Life history strategies of northern form Dolly Varden (Salvelinus malma malma) in the western Canadian Arctic

• Author / Creator

  Morrison, Christie

• Northern form Dolly Varden char (Salvelinus malma malma) inhabit cold-water streams in the western Canadian Arctic. They are an important cultural and subsistence resource to local Aboriginal communities, yet little is known about their complex early life histories. Populations of Dolly Varden exhibit partial anadromy, where a portion of the population migrates to the ocean to feed in productive coastal waters (anadromous), while other individuals remain in freshwater year-round (residents). Residents are ‘sneak’ spawners and benefit from early maturation, while fish that migrate benefit from a larger size-at-maturation and thus a competitive advantage for spawning opportunities. According to classical life history theory, in populations that are partially anadromous, fast growing fish should migrate sooner and at smaller sizes than slow growing individuals, and the fastest growers in the population should remain as stream residents. Dolly Varden were sampled from three river systems (Rat, Big Fish, and Babbage rivers) and otoliths were used to assess size-at-age and growth patterns through back-calculation, and age-at-migration through strontium analysis. Otoliths were used as proxy measures for fish growth and size-at-age due to their ability to record life history events throughout the lifetime of the fish. Initially, the fish length – otolith length relationship was observed in order to verify proportional growth between the fish and otolith. However, a decoupling was detected during first migration where fish size dramatically increased but otolith growth did not accrete material to the same extent. Modified back-calculation equations were developed to account for this decoupling based on discontinuous piecewise regressions. The new biological intercept breakpoint method provided the most accurate representation of fish size-at-age throughout all life history stages when compared to known capture values in fish, although traditional back-calculation methods also reflected actual values for post-migratory fish. The decoupling indicates that factors other than somatic growth are important for otolith accretion. It is likely that physiological changes during smoltification that alter calcium uptake are affecting calcium deposition rates on otoliths during this short time period. Back-calculated fish lengths for anadromous and resident fish were compared to determine how early growth influences migratory behaviour, and whether Dolly Varden exhibit life history strategies that follow predictions of classical life history theory. In accordance with predictions, results showed that early migrating fish were faster growers and migrated at smaller sizes than late migrating Dolly Varden. Size-at-migration varied between river systems, with fish from the Babbage River migrating earlier and at smaller sizes than those from the Rat and Big Fish rivers. Fish on the Big Fish River migrated at much larger sizes compared with the other systems, which was likely due to local adaptations to characteristics of this river, which are much different from most North Slope systems. Contrary to predictions of life history theory, no differences were observed in growth between resident and early migrating individuals, although a trend towards increased size-at-age was observed on the Rat and Big Fish rivers. These results indicate that factors other than growth are playing a role in life history ‘decisions’. Future work on growth efficiencies and metabolic rates is needed to assess how they influence migratory and resident behaviours.

• Subjects / Keywords

  • Decoupling
  • Dolly Varden
  • Growth
  • Anadromous
  • Otolith
  • Life history
  • Resident
  • Back-calculation

• Graduation date

  Fall 2017

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3FF3MD48

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.