Wednesday, October 31, 2012

Tag and Release

After a short recess, the benthic catshark tag and release program is up and running again! This year we have added an additional two sites to the sampling protocol, namely: Santos and Darwin.

Since August 2012 we have tagged a total of 17 catsharks: Leopard = 1, Pyjama Jacket = 3 and Puffadder = 13. Unfortunately, with no recaptures yet, however, there are possible reasons for this. Negatives: (i) the tag may have fallen off – any scars would likely have healed as sharks have incredible regenerative capabilities, (ii) tagged sharks have died due to natural predation, or alternatively have been caught by fishermen and killed - as they are considered a pest species. Positives: (i) these sharks are abundant and there is a low probability of capturing the same individual more than once. Let’s hope it’s the latter!

Although most species of catshark occurring in Mossel Bay are endemic to South Africa, despite their relative abundance – information is still limited. This tag and release project therefore represents an effective, low cost tool to obtain vital information on these little studied species.

This research project aims to investigate the following key questions relating to the biology and ecology of these endemic sharks:
              i.        Diversity of benthic catsharks in Mossel Bay reef systems
            ii.        Degree of spatial variation in benthic catshark composition between Mossel Bay reef systems
           iii.        Population composition and abundance of benthic catsharks sampled in Mossel Bay

The insight gained from this study will contribute to a more comprehensive understanding about the role these catsharks play in community dynamics. These benthic sharks likely represent predators within their micro-scale habitats and are thus considered to have top-down predatory effects at the community level at which they occur.

Furthermore, most of these catsharks are listed as Near Threatened on the IUCN Red List of Threatened Species – prioritising them as species of conservation concern!!

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