A recent research that makes use of historical data has discovered exceptional evidence in favor of the "safety in numbers" theory, according to which Pacific salmon living in bigger groups are less likely to be eaten by predators.
However, certain salmon species may sacrifice safety for a meal since schooling reduces food competition.
Saving Pacific salmon
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While most people associate salmon with their spawning in freshwater streams, lead author Anne Polyakov, a doctoral student in the University of Washington's interdisciplinary Quantitative Ecology and Resource Management Program and the School of Aquatic and Fishery Sciences, noted that salmon also spend a significant amount of time feeding and growing in the ocean, as per ScienceDaily.
This study is exceptional because, despite the fact that we essentially cannot observe these fish in their natural ocean habitat, experts are still able to use this incredibly valuable dataset to derive these very convincing conclusions about how grouping affects predation risk and foraging success for individual fish.
The researchers used data from an international fisheries dataset that was compiled for these species from 1956 to 1991 to examine four species of Pacific salmon: sockeye, chum, coho, and pink.
All salmon are born in freshwater streams, migrate to the ocean to feed and grow, and then return to their native streams to lay eggs, spawn, and eventually die, resuming the lifecycle for the following generation.
This study made use of novel analyses of previously collected historical data.
Salmon capture statistics have been recorded across the North Pacific Ocean for more than 40 years by the University of Washington's Fisheries Research Institute in collaboration with the International North Pacific Fisheries Commission in an effort to manage each species.
The authors of the study examined capture data from purse seine nets, a type of fishing gear that entails lowering a net and catching every fish in a small body of water.
The size of the schools in which each fish had been swimming might be inferred by the researchers from the number of fish that were taken in one of these nets.
The historical information also included meticulous records of predator wounds on salmon as well as the stomach contents for a subset of fish that were taken.
This made for a special and significant data set since the researchers could quantify both salmon predator interactions and feeding success across a 45-year period covering the whole North Pacific Ocean.
Salmon are vital to the culture of First Nations and the economics of the West Coast.
They are also crucial prey for many animals, including the critically endangered southern resident orcas.
As habitats deteriorate and disappear, salmon do as well, as per Defenders.
As fish disappear, the quality of the ecosystem declines as well, as salmon are an essential source of nutrients. Salmon are also markers of a healthy river and marine ecosystems.
The west has experienced the collapse and extirpation of several salmon runs as a result of river damming.
Many dams make it more challenging for adults to spawn upriver and obstruct newly born salmon from migrating downstream. These obstacles prevent salmon from accessing thousands of miles of their old habitat.
Freshwater, estuaries, and the ocean are all included in the anadromous salmon's life history.
For the most part, freshwater habitats are used for spawning, incubation, and raising juveniles.
Estuaries are where juveniles are put on crucially rapid growth and make crucial osmoregulatory adjustments as they transition between fresh and saline waters.
Finally, the ocean is where significant feeding results in the majority of the body mass of the returning adults.
Salmon consume a vast range of food species during their lives, including different types of freshwater and marine invertebrates and fish.
At the same time, they are preyed upon by a diverse range of invertebrate and vertebrate predators and scavengers.
