Recruitment sources of brown trout identified by otolith trace element signatures

Figures & data

Figure 1  Sampling locations within the Motueka River catchment. Abbreviated names represent tributaries from which juvenile brown trout were sampled; GR: Graham River, BA: Baton River, UW: Upper Wangapeka River, DA: Dart River, MO: Motupiko River, RA: Rainy River, BG: Blue Glen Stream and UM: Upper Motueka River. Numbers represent where each adult brown trout was caught.

Table 1  Catchment area, flow, land cover types and rock types (Basher 2003) of each of the eight tributaries for which trace element signatures were generated.

Tributary	Area (km^2)	Annual mean flow (l/s)	Land cover	Geology
RA	105	1794	Native forest, exotic forest and pastoral	Moutere gravel
MO	344	5152	Native forest, exotic forest and pastoral	Moutere gravel
BG	25	1700	Native forest and exotic forest	Maitai sedimentary
DA	81	2750	Native forest, exotic forest, scrub and tussock	Separation point granite
UM	163	7067	Native forest, exotic forest, scrub and tussock	Maitai sedimentary and ultramafics
UW	320	18697	Native forest, scrub and tussock	Old sedimentary, complex mud stone, marble and schist
GR	40	2100	Native forest and scrub	Separation point granite, complex mud stone, complex igneous and marble
BA	212	9032	Native forest, exotic forest scrub, tussock and pastoral	Separation point granodiorite, complex mud stone, old sedimentary, complex igneous, separation point granite, old conglomerate, marble and schist
Abbreviated names for the tributaries are described in Fig. 1.

Table 2  Sample dates and results of multivariate analysis of Sr:Ca, Rb:Ca, Ba:Ca and Mn:Ca ratios for each tributary over all sampling occasions.

		pilla's trace
Tributary	Sample Dates	Value	F Statistic	Sig.
BA	Feb05, Apr05, Apr06	1.31	4.73	0.002
BG	Feb05, Apr05, Apr06	0.98	2.42	0.052
DA	Feb05, Apr05, Apr06	1.01	2.30	0.068
GR	Feb05, Apr06	0.79	4.77	0.059
MO	Feb05, Apr06	0.73	3.35	0.109
RA	Feb05, Apr05, Apr06	1.12	3.11	0.019
UM	Feb05	NA	NA	NA
UW	Feb05, Apr06	0.93	15.78	0.005
Abbreviated names for the tributaries are described in Fig. 1.

Figure 2  Photo showing sectioned adult otolith and ablated transect (LA Transect) highlighted by dashed horizontal lines. The element profile for Sr:Ca ratios is shown and represents Sr:Ca ratio levels as they relate to the ablated transect directly below it. Arrow marked ‘B’ indicates the primordium of the otolith, and the centre of the profile. Arrows marked ‘A’ and ‘C’ indicate the sections of transect and profile from which 50 µm of data was taken to generate the natal signature for the otolith (approximated by dashed vertical lines). Note that the natal signature also considers Ba:Ca, Rb:Ca and Mn:Ca ratios, but for clarity the element profiles for these elements are not shown.

Figure 3  Mean (±SE) element:Ca ratios from the otoliths of juvenile brown trout (n=5) from eight tributaries on each sampling occasion. Abbreviated names for the tributaries are described in Fig. 1.

Figure 4  Trace element signatures obtained from the otoliths of juvenile brown trout collected from eight tributaries in the Motueka River Catchment. Groupings for each of the three plots are based on discriminant functions 2, 3 and 4 versus function 1; all obtained through linear discriminant function analysis of Sr:Ca, Rb:Ca, Ba:Ca and Mn:Ca ratios. Ellipses represent 95% confidence ellipses calculated around the group means. Abbreviated names for the tributaries are described in Fig. 1.

Table 3  Capture location and predicted natal tributaries of the 23 adult brown trout sampled.

Adult trout ID	Capture location	Predicted natal tributary	Posterior probability	Mahalanobis distance
1	Motueka Tidal	Unknown	0.688	24.053
2	Motueka Tidal	RA	1.000	10.915
3	Motueka Tidal	UW	0.993	7.840
4	Motueka Tidal	MO	0.996	7.751
5	Motueka Tidal	Unknown	1.000	18.879
6	Motueka Tidal	Unknown	1.000	19.785
7	Motueka Lower	Unknown	0.935	46.986
8	Motueka Lower	BA	0.855	6.344
9	Motueka Mid	Unknown	0.951	31.883
10	Motueka Mid	DA	0.993	7.723
11	Motueka Mid	MO	0.963	7.241
12	Motueka Mid	Unknown	1.000	40.955
13	Motueka Mid	RA	0.878	9.021
14	Motueka Mid	Unknown	0.980	30.119
15	Motueka Mid	GR	0.808	10.904
16	Motueka Mid	DA	1.000	8.143
17	Wangapeka Lower	Unknown	0.995	22.258
18	Wangapeka Lower	Unknown	0.742	16.569
19	Wangapeka Lower	Unknown	1.000	40.446
20	Wangapeka Lower	Unknown	0.610	5.488
21	Wangapeka Mid	DA	0.999	7.511
22	Wangapeka Upper	BA	1.000	9.357
23	Wangapeka Upper	Unknown	0.947	11.360
Posterior probability of group membership and squared Mahalanobis distance from that group centroid as generated by linear discriminant function analysis are shown. Natal tributary prediction was conducted only where posterior probability was >0.786 and squared Mahalanobis distance <11.205. Abbreviated names for the tributaries are described in Fig. 1.

Basher LR 2003 The Motueka and Riwaka Catchments . Landcare Research Technical Report . Landcare Research , Lincoln, , New Zealand .

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