Experimental Gill Nets Research Articles

Use of Spatial Resources by Fishes in Grayrocks Reservoir, Wyoming

ABSTRACT Relative abundance of fishes in different habitat types and sampling areas of a reservoir in eastern Wyoming was assessed with experimental gill nets during summer 1989. Seven of 12 species captured in the gill nets were numerous enough to enable statistical evaluation: quillback (Carpiodes cyprinus), common carp (Cyprinus carpio), walleye (Stizostedion vitreum), gizzard shad (Dorosoma cepedianum), shorthead redhorse (Moxostoma macrolepidotum), channel catfish (Ictalurus punctatus), and yellow perch (Perca flavescens). All seven species were significantly more numerous in samples from littoral and offshore bottom areas than in samples from offshore surface areas throughout the summer. Common carp and walleye were significantly more abundant in the upstream portion of the reservoir throughout the summer, whereas quillback, gizzard shad, shorthead redhorse, and channel catfish were more abundant in the upstream portion during early summer.

A Method for Estimating Gillnet Selectivity of Walleye (Stizostedion vitreum vitreum) in Muitimesh Multifilament Gill Nets in Lake Erie, and Its Application

A new method is described for adjusting gillnet catches for gear selectivity. Twelve years (1978–89) of walleye (Stizostedion vitreum vitreum) catches (n = 10 761) were pooled to derive frequency distributions of the ratios of fish girth and mesh perimeter for 11 mesh sizes. A gamma function was fitted to each of the 11 frequency distributions so that a selectivity curve could be derived for experimental gill nets used in Lake Erie, or any combination of meshes. An encounter model based on the swimming speed of walleye was used to estimate the probability of walleye encountering gill nets. Adjustments were made to walleye catches for both retention and encounter probabilities. Annual mortality and recruitment rates were compared for standardized and raw data from 1978 to 1989.

Relations of Gill-Net Catches of Walleyes and Angler Catch Rates in Ohio Waters of Western Lake Erie

Catches of walleye Stizostedion vitreum in fall gill-net surveys in western Lake Erie were good indicators of angler catch rates the following summer. Experimental gill nets fished near the lake surface and at the bottom efficiently captured enough walleyes to determine relative densities of individual age-groups. Simple linear models with surface gill-net catches as independent variables explained 85–97% of the variability in angler catch rates. Slopes of the relations indicated that walleyes were less vulnerable to angling at ages 2 and 3 than at ages 4 and 5. Relations of bottom gill-net catches to angler catch rates were not as well defined and indicated significant differences only between ages 3 and 5. These findings illustrate the value of fall gill-net surveys in western Lake Erie for predicting walleye sport catches and evaluating potential sport-fishery regulations.

Seasonality, depth and habitat distribution of breeding males of Oreochromis spp., ‘chambo’, in Lake Malawi National Park

The temporal pattern of breeding by chambo, Oreochromis spp., and the vertical and horizontal distribution of territorial males at the Golden Sands‐Chembe beach were examined in the Cape Maclear region of Lake Malawi National Park. The breeding season began in September and ended in April, and the number of breeding males between 3 and 15 m was approximately 25 ha. Along the beach studied, the highest concentrations of nests were found at the ends of the beach near rocks, and the lowest number of breeding males occurred in front of Chembe villageResults from experimental gill netting demonstrated that the catches of chambo within the 100‐m Lake Malawi National Park ‘no fishing zone’ were identical to those outside the 100‐m zone, suggesting that fishermen would suffer little or no loss in catch by being encouraged to fish more than 100 m from the shore. Such a reduction in fishing and disturbance of the shallow water breeding grounds would probably enhance the chambo fishery. Preliminary data are provided on the chambo nest forms found in the Cape Maclear region, and further research is suggested to resolve the question of how many species comprise the genus Oreochromis in Lake Malawi.

The Channel Catfish Fishery at Pony Express Lake, Missouri, 1963-1984

Abstract Pony Express Lake in Missouri was initially stocked in 1964 with fingerling largemouth bass Micropterus salmoides, bluegills Lepomis macrochirus, redear sunfish Lepomis microlophus, and 5-8-in channel catfish Ictalurus punctatus. The lake was opened to fishing in January 1966. Since the opening, annual supplemental stockings of 8-10-in channel catfish have been made at rates of 13-50 fish/acre. No negative effects on other species were documented that could be related to channel catfish stocking. The size distribution of channel catfish in gill-net catches, all years combined, corresponded to the size composition of angler catches except for fish less than 12.0 in. Experimental gill nets (1/2-2-in meshes) were most effective for sampling the smaller fish in the population. Channel catfish averaged 15.4 in at age 4 after completing two growing seasons in the lake. Annual daytime fishing pressure averaged 396 h/acre from 1966 through 1984, 33% of which was directed at channel catfish. Mean total an...

Occurrence of Juvenile Atlantic Sturgeon, Acipenser oxyrhynchus, in the Upper Tidal Delaware River

Eighty-nine juvenile Atlantic sturgeon,Acipenser oxyrhynchus oxyrhynchus, including 10 recaptures, were collected, tagged and released in the upper tidal Delaware River between July 1981 and December 1984. All were captured in the river channel between Roebling and Trenton, New Jersey, using bottom-set experimental gill nets during daylight hours. The species was present from July through December and collected in increased numbers in the past two years. The fork lengths ranged from 284 to 862 mm (mean±SD = 516 mm±106 mm) and the weights from 140 to 4,250 g (mean±SD = 1,369 g±815 g). Ten juvenile Atlantic sturgeon were recaptured between September 1983 and December 1984 and were at large from one to 418 d. Recapture data suggest that these sturgeon utilize this area annually from July through December, possibly as a nursery. Juvenile Atlantic sturgeon appear to utilize the upper tidal portion of the Delaware River for a much longer period of time and at lower temperatures than in other river systems.

The demography and management of large cyprinids in a reservoir on the Orange River, South Africa

The population dynamics of smallmouth yellowfish, Barbus holubi, and Orange River labeo, Labeo capensis, was studied in a large reservoir from 1978 to 1983. These two species made up over 90% of the catches in a fleet of experimental gillnets, but there were considerable fluctuations in catch and in the size and species composition of the catch. These variations largely resulted from changes in environmental conditions caused by hydrological management. Yellowfish breed in the inflowing Orange River, which is regulated through a large reservoir upstream. Spawning success is variable but generally good, and depends on time of spawning which is influenced by pattern of water release. The juveniles disperse well throughout the 80-km-long lake and sub-adults are generally most abundant near the dam wall where the water is clearest. Sharp decreases in water transparency caused by the short retention time of flood waters in the two impoundments greatly reduced the carrying capacity of the lake for yellowfish, and resulted in declining body condition and large-scale mortalities. This species could probably withstand intensive exploitation in the lake. Orange River labeo breed throughout the lake, but conditions for spawning and early survival are variable, leading to variable reproductive success. This species is relatively stationary, but dispersal in the lake is enhanced when decreased water transparency reduces food production. Although growth is very poor at times of high turbidity, mortality remains low and the ultimate size reached by individual fish varies little. Therefore, this species cannot sustain an intensive fishery, but lends itself well to exploitation on an accumulated stock basis. A fishery for labeo should complement a commercial fishery for yellowfish.

Potential Fisheries Yield from Smallwood Reservoir, Western Labrador, with Special Emphasis on Lake Whitefish

An experimental gillnetting program in the summers of 1974, 1976, and 1979 on seven major lakes of Smallwood Reservoir in western Labrador showed lake whitefish (Coregonus clupeaformis) and lake trout (Salvelinus namaycush) to be the dominant species in terms of numbers and relative biomass. Length-frequency distributions of lake whitefish and lake trout were typical of unexploited northern fish populations while the age structure of whitefish was relatively young for unexploited populations. Slow-growing but early-maturing dwarf lake whitefish populations also were documented in two lakes of the reservoir. A long-term potential yield of 2.85 kg/hectare/year for all species combined was calculated for the reservoir. The proportion of this yield attributable to lake whitefish was 45.7%. Surface gill nets were more efficient in capturing marketable-size whitefish, with the 76- and 102-mm mesh taking the highest percentage. There was a large incidental catch of lake trout in the bottom nets, with the 102-mm mesh being the most efficient. Recommendations for the development of a fishery on the reservoir were proposed, based on the findings of the experimental gillnetting program.

The migrations of anadromous cisco (Coregonus artedii) and lake whitefish (C. clupeaformis) in estuaries of eastern James Bay

Experimental gill-netting and tagging programs were undertaken in the Eastmain and La Grande rivers of James Bay to determine the migratory patterns of anadromous cisco (Coregonus artedii) and lake whitefish (C. clupeaformis). Cisco and whitefish were found to differ in the distribution of juveniles during summer, in the upriver migration of mature fish, and in the selection of overwintering sites. Models are presented to illustrate the general life cycles of anadromous cisco and lake whitefish in James Bay.

Nearshore Spatial Distribution of Fishes in Gill Net Samples, Cayuga Lake, New York

Cayuga Lake fishes were collected monthly with experimental gill nets at depths of 2 to 31.5 m. Horizontally-placed nets were arranged to allow determinations of vertical and inshore-offshore variation in fish distribution and occupied temperatures. Warmwater species concentrated in inshore and surface waters at 19-23° C during the summer. Coldwater species concentrated in hypolimnetic waters at 9-15° C during the summer. Seasonal inshore-offshore movements were evident with all species except those which were captured only close to shore (northern pike, carp, smallmouth bass, white sucker). Depth ranges in which greatest numbers of common species occurred in the summer (July-September) were: alewife, inshore and surface to 15.3 m; lake trout, 15.3 to 30.5 m or more; northern pike, inshore and surface to 15.3 m; rainbow smelt, 7.6 to 30.5 m or more; spottail shiner, inshore and 7.6 m; trout-perch, inshore and 7.6 to 15.3 m; yellow perch, inshore and 7.6 to 15.3 m. Mean occupied temperatures (° C) of common species during the summer were: alewife 18.4 to 20.9; lake trout, 12.5 to 13.6; northern pike, 19.4; rainbow smelt, 10.4-14.4; spottail shiner, 19.6 to 21.5; trout-perch, 18.7-21.3; yellow perch, 19.4 to 21.0. Depth distribution was obviously influenced by temperature preferences and also by availability of food in certain species. Catch size was directly related to water temperatures in several species.

Subsistence fish exploitation and implications for management in the Baram River system, Sarawak, Malaysia

Introduction of gillnets to the subsistence fishery caused an apparent decline in catch per effort on the Baram River, Sarawak. Fishermen ranked gillnets and castnets respectively as their most effective fishing gears, and the annual fish catch, estimated by extrapolation from experimental gillnet samples, was 54 000 to 76 000 kg. A catch estimate of 14.2 to 19.6 kg ha −1 year −1 from the river was in good agreement with the 19 kg ha −1 year −1 from the intensively exploited Lake Bangweulu system, Zambia, which has similar characteristics. Comparisons between heavily and lightly exploited areas suggested that subsistence fishing with a variety of gears was not species or size selective, and that maintenance of species diversity could be important in maintaining a high catch per effort. The balanced approach to exploitation was establishing an equilibrium between subsistence fishermen and their resource. External incentives which influence catch size or composition should be preceded by research on fish community structures and ecological production within the system.

Changes in experimental gillnet catches from the Kafue Floodplain, Zambia, since construction of the Kafue Gorge Dam

The Kafue Floodplain fishery produces an annual fish yield of about 5000 tonnes. The 1971 closure of the Kafue Gorge Dam downstream from the floodplain modified flooding patterns. Pre‐impoundment studies predicted this modification would increase fish stocks. Experimental gillnets set in 1975 and 1976 caught 18 species on a regular basis, nine of which were abundant enough for comparison with catches in similar gillnet samples taken prior to completion of the Kafue Gorge Dam. Of these nine species, experimental gillnet catches of three predator species were smaller in 1975–76 than in 1969–70. Catches of only one species increased significantly. Whether this change is due to the modified flooding pattern is unclear; unusually dry flood conditions in 1973 and increased fishing effort may have contributed.

Effects of Fisheries on Eurasian Perch (Perca fluviatilis) in Windermere

A review of literature indicated that a wartime (1941–48) trap fishery reduced the Eurasian perch (Perca fluviatilis) population very considerably. An experimental gillnet fishery for northern pike (Esox lucius) from 1944 to 1975 presumably contributed to keeping the perch population low through increased predation. The gillnet fishery reduced the average size of the pike, and their growth rate increased, in turn increasing the predation on younger perch. This predation controlled recruitment to the adult perch population. Pike predation is given as one factor in a model explaining year-class fluctuations. Key words: Percidae, exploitation, year-class fluctuations, Perca predation, year-class model

Distribution and Condition of Fishes in a Small Reservoir Receiving Heated Waters

The effects of a thermal effluent on the distribution and condition of fishes were determined in a 330-ha reservoir in northeastern Texas. Fish were collected at five stations with 41-m experimental gill nets and a 6.1-m seine every 2 weeks between May 1971 and June 1972. Water temperatures at the mouth of the effluent canal were highest (42.2 C) in July and were typically 3-8 C higher at this location than in other areas of the reservoir. Two forage species (Mississippi silversides, Menidia audens, and pugnose minnow, Notropis emilae) were never found near the mouth of the effluent canal. White crappie (Pomoxis annularis) and river carpsucker (Cyprinus carpio) may have been attracted to the effluent area in spring and summer. Channel catfish, (Ictalurus punctatus), gizzard shad (Dorosoma cepedianum), threadfin shad (D. petenense), and bluegill (Lepomis macrochirus) were rather evenly distributed over the entire reservoir during all seasons. The size and condition of fishes collected at the mouth of the effluent canal were not significantly different from those of fish collected at other stations in the reservoir, although the condition coefficients of channel catfish, river carpsucker, gizzard shad, threadfin shad, and bluegill were lower than those reported for these species in other parts of the United States. The results suggest that in a small reservoir like North Lake the effects of a heated effluent on fish populations may be generalized over the entire body of water, particularly when a cool-water refuge area is present beneath the heated surface stratum.

Growth Changes of the Bloater (Coregonus hoyi) of the Apostle Islands Region of Lake Superior

Abstract Studies were based primarily on 3,097 bloaters collected in experimental gill nets and bottom trawls fished in 1958–65 in the Apostle Islands region of Lake Superior. The average size of bloaters increased considerably during the period. The percentage longer than 8.9 inches increased from 45% in 1959 to 99% in 1965. Calculated lengths were without exception higher in 1962–65 than in 1958–61. Growth in length and weight showed nearly steady improvement from 1951 to 1964. The species composition of chubs has apparently changed considerably over the past 40 years. The bloater has replaced the shortjaw cisco (C. zenithicus) as the principal species in commercial landings of chubs in Wisconsin. Annulus formation of bloaters extended from mid-May to August. Growth was slow during the spring and early summer but increased sharply in August. Age-group VI was dominant in the samples. Fluctuations in year-class strength were slight. Females outnumbered males in all age groups above III. The sex compositio...

Bathymetric Distribution of Fish in the Apostle Islands Region, Lake Superior

Records of seasonal and “all-season” (April-December) bathymetric distribution are given for 17 species of fish taken in bottom trawls and experimental gill nets fished on the bottom in 1958–63 in the Apostle Islands region of Lake Superior. The data are based on catches from 578 trawl tows at 2–59 fathoms and 301,900 linear feet of gill nets fished at 2–89 fathoms. Size of the fish varied widely among different species from the same gear and the same species from different gears. Seasonal differences in depth distribution were greatest for lake trout, bloaters, round whitefish, and older smelt, which exhibited an inshore movement in the summer and fall, and for longnose suckers, which migrated to deeper water with progress of the seasons. The all-season bathymetric distributions varied considerably among species. Round whitefish, 0- and I-group smelt, longnose suckers, ninespine sticklebacks, and johnny darters were most abundant at < 10 fathoms. Concentrations of lake trout, lake herring, lake whitefish, older smelt, trout-perch, and burbot were greatest at 10–29 fathoms. Pygmy whitefish were most common at 30–39 fathoms, bloaters and spoonhead sculpins at 40–49 fathoms, and shortjaw ciscoes, slimy sculpins, and fourhorn sculpins at 50–59 fathoms. The kiyi was most abundant at 70–79 fathoms.

Movements of Hatchery-Reared Lake Trout in Lake Superior

The history of stocking of lake trout (Salvelinus namaycush) in the Great Lakes is reviewed.The study of movements is based on capture of 24,275 fin-clipped lake trout taken in experimental gill nets and trawls and commercial gill nets.Yearling lake trout planted from shore dispersed to 15-fath (27-m) depths in [Formula: see text]. Most fish remained within 2 miles (3.2 km) of the planting site 2 months, but within 4 months some fish had moved as much as 17 miles (27 km). The highest abundance of planted lake trout was in areas 2–4 miles (3.2–6.4 km) from the planting site even 3 years after release. Distance moved and size of fish were not correlated.Dispersal of lake trout begins at planting and probably continues until the fish are mature. Most movement was eastward in southern Lake Superior and followed the counterclockwise surface currents. Movement is most rapid in areas of strong currents and slowest in areas of weak currents or eddies. Movement to areas west of the Keweenaw Peninsula was insignificant from plantings in Keweenaw Bay and nil from other plantings farther east. Lake trout planted in the eastern third of the lake dispersed more randomly than those planted farther west. Few fish moved farther offshore than the 50-fath (91-m) contour. Lake trout planted in Canadian waters made insignificant contributions to populations in US waters.

Selectivity and Efficiency of Experimental Gill Nets in South Bay and Georgian Bay of Lake Huron

Gill-net selectivity curves for ciscoes (Coregonus artedii), round whitefish (Prosopium cylindraceum), chub species (mainly Coregonus hoyi, with a few representatives of C. reighardi), yellow perch (Perca flavescens), and white suckers (Catostomus commersoni) were obtained from the analysis of catch statistics of experimental nylon gill nets fished in Georgian Bay in 1958 and 1959 and in South Bay during the period of 1954 to 1959 inclusive. The method for analysis of the data is similar to that developed by McCombie and Fry (1960). The relative efficiency of nylon and cotton gill nets in catching these species has been compared on the basis of catches of each material made in South Bay. Nylon gill net was found to be 1.3 to 3.6 times as effective as cotton, depending on the species. With the exception of yellow perch, the size composition of catches made with nylon and cotton nets does not differ significantly.

Age and Growth of Walleyes in Clear Lake, Iowa, 1935–1957

Interpretation of walleye (Stizostedion vitreum vitreum) scales by three investigators revealed some differences in detail, but the data derived appeared to be basically reliable. Most fish were collected in experimental gill nets. Lengths at annuli were calculated using straight-line relationship with an intercept of 3.26 inches, total length. Growth rate of a year class, as indicated by mean length at the third annulus, was negatively correlated with abundance of the year class (r = −0.78, 11 d.f.). Walfordˈs growth transformation did not give an entirely satisfactory fit but gave a maximum length of 31.1 inches and a k of 0.836. Variations in these values with different treatment of the data were indicated. Fitting a Walford transformation to increments gave: Lt+1 = 28.8 inches (0.172) + 0.828 Lt. The correlation coefficient, r, between the annual increment indexes and the mean May to September temperatures was 0.565. Adding April and October temperatures lowered the correlation. Instantaneous growth rates, i, decrease rapidly with age and with increased length. Several indexes to growth during calendar years using i values and Parker and Larkinˈs Lz values, were tried, but the Hile increment indexes gave the best correlation with summer temperatures. Growth of female walleyes was faster than that of males.

Gill Nets for Sampling Fish Populations in Minnesota Waters

Abstract Reliability of standard experimental gill nets for estimating comparative size of perch, pikeperch, and pike populations is considered in the light of 31 series of gill-net catches from Minnesota lakes. Factors influencing the catch of gill nets are discussed. Because of the wide range of errors associated with means of series of gill-net catches, comparison of catch means at a probability level greater than 80 percent appears to be not practically feasible. A table showing error of means of series of net catches at this probability level is included.