Save the salmon, Save the whales – by Kat Middleton



In British Columbia, salmon are culturally important to First Nations and are highly valued by commercial and recreational fishing industries. Pacific salmon have been commercially harvested since the late 1800’s, which has significantly contributed to the reduction of wild salmon populations over the last century. These wild salmon stocks experienced declines due to overfishing but also due to habitat degradation and unfavourable changes in ocean productivity. Approximately 30 years ago, the total abundance of North Pacific salmon doubled due to the introduction of hatchery enhancement programs, a more productive ocean climate, and improvements to the management of commercial fisheries. By the mid 90’s the situation changed drastically where many of these stocks began declining and continue to do so today. Although enhancement programs and other efforts have been established to help reduce the decline in these stocks, many researchers believe that a variable ocean climate and the reduced marine survival for North Pacific salmon are contributing factors to this decline. Of all 5 species of Pacific salmon in BC, Chinook salmon (also known as Spring salmon) are the least abundant. Populations declined through the 1970-1990’s and those that currently remain somewhat healthy are highly dependant on hatchery enhancement programs. Chinook salmon are the main prey for resident killer whales as they prefer the large size and high fat content of this species as well as their year-round availability near shore in the Pacific Northwest.

Seine vessel fishing for salmon near Robson Bight.

I became interested in the survival of Chinook salmon when I learned that they were the primary prey of resident killer whales out here in British Columbia. This highly influenced my choice in graduate work, as my Master’s thesis looked at the growth and overwinter mortality of juvenile Chinook on the northwest tip of Vancouver Island. After completing my degree, I interned on San Juan Island with the Centre for Whale Research researching the southern resident killer whale population. From this internship, I became even more interested in the relationship between these two endangered species. I am currently working as a warden here with the Robson Bight Marine Warden program and I have been thinking a lot about the delay and overall elusiveness of the northern resident killer whale population this summer in Johnstone Strait. It seems that the northern residents have been spending more time hunting rather than playing and rubbing on the beaches at the Robson Bight Michael Bigg Ecological Reserve.

Both northern and southern resident killer whale mortality rates have been correlated with the overall abundance of Chinook salmon on the BC coast. Dr. John Ford and his colleagues determined that in years of high Chinook salmon abundance, there was a decrease in mortality rates for both resident killer whale populations, while in years of low Chinook salmon abundance mortality rates were high. This research suggests that Chinook salmon are a limiting factor for resident killer whales and declines in these stocks are a direct threat to resident orca populations. Both northern and southern resident killer whale populations have been documented traveling larger distances in the winter months, likely to find prey, which has become less abundant in their traditional range. More of their time may be spent foraging and traveling when prey availability is low. Not only are Chinook salmon populations reduced, but the size and quality of these fish has declined by up to 45% over the last few decades. A decline in food quality for the resident killer whales means that they need to spend more energy finding more fish for the same amount of fat they would have gotten with less fish 30 years ago. If more time is spent foraging and traveling longer distances to find enough food, the resident killer whale populations have less time to spend socializing. For northern residents socializing includes rubbing on beaches here in Robson Bight and for both populations: breaching, spy hopping, tail lobbing and overall tactile behaviour. Socializing is a significant part of their culture and is important in maintaining family bonds, which help with hunting for salmon.

Northern resident orca with a chinook salmon on her rostrum

Two female resident orca sharing a chinook salmon.

We know that Pacific salmon are a keystone species as they affect the productivity and biodiversity of forests, rivers and estuaries and all organisms connected through this complex biological network, including these apex predators. Although the river and estuarial ecologies of Pacific salmon have a significant impact on the coastal environment, most of their life is spent in the open ocean, and a better understanding of this portion of their life cycle is crucial in answering further questions on the decline of many species. If we can develop a significant knowledge base on the marine life of Pacific salmon, we will have better insight into one of the most important ecological foundations of the northwest coast.

References:

Fisheries and Oceans Canada. 2008. Recovery Strategy for the Northern and Southern Resident Killer Whales (Orcinus Orca) in Canada. Species at Risk Act Recovery Strategy Series, Fisheries and Oceans Canada, Ottawa, ix-81pp.

Ford, J.K.B. et al. 2010. Linking killer whale survival and prey abundance: food limitation in the oceans apex predator? Biol Letters. 6. 139-142.

Middleton, K.R. 2011. Factors affecting the overwinter mortality and early marine growth in the first ocean year of juvenile Chinook salmon in Quatsino Sound, British Columbia. M.Sc. Thesis. University of Victoria, Victoria, BC.

Comments are closed.