesis, we describe the status of ciscoes in Lake Superior during 1970-2006 and provide a comprehensive review of their ecology. Better understanding of age estimation techniques, application of hydroacoustic and midwater trawl sampling, and compilation of long-term data sets have advanced our understanding of the species. Management agencies contemplating rehabilitation of cisco populations should recognize that (1) knowledge of cisco ecology and population dynamics is increasing; (2) ciscoes are long-lived; (3) Great Lakes populations are probably composed of both shallow-water and deepwater spawning forms; (4) large year-classes can be produced from small adult stocks; (5) large variation in year-class strength is probably intrinsic to Great Lakes populations; (6) despite the longevity and early maturity of ciscoes, stocks can be overfished because large year-classes are produced infrequently; (7) regional environmental factors appear to play a large role in reproductive success; and (8) rainbow smelt Osmerus mordax are likely to have a negative effect on cisco recruitment under certain conditions. A top-down approach for rehabilitating lake trout Salvelinus namaycush in Lake Superior probably benefited cisco recovery through lake trout predation on invasive rainbow smelt populations. We argue that managing for populations of exotic alewives Alosa pseudoharengus to support popular recreational fisheries of exotic Pacific salmonids in the other Great Lakes conflicts with stocking efforts to rehabilitate native lake trout in those lakes. If native fish rehabilitation is a serious and primary goal for management agencies in the Great Lakes basin, we propose that an ecosystem-based approach to modifying the environment for the benefit of native fish species (i.e., decimation or eradication of invasive species) is required. [ABSTRACT FROM AUTHOR]

The National Marine Fisheries Service has encouraged regional management councils to develop fisheries ecosystem plans that, among other things, identify the bycatch species within each fishery and describe each species' spatial and temporal distribution. Horseshoe crabs Limulus polyphemus have been harvested along the eastern coast of the USA since the 1800s; however, a fishery management plan was only recently created for this species, and bycatch in the horseshoe crab trawl fishery has not been quantified. We identified species likely to be caught as bycatch in the commercial fishery by using species composition data from a fishery-independent horseshoe crab trawl survey conducted in 2005 and 2006. Seventy-six taxa were caught, including 47 finfish species from 33 families. Skates (family Rajidae) comprised more than one-half of the total biomass caught, and horseshoe crabs comprised one-third of the total biomass. Catch per unit effort (kg/km towed) was greatest for little skate Leucoraja erinacea, winter skate Leucoraja ocellata, horseshoe crab, and clearnose skate Raja eglanteria. We also caught species that are currently on the World Conservation Union's Red List (e.g., Atlantic sturgeon Acipenser oxyrinchus) and unmanaged within U.S. waters (e.g., cownose ray Rhinoptera bonasus and smooth dogfish Mustelus canis). Nonmetric multidimensional scaling was used to cluster sites based on species abundance. The sites strongly clustered into two distinct groups, suggesting that species composition differs between northern and southern sites. Bottom water temperature was a significant factor in determining species composition, explaining almost 70% of the variation in species composition among sites. The results of this study provide managers with a better understanding of which nontarget populations may be affected by the horseshoe crab trawl fishery, a first step in understanding the broader ecosystem-level effects of this fishery. [ABSTRACT FROM AUTHOR]

A geographical information systems technique for visualizing spatial data was used in conjunction with standard analytical procedures to examine the size-specific distribution of brown shrimp Farfantepenaeus aztecus in nearshore nursery areas and open waters of the Mississippi Sound. Brown shrimp abundance was assessed during 2000, 2001, and 2002 by means of an otter trawl along 10 transects consisting of three stations each. The number of brown shrimp, together with the dissolved oxygen, temperature, and salinity values, were collected at each sampling station. A decreasing trend in salinity was observed from east to west. The highest salinities were measured in 2000. No temporal patterns in dissolved oxygen or temperature were apparent. Brown shrimp showed the highest abundances in western Mississippi Sound, an area adjoining the extensive marshes of St. Tammany and St. Bernard parishes in Louisiana. The average size of the brown shrimp in the western sound was smaller than that of the brown shrimp in other areas, indicating continued recruitment in the former area. [ABSTRACT FROM AUTHOR]

We compared trawling with electrofishing for assessing populations of black crappie Pomoxis nigromaculatus in two shallow central Florida lakes. Lakes Jackson and Weohyakapka were sampled with both gears from November 2005 through March 2006. Size-selective biases were apparent, the trawl nets consistently collecting small individuals less than 100 mm in total length (TL), whereas electrofishing collected significantly larger, more adult fish exceeding 200 mm TL. The Kolmogorov-Smimov two-sample test indicated that the size structure of the fish captured in the two types of gear differed significantly. The total annual mortality estimates were 28% and 72% for electrofishing on both lakes, 55% for otter trawls on Lake Jackson. The age ranges for catch curves derived from the two gears also displayed large differences in mortality estimates or gave no mortality estimate at all. Trawls tended to collect younger age-classes, whereas electrofishing tended to collect larger age-classes; thus, data collected with the two gears may represent different aspects of mortality in the population. When aquatic macrophyte cover is low so that both gears can be used, we recommend that otter trawl sampling be used to assess the recruitment of juvenile crappies and that simultaneous electrofishing be conducted to collect larger fish for the determination of age and growth. Fisheries biologists should be careful when using just one gear to evaluate crappie populations given that the size-selective biases associated with both trawling and electrofishing can influence basic mortality and length-frequency assessments. [ABSTRACT FROM AUTHOR]

An annual daytime bottom trawl survey of the Lake Superior fish community designed in 1978 does not adequately assess the entire community. Whereas recent studies have recommended that pelagic species be surveyed with a combination of acoustic and midwater trawling methods (AC-MT), we used bottom trawling to study the effects of depth, diel period, and season on biomass estimates and the sizes of bottom-oriented species. Day and night bottom trawl samples were collected within 48 h at three depths (30, 60, and 120 m) at a Lake Superior site during eight sampling periods that included two seasons each year (early summer and late summer to early fall) for 2 years (2004 and 2005). Depth significantly affected the biomass of seven of the eight species analyzed, while diel period affected the biomass of six species. For most species, average biomass levels were higher at night. The effect of season on biomass was comparatively low (three species were significantly affected). Depth significantly affected the sizes of six bottom-oriented species, as the average length of most species increased with depth. The effects of diel period (three species) and season (one species) on average length were comparatively small. By adding night bottom trawl samples to night AC-MT collections, the entire fish community of Lake Superior can be monitored with a single lakewide survey employing multiple gears. The establishment of offshore sampling (i.e., where depths exceed 80 m) will provide estimates of deepwater species that have been largely undersampled by the 1978-designed survey. We recommend that the present fish community survey be maintained, albeit at a reduced level, until a nighttime survey time series is well established (in 3-5 years). [ABSTRACT FROM AUTHOR]

The relationship between the growth rates and abundance of yellow perch Perca flavescens was evaluated in the Indiana waters of Lake Michigan from 1984 to 2004. Relative abundance values were taken from trawl catch per unit effort, while growth rates were determined by back-calculation. Abundance was approximately one order of magnitude higher during the mid-1980s than in 1990-2004. Growth rates were negatively related to relative abundance and were sexually dimorphic (females grew faster than males). Regression analysis indicated that approximately one-half of the observed variation in growth was related to abundance; this was most apparent with smaller and younger fish. Lee's phenomenon was shown to be present during periods of high exploitation and not present during periods of low exploitation. Both intraspecific competition and physiological changes associated with age at maturity are plausible explanations for these relationships. [ABSTRACT FROM AUTHOR]

Evaluation of the biases in sampling methodology is essential for understanding the limitations of abundance and biomass estimates of fish populations. Estimates from surveys that rely solely on bottom trawls may be particularly vulnerable to bias if pelagic fish are numerous. We evaluated the variability in the vertical distribution of fish biomass during the U.S. Geological Survey's annual spring bottom trawl survey of Lake Superior using concurrent hydroacoustic observations to (1) test the assumption that fish are generally demersal during the day and (2) evaluate the potential for predictive models to improve bottom trawl-determined biomass estimates. Our results indicate that the assumption that fish exhibit demersal behavior during the annual spring bottom trawl survey in Lake Superior is unfounded. Bottom trawl biomass (BBT) estimates (mean ± SE) for species known to exhibit pelagic behavior (cisco Coregonus artedi, bloater C. hoyi, kiyi C. kiyi, and rainbow smelt Osmerus mordax; 3.01 ± 0.73 kg/ha) were not significantly greater than mean acoustic pelagic zone biomass (BAPZ) estimates (6.39 ± 2.03 kg/ha). Mean BAPZ estimates were 1.6- to 4.8-fold greater than mean BBT estimates over 4 years of sampling. The relationship between concurrent BAPZ and BBT. estimates was marginally significant and highly variable. Predicted BAPZ estimates using cross-validation models were sensitive to adjustments for back-transforming from the logarithmic to the linear scale and poorly corresponded to observed BAPZ estimates. We conclude that statistical models to predict BAPZ from day BBT cannot be developed. We propose that night sampling with multiple gears will be necessary to generate better biomass estimates for management needs. [ABSTRACT FROM AUTHOR]

The spiny dogfish Squalus acanthias was once classified as an underutilized species along the U.S. East Coast, but it constituted a lucrative fishery in the 1990s until recruitment overfishing caused stock collapse. Coastwide restrictions currently apply; federal stock assessment models use bycatch mortality estimates of 50% for trawling, 75% for gill netting, and 100% for hook-and-line fishing. This study examined mortality at the southern end of commercial fishing operations caused by trawling for 30- and 90-min periods and by gill nets of various mesh sizes set for 19- to 24-h periods. Both experiments used tagged and untagged fish placed in rectangular cages anchored to the seafloor for 48 h. Tags were the Floy SS-94 single-barb nylon dart with a stainless steel wire insert. A total of 635 spiny dogfish were captured by trawl and all were alive, for a 0% initial mortality rate. A total of 2.284 spiny dogfish were collected by gill net for an initial mortality rate of 17.5%. There was no additional mortality in the 480 trawl-caught fish held for 48 h, but there was 33.3% mortality among the 480 gill-net-caught fish held under the same conditions, for an overall gill-net mortality rate of 55.0%. Examination of subsampled catches indicated that 88.6% of gill-net-caught fish had gill-net marks on the head and 41.2% had gill-net marks on the girth but, interestingly, 26.1% of trawl-caught fish had the same markings, indicating prior gill-net capture and release. Female spiny dogfish caught by gill net had a 3.6% abortion rate, compared with zero incidences of those caught by trawl. There was no significant difference in mortality between tagged and untagged fish caught by trawl or by gill net. Tag loss after 48 h was less than 1%. [ABSTRACT FROM AUTHOR]

Recent predator demand and prey supply studies suggest that an annual daytime bottom trawl survey of Lake Superior underestimates prey fish biomass. A multiple-gear (acoustics, bottom trawl, and midwater trawl) nighttime survey has been recommended, but before abandoning a long-term daytime survey the effectiveness of night sampling of important prey species must be verified. We sampled three bottom depths (30, 60, and 120 m) at a Lake Superior site where the fish community included all commercially and ecologically important species. Day and night samples were collected within 48 h at all depths during eight different periods (one new and one full moon period during both early summer and late summer to early fall over 2 years). Biomass of demersal and benthic species was higher in night bottom trawl samples than in day bottom trawl samples. Night acoustic collections showed that pelagic fish typically occupied water cooler than 15°C and light levels less than 0.001 lx. Using biomass in night bottom trawls and acoustic biomass above the bottom trawl path, we calculated an index of acoustic detectability for each species. Ciscoes Coregonus artedi, kiyis C. kiyi, and rainbow smelt Osmerus mordax left the bottom at night, whereas bloaters C. hoyi stayed nearer the bottom. We compared the biomass of important prey species estimated with two survey types: day bottom trawls and night estimates of the entire water column (bottom trawl biomass plus acoustic biomass). The biomass of large ciscoes (>200 mm) was significantly greater when measured at night than when measured during daylight, but the differences for other sizes of important species did not vary significantly by survey type. Nighttime of late summer is a period when conditions for biomass estimation are largely invariant, and all important prey species can be sampled using a multiple-gear approach. [ABSTRACT FROM AUTHOR]

Fish abundance indices obtained from annual research trawl surveys are an integral part of fisheries stock assessment and management in the Great Lakes. It is difficult, however, to administer trawl surveys using a single vessel--gear combination owing to the large size of these systems, the jurisdictional boundaries that bisect the Great Lakes, and changes in vessels as a result of fleet replacement. When trawl surveys are administered by multiple vessel--gear combinations, systematic error may be introduced in combining catch-per-unit-effort (CPUE) data across vessels. This bias is associated with relative differences in catchability among vessel-gear combinations. In Lake Erie, five different research vessels conduct seasonal trawl surveys in the western half of the lake. To eliminate this systematic bias, the Lake Erie agencies conducted a side-by-side trawling experiment in 2003 to develop correction factors for CPUE data associated with different vessel--gear combinations. Correcting for systematic bias in CPUE data should lead to more accurate and comparable estimates of species density and biomass. We estimated correction factors for the 10 most commonly collected species age-groups for each vessel during the experiment. Most of the correction factors (70%) ranged from 0.5 to 2.0, indicating that the systematic bias associated with different vessel-gear combinations was not large. Differences in CPUE were most evident for vessels using different sampling gears, although significant differences also existed for vessels using the same gears. These results suggest that standardizing gear is important for multiple-vessel surveys, but there will still be significant differences in catchability stemming from the vessel effects and agencies must correct for this. With standardized estimates of CPUE, the Lake Erie agencies will have the ability to directly compare and combine time series for species abundance. [ABSTRACT FROM AUTHOR]

Rehabilitation of lake sturgeon Acipenser fulvescens in the Great Lakes would benefit from a greater understanding Acipenser fulvescens in the Great Lakes would benefit from a greater understanding of early life stage attributes. The objectives of this study were to determine the efficacy of active and passive sampling gears for capturing age-0 lake sturgeon and evaluate whether the most effective gear types were size selective. Fish were collected by means of active (i.e., wading, haul-seine, backpack electrofishing, snorkeling surveys, and bottom trawls) and passive (i.e., gill nets, set lines, and fyke nets) sampling gears from June to November of 2002 and 2003 in the lower Peshtigo River, Wisconsin, and nearshore waters of Green Bay. Mean catch per unit effort (CPUE) was greatest for day wading (0.036 fish/min), followed by day haul-seine surveys (0.029 fish/min), night wading (0.020 fish/min), and night haul-seine surveys (0.015 fish/min). Night wading surveys captured the greatest number of fish (N = 118). Day and night electrofishing (CPUE = 0.008 and 0.013 fish/min, respectively), snorkeling (CPUE = 0.010 fish/ min), and gill nets (CPUE = 0.026 fish/d) were less effective gear types, while bottom trawls, set lines, and fyke nets did not capture fish. Smaller fish were captured during day wading and haul-seine surveys (median = 71 and 68 mm, respectively) than during night wading and haul-seine surveys (median = 120 and 133 mm, respectively). Based on these results, we recommend the use of wading and haul-seine surveys to collect age-0 lake sturgeon in shallow lotic and lentic systems, such as the lower Peshtigo River and Green Bay, that are characterized by low current velocity and high water clarity. [ABSTRACT FROM AUTHOR]

Coordinated acoustic and trawl surveys were performed to locate aggregations of adult eulachon Thaleichthys pacificus in the lower Fraser River, British Columbia, during spring 2001 and 2002. Aggregations were encountered in one portion of the study area in both years. They contained mature, spawning, and spent eulachon of both sexes, of which over 80% were spent males. These groups were 880-2,000 m long and averaged 117-140 m wide. Within them, mean fish density was 0.27-0.29 fish/m³ and species composition was 87-99% eulachon. They occurred in 6-8.5 m of water over substrate that was mainly sand with a small fraction of pea gravel. We did not determine whether these eulachon spawned in that area or had congregated there for another purpose, such as holding or migration. Other species occasionally encountered in appreciable numbers were juvenile pink salmon Oncorhynchus gorbuscha and chum salmon O. keta. Mean in situ target strengths of eulachon were -53.3 dB at 123 kHz and -50.3 dB at 208 kHz. Coordinated acoustics and trawling were effective for locating eulachon aggregations at low to moderate flows (river discharge of 3,200 m³/s or less), but were hampered by entrained debris during higher flows of spring runoff. Under suitable river conditions, the high resolution and rapid spatial coverage of this technique are apt for habitat preference studies and point source environmental assessments in large, turbid rivers. [ABSTRACT FROM AUTHOR]

Our objective was to determine the effects of the extent and duration of seasonal flooding (meters above normal pool) on recruitment indices for threadfin shad Dorosoma petenense, white crappies Pomoxis annularis, and largemouth bass Micropterus salmoides in Hugo Reservoir, Oklahoma. We used simple linear regression to examine the relations between seasonal pool elevation exceedence duration (number of days for which elevation exceeded target values) and (1) mean monthly (June-September) estimates of age-0 threadfin shad abundance in midwater trawls; (2) white crappie abundance estimates from May and June trawl samples and November trap-net samples; and (3) fall electrofishing samples of age-0 largemouth bass. Due to the large number of relations tested, we could not discount the possibility that a significant positive relation between threadfin shad trawl catches in July-September and winter exceedence duration (≥123.8 m) occurred by chance. No relation was found between elevation and age-0 white crappie catch in trawls or trap nets. Summer exceedence duration (≥ 123.8 m) was positively related to largemouth bass recruitment. The results of this study indicated that a water level management plan that calls for holding water in the flood pool during summer would enhance recruitment of largemouth bass in Hugo Reservoir. [ABSTRACT FROM AUTHOR]

We conducted a study from 1998 to 2001 to determine the efficacy of a benthic trawl designed to increase species detection and reduce the incidence of zero catches of small-bodied fishes. We modified a standard two-seam slingshot balloon trawl by covering the entire trawl with a small-mesh cover. After completing 281 hauls with the modified (Missouri) trawl, we discovered that most fish passed through the body of the standard trawl and were captured in the cover. Logistic regression indicated no noticeable effect of the cover on the catch entering the standard portion of the modified trawl. However, some fishes (e.g., larval sturgeons Scaphirhynchus spp. and pallid sturgeon S. albus) were exclusively captured in the small-mesh cover, while the catch of small-bodied adult fish (e.g., chubs Macrhybopsis spp.) was significantly improved by use of the small-mesh cover design. The Missouri trawl significantly increased the number and species of small-bodied fishes captured over previously used designs and is a useful method for sampling the benthic fish community in moderate- to large-size river systems. [ABSTRACT FROM AUTHOR]

We tested the potential of a selective flatfish trawl to reduce bycatch of slope rockfish in the upper continental slope bottom-trawl fishery (250-500 m) on the U.S. West Coast. The trawl we tested differed from typical slope trawls in that it was a low-rise, two-seam trawl with a severely cut back headrope. We used an alternate haul, randomized block design to compare catches of the experimental trawl with those of a typical four-seam, high-rise trawl and to examine diel changes in catch rates for both trawls. The experimental trawl produced catches similar to the control trawl for all commercially valuable flatfish, except arrowtooth flounder Atheresthes stomias, which was reduced 24%. Catches of most rockfish and roundfish were significantly reduced in the experimental trawl (50-94% depending on species). However, the catches of darkblotched rockfish Sebastes crameri and redbanded rockfish S. babcocki were not reduced significantly in the experimental trawl. Nighttime catches were reduced 30-99% for most rockfish species, the greatest reductions occurring in the experimental trawl. The large nighttime catch reduction for several rockfish species for both trawls along with no catch reduction in Dover sole Microstomus pacificus, suggests that fishing only at night may be a viable bycatch-reduction strategy for some rockfish species. The diel and depth-related variation in catch rates we noted for the selective flatfish trawl indicates that catches by this trawl may be especially sensitive to physical and environmental factors such as time of day, depth, or turbidity. [ABSTRACT FROM AUTHOR]

We developed a surface pair-trawl system to detect juvenile Pacific salmon Oncorhynchus spp. marked with passive integrated transponder (PIT) tags as they migrate through the upper Columbia River estuary. The trawl was fitted with a detection antenna in its cod end and was deployed by two vessels. Fish entering the trawl body exit after passing by the detection antenna. Detection data were recorded by electronic components housed in a small boat tethered to the trawl. The system was modified extensively after its first deployment in 1995 and by 2001 was performing reliably under a variety of weather conditions and river flows. From 1995 to 2001 the device detected 29,699 PIT-tagged juvenile salmon. During extended daily sampling periods, we detected nearly 2% of all PIT tags previously detected at Bonneville Dam, which is located 159 rkm upstream from the study area. [ABSTRACT FROM AUTHOR]

Fishermen must use small-mesh bottom trawls to capture certain species of fish that cannot be retained by standard groundfish mesh sizes. These fisheries are subject to bycatch limits when such trawls are used in areas where regulated species reside. Bycatch of regulated flatfish in the small-mesh bottom trawl fishery for silver hake Merluccius bilinearis in the northwestern Atlantic is a concern of management because silver hakes are captured in areas where juvenile regulated flatfish are common. An evaluation of flatfish and silver hake behaviors using low-light underwater cameras suggested that the two species could be separated within the mouth of a bottom trawl. Using the alternate tow method, four different large-mesh panels positioned in the lower belly of the trawl were separately evaluated. One of them proved to be effective in reducing flatfish bycatch while not reducing the catch of silver hakes; a large-mesh panel constructed of 40.6-cm (16-in) stretched mesh that was diamond shaped using orange-colored nylon twine 1.6 mm (0.06 in) in diameter in the lower belly resulted in a 73% reduction in flatfish catch with no effect on the catch of silver hakes. [ABSTRACT FROM AUTHOR]

Presents a study that evaluated the estimation of the trawling effort and bycatch in the Gulf of Mexico shrimp fishery. Background on bycatch in the Gulf shrimp fishery; Methodology of the study; Definition of the habitat zones used to describe trawl effort and bycatch.

Presents a study that evaluated the spatial distribution of U.S. west coast bottom-trawl effort in relation to areas of prime habitat for rockfish Sebastes between 1992 and 2001. Monthly maximum rockfish catch limits for trawlers; Reason for the decline in shelf rockfish stocks; Use of a logbook data in the study.