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Marine Research

 

Opportunistic boat-based data collection with Ocean Blue Adventures

We regularly join Ocean Blue Adventures on their commercial whale and dolphin watching trips to record opportunistic sightings of marine animals such as whales, dolphins, seals, sharks, seabirds and turtles. When whales and dolphins are encountered we take dorsal fin photographs for photo-identification. Sightings of injured and entangled seals at the Robberg colony are also recorded to tie in with ongoing seal-shark and seal-fisheries interaction research. All data is intended for use in collaborative research and citizen science projects, and will provide us with information on aspects such as the spatial distribution of various species within the bay, individual movement patterns, changes in group sizes and population health.

Plettenberg Bay humpback dolphin project

We are currently in the process of establishing a monitoring project which will focus on the endangered Indian Ocean humpback dolphin. The species was recently listed as endangered in South African waters and faces a number of anthropogenic threats due to its preference for shallow coastal waters. With an estimated population size of 500 individuals, it is considered to be South Africa’s most endangered resident marine mammal. Dedicated boat-based surveys will be conducted each month to collect sighting and photo-identification data. This project will be run in collaboration with Nelson Mandela University and data will contribute towards collaborative research projects which aim to increase our knowledge of the species, assess trends in population numbers and inform conservation and management decisions.

Marine mammal stranding response and necropsy

In collaboration with the Port Elizabeth Museum, our researchers regularly attend to dead whales, dolphins and seals ashore to collect entire carcasses or parts thereof, perform necropsies (dissections) and temporarily store samples for research and collection purposes of the museum. Samples are used in various ongoing studies on marine mammal morphology, taxonomy, population structure, diet, health, fisheries interactions and predator-prey interactions. They also attend to live seals ashore to capture, hold in temporary confinement, tag, move and/or release them.

Seal population growth monitoring

As part of ongoing collaboration with the Port Elizabeth Museum, our researchers perform dedicated boat-based surveys to Robberg Peninsula to monitor the number of seals that haul out, and, from November-February the number of new-born pups. This long-term monitoring project will allow further examination of local seal population growth. It will also allow new research on the impact of easterly storms on pup survival at this colony. Reliable pup counts over the next few breeding seasons will inform managing authorities of the possible change of the status of the colony from a former haul out site to a full-on breeding colony.

Seal diet monitoring

In collaboration with the Port Elizabeth Museum, our researchers collect monthly scats samples to update the current diet of Cape fur seals that haul out on Robberg Peninsula. Scats are routinely processed and prey remains identified for future analyses. Data will be used to aid in studies on seal-fisheries operational interactions, biological competition between seals and fisheries, and trophic ecology to examine the role of seals in the Agulhas Current. This is especially important in terms of recent changes that has taken place in this ecosystem.

Seal tag re-sights

During the end of January each year our researchers intend to tag, weigh, sample and release ~100 pups at the Robberg Peninsula seal colony. Subsequent tag re-sights will be recorded during routine boat-based surveys to assess the effectiveness of different types of flipper tags in terms of tag retention. Tagging pups will also allow long-term research on specialist seal behaviour via re-sights of tagged seals in estuaries, those incidentally captured in trawl nets and deliberately killed during other fishing operations. Stranded new-borne pups that are rescued, treated and released back at the colony during the breeding season are fitted with flipper tags as part of an existing research project of the Port Elizabeth Museum, which aims to assess the success of rehabilitation efforts.

Seal-shark interactions

In collaboration with the Port Elizabeth Museum, our researchers record the presence of great white sharks and their interactions with seals during opportunistic boat-based surveys and dedicated land-based observations in Robberg MPA. This consists of monitoring seal movements (and group size), recording direct sightings of sharks and shark predation attempts on seals, as well as examining shark-inflicted wounds on dead seals washed ashore and those photographed on live seals that haul out at the Robberg colony. Data will be used to examine the seasonal presence of white sharks and its impact on seal behaviour. We will also use data in an attempt to estimate shark predation rates to assess its significance as a mortality factor on the Robberg seal colony. Continued monitoring of white shark presence and the percentage of seals exhibiting bite wounds could provide a useful indicator to any changes in the abundance and behaviour of sharks in the area, especially in relation to continued local seal population growth, potential environmental changes, fluctuations in prey availability and possible shark cage diving activities in future.

Seal-fisheries interactions

Our biologists distribute questionnaires and conduct opportunistic interviews with fishermen to obtain their opinion on the impact of Cape fur seals on local fish stocks and recreational angling in the Robberg Marine Protected Area (MPA). Circulation of questionnaires was recommended by Cape Nature and the Department of Environmental Affairs (DEA) after negative feedback received from fishermen at the recent MPA rezonation meeting held in August 2017. Although independent of the rezonation process, questionnaire surveys will form part of our seal biologist’s broader PhD study, which aims to update the current nature and extent of seal-fisheries interactions in the Agulhas Current, to inform management with scientific advice. For the recreational rock & surf angling component, questionnaire results will be compared to independent observations made from cliff-top vantage points, as well as results from seal diet analysis. This will allow critical evaluation of the current perceptions of recreational anglers that fish in the MPA.

Seal presence in estuaries

Fishermen have encountered Cape fur seals in the Keurbooms River estuary for many years and there are numerous anecdotal reports of them preying on important recreational fish species that are also of conservation concern. In the past, due to public pressure, this has lead to the issuing of exemption permits for the selective removal of ‘rogue’ seals by river management authorities. However, the existence of river-specialists, whether such individuals have a greater impact on estuarine fish species than individuals in the general population, and the potential effect of their removal, has not been examined.

In collaboration with the Port Elizabeth Museum and DEA, our researchers have set up a project to track the movement of Cape fur seals that frequent the estuary. We conduct dedicated boat-based surveys to record the presence, identity, behaviour and habitat preference of these seals. Using photo-ID techniques we have identified a number of individuals with unique flipper scars. Prey species are identified from photos taken during predation events. With this we aim to determine whether individual seals specialize in feeding on estuarine fish species, and whether their behaviour is seasonal, tidal, sex or age specific. The study further aims to place the impact of river seals into context with current recreational fishing pressure. Results will have important implications for management as it will provide new data on the existence of river specialists, which may be important for the development of future conflict mitigation measures, should they be needed.

Tag and release fishing

When there is an opportunity, we join Ocean Blue Adventures’ manager and experienced angler, Charlie Lilford, on fish tagging trips in the Keurbooms River estuary. As it is tag and release, the information of the species of fish caught is recorded along with the tag number before the fish is released. These fish are eventually re-caught somewhere further along the coastline and the information from their tags are sent in to a national database at the Oceanographic Research Institute (ORI) in Kwazulu Natal. The information that is gathered shows the distance that each fish has travelled from the time of its release to the time of its capture, along with the size increase that has occurred during its release period. Some amazing information has already been captured since the start of this long-term monitoring project.