The importance of measuring biotic and abiotic factors in the lower egg pocket to predict coho salmon egg survival

Abstract

Based on results from simulated redds of coho salmon Oncorhynchus kisutch, the amount of fine sediment <0·5 mm in the lower half of the egg pocket, rather than the entire egg pocket of the redd, was a strong predictor of egg survival to hatching ( r2 = 0·62). The relationship was much stronger than observed in other studies, which typically ignore egg pocket structure. Abundance of a fish egg‐eating worm, Haplotaxis ichthyophagous, an oligochaete that may have been attracted to fine sediment and dead eggs in the egg pocket, was also associated with a decrease in egg survival. The worm, however, accounted for little of the variance in survival compared to fine sediment. Only 10% fine sediment (<0·5 mm) in the lower pocket was required to decrease survival from 100 to 5%. Other abiotic factors had weaker (gravel permeability) or non‐existent (dissolved oxygen) correlations with survival.

An experimental assessment of the effectiveness of gravel cleaning operations in improving hyporheic water quality in potential salmonid spawning areas

“…How spates might influence grain size composition of the stream bed could be observed at the study site Buelgenauel, where the amount of fine sediments was significantly decreased after high discharge events in February and March 2002. This process is necessary for the oxygenation of the interstitial pore water below the stream bed surface, which could be crucial for a successful development of salmonid eggs and larvae (Ingendahl, 2001;Meyer, 2003;Youngson et al, 2005). In contrast, the lack of discharge dynamics in gravel streams results in an increasing accumulation of fine sediments, which can lead to clogging effects preventing perfusion of oxygen-rich water through the deeper sediment layers (Blaschke et al, 2003;Meyer, 2003), a situation typical for regulated streams (Sear, 1993).…”

“…This process is necessary for the oxygenation of the interstitial pore water below the stream bed surface, which could be crucial for a successful development of salmonid eggs and larvae (Ingendahl, 2001;Meyer, 2003;Youngson et al, 2005). In contrast, the lack of discharge dynamics in gravel streams results in an increasing accumulation of fine sediments, which can lead to clogging effects preventing perfusion of oxygen-rich water through the deeper sediment layers (Blaschke et al, 2003;Meyer, 2003), a situation typical for regulated streams (Sear, 1993). It is reported from field and laboratory studies that already low amounts of (infiltrated) fines might negatively affect embryo survival (Phillips, 1971;Greig et al, 2005;Levasseur et al, 2006).…”

“…Infiltration of fine grains (<2 mm) can reduce the exchange of oxygen-rich surface water with oxygen-deficient water within the gravel bed, which is more pronounced with increasing depth (Wu, 2000;Meyer, 2003). Additionally, microbial oxygen consumption occurs if the fines contain a certain, even low amount of particulate organic matter (POM) stimulating microbial activity (Soulsby et al, 2001a).…”

“…Many studies conducted in recent years have therefore focused on the environmental conditions in the hyporheic zone of gravel streams concluding that clogging of the interstices by intrusion of fine grains, as well as low oxygen levels are the most important factors affecting embryo survival (e.g. Phillips, 1971;Argent and Flebbe, 1999;Soulsby et al, 2001b;Armstrong et al, 2003;Meyer, 2003;Hanrahan et al, 2005;Youngson et al, 2005;Julien and Bergeron, 2006;Levasseur et al, 2006).…”

Influence of Cougar Reservoir Drawdown on Sediment and DDT Transport and Deposition in the McKenzie River Basin, Oregon, Water Years 2002-04

“…Fine sediment can clog pore spaces in the streambed, decreasing subsurface flow (Brunke and Gonser, 1997) and potentially decreasing the dissolved-oxygen (DO) concentration in the pore water. Such a decrease in pore-water DO concentration could negatively affect developing eggs of salmonids (Meyer, 2003), such as those present in the McKenzie River basin, including several threatened or endangered species. Additionally, the potential that deposited fine sediment could be contaminated with residual DDT or its metabolites from historical spraying practices caused additional concern for toxicity to salmonid larvae as they developed within the spawning gravels.…”