Comparison of sinking and floating gill nets for collecting shads (Dorosoma spp.) in shallow Florida lakes

Figures & data

Table 1 Long-term averages of Secchi depth (m), chlorophyll a concentration (μg/L), total nitrogen concentration (μg/L) and total phosphorus concentration (μg/L) for the 3 study lakes. The estimated lake-wide coverage of aquatic plants (%) and average depth (m) are also provided. All data were collected and reported by Florida LAKEWATCH (2008, 2009).

	Lake
	Minneola	Eloise	Harris
Surface area (ha)	764	469	5580
Secchi depth	1.3	0.9	0.6
Chlorophyll a	6	42	58
Total nitrogen	1093	1242	1780
Total phosphorus	26	37	35
Plant coverage	<1	19	<1
Water depth	3.0	3.4	3.1

Table 2 Adjusted mean catch rate (fish/net set/h; standard error in parentheses), coefficient of variation (CV), and minimum (MIN) and maximum (MAX) sizes of gizzard shad and threadfin shad collected in experimental gill net sets. Floating catch rates were adjusted by dividing raw values by 1.33.

Species	Lake	Net Type	Mean	CV	Min	Max	N
Gizzard shad	Eloise	Float	6.52 (0.89)	61	0.38	14.70	20
		Sink	14.86 (1.84)	55	4.50	32.44	20
	Harris	Float	4.00 (0.85)	93	0.33	12.33	19
		Sink	32.46 (3.09)	42	7.56	69.60	19
	Minneola	Float	0.00 (0.00)	—	0.00	0.00	20
		Sink	0.23 (0.09)	174	0.00	3.00	20
Threadfin shad	Eloise	Float	2.13 (0.37)	78	0.00	5.01	20
		Sink	15.92 (4.31)	121	0.89	73.33	20
	Harris	Float	3.71 (0.80)	94	0.00	12.78	19
		Sink	15.44 (3.97)	112	0.44	57.60	19
	Minneola	Float	0.09 (0.08)	364	0.00	1.50	20
		Sink	0.18 (0.08)	213	0.00	1.50	20

Figure 1 Adjusted mean catch rates (CPUE) with standard error bars for gizzard shad (GISH) and threadfin shad (THSH) collected using floating (black bars) and sinking (gray bars) experimental gill nets at lakes Eloise, Harris, and Minneola in winter 2007–2008. Floating catch rates were adjusted by dividing raw values by 1.33.

Figure 2 Length-frequency distributions for gizzard and threadfin shad collected by floating (black bars) and sinking (gray bars) experimental gill nets at lakes Eloise, Harris and Minneola, Florida from December 2007 to March 2008.

Table 3 Estimated number of samples needed to collect 400 fish for length-frequency comparisons (N₄₀₀ ), to detect a 50% change in log10(CPUE+1) with a power of 0.8 and Type I error rate of 0.05 (N_LCPUE ), and to detect the presence of the species with 90% probability (N_pres ). Sample sizes for gizzard and threadfin shad are provided for both floating (Float) and sinking (Sink) nets in each lake.

Species	Lake	Net Type	N400	NLCPUE	NPres
Gizzard shad	Eloise	Float	22	7	1
		Sink	12	3	1
	Harris	Float	34	22	1
		Sink	5	1	1
	Minneola	Float	—	—	—
		Sink	—	—	6
Threadfin shad	Eloise	Float	68	17	1
		Sink	11	16	1
	Harris	Float	37	26	1
		Sink	11	21	1
	Minneola	Float	—	—	22
		Sink	—	—	8