Strategic Pinniped Predator Control as it relates to early timed Fraser River Chinook and Steelhead

While we are aware there is not just one ‘smoking gun’ that is responsible for the dwindling early Fraser River run of chinook salmon and steelhead stocks in BC there is one particular crisis that needs immediate action. There are several steps needed to be done to rebuild the stocks of concern over the long term such as moving to marked selective fishery (MSF), selective harvest methods in river for First Nations, healthy funding to improve effectiveness of enhancement and hatcheries but one crisis we need to solve right now is the excessive pinniped consumption of juvenile chinook/smolts at specific river mouth choke points.

We need strategic predator control programs as problem pinnipeds are taking full advantage of the confined channels of the Lower Fraser River to target juvenile salmon and steelhead. Now that the majority of the connectivity of the Fraser estuary has been lost, how can smolts evade predators?   100 years ago the juvenile salmon and steelhead could utilize the massive Fraser Estuary to migrate and feed.  Now, the out migrating smolts are concentrated in shipping channels making them easy targets for predators. To make matters worse, the rock jetties and log booms give the predators perfect haul outs to rest after they eat! Control programs could include a First Nations limited harvest that focuses on these specific river mouth choke points where problem pinnipeds target vulnerable salmon.  The Fraser River Estuary is not what it was 100 years ago, we need pinniped management actions that take this into account.

Pinnipeds (both sea lions and harbour seals) have had a huge increase in BC waters since back in the early 70’s when legislation was put into place to protect marine mammals. Harbour seal populations in BC have stabilized overall in BC waters in recent years, however, they have overpopulated large areas such as southern Georgia Strait. Sea lion numbers have also drastically increased in BC in recent years.   Fisheries managers need to take pinniped management seriously no matter how socially and politically uncomfortable it is. 

There has been several research studies on this topic and there doesn’t seem to be an argument as to whether it is happening or not but rather the actual number/percentage of salmon the pinnipeds consume. 

The research shows that while pinnipeds do have a diet that includes other fish types, the research also shows that pinnipeds eat a very high percentage of out migrating salmon smolts. The number of chinook salmon consumed by pinnipeds is reported to be as high as 50%. A disturbing estimate of 74% of out migrating steelhead are also eaten on their journey into Georgia Strait.

Shocking to also know that this percentage of chinook consumed does not include adult chinook that are also consumed by pinnipeds.  The pinnipeds prefer to consume larger size juvenile chinook and so target those larger juveniles over the smaller ones. Those larger juvenile chinook are known as “stream type” chinook. The ‘stream type’ chinook spend up to 2 years in river and therefore grow larger before their out-migrating journey to the ocean. ‘Ocean type’ chinook stocks spend only a few months or less before heading out to the ocean as smaller size juveniles. The ‘ocean type’ chinook are doing much better than the ‘stream type’. What is an alarming observation is that the early Fraser River runs of chinook that are experiencing drastically dwindling numbers are those “stream type” chinook that are larger in size when they travel out to sea. Pinnipeds target these larger juveniles (stream type) and gorge on them so it makes sense then that we are seeing a drastic drop in stream type chinook stocks. The early Fraser River “stream type” chinook that are in a serious crisis are referred to as “ 4-2’s “ and “ 5-2’s “. The ‘4’ and ‘5’ refers to their age upon returning to spawn and the ‘2’ refers to their time spent in river as smolts or juveniles.  

We need to have predator control program in place immediately before it is too late. Opening up a limited First Nations harvest in specific ‘problem’ areas would be an effective and efficient way to protect the stocks and be a positive start to a longer term rebuilding process.

A strategic plan for pinniped control is needed now as a critical step to rebuilding the early Fraser River chinook stocks that are in serious trouble. The following are some eye opening quotes taken from a pinniped predation thesis written by UBC Master of Science student, Hassen Allegue:

 ” Legislation enacted in the early 1970s protected marine mammals in Canada and US, and led to an exponential recovery and stabilization of harbour seal numbers at carrying capacity in the 2000s (Jeffries et al. 2003; Olesiuk 2010). This recovery of the harbour seal numbers occurred concomitantly with declines of coho, chinook, and rockfish (Palsson et al. 2009).

There is increasing evidence that predation by harbour seal (Phoca vitulina) on young salmon (smolts) out-migrating from rivers may be a significant source of mortality for coho (Oncorhynchus kisutch) and chinook (O. tshawytscha) salmon populations in British Columbia”

The recovery of harbour seals following culling and hunting in the Salish Sea has led to speculation that predation by seals might be the main factor impeding the recovery of coho and chinook salmon (Miller et al. 2013)”

 “Although the proportion of salmon smolts consumed is relatively small in the harbour seal total diet, it was suggested that predation of harbour seal on coho and chinook smolts is likely having a substantial impact on these salmon populations”

 “The failure of coho and chinook populations to respond to reduced fishing pressure and hatchery enhancement has led to speculation that changes in early natural mortality from predators may be impeding recovery of these salmon populations (Miller et al. 2013).”

“Although the consumed juvenile salmon species appear as small percentages in the overall harbour seal diet, they may in fact represent a significant source of mortality on salmon populations when converted into numbers of individual salmon consumed—particularly for coho and chinook salmon that are of conservation concern (Irvine et al. 2009; Welch et al. 2011; Thomas et al. 2016”)

 “Harbour seals alone may be the biggest contributor to smolt predation (Riddell et al. 2009). In the SalishSea, harbour seals are present year-round and are the most abundant pinniped species (Olesiuk 2010) and their relatively large body sizes imply high energy needs (Stenson et al. 1997; Trites etal. 1997). In addition, harbour seals can inflict significant damage to prey populations, and may limit recovery of declining populations (Fu et al. 2001; Bundy 2001; Butler et al. 2006; Trzcinskiet al. 2006).

A study done by the Salish Sea Marine Survival Project with support from the Pacific Salmon Foundation, Dr Austen Thomas and UBC doctoral student Ben Nelson found that a shocking number of juvenile chinook (and coho) are being consumed by seals :

 “We discovered that from May to October, about 40-60% of juvenile coho, and about 30-50% of juvenile Chinook, could be lost to seal predation”

“When seals became federally protected in 1970, their numbers increased exponentially around the Strait of Georgia from 5,000 in 1970 to 40,000 in 2008. These numbers coincided with a precipitous decline in Chinook and Coho salmon returns to the region, triggering research efforts through the Salish Sea Marine Survival Project to determine how many juvenile salmon the seals are eating. Preliminary results have finally confirmed some long-time suspicions.

Below are quotes from a workshop “Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019” :

  “Steller sea lions (SSL) have emerged as significant predators, and now likely consume more fish and more salmon than any other predator, including humans”

 ” In BC, no stock designations but Strait of Georgia harbour seal “stock” reached carrying capacity or “k” by late 1990s or early 2000s “

 “In BC and SE Alaska, which accounts for ~80% of pup production, total and pup numbers of SSL on rookeries have increased 5-fold since 1960”

~ Public Fishery Alliance Team

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