Fraser River Studies
Leon Creek
Stream Ecology Lab
(Biology 285)

Introduction

Draining from the Camelsfoot Range, Leon Creek is a first order stream, tributary of the Fraser River. This stream, and ones like it are important to the overall health of the Fraser in that clear tributaries like Leon Creek add cool, oxygen rich water to the silted Fraser. Salmon use some of these streams for spawning and also to clean their gills of silt as they swim pass to their age old spawning grounds. A good indicator of a streams health is the amount of aquatic invertebrates it supports. On July 8, 1997 in the afternoon, we searched for and then classified any aquatic invertebrates we could find.

Procedure

Using a dip net or Surber sampler, we disturbed a stream section just above stream from our nets. We disturbed 1-4cm, 4-8 cm and a few 20-30 cm diameter rocks, collecting debris washed away by the stream in the nets. We did two dips, the first immediately downstream from the disturbed 1-4 cm diameter rocks. The 2nd, immediately down stream from the larger diameter rocks. We then transferred the contents of the first dip into a tub and began our search for aquatic invertebrates. We then transferred the second dip into a tub and carried on our search.

Visible, mobile life forms were then transferred to a petris dish to be viewed with a tripod magnifier. Using a dichotomous key, we then proceeded to identify the aquatic invertebrates we located.

Results

We located and identified the following aquatic invertebrates:

1) Megaloptera (hellgrammites, alderfly and fishfly larvae)
- These were the most prolific of all invertebrates found, most of which came from the first dip (smaller rocks), roughly 20 or 30 individuals.

2) Plecoptera (stonefly larvae)
- One was found in the 2nd dip specimen tub (from the larger disturbed rocks). This larvae was observed preying on the stony cased cadisfly fly larvae.

3) Ephemeroptera (nymphs of mayflies)
- One was found in the 2nd dip specimen tub (from the larger disturbed rocks).

4) Trichoptera (cadisfly larvae)
-Two observed without stony case, one with. The two without seemed to be harassing the one with. This larvae was also observed to be preyed upon by the stonefly larvae. All and all, the stony cased cadisfly fly larvae had a really bad last day.

Five nematodes were also found. One of which also fell prey to the stonefly larvae.

Discussion

The heavy canopy over Leon Creek, blocks out direct sun light, creating an environment not conducive to primary producer growth. This being the case, it is not surprising that the aquatic invertebrates found are detritavores. Dead organic matter (detritus) falling into the stream, is broken down and consumed by the detritavores, who form the base of the food chain in this stream. They in turn become the sustenance for carnivorous insects and fish.

Leon Creek contains coarse particulate organic matter (>1mm) and fine particulate organic matter(<=1mm). The caddisfly larvae and stonefly larvae are examples of shredders that feed on the coarse particulate organic matter. The caddisfly larvae are also considered filter feeders, and feed on the fine particulate organic matter. The stone fly larvae was also displaying it’s omnivorous side when we observed it prey on the caddisfly larvae and the nematode.

These aquatic invertebrates are valuable components to the health of Leon Creek. They break down debris that could accumulate in back eddies or slower moving water, areas possibly used for spawning. As already pointed out, they also form the base of the food chain here, feeding other components of this system. A system that has been in play for thousands of years and has evolved to this state.

Since we do not have the criteria to determine what a healthy stream with similar physical characteristics to that of Leon Creek are, we can not conclude that Leon Creek is in fact a healthy stream. I do believe however, that since Leon Creek offered us a varied selection of aquatic invertebrates, that we can assume it not unhealthy.