Chapter 1 General Introduction
2.4 Discussion
2.4.6 Conservation Status and Implication
Of all the density estimates for Taiwan and nearby regions, the present zigzag survey reported the lowest estimate, but since the survey covered much offshore area with a very small sample size, a realistic density of Taiwan’s special population should be somewhere between the under-estimated zigzag and over-estimated inshore surveys (i.e. 0.103-0.31). Even considering the over-estimation, the density estimate of the population in Taiwan was still lower than the most sustainable Hong Kong and Dafengjiang populations, which had the highest estimated abundance. Taiwan’s population density and abundance were relatively similar to those of Xiamen and Hepu, two areas already designated as Nature Reserves (Chen et al. 2008, 2009) in China.
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Table 2.1 Efforts of the 2012-13 total area zigzag survey Study date
(2012-2013)
On effort period (hour)
On effort length (kilometer)
1st season 3rd-7th July 24.67 363.88
2nd season 3rd-7th September 31.71 436.27
3rd season 20th-21th October, 3rd-4th, 10th, and 22th November
32.12 402.83
4th season 8th-9th, 13th March, 14th-15th April
30.41 437.67
5th season 15th-16th, 18th-20th June 30.03 412.6
Sum 148.94 2053.25
Table 2.2 Parameter estimates of the zigzag transect line surveys
Parameters Estimates CV (%) 95%CI
Probability of detection 0.27 21.2 0.17 0.42
Effective width (m) 136.09 21.2 87.19 212.42
Density (individual/𝐤𝐦𝟐) 0.103 42.0 0.046 0.23
Abundance (individuals) 64 42.0 29 144
Expected group size 3.18 22.8 1.97 5.12
Table 2.3 Descriptive statistics of environmental factors measured from the survey stations of zigzag transect line surveys (n=949)
Depth
Table 2.4 Descriptive statistics of environmental factors measured from the dolphin contact points of zigzag transect line surveys (n=23)
Depth
Table 2.5 Effort and study area of the 2008-12 inshore parallel survey Survey
trips
Sightings On effort length (km)
SPUE (groups/100km)
Study Area (𝐤𝐦𝟐)
2008 71 65 4212.47 1.54 141.29
2009 151 76 6001.01 1.27 220.06
2010 63 62 2458.86 2.52 137.05
2011 50 53 2189.82 2.42 149.95
2012 59 56 2395.09 2.34 149.95
2008-12 394 312 17257.23 1.81 220.06
*SPUE=Sightings per unit effort, indicating average sighting groups of 100 km on efforts surveys here
Table 2.6 Parameter estimates of the 2008-12 inshore parallel transect line surveys
Parameters Estimates CV (%) 95%CI
Probability of detection 0.28 8.5 0.24 0.34 Effective width (m) 113.63 8.5 96.17 134.27 Density (individual/𝐤𝐦𝟐) 0.31 11.5 0.25 0.39
Abundance (individuals) 68 11.5 54 85
Expected group size 3.90 4.8 3.54 4.28
Table 2.7 Comparison of 2008-2012 yearly inshore parallel transect line parameter estimates, 2008-2012 pooled dataset, and 2012-13 zigzag transect line survey.
Year Selected
*P: detection probability; ESW: effective strip width; D: density (individual/km2); CV: coefficient of variance; A: study area; N: abundance (individuals); CI: confident interval
Table 2.8 Comparison of density and abundance estimations of Chinese white dolphins in Chinese and Taiwanese waters.
Region Country D N Reference
Dafengjiang River China 0.326 114 Chen et al. 2009
Hepu China 0.111 39 Chen et al. 2009
HongKong and adjacent area
China 0.409 1028 Jefferson, 2000
Xiamen China 0.124 87 Chen et al. 2008
Western Taiwan inshore waters
Taiwan 0.193 99 Wang et al. 2007
Western Taiwan waters
Taiwan 0.103 64 This study
Western Taiwan inshore waters
Taiwan 0.310 68 This study
* D: density (individual/km2), N: abundance (individuals)
Fig. 2.1 Total area zigzag survey design in 2012-2013
Fig. 2.3 Zigzag survey tracks of the five survey seasons in 2012-2013
Fig. 2.5 Best fit model’s detection probability function (curve) and observed perpendicular distances (histogram) of the total area zigzag survey.
(a)
(b)
e
(c)
(d)
(e)
(f)
Fig. 2.6 Density histogram of environmental factors measured at the regular survey stations (dotted line) and at the contact points (solid line) during the 2012-13 zigzag survey: (a) Salinity (ppt), (b) Temperature (°C), (c) Water depth (m), (d) pH value, and (e) Turbidity (NTU) (f) Distance to shore (km)
(a) (b)
(c) (d)
(e)
Fig. 2.7 Transect line design for inshore parallel surveys in (a) 2008, (b) 2009, (c) 2010, (d) 2011 and (e) 2012.
Fig. 2.9 Best fit model’s detection probability function (curve) and observed perpendicular distances (histogram) of the 2008-2012 inshore parallel survey.