Predictions for Hypothesis One:


 

The abundance of salmon in the southern area would provide a logical explanation to the existence and abundance of resident killer whales, since it is the primary component of their diet. The Fraser River opens up into the Pacific Ocean from the mainland, just south of Vancouver.  In the fall, salmon leave the ocean to swim upstream to lay eggs, and coincidentally, Ford et al 2000 noticed a larger concentration of killer whales at the head of the river in the fall.  It has been noted that killer whales especially resident orcas, use currents as well as salmon migratory paths to be more effective at catching salmon.  The Fraser River estuary provides an ideal hunting ground for Orcas as there are multiple currents that the orcas can swim in to chase their prey. Swimming with the current allows for the whale to unknowingly attack the salmon (who also uses the same current) from behind. The use of salmon migratory pathways also helps to locate salmon in a concentrated region, and this is especially true in the fall.


 

Simila, T., Holst, JC., and Christensen, I.  1996. Occurrence and diet of killer whales in northern Norway: Seasonal patterns relative to the distribution and abundance of Norwegian spring-spawning herring. Canadian Journal of Fisheries and Aquatic Sciences. 53(4):769-779


 

This article effectively proves validity to my hypothesis that resident killer whales are located in the southern regions of British Columbia due to the presence of salmon. Since their presence is concentrated at the Fraser River estuary in the fall, which is the same time that salmon congregate to go up the river then it is likely that this is the case. The study done by Simila et al, 1996 addressed similar concerns in that they wanted to see if the killer whales followed the migratory patterns of herring.


 

Methods:

  • study conducted in fjords of northern Norway including Tysfjord and Ofot-fjord

  • photo-identified and catalogued killer whales to help identification during different occurances

  • photo-identification: B&W photographs taken, and later compared to photos taken at later sightings 

  • identified via two methods:

  • during 300 days of field work used land watch, telephone calls to pilot stations, ferries, fishing boats and research vessel

  • 10-day sighting surverys conducted in Nov. 1990 and Nov. 1991

  • determined occurence by sighting one or more individuals of the same pod in designated core areas

  • echointegration used to measure abundance of herring, and samples of fish were taken to determine sex, maturation stage and age


 

The above picture shows the yearly migration pattern (1990-1993) of herring during different seasons

1. Wintering area, 2. spawning area, 3. feeding area, 4. swawning migration, 5. feeding migration, 6. wintering migration


 

Results:

  • seasonal pattern of occurrence of killer whales during October to January and June to August

  • sightings occured in core study areas in Ofot-fjord in the fall, began to leave in January

  • encountered in high number in summer study areas

  • identified fish when feeding behaviour of killer whales was identified

  • 99/105 feedings were on herring

  • 85 feeding identifications in fall, 10 in summer

  • fall: 94% adult herring, winter: 100% adult herring, summer: 70% adult herring


 

These results strongly suggest that killer whales follow the migratory patterns of fish, specifically those that are the primary prey of that pod/clan. A similar study could be conducted with the residents killer whales off the coast of British Columbia.  Simila et al, 1996 used echointegration to determine the type of fish to be herring. Methods such as tagging have been used in studies with stellar sea lions, where the stomach contents of a killer whale has been examined and have found flipper tags amongst the content. (Heise et al, 2003) This is not an ideal method as finding stranded killer whales is uncommon and culling for research purposes is not ideal due to the limited numbers and disruption to the social hierarchy of a killer whale pod.


 

SIDE NOTE:


 

According to Wursig and Jefferson, photoidentification of cetaceans aids in the long-term identification of whales.  It can “enhance descriptions of life history parameters such as age at sexual maturity, calving intervals and reproductive and total life span.” (Wursig and Jefferson, 1990) This form of identification has been used in all of the journals and books that I have used and would be the logical choice for identifying pods and clans if a study were to be done on the migration of resident killer whales off the southern coast of British Columbia.