摘要:

A bivalve shell gape monitor, previously used to detect toxic discharges in Europe, was used to measure response of the freshwater musselAmblema plicata plicata(Say 1817) (Mollusca: Unionidae) to brief changes in water velocity. In the laboratory, overall behavior of eightA. p. plicatawas virtually unaffected by exposure once every 2 hr to a 5-min pulse of high-velocity water (45 cm/s) created with a submersible pump. In the east channel of the upper Mississippi River near Prairie du Chen, WI, multiple passes of recreational craft reduced by only a few percent the total time that sixA. p. plicatawere opened during a 2-hr period. Only six of 42 events, caused by passage of a work boat or a 6.5-m-long skiff, caused a measurable response in mussel shell gape. It was concluded thatA. p. plicatawas not greatly affected by brief changes in ambient water velocity caused by vessel passage.

ISSN:0270-5060    

DOI:10.1080/02705060.1999.9663675

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The diets of coho fry in Baker Creek, Bellingham, Washington, and an adjacent pond were examined in November through January, 1988–89. Fry in both habitats had the larger numbers of prey in early December after heavy rain, when springtails comprised more than 70% of their food items in both habitats. In January, when rainfall was low, both populations fed more on benthic invertebrates, such as taeniopterygid nymphs and simuliid larvae in the creek, and chironomid larvae in both habitats. High rainfall and flooding played an important role in making available food for juvenile coho salmon in both off-channel and creek habitats in late fall and early winter.

ISSN:0270-5060    

DOI:10.1080/02705060.1999.9663676

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Growth and growth patterns of black crappie (Pomoxis nigromaculatus) from a diverse set of 42 lakes in the southern half of Minnesota, and effects of lake productivity, climate warming, and intraspecific density on growth were determined First-year growth increments decreased with increasing mean depth and increased with increasing chlorophyll-aconcentration until concentrations reached around 100 μg/L. At concentrations above 100 μg/L, fist-year growth decreased with increasing chlorophyll-aconcentration. The number of years needed to grow to 200 mm (QAGE) was lower in lakes with low (< 3.8 per lift) catch per lift (CPUE) of black crappie in gill nets set in summer. Second- and third-year growth increments explained 71% of the variation in QAGE among lakes, but first-year growth did not explain any additional variation. Black crappie with sigmoidal growth patterns (second- or third-year increments ≥ first-year increments) reached 200 mm significantly faster than black crappie with nonsigmoidal growth (first-year growth increments were longest). Black crappie exhibited sigmoidal growth in lakes with low gill net CPUE of black crappie, and nonsigmoidal growth occurred in lakes with high gill net CPUE. Growth and growth patterns were unrelated to climate warming.

ISSN:0270-5060    

DOI:10.1080/02705060.1999.9663677

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Laboratory experiments were designed to mimic the frequency, duration, and magnitude of water velocity changes associated with towboat and barge passage at prominent mussel beds in the upper Mississippi River. Ambient water velocity was set to 11 cm·s−1, with regular 5-minute pulses of 45 cm·s−1occurring every 0.5, 2.0, or 5.0 hours. After 49 days mussels showed no significant inter-treatment differences in respiration, nitrogen excretion, O:N ratio, or tissue condition index. Additional short-term (14 days) laboratory experiments indicated additive effects of increased total suspended solids (TSS) during brief, intermittent periods of high water velocity. The 5-minute episodes of high velocity (50 cm·s−1) occurred once every 0.5 and 3.0 hours against an ambient velocity of 7 cm·s−1. TSS rose from an ambient concentration of 20 mg·liter−1to 120 mg·liter−1during the episodes of high velocity. Significantly lower nitrogen excretion and higher O:N tended to occur in high versus ambient TSS treatments; however, these differences were small and inconsistent both among species within a treatment and among treatments for a particular species.

ISSN:0270-5060    

DOI:10.1080/02705060.1999.9663678

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

ISSN:0270-5060    

DOI:10.1080/02705060.1999.9663679

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

ISSN:0270-5060    

DOI:10.1080/02705060.1999.9663664

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor