This paper ran an interesting article last week by Michael Brestovansky entitled — Report: Kona Coast Fish Eating Plastics. The article itself was interesting on a number of fronts, but the comments section at the end was enlightening in another way entirely. It shed some light on how the reading public can interpret the same article, in many different ways.
Comments were based on the range of elements in the content of the article. Each person seemed to grab onto one element or another that appealed to the senses of that person.
Readers questions ranged from whether the purpose of the article was to get the “Big Brother Government” to step in with endless bureaucracy and studies (wasting tax payers dollars) that ultimately ended in regulations requiring Joe Public to buy expensive filter systems for their home laundry; to calling for the EPA to step in and investigate the County wastewater purification system.
Sadly, neither are far fetched in today’s world, but yours truly read this report from yet again, a different perspective — from the perspective of the fish.
Just like everyone else, I grasped onto the element of content that appealed to my senses, and that’s because I work in the world of fish and fishery management. Most fishery oriented headlines deal with the subject of over fishing and collapsing fish stocks, seemingly here, there and everywhere.
And yes, many times that topic has come up in this column in the past.
In similar fashion to those who related to washing machines and waste water, I related more to this sentence: “And, because the fish studied include commercially harvested fish like swordfish and mahi-mahi, fewer fish reaching adulthood could have wide-reaching effects.”
While most of us in the world of fish are fixated with management terminology such as “Maximum Sustainable Yield” (MSY) and “Optimum Yield” (OY) and arguing about which threshold should be the one used to determine overfishing, the effects of climate change on fisheries – and more – the researchers in the article are pointing out yet another element that fishery managers should be taking into consideration.
Stock assessments of individual species are the foundation of fishery management as it is “practiced” today. Practiced being the key word. It’s like that old joke that makes your family doctor cringe.
“Doc, why should I believe you if you are still just practicing? Let me know when you have it down and don’t need to practice any longer. I’ll come back in for a check up then.”
Stock assessments are an inexact science at best, but the models and math that researchers use in stock assessments is a complex as just about anything else dreamed up in research today. It has to be. It’s foundation is based entirely on how many fish are caught, from which they then try to determine how many fish remain to be caught, and how many should be left in the ocean to spawn and procreate.
This is where the report on larvae fish eating microfibers caught my eye.
In today’s world of fishery management, the part of a stock assessment that addresses “recruitment” and “spawning biomass” relies on a natural stock eating natural food with documented, natural survival and mortality rates.
Ever look at a female lobster or crab in spawning season and see it carrying around lots and lots of eggs? Every species in the ocean spawns a certain volume of eggs to insure survival of the species. Amazingly, nature takes into account all the various critters that love to eat those eggs, how many are not strong enough to survive, how many do not get fertilized and on and on. Somehow, enough survive the larvae and fry stage to make it to adulthood, where they do their part to keep the species going.
Everyone has seen baby turtles scrambling from the nest to the surf on TV, trying to beat all their various enemies to the safety of the sea. It doesn’t end there, though. In the ocean they will run the gauntlet of even more critters who want a baby turtle breakfast. You get the idea.
Marlin and tuna and all the other ocean fish spawn like this too – only more so. Egg production range varies with age and size. A female marlin about 400 pounds can drop about 30 million eggs. A female of about 950 pounds may spawn out 100 million eggs.
I asked fishery scientist Dr. Mike Musyl how managers might take into account this “new” problem of larvae mortality and/or a reduction in larval development because of plastic ingestion, relative to many levels of fishery management.
As mentioned earlier, this aspect of fishery management gets pretty darn complex, but don’t take it from me. Dr. Musyl explains it this way:
“Typically scientists would provide what’s called a stochastic estimate (having a random probability distribution or pattern that may be analyzed statistically but may not be predicted precisely) rather than using a “deterministic” estimate (fully estimated). In other words, you want wiggle room to try and account for uncertainty in the estimate. Bayesian models could be used to incorporate all of the information that is known into the model. I think you would have to assume plastic is killing them rather or making them less fit. Having said that, because there is much uncertainty in larval dynamics in marlin the first place, now we’re talking about relative degrees of fudge factors for uncertain estimates. Note that for post-release mortality, I always couch the estimate in 95% confidence intervals. We do that for several reasons including providing the reader with some sense of power and precision in the estimate. I would try and fit the data to various bathtub curves using available information on marlin fishing (F) and natural (M) mortality rates for adults and larvae.”
Dr. Mike took a deep breath and continued, “Remember too that various estimates are presented under varying circumstances to cover a range of possibilities and probabilities. For example, with 10% larvae succumbing to plastic toxicity, we estimate the parental biomass about 4-5 years henceforth would be X (+/- 95% CI) if fishing mortality is Y and natural mortality Q and assuming adequate larval habitat, etc.”
So there ya have it! Everyone picks sections of articles out that resonate with them, and when I read the “Kona Fish Eating Plastic” article my mind focused on the question. What will this mean to fish stocks, stock assessments and contributing to overfishing?”
Thanks to Dr. Mike Musyl, I got my answer, but I’m thinking it may be simpler in the long run for me to just go buy a filter for my washing machine.
