Discrimination of Juvenile Red Snapper Otolith Chemical Signatures from Gulf of Mexico Nursery Regions

Figures & data

FIGURE 1 Nursery regions along the continental shelf of the Gulf of Mexico (Gulf), where age-0 red snapper representing the 2005–2007 year-classes were sampled. The 200-m depth contour indicates the continental shelf edge (regions: EG = eastern Gulf; NCG = north-central Gulf; NWG = northwestern Gulf; SWG = southwestern Gulf; MEX1 = Mexico region 1; MEX2 = Mexico region 2).

FIGURE 2 Specific locations where age-0 red snapper were sampled during fall 2005–2007. The 200-m depth contour indicates the continental shelf edge. Nursery region codes are defined in Figure 1.

TABLE 1 Sample size and size range of age-0 red snapper (2005–2007 year-classes) collected from six nursery regions in the Gulf of Mexico (Gulf; regions: EG = eastern Gulf; NCG = north-central Gulf; NWG = northwestern Gulf; SWG = southwestern Gulf; MEX1 = Mexico region 1; MEX2 = Mexico region 2).

Year-class	Region	Sample size	Size range (mm TL)
2005	EG	20	76–106
	NCG	30	65–146
	NWG	30	83–150
	SWG	30	61–145
	MEX1
	MEX2
2006	EG
	NCG	30	70–148
	NWG	30	71–149
	SWG	30	71–150
	MEX1	30	95–140
	MEX2	29	160–230
2007	EG	29	68–150
	NCG	30	65–146
	NWG	30	63–141
	SWG	30	53–149
	MEX1	22	75–220
	MEX2	30	60–230

FIGURE 3 Mean (±SE) region- and year-class-specific otolith constituents for age-0 red snapper sampled from six Gulf of Mexico nursery regions in 2005–2007. Nursery region codes are defined in Figure 1.

TABLE 2 Single-factor ANOVA results for year-class variation in otolith elemental and stable isotope ratios for age-0 red snapper collected from six Gulf of Mexico (Gulf) nursery regions (MS = mean square; %ω² = variance component percentage of the total variance for each ANOVA; *P < 0.05; **P < 0.01; ***P < 0.0001).

		Ba:Ca			Li:Ca			Mg:Ca			Mn:Ca			Sr:Ca			δ^13C			δ^18O
Region or factor	df	MS	F	%ω^2	MS	F	%ω^2	MS	F	%ω^2	MS	F	%ω^2	MS	F	%ω^2	MS	F	%ω^2	MS	F	%ω^2
Eastern Gulf
Year-class	1	31.99	16.85**	40	160.94	39.46***	62	3.73 × 10^−6	0.01	4	0.83	1.75	3	3.21 × 10^−6	0	4	3.72	15.46**	38	2.92	99.25***	81
Residual	47	1.90		60	4.08		38	5.57 × 10^−4		96	0.48		97	8.75 × 10^−3		96	0.24		62	0.03		19
North-central Gulf
Year-class	2	6.93	1.02	0	3.92	3.97*	9	2.24 × 10^−4	0.26	2	91.26	11.58***	26	1.70 × 10^−2	1.35	1	0.47	4.49*	10	0.02	0.34	2
Residual	87	6.82		100	0.99		91	8.59 × 10^−4		98	7.88		74	1.26 × 10^−2		99	0.11		90	0.05		98
Northwestern Gulf
Year-class	2	93.51	7.01**	17	8.51	19.17***	38	1.22 × 10^−3	1.71	2	19.89	5.18**	12	1.11 × 10^−1	8.49**	20	0.48	3.61*	8	0.98	13.45***	29
Residual	87	13.34		83	0.44		62	7.12 × 10^−4		98	3.84		88	1.31 × 10^−2		80	0.13		92	0.07		71
Southwestern Gulf
Year-class	2	36.81	3.06	6	3.96 × 10^−3	0.02	3	5.38 × 10^−3	5.27**	12	20.73	3.86*	9	6.61 × 10^−1	18.65***	37	2.49	12.58***	28	1.62	20.48***	39
Residual	87	12.02		94	0.18		97	1.02 × 10^−3		88	5.37		91	3.55 × 10^−2		63	0.20		72	0.08		61
Mexico region 1
Year-class	1	116.62	11.5**	29	6.43	16.87***	38	4.78 × 10^−2	35.87***	58	0.06	0.02	4	2.35 × 10^−1	9.9**	26	2.37	6.38*	17	5.31	56.38***	69
Residual	50	10.14		71	0.38		62	1.33 × 10^−3		42	3.65		96	2.37 × 10^−2		74	0.37		83	0.09		31
Mexico region 2
Year-class	1	0.01	0	3	3.58 × 10^−3	0	3	1.03 × 10^−2	6.74*	16	2.64	0.96	0	5.33 × 10^−3	0.17	3	1.40	4	9	0.18	2.64	5
Residual	57	2.37		97	1.74		97	1.53 × 10^−3		84	2.74		100	3.22 × 10^−2		97	0.35		91	0.07		95

FIGURE 4 Jackknifed classification percentages estimated with quadratic discriminant function analysis (QDFA) of otolith chemical signatures from age-0 red snapper that were sampled in six Gulf of Mexico nursery regions during 2005–2007 (bar colors represent QDFA-assigned regions; x-axis shows the region of sample collection). “ALL” indicates all three year-classes combined. Nursery region codes are defined in Figure 1.

TABLE 3 Total canonical structure coefficients (canonical variates [var] 1 and 2) for discriminant function analyses comparing region- and year-class-specific otolith chemical signatures of age-0 red snapper for the 2005–2007 year-classes.

	2005		2006		2007		All year-classes
Constituent	Var 1	Var 2	Var 1	Var 2	Var 1	Var 2	Var 1	Var 2
Ba:Ca	0.488	−0.133	0.252	0.185	−0.038	−0.240	−0.048	0.235
Li:Ca	0.311	0.367	0.365	−0.840	−0.658	1.251	−0.527	0.983
Mg:Ca	−0.143	0.380	−0.128	−0.107	0.110	0.225	0.013	0.154
Mn:Ca	−0.556	1.036	0.680	0.693	1.041	0.751	0.888	0.574
Sr:Ca	−0.303	0.163	−0.084	0.569	0.131	0.075	0.283	−0.014
δ^13C	0.356	0.851	−0.500	−0.426	−0.239	−0.311	−0.357	−0.231
δ^18O	2.078	0.489	−1.243	0.810	−1.059	0.017	−1.095	0.333

FIGURE 5 Canonical plot scores of otolith chemical signatures for age-0 red snapper (2005–2007 year-classes) sampled from six nursery regions in the Gulf of Mexico (canonical = canonical variate). Ellipses indicate 95% confidence levels; “ALL” indicates all three year-classes combined. Nursery region codes are defined in Figure 1.