Longfin Smelt Research Articles

Status of Splittail in the Sacramento–San Joaquin Estuary

Analysis of data from four extensive fish surveys in the Sacramento–San Joaquin estuary indicated that splittail Pogonichthys macrolepidotus, endemic to the Central Valley of California, declined by 62% over a 13-year period. Splittails are now found mostly in the estuary, a fraction of their former range. In a gill-net survey in August 1994, 50% of the splittails taken in the estuary were from the Suisun Bay area, and 50% were just upstream in shallow, well-vegetated areas. Splittails migrate into freshwater to spawn, and river outflow carries juveniles into productive, shallow, low-salinity areas downstream. The high correlation of abundance of young with river outflow (average r2, 0.60) and a weak stock–recruitment relationship (r2 = 0.22) indicate that spawning success depends on favorable environmental conditions created by high outflows, such as the number of days that lowland areas remain flooded in the spring. A repeated-measures analysis of variance indicated that splittails prefer shallow, low-salinity habitats. The reductions in splittail abundance and range and the movements and habitat preferences of splittail young and adults correspond to trends and habits of two other species characteristic of the estuary, delta smelt Hypomesus transpacificus and longfin smelt Spirinchus thaleichthys. The largest threats to these three species are changes in water management and increases in water diversions that reduce spawning and rearing areas and other low-salinity habitats in Suisun Bay.

Allozyme Analysis of Delta Smelt, Hypomesus transpacificus and Longfin Smelt, Spirinchus thaleichthys in the Sacramento-San Joaquin Estuary, California

Two species of smelt (Osmeridae), Hypomesus transpacificus and Spirinchus thaleichthys, found in the Sacramento-San Joaquin estuary recently have declined in abundance, and H. transpacificus has been threatened by the introduction of nonnative Hypomesus nipponensis. We conducted an allozyme analysis of five species of smelt found in California to determine whether the threatened populations are distinct genetically and to evaluate the possibility of introgression of foreign alleles in H. transpacificus. Native H. transpacificus and introduced H. nipponensis differed genetically (Nei's D = 0.883) and were allelically distinct at 13 of 22 loci. Hypomesus transpacificus is more similar genetically to the native marine species, Hypomesus pretiosus (Nei's D = 0.400) than to H. nipponensis, strongly supporting the interpretation that H. transpacificus and H. nipponensis are distinct species. Populations of S. thaleichthys from Washington and the Sacramento-San Joaquin delta are similar genetically (Nei's D = 0.005). However, gene frequencies among these two populations of S. thaleichthys differed significantly, suggesting that current gene flow between them is restricted. This result, combined with geographic isolation suggests that the delta population of S. thaleichthys warrants management as an isolated and genetically distinct entity.

Horizontal and vertical movements of telemetered rainbow trout (Oncorhynchus mykiss) in Lake Washington

In summer and fall 1989, six rainbow trout (Oncorhynchus mykiss) were tracked in Lake Washington with ultrasonic transmitters for a total of 349 h to determine their movements in relation to the distribution of possible prey species. The trout moved primarily in the nearshore area at an average velocity of 12.4 cm/s (~ 0.25–0.3 body lengths/s). Five of the six fish made one more rapid (>1 body lengths/s) excursion across the lake, then continued moving in the nearshore zone. The trout were generally inactive, staying close (<50 m) to shore at night, and became more active near dawn; however, the highest average velocities were at dusk. They spent over 90% of their time in the top 3 m of the water column and 10% in brief (2 min), shallow (mean 6.6 m) dives. Dives occurred most frequently at dawn and during the day (0.8/h), less often near dusk (0.5/h), and seldom at night (0.1/h). The depth distribution and movement patterns suggest that the trout were feeding on Daphnia pulicaria during the day, in both nearshore and offshore areas, supplementing this diet with nearshore fishes such as prickly sculpins (Cottus asper). Predation on pelagic planktivores (longfin smelt, Spirinchus thaleichthyes, and juvenile sockeye salmon, Oncorhynchus nerka) was unlikely because the trout were primarily found nearshore and near the surface, whereas the planktivores are primarily offshore and closer to the bottom.

Feeding Behavior of Longfin Smelt (Spirinchus thaleichthys) May Affect Water Quality and Salmon Production in Lake Washington

Feeding Behavior of Longfin Smelt (<i>Spirinchus thaleichthys</i>) May Affect Water Quality and Salmon Production in Lake Washington

Diet and growth of longfin smelt and juvenile sockeye salmon in Lake Washington

Diet and growth of longfin smelt and juvenile sockeye salmon in Lake Washington

Relationship between abundance, growth, egg size and fecundity in a landlocked population of longfin smelt, Spirinchus thaleichthys

Sixteen year‐classes of longfin smelt, Spirinchus thaleichthys, show a consistent pattern of alternating year‐class strength between even (strong) and odd (weak) years. A recent (1989) odd year‐class grew as well as, if not better than, the late 1960s odd year‐classes. However, fish in the even year‐classes (1988 and 1990) were significantly smaller in size then the 1966 and 1968 cohorts. Associated with this reduction in growth of the even year‐class fish is a decline in fecundity. Fecundity of the odd year‐classes of smelt was also smaller than in the early 1960s. Mean egg diameter and gonadosomatic index were not statistically different between 1988 and 1989 year‐classes but the relative fecundity was higher for the 1988 year‐class than for 1989, suggesting a higher reproductive investment in the even year‐class. Reduction in growth and associated reproductive traits is considered to result from a reduction in the abundance of mysids, a preferred prey species.

Relationship between abundance, growth, egg size and fecundity in a landlocked population of longfin smelt, Spirinchus thaleichthys

Sixteen year-classes of longfin smelt, Spirinchus thaleichthys, show a consistent pattern of alternating year-class strength between even (strong) and odd (weak) years. A recent (1989) odd year-class grew as well as, if not better than, the late 1960s odd year-classes. However, fish in the even year-classes (1988 and 1990) were significantly smaller in size then the 1966 and 1968 cohorts. Associated with this reduction in growth of the even year-class fish is a decline in fecundity. Fecundity of the odd year-classes of smelt was also smaller than in the early 1960s. Mean egg diameter and gonadosomatic index were not statistically different between 1988 and 1989 year-classes but the relative fecundity was higher for the 1988 year-class than for 1989, suggesting a higher reproductive investment in the even year-class. Reduction in growth and associated reproductive traits is considered to result from a reduction in the abundance of mysids, a preferred prey species.

Seasonal and Diel Food Habits of Rainbow Trout Stocked as Juveniles in Lake Washington

Abstract I examined food habits of rainbow trout Oncorhynchus mykiss in Lake Washington, Washington, for relationships to the spatial and temporal distribution of their prey. Rainbow trout smaller than 250 mm (fork length) ate primarily Daphnia pulicaria during summer and autumn; larger fish were piscivorous throughout the year. Longfin smelt Spirinchus thaleichthys made up the largest fraction of fish prey in the diet of rainbow trout from the nearshore zone during autumn and winter, whereas prickly sculpin Cottus asper (in 1984) and yellow perch Perca 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 fract...

Simulation of the Effect of Rainbow Trout Introduction in Lake Washington

We developed a simulation model based on energetics, habitat selection, feeding selectivity, and population dynamics to examine the effect of introductions of rainbow trout Oncorhynchus mykiss on parr of sockeye salmon O. nerka and longfin smelt Spirinchus thaleichthys resident in Lake Washington (Washington State). We modeled growth and population dynamics of rainbow trout cohorts introduced between 1981 and 1984, and compared results with length-at-age data obtained from marked released fish and with data on diets. Graphical comparisons indicated a reasonable fit to the growth data over the 150–400-mm size range. The model gave a close prediction of the size at which rainbow trout begin to eat fish, these results being sensitive to a size-selective feeding function. Diet data showed that model predictions for the major prey fish (longfin smelt and sockeye salmon) were reasonable. However, prey vulnerability had to be set lower for sockeye salmon than for longfin smelt to produce reasonable rainbow trout diets. Simulation experiments examined the effect ofaltered rainbow trout enhancement, fishing pressure, prey vulnerability, and prey abundance and species composition on prey fish survival. These experiments indicated that the effect of rainbow trout predation on prey fish strongly depended both on the magnitude of rainbow trout introductions and on the prey fish abundance and species composition, which varied from year to year.

Effects of River Flow on Abundance of Young Chinook Salmon, American Shad, Longfin Smelt, and Delta Smelt in the Sacramento-San Joaquin River System

Abstract Annual abundance indices for young fall-run chinook salmon (Oncorhynchus tshawytscha), American shad (Alosa sapidissima), and longfin smelt (Spirinchus thaleichthys) increased directly with river flow rates during the spawning and nursery periods. Annual abundance of young delta smelt (Hypomesus transpacificus) did not vary with river flow. Several factors associated with flow could explain the relationships described for chinook salmon, American shad, and longfin smelt. The one factor common to all affected species was that dispersal of young increases when flows increase, which probably results in decreased density-dependent mortality.

Abundance, Growth, and Spawning of the Longfin Smelt in Lake Washington

Abstract Abundance and growth data indicated a 2-yr life cycle for longfin smelt with even-numbered year-classes being more abundant and showing a lower growth rate than the odd. The Cedar River was the major spawning area. The peak of the spawning run occurred during mid-March in 1970 and mid-February in 1971. The average size of spawning adults decreased as the spawning runs progressed. Males were consistently larger than females and dominated in numbers throughout the runs by a 3:2 ratio. The time of the spawning migration was related to body size; the larger adults of the odd year-class spawn earlier in the year than the smaller adults of the even year-class.

Purse Seining for Juvenile Salmon and Trout in the Columbia River Estuary

Abstract A 28-foot gillnetter was modified to catch juvenile salmon and steelhead trout by purse seining in the estuary of the Columbia River. This vessel and equipment enabled effective sampling with relative economy, practicality, and safety. The main limitation was the lack of space for handling fish. Juvenile salmon and steelhead trout comprised the majority of the catch. Also taken in large numbers were surf smelt, American shad, northern anchovy, and longfin smelt in brackish water and peamouth in fresh water. The incidental catch included cutthroat trout, Pacific herring, eulachon, threespine stickleback, carp, shiner perch, starry flounder, and largescale sucker.