Egg Pocket Research Articles

Egg burial depth by sockeye salmon (Oncorhynchus nerka): implications for survival of embryos and natural selection on female body size

We studied the relationship between female sockeye salmon (Oncorhynchus nerka) body size and egg burial depth in a small Alaskan stream to better understand the ways in which stream-bed scour or digging by other females might destroy embryos. Two different measurements of egg burial depth were taken: depth from the original stream-bed surface to the top of the egg pocket and depth from the disturbed substrate directly above the egg pocket to the top of the egg pocket. The former may represent the depth to which stream-bed scouring would have to go to reach the eggs, but the latter represents the depth to which a second female would have to dig to disturb the egg pocket. Larger females buried their eggs deeper, relative to the original substrate level, than smaller females. This suggests that streams with frequent scour events would select for larger females. However, mean depth from the disturbed substrate level was significantly shallower than mean depth from the original stream-bed level, suggesting that even the smallest females could dig deep enough to disturb the egg pockets of the largest females. Finally, the egg burial depth - fish size relationship that we observed was compared with published data on other salmonid species, revealing considerable variation but a clear positive relationship between female size and burial depth. Because embryonic survival is affected by scour and nest disturbance, and because changes in fish body size, density, and flow regime can affect the vulnerability of embryos to such mortality, we recommend further, standardized measurements of the relationship between egg burial depth and female body size.

Riverine salmonid egg burial depths: review of published data and implications for scour studies

Published data on salmon, trout, and charr egg burial depths are highly variable and inconsistent. Primary sources of variation include elevation datum and portion of the egg pocket referenced to; differences in spawning behavior and the number, thickness, and location of egg pockets; relationships between egg depth, fish species, and corresponding size of female and spawning substrate and velocity characteristics; sampling method; presence of excavation barriers; redd superimposition; and scour and fill by hydraulic and other mechanical processes. Such sources of variability in the reported data have important implications for studies of scouring processes in salmonid spawning areas that require accurate identification of egg burial depths for predicting and preventing potential scour impacts. Cumulative measurement error and unexplained variation may amount to 5-20 cm or more in published values. The most relevant data for scour impact assessments are depths from the original stream bed elevation down to the top of the main egg pocket. Frequency distribution data are needed for determining probabilities and cumulative levels of scour impacts and for managing genetic diversity as well as population size. Preliminary depth threshold criteria are proposed for use now, pending further research.

Persistence of egg pocket architecture in redds of chum salmon, Oncorhynchus keta

Analysis of frozen cores of gravel surrounding the egg pockets of chum salmon, Oncorhynchus keta, collected in the fall revealed that spawning activity by females purged about 75 % of the fine sediments from the stream bed. The egg pocket was one of four distinct vertical strata detected in the cores. There was an undisturbed layer below the egg pocket, and separate bridge and cover strata above the egg pocket, all defined by different particle size distributions. However, by spring most of the egg pockets had been infiltrated with fine sediment and the particle size distribution approached background levels. The most likely physical factors responsible for these results were: (1) intrusion of fine sediments through the cleaned surface gravel, (2) lateral subsurface migration of fine sediment into interstitial voids, (3) scour of the surface gravel and subsequent deposition of a sand rich bedload, and (4) superimposed spawning activity of other fish, causing disturbance of the cleaned surface gravel and exposing the egg pocket to intrusion of fine particles. We conclude that, while female salmon substantially affect the physical environment of their embryos, subsequent sediment transport processes and fine bedload flux tend to return this environment to pre-spawning conditions.

Stream-bed scour, egg burial depths, and the influence of salmonid spawning on bed surface mobility and embryo survival

Bed scour, egg pocket depths, and alteration of stream-bed surfaces by spawning chum salmon (Onchorhynchus keta) were measured in two Pacific Northwest gravel-bedded streams. Close correspondence between egg burial depths and scour depths during the incubation period suggests an adaptation to typical depths of bed scour and indicates that even minor increases in the depth of scour could significantly reduce embryo survival. Where egg burial depths are known, expressing scour depth in terms of bed-load transport rate provides a means for predicting embryo mortality resulting from changes in watershed processes that alter shear stress or sediment supply. Stream-bed alteration caused by mass spawning also may influence embryo survival. Theoretical calculations indicate that spawning-related bed surface coarsening, sorting, and form drag reduce grain mobility and lessen the probability of stream-bed scour and excavation of buried salmon embryos. This potential feedback between salmon spawning and bed mobility implies that it could become increasingly difficult to reverse declines in mass-spawning populations because decreased spawning activity would increase the potential for bed scour, favoring higher embryo mortality. Further analysis of this effect is warranted, however, as the degree to which spawning-related bed loosening counteracts reduced grain mobility caused by surface coarsening, sorting, and redd form drag remains uncertain.

Spatial and temporal variation in dissolved oxygen in natural egg pockets of chum salmon, in Kennedy Creek, Washington

The effects of dissolved oxygen (DO) on incubating salmonid embryos have been studied extensively in the laboratory but there is little information on levels experienced by salmon embryos in complex natural channels. We monitored 33 natural egg pockets of chum salmon Oncorhynchus keta, from shortly after spawning until emergence, and found that DO levels varied considerably among and within egg pockets over time. Egg pocket DO levels varied from 2–10 mg l−1 at the time of spawning and generally declined during incubation but the declines did not occur in all pockets and were not always steady. Much of the variability may be attributed to local channel topography. Pool tailouts had the highest and least variable DO levels whereas levels in lateral bars were generally lower and more variable. Levels in glides and riffles tended to be intermediate between those in pool tailouts and lateral bars. In spite of the variation in DO levels and habitats used by chum salmon, DO levels were not correlated with egg pocket sediment composition (per cent of the sample<1.0 or 4.0 mm diameter) or with the egg pocket's depth.

Spatial and temporal variation in dissolved oxygen in natural egg pockets of chum salmon, in Kennedy Creek, Washington

The effects of dissolved oxygen (DO) on incubating salmonid embryos have been studied extensively in the laboratory but there is little information on levels experienced by salmon embryos in complex natural channels. We monitored 33 natural egg pockets of chum salmon Oncorhynchus keta, from shortly after spawning until emergence, and found that DO levels varied considerably among and within egg pockets over time. Egg pocket DO levels varied from 2–10 mg l−1 at the time of spawning and generally declined during incubation but the declines did not occur in all pockets and were not always steady. Much of the variability may be attributed to local channel topography. Pool tailouts had the highest and least variable DO levels whereas levels in lateral bars were generally lower and more variable. Levels in glides and riffles tended to be intermediate between those in pool tailouts and lateral bars. In spite of the variation in DO levels and habitats used by chum salmon, DO levels were not correlated with egg pocket sediment composition (per cent of the sample<1.0 or 4.0 mm diameter) or with the egg pocket's depth.

Inter- and intra-specific variability in female salmonid spawning behaviour

Egg pocket characteristics determined from the excavation of 29 stranded redds made by Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) in the River Vosso in western Norway are presented. The egg pockets of Atlantic salmon were, on average, deeper (27.0 vs. 14.8 cm) and contained more eggs (707 vs. 148) than those of brown trout. An adaptive "test-digging" behaviour was indicated by the finding of a significant association between false redds and gravel classified as low-quality spawning substrate. Based on fecundity data and number of eggs per redd, it was estimated that individual Atlantic salmon and brown trout deposited their eggs in 8.4 and 5.7 different redds, respectively. A 100-year data series indicates that the high proportion of stranded salmon redds (23%) can be attributed to the high frequency (27% of the years) and random occurrence of low water discharge rates. Estimated probabilities of extinction and associated variances in fitness assigned different spawning behaviours suggest that the temporal and spatial variation in offspring survival produces a selective advantage for the multiple-redd tactics over the single-redd tactic. Moreover, in contrast to iteroparous salmonids, semelparous Oncorhynchus species invariably place all their offspring in one redd. This dichotomy can most likely be ascribed to the provision of parental care (i.e., redd guarding) by semelparous salmonids.

Attributes of Yellowstone Cutthroat Trout Redds in a Tributary of the Snake River, Idaho

We characterized spawning sites of Yellowstone cutthroat trout Oncorhynchus clarki bouvieri, described the microhabitat of completed redds, and tested the influence of habitat conditions on the morphology of completed redds in Pine Creek, Idaho. Cutthroat trout spawned in June as flows subsided after peak stream discharge. During spawning, minimum and maximum water temperatures ranged 4–9°C and 16–20°C, respectively. Trout spawned where water depths averaged 20 cm beside redds and 22 cm upstream of redds. Water velocities averaged 42 cm/s beside redds and 46 cm/s upstream of redds. More than 80% of the redds were constructed in water 10–30 cm deep with velocities of 25–60 cm/s. Trout spawned in gravel with particles up to 100 mm in diameter. Most of the substrate was smaller than 32 mm; an average of 20% was less than 6.35 mm and 5% was less than 0.85 mm. The geometric mean particle size of the spawning gravel averaged 16.6 mm and the fredle index averaged 8. Microhabitat conditions differed within completed redds. Water depth decreased and velocity increased from the redd pit downstream to the leading edge of the tailspill and to the tailspill crest. The redd shape may facilitate movement of water through the egg pocket. Redds averaged 1.58 m long by 0.60 m wide, and the pit covered an average of 46% of the redd area. Water depths and velocities in redds were correlated with water depths and velocities adjacent to redds. Redd dimensions were typically not correlated with water depths, velocities, or particle size distributions, suggesting that other factors such as the size of spawning fish may influence redd dimensions.

Brook trout (Salvelinus fontinalis) embryo habitat and timing of alevin emergence in a lake and a stream

We assessed redd characteristics of brook trout in a lake and a stream and alevin emergence in the lake. Both populations spawned over upwelling groundwater. In the lake site fish deposited eggs 7–19 cm in the sediment in an egg pocket that contained large-particle substrate. A similar vertical distribution of eggs (16–20 cm) and substrate occurred in the stream; however, in addition to the digging action of the female, the flow conditions in the stream appeared to produce coarser surface sediment conditions. Groundwater offered a high concentration of dissolved oxygen and, relative to lake water, less variable temperature and pH regimes for incubating eggs. Alevin emergence extended over a 71-day period, coinciding with the spring thaw and an episodic pH depression.

Description of Brown Trout Redds in a Mountain Stream

We sampled redds of brown trout Salmo trutta in a mountain stream to describe egg location and substrate composition after spawning and during egg incubation. A single-probe freeze-coring device was used to sample egg depth and substrate composition. We found eggs throughout redds but most often in the front half of the tailspill (the substrate mound that accumulates as the redd is excavated progressively upstream). Eggs were buried between 2 and 23 cm below the substrate surface but were most frequently 9–12 cm deep. Spawning fish cleaned substrate particles less than 6.3 mm in diameter from egg pockets, yet the percentage of particles smaller than 1.7 mm in egg pockets was correlated with that outside redds. Egg pockets contained particles larger than 50 mm more often than did any other location, indicating that particles of this size were used as egg pocket centrums. The percentage of 1.7-mm and smaller particles in egg pockets was higher in winter than in fall. We conclude that (1) spawning brown trout 20–40 cm in total length substantially alter the substrate in egg pockets; (2) the amount of fine sediment in egg pockets is positively correlated with that in the adjacent streambed; and (3) fines accumulate in egg pockets during the incubation period.

Oviposition behavior ofNeodiprion fulviceps (Cresson) (Hymenoptera: Diprionidae) on ponderosa pine

Basic information on oviposition behavior of Neodiprion fulvicepsis presented. We present evidence which suggests that adults possess circadian rhythms for emergence and female oviposition activity. A behavioral catalog was developed and it was found that females, while inactive, spend 54% of their time oriented basally on needles and, while active, 18% of their time walking up and down needles. A description of the oviposition sequence and time spent in each step is presented. It was determined that females spend a significantly longer time cutting the first egg pocket than successive egg pockets. We also present evidence of an oviposition deterrent factor.

Substrate Alteration by Spawning Brook Trout in a Southeastern Wyoming Stream

To measure the changes in substrate composition produced by spawning brook trout Salvelinus fontinalis, we collected 187 freeze-core samples, both before and after spawning, from egg pockets, inside redds but excluding egg pockets, and outside redds. In the upper strata of reddassociated samples, we found that the proportions of particles 0.85–1.70, 0.425–0.85, 0.212–0.425, and less than 0.212 mm in diameter were significantly lower in egg pockets than outside redds, and the proportions of particles 0.425–0.85, 0.212–0.425, and less than 0.212 mm in diameter were also lower in egg pockets than in other areas inside redds. Samples collected outside redds were similar to samples collected before spawning. We observed no significant correlations between the proportion of fine sediment in samples from outside redds (and presumably the proportion present before spawning) and the proportion of fine sediment in egg pockets. In vertically stratified samples, the lower strata contained a greater proportion of the smaller substrate particles than the upper strata. Spawning brook trout removed fine sediment from the substrate during redd construction, and this removal was most apparent in the egg pocket. Thus, egg pockets, rather than entire redds, should be the focus of studies of survival to emergence.

Critical Review of Variables Used to Define Effects of Fines in Redds of Large Salmonids

Abstract Laboratory studies have not duplicated the structure and composition of egg pocket centrums in redds of large salmonids, and thus have not accurately modeled survival of embryos and alevins in natural egg pockets. Field studies of capped natural redds have related survival to conditions in the redds or surrounding areas but not demonstrably in egg pockets. These data probably do not accurately reflect conditions faced by embryos or emerging alevins. The few data on egg pocket characteristics indicate that geometric mean particle diameter, fredle index, and permeability are higher in gravel surrounding the embryos than elsewhere, Survival to alevin emergence usually regresses positively on each of these factors separately and on dissolved oxygen in intragravel water. Survival to emergence usually relates negatively to percentages of small fines. Quantitative predictors depend upon careful definition of egg pocket structure through field surveying of egg pocket centrum locations and on intensive st...

Stranded redds of quinnat salmon in the Mathias River, South Island, New Zealand

Abstract In May and June 1974 seven naturally made, stranded redds of quinnat salmon Oncorhynchus tshawytsha (Walbaum) were excavated. Ova numbers per redd varied from 2295 to 6510 and per egg pocket from 99 to 1608. Egg pocket depths varied from 18 cm to 43 cm. The ova were found to be healthy.

ROW-TYPE OVIPOSITION IN NEODIPRION SAWFLIES AS EXEMPLIFIED BY THE EUROPEAN PINE SAWFLY, N. SERTIFER (GEOFF.)

Many Neodiprion sawflies lay their eggs in a row in small pockets cut into the edges of the mature needles of various pines. These rows of eggs are remarkable for the regularity of the spacing between successive egg pockets. The regularity of egg spacing by N. sertifer is shown to arise from a stereotyped pattern of leg movements during the shift between the sites of successive egg pockets. Spacing is effected by two sets of leg movements, in each of which the three pairs of legs move forward in order from back to front. While the effective forward movement of all legs is the same, the total forward movement of the metathoracic legs is greater than that of the other legs by an amount equal to the length of an egg pocket. The metathoracic legs retrace their steps by this length as the initial incision for each new egg pocket is cut, evidently providing the force by which this incision is made. The grip-points of the legs are on the needle edge opposite to that receiving eggs, so that the wider the needle, the greater the proportion of leg length required to reach across it, and the smaller the proportion of leg movement reflected in the spacing between eggs. In this way egg spacing varies inversely with needle width. Observations on copulation, antennal movement, and related oviposition behavior are included.