Subject: Re:[NatureList] Unionids of the Jock River @ the Dwyer Hill Rd
Everyone,
On the way back from Mississippi Lake, I stopped at the Jock River to see how things had changed since Eric Snyder and I found drought-exposed Unionid shells here on 28 July... skip to contents
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Field notes of Frederick W. Schueler --- 4 October 2001
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Canada: Ontario: Ottawa-Carleton Region: Goulbourn: Jock R/Dwyer Hill Rd. 31G/4, UTM 18TVF20 233 0.5 45.15180N 75.97535W. TIME: 1845-1903. AIR TEMP: 17 ca, clear, sunset, windy. HABITAT: dry riffle of rocky muddy slow creek in ungrazed pasture, no flow. 2001/196/d, Unionidae (Unionid Mussel) (Mollusca). 170 shells, prey of predator, specimens. stopped to see if stream was flowing & fd many new shells. ...still no flow though water higher than it was at lowest - several big (40 cm) fish along the shore of the under-bridge pool, and many Rana tadpoles among pebbles and sparse weeds at its shallow upstream edge. Gathered almost all of the freshly opened shells between the pools on the surface of the gravelly riffle - about 10 m of riffle. An astonishing number of un-munched clams, most with fairly wide periostracum fringes beyond the calcified shell - a few shells with single puncture holes, appropriate for a Raccoon canine, in each valve as if found by Procyon by smell after the Unionids died in the substrate. Gathered a full 7 litre popcorn bag - a late drought mortality sample. (These specimens now deposited in the New Brunswick Museum - 26 October 2001).
In comparison with the sample of 120 shells found here on 28 July, Elliptio (56, 62), Lampsilis radiata (5, 10), Pyganodon (11, 12), and Lasmigona costata (9, 10) haven't changed in abundance (p=0.05 2 x 2 G tests of each species vs the rest of the sample), while Anodontoides ferrusacianus (16, 0, G=23) seems to have decreased, and Lasmigona costata (2, 13, G=5.9), and Strophitus undulatus (21, 63, G=13) seem to have increased - but it's not clear what this means. Does decreased abundance mean that only those individuals that were on the surface when the water receeded were vulnerable to predation, and others are successfully estivating through the drought, or that they were wiped out early so that there were none available to predators during August and September? And have the species that increased been more resistant to drought, only dying or falling to predation at the last extremity, or were they, once surface-living individuals were picked off, the more vulnerable. I suppose the question could only be answered now by digging up the whole riffle to see which species, if any survive, or by a cm-by-cm survey of the riffle once the water returns to find and identify living individuals.
It's too bad we didn't get a sample here during the 1999 drought, because I'm sure that the age structure and species composition of the sub-populations in this riffle will be strongly influenced for years by this mortality, and it's possible that the large number of young indiduals suggests that bigger ones died in 1999.
(same location) TIME: 1845-1903. 2001/196/da, Elliptio complanata (Eastern Elliptio) (Mollusca). 62 shell, prey of predator, specimen. 53 fresh, 9 not-fresh, largest 115 mm. Fresh pairs: 78, 83.5, 69, 78.5, 67.5, 65, 62.5, 75.5, 82, 79, 75.5, 78.5, 83.5, 71.5, 68, 73.5, 71.5, 50, 76.5, 74, 79, 72.5, 77, 66, 76, 65.5, 76.5, 68, 79.5, 75.5, 79, 70.5, 65.5, 69.5, 66, 57, 56, 47.5, 65.5, 60.5, 67, 58, 61, 86, 84, 87, 72.5, 71, 78, 72, 55 mm.
fresh valves: 82, 67 mm.
fresh: n=53 mean=71.25 (47.50 - 87.00) st.dev.=8.95
not-fresh pairs: 71, 84, 77, 72, 79.5, 115, 72, 73, the big one is very thick-shelled and anteriorly inflated.
not-fresh valves: 70 mm
not-fresh: n=9 mean=79.28 (70.00 - 115.00) st.dev.=13.35
(same location) TIME: 1845-1903. 2001/196/db, Pyganodon grandis (Common Floater) (Mollusca). 12 shell, prey of predator, specimen. 11 fresh, 1 not-fresh, largest 100.5 mm. Fresh pairs: 63, 65, 71.5, 68.5, 65, 62, 67, 59.5 mm.
fresh valves: 63.5, 60 ca, 66 ca mm.
fresh: n=11 mean=64.64 (59.50 - 71.50) st.dev.=3.42
old valve: 100.5
(same location) TIME: 1845-1903. 2001/196/dc, Lampsilis radiata (Eastern Lamp-Mussel) (Mollusca). 10 shell, prey of predator, specimen. fresh, largest 97 mm. No clear sexual dimorphism - nacres white - larger shells unrayed.
male-like fresh pairs: 97, 70.5, 63, 79.5, 95 mm. n=5 mean=81.00 (63.00 - 97.00) st.dev.=13.33
female-like fresh pairs: 86.5, 82.5, 88, 89, 85.5 mm. n=5 mean=86.30 (82.50 - 89.00) st.dev.=2.25
pooled - n=10 mean=83.65 (63.00 - 97.00) st.dev.=9.92
(same location) TIME: 1845-1903. 2001/196/dd, Lasmigona costata (Fluted Shell) (Mollusca). 13 shell, prey of predator, specimen. fresh, largest 98.5 mm. Fresh pairs: 98.5, 86.5, 84.5, 82, 74, 69.5, 57, 58.5, 59, 49, 65, 58, 70 ca mm. n=13 mean=70.12 (49.00 - 98.50) st.dev.=13.83
(same location) TIME: 1845-1903. 2001/196/de, Lasmigona compressa (Brook Lasmigona) (Mollusca). 10 shell, prey of predator, specimen. fresh, 8 pairs, 2 valves, largest 76.5 mm. Fresh pairs: 76.5, 63, 63, 59.5, 62.5, 55, 45, 45 mm.
fresh valves: 59, 64 mm.
fresh: n=10 mean=59.25 (45.00 - 76.50) st.dev.=8.85
(same location) TIME: 1845-1903. 2001/196/df, Strophitus undulatus (Squaw-Foot) (Mollusca). 63 shell, prey of predator, specimen. 52 fresh pairs, 11 fresh valves, 1 not-fresh pair, largest 80.5 m. Fresh pairs: 68, 61, 63.5, 53, 67, 77, 66.5, 75, 66.5, 80.5, 68, 64.5, 62, 62, 58, 56.5, 53, 70, 70.5, 56.5, 52, 76.5, 63, 70, 58.5, 60, 56, 61, 64, 67, 70.5, 64, 54, 46, 52, 68.5, 64, 57, 56.5, 52, 45, 60.5, 50.5, 52.5, 52, 60, 49, 61.5, 56, 73.5, 70.5 mm.
fresh valves: 70, 70.5, 65, 61, 65.5, 61.5, 61.5, 62, 60.5, 59.5, 61.5 mm.
fresh: n=62 mean=61.95 (45.00 - 80.50) st.dev.=7.63
not-fresh pair: 73 mm.
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