Largemouth bass consumption demand on hatchery rainbow trout in two Washington lakes

Figures & data

Figure 1 Map depicting the bathymetry (in meters), macrophyte distribution (shaded), sampling transects (numbered), and location of North and South Twin Lakes, Washington. North Twin Lake transects were utilized for largemouth bass population analysis in 2004 and all transects in both lakes were utilized in the 2005 diet analysis. Arrows represent approximate location of hatchery rainbow trout release sites.

Table 1 Hatchery-raised rainbow trout (Oncorhynchus mykiss) stocking rates and size ranges in North and South Twin Lakes for 2005.

		Numbers		Size range
Season	Months	North Twin	South Twin	(mm)
Spring	Apr–Jun	24,043	17,026	215–370
Summer	Jul	13,786	4,450	215–370
Fall	Sept–Oct	81,046	77,449	100–160
Total		122,115	98,925

Table 2 Energy density estimates taken from the literature of fish and invertebrates common to the Twin Lakes.

		Energy density
Taxon		(J/g)
Largemouth bass	Micropterus salmoides	5784 ^a
Golden shiner	Notemigonus crysoleucas	5078 ^a
Rainbow trout	Oncorhynchus mykiss	6069 ^b
Mayfly	Ephemeroptera	4705 ^c
Scud	Amphipoda	4428 ^c
Odonate	Odonata	2775 ^c
Midge	Diptera	2566 ^c
Crayfish	Decapoda	4508 ^c

Table 3 Schnabel multiple-census population data for North Twin Lake, 2004. Numbers are largemouth bass recaptured (marked), unmarked (captured), and marked (at-large) during each sampling period.

Period	Recaptured	Unmarked	Total	Marked
1	0	193	193	0
2	2	104	106	193
3	2	144	146	297
4	4	72	76	441

Table 4 Population estimates (N) and confidence intervals (CI) for largemouth bass feeding groups (FG) sampled from North and South Twin Lakes, 2005. Percentages are proportions of the total population for each feeding group.

FG (mm)	%	N	95% CI
North Twin Lake
100–199	22	2,677	1428–5353
200–299	70	8,517	4542–17,034
⩾300	8	973	519–1947
South Twin Lake
100–199	64	14,795	7891–29,590
200–299	31	7166	3822–14,333
⩾300	5	1156	616–2312

Table 5 Mean length (mm), range (in parenthesis), and sample size (n) of prey consumed by largemouth bass by feeding groups (FG) in North (NT) and South Twin (ST) lakes, 2005. Age estimates are for largemouth bass.

		Invertebrates		Crayfish		Golden shiner		Rainbow trout
FG (mm)	Age (yr)	NT	ST	NT	ST	NT	ST	NT	ST
<100	0	3	3.8	0	0	0	0	0	0
		(1.8–7)	(1.5–6)
		n = 5	n = 2
100–199	1–2	9	8	0	44	28	16.8	0	0
		(3–23.3)	(2–20.2)		(18–70)	(10–80)	(8–25)
		n = 65	n = 87		n = 2	n = 23	n = 8
200–299	2–4	10.4	10.6	49	51.4	35	43.9	0	0
		(3.8–24.3)	(4–24.5)	(11–120)	(9–120)	(19–65)	(16–100)
		n = 80	n = 70	n = 5	n = 26	n = 15	n = 7
⩾300	⩾4	13.2	12.9	95	88.3	133	120.4	0	168
		(8–21)	(8–21.3)	(90–100)	(50–120)	(100–190)	(28–180)		(130 –210)
		n = 6	n = 3	n = 2	n = 6	n = 8	n = 9		n = 5

Figure 2 Relationship between prey lengths versus largemouth bass size classes in North Twin Lake (left) and South Twin Lake (right), 2005.

Figure 3 Daily consumption of crayfish, golden shiner, rainbow trout, and invertebrates by largemouth bass feeding groups (100–199, 200–299, ⩾ 300 mm) in North Twin Lake (left) and South Twin Lake (right) during 2005 as estimated by a bioenergetics model.

Figure 4 Total consumption in metric tonnes (± 95% confidence interval) from June 1 to October 18 of golden shiner, rainbow trout, crayfish, and invertebrates by largemouth bass feeding groups (100–199, 200–299, ⩾300 mm) in North and South Twin Lakes during 2005 as estimated by a bioenergetics model.

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