Stable isotope analysis of fish eye lenses: reconstruction of ontogenetic trends in spatial and trophic ecology of elasmobranchs and deep-water teleosts

• Main Author: Quaeck, Katie
• Format: Thesis
• Language: English
• Published: University of Southampton 2017
• Subjects: Lamna nasus; Squalus acanthias
• Online Access: https://eprints.soton.ac.uk/415526/; https://eprints.soton.ac.uk/415526/1/Quaeck_Katie_PhD_Thesis_Oct_17.pdf

Studying ontogenetic trends in diet and habitat use of endangered sharks and deep-water teleosts is logistically challenging and expensive, due to the remote and inaccessible nature of the pelagic realm, and the extent of many marine migrations. Chemical analysis of inert, organic, incrementally formed tissues represents a window to retrospectively study whole life-history ecology, however these tissues are rare or absent in many fishes. The fish eye lens is a unique tissue, formed via the sequential deposition of protein-filled fiber cells, which undergo no subsequent remodelling once formed. Despite having great potential to record chemical variations reflecting foraging behaviour, lenses have received relatively little analytical attention. In this thesis I have explored the suitability of fish lenses for recovery of retrospective ontogenetic chemical information, focusing particularly on pre-birth and early juvenile life histories in elasmobranchs. I have confirmed consistent relationships between the body size and lens diameter of four study species (Aphonopus carbo, Coryphaenoides rupestris, Lamna nasus and Squalus acanthias), which allows recovery of a body size-referenced lens samples. Growth relationships reveal that a large proportion of lens tissue in elasmobranchs is deposited pre-birth, opening a previously unrecognised opportunity to study maternal provisioning from tissues of the offspring as adults. I have confirmed that transects of stable isotope compositions across lenses show bilateral symmetry, reflecting the sequential deposition of eye lens tissue. Muscle-lens tissue offsets were examined in S. acanthias and C. rupestris, identifying the potential for species-specific differences, possibly driven by variability in taxon-specific lens protein expression. I have then applied the validated lens sampling protocol to recover cross-generational life history movement and diet ecology information in three study species. Focusing on pre-birth ecology requires some understanding of the isotopic ...