Abundance and harvest proportion of river turtles in Missouri

Figures & data

Figure 1. Map of the five units (10 1-km sites in total, indicated with squares) trapped for mark–recapture and mock harvest during the 2011 and 2012 field seasons on the Missouri, Osage, and Gasconade Rivers in central Missouri. MOJ = Missouri River at Jefferson City unit (river mile [RM] 137 and RM 134, trapped in 2012); MOM = Missouri River at Mokane unit (RM 128 and RM 122, trapped in 2011); MOH = Missouri River at Hermann unit (RM 103 and RM 94, trapped in 2011 and 2012); OS = Osage River unit (RM 5 and RM 7, trapped in 2011 and 2012); GA = Gasconade River unit (RM 9 and RM 10, trapped in 2011 and 2012).

Table 1. Sites sampled during the 2011 and 2012 field seasons on the Missouri, Osage, and Gasconade Rivers in central Missouri. Unit represents the pairs of sites grouped by location. Numbers in the ‘Site’ column represent the randomly selected river mile one each river within which each 1-km trap site was located. Year(s) sampled represents the year or years when each site was sampled. Unit codes are defined as follows: MOH = Missouri River at Hermann; MOM = Missouri River at Mokane; MOH = Missouri River at Hermann; MOJ = Missouri River at Jefferson City; OS = Osage River; GA = Gasconade River.

River	Unit	Site (River mile)	Year(s) sampled
Missouri	MOH	94	2011, 2012
		103	2011, 2012
	MOM	122	2011
		128	2011
	MOJ	134	2012
		137	2012
Osage	OS	5	2011, 2012
		7	2011, 2012
Gasconade	GA	9	2011, 2012
		10	2011, 2012

Table 2. Abundance estimates () per 2 km of river for snapping turtles (Chelydra serpentina, CSNT), smooth softshell turtles (Apalone mutica, SMSS), and spiny softshell turtles (Apalone spinifera, SPSS) in harvested (Missouri River) and unharvested (Osage River, Gasconade River) trapping units in central Missouri. Unit = 2-km trapping units. Trap nights = number of nights spent at each site (number of traps per unit multiplied by the total number of nights spent per unit); n = number of individual turtles caught within each unit. Proportion recaptures = proportion of individuals that had been recaptured at least one time following initial capture. Mean capture probability = the mean nightly probability that an individual will be captured during a given trap night. Capture proportion = expected proportion of the population captured at least once during the span of each trap run. Unit codes are defined as follows: MOH11 = Missouri River at Hermann 2011; MOM11 = Missouri River at Mokane 2011; MOH12 = Missouri River at Hermann 2012; MOJ12 = Missouri River at Jefferson City 2012; OS11 = Osage River 2011; GA11 = Gasconade River 2011; OS12 = Osage River 2012; GA12 = Gasconade River 2012. An asterisk (*) indicates units where estimation of was not feasible due to lack of recaptures.

Species	River status	Unit	Trap nights	n	Proportion recaptures	Mean capture probability		SE	LCI	UCI	Capture proportion
CSNT	Harvested	MOH11	482	5	0.375	0.116	5	1.44	5.01	14.88	0.86
		MOM11	482	5	0.444	0.146	5	1.09	5.00	10.08	0.90
		MOH12	502	11	0.214	0.031	35	21.11	16.91	118.50	0.34
		MOJ12	480	6	0.143	0.038	14	11.78	7.09	70.85	0.40
	Unharvested	OS11	601	31	0.184	0.031	70	21.14	45.64	136.50	0.44
		GA11	547	41	0.406	0.09	55	6.32	46.93	73.49	0.74
		OS12	492	32	0.059	0.014	208	137.90	77.48	714.80	0.15
		GA12	480	12	0.143	0.045	27	14.84	14.93	87.81	0.44
SMSS	Harvested	MOH11	482	140	0.235	0.044	300	36.50	242.70	388.60	0.47
		MOM11	482	39	0.114	0.023	148	58.72	79.22	332.00	0.26
		MOH12	502	45	0.151	0.030	136	41.33	83.77	257.50	0.33
		MOJ12	480	11	0.000		*
	Unharvested	OS11	601	8	0.000		*
		GA11	547	4	0.000		*
		OS12	492	5	0.000		*
		GA12	480	37	0.362	0.098	51	6.68	42.47	70.81	0.99
SPSS	Harvested	MOH11	482	10	0.474	0.155	10	1.10	10.00	17.40	0.94
		MOM11	482	12	0.294	0.073	18	5.54	13.43	39.76	0.64
		MOH12	502	29	0.293	0.065	49	10.09	36.64	79.73	0.59
		MOJ12	480	19	0.000		*
	Unharvested	OS11	601	4	0.000		*
		GA11	547	19	0.000		*
		OS12	492	2	0.000		*
		GA12	480	44	0.279	0.074	72	11.82	56.69	106.00	0.61

Figure 2. Histograms showing the distribution of the total number of individual turtles, not including recaptures, caught during mark–recapture periods and mock harvest periods during the 2011 and 2012 field seasons in central Missouri. Plots are broken down by sex (female, male, unknown) and by life stage (adult, juvenile, hatchling; designations based on Johnson [2000]), for each species (CSNT = snapping turtle, Chelydra serpentina; SMSS = smooth softshell turtle, Apalone mutica; SPSS = spiny softshell turtle, Apalone spinifera), and river of capture (Missouri River, Gasconade River, Osage River).

Table 3. Expected harvest proportions for snapping turtles (Chelydra serpentina, CSNT), smooth softshell turtles (Apalone mutica, SMSS), and spiny softshell turtles (Apalone spinifera, SPSS) in harvested (Missouri River) and unharvested (Osage River, Gasconade River) trapping units in central Missouri. Harvest proportion represents the expected proportion of each population that was captured (‘harvested’) during each mock harvest (see Table 2). Unit = 2-km trapping unit. Trap nights = total number of nights spent at each site (total number of traps per unit multiplied by the total number of nights spent per unit); n = total number of turtles caught within each unit. Proportion recaptures = proportion of the total number of captured individuals that had been recaptured at least one time following initial capture. Variance was estimated using the Delta Method (Powell 2007). Unit codes are defined as follows: MOH11 = Missouri River at Hermann 2011; MOM11 = Missouri River at Mokane 2011; MOH12 = Missouri River at Hermann 2012; MOJ12 = Missouri River at Jefferson City 2012; OS11 = Osage River 2011; GA11 = Gasconade River 2011; OS12 = Osage River 2012; GA12 = Gasconade River 2012. An asterisk (*) indicates units where estimation of harvest proportion was not feasible due to lack of recaptures.

Species	River status	Unit	Trap nights	n	Proportion recaptures	Harvest proportion	SE
CSNT	Harvested	MOH11	164	3	0.333	0.568	0.27
		MOM11	163	1	1.000	0.249	0.23
		MOH12	176	3	0.667	0.086	0.07
		MOJ12	160	2	1.000	0.139	0.15
	Unharvested	OS11	144	14	0.214	0.199	0.08
		GA11	147	7	0.571	0.128	0.05
		OS12	172	14	0.071	0.067	0.04
		GA12	160	7	0.143	0.260	0.17
SMSS	Harvested	MOH11	164	35	0.229	0.117	0.02
		MOM11	163	13	0.231	0.088	0.04
		MOH12	176	12	0.167	0.088	0.03
		MOJ12	160	4	0.000	*
	Unharvested	OS11	144	0	0.000	*
		GA11	147	3	0.000	*
		OS12	172	3	0.000	*
		GA12	160	17	0.529	0.336	0.08
SPSS	Harvested	MOH11	164	8	0.500	0.792	0.15
		MOM11	163	4	0.250	0.219	0.12
		MOH12	176	3	0.667	0.062	0.04
		MOJ12	147	6	0.000	*
	Unharvested	OS11	144	0	0.000	*
		GA11	160	5	0.000	*
		OS12	172	1	0.000	*
		GA12	160	17	0.529	0.236	0.06

Johnson TR. 2000. The amphibians and reptiles of Missouri. Jefferson City (MO): Missouri Department of Conservation; p. 400.

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Powell LA. 2007. Approximating variance of demographic parameters using the delta method: a reference for avian biologists. The Condor. 109:949–954.

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