Predatory fish like tuna accumulate extra mercury by eating other fish.
Because they are low in the food chain, sardines are low in contaminants, such as mercury, relative to other fish commonly eaten by humans, and have a relatively low impact in production of greenhouse gases.
For comparison (bluefin tuna):
since bluefins require so much food per unit of weight gained, up to 10 times that of salmon, if bluefins were to be farmed at the same scale as 21st-century salmon farming, many of their prey species might become depleted
I don't want to diminish the tragedy, but... this reminds me of a joke I first heard told by Garrison Keillor, but it was already old when he told it. Here's a link to one version: https://www.maxtrescott.com/max_trescott_on_general_a/2011/02/aviation-joke-hunting-for-moose-in-alaska.html
The following is a joke -- not real -- the NBC story is real, but the following is NOT:
Two hunters hire an Alaskan bush pilot to flythem in his float plane out into the Alaskan wilderness for a week long moose hunt. After landing on a lake and dropping them off with all their gear, he reminds them of of the terms, saying, "I’ll be back in a week to pick you up but you can only have one moose between you. The airplane’s not big enough to carry any more than that." The hunters agree and head out as the pilot flies off.
A week later he returns to find the hunters waiting with their gear and a wealth of meat including two whole moose heads complete from racks to delap to neck. The pilot is furious. He shuts down and jumps out of the plane. “You idiots, I told you one moose. Now we’re going to have to leave the other here to rot. What were you thinking?”
One of the hunters replies, “Last year we paid the our an extra $500 and he flew us out.”
The pilot refuses, "It's not the money, it's the weight!"
"Well that's B.S.," says a hunter, "Cuz' our pilot last year had the same type of plane as you and he took off just fine."
After much back and forth, the pilot relents. They load up all their gear, strap one head to each wing and the pilot fires up the plane to takeoff. The aircraft hops and skips on the water, lifts off and stays in ground effect until the last possible moment. The pilot pulls up, clearing the trees at the end of the lake by inches. The aircraft climbs out slowly but not high enough to get over the low, forrested hills and they crash in a tumble of spruce.
Everyone survived with minor injuries, but the pilot was knocked unconscious in the crash. He was attended by one of the hunters. As he came to, and, as so often is the case, he asked “where are we?” The hunter looked toward the crash and then back to the lake. ”I’m not absolutely sure,” he said, “but it looks as if you got us about a quarter mile further than our pilot did last year."