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Effects of salinity on striped bass eggs and larvae from the Savannah River, Georgia

Operation of a tide gate installed in the Savannah River by the U.S. Army Corps of Engineers to reduce dredging activities increased salinities upstream in important spawning habitat for striped bass Morone saxatilis . To assess the effects of salinity on survival and growth of striped bass at early life stages, newly fertilized eggs and 48‐h‐posthatch larvae were exposed to serial dilutions of seawater, with salinities ranging from 0 to 33‰ (g/L) in increments of 3‰; in addition, older larvae (5‐d posthatch) were exposed to salinities of 0, 6, 12, 18, and 24‰. Eggs were exposed until 24 h posthatch, 48‐h‐posthatch larvae were exposed for 10 d, and 5‐d‐posthatch larvae were exposed for 6 d. Eggs died within 24 h in salinities greater than 18‰. Both survival and total length of larvae hatched from eggs exposed to salinities of 15‰ or higher were reduced. Percent mortality and mean total lengths of newly hatched larvae followed the same pattern for each of three sets of salinity regimes (i.e., changes in salinities over time) that striped bass eggs might encounter during passage downstream in the Savannah River. Hardening eggs in freshwater did not increase survival or length of hatched larvae over that shown by eggs hardened in saline water. The 5‐d‐posthatch larvae were less sensitive to salinity than the 48‐h‐posthatch larvae. Survival of larvae was negatively correlated with both salinity and exposure time. For 48‐h‐posthatch larvae, the 10‐d LC50 (the salinity lethal to 50% of the test fish within 10 d) was 10‰. Probabilities of survival for larval striped bass exposed to different salinities for different amounts of time can be estimated from curves generated from models of survival analysis. Salinities judged to be critical to Savannah River striped bass eggs and larvae are those greater than 9‰.

Georgia↗

Tag recovery estimates of migration of striped bass from spawning areas of the Chesapeake Bay

In 1988–1991 striped bass Morone saxatilis were collected for tagging from various spawning areas within the Hudson River (New York) and the Chesapeake Bay (Maryland). The fish were tagged and released during traditional periods of spawning and recovered by commercial and recreational fishermen. The proportion of fish that migrated in spring–fall from spawning areas in Chesapeake Bay to more northern waters of mid‐Atlantic and New England states was estimated from the geographically stratified tag returns. Most of the tagged fish were 40–100 cm total length (TL). The estimated proportion of migrant striped bass increased with body size, and nearly all fish larger than 100 cm TL left the bay during the spring–fall migration. Sex‐specific differences in migration appear to be associated with the differences in body size of mature males and females, thus lending support to previously hypothesized patterns of striped bass migration.

Maryland↗

Evidence for lack of homing by sea lampreys

Recently metamorphosed sea lampreys Petromyzon marinus were captured in the Devil River, a tributary to Lake Huron, during summer and autumn 1990. They were tagged with a coded wire tag and returned to the river to continue their migration to Lake Huron to begin the parasitic (juvenile) phase of their life. During the spawning run in spring 1992 when the tagged animals were expected to mature and return to spawn, sea lampreys were trapped in nine tributaries to Lake Huron, including the Devil River; 47,946 animals were examined for coded wire tags, and 41 tagged animals were recovered. None of the 45 mature sea lampreys captured in the Devil River in 1992 were tagged, a proportion (0%) significantly lower than the proportion of the recently metamorphosed sea lampreys tagged in 1990. The distribution of tag recoveries among streams lakewide, however, was proportional to catch. Tagged sea lampreys did not appear to home, but instead seemed to select spawning streams through innate attraction to other sensory cues.

Transactions of the American Fisheries Society↗

Growth and survival of newly parasitic sea lampreys at representative winter temperatures

Larval sea lampreys Petromyzon marinus begin to metamorphose into their parasitic phase in July and migrate to the Great Lakes either in autumn, when they immediately feed on fish, or in spring after overwintering in the stream substrate. Survival and growth of newly parasitic autumn migrants (mean weight, 4.18 g) differed significantly between temperature treatments when sea lampreys were held over winter and allowed to feed on longnose suckers Catostomus catostomus at either the maximum available temperature (&tilde;4&deg;C) or normal surface temperature (minimum <1&deg;C) in the Great Lakes during winter. Survival from December 1990 to June 1991 was 60% for the animals held in the warmer water but only 30% for the animals held in the colder water until 23 April. The average increase in weight was 8.23 g for the 35 survivors in the warmer water but only 5.15 g for the 17 survivors in the colder water. Average increases in weight from December to May for sea lampreys at both temperatures were 3.8 to 6.6 times greater than increases reported previously. A newly metamorphosed sea lamprey that migrates to the Great Lakes in autumn could be 2.5 to 3 times larger in June than one that overwinters in the stream substrate, where it cannot feed, and migrates in spring. Hence, autumn migrants may have an advantage in growth and survival over spring migrants, particularly if food supply is adequate in the warmest stratum of the lake during winter.

Transactions of the American Fisheries Society↗

Evidence of impaired reproduction by Western mosquitofish inhabiting seleniferous agricultural drainwater

Western mosquitofish Gambusia affinis from the San Luis Drain (SLD), a major conveyance system for seleniferous agricultural subsurface (tile) drainage water in the San Joaquin Valley, California, experienced lower reproductive success than did mosquitofish from a nearby reference area (Pond 26 at the Volta Wildlife Area, VOLTA) that had no history of receiving tile drainage. At birth, mean survival of SLD fry was 70% in 1984 and 77% in 1985, whereas mean survival of VOLTA fry was greater than 99% in 1984 and 97% in 1985. Measurements of total length (TL) of offspring born to SLD females in 1985 showed that stillborn fry (mean TL, 7.5 mm) were significantly shorter than live fry (mean TL, 9.4 mm). In addition, most stillborn fry were at earlier stages of development (contained prominent yolk sacs or occasionally resembled eyed embryos) than most live fry (yolk sacs were fully resorbed). In comparison, stillborn and live fry born to VOLTA females did not differ significantly in TL (mean for stillborn fry, 7.1 mm; mean for live fry, 7.5 mm), and nearly all fry had resorbed their yolk sacs. Mosquitofish from the SLD contained over 100 μg/g (whole‐body concentration in dry weight) of selenium, whereas those from VOLTA averaged 1.5 μg/g. Although experiments are still needed to establish cause and effect, the high incidence of abnormal births of mosquitofish from the SLD is seemingly a response to selenium toxicity.

California↗

Ebb and flow of encroachment by nonnative rainbow trout in a small stream in the southern Appalachian Mountains

Brook trout Salvelinus fontinalis is the native salmonid species of streams in the southern Appalachian Mountains. The present distribution of this species, once widespread from headwaters to lower reaches of large streams, is restricted to mostly headwater areas. Changes in the distribution of native brook trout in the presence ofˈ nonnative rainbow trout Oncorhynchus mykiss have been documented in Great Smoky Mountains National Park. When rainbow trout were first found in a tributary (Rock Creek) in the park in 1979, a study was begun to assess changes through time in distribution and abundance of rainbow trout in Rock Creek and to compare the brook trout and rainbow trout associations in Rock Creek with associations found in other park streams. Abundance of brook trout was low in the downstream sections of Rock Creek in 1979–1993. Brook trout abundance was highest in the steep‐gradient, pool‐dominated headwater section which was only 2 km from the confluence of Rock Creek and Cosby Creek. Rainbow trout were present in low densities in Rock Creek during the same period. Although rainbow trout were most abundant in the lower stream sections and never found in the headwater section, adult and age‐0 rainbow trout were found in the middle section in 1988. Rainbow trout were absent in the middle section in 1991, but one large adult rainbow trout was present in the section in 1992 and 1993. Floods, freshets, and periods of low stream discharge appeared to play an important role in the distribution and population structure of rainbow trout in Rock Creek. The lower portion of Rock Creek was poor trout habitat because the sections were dominated by cobble–rubble substrate and shallow riffle areas. Stream habitat appeared to be better suited for brook trout than for rainbow trout in the steep‐gradient upstream sections which were dominated by boulder‐cobble substrate and deep pools. The results of this study suggest that encroachment by rainbow trout can exhibit considerable ebb and flow in steep‐gradient tributaries in the park, and they suggest substantial evolutionary adaptation by brook trout to the hydrological conditions in the Rock Creek drainage.

North Carolina, Tennessee↗

A non-lethal measure of smolt status of juvenile steelhead based on body morphology

A nonlethal morphometric method to assess smolt status of juvenile steelhead Oncorhynchus mykiss was validated. Fish were collected from hatcheries before release and during their seaward migration in a large river system. Fifteen anatomical landmarks were digitized from photographs of each fish, resulting in 34 morphometric characters based on a truss network. Principal component and canonical discriminant function analyses were used to assess smolt status. A single canonical variate was significantly correlated with gill Na + ,K + ‐ATPase activity, a commonly used measure of smolt status. This nonlethal method may be a useful measure of smolt status when sacrificing fish is not desirable or possible; it requires little training to perform, but it does require a larger sample size than some other methods.

Transactions of the American Fisheries Society↗

Developmental instability in the Pacific Hake parasitized by the Myxosporean Kudoa spp.

A morphometric study of the otoliths of a population of Pacific hake Merluccius productus was conducted to detect developmental instability (DI) related to parasitism by Myxosporeans, Kudoa spp. We report a link between parasitism and DI, which we measured as fluctuating asymmetry by comparing the right–left differences in otolith shape, width, and weight in the same fish. Otolith shape provided the most sensitive measurement of DI asymmetry. Results suggest that Kudoa spp. could be a strong agent of selection in the Pacific hake.

Transactions of the American Fisheries Society↗

Spawning of the shortnose sturgeon the Merrimack River, Massachusetts

We tracked 10 ultrasonically tagged shortnose sturgeons Acipenser brevirostrurn during spring in the Merrimack River to investigate spawning. Seven fish in 1989 and six fish in 1990 were tracked intensively to identify the timing and location of spawning and to characterize spawning habitat. In mid‐April 1989 and 1990, fish moved upstream to just below head of tide, concentrating in a 2‐km reach at river kilometers 30–32 (measured from the mouth) at Haverhill, Massachusetts. The estimated spawning time was a 5‐d period (26–30 April) in 1989 and an 8‐d period (22–29 April) in 1990. Spawning sites covered about 10.5 ha in 1989 and 13.5 ha in 1990. Fish spawned as river temperature increased from 9.6 to 14.0°C and river discharge decreased from 390 to 240 m 3 /s. Physical characteristics of spawning sites were boulder–rubble substrate, water depth of 1.8–5.5 m, and bottom water velocity of 0.3–0.7 m/s. We captured no ovulating females but verified successful spawning in 1990 by capturing two live embryos. Gill‐net captures and telemetry during spring showed that some males moved to the spawning area annually. The low abundance estimates of spawning fish (9 in 1989 and 16 in 1990) indicate that the shortnose sturgeon population in the Merrimack River is the smallest yet identified and is likely vulnerable to extirpation.

Massachusetts↗

Feeding response by northern squawfish to a hatchery release of juvenile salmonids in the Clearwater River, Idaho

We collected gut contents from northern squawfish Ptychocheilus oregonensis captured in the Clearwater River, Idaho, 0–6 km from its confluence with the Snake River, following the release of 1.1 million yearling chinook salmon Oncorhynchus tshawytscha from the Dworshak National Fish Hatchery. Before the hatchery release, northern squawfish gut contents (by weight) in the study area were 38% crayfish Pacifastacus spp., 26% insects, 19% nonsalmonid fish, and 16% wheat kernels Triticum spp. Juvenile salmonids constituted 54% of gut contents about 24 h after the hatchery release, 78% after 5 d, and 86% after 7 d. The mean number of salmonids per gut (1.2) after release was higher than typically seen in guts from northern squawfish collected in mid-reservoir areas away from hydroelectric dams on the Snake and Columbia rivers. Length-frequency distributions of juvenile salmonids eaten and those captured in a scoop trap 4 km upstream of the study area indicated that northern squawfish were selectively feeding on the smaller individuals. We attribute the high rates of predation in the study area to the artificially high density of juvenile salmonids resulting from the hatchery release and to the physical characteristics of the study area in which the river changed from free flowing to impounded. Our results suggest that northern squawfish can quickly exploit hatchery releases of juvenile salmonids away from release sites in the Columbia River basin.

Idaho↗

First record predation on white sturgeon eggs by sympatric fishes

We report the occurrence of white sturgeon Acipenser transmontanus eggs in guts of four species of fish from the Columbia River. Three of the species—northern squawfish Ptychocheilus oregonensis , largescale sucker Catostomus macrocheilus , and prickly sentpin Cottus asper —are native to the river and one, common carp Cvprinus carpio , is exotic.

Oregon, Washington↗

Effects of implanted transmitters on adult bluegills at two temperatures

Laterally compressed panfishes are small and have limited intraperitoneal space; thus, they may suffer adversely from surgically implanted transmitters even if the transmitter meets the generally recommended ratio of transmitter weight to fish weight of 2%. We studied the effects of intraperitoneal transmitters (2.81 g) on survival, growth, healing, and health of bluegills Lepomis macrochirus (mean weight 133 g) held for 8 weeks at 6°C and 20°C. Radio‐tagged bluegills at 20°C had a mortality rate of 10% and tag loss rate of 15%. At 6°C, bluegills had no mortality or tag loss. Radio‐tagged and reference fish fed in both 20°C raceways; however, a few reference fish appeared dominant at feeding time. This dominance by a few reference fish was also indicated by a large weight gain for three reference fish in each 20°C raceway. At 6°C, neither reference fish nor radio‐tagged fish fed activity. Radio‐tagged fish held at 20°C exhibited pelvic fin erosion, erythema and necrosis at the antenna exit and at suture insertions, and lost or loose sutures, effects not observed in other test fishes. Examination of fish held at 20°C also showed enclosure of the transmitters in a fibrous capsule and adhesion of visceral organs. Epithelialization over the incision occurred in radio‐tagged bluegills at both temperatures, but there was little further healing at 6°C. At 20°C, tissue responses included chronic inflammation and dermal granulation. Radio‐tagged fish did not appear to be more susceptible than reference fish to bacterial infection. Mortality, adverse morphological effects, altered behavior, and limited healing in blue‐gills suggest that implanted transmitters impaired their health. Thus, movement and habitat use data collected by telemetry for this species and perhaps for other panfishes should be interpreted with caution.

Transactions of the American Fisheries Society↗

Competition between nonindigenous ruffe and native yellow perch in laboratory studies

The ruffe Gymnocephalus cernuus is a European percid that was accidently introduced in Duluth Harbor, Lake Superior. This nonindigenous species is closely related to yellow perch Perca flavescens , and because the two species have similar diets and habitat requirements, they are potential competitors. Laboratory studies in aquaria and pools were conducted to determine whether ruffe can compete with yellow perch for food. Ruffe had capture rates similar to those of yellow perch when food was unlimited. Ruffe spent more time than yellow perch over a feeding container before leaving it and searching again, and they also required less time to ingest (or handle) prey. However, the presence of yellow perch shortened the time ruffe spent over foraging areas when food was more limited. In addition, yellow perch were more active than ruffe, as indicated by their more frequent visits to a feeding container. Hence, the outcome of exploitative competition was not conclusive; ruffe appear to have the advantage in some behaviors, yellow perch in others. Ruffe were much more aggressive than yellow perch, and interference competition may be important in the interactions between these species. Our results indicate that ruffe might compete with native yellow perch.

Minnesota, Wisconsin↗

First-year growth, recruitment, and maturity of walleyes in western Lake Erie

In some lakes, first-year growth of walleyes Stizostedion vitreum has been identified as an important factor governing recruitment of juveniles to the adult population. We developed a regression model for walleye recruitment in western Lake Erie by considering factors such as first-year growth, size of the spawning stock, the rate at which the lake warmed during the spring, and abundance of gizzard shad Dorosoma cepedianum . Gizzard shad abundance during the fall prior to spring walleye spawning explained over 40% of the variation in walleye recruitment. Gizzard shad are relatively high in lipids and are preferred prey for walleyes in Lake Erie. Therefore, the high degree of correlation between shad abundance and subsequent walleye recruitment supported the contention that mature females needed adequate lipid reserves during the winter to spawn the following spring. According to the regression analysis, spring warming rate and size of the parental stock also influenced walleye recruitment. Our regression model explained 92% of the variation in recruitment of age-2 fish into the Lake Erie walleye population from 1981 to 1993. The regression model is potentially valuable as a management tool because it could be used to forecast walleye recruitment to the fishery 2 years in advance. First-year growth was poorly correlated with recruitment, which may reflect the unusually low incidence of walleye cannibalism in western Lake Erie. In contrast, first-year growth was strongly linked to age at maturity.

Transactions of the American Fisheries Society↗

Causes of declining survival of lake trout stocked in U.S. waters of Lake Superior in 1963-1986

Survival of the 1963-1982 year-classes of stocked yearling lake trout Salvelinus namaycush declined significantly over time in Lake Superior. To investigate possible causes of this decline, a Ricker model of stock-recruitment was used to describe the catch per effort (CPE) of age-7 stocked lake trout in the Michigan, Minnesota, and Wisconsin waters of Lake Superior as functions of the numbers of yearlings stocked 6 years earlier (an index of density dependence), the density (CPE) of wild adult lake trout (an index of predation), and large-mesh (a?Y 114-mm stretch-measure) gill-net fishing effort (an index of fishing mortality). Declining CPE of stocked lake trout in Michigan and Wisconsin was significantly associated with increasing large-mesh gillnet fishing effort. Declining CPE of stocked lake trout in Minnesota was significantly associated with increasing density of wild lake trout. Declining survival of stocked lake trout may therefore have been caused by increased mortality in large-mesh gill-net fisheries in Michigan and Wisconsin, and by predation by wild lake trout that recently recolonized the Minnesota area. We recommend that experimental management be pursued to determine the relative importance of large-mesh gillnet fishing effort and of predation by wild lake trout on the survival of stocked lake trout in U.S. waters of Lake Superior.

Transactions of the American Fisheries Society↗

Discrimination among spawning concentrations of Lake Superior lake herring based on trace element profiles in sagittae

Little is known about the stock structure of lake herring Coregonus artedi in Lake Superior, and recent increases in harvestable stock sizes has led to expanded exploitation in some areas. Research on marine teleosts has demonstrated that chemical differences in sagittal otoliths can be used for identification of fish stocks. We used plasma emission spectrophotometry to measure the concentrations of 10 trace elements in the sagittal otoliths from lake herring captured at eight spawning sites in Lake Superior and from Little Star Lake. an inland lake outside the Lake Superior basin. Discriminant function analysis indicated that elemental concentrations provided site‐specific information but that considerable overlap existed among some locations, especially those in western Lake Superior. Correct classification rates varied from 12.0% to 86.1% and were generally higher for spawning locations from embayments in eastern Lake Superior and for the outgroup population from Little Star Lake. The results presented here demonstrate the potential usefulness of this technique for strictly freshwater species, especially those that live in highly oligotrophic waters such as Lake Superior.

Lake Superior, Little Star Lake↗

Trout production dynamics and water quality in Minnesota streams

We sampled fish assemblages and quantified production dynamics of brook trout Salvelinus fontinalis , brown trout Salmo trutta , and rainbow trout Oncorhynchus mykiss in 13 southeastern Minnesota streams during 1988–1990 to examine the influence of water quality on fish populations in fertile trout streams. Fish assemblages in 15 stream reaches were abundant, but low in diversity; 13 species were collected. Parameter means (ranges) over the reaches were species richness, 4.1 (1–8); density, 29,490 (1,247–110,602) fish/ha; and biomass, 253.5 (49.6–568.6) kg/ha. Means (ranges) for salmonids were annual mean density, 2,279 (343–8,096) fish/ha; annual mean biomass, 162.0 (32.5–355.5) kg/ha; and annual production, 155.6 (36.7–279.6) kg/ha. Salmonid production and mean biomass were greater during the spring‐fall interval than during fall‐spring; young cohorts (ages 0–1) contributed the greatest proportion to population biomass and production. Salmonid annual production‐to‐mean‐biomass ratio (P/B) averaged 1.06 (0.64–1.42), and means were significantly different among species (1.03 for brown trout, 1.54 for brook trout, and 1.92 for rainbow trout). A significant linear model was developed that describes P/B as an inverse function of population age structure and may be used to improve accuracy in approximations of annual production from mean biomass. Fish density, biomass, or production were not correlated with eight water quality variables describing ionic and nutrient content in these streams, but when data from other United States streams with a wide range in alkalinity were incorporated, salmonid production was strongly, positively correlated with alkalinity. The wide range in fish population and production statistics and their lack of correlation with water quality suggest that no uniform fish carrying capacity exists among these streams and that factors other than water fertility limit fish density, biomass, and productivity at this spatial scale, but the overall maximum production rate in the region may be governed by water quality.

Minnesota↗

Age and growth of alewives in the changing pelagia of Lake Ontario, 1978-1992

We documented the age and growth of alewives Alosa pseudoharenqus in Lake Ontario during 1978-1992 and determined if growth was affected by intraspecific competition for epilimnetic zooplankton, lake temperature, or demand of salmonine piscivores for prey. Ages of juvenile alewives were determined from scales during 1978-1983, and ages of juvenile and adult alewives were determined from otoliths during 1984-1992. Indices of abundance for alewives were calculated from spring bottom trawl catches in 1978-1992; zooplankton density and epilimnetic temperature were monitored at two stations during 1981-1991; and salmonine demand each year during 1978-1992 was calculated with a simulation model. Although we encountered 11-year-old alewives, few fish lived longer than 7 years, and most fish in the population were younger than 6 years. Mean sizes at ages 1, 2, and 3 in spring averaged 93 mm (5.1 g), 133 mm (17 g), and 149 mm (22 g), but from age 3 to age 8, mean size increased by only 5-7 mm and 2-3 g per year. Female alewives lived longer than male alewives and were always longer than male alewives at age 4 and older. Epilimnetic temperatures were suitable for rapid growth of juvenile alewives each year. Lake temperature had the potential to affect growth of adults but adult growth was not correlated with temperature suitability indices perhaps because temperature regimes differed among lake regions and alewives were mobile. Growth of alewives was not correlated with salmonine demand for prey. Competition for zooplankton among the two youngest alewife cohorts affected growth of age-1 alewives. Zooplankton density declined sharply in 1986, and should it decline again, growth of age-1 alewives will slow, unless numbers of age-0 alewives fall. Whether growth of age-1 fish declines or numbers of age-0 fish fall, the result of another decline in zooplankton density will be a reduction in the production of alewives needed to support piscivores.

Transactions of the American Fisheries Society↗