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Title: Population connectivity of a commercial loliginid squid (Doryteuthis gahi)
Author: Jones, Jessica Briony
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2019
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This thesis aimed to improve our understanding of population structure and connectivity in a commercially important squid species on the Patagonian shelf (Doryteuthis gahi). Ontogenetic migrations of two spawning cohorts in Falkland Island waters were confirmed using trace element analysis of statoliths. Elemental concentrations showed clear relationships with environmental conditions at the time of incorporation. High-resolution elemental chronologies were developed which were temporally stable over consecutive years and the ontogenetic patterns of each cohort were unique. These chronologies can be used to investigate population structure and connectivity. Large-scale connectivity was investigated by comparing body measurements, meristic characters and statolith outlines between populations of D. gahi from Peru and the Falkland Islands. Linear discriminant analysis indicated a correct classification rate to geographic region of 94.1% for body measurements and 87.6% for statolith outlines. Inconsistencies were found between the taxonomic description (pointed teeth on the tentacular club sucker rings) and the Peruvian population (square truncated teeth). Results align with recent genetic evidence showing two highly divergent groups; one originating from Peru and the other from Chilean/Falkland waters. Intra-specific analyses of body shape were undertaken in Falkland Island waters. Allometric growth trajectories suggested a large 'super-bull' form exists, characterised by an elongated body shape, heavier fin and a larger fin area. This morph may indirectly provide spatial connectivity using their enhanced gliding abilities. Males of the super-bull morph from the autumn spawning cohort were significantly older and were present on feeding grounds long after their purported return migration to spawning grounds, potentially maintaining temporal connectivity. Mixed modelling found a significant negative relationship between temperature in early ontogeny and size. It is clear that environmental factors are driving much of the plasticity in this population. This information is fundamental for understanding how the heterogeneous marine environment will effect cephalopod populations in future years.
Supervisor: Witte, Ursula ; Kuepper, Frithjof ; Pierce, Graham J. ; Brickle, Paul ; Arkhipkin, Alexander Sponsor: Falkland Islands Fisheries Department
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Loliginidae ; Otoliths, Fossil ; Cephalopoda ; Animal populations