Salmon are an iconic species in Alaska’s seas, known for their remarkable migrations from ocean feeding grounds back to inland spawning sites. But when it comes to their diet and feeding habits in the ocean, much remains unknown about these fish. One question researchers have tried to unravel is whether salmon exhibit cannibalistic behavior, eating juveniles of their own species.
According to recent studies of salmon diets and predatory interactions in Alaskan waters, evidence indicates salmon do sometimes consume smaller salmon, though not necessarily of their same species. This reveals complex food web connections and sheds light on the opportunistic feeding strategies salmon employ to survive in Alaska’s nutrient-rich but highly competitive ocean ecosystems.
Decoding Diets: What Do Salmon Eat?
Thorough records of stomach contents from decades of salmon research provide insights into dietary habits. Like most fish, salmon are omnivores whose diets change as they grow. Young salmon feed on zooplankton and insects. As adults, they shift to eating fish, squid and crustaceans. The most common prey found in adult salmon stomachs are smaller forage fish like herring, sand lance and juvenile pollock.
Interestingly, remains of juvenile salmonids – the family containing salmon – also frequently appear in the stomach contents of adult salmon. These could potentially represent cases of cannibalism if larger older salmon are eating young of their same species. However definitively proving cannibalism requires genetic analysis to confirm if consumed salmonids are the same species.
Opportunistic Foragers: Salmon Eat What’s Available
Rather than seek out their own species, evidence suggests salmon are opportunistic foragers. They appear to eat whatever suitable prey is abundantly available. Salmon waiting to spawn don’t feed actively. But younger adults wandering ocean feeding grounds consume whatever common small fish cross their path.
With multiple salmon species co-existing in Alaska’s waters, juveniles of any species serve as potential prey. While genetic data to pinpoint intra-species cannibalism is limited, salmon readily eat young of related species when available. essentially exhibiting cannibalistic tendencies at the salmonid family level.
Researchers emphasize adult salmon are not deliberately hunting their own offspring. But crowded ocean conditions with massive schools of juvenile salmon provide easy meals for roving adult salmon, regardless of species. So while not true cannibalism, adult salmon preying on any young salmonids does impact population dynamics.
Predatory Behavior: Survival in a Tough Ecosystem
Though their life cycle seems cyclical, salmon exist in a complex and ever-changing ocean ecosystem. Prey availability fluctuates, competing species abound, and predators lurk at every stage. Like any wild fish, salmon must adopt flexible feeding strategies using the resources at hand.
Exhibiting predatory – occasionally cannibalistic – inclinations when small fish are abundant enables salmon to endure Alaska’s harsh, nutritionally variable ocean environment. Though cold-blooded, salmon are finely tuned ocean predators, evolving to take advantage of ephemeral food sources. Their opportunistic feeding provides calories to migrate, evade predators, and successfully return upriver to spawn.
Once inland, surviving spawners cease eating altogether, focused solely on reproduction. Thankfully, their evolved predatory skills sustain adult salmon during ocean phases, ensuring the next generation hatches to make the journey back to the sea and complete the salmon life cycle. Understanding what salmon eat, and their role as oceanic predators and prey, provides insights into sustaining their iconic Alaskan runs into the future.
Salmon Consume More Than Just Other Fish
While small fish make up a large portion of adult salmon diets, they also feed on other ocean creatures. Squid, crustaceans like krill and amphipods, marine worms, and even jellyfish have all been found in salmon stomach contents.
Salmon diet composition changes depending on availability. In certain times and places, non-fish food items may occur more frequently in salmon stomachs, especially for leaner years with low small fish numbers. Squid and jellyfish in particular appear more often in warmer, low food years when forage fish are scarcer.
Young salmon feeding in coastal zones also exhibit more diverse diets, including marine and terrestrial insects, amphipods, mollusks and other aquatic invertebrates. Estuaries provide a nutrient-rich transition habitat on juvenile salmon migrations where they opportunistically consume whatever foods are present.
The variety of potential foods salmon exploit reveals their dietary plasticity. Though fish dominate food intake, salmon readily digest diverse prey sources based on local abundance. This adaptability provides calories needed for salmon growth and survival across a range of ocean conditions.
Cannibalism More Likely in Hatcheries Than Wild
While cases of salmon preying on other juvenile salmon occur among wild populations, cannibalism is far more prevalent in hatcheries. Raising large numbers of salmon fry in confined spaces can lead to behavioral issues and aggression.
Without space to establish normal territories, salmon focus territorial aggression on each other. Fin nipping often escalates to attacks on entire fish, with dominant individuals consuming weaker tankmates. Genetic testing confirms true cannibalism of the same species and stocks within hatcheries.
Managing tank densities, fish handling, and water flow can help reduce cannibalism in hatcheries. But eliminating it entirely remains challenging when raising salmon fry in completely artificial environments. This highlights the complexities of replicating natural conditions for healthy salmon development.
Predation and Balance in the Food Chain
As ocean predators and prey, salmon play an integral ecological role in Alaska’s waters. Along with eating smaller fish, adult salmon are food for larger predators like seals, sea lions, and certain whales. Birds also opportunistically feed on juvenile salmon.
This interplay between predator and prey shapes natural population balances. When salmon decline, food supplies diminish for dependent predators. Conservation efforts benefit the entire ecosystem by sustaining salmon abundance and their position within the food web.
Understanding salmon’s predatory behavior provides one piece of the puzzle. Whether feeding on related salmonids or diverse ocean prey, salmon’s opportunistic dietary strategies equip them for survival in the challenging, ever-changing conditions of Alaska’s northern seas.
Stopping Sea Lice: The Only Alliance Between Welfare and Economic Interests
Another bad thing about being confined and living in an unnaturally high density is that the number of infectious diseases like pancreatic disease, cardiomyopathy syndrome, and infectious pancreatic necrosis goes up. But sea lice are the main disease threat to Atlantic salmon, and the problem is so bad that it threatens the very existence of the Atlantic salmon farming industry. We’ve previously covered aquaculture’s sea lice problem in an earlier post.
Sea lice are parasites that do well in open-net farms because there are so many hosts. This means that sea lice populations can grow beyond what salmon can handle; the risk of infection from sea lice is 70 times higher near salmon farms. Sea lice feed on salmon skin, causing scarring, infections, fin loss, and death. Sea lice are especially dangerous for young salmon because they aren’t used to dealing with them because they don’t normally come across adult fish until much later in life. Most open-net salmon farms are in tidal estuaries that are in the way of wild salmon juveniles’ migration routes. This means that sea lice also pose a threat to wild salmon populations. Record-low catches of wild salmon on the west coast of Scotland show that the population of these fish is collapsing to the point of extinction.
Current methods to manage sea lice infestation include insecticide use and thermal delousing. However, sea lice are becoming increasingly resistant to insecticides, leading to the preference of thermal delousing as an alternative. Thermal delousing involves pouring hot water (28-34° C, or 82-93° F) on salmon to remove sea lice, but “thermal delousing causes panic behavior and increased salmon mortality, and that treatment is likely to be painful” according to Susanna Lybæk of the Animal Protection Alliance. The salmon farming industry is exploring the stocking of other fish species in salmon farms, such as wrasse and lumpfish, to feed on sea lice; however, there are additional welfare concerns that would arise from farming these other fish, such as maladaptive aggression, disease, and the fact that salmon would prey on these other fish species intended to reduce the suffering of salmon.
If you want to get rid of sea lice more effectively, you should run open-net farms in deeper or colder water, where the lice can’t survive. Improving inland salmon farms that are open for life and use both freshwater and saltwater to keep the environment free of sea lice is another idea. Both of these solutions, however, assume that salmon farming will continue. Unfortunately, this is likely to happen for the foreseeable future because of the high demand for fish products around the world.
Even without sea lice, Atlantic salmon farming can harm wild salmon ecosystems if feedlot nets are broken, usually by storms or animals that eat salmon, like seals. We’ve covered a study on escaped farmed salmon in an earlier post. There aren’t many genes in farmed Atlantic salmon, and if any escape, they can breed with wild salmon. This makes it harder for them to adapt and survive in certain habitats, population sizes, and genetic differences.
Farmed Atlantic Salmon: A Life Not Worth Living?Author:
Salmon is Europe’s most farmed fish, and it’s also one of the most expensive fish in the world. There are 18 1% of global fish trade value, yet they make up only 2. 8% of global aquaculture. Because of this, salmon aquaculture is one of the most studied ways to farm fish because they are so profitable and tend to be found in countries with lots of money. But there are still a lot of things we don’t know about the welfare of farmed salmon. What we know about the welfare of salmon may help us figure out how to help other species of farmed fish. As we talked about in a different post, consumers may not care much about the welfare of farmed fish. However, there is some encouraging evidence that some consumers are willing to pay more to make sure that higher welfare standards are met for farmed fish.
A recent report published by the Fish Welfare Initiative identified key welfare issues in Atlantic salmon farming operations and suggested future research directions. The main findings of the report were:
- Salmon don’t do well in farms and don’t have a “life worth living” according to the Farm Animal Welfare Council’s standards.
- When sea lice get into Atlantic salmon farms, they threaten the very existence of both the farms and the wild salmon that live nearby.
- Salmon feed from farms is made up of other fish and poultry meal, which makes problems with animal welfare in the supply chain even worse.
- The salmon farming industry has started to use methods of killing land animals, but these may not be the most humane ways to kill fish.
- More research needs to be done to find out if aquaculture operations can make salmon do things they like.
People still argue about whether or not fish are sentient, which is sad. However, the welfare of farmed fish is a very important issue for animal rights activists who want to make a difference in the lives of millions of animals. Below, we take a close look at the FWI report, and offer supplemental resources wherever possible.
Farm Raised Salmon EXPOSED…what you’re actually eating.
FAQ
Are salmon solitary fish?
Why not eat salmon?
Are GE salmon a threat to wild salmon?
What is cannibalism in fish?
Provided by the Springer Nature SharedIt content-sharing initiative Cannibalism is a common phenomenon that occurs in over 30 fish families. Most of the species are valuable objects of aquaculture and cannibalism is highly
How common is cannibalism in fish?
While the team catalogued more than 1,000 publications reporting the behavior in both fresh and saltwater fishes, they found that cannibalism has only been observed in approximately one percent of the 30,000 fish species known worldwide.
Do tropical fish have more cannibalism than temperate fish?
And this jives with what was found in earlier research—tropical fishes seem to engage in less cannibalism than temperate fishes. Pereira and her coauthors suggest that this is because tropical waters tend to contain more biodiversity. And where there are plenty of other fish in the sea, evolution should favor eating other species before your own.
How do I know if a fish farm has cannibalism?
Due to the complex causes of cannibalism, diagnostics should always start with case history—gathering information from the owner of the fish farm, which should be as extensive as possible. The questions should include the exact percentage of losses with a particular interest in the age of fish and the diversity in growth.