摘要:

Growth, mortality, fecundity, egg diameter, and age at maturity were determined from samples of 270 paddlefishPolyodon spathulacollected from the Atchafalaya River basin and Lake Pontchartrain, Louisiana, during a commercial harvest moratorium from 1987 to 1989. Early growth of paddlefish determined from back-calculation of annular measurements on dentary cross sections was high relative to paddlefish populations in the upper Mississippi River drainage; lengths of age-1 fish ranged from 411 to 455 mm in eye-fork length. Natural mortality of Louisiana paddlefish was high (26–48%), and data suggested a reduction in age at maturity (100% females mature at age 10), lower fecundity (average fecundity, 9,500 eggs/kg body weight), and larger eggs (average diameter, 2.67 mm) relative to other paddlefish populations. Changes in reproductive life history characteristics may reflect rapid growth and high natural mortality rates. As the postmoratorium commercial fishery for Louisiana paddlefish develops, conservative harvest regulations should be promulgated until the effects of harvest on paddlefish stock dynamics can be determined.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1992)121<0378:GFAMOP>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The relation of oxygen consumption to ambient temperature and group size was studied in juvenile American shadAlosa sapidissimaat three group sizes: 5 or 6 (small), 9–13 (medium), and 41–48 (large) fish per 500-L tank. Oxygen consumption rates, water temperatures, and behavior were measured concurrently in the three group-size treatments. Schooling predominated in large groups, whereas aggregating behavior dominated medium and small groups. Fish in small or medium groups consumed oxygen at two to four times the rate of fish in large groups (0.36 or 0.25 versus 0.11 mg O2/[g biomass·h]). This group-size-related respiratory rate reduction could be caused by the effect of calming, type of swimming, swimming speed, or hydrodynamic advantage.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1992)121<0385:NGMRRI>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Large numbers of spawning, anadromous clupeid fish (Alosaspp.) ascend North American coastal rivers and streams annually. In many regions, post-spawning mortality is high, resulting in potentially significant inputs of marine-derived animal detritus to tidal and nontidal freshwater systems. I estimated retention of carcasses and assessed the mechanism(s) of biological processing for carcasses of migratory blueback herringAlosa aestivalisin the James River, Virginia. In a first experiment, 418 tagged and weighed carcasses placed in the river were transported downstream at an average rate of 986 m/h. In a second experiment, 72 carcasses were fixed in the river as artificial substrates and recovered over the next 192 h. Instantaneous decomposition rates averaged 0.015/h, and the predicted mean time to complete decay was more than 240 h. An aquatic saprolegniale fungus (Saprolegniasp.) heavily colonized most carcasses after 48 h. No aquatic macroinvertebrates were associated with any recovered carcass, although potential scavenger taxa were common in the benthic community.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1992)121<0390:FAPSOP>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Young-of-the-year Bear Lake sculpinCottus extensusfeed throughout the day on benthic invertebrates and cease feeding at night when they migrate to the metalimnion. We investigated their reliance on vision by conducting feeding trials at different light levels in the laboratory. Feeding rate reached a maximum at intermediate light levels (near 1016photons·m−2·s−1; approximately 1 lux) but decreased as light intensity increased beyond this range. At this maximum rate, the fish fed nine times faster than they were able to feed in the dark, showing that young Bear Lake sculpin rely heavily upon vision to feed. The light intensity at which feeding was greatest corresponded to intensities found on the bottom of Bear Lake (40–60 m) during the day.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1992)121<0395:VFBJBL>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

I examined the short- and long-term low-temperature tolerance of American plaiceHippoglossoides platessoides, a coldwater flatfish species, in an attempt to relate temperature tolerance in the laboratory to declines in the species' abundance following years with unusually cold water temperatures. American plaice were very tolerant of rapid declines in temperature over 96 h, and no fish died when placed in temperatures of less than –1.30°C until acclimation temperatures were above 10°C. They also survived 77 d at –1.40°C; although they were more active at that temperature than fish at 0.18°C, they did not eat, and they lost weight. The observed declines in population biomass may have been caused by starvation rather than by cold itself.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1992)121<0399:LTOAPI>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

ISSN:0002-8487    

DOI:10.1577/1548-8659-121.3.403

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor