Brown trout growth in Minnesota streams as related to landscape and local factors

Figures & data

Figure 1. University of Minnesota researchers B. Vondracek (right) and W. E. French sampling brown trout in the Driftless Ecoregion of southeast Minnesota.

Table 1. Brown trout sampling information (UTM coordinates; elevation (m); number of age-1, age-2, and age-3 individuals) and growth metrics (mean back-calculated length-at-age-1 (MBLAA-1), age-2 (MBLAA-1), and age-3 (MBLAA-3)) in southeast Minnesota streams.

Stream	UTM	Elevation	Age-1	Age-2	Age-3	MBLAA-1	MBLAA-2	MBLAA-3
Beaver	577,026, 4,889,127	219.9	52	16	12	126.0 (2.4)^d	201.6 (3.2)^d	266.3 (2.8)
Forestville	561,631, 4,831,893	324.8	28	13	39	144.8 (3.8)^a^,^b	228.7 (3.7)^a^,^b^,^c	278.7 (4.3)
Gribben	587,631, 4,839,986	262.8	39	38	4	129.6 (2.6)^c^,^d	203.1 (3.8)^d	281 (14.1)
Hay	532,802, 4,925,099	259.0	30	18	4	140 (3.2)^a^,^b^,^c	215.6 (3.9)^c	279 (5.5)
MBW	572,079, 4,876,366	304.1	24	13	20	132.1 (4.3)^b^,^c^,^d	238.1 (5.2)^a^,^b	284.8 (7.7)
SBW	581,763, 4,880,221	235.9	38	18	26	149.3 (3.5)^a	239.5 (3.7)^a	289.6 (5.5)
Winnebago	625,126, 4,823,555	239.9	42	31	7	123.4 (3.5)^d	220.3 (6.3)^b^,^c	304.5 (7.6)

Note: Different letters (a, b, c, and d) denote significant differences (Tukey's Honestly Significant Difference test, p < 0.05) among streams within growth metric categories (e.g. MBLAA-1, MBLAA-2). MBW = Middle Branch Whitewater, SBW = South Branch Whitewater.

Table 2. Landscape and local factors in southeast Minnesota streams.

Stream	Area	TS	% forested	% grassland	% cultivated	RA
Beaver	29.1	0.44	10	85	5	90
Forestville	41.9	0.21	55	43	2	49
Gribben	20.4	0.25	45	45	10	151
Hay	54.6	0.39	15	35	50	80
Middle Branch Whitewater	78.2	0.52	15	45	40	44
South Branch Whitewater	202.1	0.50	35	50	15	80
Winnebago	61.6	0.34	13	82	5	98

Note: Area = drainage area (km²), TS = thermal sensitivity (air–water temperature regression slope), % forested = forested riparian percentage, % grassland = grassland riparian percentage, % cultivated = cultivated riparian percentage, and RA = brown trout relative abundance (individuals per hour).

Table 3. Results of linear mixed-effects modeling to explain variation in brown trout growth among southeast Minnesota streams as a function of stream drainage area (Area, km²), stream thermal sensitivity (TS, air--water temperature regression slope), % forested riparian area (For), % grassland riparian area (Grass), % cultivated riparian area (Cult) and brown trout relative abundance (RA, individuals per hour).

Model	N	K	AIC	AICc	ΔAICc	wi
Growth = Area + For + RA + (1 + Area|Age)	7	5	10,323.79	10,323.92	0.00	0.46
Growth = Area + For + Grass + RA + (1 + Area|Age)	7	6	10,325.24	10,325.41	1.49	0.22
Growth = Area + Grass + RA + (1 + Area|Age)	7	5	10,326.34	10,326.47	2.55	0.13
Growth = Area + TS + Grass + (1 + Area|Age)	7	5	10327.85	10327.99	4.07	0.06
Growth = Area * RA + For + (1 + Area|Age)	7	4	10,329.22	10,329.38	5.46	0.03
Growth = Area + TS + Grass + RA + (1 + Area|Age)	7	6	10,329.40	10,329.57	5.65	0.03
Growth = Area * RA + For + Grass + (1+Area|Age)	7	5	10,329.84	10,330.05	6.13	0.02
Growth = Area * RA + Grass + (1 + Area|Age)	7	4	10,330.95	10,331.12	7.20	0.01
Growth = Area + TS + RA + (1 + Area|Age)	7	5	10,331.53	10,331.66	7.74	0.01
Growth = Area + TS + For + RA + (1 + Area|Age)	7	6	10,331.78	10331.95	8.03	0.01
Growth = Area + TS + (1 + Area|Age)	7	4	10,331.92	10,332.03	8.11	0.01
Growth = Area + TS + For + Grass + (1+Area|Age)	7	6	10,332.02	10,332.19	8.27	0.01
Growth = Area + TS + For + Grass + RA + (1+Area|Age)	7	7	10,333.01	10,333.22	9.30	0.00
Growth = Area + TS + For + Grass + Cult + RA + (1 + Area|Age)	7	8	10,333.01	10,333.22	9.30	0.00
Growth = Area + RA + (1 + Area|Age)	7	4	10,337.36	10,337.47	13.55	0.00

Note: N = sample size (number of streams); K = number of parameters (fixed effects plus intercept and error); AIC = Akaike's information criterion; AICc = AIC corrected for small sample size; ΔAICc = difference in AICc between each model and the most supported model; w_i = Akaike weight (relative strength of evidence for each model).

Table 4. Intercepts and coefficients for the two most parsimonious linear mixed-effects models and the model-averaged estimator to explain variation in brown trout growth among southeast Minnesota streams.

Model	wi	Age	Intercept	Area	For	Grass	RA
Growth = Area + For + RA + (1 + Area|Age)	0.46	1	110.6	6.61	0.23	–	−0.09
		2	162.7	14.77	0.23	–	−0.09
		Global	136.6	10.69	0.23	–	−0.09
Growth = Area + For + Grass + RA + (1 + Area|Age)	0.22	1	119.9	6.23	0.16	−0.12	−0.08
		2	172.5	14.26	0.16	−0.12	−0.08
		Global	146.2	10.25	0.16	−0.12	−0.08
Model-averaged		1	76.9	4.39	0.14	−0.03	−1.08
		2	112.3	9.89	0.14	−0.03	−0.06
		Global	94.6	7.14	0.14	−0.03	−0.06

Note: w_i = Akaike weight (relative strength of evidence for each model).