Factors affecting energy transfer to higher trophic levels can determine the survival and
production of commercially important species and thus the success of fisheries
management regimes. Juvenile salmon experience particularly high mortality during
their early marine residence, but the root causes of this mortality remain uncertain. One
potential contributing factor is the food quality encountered at this critical time. The
nutritionally vital essential fatty acids (EFA) docosahexaenoic acid (DHA, 22:6n-3) and
eicosapentaenoic acid (EPA, 20:5n-3) are essential to all marine heterotrophs, and their
availability has the potential to affect energy transfer through a limitation-driven food
quality effect. Assessing variability in DHA and EPA in an ecologically important prey
species of juvenile salmon could give insight into the prevalence and severity of food
quality effects. On the west coast of Vancouver Island (WCVI), one such species is the
calanoid copepod Calanus marshallae. This omnivorous species possesses a high
grazing capacity and the ability to store large amounts of lipids. As it is also an important
prey item for a diverse array of predators, including juvenile Pacific salmon, C.
marshallae plays a key role in energy transfer from phytoplankton to high-trophic
iv
consumers. This study quantified spatiotemporal variability in the quality of C.
marshallae as prey for higher trophic levels using three polyunsaturated fatty acid
indicators: DHA:EPA, %EFA and PUFA:SFA (polyunsaturated fatty acids to saturated
fatty acids). Samples were collected on the WCVI in May and September of 2010 and
May 2011. The environmental parameters included in the analysis were the phase of the
Pacific Decadal Oscillation (PDO), sea surface temperature (SST), latitude, station depth,
and season (spring versus late summer). Despite a phase shift in the PDO from positive
to negative, overall means of the fatty acid indicators did not vary between May 2010 and
May 2011. Same-station %EFA values rarely fluctuated more than 5%. DHA:EPA
ratios were more variable but without a discernable pattern, while PUFA:SFA ratios
decreased in shelf stations and increased offshore. Contrary to expectations, fatty acid
indicators showed a weak positive correlation or no relationship with SST, nor was there
a relationship with latitude. The narrow temperature range observed across all stations
suggests that temperature may not play a significant role in PUFA availability off the
WCVI. There were, however, significant relationships between the fatty acid indicators
and bottom depth and season. Shelf and slope stations showed significantly higher
%EFA and PUFA:SFA than did offshore stations (depth >800 m), with this gradient
appearing stronger in May than September. While the food quality represented by C.
marshallae was consistent across all shelf stations, the lower food quality observed
offshore could potentially affect juvenile salmon growth along the WCVI where the shelf
narrows to less than 5 km. / Graduate / dpbevan@uvic.ca
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/5980 |
| Date | 21 April 2015 |
| Creators | Bevan, Daniel |
| Contributors | Dower, John F. |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
| Rights | Available to the World Wide Web, http://creativecommons.org/publicdomain/zero/1.0/ |
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