Pop Nets Research Articles

Introduced Spartina anglica modifies fish habitat in southern temperate succulent saltmarshes

Vegetation changes in saltmarsh habitat can influence fish assemblages and abundance. In Tasmania, Australia, mid‐latitude succulent saltmarsh communities have been invaded by the introduced tall grass, Spartina anglica. Eradication efforts have been ongoing since the 1990s with purported benefits for fish access to intertidal foraging grounds, but a lack of knowledge of the impact of S. anglica on fish limits understanding of the benefits and effectiveness of native habitat restoration. Here, we investigate whether fish assemblages in native saltmarshes and non‐native S. anglica grassland differ in species diversity, fish abundance, and size class distribution. We used buoyant pop nets to sample fishes in Sarcocornia quinqueflora herbland and S. anglica grassland swards at three sampling stations in northwest Tasmania. Very few individuals and low species diversity were recorded in both vegetation types at the sampling station with the most well‐established S. anglica infestation. Elsewhere, richness and diversity were higher in S. quinqueflora herbland. Overall fish abundance was higher in S. quinqueflora than in S. anglica, with a very strong effect at one sampling station. Fewer small individuals of the numerically dominant Atherinosoma microstoma were recorded in S. anglica, potentially indicating impaired nursery function. Our results provide important insights for S. anglica control, as we are the first to demonstrate a relationship between S. anglica presence and fish characteristics in southern Australian saltmarsh. These results indicate that S. anglica control is valuable for fish conservation. An extension of our research to document the effects of S. anglica removal on fishes is desirable.

Juvenile Fish Associated With Pondweed and Charophyte Habitat in the Curonian Lagoon

Submerged macrophytes are essential elements of sublittoral ecosystems to maintain a diverse fish fauna. The aim of this study was to assess juvenile fish associated with macrophyte habitats in the Curonian Lagoon by means of modified pop net method. We focused on two dominant littoral habitats with different structure (pondweed and charophyte stands). The pop nets sampling was carried out on two study sites located in the freshwater and oligohaline part of the lagoon in July and September 2019-2020. Our upgraded pop nets reduced the risk of under sampling and are recommended for monitoring fishes since this method has relatively low disturbance on fish behavior and on the habitat itself. The most efficient time of sampling with pop nets in shallow macrophyte habitats is at night, where at least 4 samples collected are sufficient to represent the biggest part (> 70%) of the fish assemblage, but the sampling covering different times of day is recommended. In total, 14 juvenile species were recorded, where perch and European roach dominated (respectively 48% and 24%). Half of the species (8) were associated with macrophyte stands, although water salinity and temperature were the most important factors explaining the variance of fish abundance followed by the sampling time and the biomass of macrophytes. Based on the abundance and the duration of species within these habitats, European roach, nine-spined and three-spined stickleback were mainly associated with the pondweed biomass and stands, while spined loach, round goby, perch, ruffe and gudgeon were mainly associated with the charophyte biomass and stands. The increase of charophyte stands since 2005 affected the fish assemblage where it should have enhanced the abundance of perch, ruffe, spined loach and partly round goby.

A systematic review of methods used to study fish in saltmarsh flats

There is a growing body of research highlighting the importance of saltmarshes as habitats for fish for feeding, refuge from predation and reproduction. However, more work is needed on fish on vegetated marsh flats (or surfaces). We reviewed 60 studies that used 21 methods to sample fish assemblages on saltmarsh flats. Drop samplers, fyke nets and pop nets were most frequently employed, with considerably more studies being conducted in graminoid than succulent marsh. Reporting of sampling temporal and tidal details, environmental variables and fish attributes was inconsistent. Most of the papers focussed on one or more of conservation management, comparisons among habitat types, and the use of saltmarsh (including fish activity type or residency status). Important potential areas of research include the relationships between the fish assemblages of saltmarsh flats and coastal fisheries, the effects of invasive plant species and marsh restoration efforts in areas outside the United States, and the potential effects of sea-level rise on vegetated flats as fish habitat. Sampling methods that provide density measures are likely to be most useful for most of this research. Thus, drop samplers and pop nets are an appropriate choice, the former in graminoid saltmarshes and the latter in succulent saltmarshes.

Expanding fish productivity in Tasmanian saltmarsh wetlands through tidal reconnection and habitat repair

Fish use of coastal saltmarsh wetlands has been documented for many parts of Australia with the notable exception of Tasmania. An initial investigation to examine the diversity, density and patterns of fish use in the Circular Head coast saltmarshes of north-west Tasmania was undertaken. To aid decision making in repair strategies, the effect of saltmarsh condition on fish assemblages was studied using paired sites of predominantly unaltered and altered saltmarshes where levees were present. In all, 851 fish from 11 species were caught in 37 of the 48 pop nets. Three species, Aldrichetta forsteri, Arripis truttaceus and Rhombosolea tapirina, are important to commercial and recreational fisheries and contributed ~20% of the total catch numbers. The mean density of >72 fish per 100m2 is the highest yet reported from Australian studies and indicates that Tasmanian saltmarshes provide higher value habitat for fish compared with elsewhere in Australia, likely due to more frequent and prolonged flooding, and the lack of adjacent mangroves. There was no significant difference in fish assemblages between unaltered and altered marshes. The results suggest that restoring basic saltmarsh structure through tidal reconnection will deliver substantial benefits for fish productivity through habitat expansion.A

Larval Sucker Distribution and Condition before and after Large-Scale Restoration at the Williamson River Delta, Upper Klamath Lake, Oregon

We monitored the response of endangered Lost River sucker (Deltistes luxatus) larvae and shortnose sucker (Chasmistes brevirostris) larvae prior to, and during the first 2 seasons after, restoration of historic wetlands at the mouth of the Williamson River, Upper Klamath Lake, Oregon. In 2006 and 2007 (prerestoration) and in 2009 and 2010 (postrestoration), we used pop nets set in shallow-water (<1-m-deep) wetland habitats to document the distribution and condition of larval fish throughout the Williamson River Delta Preserve, as well as at a reference site along the Goose Bay shoreline in Upper Klamath Lake. From prerestoration to postrestoration, we witnessed significant declines in abundance of larval suckers at the reference site along the Goose Bay shoreline but no similarly significant declines in the 2 pilot restoration projects (t = 9.92, df = 400, P < 0.0001; t = 0.8, df = 400, P = 0.3438). In 2009 and 2010, larvae were documented using the newly restored portions of the delta. Larval suckers captured during pre- and postrestoration in the pilot areas and during postrestoration in the restored areas of the preserve were more likely to have fuller guts than larvae captured at the reference site along the Goose Bay shoreline. Throughout the study, length trends were more variable than gut fullness trends: larvae captured in pilot areas prior to restoration were larger than those captured after restoration, and larvae captured at the reference site postrestoration were on average larger than postrestoration sucker larvae from the restored and pilot areas.

Comparisons of Catch and Precision of Pop Nets, Push Nets, and Seines for Sampling Larval and Juvenile Yellow Perch

Abstract Abundance estimates of larval and juvenile fish require unbiased and precise sampling techniques. Even if an appropriate sampling technique is chosen, fish abundance estimates can be inaccurate if there is no assessment of the gear precision. Our first objective was to compare catch characteristics of pop nets, push nets, and seines for sampling occurrence, abundance, and size of age-0 yellow perch Perca flavescens in shallow habitats with different vegetation densities. The second objective was to estimate the precision (coefficient of variation (CV)) with which each sampling gear measured larval and juvenile yellow perch abundance. Larval fish were collected in May 2003 via pop nets and push nets, and juveniles were collected in July 2003 via pop nets and seines. Significant differences in yellow perch occurrence and abundance were observed between sampling gears and sampling periods. May occurrence and abundance of larval yellow perch were higher for push nets than for pop nets in open-water h...

Linkages between seagrass, mangrove and saltmarsh as fish habitat in the Botany Bay estuary, New South Wales

Shallow-water vegetated estuarine habitats, notably seagrass, mangrove and saltmarsh, are known to be important habitats for many species of small or juvenile fish in temperate Australia. However, the movement of fish between these habitats is poorly understood, and yet critical to the management of the estuarine fisheries resource. We installed a series of buoyant pop nets in adjacent stands of seagrass, mangrove and saltmarsh in order to determine how relative abundance of fishes varied through lunar cycles. Nets were released in all habitats at the peak of the monthly spring tide for 12 months, and in the seagrass habitat at the peak of the neap tide also. The assemblage of fish in each habitat differed during the spring tides. The seagrass assemblage differed between spring and neap tide, with the neap tide assemblage showing greater abundances of fish, particularly those species which visited the adjacent habitats when inundated during spring tides. The result supports the hypothesis that fish move from the seagrass to the adjacent mangrove and saltmarsh during spring tides, taking advantage of high abundances of zooplankton, and use seagrass as a refuge during lower tides. The restoration and preservation of mangrove and saltmarsh utility as fish habitat may in some situations be linked to the proximity of available seagrass.

Comparisons of fish catches using fyke nets and buoyant pop nets in a vegetated shallow water saltmarsh flat at Towra Point, NSW

The selection of appropriate sampling methods is a prerequisite for the design of any survey detailing nekton assemblages. In the present study two commonly used saltmarsh fish sampling methods, the fyke net and the buoyant pop net, were used to compare the assemblages of fish caught in a saltmarsh flat during monthly spring tides over a twelve month period. Both nets were made of 2mm mesh. A total of 3514 fish and crustaceans of 21 species were captured by 48 fyke net sets and 818 fish of 16 species were captured by 48 pop net releases. Fyke and pop nets recorded significantly different (ANOSIM: P<0.001) assemblages, with higher proportions of Pseudomugil signifer caught in the fyke nets and Ambassis jacksoniensis in the pop nets. Five species, Sillago cilliata, Rhabdosargus sarba, Redigobius macrostoma, Taeniodes mordax and Metapenaeus macleayi, were caught in the fyke nets only. Significant differences in the size of fish caught were recorded for two species, Gobiopterus semivestitus and Gerres subfasciatus, with larger fish on average caught in the pop nets. The result suggested that pop nets are less efficient at catching smaller fish.

Temporal Variations in Fish Catch Using Pop Nets in Mangrove and Saltmarsh Flats at Towra Point, NSW, Australia

Fish assemblages utilising saltmarsh and mangrove during spring tides were surveyed over a 12-month period using buoyant pop nets. A total of 48 net releases in the saltmarsh identified 16 species, at a density of 0.56 fish m−2, with six species being of commercial importance. The same number of releases within the mangrove collected a total of 23 species at a density of 0.76 fish m−2. However, fish density was higher within the saltmarsh than the adjacent mangrove when corrected for water volume. Multidimensional scaling revealed different assemblages of fish in the two habitats, with higher numbers of Ambassis jacksoniensis and Pseudomugil sp. in the saltmarsh and higher numbers of Mugilogobius sp. and Acanthopagrus australis in the mangrove. The result suggests a potentially significant role for saltmarsh as a fish habitat in the estuaries of southeast Australia.

Modification of saltmarsh for mosquito control in Australia alters habitat use by nekton

The most common modification of saltmarsh habitat for mosquito control in Australia is runnelling, a system of shallow channels increasing seawater exchange in pools high on the marsh. Local effects within the immediate vicinity of runnels were examined by testing the hypothesis that fish assemblages immediately alongside runnels differ from those further away. Nekton assemblages were sampled using pop nets in winter (May) and summer (December) on a saltmarsh in southeast Queensland, alongside runnels and further (30 m) away, at two distances from a mangrove-lined intertidal creek. Nekton assemblages were dominated numerically (50–80%) by one or two species of small fish (Ambassis marianus, Mugilogobius stigmaticus), and a commercially important prawn, Fenneropenaeus merguiensis. In winter, nekton assemblages alongside runnels were significantly different from those further away. Species richness, total nekton densities and densities of several individual species were higher away from runnels, but only at sites far from the creek. No differences in species richness or densities were found in summer. During both periods, nekton assemblages differed strongly with distance from the creek, with more species and higher densities of most species near the creek. For most species, the overall effect of runnelling appears to be a reduction in abundances in the immediate vicinity of runnels, at some times of year. This is probably related to lower prey availability near runnels. Given the extent of runnelling in some parts of Australia, even this local reduction in densities extending no more than 30 m from runnels means that nekton may be adversely affected over a large total area. The apparent influence of runnels on nekton densities highlights the potential effects of saltmarsh modification on non-target animals that should be considered as this management technique becomes more prevalent.

Fish and invertebrate assemblages in seagrass, mangrove, saltmarsh, and nonvegetated habitats

Many studies compare utilization of different marine habitats by fish and decapod crustaceans; few compare multiple vegetated habitats, especially using the same sampling equipment. Fish and invertebrates in seagrass, mangrove, saltmarsh, and nonvegetated habitats were sampled during May–August (Austral winter) and December–January (Austral summer) in the Barker Inlet-Port River estuary, South Australia. Sampling was undertaken using pop nets in all habitats and seine nets in seagrass and nonvegetated areas. A total of 7,895 fish and invertebrates spanning 3 classes, 9 orders, and at least 23 families were collected. Only one fish species,Atherinosoma microstoma, was collected in all 4 habitats, 11 species were found in 3 habitats (mangroves, seagrass, and nonvegetated), and 13 species were only caught in seagrass and nonvegetated habitats. Seagrass generally supported the highest numbers of fish and invertebrates and had the greatest species richness. Saltmarsh was at the other extreme with 29 individuals caught from two species. Mangroves and nonvegetated habitats generally had more fish, invertebrates, and species than saltmarsh, but less than seagrass. Analyses of abundances of individual species generally showed an interaction between habitat and month indicating that the same patterns were not found through time in all habitats. All habitats supported distinct assemlages although seagrass and nonvegetated assemblages were similar in some months. The generality of these patterns requires further investigation at other estuaries. Loss of vegetated habitats, particularly seagrass, could result in loss of species richness and abundance, especially for organisms that were not found in other habitats. Although low abundances were found in saltmarsh and mangroves, species may use these habitats for varying reasons, such as spawning, and such use should not be ignored.

Assessing patterns of fish zonation in temperate mangroves, with emphasis on evaluating sampling artefacts

Mangroves and mudflats are a conspicuous element of temperate estuaries in south- eastern Australia, but our understanding of their use by fish is poor. A combination of experimental and survey methods were used to investigate (1) the utility of pop nets in sampling fishes and (2) pat- terns in fish assemblages among mangrove zones (forest, edge, mudflat) in 2 large embayments between October 2003 and January 2004. In the experimental assessment of pop net artefacts, there were no statistically significant differences (p >> 0.05) in assemblage structure, species richness (number of species) or abundances of fish among net disturbance treatments regardless of structure (seagrass or unvegetated sand). These results were not simply due to type II errors. The statistical power to observe an effect of net disturbance on fish abundances and species richness generally exceeded 80%. In the pop net survey of fish using mangrove zones, only 15 species of fish (9 families) were caught, but assemblages varied strongly among zones. Small (<30 mm) benthic gobiids, such as Pseudogobius olorum Sauvage 1880 and Mugilogobius paludis Whitley 1930, and juveniles of the atherinid Atherinasoma microstoma Gunther 1861 dominated catches in the forest. The sillaginid Sil- laginodes punctata Cuvier 1829, the tetraodontid Tetractenos glaber Freminville 1813 and a further 2 species of gobiid, Arenigobius frenatus Gunther 1861 and Favonigobius lateralis Macleay 1881, dominated catches along the edge and over the mudflat, but these species were more abundant along the edge. Fish densities were significantly lower (p < 0.05) in the mudflats (0.37 ± 0.05 fish m -2 ) than in the forest (1.98 ± 0.36) or at the edge (1.42 ± 0.43); species richness was greater along mangrove edges (0.25 ± 0.19 species m -2 ) than in the forest (0.17 ± 0.06) and in the mudflats (0.12 ± 0.02); bio- mass was greater (but not significantly) at the edge (4.64 ± 2.09 g m -2 ) and in the mudflats (4.06 ± 1.79) than in the forest (1.20 ± 0.38). Seine nets caught fewer individuals (0.95 ± 0.17 fish m -2 ) and species (0.03 ± 0.01 species m -2 ), and lower biomass (1.15 ± 0.21 g m -2 ) than pop nets (see above) in mudflats. Differences in the fish assemblage structure among zones suggest that overall fish biodi- versity may increase in fragmented mangrove landscapes as relative amounts of edge to area increase, but this could detrimentally affect abundances and species richness of resident mangrove fishes.

Assessing effects of diel period, gear selectivity and predation on patterns of microhabitat use by fish in a mangrove dominated system in SE Australia

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 294:257-270 (2005) - doi:10.3354/meps294257 Assessing effects of diel period, gear selectivity and predation on patterns of microhabitat use by fish in a mangrove dominated system in SE Australia Timothy M. Smith1, Jeremy S. Hindell1,2,* 1Department of Zoology, University of Melbourne, Parkville, Victoria 3010 Australia2Marine and Freshwater Systems, Department of Primary Industries, PO Box 114, Queenscliff, Victoria 3225, Australia *Corresponding author. Email: jeremy.hindell@dpi.vic.gov.au ABSTRACT: The relative value of temperate mangroves to fish, and the processes driving patterns of microhabitat use within this habitat, are unknown. There are 3 quickly identifiable microhabitats within temperate Australian mangroves: (1) forest (the area of mangroves with trees); (2) pneumatophores (the area directly seaward of the forest without trees but with pneumatophores [aerial roots]); and (3) channel (the area directly seaward of the pneumatophores without gross structural attributes such as trees or pneumatophores). Duplicate fyke and gill nets were both initially used to sample fish in the 3 microhabitats described above. Sampling took place across the seaward edge of mangroves on 10 sampling occasions (5 night and 5 day), in a large estuarine system in SE Australia. Fish assemblages (693 fish from 20 species and 15 families) varied significantly (p < 0.05) between the forest and the channel, and between diel periods for each gear (net type), but there was little difference in the assemblage structure of fish between forest–pneumatophore or pneumatophore–channel microhabitats. Juvenile lifestages (61% of all fish) and commercially important taxa (76%) were common. Abundance, biomass and species richness of fish were generally lower in the forest than the other microhabitats, but this pattern varied significantly (p < 0.05) between diel periods, among sampling occasions, and with water depth. Highly quantitative pop nets provided a preliminary assessment of whether differential gear selectivity caused patterns between microhabitats, but less rich fish assemblages were again recorded in forests than in pneumatophores. The importance of predation in structuring fish assemblages across microhabitats was assessed by measuring survival of juvenile fish tethered in 3 predation treatments (predator exclusion, cage control, and uncaged). Survival rates were high across the predator treatments and did not vary among microhabitats. The variation in fish assemblages across microhabitats within mangroves was not consistent with a model of mangrove structure providing a refuge for juvenile fish from predation, but instead could indicate differences in efficiency of gear types among microhabitats and/or other ‘edge effect’-driven processes such as the provision of food and/or shelter. KEY WORDS: Temperate · Mangroves · Fish assemblages · Microhabitat · Predation · Diel Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 294. Online publication date: June 09, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

Fish use of subtropical saltmarshes in Queensland, Australia: relationships with vegetation, water depth and distance onto the marsh

Saltmarshes in subtropical Queensland, Australia, are assumed to provide habitat for fish, yet there has been no evidence as to whether fish actually occur on the intertidal flats that con- stitute the main area of marshes. Nor has there been any assessment of differences in fish use of veg- etated habitat and the extensive unvegetated saltpans that occur naturally and because of human activities. Fish were sampled from the intertidal flats of 2 saltmarshes in subtropical Queensland using floorless, buoyant pop nets (25 m 2 ) on sets of spring high tides in summer (during day) and win- ter (at night). A total of 23 species was collected, with densities ranging up to 0.46 fish m -2 . Catches were dominated numerically by small, estuarine-resident species such as glassfish (Ambassidae) and gobies (Gobiidae). Economically important species such as bream (Sparidae), whiting (Sillaginidae) and mullet (Mugilidae) also contributed substantially (up to 92%) to the catch. Fish assemblages were compared in adjacent patches of intertidal vegetated and unvegetated habitat, at distances vary- ing from 3 to 413 m onto the marsh. Fish densities were highly variable among patches on a marsh, and also varied between sampling periods and between marshes. Species richness and the densities of common species differed little between vegetated and unvegetated habitats. Two species, Mugilo- gobius stigmaticus and Atherinomorus ogilbyi, had higher densities in vegetated habitat, but only at 1 sampling time and marsh. Fish occurred at all distances onto the marsh. Species richness and the densities of some species were positively related to water depth and negatively related to distance onto the marsh at one, but not the other marsh. This study provides the first evidence that, despite the relatively low duration and frequency of inundation of marshes, there is widespread use by fish of intertidal saltmarsh flats in Australia.

Fish use of an inundated saltmarsh flat in a temperate Australian estuary

Abstract Fish associated with Australian saltmarshes have previously been sampled from within creeks or semi‐permanent pools on the marsh; this is the first record of fish use of marsh flats inundated on high tides but emergent on low tides. Buoyant pop nets (9 m2, 1 mm mesh) were used to collect fish from two areas of the marsh flat on Torrens Island in the Barker Inlet‐Port River estuary. South Australia. Fyke nets of the same mesh size were used to collect fish from small creeks draining the marsh flat. Fish were caught in only four of 48 pop net releases, for a total of 19 fish of two species (families Gobiidae and Atherinidae). A total of 1109 fish from six species were caught in creeks draining the same areas, and the two species caught on the flats were the most common species in the creeks. Economically important species were poorly represented, with just four specimens of the mugilid Aldrichetta forsteri (Valenciennes).

Comparison of fish catches from a buoyant pop net and a beach seine net in a shallow seagrass habitat

A large (25 m2), remote-release buoyant pop net, 1989), and to do this, a buoyant pop net was designed floorless to permit normal behaviour by benthic fish, and a with the aim of making a more complete cat&. The beach seine net were comparing the catch seine net is also unwieldy when fish need to be collected the 2 net types. Both nets were made of 1 mm mesh, aimed at catchina fish from 10 to 100 mm Iona. The Q ~ Q net cauaht from defined The pop net permits 1 . more figh than the selne net, mainlydbecause 9 tlmes mzre tlon of fish from such areas, for example from experiFavonigobius lateraLis were caught in the pop net. Apart from mental plots in which habitat has been manipulated. species such as E lateralis that dwell on the sea bed, the seine ~~~~~~t pop nets usually consist of 4 mesh walls, net catches small fish as well as the pop net, and for some species is a faster, cheaper collection method for survey work. depressed prior to release, and a mesh floor. Such traps H ~ ~ ~ ~ ~ ~ , as net catches can about rank can be lifted clear of the water to collect ensnared fish. order of abundances of species, its main use may be in colSmall pop nets (area 5.6 m2) have been used in vegeletting presence'absence data. The POP net gives a more tated backwaters of a river (Dewey et al. 1989) while a accurate estimate of bottom-dwelling species, and is useful larger net (14,5 m2) was tested for estimating fish where fish need to be collected from small, deflned areas such as ex~erimental ~ l o t s . abundance associated with artificial structures in lakes (Larson et al. 1986). In the present study, a floorless

How Depth and Interstice Size of Artificial Structures Influence Fish Attraction

Abstract Adding artificial structures to lakes has been common, but guidelines for ensuring the utility of these additions are lacking. We used pop nets to evaluate fish use of artificial structures with two interstice sizes (40 and 350 mm) placed at two depths (3.0 and 4.5 m) in an Ohio reservoir. Bluegills Lepomis macrochirus preferred 40-mm interstices at 3.0 m. Pumpkinseeds Lepomis gibbosus and bullheads Ictalurus spp. also preferred denser structures but at the 4.5-m depth. White crappies Pomoxis annularis showed no preference, and their use of structures declined as summer progressed, probably because they moved to water deeper than 4.5 m. Catches of gizzard shad Dorosoma cepedianum were greatest from 4.5-m-deep structures, but no interstice size preference was evident. We found no relation between use of structures and a narrow range of physicochemical variables. Fisheries managers should use dense materials in structures to attract sunfish and bullheads. They can expect greater use of shallow stru...

Comparison of Fish Catches with Buoyant Pop Nets and Seines in Vegetated and Nonvegetated Habitats

Abstract Two models of pop nets were developed to sample fish in shallow riverine waters, one for use in vegetated areas and the other for nonvegetated areas. Both nets have a mechanical release mechanism that can be tripped from the water surface. Replicated field tests were conducted to compare pop-net catches with bag-seine collections every 2 weeks from May through mid-October. Overall, total catch per effort did not vary significantly (P < 0.05) between the two gears at either the vegetated or nonvegetated site. However, collections with the pop net were not as diverse as with the seine at either sampling site, perhaps because the area sampled by pop nets (5.6 m2) was smaller than the area swept by the average seine haul (70-140 m2). The pop net effectively sampled fish in shallow nonvegetated habitats and was useful in heavily vegetated areas where seining or electroshocking was difficult.

Distribution and Abundance of Fishes Associated with Submersed Aquatic Plants in the Potomac River

The distribution and abundance of fishes in submersed aquatic plants of three relative densities (no plants, intermediate plant density, high plant density) were estimated in the tidal Potomac River near Alexandria, Virginia. Fish were sampled with a boat-mounted electroshocker at night in May (when plants were emerging), August (peak plant densities), and November (plant senescence) of 1986. Mean densities of all plants ranged from 9 to 33 g/m2 (dry-weight basis) in May, and 400 to greater than 1,000 g/m2 in August and November. Hydrilla verticillata was usually the dominant aquatic plant. In May, overall mean fish abundance was highest in areas of high plant density (36 fish/5 min shocking), whereas in August and November fish abundance was highest in areas of intermediate plant densities (100 and 62 fish/5 min electroshocking, respectively). Areas without plants contained a relatively high number of filter-feeding fishes, including Atlantic menhaden Brevoortia tyrannus and blueback herring Alosa aestivalis. The fish assemblage in the vegetated sites comprised mainly brown bullhead Ictalurus nebulosus, banded killifish Fundulus diaphanus, pumpkinseed Lepomis gibbosus, largemouth bass Micropterus salmoides, and yellow perch Perca flavescens. The bay anchovy Anchoa mitchilli, white perch Morone americana, and inland silverside Menidia beryllina were distributed throughout all three sites during the study. Fish also were sampled with pop nets in aquatic plants and with seines between shore and the plant beds. More than five times more fish (9.8/m2) were collected with pop nets in areas with intermediate plant density, where there were several codominant plant species, than in areas with dense hydrilla (1.8 fish/m2). Shore-zone fish densities estimated with seine hauls were higher in areas adjacent to dense hydrilla beds (9 fish/m2) than in areas with no plants (1.5/m2) or near intermediate plant densities (3.3/m2), but the number of fish species was lowest near hydrilla.