Nymph Survey Through the Seasons

[afishinado]

Dave,

I find this survey as well as as future ones very interesting.

Thanks for your efforts.

I am interested to see the size of most macros, mayflies in particular, grow to bigger specimens in the spring when they are near their hatching stage. And in summer pretty much not be present in the egg stage or be very tiny.

Looking forward to the next survey in the spring.

 

[dc410]

Nice job, Dave. Very interesting, but obviously somewhat predictable results. Nice photos as well. This will be fun to watch as the seasons roll on.

 

[nomad_archer]

Wow that is really interesting. For me I am still learning to identify the macro categories so this is really, really, really valuable. Also makes me think that I may want to add a few more mayfly nymph patterns to the box if I hit the breeches next week.

It is amazing how big the stoneflies are relative to everything else.

 

[troutbert]

The scuds in the "middle" stretches of the Breeches is interesting and kind of surprising. In a good way.

 

[Dave_W]

troutbert wrote:
The scuds in the "middle" stretches of the Breeches is interesting and kind of surprising. In a good way.

Indeed.
Moreover, the numbers of scuds in Breeches this month (April) is even higher and I think they're a bit larger too. I was really surprised how many turned up today.

 

[Dave_W]

I have completed re-surveying these spots this month (April).

Of note: all three streams showed dramatic increases in macro biomass since January - considerably more so than I expected. There were a few surprises too.

I'll get the numbers and photos together shortly and we can compare them with the last survey.

 

[Troy]

Very interesting stuff! Thanks!

 

[Dave_W]

Here are the bug counts for April:
CONOCOCHEAGUE:
Mayflies:18
Caddis: 14
Stoneflies: 2
Scuds and Cress Bugs: 0
Aquatic Worms: 1
Two midge larvae

YELLOW BREECHES:
Mayflies:78
Caddis:1
Stoneflies: 0
Scuds:44
Cress Bugs: 1
One crayfish

LETORT:
Mayflies: 13
Caddis: 5
Stoneflies: 0
Scuds: 27
Cress Bugs: 210
Other: 0

 

[Dave_W]

looking at Breeches, note that mayflies in the same riffle went from 48 (in January) to 78 (April) and scuds went from 6 to 44! Only caddis dropped from winter to springtime, from 6 down to 1.

On Conococheague, note that mayflies more than doubled, 18 (Apr)up from 7 (Jan). Caddis, stoneflies and worms stayed about the same.

For Letort, Mayflies rose from 2 (Jan) to 13 (Apr). Scuds were a bit higher in April, but cress bugs, interestingly, jumped from 134 (Jan) up to an astonishing 210 (Apr). There were also 5 caddis nymphs in April whereas there had been none in January. Letort isn't known for caddisflies, but clearly they are there. No stoneflies in Letort (so far).

With respect to size - while I did not take measurements - a cursory glance suggested to me that mayflies were indeed larger as were scuds and cress bugs. Stoneflies and caddis, on the other hand, seemed to be about the same. In Breeches in particular, mayflies were bigger on average and it seemed that there were more March Browns and they were the biggest in this stream. The MB nymphs in YB did not have noticeably dark wingcases.

On Letort, the mayfly nymphs were slightly larger, and were very dark (overall, not just wingcases).

Stoneflies showed little change but the biggest surprise was that a large Pteronarcys stonefly nymph turned up again in Conococheague. Since this is a rare bug (at least in my surveys) and this was the exact same spot in the same riffle, I assumed that perhaps I'd caught the same bug as I'd caught in January. The size and color were the same. However, I decided to conduct a couple more seine kicks in the same riffle and, lo and behold, I got another smaller Pteronarcys along with several Perlid golden stones that I didn't get in the counted survey. I think it is safe to say that Pteronarcys salmonflies are prevalent in that riffle.

 

[Dave_W]

Here are pics of some of the bugs for April.

Note the generally dark color of the mayflies in Letort. Also note the prevalent and fairly large March Browns in Breeches.

 

[Dave_W]

Having re-visited the three riffles last month (July) that were surveyed in April, the results across the three streams showed noticeably fewer macros. While I expected to find fewer and smaller nymphs in summer, this drop was more pronounced than I had predicted.
Here are the results for July:

CONOCOCHEAGUE:
Mayflies:4
Caddis: 3
Stoneflies: 0
Scuds and Cress Bugs: 0
Crayfish: 1

YELLOW BREECHES:
Mayflies:38
Caddis:1
Stoneflies: 0
Scuds:48
Cress Bugs:0

LETORT:
Mayflies: 1 (very small)
Caddis: 0
Stoneflies: 0
Scuds: 6
Cress Bugs: 26
Other: 3 Crayfish, 1 Worm

 

[Dave_W]

In particular, note the steep drop off of mayflies at all locations.

While one would expect to see fewer nymphs due to hatching in the previous weeks, this suggests that opportunistic trout may be more likely to be focused on other forage species.

Breeches, for example, dropped from 78 mayfly nymphs in April down to 38 in July. On Conococheague, mayflies dropped from 18 in April down to 4 in July. Letort mayflies dropped from 13 down to just 1 very small nymph.

In addition to such drops in numbers, the mayflies were notably smaller at all stations.

Cress bugs were much fewer at Letort, however I should note that seining Letort was hard this summer. Unlike Breeches and Conococheague, which had lower water levels this month, Letort was choked with weeds in the survey riffle and water levels were actually much higher and slower than in the spring and this may have impacted the number of macros captured.

A brief side observation is that crayfish increased since springtime.

 

[Dave_W]

Will return to these spots in October and check again.

After the final survey in October, I'll re-capitulate the results and write up a conclusion. This may be posted in article format on the home page.
DW

 

[Dave_W]

The survey is complete. I made a small adjustment and did the autumn survey early in November rather than October. The results for November are:

BREECHES:
Mayflies: 29
Caddis: 6
Stoneflies: 0
Scuds: 43
Cress Bugs: 1
Other: 1 crayfish and 2 worms

CONOCOCHEAGUE:
Mayflies: 9
Caddis: 19
Stoneflies, Scuds, Cress Bugs: 0
Other: 1 worm

LETORT:
Mayflies: 5
Caddis/ Stoneflies: 0
Scuds: 50
Cress Bugs: 109
Other: 1 crayfish, 4 "blood worm" midges, 3 worms

 

[Dave_W]

Once again, the results verify the observation that nymphs in these streams are, generally, quite small. Most of them were under a quarter of an inch in total body length this month, and many were much smaller. I placed a few in the viewing trays to be photographed and these were often among the larger specimens that I was able to get a hold of. The upper image shows some macros from Breeches in November and the lower image is from Letort for comparison....

 

[afishinado]

Great info, Dave. Thanks for sharing.

I would guess that most of us have way too many mayflies initiations in our fly boxes and ones that are a lot larger than the actual insects inhabiting the stream.

Lesson learned.

 

[Fredrick]

Great post Dave I have to make sure I follow this one for now on.

 

[albatross]

Thanks Dave, very illuminating.

 

[redietz]

I'm wondering how much bias (of the distribution of types) is built into the results by sampling in riffles rather than pools. I would expect that species that feed on rotting leaves to be under represented, for example. Also, how many caddis get missed because they're firmly attached to rocks? (It would have been interesting to divide caddis into cased vs free living.)

I'm not saying the data you have isn't valuable, just wondering what your thoughts are about biases?

At any rate, thanks for taking the time to do this.

 

[afishinado]

Results posted in the PAFF blog.

And Tweeted to the PFBC site here.