Distribution and diversity of octocorals from longline by-catch around South Georgia, UK
Author(s)
Taylor, Michelle Lisa
Type
Thesis
Abstract
In recent decades man’s forays into the deep sea have been increasingly frequent and
wide-reaching; the most immediately intense and widespread activity being fisheries.
United Nations (UN) General Assembly Resolutions on Sustainable Fishing on the
High Seas call for assessment of fishing impacts with the aim of helping fisheries to
avoid damaging vulnerable marine ecosystems.
Octocorals form the majority of by-catch in the bottom-longline fishery for
Patagonian toothfish, Dissostichus eleginoides Smitt, 1898, around South Georgia. I
employed several methods to investigate octocoral extent, location and diversity using
by-catch from this fishery. Preliminary video analysis from camera arrays attached to
bottom-longlines found whip corals interacted with longlines less than bushy, fanshaped
corals or Stylasteridae. Stylasteridae were however very fragile with 42% of
interactions likely resulting in mortality through dislodgement.
Deep-sea octocorals are relatively understudied with many families and genera
requiring revision and, as such, morphologically identifying octocorals is a difficult
task; I thus investigated by-catch diversity by embedding octocorals caught from this
South Georgia fishery into a wider Octocorallia phylogenetic tree. Three polyphyletic
groups were resolved. Putative species numbers were estimated from morphological
and phylogenetic analysis. Morphological identifications of one family of octocorals,
Primnoidae, were compared to phylogenetic trees and the probability species were
monophyletic tested using the statistical programme, Species Delimitation for
Geneious. Six families, at least 21 genera (including three new discoveries)
composing of a minimum of 34 species were caught as by-catch. Thouarella Gray,
1870, was the most common genus caught and a revision of this genus is presented.
Using recently created fine scale (150 m by 150 m) bathymetry of South Georgia, a
depth-derived megahabitat map was created and octocoral occurrence data used to
predict octocoral habitat suitability. Shelf troughs, crest and slope areas were
highlighted as highly suitable octocoral habitat which substantially overlaps fishing
areas. Current management protection regulations were found to protect highly
suitable octocoral habitat.
wide-reaching; the most immediately intense and widespread activity being fisheries.
United Nations (UN) General Assembly Resolutions on Sustainable Fishing on the
High Seas call for assessment of fishing impacts with the aim of helping fisheries to
avoid damaging vulnerable marine ecosystems.
Octocorals form the majority of by-catch in the bottom-longline fishery for
Patagonian toothfish, Dissostichus eleginoides Smitt, 1898, around South Georgia. I
employed several methods to investigate octocoral extent, location and diversity using
by-catch from this fishery. Preliminary video analysis from camera arrays attached to
bottom-longlines found whip corals interacted with longlines less than bushy, fanshaped
corals or Stylasteridae. Stylasteridae were however very fragile with 42% of
interactions likely resulting in mortality through dislodgement.
Deep-sea octocorals are relatively understudied with many families and genera
requiring revision and, as such, morphologically identifying octocorals is a difficult
task; I thus investigated by-catch diversity by embedding octocorals caught from this
South Georgia fishery into a wider Octocorallia phylogenetic tree. Three polyphyletic
groups were resolved. Putative species numbers were estimated from morphological
and phylogenetic analysis. Morphological identifications of one family of octocorals,
Primnoidae, were compared to phylogenetic trees and the probability species were
monophyletic tested using the statistical programme, Species Delimitation for
Geneious. Six families, at least 21 genera (including three new discoveries)
composing of a minimum of 34 species were caught as by-catch. Thouarella Gray,
1870, was the most common genus caught and a revision of this genus is presented.
Using recently created fine scale (150 m by 150 m) bathymetry of South Georgia, a
depth-derived megahabitat map was created and octocoral occurrence data used to
predict octocoral habitat suitability. Shelf troughs, crest and slope areas were
highlighted as highly suitable octocoral habitat which substantially overlaps fishing
areas. Current management protection regulations were found to protect highly
suitable octocoral habitat.
Date Issued
2011
Date Awarded
2012-01
Advisor
Agnew, David
Quicke, Donald
Creator
Taylor, Michelle Lisa
Publisher Department
Life Sciences
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)