As most folks are now aware, thousands of dead Atlantic herring have been washing up along the shores of the Bay of Fundy in Nova Scotia and citizens and researchers are considering a multitude of explanations. Is it a virus? a bacterium? fishing related, pollution, sprays, or perhaps the new tidal generating system that was just installed? So far no one seems to have the answer.
During the process of considering similar previous fish mortality events, the relationship between toxic phytoplankton and the food that herring most likely eat and the possibility of a kill from domoic acid became a consideration. Domoic acid can be fatal to humans and you may remember shellfish closures that occurred as a result of outbreaks. It’s caused by Harmful Alga Blooms (HABs for those who like acronyms) that are well known around the world. The phytoplankton that produces the toxin is eaten by various filter feeders and zooplankton. These forage species are eaten by larger sea creatures and the toxin moves on up the food chain to larger animals causing death.
As it turns out, there are records of fish mortalities from HABs at locations around the world. Here are a few from Wikipedia:
Massive fish die-offs have been caused by HABs. In 2016, 23 million salmon which were being farmed in Chile died from a toxic algae bloom. To get rid of the dead fish, the ones fit for consumption were made into fishmeal and the rest were dumped 60 miles offshore to avoid risks to human health.The economic cost of that die-off is estimated to have been $800 million.
Other countries have reported similar impacts, with cities such as Rio de Janeiro Brazil seeing major fish die-offs from blooms becoming a common occurrence. In early 2015, Rio collected an estimated 50 tons of dead fish from the lagoon where water events in the 2016 Olympics were planned to take place.
In May 2015, researchers in Santa Cruz California witnessed a mass die-off of anchovies in the Monterey Bay due to a red tide and the high level of domoic acid it produced. Biologists then began receiving reports of dead seabirds which had apparently been feeding on the poisoned fish which were lying up and down the West Coast. Similar fish die-offs from toxic algae or lack of oxygen have been seen in Russia, Colombia, Viet Nam, China, Canada, Turkey, Indonesia, and France.
With one exception, the Nova Scotia herring death fit the pattern from a toxic death similar to these. The object of these articles is to get basic information out for consideration. This is not a scientific paper. So … here’s the shorter story, gleaned from the literature.
- ABOUT THE TOXIN. Amnesic shellfish poison (ASP; domoic acid) is produced by Pseudo-nitzschia in eastern and northern Prince Edward Island, P. pseudodelicatissima in the Bay of Fundy, and unknown source(s) on the south shore of Nova Scotia, Georges/Browns Banks, and in Newfoundland. Because of human deaths related to the shellfish industry, the toxic diatom has been associated with commercial shellfish species. But, it seems, this tiny phytoplanktonic species has broader impacts throughout the marine system.
2. THE SHORTER STORY: Copepods eat the toxic diatom Pseudo-nitzschia, Atlantic herring eat copepods, HERRING DIE.
Calanus finmarchicus often dominates North Atlantic zooplankton assemblages and is a primary dietary component of many marine species including herring, seabirds and the endanger North Atlantic Right Whale. C. finmarchicus consumes the Domoic Acid producing Pseudonitzschia and retains the toxin. Hence there is potential for C. finmarchicus to transfer the toxin to other marine species where toxic Pseudonitzschia is present.
3. THE SHORTER STORY: Krill eat the toxic diatom Pseudo-nitzschia, Atlantic herring eat krill, HERRING DIE.
Over the past decade, blooms of the domoic acid (DA) producing diatom Pseudonitzschia have been responsible for numerous deaths of marine species. Euphausiids (krill) are important members of the local zooplankton grazer community in the Bay of Fundy and are important in the diet of many marine species including Atlantic herring. Research findings provide compelling evidence for the role of krill as a potential transfer agent of the phycotoxin demoic acid to marine species including herring.
4. THE VICTIM
From afar, the circumstances surrounding the mass deaths of so many herring in the Bay of Fundy fits exactly with those seen elsewhere. But in the absence of an analysis, it is impossible to tell whether or not domoic acid toxin derived from herring prey was involved. Hopefully, the folks who are testing samples will take this possibility into account.
5. THE MISSING LINK
Generally speaking, gulls and other species take advantage of mass mortalities by feeding on the remains. Researchers have mentioned seabird mortailities at other locations where species have died from domoic acid toxin. As yet, there have been no such reports from the Nova Scotia kills.