MARINE MAMMAL SCIENCE, 16(1):65-79 (January 2000) 0 2000 by the Society for Marine Mammalogy

HABITAT USE AND PREFERENCES OF

SOUSA CHINENSIS IN ALGOA BAY, SOUTH AFRICA

INDO-PACIFIC HUMPBACK DOLPHINS

LESZEK KARCZMARSKI] Centre for Dolphin Studies, Port Elizabeth Museum,

P. 0. Box 13147, Humewood 6013 and

Department of Zoology, University of Port Elizabeth, P. 0. Box 1600, Port Elizabeth 6000, South Africa

E-mail: karczmal@tamug.tamu.edu

VICTOR G. COCK CROFT^ Centre for Dolphin Studies, Port Elizabeth Museum,

P. 0. Box 13147, Humewood 6013, South Africa

ANTON MCLACHLAN~ Department of Zoology, University of Port Elizabeth, P. 0. Box 1600, Port Elizabeth 6000, South Africa

ABSTRACT

This paper examines environmental and behavioral determinants of the habitat use and preferences of Indo-Pacific humpback dolphins inhabiting the Algoa Bay region on the south Eastern Cape coast of South Africa. In order to quantify the habitat use and preference, two indices were used, the Coef- ficient of Area Use (AU) and the Activity Index (AI). The dolphins inhabit a narrow strip of shallow, inshore waters of Algoa Bay and remain mostly within 400 m of the shore, in water less than 15 m deep, with no apparent preference for clear or turbid water. Water depth is probably the main factor limiting their inshore distribution, and the 25-m isobath seems to represent the critical depth. Within this confined, inshore distribution, dolphin activ- ities concentrate in the vicinity of rocky reefs-their primary feeding grounds. Dolphin dependence on these shallow-water habitats is evident throughout the year and, consequently, the inshore shallow reefs are identified as the “key habitat” which is of primary importance for humpback dolphins in Eastern

Present address: Marine Mammal Research Program, Texas A&M University at Galveston,

Present address: Centre for Dolphin Studies, P. 0. Box 1856, Plettenberg Bay 6600, South 4700 Ave. U, Bldg. 303, Galveston, Texas 77551, U.S.A.

Africa. 5 Present address: College of Science, SQU, P. 0. Box 36, SQU 123, Oman.

65

66 MARINE MAMMAL SCIENCE, VOL. 16. NO. 1. 2000

Cape waters. The dolphins’ dependence on this restricted type of habitat within an already restricted inshore distribution makes them particularly vul- nerable to alteration or loss of this habitat.

Key words: Indo-Pacific humpback dolphin, Soma chinensis, inshore distri- bution, habitat preference and use, behavior, Coefficient of Area Use, Activity Index, coastal zone conservation/management, Algoa Bay-Eastern Cape-South Africa-Indian Ocean.

Habitat-use patterns are commonly believed to be a function of the habitat heterogeneity and the biological requirements of a species (Rosenzweig 198 1). A population’s home range typically represents a heterogeneous environment where areas rich in resources are scattered throughout areas poor in resources. While the abundance, distribution and availability of resources within the environment determine the size of an area which will fulfil the animals’ bio- logical requirements, the varied use of habitat patches indicate the importance of various habitats in their daily lives (McNab 1963, MacAtthur and Pianka 1966, Samuel et al. 1985, Brown 1988). The home range of any wild animal population needs to encompass a minimum amount of the preferred habitats (so called “key habitats”) and is likely to be larger when patches of these habitats are smaller and more dispersed. An adequate identification of key habitats within a population’s home range, and core areas where biologically and socially important behaviors concentrate, is an important part of under- standing the species’ ecology and crucial for the conservation and management of any wild animal population.

Indo-Pacific humpback dolphins inhabit coastal waters of the Indian Ocean and western Pacific (Ross et al. 1994) and are known to occur along the east and south coast of South Africa (Ross 1984). These coastal dolphins do not appear to be abundant anywhere, and their inshore distribution renders them particularly susceptible to the effects of human activities in the coastal zone and general degradation of inshore habitats (Klinowska 1991, Reeves and Leatherwood 1994, Cockcroft and Krohn 1994). In South Africa there is a great deal of concern regarding the continued survival of this species, and the problem appears to be particularly severe in KwaZulu-Natal waters, where the continuing incidental mortality of humpback dolphins in shark nets could lead to their local extirpation (Cockcroft 1990, 1994).

There have been very few studies of humpback dolphins (e.g., Saayman and Tayler 1979), and in general the species remains poorly known. There was an obvious need for more detailed study, which would contribute to our knowl- edge of this species and help to formulate conservation recommendations. This paper reports part of a larger ecological research of humpback dolphins in the Algoa Bay region (Karczmarski 1996) and presents results of an attempt to learn about their habitat preferences and pattern of habitat use in the inshore waters of Algoa Bay. Data presented here provide the basis for identifying humpback dolphin critical habitats in Eastern Cape waters, which should be considered in integrated coastal zone management. Furthermore, this work represents an important step towards understanding the dependence of these

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KARCZMARSKI ET AL.: INDO-PACIFIC HUMPBACK DOLPHINS 67

animals on the restricted, shallow-water, inshore marine environment and, as such, should be of value in other areas where there is little knowledge of humpback dolphins and their ecological requirements.

METHODS

Study Area

Algoa Bay is the easternmost and largest of several half-heart-shaped bays found on the southeast coast of South Africa (Fig. 1). The Bay is flanked on the western side by Cape Recife (34"02 'S , 25'42'E) and on the eastern side by the less prominent Cape Padrone (33"46 'S , 26"28'E). Over most of Algoa Bay the depth is <50 m (Fig. 1). The mean spring and neap tidal ranges are 1.61 m and 0.51 rn, respectively.

68 MARINE MAMMAL SCIENCE. VOL. 16. NO. 1. 2000

Survey Procedure

Sea- and land-based surveys were undertaken over approximately 55 km of coastline of the southwestern part of Algoa Bay (Fig. 1) throughout a three- year period, from May 1991 to May 1994. Daily land-based surveys usually started 1-2.5 h after sunrise (weather permitting) and were conducted by one, or occasionally two, observers. Observations of the inshore waters to approxi- mately 1 km offshore, were carried out from several, in many cases visually overlapping, vantage points. The coastal zone was scanned with both the un- aided eye and binoculars for 10 min at each vantage point, with equal level of search effort allocated to “inshore” (1500 m of the shore) and “offshore” (>500 m to approximately 1 km offshore) “sections” of the coastal waters. Two pairs of hand-held binoculars (9 X 35 and 20 X 60) were used. The sea state equivalent to Beaufort Scale 3 was the upper limit for the surveys to be continued.

Sea-based surveys were opportunistic and limited by both the presence of dolphins and weather conditions. Once a group of dolphins was sighted from land, a photo-identificarion boat survey was launched. Sea work was conducted using a 3.5-m inflatable boat powered by a 30-HP outboard engine. Initially, the boat progressed approximately 1 km past the dolphin group, to ensure that all members of a group were located. Dolphins were photographed using a motorized camera equipped with a variable length (70-210 mm, maximum aperture 1:3.6) lens and 100 ASA color positive film. Individuals were sub- sequently identified following the procedure described by Karczmarski and Cockcroft (1998). Water clarity (Secchi disc depth) was recorded, starting from January 1992.

During boat surveys the maximum possible time was dedicated to following dolphin groups and recording their membership (ID photographs), activities and habitat use. Consequently, although any one survey could cover a maxi- mum of about 55 km of coastline, the length of surveys varied considerably (min. = 12 km; max. = 35 km), as did the time spent at sea. When the weatherhea conditions precluded boat surveys, the activity and movement of dolphins were monitored from land-based vantage points. When a group of dolphins was sighted and the dolphin follow begun, searching for other groups was limited to the area within visual range from the first group. Estimates of group size and composition were repeated several times during a survey. Group activity/behavior (the predominant activity of the majority of the group mem- bers) was recorded at the commencement of each sighting and, thereafter, randomly in 5-min intervals throughout the survey. For each of the 5-min intervals, the length of time spent in different behaviors (see definitions below) was estimated as a percentage. The location of dolphin groups and direction of movement were repeatedly recorded using landmarks and subsequently plot- ted on a chart. The water depth was estimated from hydrographic charts (S.A. Navy) and bathymetry maps (S.A. Geological Survey).

For comparative purposes, several boat surveys were performed in the south- western part of St. Francis Bay, along about 20 km of coastline, with the most

KARCZMARSKI ET AL. : INDO-PACIFIC HUMPBACK DOLPHINS 69

southerly point at Cape St. Francis (Fig. 1). Occasional shore-based surveys took place in Sardinia Bay, Sea ViewIMaitlands River beach, off Van Stadens River mouth, Gamtoos River mouth, and in Jeffreys Bay (Fig. 1).

Data A na lysis

The number of sightings (groups or solitary animals) recorded in Algoa Bay was corrected for effort (number of hours). The stretch of coastline with fre- quent sightings was then divided into 31 sectors, each approximately 500 m in length. A Coefficient of Area Use (AU) , which ranges from 0.0 to 1.0 and represents the time spent by dolphins in a particular sector as a proportion of the total observation time in that day, was calculated for each of these sectors as AU = 012; where D is the time spent by dolphins in a particular sector, and T is the total observation time on any one day.

If the localization of dolphins in a particular sector was not clear, they were considered to be in both neighboring sectors. Subsequently, a mean Coefficient of Area Use was calculated for each of the 31 sectors. General structure of the seabed (the ratio of rocky reef to sandy bottom expressed as percentage) in each of these sectors was assessed using aerial photographs (photographs by W. L. Illenbetger, Long Term Monitoring Program, Institute for Coastal Re- search, University of Port Elizabeth) and side-scan sonar data (H. Phipps, S.A. Geological Survey, Cape Town).

Dolphin activity over this stretch of coastline was quantified using an Ac- tivity Index (Al). This index (ranging from 0.0 to 1.0) was used to represent the time the animals were engaged in a particular activity (behavior) within a sector, as a proportion of the total time spent by dolphins in this sector during any one day: A1 = BIS, where B is the time dolphins were engaged in a particular activity (behavior) within a sector, and S is the time spent by dolphins in any one sector. The Index of Activity, and subsequently mean Al, were calculated separately for each of the four categories of behavior (see def- init ions below).

Definitions

Behavior of dolphins is classified into four categories (see also Karczmarski and Cockcroft 1999):

Foraginglfeeding-consisted of frequent and asynchronous dives in varying directions in one location; surfacing and respiration displayed no obvious pat- tern; dolphins often chased fish, and occasionally fish capture was seen.

Travelling-consisted of persistent, directional movement, with all group members diving and surfacing synchronously; chasing of fish or even social behavior were extremely uncommon during this behavior.

Resting-consisted of a low level of activity, with the dolphins apparently floating stationary and motionless at the surface, with some occasional slow forward movement.

Socializing and playing-consisted of various vigorous activities including

70 MARINE MAMMAL SCIENCE, VOL. 16, NO. I , 2000

leaping out of the water, riding waves in the surf zone, high speed movement with frequent direction changes and prolonged body contact with other dol- phins.

The term “group” refers to any aggregation of more than one dolphin, including all age classes, within visual range of the survey team. Typically, these animals were in apparent association and engaged in similar activities for most of the observation period. Each time a group was observed, i t was recorded as a “sighting.” The term “sighting,” however, has a wider meaning and includes solitary animals.

Two seasons, summer and winter, are distinguished here. “Summer” is de- fined as the period when the mean temperature of the inshore surface water is higher than the annual mean (18°C). The period when the surface water temperature drops below this annual mean is referred to as “winter” (for details see Karczmarski 1996, Karczmarski et al. 1999). In general, the first days of May mark the beginning of “winter” and late October marks the beginning of “summer”.

RESULTS

Data Base

Groups and solitary humpback dolphins were seen 113 times and observed for over 320 h. The majority of times (104) were in Algoa Bay. Two sightings each were recorded in Sardinia Bay, off Van Stadens River mouth and Cape St. Francis and one sighting each in Noordhoek (the ocean side of Cape Recife), Maitlands River beach/Sea View, and off Jeffreys Bay beach (Fig. 1). Seventy- seven sea-based surveys were completed, 68 in Algoa Bay and nine in St. Francis Bay (189 h of direct dolphin follows). Photographs recording group membership were taken during 60 sea surveys (162 h), of which 58 (157 h) were in Algoa Bay.

Dzstribzctzon of Szghtingj

During shore-based surveys in Algoa Bay, humpback dolphins were pre- dominantly seen within 200-400 m of the shore (58.6% of sightings), in water less than 15 m deep (91.3% of sightings) (Fig. 2), and generally re- mained there for the entire duration of the observation time (including both the shore-based surveys followed by photo-ID boat surveys and the exclusively land-based surveys). During only six sightings (5.8%) were dolphins seen ven- turing >500 m from the shoreline. Five of these groups were being followed by boat and two of them were seen venturing about 1-1.5 km offshore (depth 20-<25 m). In all these instances the animals were travelling and the events were short-term, with the dolphins moving back inshore after about an hour.

Humpback dolphins were recorded with similar frequency throughout the tidal cycle and often remained in the area for several hours apparently unaf- fected by the changing tide (see also Karczmarski and Cockcroft 1999, Kar-

KARCZMARSKI ET AL. : INDO-PACIFIC HUMPBACK DOLPHINS 71

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Fzgure 2. Distribution of sightings of Indo-Pacific humpback dolphins (A = dis- tance offshore, B = water depth) recorded in Algoa Bay between May 1991 and May 1994.

czmarski et al. 1999). Sightings occurred throughout a wide range of water clarity conditions (2.25-12.0 m) with a mean Secchi disk reading of 4.5 m during both winter (n = 16, SD = 1.67) and summer (n = 31, SD = 1.80) and no obvious preference for any particular water clarity conditions. There was little difference in water clarity recorded during photo-ID boat surveys from that as sampled randomly during dolphin absence (Mann-Whitney, U = 843.00, n = 97, P > 0.2).

72 MARINE MAMMAL SCIENCE, VOL. 16, NO. 1, 2000

Figure 3. Pattern of habitat use displayed by humpback dolphins along 15 km of coastline between Cape Recife and Port Elizabeth harbor (a) (above). Mean Coefficient of Area Use (b) (see p. 73) and mean Activity Index for various categories of behavior (c) (see p. 74) were calculated for three-year period between May 1991 and May 1994. Error bars indicate one standard deviation. Distribution of inshore rocky reefs according to aerial photographs and S.A. Geological Survey side-scan sonar data.

During the majority of surveys in Algoa Bay (91.3%), the animals remained for several hours within the 15-km-long stretch of coastline between Cape Recife and Port Elizabeth harbor (Fig. 3a). Sightings northeast of Port Eliz- abeth harbor were extremely rare (n = 3). Although during -29% of sight- ings, dolphins, after spending several hours in the area between Cape Recife and Port Elizabeth harbor, were seen moving past the harbor area in a north-

KARCZMARSKI ET AL.: INDO-PACIFIC HUMPBACK DOLPHINS 73

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easterly direction, they displayed little behavior other than fast, directional movement (travelling).

Of the nine sightings of humpback dolphins recorded outside Algoa Bay, all occurred <500 m from the shore, in water <20 m deep, with five of these sightings in water 1 1 5 m deep.

Pattern of Habitat Use

Dolphin activity was not evenly distributed over the 31 sectors (each a 500- m length of coastline) of the most extensively used stretch of coastal zone between Cape Recife and Port Elizabeth harbor (Fig. 3a). AU varied signifi- cantly between sectors (Kruskal-Wallis ANOVA, K W = 192.29, n = 640, P < O.OOOl), with high values significantly correlated with the distribution of natural and man-made reefs (Spearman Rank Correlation, r = 0.73, n = 31, P < 0.0001) (Fig. 3b). This pattern was similar for both summer and winter (Mann-Whitney, U = 454.00, n = 31, P > 0.7).

A1 varied significantly between sectors for travelling (Kruskal-Wallis AN- OVA, K W = 139.49, n = 338, P < 0.0001) and foraginglfeeding (Kruskal- Wallis ANOVA, K W = 117.42, n = 343, P < O.OOOl), but not significantly for resting (Kruskal-Wallis ANOVA, KW = 21.02, n = 112, P > 0.1) nor

7 4 MARINE MAMMAL SCIENCE, VOL. 16, NO. 1, 2000

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for socializing and playing (Kruskal-Wallis ANOVA, KW = 20.41, n = 186, P > 0.4). The mean A1 for travelling was considerably higher along open stretches of coastline, sandy shores, and sectors with extensive human activity (sea traffic, tourists, etc.). In contrast, foraginglfeeding was more intensive in the vicinity of shallow rocky reefs and relatively sheltered areas (Fig. 3c). Generally, the proportion of shallow rocky reefs in each of the 31 sectors was significantly correlated with the mean AI for foraging/feeding (Spearman Rank Correlation, r = 0.70, n = 29, P < O . O O O l ) , but signifi-

KARCZMARSKI ETAL. : INDO-PACIFIC HUMPBACK DOLPHINS 75

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Figure 4. Values of mean Activity Index (AZ) calculated for various behaviors dis- played by humpback dolphins in sectors with high mean Coefficient of Area Use ( A U ) in southwestern Algoa Bay between May 1991 and May 1994.

cantly negatively correlated with the mean A1 for travelling Y = -0.60, n = 29, P < 0.001).

Despite high A1 values, foraginglfeeding along the Port Elizabeth harbor wall was observed only in the early morning, and the area was generally avoided when inshore boat traffic increased. The mean AIs for resting and socializing and playing were low across all sectors (Fig. 3c) and not correlated with the general structure of the seabed (Spearman Rank Correlation, r = 0.32, n = 29, P > 0.1 and Y = 0.27, n = 29, P > 0.1, respectively).

For the most extensively used sectors of coastal zone (mean AU 2 %T, where T represents the highest mean A U ) AI varied significantly between the four categories of behavior (Kruskal-Wallis ANOVA, K W = 306.90, n = 696, P < 0.0001). The dominant behavior was foraging/feeding (Dunn's Multiple Comparisons Test, P < O.OOl) , with the mean AI value across all these sectors (0.75) at least three times higher than the mean A1 value for other categories of behavior (Fig. 4). In the remaining part of the 31 sectors (mean AU < %T), A1 values also varied significantly between behavioral categories (Krus- kal-Wallis ANOVA, K W = 95.86, n = 283, P < 0.0001) with travelling being dominant (Dunn's Multiple Comparisons Test, P < 0.001). However,

76 MARINE MAMMAL SCIENCE. VOL. 16. NO. 1. 2000

the differences between A1 values were less prominent, with mean A1 for travelling about twice that for foraging/feeding.

During all sightings of humpback dolphins outside Algoa Bay, foraging/ feeding was observed only along rocky shores, while travelling was seen along both rocky and sandy coastal zones.

DISCUSSION

Humpback dolphins inhabit a narrow strip of shallow inshore water off Algoa Bay and display no apparent preference for clear or turbid water. Their activities are not evenly distributed over the coastal zone, and their preference for shallow rocky reefs, which form their primary feeding grounds, is evident throughout the year.

With over 80% of sightings recorded in Algoa Bay within <400 m of the shore, it needs to be stressed that there is a possible bias introduced by the obvious decrease in sighting efficiency with increasing distance from the shore. In other words, offshore groups of dolphins have lower “probability” of being seen. Nevertheless, whenever seen from the shore or followed by boat, hump- back dolphins remained in very close proximity to the shore, generally well within what could be called a visual limit for the land-based observations. Furthermore, the restricted shallow-water and predominantly inshore distri- bution of humpback dolphins has also been reported by several other research- ers (for review see Ross e t al. 1994). The only known sightings of humpback dolphins several kilometers from the shore occurred in areas where the water was still shallow (Corkeron 1990, Durham 1994). Consequently, water depth is suggested to be the main factor limiting the species’ inshore distribution. With respect to water depth, humpback dolphins display less ‘‘flexibility” than some other coastal cetaceans. Bottlenose dolphins, for instance, although also occurring predominantly close inshore in Algoa Bay, ventured into waters about 25-30 m deep and 2.5-3 km offshore far more often than did hump- back dolphins (L. Karczmarski, unpublished data). This was also observed in Plettenberg Bay (Saayman and Tayler 1979) and along the KwaZulu-Natal coast (Durham 1994).

In Algoa Bay, humpback dolphin activities concentrated along a stretch of coastline between Cape Recife and the Port Elizabeth harbor, within which are abundant rocky reefs and coves. This part of the bay’s coastal zone contrasts with that northeastward of the harbor, which is characterized by an exposed sandy shoreline. Humpback dolphins were seldom seen along this sandy coast- line, and those seen were amongst the smallest groups. It is likely that the long stretch of exposed sandy shoreline of northeastern Algoa Bay offers fewer prey resources and therefore is not particularly attractive to humpback dol- phins. If so, an extensive sandy coastline lacking inshore reefs or estuarine systems, could possibly form an ecological (or even geographical) barrier, lim- iting humpback dolphin movement/distribution.

Although the diet of humpback dolphins has been poorly documented, they seem to feed predominantly on estuarine and reef-associated fish and neritic

KARCZMARSKI ET AL. : INDO-PACIFIC HUMPBACK D O L P H I N S 77

cephalopods (Barros and Cockcroft 199 1). The shallow inshore reefs preferred by humpback dolphins in Algoa Bay constitute important nursery areas for several fish species off the South African coast (Wallace 1976). Thus, hump- back dolphins in Algoa Bay appear to be found mostly in the areas of greatest abundance of their prey. The inshore reefs in Algoa Bay serve a specific be- havioral function and are the focus of most of the dolphins’ foraging/feeding activity, as observed also in Plettenberg Bay, about 250 km to the west (Saay- man and Tayler 1979).

In KwaZulu-Natal, humpback dolphins prefer the vicinity of large estuarine systems, which are thought to be particularly abundant in prey species (Dur- ham 1994). A similar distribution, but including also mangrove-based coastal lagoons, has been reported for other areas (Ross e t al. 1994). However, the Eastern Cape estuaries are generally small and shallow and probably support relatively low numbers of inshore prey, which explains why little activity of humpback dolphins was recorded there. A number of animal species, both marine (e.g., Garshelis and Garshelis 1984, Hanson and Defran 1993) and terrestrial (e.g., De Vore and Hall 1965, Whitten 1982), are known to move quickly over areas with few food resources and spend extended periods of time in areas with abundant food.

It seems likely that the apparent preference for turbid waters observed in humpback dolphins in some areas (Corkeron 1990, Durham 1994) is a sec- ondary result of their preference for a shallow-water coastal habitat and dis- tribution of their prey. An increased abundance of prey species will attract humpback dolphins to turbid waters of large estuarine systems (e.g., Richards Bay in northern KwaZulu-Natal, Durham 1994), as well as to clear waters around shallow rocky reefs (present study). As reported here for Algoa Bay, Saayman and Tayler (1979) often observed humpback dolphins along rocky coastlines in Plettenberg Bay in water with clarity of up to 24 m.

Humpback dolphins in Algoa Bay did not display a clear habitat preference for resting and socializing and playing. It is possible that these behaviors depend predominantly on the previous sequence of behaviors (see also Kar- czmarski and Cockcroft 1999), not the habitat, as suggested for killer whales (Orcznw orca) in the Pacific Northwest (Heimlich-Boran 1988).

The apparent lack of seasonal differences in the pattern of area/habitat use by humpback dolphins in Algoa Bay suggests that although the abundance of inshore resources seems to vary seasonally (as discussed in Karczmarski 1996, Karczmarski et al. 1999), areas around inshore reefs, at least in the Eastern Cape waters, provide the largest quantity of prey and represent the key habitats for this dolphin species throughout the year. Thus, humpback dolphins appear to be dependent on a restricted type of habitat within an already restricted inshore distribution. They are, consequently, particularly vul- nerable to alteration or loss of this habitat. The small size of humpback dol- phin groups and their generally low population numbers (Karczmarski 1996) may possibly reflect a low carrying capacity of inshore waters.

Identification and subsequent protection of habitats critical to dolphins seems one way of ensuring a sufficient amount of space, shelter, and food for

78 MARINE MAMMAL SCIENCE, VOL. 16, NO. 1 , 2000

the animals. In Eastern Cape waters where the inshore shallow reefs are of primary importance for humpback dolphins, coastal developments which in- clude shoreline alteration, siltation, or removal of coastal reefs should be planned carefully. A large alteration of the rocky shoreline could destroy dol- phin feeding grounds and/or reduce the nursery areas of dolphin prey species. On a larger scale, however, both the habitat quantity and quality need to be considered. The habitat quantity scales the total population size and may influence aspects of its distribution. The habitat quality or, in other words, the ecological status of the environment, abundance of resources (food, shelter, breeding sites, etc.), and degree of disturbance, determines the adaptedness of the species and probability of its continuous survival (Gilpin and Soul6 1986). Consequently, the conservation of humpback dolphins needs to be seen as an integral part of the conservation and management of the coastal zone ecosys- tem. Where this is not sufficiently appreciated, the marine habitat deteriorates, as do inshore delphinid populations.

ACKNOWLEDGMENTS

This work would not have been possible without the financial assistance of the Foundation for Research Development (FRD) and W W F South Africa, which are grate- fully acknowledged. We wish to express our thanks to Werner L. Illenberger (Long Term Monitoring Program, ICR, University of Port Elizabeth) for providing us with aerial photographs of the Algoa Bay region and to Hayden Phipps (S.A. Geological Survey, Cape Town) for the side-scan sonar data. The indispensable help of Meredith Thornton, Jimmy Henderson, and Shane Norris during many hours of field-work will always remain greatly appreciated. Lastly, the senior author wishes to thank An De Ruyck and Deo Winter of the Zoology Department, University of Port Elizabeth, for their invaluable support throughout the study.

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KARCLMARSKI, L. 1996. Ecological studies of humpback dolphins Soma chinensis in the Algoa Bay region, Eastern Cape, South Africa. Ph.D. thesis, University of Port Elizabeth, Port Elizabeth. 202 pp.

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Received: 2 1 September 1998 Accepted: 16 March 1999