Mean Bottom Temperature Research Articles

Trophic status of three large Missouri River reservoirs

Bolgrien, D.W., J.V. Scharold, T.R. Angradi, T.D. Corry, E.W. Schwieger and J.R. Kelly. 2009. Trophic status of three large Missouri River reservoirs. Lake Reserv. Manage. 25:176–190. Probability-based surveys conducted between 2001–2004 characterized the three large reservoirs of the Missouri River—Lake Oahe, Lake Sakakawea, and Fort Peck Lake—as mesotrophic to eutrophic, phosphorus (P) limited, and generally supporting cold water habitat (bottom waters <15°C and dissolved oxygen [DO] concentrations >5 mg/L) in midsummer. Riverine zones were shallower, warmer, more eutrophic, and had lower DO and higher suspended matter concentrations than lacustrine zones. Similar, although more variable, differences were found between bays and open-water areas. Between sampling years, water levels decreased in each reservoir. In the first year of sampling, area-weighted mean reservoir trophic status index based on chlorophyll (TSIchl) was about 37 in all three reservoirs. Sixty percent of Oahe and Sakakawea and 40% of Fort Peck had TSIchl> 50. Trophic status index based on Secchi depth (TSISD) averaged about 50 in each reservoir across years. Because mean TSIchl< TSISD, light attenuation was considered to be silt, not algae, dominated. Trophic status index based on total P (TSITP) and the ratio of N:P concentrations indicated that the reservoirs were very P limited. Mean bottom temperature and DO concentration in Oahe were unchanged between years at about 19°C and 7.5 mg/L, respectively. Bottom temperatures in Sakakawea increased (from 15°C to 21°C) and DO concentration decreased (from 7.3 mg/L to 6.0 mg/L) with lower water levels. In Fort Peck, bottom temperature remained about 18°C, but DO concentration fell from 7.23 mg/L to 4.96 mg/L. Results show that surveys successfully characterized important environmental conditions throughout these large reservoirs.

Below the Convergence

Below the Convergence

Growth changes in bighand thornyhead Sebastolobus�macrochir off the Pacific coast of northern Honshu, Japan

The biomass of bighand thornyhead Sebastolobus macrochir was increased by the high recruitment success of the 1999–2002 year classes off the Pacific coast of northern Honshu, Japan. In this study, the growth of bighand thornyhead was examined over a 9-year period from 1996 to 2004 in this area. The growth of the 1999 year class and the 2000–2002 year classes was reduced at 3 and 2 years old, respectively, while the 1999–2002 year classes were smaller than the 1993–1998 year classes. In 2-, 3- and 4-year-old fish, the relationship between abundance and mean standard length was expressed by negative linear regressions, while fish became smaller when abundance of the year class was larger. Mean bottom temperatures were stable at depths of 350–900 m; variations in water temperature were small in the main distribution area of bighand thornyhead. We discuss the factors affecting the growth of bighand thornyhead via changes in the demersal fish community and feeding habits.

Community structure of eastern Bering Sea epibenthic invertebrates from summer bottom-trawl surveys 1982 to 2002

Catches of invertebrates from the annual summer bottom-trawl surveys in the eastern Bering Sea between 1982 and 2002 were analyzed to describe the composition and spatial distri- bution of epibenthic invertebrate communities. A persistent characteristic is distinct inshore and offshore community types separated by the dynamic oceanographic inner front that generally co- incides with the 50 m isobath. This typical spatial distribution of the 2 communities corresponds closely with surficial sediment type and previously reported patterns for groundfishes and infaunal invertebrates. The biomass of the inshore assemblage is overwhelmingly dominated by the sea star Asterias amurensis, whereas Gastropoda, Paguridae and the snow crab Chionoecetes opilio domi- nate the offshore assemblage. Variations in the typical inshore- offshore pattern occurred in 1982- 84, 1987- 88, 1998- 99 and 2001- 02, when there were substantial reductions in the spatial extent of the inshore community, especially in the Bristol Bay area. During these reductions, epiben- thos in Bristol Bay shifted from the inshore type to either offshore or an undefined community type. In general, reductions in the inshore domain were correlated with a mean bottom temperature in the survey area that was higher than normal in the preceding summer. Extreme El Nino events coincided with sizable contractions of the inshore community in 1982- 84 and 1998- 99. Spatial variability in the epibenthic communities may thus reflect the influence of environmental changes on interannual and decadal scales. Evidence suggests that mobile taxa, especially crabs, may be migrating offshore toward cooler waters, thereby rearranging the epibenthic communities.

Length at sex transition in northern shrimp (Pandalus borealis) off West Greenland in relation to changes in temperature and stock size

Abstract Length at sex transition of northern shrimp (Pandalus borealis) off West Greenland decreased in the years 1991–2002. A pronounced increase in bottom temperature occurred in the middle of this period, and stock size increased substantially during the past years. Length at sex transition differed within the area and the possible effects of changing temperature and abundance were studied for five different regions on the West Greenland shelf. On average, length at sex transition declined by 1.7 mm carapace length (CL) and mean bottom temperature increased by 1.9 °C. The change in length at sex transition was significantly correlated with bottom temperature in three out of the five regions and for all regions combined. No clear density-dependence was detected despite of a substantial increase in northern shrimp density in parts of the area and no evidence was found that northern shrimp decrease size at sex change during periods of low female abundance to compensate for a decreased reproductive potential. The observed change in length at sex transition was apparently independent from the fishery. Earlier maturation due to higher temperature was identified as the principal cause for the decrease in the length at sex transition. Because maximum female length is regarded to be proportional to length at sex transition and female fecundity increases with size, total egg production of a given year class over its lifespan would be lower when sex transition occurs at a smaller size if not compensated otherwise, e.g. through an increase of the proportion of females that spawn in each instead of every second year.

Spatial distribution and feeding habits of the shrimp Crangon uritai as a predator on larval and juvenile marbled sole Pleuronectes yokohamae

: To examine predation on larval and juvenile Pleuronectes yokohamae by Crangon uritai, the spatial distribution and feeding habits of C. uritai were studied. Crangon uritai fed on various prey, including P. yokohamae. Density-dependent predation on juvenile Crangon spp., larval and juvenile gobiid fish Chaenogobius heptacanthus, mysids, and gammarids was observed. The abundance of alternative prey might, therefore, play an important role in reducing the pressure of predation on P. yokohamae. In each year, C. uritai migrated from depths of 10 m in March to depths of 3 m in May. There was a significant negative correlation between the weighted mean depth (WMD) of C. uritai and the weighted mean bottom water temperature (WMBWT). The migration was, therefore, delayed in the cold spring, during which C. uritai occupied depths of approximately 10 m. In contrast, no significant correlation was found between the WMD of P. yokohamae and WMBWT. Settlement of P. yokohamae began at depths of 15 m, mainly during early April. The spatial distributions of these two organisms show greater overlap during the cold spring, resulting in increased opportunities for predation.

Characteristics of Deep Pools Used by Adult Summer Steelhead in Steamboat Creek, Oregon

Abstract This study examined environmental factors that affect deep-pool use by adult summer steelhead Oncorhynchus mykiss in Steamboat Creek, Umpqua River basin, Oregon. Deep pools (>0.8 m depth) represented only 4% of the available habitat area, and 39% of these pools had a mean bottom temperature not exceeding 19°C. Fish and habitat surveys were conducted in August and the first half of September of 1991 and 1992. The presence of adult summer steelhead in pools was determined by snorkeling and visual inspection, and the physical, chemical, and geomorphic characteristics were measured. Differences in deep-pool use by summer steelhead and their relationship to environmental characteristics were assessed by descriptive canonical discriminant analysis. The canonical function explained 69% of the variation in deep-pool use and defined a gradient from long, shaded deep pools with a coarse substrate and colder bottoms (which fish used) to shorter, shallower, sunny pools with fine particulate substrate, homoge...

Influence of Water Temperature in Use of Deep Pools by Summer Steelhead in Steamboat Creek, Oregon (USA)

This study examined use of deep pools (>0.8 m mean depth) based on thermal characteristics by adult summer steelhead in Steamboat Creek, Oregon. Steamboat Creek had a heterogenous thermal profile, with some segments exceeding the preferred temperature of steelhead. Deep pools were scarce (4% of the total habitat types), and 39% of them were identified as cool pools (mean bottom water temperature 19°C). Adult summer steelhead were found primarily in deep pools, avoiding other habitats such as glides, riffles, and even cool tributary junctions. Adult abundance in deep pools did not show significant variation between years and was inversely associated with mean bottom temperature. Use of cool pools was estimated to be 11 times the use of warm pools. However, the presence of unoccupied cool pools suggested that other ecological variables may be involved in pool selection.

Seasonal variation of Chironomus nipponensis (Diptera) voltinism in the deep mesotrophic Lake Kizaki, Japan

The seasonal variations of chironomid populations, especially, Chironomus nipponensis, which was the dominant species, were studied at three different depths in mesotrophic Lake Kizaki from April 1985 to December 1986. Size frequency distributions of C. nipponensis larvae at Station 2 (13 m depth) and Station 3 (26 m depth) were usually bimodal with two cohorts. At Station 2, C. nipponensis larvae had a one-year generation time, while at Station 3, all C. nipponensis larvae took 1.5 years to develop into adults. At Stations 2 and 3, annual mean bottom water temperature and total effective temperature (degree-days above 2.5 °C) were 7.3 ± 1.1 °C 1,760 degree-days (12 months; from April 1985 to March 1986), and 5.6 ± 0.4 °C 1,753 degree-days (18 months; from April 1985 to September 1986), respectively. At Station 3, the low water temperature and dissolved oxygen concentration during summer-fall might suppress the growth of C. nipponensis larvae. Bottom water temperature and low dissolved oxygen concentration were too low to allow the growth of C. nipponensis within a year. In these circumstances, the spatial seasonal variation in voltinism of C. nipponensis population is suggested in mesotrophic Lake Kizaki.

Female reproductive biology and spawning periodicity of two species of king prawns, Penaeus longistylus Kubo and Penaeus latisulcatus Kishinouye, form Queensland's East Coast Fishery

In the coastal region of central Queensland female red-spot king prawns, P. longistylus, and the western or blue-leg king prawns, P. latisulcatus, had high mean ovary weights and high proportions of advanced ovary development during the winter months of July and August of 1985 and 1986. On the basis of insemination, both species began copulating at the size of 26-27 mm CL, but P. longistylus matured and spawned at a smaller size than P. latisulcatus. Abundance of P. longistylus was generally three to four times greater than that of P. latisulcatus but the latter was subject to greater variation in abundance. Low mean ovary weight and low proportions of females with advanced ovaries were associated with the maximum mean bottom sea-water temperature (28.5�C) for both species. Population fecundity indices indicated that peaks in yolk or egg production (a) displayed a similar pattern for both species, (b) varied in timing from year to year for both species and (c) were strongly influenced by abundance. Generally, sample estimates of abundance and commercial catch rates (CPUE) showed similar trends. Differences between the two may have been due to changes in targeted commercial effort in this multi-species fishery.

Influence of the abiotic marine environment upon the benthic species community in the eastern Bering Sea-I. Fluctuations of the water temperature and the salinity in the eastern Bering Sea.

The water temperature and the salinity at the botton layer of the eastern Bering Sea were analyzed in order to elucidate the fluctuation of the Alaskan Stream Extension Water during the summers from 1963 to 1977. Tish warm and saline water mass prevailed from 1965 until 1969 and weakened after 1970. There was significand positive correlation between the fluctuation of average of the corrected monthly mean sea level of May and June and the fluctuation of the mean bottom temperature from 1963 to 1974 excluding 1968 and 1973 (r=0.76, P<0.02).

Changes in Abundance and Certain Biological Characteristics of Grand Bank American Plaice, Hippoglossoides platessoides

Commercial exploitation of American plaice on the Grand Bank increased from the early 1950s reaching a peak of about 90,000 tons in the mid-1960s. Catches have subsequently declined to about 45,000–50,000 tons annually. The increased exploitation of plaice was reflected in declines in catch per hour and stock abundance of fully vulnerable age-groups and an increase in the rate of instantaneous fishing mortality (F). The documentation of these was particularly strong in ICNAF Division 3L, but appeared to be somewhat erratic in 3N, probably because of incomplete sampling of the stock prior to the mid-1960s.Average size at age increased gradually from the early 1950s to the 1970s apparently because of increased growth rate in the initial 2 or 3 yr of life. Coupled with the increased size at age were significant declines in the age at sexual maturity.Significant correlations were found between stock abundance and asymptotic length (L∞), and size at age 5 and 10 in Division 3L and while positive trends could be demonstrated between some of these and mean bottom temperature, the correlations were not significant.

Observations on the Ecology and Life Cycle of Prochristianella penaei Kruse (Cestoda: Trypanorhyncha)

Examinations of Penaeus aztecus and P. setiferus from the Galveston Bay area show Prochristianella penaei plerocerci to be common in these shrimp, thus extending the known range of this tapeworm to the western Gulf of Mexico. Two years of repeated sampling of shrimp from Clear Lake, a secondary bay in the Galveston Bay system, showed patterns of infection which provided useful leads both to the ecological area where infection of shrimp occurs and the identity of the parasite's definitive host. The relationship found between shrimp size and incidence of infection, when considered with the known migratory habits of Penaeus aztecus and P. setiferus, suggests that these decapods are uninfected when they enter the bay and are usually infected by the time they leave. Since this pattern showed a rather brackish bay (1%o to 10%o) to be a probable site in which infection of shrimp takes place, it was assumed that (1) the first intermediate host of ProchristianeUa penaei also inhabits such areas and (2) the range of the elasmobranch final host includes low salinity areas, permitting completion of this cestode's life cycle. The latter point postulates a broad salinity tolerance range for the final host. Discovery of the adult tapeworm in Dasyatis sabina, a ray noted for the extent of its salinity tolerance, lends support to these assumptions. Despite our long acquaintance with penaeid shrimp (e.g., Linnaeus provided the first description of the white shrimp, Penaeus setiferus), and the continually increasing commercial importance of these animals during the last 40 years, thorough examinations of shrimp for parasites have not been reported prior to the Florida studies of Hutton et al. and Kruse, both in 1959. As a result, our present knowledge of the ecology and life cycles of shrimp parasites is slight. This situation is particularly true in the western Gulf of Mexico, one of the most productive shrimp habitats in the world. In 1959, Dr. Edward Chin brought to me for identification a small, white cyst in the digestive gland of a shrimp collected from Galveston Bay. The cyst proved to be the plerocercus stage of a trypanorhynch cestode identical to that described by Kruse (1959) as Prochristianella penaei. Since no information is available on the incidence of this parasite except in Florida waters, a survey was undertaken to determine the frequency with which the worm occurred in shrimp from the Galveston area. In addition, the dearth of information on trypanorhynch life cycles coupled with the need for a better understanding of shrimp ecology suggested a search for the undescribed Received for publication 2 December 1964. *Contribution No. 194, Bureau of Commercial Fisheries Biological Laboratory, Galveston, Texas. stages in the life history of P. penaei. The results of the survey work showed seasonal pa terns of infection which proved useful in ascertaining both the ecological area where inf ction of shrimp occurs and the identity of the parasite's definitive host. MATERIALS AND METHODS In selecting possible sites for regular sampling stations, consideration was given to the fact that both Penaeus aztecus, the brown shrimp, and P. setiferus, the white shrimp, are migratory in habit. T available life cycle information on these locally abundant species (Viosca, 1920; Weymouth, Lindner, and Anderson, 1933; and Burkenroad, 1934, 1939) indicates that spawning and larval development occur only offshore, the resulting postlarvae (about 0.5 inch in length) moving shoreward to bays, where they spend several months of rapid growth to subadult size (3 to 5 inches long) before migrating offshore again to attain adulthood and spawn. Thus, bays appear to provide important pasture areas for these animals prior to their return to the open waters of the Gulf of Mexico where they were spawned. Since Clear Lake, a secondary bay in the Galveston Bay complex (Fig. 1), was being sampled for shrimp fairly regularly by other workers at this lab ratory, and had been shown to harbor an abundance of both P. aztecus and P. setiferus (Chin, 1961), it was selected as an area for regular sampling. Monthly mean bottom temperatures for Clear Lake range from 10 to 30 C, and bottom salinity is usually between 1%o and 10%o. Offatts Bayou, another secondary bay in the Galveston Bay system, has a comparable temperature regime but a higher salinity range (15%o

Some Observations on Permafrost Distribution at a Lake in the Mackenzie Delta, N.W.T., Canada

Reports investigations of the thawing effect of water on permafrost in northern Mackenzie District during Apr 1961. Holes were drilled under the center of a small, shallow lake with a mean bottom temperature higher than 32 degrees F and at various distances to the west of the lake. Hand probings were made near the edge of the lake, soil and water samples taken, ground temperatures measured, altitude and various terrain surveys made. It was found that the sediments below the center of the lake were unfrozen to bedrock; but the position of the permafrost table rose progressively toward shore and the thawing effect was confined to the ground lying under the lake. The thermal effect of the lake however, extended for some distance beyond.