Stable isotope values of Marion Island myctophids using otoliths from fur seal faecal samples
Dissertation (MSc (Zoology))--University of Pretoria, 2023. Lanternfish (Myctophidae) are abundant mesopelagic fishes in the Southern Ocean ecosystem and represent a large dietary component for sentinel marine predators, such as seals and seabirds. Their contribution to diets of predators can be qua...
| Other Authors: | , , |
|---|---|
| Format: | Doctoral or Postdoctoral Thesis |
| Language: | English |
| Published: |
University of Pretoria
2023
|
| Subjects: | |
| Online Access: | http://hdl.handle.net/2263/91307 https://doi.org/10.25403/UPresearchdata.23634603.v1 https://doi.org/10.25403/UPresearchdata.23634603 |
| Summary: | Dissertation (MSc (Zoology))--University of Pretoria, 2023. Lanternfish (Myctophidae) are abundant mesopelagic fishes in the Southern Ocean ecosystem and represent a large dietary component for sentinel marine predators, such as seals and seabirds. Their contribution to diets of predators can be quantified indirectly using stable isotope mixing models. However, bivariate isotope mixing models require nitrogen (δ15N) and carbon (δ13C) isotope values of potential prey items, which is often lacking. Published stable isotope values of potential prey from geographically dissimilar sites are often used to parameterise the isotope-based mixing models, which might not be adequate, especially when variation in the isotope values at the base of food web exists. Acknowledging the inherent, but often unavoidable spatial assumption using extrinsic data for local modelling, in this dissertation I aimed to generate isotope values for myctophids, specific to the sub- Antarctic Prince Edward Islands (PEIs; Chapter 2), which can be used to refine previous dietary models of sentinel marine predators at PEIs (Chapter 3). Firstly (Chapter 2), muscle values were required for myctophids utilised by marine predators at PEIs. Fur seals (Arctocephalus spp.) with known foraging areas were used as bio-samplers of the myctophid community, whereby myctophid otoliths were recovered from faecal samples collected around seal colonies breeding at the PEIs. The required stable isotope difference between muscle and otoliths (otolith-to-muscle offset) was established using pairs of fresh muscle and otolith samples of Electrona antarctica (n = 6) and Gymnoscopelus opisthopterus (n = 2) from Dronning Maud Land, Antarctica. The average otolith-to-muscle offset used was -1.3 ± 0.4‰ for δ13C and 1.6 ± 0.3‰ for δ15N. Using these otolith-to-muscle offsets, the muscle δ13C and δ15N values of myctophids could be estimated where only faecal otoliths are available, provided that an additional oxidative cleaning step was used to account for faecal ... |
|---|