|
|
Short-Term Impact
of Vessel Traffic
on the Hawaiian Humpback Whale
(Megaptera novaeangliae)
Marsha Green and Ronald G. Green Albright College
Paper presented at
annual meeting of
the Animal Behavior Society, June 1990, SUNY,
Buffalo, NY
Increasing levels of tourism in the past decade and the resulting increase in vessel traffic in the habitat of humpback whales in Hawaii have caused heightened scientific and public concern around the impact of boats on this endangered species. There is little evidence to suggest either a marked increase or decrease in the number of humpback whales since their protection by international agreement in 1966. Baker et al, 1987 suggest the lack of recovery may be due to a depressed reproductive rate of female humpback whales. The causes of this depressed reproductive success are not known at present but may be related to the increase of vessel traffic.
The near-shore areas appear to be preferred habitat for cow/calf pods throughout the Hawaiian islands (Herman and Antinoja, 1977, Glockner-Ferrari and Ferreri, 1985). Evidence indicates that cow/calf pair prefer the shallow, protected waters for resting, nursing, and possibly avoiding sharks and disturbance by other whales (Glockner-Ferrari and Ferreri, 1985). However, Ferrari's 1985 data indicates that cow/calf pods have been moving offshore since 1977. Abandonment of the near-shore waters could be harmful to the recovery of the Hawaiian humpback whale population as the area available for calving may be a critical factor in determining the eventual size of the population.
In addition to indirect evidence provided by the changes in whale distribution, other studies indicate that boat traffic also has an immediate impact on the behavior of humpback whales. Both Baker et al's (1982, 1983) observations in Alaska and Bauer et al's (1986) research in Hawaii indicate that approaching vessels result in short-term changes in humpback whale behavior including increased time spent underwater and movement away from the path of the vessel. There are several instances when gray whales abandoned certain bays or lagoons and researchers argued that it was due to increased vessel traffic (Gand, 1974, Gilmore and Ewing, 1954).
It is essential that the humpbacks' preferred wintering grounds, and especially the near-shore waters, continue to be available if the species is to reach its optimum population level. Consequently, we began a long term research project to further asses the impact of vessel traffic on the distribution and behavior of the endangered Hawaiian humpback whale. This paper reports the results of the first phase of this project.
Method
Two elevated shore observation sites in west Maui, Hawaii were used to collect data from January through March, 1989. A table of random numbers was used to determine which site would be used on a particular day. The location, movement, and behavior of whales and boats were recorded using a digital theodolite with 30 power magnification. We obtained angles of depression or vertical deviation and angles of horizontal deviation to the object sighted which allowed for an accurate determination of the position of the object relative to the sighting platform.
There were usually four observers at the site. One person specialized in operating the theodolite, one person recorded the data and two people spotted whales and boats with binoculars. Observations were recorded on fifteen pods of whales before, during, and after they were approached within one half-mile by a boat.
Behaviors were initially recorded when there were no boats within two miles of the pod. This was the before boat period. When a boat in the distance appeared to be approaching the pod the movement of the vessel was recorded, as well as the movement and behaviors of the focal pod. A boat period was defined as starting when boat came within 1/2 mile of the pod and lasted for as long as the boat remained within a 1/2 mile radius. After the boat left the 1/2 mile radius, we continued to record whale behavior and movement for as long as the pod remained in clear view. We had no control over the movement of the boats which consisted of fishing boats, speedboats, whale-watch boats, and sailboats under power.
Behaviors in the before boat and boat periods were not significantly variable from one 10 min interval to another 10 minute interval of the same condition. Therefore the analyses were of the entire before boat and boat period regardless of length. Because recovery from a boat must eventually occur, after boat behaviors were analyzed only for the first 20 min after the boat left the 1/2 mi radius. Since some whale behaviors changed significantly from the first 10 min to the second 10 min after a boat left this 20 min period was divided into two 10 min segments, the transition period and the after boat period.
Results
ANOVA's were performed on five different behaviors over the four time periods (before boat, during boat, transition and after boat periods).
The five dependent measures were the percentage of time spent underwater, the maximum down time, the number of surface behaviors, speed of travel and magnitude of direction change.
Percentage Down Time. Down time was counter as anytime the pod was down for more than 30 sec following a fluke up or down dive, a peduncle arch or a slip under. ANOVA showed that pods stayed down a significantly greater percentage of time after the boat period which was the second 10 min time after the boat left than in the other three periods (P<.05)
Maximum Down Time. Maximum down time was the longest single down time in each time period. Maximum down times were significantly longer in the 10 min after boat period than in the transition period (p<.05) and almost significantly longer in the after boat period than the boat period (p <.06). Maximum down times in the first 20 min after the boat left were significantly longer than in the transition period, the boat period or the after boat period. (p<.05).
Miles/Hour. Pods showed a significant decrease in speed in travel in the first 20 min after the boat left the 1/2 mi area as compared to the before boat or boat periods (p<.05).
Surface Behaviors. We created a quantitative measure of surface behaviors in order to do ANOVA. We counted the number of surface behaviors/min for each time period excluding blows, dives, and peduncle arches and divided by the number of whales in the pod to get a measure of "behaviors/min/whale." The most commonly observed surface behaviors were tail slaps, pec fin slaps, and breaches. ANOVA showed no significant changes in numbers of surface behaviors due to the large variability in activity levels between pods. However, the rather dramatic trend was for surface behaviors to decrease while the boat was within 1/2 miles of the pod and for the first 10 min after the boat left. Behaviors were 243% higher in the before boat period as compared to the boat period or the first 10 min after the boat left. In the second 10 min after the boat left surface behaviors started to increase but did not return to the before boat level. In this after boat period surface behaviors increased 157% over behaviors in the boat period.
Change in Direction of Travel. Change in direction of travel was defined as the degree of change in the pod's direction of movement measured in compass points from the end of the before boat period to the end of the boat period. Comparisons of experimental pods with a 20 min no boat period followed by a 20 min boat period to control pods with a 20 min no boat period followed by a second 20 min no boat period showed that experimental pods changed their direction significantly more than control pods from the before boat period (p<.01). The direction of movement was consistently changed to head away from the boat.
Discussion
The results of this study support previous findings that boats have several short-term effects on whales. While a boat was within 1/2 mile of a pod surface behaviors decreased and changes in direction of movement increased. Furthermore our results show the effects of a boat last for at least 20 min after the boat leaves the 1/2 mi area. During the first 20 min after whales significantly increase their maximum dive time and decrease their speed of travel. During the second 10 min after the boat leaves they significantly increase the percentage of time they spend underwater. These results confirm those of previous studies (Baker et al 1982 and 1983; Bauer and Herman, 1986) which reported that humpbacks respond to vessels by decreasing their time at the surface, increasing their dive time and changing their direction of movement.
These results suggest that while in Hawaii whales have two vessel avoidance strategies: a) moving away from a boat that is within 1/2 mile and is approaching and b) decreasing the percentage of time at the surface, increasing maximum dive time and decreasing speed of travel after the boat leaves the 1/2 mi area. Baker, Herman, Bays and Bauer (1983) refer to the second strategy of increased dive time and decreased movement as vertical avoidance. The first strategy of moving away from an approaching boat could be seen as horizontal avoidance.
Dolphin (1987) found that humpbacks in Alaska normally perform dives of less than 4-6 min with an average dive of 2.8 min. The average maximum down times observed in the current study ranged between 4.4 and 5.5 min for all time periods except the after boat period when the average maximum down time was 7.83 min. Dolphin (1987) found that after dives exceeding 6 min in duration, humpbacks showed marked increases in percentages of time spent at the surface. He argued that this increased time at the surface is needed to repay the incurred oxygen debt and return blood pH do predive levels. He also noted that after a series of such dives humpbacks may appear fatigued. Although long dives in Hawaii are probably less stressful than those in Alaska because of warmer water it seems possible that any consequent lowered metabolic rate, circulatory changes, and oxygen debt could especially adversely affect lactating females and the growth and development of calves. This could be particularly detrimental to animals when a series of boats is around them over a long period of time. We frequently observed such a progression of boats around a pod.
If one interprets the behavioral changes we observed as signs of stress, boats nearby for prolonged periods of time could have long term detrimental effects on the physiology and reproductive behavior of whales. Field and laboratory studies show that mammals living under prolonged stressful situations show various physiological and behavioral changes including lowered reproductive rates, decreased lactation, delayed growth and sexual maturation and decreased resistance to disease (Calhoun, 1962m 1973). Some of these effects on reproduction persist even into subsequent generations (Christian, 1978). Stress resulting from increased boat traffic may be one reason for the depressed reproductive rate of female humpback whales (Baker, Perry & Herman, 1987). Consequently, it would seem prudent to develop and implement effective ways to minimize the impact of vessel traffic on the endangered humpback whale.
Since various whale researchers cite the importance of shallow, near-shore waters as important cow/calf habitat it may be especially important to protect these waters in Hawaii from excessive vessel traffic. The Hawaii State Legislature passed a bill in April, 1990 which prohibits the operation of parasail boats, jet skis, and other fast-moving boats in the near-shore waters in south and west Maui. The bill is currently waiting for Governor Waihee's signature.