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Supplemental Feeding for Ecotourism Reverses Diel Activity and Alters Movement Patterns and Spatial Distribution of the Southern


Science & Tech  (tags: study, world, scientists, science, research, safety, animals, health, investigation )

JL
- 470 days ago - plosone.org
Southern stingrays, Dasyatis americana, have been provided supplemental food in ecotourism operations at Stingray City Sandbar (SCS), Grand Cayman since 1986, with this site becoming one of the world's most famous &heavily visited marine wildlife inter



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JL A. (274)
Saturday March 30, 2013, 9:43 am

Research Article
Supplemental Feeding for Ecotourism Reverses Diel Activity and Alters Movement Patterns and Spatial Distribution of the Southern Stingray, Dasyatis americana

Mark J. Corcoran,

Bradley M. Wetherbee,

Mahmood S. Shivji mail,

Matthew D. Potenski,

Demian D. Chapman,

Guy M. Harvey

Abstract

Southern stingrays, Dasyatis americana, have been provided supplemental food in ecotourism operations at Stingray City Sandbar (SCS), Grand Cayman since 1986, with this site becoming one of the world’s most famous and heavily visited marine wildlife interaction venues. Given expansion of marine wildlife interactive tourism worldwide, there are questions about the effects of such activities on the focal species and their ecosystems. We used a combination of acoustic telemetry and tag-recapture efforts to test the hypothesis that human-sourced supplemental feeding has altered stingray activity patterns and habitat use at SCS relative to wild animals at control sites. Secondarily, we also qualitatively estimated the population size of stingrays supporting this major ecotourism venue. Tag-recapture data indicated that a population of at least 164 stingrays, over 80% female, utilized the small area at SCS for prolonged periods of time. Examination of comparative movements of mature female stingrays at SCS and control sites revealed strong differences between the two groups: The fed animals demonstrated a notable inversion of diel activity, being constantly active during the day with little movement at night compared to the nocturnally active wild stingrays; The fed stingrays utilized significantly (p80% of individuals captured) at SCS. For manual tracking, external transmitters (V16-4H-01, Vemco, Nova Scotia, Canada, 16 mm diameter x 65 mm, 10 g in water, frequencies 51–81 kHz, lifespan 218 d) were attached to the right pelvic fin using a Peterson disk tag following the method of [29]. Handling time (capture to release) for each animal did not exceed seven minutes. Tracking was conducted from a 7 m boat equipped with a hull-mounted directional hydrophone (Vemco model VH10) and portable receiver (Vemco model VR60-01-02-07-08) crewed by a minimum of two people: a tracker/driver and an assistant responsible for anchoring and navigation [30]. Stingrays were manually tracked from 11to 72 h (Table 1) and their position recorded every ten minutes using a handheld GPS, with a total of 2,542 geographic positions recorded. Individual stingrays manually tracked for up to 72 h were followed for 3 non-contiguous 24-hr periods. All stingrays with external transmitters attached were released in good condition, judged by observations that the fed animals immediately returned to tourists to receive food handouts, and the wild stingrays swam off robustly after release.
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Table 1. Fed and wild southern stingray individuals tracked by manual telemetry at Grand Cayman.
doi:10.1371/journal.pone.0059235.t001
Automated Telemetry

We assessed longer-term (up to 389 days) site fidelity and movement patterns of the fed, mature females at SCS through use of automated acoustic receivers (Vemco model VR2-69.0 KHz-1.03-2-1431-C-211). Individually coded transmitters (V16-4H-01-R04K, Vemco 16 mm × 65 mm, 10 g in water, frequency 69 kHz, random pulse rates, lifespan 570 d) were coated with a thin layer of wax (50% beeswax, 50% paraffin wax) and surgically implanted in five mature females ( = 102.2±8.0 cm DW) (Table 2). Transmitters were inserted in the body cavity through a 20 mm incision in the ventral surface and the incision closed with four stitches with non-absorbable silk sutures. Two acoustic receivers encased in PVC housing for protection were anchored to the bottom 180 m apart on opposite sides of SCS at a depth of 3.5 m (Fig. 2). Range tests determined that the effective listening radius of the receivers was approximately 190 m, covering approximately 70% of the SCS supplemental feeding area. Receiver A was deployed for 389 days and receiver B for 202 days due to damage caused by a boat.
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Figure 2. Locations and approximate detection ranges of two bottom-fixed, acoustic receivers.

The receivers were used for longer-term, automated tracking of five mature female fed southern stingrays at Stingray City Sandbar (SCS), Grand Cayman.
doi:10.1371/journal.pone.0059235.g002
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Table 2. Sex, size and detection duration of fed stingrays implanted with acoustic transmitters and monitored using two automated receivers deployed at Stingray City Sandbar (SCS), Grand Cayman.
doi:10.1371/journal.pone.0059235.t002
Data Analysis

Stingray tracks obtained by manual telemetry were overlaid on a photo-mosaic image of Grand Cayman Island using Arc View 3.2 GIS software. Stingray “core areas” (i.e. the area most frequently used by an animal) were calculated using 50% kernel utilization distribution, and “activity spaces” (i.e. the area that an animal traverses in the scope of normal activities) were calculated using a 95% kernel utilization distribution with the Animal Movement Analyst Extension (AMAE) program for Arc View GIS. The percent daily overlap in daytime core activity areas for fed vs. wild female tracked stingrays was calculated by determining overlap between the combined 50% kernel utilization distribution for each animal. Stingray rates of movement (ROM) were calculated by dividing the distance between successive position fixes by the sampling time interval using AMAE. Activity space and ROM data for each animal were divided into daytime and nighttime periods based on local sunrise and sunset, and the data subsequently pooled into “fed” and “wild” groups for comparison. Pooled day, night and total 24 hr activity spaces and ROM were compared within and between each group using a Mann-Whitney U-test. Pooled activity spaces and ROM were also compared over periods of high, low, incoming and outgoing tides using a Kruskal-Wallis test. High and low tidal phases were defined as the periods from one hour before to one hour after maximum and minimum water level.

Automated telemetry data collected with the VR2 receivers were examined using VR2PC software (Vemco, Version 1.12). To assess the degree of site attachment for each animal tracked by this method, detections of individual transmitters on the two acoustic receivers were sorted into hourly bins, and the presence of rays at SCS expressed as a percent of days an animal was present over the entire monitoring period. To assess if there was an overall temporal periodicity in the presence of the five female stingrays at the SCS over the receiver deployment periods, we conducted a time series analysis using a Fast Fourier Transformation (FFT) with Hamming window smoothing in SigmaPlot 11.0. The FFT decomposes time-series data into component sinusoidal waves of different frequencies, with the size of the spectral peaks in the resulting periodogram indicating the relative strength of the periodic components [31]. The FFT was conducted for the five animals for each receiver and both receivers combined.
Results

Over the course of the February 2002–August 2003 study period, we captured 164 unique stingrays at SCS and 55 unique stingrays at the control sites (total of 219 unique stingrays). Ninety four percent of fed stingrays were recaptured at least once, 87% were recaptured at least twice and some animals were recaptured up to 11 times over the 19 months at SCS, totaling 986 individual recaptures at this site. Based on presence of scars from prior genetic tissue sample removal, PIT tag retention in recaptured animals at SCS was 100% during this period. With the exception of one animal, all recaptures at SCS were of stingrays originally tagged at this site. In contrast, only 22% of the wild stingrays were recaptured, all within 1 km of their original tagging sites.

Overall, there were several strong contrasts in movement and habitat use patterns between fed and wild stingrays: 1) Fed female stingrays had significantly smaller average daytime, nighttime and total (24 hr) activity spaces (total activity space = 0.13±0.08 km2) than wild female stingrays (total activity space = 0.88±0.17 km2) (Mann Whitney U test, P0.05). Tidal phase had no influence on activity space or ROM for either group (Kruskal-Wallis test, P>0.05).
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Figure 3. Comparative activity space sizes of fed and wild female stingrays.

Activity space sizes, based on 95% kernel contours, of fed (open bars, n = 5) and wild (filled bars, n = 5) southern stingrays tracked manually at Grand Cayman during day, night and 24 hour periods. The thick horizontal lines inside the boxes represent the medians, the box edges show the upper and lower quartiles, and the whiskers represent minimum and maximum values.
doi:10.1371/journal.pone.0059235.g003
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Figure 4. Comparative overlap in daytime core activity areas of fed and wild female stingrays.

Core areas are based on 50% kernel contours of five stingrays manually tracked at each site. A) the Stingray City Sandbar (SCS) supplemental feeding site, and B) the South Sound control site.
doi:10.1371/journal.pone.0059235.g004
Fed Stingray Movements – Manual Telemetry

All the tracked fed female stingrays remained active (i.e. displayed almost continuous movements without stationary periods) at SCS during daytime supplemental feeding periods. In addition to their telemetry tracked movements, the continuous activity of the tagged stingrays was also easily visually observable due to the shallow depth (0.5–1.5 m) and water clarity at the SCS. Less than one hour after cessation of daily supplemental feeding, which normally ended around 1700 h with the departure of ecotourism operators, all manually tracked female stingrays moved to the adjacent patch reef site ~ 200 m north of SCS (Fig. 1); here they buried in the sand and remained stationary for several hours among aggregations of 20–30 individuals, with their heads oriented into the current. Between 1930 and 2130 h, the female stingrays moved from this aggregation area to individual “resting” locations within a 600 m radius of SCS where they sat stationary on the bottom with little to no further movement for several hours (stationary phase average ± sd = 5.8±1.9 hrs). Stingray individuals 3 and 5 (Table 1) were tracked for 72 hours and both exhibited strong fidelity to the same nighttime “resting” locations each night.

All tracked stingrays returned to SCS at least one hour prior to arrival of tourist boats and commencement of supplemental feeding the following day (around 0600 h). Fed female stingrays had significantly larger nighttime (0.21±0.19 km2) than daytime activity spaces (0.014±0.003 km2) (Mann-Whitney U-test, P15 m depth (Fig. 7). Stingray individuals 10 and 11 (Table 1), each tracked for 48 hrs (two non-contiguous 24 h periods), showed fidelity to specific daytime locations outside the fringing reef on both days. No foraging by the tracked stingrays was observed during most (see below) of the day, when they were mostly stationary with the exception of traveling to and from the lagoon. However, the tracked and several non-tracked wild stingrays were observed foraging during early morning (0500–0700 h) and nighttime periods inside the lagoon over sand flat and grass plain zones. All five tracked wild females moved back into the lagoon from outside the fringing reef between 1515 and 1730 h and foraged over relatively large areas at night; subsequently, they had significantly larger activity spaces at night (0.63±0.36 km2) than during the day (0.27±0.09 km2) (Mann-Whitney U-test, P
 

Kit B. (277)
Saturday March 30, 2013, 10:07 am

Fascinating study that does seem to offer proof that the forms of artificial feeding disrupts normal patterns and behaviors. The problem with doing any thing about this just might be wrapped in one word: Tourism. That is translated into dollars, and that means those making real money, are not about the surrender the benefits to themselves over the deleterious affect on the wildlife.
 

Michael Kirkby (83)
Saturday March 30, 2013, 10:48 am
I much prefer stingrays in their natural habitat.
 

Carol D. (104)
Saturday March 30, 2013, 11:03 am
Stingrays belong in the ocean
 

JL A. (274)
Saturday March 30, 2013, 11:08 am
Excellent comments Kit, Michael and Carol--unfortunately: You cannot currently send a star to Kit, Michael or Carol because you have done so within the last day.
 

Birgit W. (140)
Saturday March 30, 2013, 12:57 pm
Leave them alone!
 

JL A. (274)
Saturday March 30, 2013, 1:31 pm
You cannot currently send a star to Birgit because you have done so within the last day.
 

janet f. (29)
Saturday March 30, 2013, 3:04 pm
Eco-tourism should not interfere with the survival instincts of the animals. This is just stupidity for money and has no benefit to the animals.
 

JL A. (274)
Saturday March 30, 2013, 3:09 pm
You cannot currently send a star to janet because you have done so within the last day.
 

Angelika R. (146)
Saturday March 30, 2013, 4:56 pm
One of these confusng headlines to me, hard to understand(for me), especially when cut off..
I still don't understand the word "diel", though I read the article. Will these stingrays( not exactly my favs, >i admit) now sufffer from obesity or what ?
 

Angelika R. (146)
Saturday March 30, 2013, 5:00 pm
Why supplemental feeding in the first place, people, especially so called "Ecotourists" would enjoy watching them much more without any kind of human involvement in their natural habits, I think ?
 

JL A. (274)
Saturday March 30, 2013, 6:27 pm
You cannot currently send a star to Angelika because you have done so within the last day.
They get lazy--"The fed animals demonstrated a notable inversion of diel activity, being constantly active during the day with little movement at night compared to the nocturnally active wild stingrays"

di·el
[dahy-uhl, dee-]
adjective Biology .
of or pertaining to a 24-hour period, especially a regular daily cycle, as of the physiology or behavior of an organism.

Night and day behaviors are switched.
 

Suheyla C. (229)
Saturday March 30, 2013, 7:19 pm
Thank you J.L.
 

JL A. (274)
Saturday March 30, 2013, 8:17 pm
You are welcome Suheyla.
 

Tamara Noforwardsplz (185)
Saturday March 30, 2013, 9:40 pm
This was a very interesting article and it has demonstrated, once again, that humans need to stay out of animal habitat and stop trying to make money by disrupting natural behaviors. What are the long term effects going to be for these sting rays? And why do people think they have the right to just jump on in anywhere there is an animal and expect there will be no consequences to their invasions? Humanity just does not get it. Animals have their habitats and we have houses etc. They should not be mixed. Thanks J L.
 

Sherri G. (111)
Sunday March 31, 2013, 2:40 am
Capitalism and greed knows no geographic boundary. Is there any living thing we will not exploit. I am not a scientist but this isn't rocket science either. Mess with any specie's habitat and food something detrimental is going to happen. It will be too late to alter the human meddling which will of course upset the stingrays natural balance. Can't we leave leave the balance of nature to nature?
 

Ruth S. (313)
Sunday March 31, 2013, 6:33 am
They belong in their natural environment.
 

JL A. (274)
Sunday March 31, 2013, 8:02 am
You are welcome Tamara.
You cannot currently send a star toSherri because you have done so within the last day.
You cannot currently send a star to Tamara because you have done so within the last day.
 

Melania Padilla (173)
Tuesday April 16, 2013, 9:55 am
Noted
 
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