The Effect of Coho Spawning on the Benthic Invertebrates of the Platte River, Benzie County, Michigan

Abstract

This study was undertaken to determine what effects a spawning run of coho salmon would have on the benthos of the Platte River, Benzie County, Michigan. It was hypothesized that the physical disruption of the substrate, by spawning salmon, would reduce the density of benthos by dislodging the organisms and causing their downstream displacement. Estimates of density of benthic invertebrates were made in two control sections (salmon excluded) and in one experimental section (salmon having free access) in May and August 1967 prior to coho spawning run, and in December 1967 and May 1968 after the run. Coho spawning activity in the fall of 1967 disturbed the bottom materials. The densities of 12 taxa, as well as the total number and total weight of organisms per square foot, decreased significantly in samples collected in December after disruption. The decrease in total nmnber of organisms per square foot in the experimental section as compared to the controls was 270.5; the decrease in weight in the experimental section was 1.97 grams. This is a percent decrease in the experimental section relative to the controls of 66% for total number and 78% for total weight. In May 1968, the nmnber of organisms per square foot was still significantly lower in the experimental section (57.4 per square foot), but weight of organisms per square foot was not. The percent decrease in the experimental section relative to the controls for total number was 39%. Three of twelve taxa, whose density was reduced in the fall of 1967, were still lower in May 1968. Complete recovery of benthos was not observed in the 5-month period from December to May.

Crying wolf, crying foul, or crying shame: alien salmonids and a biodiversity crisis in the southern cool-temperate galaxioid fishes?

“…Bryophyte communities growing on stream cobbles may indicate habitat stability where galaxiid may persist. Similar impacts of salmonid spawning have been described for North American streams-digging of redds may reduce or dislodge benthic invertebrate faunas, and disturb populations of small fish species, especially those living within substrate gravels (Hildebrand 1971;Krueger and May 1991) in similar manner as galaxiids do in New Zealand streams. There are potential impacts on both galaxiid fish and their food supplies.…”

Geomorphological implications of engineering bed sediments by lotic animals

“…For example, large-meshed cages would exclude big fish (Hildebrand, 1971), electricity could be used to exclude invertebrates and smaller fish (Bretschko and Klemens, 1986;Pringle and Blake, 1994), selective toxic products would reduce particular groups of organisms (e.g., insecticides; Wallace et al, 1993), artificial shading would inhibit growth of benthic algae and macrophytes, or by-hand manipulation of large organisms such as big mussels or macrophytes would affect their abundance. In my view, combining these means to manipulate the abundance of lotic animals and plants in real rivers with a simple approach to assess τ c for varying types of sediments should be the fastest way to identify promising subsequent research routes.…”

The effect of salmon redd excavation on stream substrate and benthic community of two salmon spawning streams in Canterbury, New Zealand

“…However, statistical comparisons between invertebrate abundance for the summer and spring samples of the two spawning streams (before and after spawning) showed no significant difference, hence one could assume that recolonisation is almost complete by September. Hildebrand (1971) found that benthic invertebrate abundance in the Platte River, reduced for the first time by spawning coho salmon, had not recovered to control levels after six months. He assumed recolonisation would be complete by summer, but the longer term impacts of salmon spawning on the benthos were not studied.…”

“…Hildebrand (1971) found that first spawning by salmon in a previously un- disturbed river, significantly reduced the benthic invertebrate biomass (78% reduction by weight) and recovery was not complete after 6 months.…”