摘要:

Large water-use facilities are often equipped with vertically travelling debris barriers known as Ristroph screens. Although made in a variety of configurations, all such screens are equipped with some manner of fish-catching troughs or rails, and all operate on the principle of direct contact and active removal of impounded fish and debris. The imposed fish mortalities associated with these machines are commonly attributed to the consequences of impingements (to fish being flattened against the screening by the force of the inflowing water), but the laboratory and field experiments reported here imply that in those circumstances where the screens travel continuously and where water speeds are moderate, the major underwater injuries are attributable instead to buffeting of captured fish within the fish troughs proper. Dye studies of the flows peculiar to various manufacturer's trough designs showed the water within a trough confines to be sheardriven by the main flow, which produced a longitudinal vortex of such strength that captive fish were swirled about and thrust repeatedly against the screen structure. Captured fish often escaped an ascending trough just before its leading edge broke the water surface, and their repeated encounters with the fish recovery apparatus increased the risk of mortality. From flow analyses of reshaped trough and screen profiles, a flow spoiler was devised that eliminates the trough vortex and buffeting of captive fish. The escape of fish at the water surface was eliminated by means of an auxiliary screen affixed to the leading edge of each fish trough. Field experiments revealed other sources of mortality, chief of which was the entanglement of fish in captured debris. As a countermeasure, the order of removing fish and debris was reversed. A reconfigured machine, including the redesigned fish-catching apparatus, was installed and tested at a nuclear generating station on the Hudson River estuary. In tests similar to those on the unimproved machine, injuries and deaths were reduced from 53 to 9% for striped bassMorone saxatilis, from 64 to 14% for white perchMorone americana, from 80 to 17% for Atlantic tomcodMicrogadus tomcod, and from 47 to 7% for pumpkinseedLepomis gibbosus. Striped bass losses to the debris removal system were reduced from 23% of recoveries to zero, white perch losses from 33% to l.3%, and Atlantic tomcod losses from 20% to 0.3%. Release-recovery experiments with juvenile striped bass and white perch revealed probabilities of capture characteristic of weak and strong swimmers.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1990)119<0393:FDAFRE>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Evidence suggests that the capacity for growth (i.e., maximum growth potential) within a species may vary inversely with the length of the growing season across a latitudinal gradient. I evaluated this hypothesis with data on three species—American shadAlosa sapidissima, striped bassMorone saxatilis, and mummichogFundulus heteroclitus—having wide latitudinal ranges (≈29–46°N) along the east coast of North America. For each of these species, the length of the first growing season decreases by a factor of about 2.5 with increasing latitude within the species' range, yet body size at the end of the first growing season is independent of latitude. Northern fish must, therefore, grow substantially faster within the growing season than do southern fish. This “countergradient variation” in growth rate may be more widespread than has been recognized. A similar latitudinal pattern in growth rate has a genetic basis in the Atlantic silversideMenidia menidia, and data on Atlantic salmonSalmo salar, largemouth bassMicropterus salmoides, and several marine invertebrates also support the hypothesis of countergradient variation. Moreover, the capacity to grow rapidly within the growing season in high-latitude environments may be an adaptive response to size-selective winter mortality (i.e., the tendency of small fish to die more readily than large fish), a phenomenon known to occur in numerous fish species. The countergradient variation model has important implications for choosing genotypes with high growth rates for aquaculture, transplantation of natural stocks across latitudes, and elucidation of the trade-offs between growth rate and other physiological or life history traits.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1990)119<0416:TRBCFG>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Allelic products of seven isozyme loci were used to identify presumptive hybridization between chinook salmonOncorhynchus tshawytschaand coho salmonO. kisutchin northern California. First-generation hybrid salmon (N= 3) were observed in samples from a tributary creek to the Trinity River; from rearing ponds at Camp Creek, a tributary to the Klamath River (N= 14); and from the ocean salmon fishery near Eureka (N= 2). The sample from the Camp Creek rearing ponds consisted of progeny from an inadvertent cross of coho and chinook salmon by hatchery personnel at the Irongate Hatchery. In addition to the artificial production of hybrid salmon at Irongate Hatchery, the alteration of traditional salmon spawning routes by Lewiston Dam on the Trinity River may have lead to natural hybridization between chinook and coho salmon in Deadwood Creek. Accurate quantification of the occurrence of hybridization was impossible due to nonrandom sampling of populations, but we presume to have underestimated the actual hybridization between these two species.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1990)119<0431:BGDONA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

During two spawning seasons, triploidy was induced in white crappiePomoxis annularisby temperature shock 5 min after artificial fertilization. Heat shocks of 36–40°C for 1–5 min resulted in 0–10% triploidy. Cold shocks of 5°C for 45 min and 60 min yielded 0–24% and 72–92% triploidy, respectively. Triploids were identified initially by chromosome counts in 1987, but examination of confirmed diploids and triploids indicated that they could be distinguished unambiguously on the basis of measurements of erythrocyte nuclear major axis. Erythrocyte nuclear minor axis and volume were substantially less reliable for identifying triploids. Flow cytometry was used to identify triploids in 1988. Limited data on juvenile fish revealed no significant size difference between diploids and triploids in most of the treatment groups.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1990)119<0438:IOTIWC>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Users of stock production models assume that a time series of catch-per-effort data reflects changes in the size of a self-sustaining biological population. This assumption is often violated in analyses of fisheries that have undergone changes in the areal coverage of the fishing fleet because the fraction of the population that is available to fishing also changes. Furthermore, the problem is aggravated when there is biomass transfer (in the form of migration) between the exploited and unexploited segments of the population. We present a general production model that can be used to understand the dynamics of equilibrium population size and yield as functions of fishing mortality and exploitable population fraction. We then develop two simple subsets of this model in which biomass transfer is either nil or high between the unexploited and exploited fractions, and we discuss methods to estimate the models' parameters given data on catch, effort, and area. The application of the models is illustrated with data on the fishery for yellowfin tunaThunnus albacaresin the eastern Pacific.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1990)119<0445:EPMTIF>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

BluefishPomatomus saltatrixin the western north Atlantic spawn in the South Atlantic Bight in spring and the Mid-Atlantic Bight in summer. We performed back-calculations to length at age 1 from scales of fish captured during June–September 1986 and 1987 from Long Island, New York, to determine if spring- and summer-spawned fish could be identified among summer-spawning adults captured in the New York Bight. Analysis of gonads confirmed that the summer spawning season off New York is a temporally distinct event occurring from late June to late August, with peak activity in July. All fish used for back-calculations were in spawning condition, and most had lengths at age 1 characteristic of a spring birth date (mean length, 26.5 cm). This observation does not support the hypothesis that spring and summer spawners are two different stocks of fish. Contemporary stocks of adult bluefish along the mid-Atlantic coast may consist largely of spring-spawned fish.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1990)119<0455:SSAFGO>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Abnormalities including contortion of the body and reduction of the jaws and pectoral fins occurred among 2–25% of the yolk-sac Pacific herring larvaeClupea harengus pallasicollected in 1985 from Kulleet Bay, a spawning area on Vancouver Island, British Columbia. An additional 4–68% of the post-yolk-sac larvae had underdeveloped lower jaws. Abnormal larvae were distinguished from healthy larvae through discriminant analysis of morphometric characters. The high frequency of larval abnormalities in 1985 may have been related to unseasonably sunny, warm weather during the 14-d incubation of the eggs, which resulted in stress to eggs exposed to sun and warm air during especially low midday tides. Underdeveloped jaws affected feeding by postyolk-sac larvae, as evidenced by lack of food in the guts and by shallow body depths characteristic of starvation.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1990)119<0463:MAOAPH>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

We made estimates of annual production of stream trout in two Lake Superior tributaries in northeastern Minnesota in 1977–1978. The Caribou River (total alkalinity, 34 mg/L as CaCO3) drains part of the north shore of Lake Superior in an igneous rock geology. The Blackhoof River (total alkalinity, 83 mg/L) drains glacial drift and lake clay at the western end of Lake Superior. Annual production of brook troutSalvelinus fontinalisin the Caribou River was estimated to be 58.0 kg (wet weight) per hectare, reflecting low water fertility. In the Blackhoof River, annual production was 43.5 kg of brown troutSalmo truttaand 95.7 kg of juvenile rainbow troutOncorhynchus mykissper hectare, The total salmonid production of 139.2 kg/hectare in the Blackhoof River appeared to reflect an intermediate level of water fertility. Ratios of annual production: mean standing stock (P/B) were calculated to be 2.2 for juvenile rainbow trout, 1.7 for brook trout, and 0.9 for brown trout. These values suggest an inverse relation betweenP/Band number of age-groups present (three for rainbow trout, four for brook trout, and six for brown trout).

ISSN:0002-8487    

DOI:10.1577/1548-8659(1990)119<0470:APAPBR>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

I examined food habits of rainbow troutOncorhynchus mykissin Lake Washington, Washington, for relationships to the spatial and temporal distribution of their prey. Rainbow trout smaller than 250 mm (fork length) ate primarilyDaphnia pulicariaduring summer and autumn; larger fish were piscivorous throughout the year. Longfin smeltSpirinchus thaleichthysmade up the largest fraction of fish prey in the diet of rainbow trout from the nearshore zone during autumn and winter, whereas prickly sculpinCottus asper(in 1984) and yellow perchPerca flavescens(in 1985) were most important in spring and summer. Rainbow trout in the offshore zone (>15 m deep) ate mostly longfin smelt in spring and summer. Longfin smelt exhibited a 2-year cycle of abundance that appeared to influence the feeding habits of rainbow trout. During 1984, the adult longfin smelt population was large and provided the major prey of rainbow trout. When adult longfin smelt were less abundant during the 1985 winter, the fish fraction of the rainbow trout diet and the apparent ration size were roughly half the levels observed the previous winter.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1990)119<0475:SADFHO>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Historical variation in the abundance of bloaterCoregonus hoyiin Lake Michigan may have involved a link between growth rates of juvenile bloaters and the species and size distributions of zooplankton. These distributions have varied dramatically in response to fluctuations in abundance of alewifeAlosa pseudoharengus. Bloater recruitment was poor from the mid1960s to the mid-1970s. If bloater growth rates were reduced when large zooplankton were rare, as in the mid-1960s, juvenile bloaters would have been exposed to size-dependent mortality sources longer and, hence, would have experienced poor survival. Two sets of experiments were used to test this hypothesis. First, we investigated changes in prey size selectivity during the ontogeny of bloater. Our experiments showed that the size of prey that elicited significant positive selectivities increased from 0.3 mm in 20-mm bloaters to 2.3 mm in 100-mm bloaters. These results were then used to predict the outcome of 30-d growth experiments involving two controlled zooplankton distributions as food sources. We predicted successfully that fish longer than 40 mm would experience reduced growth when denied access to larger-bodied zooplankton. We suggest that the availability of appropriate sizes of zooplankton may have profound effects on the growth of juvenile fish and subsequent recruitment.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1990)119<0483:EOCITZ>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor