摘要:

An objective method of measuring shell hardness of Dungeness crab Cancer magister is necessary because the time elapsed since molting is used in part by fishery managers to set commercial seasons. Limiting the catch of soft-shelled crabs in a fishery is important to decrease mortality from handling and to maintain product quality. We developed a durometer to measure shell hardness of Dungeness crabs. The durometer accurately measured the pressure required to produce shell indentation of a given depth, which indicates hardness of the crab shell in durometer units of 0–100. To calibrate the durometer, we collected 27 recently molted male Dungeness crabs from waters of Kodiak Island, Alaska, and measured the shell hardness monthly for one year in the laboratory. The nonlinear relation between durometer reading (Y) and month (X) was analyzed. Of several models evaluated, the cumulative logistic function Y = β0/(1 + e(X−β1)/β2) provided the best fit (b0= 82.2, b1= 2.7 b2= −1.5). Estimation of months since molt was obtained from the inverse relation x = b2loge(b0/y − 1) + b1and 95% confidence limits from graphic interpolation. We estimated month of molt from survey and commercial catch data, and we discuss the effect of temperature on durometer calibration. Shell condition from survey data from four Kodiak bays was classified by using a probabilistic neural network. Classification of new-shell versus other shell hardness resulted in a 90.8% correct classification at a durometer reading of 66. The use of the durometer as a standardized management tool removes the subjectivity of existing shell hardness methods.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0581:ADTMSH>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Abiotic factors that may regulate growth, recruitment, and mortality of warmwater fishes in reservoirs of the Midwest and southeast United States are poorly understood. I examined the effect of reservoir temperature on the growth of white crappies Pomoxis annularis in a Kentucky reservoir to test the hypothesis that warm summer epilimnion temperatures may constrain white crappie growth and describe annual patterns of seasonal growth. Each year reservoir stratification reduced epilimnion volume as summer progressed and prevented white crappie use of cooler hypolimnetic waters due to low dissolved oxygen conditions below the thermocline. Water temperature at the 3-m depth explained significant portions of variability in growth of both juvenile (age-1) and adult (age-2) white crappies during 1989–1993. Higher temperatures resulted in slower instantaneous growth rates, and growth usually decreased during Jul and Aug. Seasonal growth rates differed between juvenile and adult white crappies. Juveniles grew more rapidly than adults and completed most of their annual growth during April–Jul. Growth rates of adults peaked during Jun–Jul in 3 of 5 years and 1 and 2 months later during the other years. Minor length differences in April among five year-classes of each age did not result in growth advantages during April–Oct. Some somatic growth was detected during Oct–April for three of four year-classes. These results supported the hypothesis that typical summer temperatures in some warmwater reservoirs may suppress growth of white crappies. Defining relations between seasonal growth patterns and water temperature and dissolved oxygen conditions in reservoirs will help set expectations for fisheries and provide direction for management strategies.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0591:GOWCIR>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

–We evaluated the length distribution and catch rates of paddlefish Polyodon spathula collected in three mesh sizes of gill nets in Keystone Reservoir, Oklahoma, during the winters of 1996–1998. In all, 1,454 paddlefish were collected in monofilament gill nets with bar measures of 127, 152, and 203 mm. Mean lengths of paddlefish increased with increasing mesh size. The smallest and the largest mesh sizes caught age-0 paddlefish in 1996, a year when 152-mm mesh was not used and the only year we collected age-0 paddlefish. Median catch rates for all sizes of paddlefish were highest in 152-mm-mesh net and lowest in 127-mm-mesh nets. For population size and age structure sampling, we recommend a range of mesh sizes (e.g., 127–203 mm) to collect the broadest size range of paddlefish. To collect sexually mature fish for broodstock, we recommend using large mesh sizes (e.g., 152 and 203 mm) to increase catch rates of adult paddlefish and reduce bycatch of other species. Net height (4.6–9.1 m) and duration of net set (16–22 h) did not significantly influence catch rates. Other gill-net variables (e.g., net length) need to be evaluated to determine their potential influence on catch rates of paddlefish.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0599:EOPLDA>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

We compared fish growth and abundance from the western basin of Lake Erie before (1983–1988) and after (1989–1993) establishment of zebra mussels Dreissena polymorpha to determine if growth and abundance of age-0 fish changed following zebra mussel introduction. We found no significant differences in age-0 growth for yellow perch Perca flavescens, walleye Stizostedion vitreum, freshwater drum Aplodinotus grunniens, gizzard shad Dorosoma cepedianum, alewife Alosa pseudoharengus, white bass Morone chrysops, white perch Morone americana, spottail shiner Notropis hudsonius, emerald shiner Notropis atherinoides, trout-perch Percopis omiscomaycus, and rainbow smelt Osmerus mordax before and after zebra mussel establishment. Zooplankton abundance may still be sufficient following zebra mussel establishment to support the same age-0 fish growth. Fish may be switching earlier or relying more on other prey types, especially the more abundant benthic invertebrates. Some fish may be supplementing their diet with zebra mussel veligers, although this has not been documented. No change in fall abundance was observed, except that the abundance of age-0 yellow perch increased significantly after zebra mussel establishment.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0604:CIAFGA>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Setlines were constructed and used to capture lake sturgeon Acipenser fulvescens in the St. Clair River, a Great Lakes connecting waterway. Particularly strong current, steep bottom contours, and water depths exceeding 18 m make traditional sampling methods in this area problematic. We constructed six setlines, each with 25 hooks (a total of 150 hooks), for a cost of about US$60 each. Hooks were baited with a variety of cut and whole fish. Sixty-seven sets in May and Jun of 1997 caught 84 lake sturgeon. The only other fish caught was one northern pike Esox lucius. Round goby Neogobius melanostomus, an introduced exotic species, was the most successful bait used. Lake sturgeon caught on setlines ranged in weight from 0.8 kg to 45.5 kg. Most lake sturgeon were hooked in the mouth and experienced little visible damage or stress, but about 20% of the fish were hooked outside the mouth (snagged) and in a few cases considerable bleeding and tissue damage occurred. The highest incidence of snagging coincided with peak spawning activity and may be related to a behavioral change associated with spawning. We found that setlines provided an effective, low-cost method for collecting lake sturgeon in the difficult physical conditions present in the St. Clair River.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0610:COLSWS>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

We measured scour of the redds of chinook salmon Oncorhynchus tshawytscha on dredge tailings and natural substrates in three tributaries of the Klamath River, California. We measured maximum scour with scour chains and net scour by surveying before and after high winter flows. Scour of chinook salmon redds located on dredge tailings exceeded scour of redds on natural substrates, although the difference varied among streams. Our results show that fisheries managers should consider the potential negative effects of dredge tailings on the spawning success of fall-spawning fishes such as chinook salmon and coho salmon O. kisutch.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0613:SOCSRO>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Before-and-after surveys at several southern California sites indicated that populations of endangered tidewater goby Eucyclogobius newberryi persisted through heavy flooding in 1995. This was contrary to our expectations that flooding might have led to extirpation in some smaller wetlands. There was also no significant change in tidewater goby density before and after the flooding. Several apparent recolonization events coincided with the flood, suggesting that flooding may be important for the long-term persistence of the species.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0618:PPAROE>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0623:CTOHSC>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0626:TOHSCR>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor