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Sharkbites Saturday

Ecotourism may impact white shark activity levels

Article: Huveneers C, Watanabe YY, Payne NL, Semmens JM (2018) Interacting with wildlife tourism increases activity of white sharks. Conserv Physiol 6(1): coy019; doi:10.1093/conphys/coy019.

Guest author: Jamie Lockwood

Introduction

Wildlife tourism is becoming increasingly more prevalent, and as a result humans are interacting with wild animals that previously were more secluded. This interaction calls for the research of how targeted species might be affected. White sharks were specifically chosen for this study because of the blossoming tourist attraction of cage-diving offered in Australia, South Africa, the United States, Mexico, and New Zealand. Their ominous size and elusive nature have made them a tourism magnet.

This study set out to determine if individual health of white sharks was affected by the growing cage-diving industry. It was hypothesized that sharks would become more active as their interaction with cage-diving vessels increased. The findings of this study will help create a more complete understanding of how human activity can impact individuals and subsequently their ecological environments.

Methods

Three cage-diving vessels were monitored to survey the South and North Neptune Island regions which are approximately 30 km south of the Australian mainland. Two boats appealed to the sharks’ sense of olfactory through chum which consisted mostly of southern Bluefin tuna. However, the third boat used audio to bait white sharks towards the vessel. Individual sharks were monitored with tags that measured and recorded swim speed relative to an attached propeller, depth, temperature, and acceleration. The tag was designed to detach from the shark after about one week, and would float to the surface to be collected by the researchers. The sharks’ activity was monitored and analyzed in relation to their interactions with the cage-diving ships. A calculated value of average overall dynamic body acceleration was used as a proxy for metabolic rate, so that conclusions about energy usage and cost could be drawn from this study.

The study consisted of ten individual sharks which were all studied in this manner. Their movements were recorded in multiple different contexts to create base movement data. These contexts included: when sharks were in the Neptune island area but cage-diving boats were not, when sharks were in the area but not interacting with the present cage diving boats, during the night when there is no cage diving, and when there were not in the area at all. These contexts help create a more complete display of how white sharks regularly spend their energy. These scenarios created multiple controls so that when compared to the activity spent while sharks were interacting with cage-diving boats, more significance could be drawn.

Example of an accelerometer package deployed on a white shark (Carcharodon carcharias) (From Huveneers et al. 2018).

 

Results

Plots showing the effects of different contexts on white shark activity metrics. Median values are indicated by the bold horizontal bar; the length of the box is the inter-quartile range; whiskers represents 1.5 inter-quartile range; circles are outliers; and asterisks are extreme values (From Huveneers et al. 2018).

The most compelling metric that sets apart shark interactions with all other measurements was the frequency of burst movements during one hour. Burst events were defined based off of a shark’s overall dynamic body acceleration (ODBA) and are further described as short energy spurts that a shark expends to suddenly and dramatically increase swim speed. The amount of burst events was 61% higher in interaction contexts than all other scenarios. Other metrics like swim speed and tailbeat frequency were similar between the assessed situations.

In all, it was found that the data collected when sharks were interacting with the vessels was significantly different from all other movement contexts supported mostly by the amount of burst events, overall dynamic body acceleration, and the number of ascensions.

Discussion

Based on this study, it is evident that white sharks increase their activity during interactions with cage-diving operations. This suggests that the cage-diving industry could influence white shark energy budgeting and usage. In normal circumstances, a white shark expends bursts of energy with the goal of caloric intake. In which, the biological benefit outweighs the energy cost. However, it is against industry regulations for cage-diving operators to feed white sharks, and there are strict limits on how much bait may be deployed. Therefore, the energy white sharks are spending during their interactions with cage-diving vessels is not rewarded. As apex predators, this not only affects the individual sharks, but seemingly all other organism that share their habitat. In the event that white sharks waste too much energy entertaining the cage-diving industry, less energy can be budgeted on hunting, which helps regulate population sizes of fishes and other organisms that fall below white sharks on the food chain. The study provides an example of how wildlife tourism affects marine life on an individual basis, but hints towards how an entire ecosystem might be negatively affected. This gives us a more complete understanding of how anthropogenic influences yield behavioral responses from wildlife.

 

 

 

 

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