MARB 403 Lab 3

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Our group led this discussion

Common Bottlenose Dolphin

Authors:

Michael D. Scott
Randall S. Wells

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Decline in Relative Abundance of Bottlenose Dolphins Exposed to Long-Term Disturbance

Authors:

Lars Bejder
Richard Connor
Cindy Flaherty
Nick Gales
Mike Heithaus
Michael Krützen
Janet Mann
Amy Samuels
Jana Watson-Capps
Hal Whitehead

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This only includes the sections I worked on for the presentation

Methods

Experimental Design

Experimental site: GPS-Tracking tourism boats in a 36 km² Control site: adjacent 36 km² site with minimal activity: no tourism and little research boats

3 time periods:

T0 (Mar 1988 — Apr 1993): before tourism
T1 (May 1993 — Jul 1998): 1 tour vessel
T2 (Aug 1998 — Jan 2003): 2 tour vessels

exposure estimated in each time period and in each location (6 data points)

encounter = at least 1 minute within 50 m of dolphins (based on license)

Data sources:

long-term research database
188 monitored tour trips in 2000 (representative of all years of operation)

abundance based on photo ID from survey records:

Time Period	Tourist Area		Control Area
Time Period	No. dolphins identified	% identified as individuals	No. dolphins identified	% identified as individuals
T0	2714	90.4%	42	71.4%
T1	6261	90.7%	1548	73.2
T3	8863	94.6	1812	76.3

Note: % identified = # dolphins identified / total # dolphins observed

Both areas divided into grid squares (repeated for 1 and 4 km²)

Dolphin abundance estimation formulas

{\begin{aligned}y_{1j}&={\frac {s_{j}\,q\,x_{1j}}{1+q\,x_{1j}}}\\y_{2j}&={\frac {s_{j}\,q\,x_{2j}}{1+q\,x_{2j}}}\,(1+p)\\\end{aligned}}

$y(j,t)\to y_{tj}$ — number of identified individuals per square per period (dependent variable)
$x(j,t)\to x_{tj}$ — total number of survey records per square per period (independent variable)
$s(j)\to s_{j}$ — estimated number of dolphins in a particular square (estimated variable)
$p$ — proportional rate of change of dolphin abundance between time periods (assumed equal for all squares) (estimated constant)
$q$ — rate of population size increase in each square (assumed equal for all squares) (estimated constant)

Results

Dolphin Exposure to Tour and Research Vessels

Averaged

encounters per trip: 1.86
duration: 10.63±7.33 minutes
daily trips for T1: 2.5 (out of 4 possible)
daily trips for T2: 5.5 (out of 8)

Time spent with dolphins (in hrs/day) by type of vessel
Time Period	Tourist Area			Control Area
Time Period	Tour	Research	Total	Tour	Research	Total
T0	0	0.54	0.54	0	0.006	0.006
T1	0.82	0.41	1.23	0	0.039	0.039
T2	1.82	0.77	2.59	0	0.099	0.099

Changes in Dolphin Abundance

Little change from T0 to T1 in both areas and both grid sizes

Change in Dolphin Abundance from T1 to T2

Note: CI95 = 95% confidence interval

there is a 95% chance that the actual change in dolphin abundance is within this range

Recall that dolphin abundance values are estimates of the actual population

	Tourist Area		Control Area
	% change	95% CI	% change	95% CI
1 km² grid	-14.9% / km²	[-20.8%, -8.23%]	+8.5% / km²	[-4.0%, +16.7% ]
4 km² grid	-18.2% / 4 km²	[-25.02%, -0.77%]	+2.4% / 4 km²	[-14.16%, +20.57%]

Overall trend: significant decrease in tourist area, nonsignificant increase in control area

1 km² grid size result was more conservative (smaller confidence interval)

On average, every 1 in 7 dolphins left

Discussion