Distribution habitat use and behaviour of cetaceans in the Greater Dyer Island area Western Cape South Africa

Abstract

This thesis is a study of the occurrence, behaviour, spatial distribution, and temporal distribution of cetaceans in the Greater Dyer Island area, Western Cape, South Africa. Three main methods were used in the study: Analysis of data from a local whale-watching vessel (WWV) (2000 2012), visual land-based theodolite tracking (during four southern right whale seasons (August December) from 2011 2014 and one summer/autumn season in 2013), and passive acoustic monitoring (PAM) using a single bottom moored hydrophone (DSG-Ocean Loggerhead) in the months of January/February, September, and October, 2014). Methods were chosen, due to suitability, cost efficiency, and because they complement each other. Data from the WWV covered more than a ten-year period and provided indications of temporal and spatial distribution trends, but data were limited with respect to survey effort and behavioural data. Shore-based observations provided spatial, temporal, and behaviour patterns of the cetacean species in the area, but the method is labour intensive, requires daylight and is restricted by weather conditions. PAM could be conducted 24 hours a day and in poor weather conditions and enabled a temporal extension of the monitoring of cetaceans in the area, but individual hydrophones, are expensive and can break down or be lost. Simultaneous visual observations and PAM were used to investigate the vocalisation patterns of southern right whales and the possibility of using PAM to monitor presence of southern right whales. An analysis of the consistency and validity of the opportunistic data from the WWV was conducted before the data was used in a spatial and temporal analysis. The Consistency Index (CI) was defined as the proportion of times a data field was recorded per total number of trips during all years. The validity of the data were assessed to determine accuracy of the data. The validity and consistency analysis of the sighting records revealed that the dataset was useful but data fields varied considerably in their consistency of collection. The trip duration and route was recorded in less than 5% of cases, making analysis of temporal and spatial patterns difficult. The validity of species identification was excellent with 100% agreement between observer records and photographic documentation in 152 encounters of seven cetacean species. Behavioural data were described in overly subjective terms, thus not allowing for any analysis of patterns. The analysis also resulted in a list of suggestions for the design of future observation sheets, and data collection methods and the development and implementation of worldwide standards are encouraged (guidelines and protocols), which should address different levels and scenarios of data collection from WWV. This work has made a novel contribution to the global research field by submission of a paper and direct communication with the whale watching subcommittee at the International Whaling Commission (IWC) concerning content in the International guidelines for platform of opportunity guiding principles on data collection . An analysis of opportunistic cetacean sightings from the local WWV consisted of more than 5500 cetacean encounters during more than 2500 trips from 2003 to 2012. Results were twofold; 1) discovering that there are five main cetacean species using the area: Southern right whales (Eubalaena australis), humpback whales (Megaptera novaeangliae), Bryde s whales (Balaenoptera brydeii), Indian Ocean humpback dolphins (Sousa plumbea), and Indo-Pacific bottlenose dolphins (Tursiops aduncus) and providing spatial and temporal distribution patterns for these species as well as the first long-term, year round dataset for this area. Three other species of incidental visitors were: Common dolphins (Delphinus delphis), killer whales (Orcinus orca) and Heaviside s dolphins (Cephalorhynchus heavisidii). 2) Showing that opportunistic data of cetacean encounters collected regularly from a WWV constitute an important source of baseline information of the wildlife abundance and distribution. Caveats and limitations of data from the WWV are discussed and advice regarding data collection from platforms of opportunities are provided. Particularly, the lack of basic data on search effort and of clearly defined behavioural categories is emphasised and standardisation of guidelines for data-collection methods worldwide is suggested. Southern right whales were by far the most frequently occurring cetaceans with a marked seasonal presence from August to December. Numbers peaked consistently between June and January each year and only a single encounter was recorded between 31 January and 26 May in the entire dataset. They appeared either as unaccompanied adults (UAs), as part of surface active groups (SAGs) or as cows accompanied by their calves (cc-pairs). Single right whales were more commonly encountered at the beginning of high season (June September) while groups of two or more were most commonly encountered in the middle of the season (July September) and the modal group size was two. Cow-calf pairs were encountered most frequently late in the season with highest encounters in October December. All right whales were predominantly located close to shore, as were the two main dolphin species. Bryde s whales and humpback whales were located farther from shore. Bryde s whales were observed in all years, except 2006. The highest encounter of Bryde s whales were between March and May. Bryde s whale calves were encountered year round. The highest number of encounters occurred during 2003 (n= 25), dropping to 0 in 2006 and then slowly increased at 1% per annum after 2006. Humpback whales showed two peaks in seasonality: the majority of animals were encountered in June (last month of low season), July and August, with a much smaller peak in late November and December. Most encounters with humpback whale cow-calf pairs occurred during October December. Humpback whale encounters varied considerably from year to year, with most encounters in 2008 (n= 28), 2011 (n= 15), and 2012 (n=12), but showed a slow average increase at 0.4% per annum. Encounters of Indian Ocean humpback dolphins were more frequent during summer months, and most encounters occurred in 2003-2007 and in 2011, a slightly negative annual trend existed (0.9%). Calves were mainly encountered occurring in December (n = 25) and January (n = 12). Indo- Pacific bottlenose dolphins showed a clear seasonal peak occurred from December to April and most encounters occurred in 2004-2006 and in 2009 with a slightly negative annual trend over time (0.2%). Seasonality of calves followed the same pattern of as adults. This study was the first to reveal that there are five cetacean species using the area and provide temporal and spatial patterns based on long term data. Shore-based observations, using a surveyor s theodolite, enabled an analysis of behaviour in addition to confirming the spatial and temporal distributions of cetacean species obtained from the WWV-data. Hourly scans were conducted to provide information on species presence, location, group size, group composition, and surface behaviour. In addition, focal groups that were tracked provided and detailed information on movements and behaviours. Effort totalled 1558 hours and 26 minutes (1204 scans) over 270 days between 24 August 2011 and 11 December 2014. All sighting data were filtered to remove periods of poor weather conditions, only observations collected at sea state ? 2 for dolphin species, and ? 5 for baleen whales were analysed. The area is an important location for nursing and socialising southern right whales and it might be a summer feeding area for Bryde s whales. The primarily observed behaviour of humpback whales was travelling and 80% of the tracked animals were travelling south-east towards Cape Agulhas. Finally, it was found that the area serves as a year round socialising and resting area for the two dolphin species. Swimming speed was calculated, using the longest focal follow from each day for southern right whales and all focal follow tracks of dolphin species. All southern right whales were found to be swimming at a speed less than 5.1 km/h.