I have recently been tasked with reviewing a paper about ecosystem dynamics in the North Atlantic Ocean. It has given me some appreciation of the difficult job of fisheries managers and the task of writing reports on the status of an ecosystem.
It is easy to demand answers and to accuse people of “not doing their job,” or blame fishery crashes on mismanagement, but it may be worth considering what it is we are asking these people to do.
When I plan my weekly grocery shopping, I do it before the weekend and limit it to one trip to the store. Not only am I trying to limit my exposure during COVID times, I also am not a great fan of grocery shopping and try to get it over with.
To do this properly requires an inventory of the fridge and the pantry, and a plan for what is going to happen during the upcoming week. How many mouths are there to feed? Is everyone at home or are there lunches to pack? Are there any invitations, special meals, celebrations or special diets to consider?
Then, there are budget considerations like what produce is in season and affordable, and what nonperishable staples are on sale?
When all these parameters are considered, the resulting load of groceries should last through the week with a little to spare. I also try to keep the recommended one to two weeks of nonperishable foods in the pantry just in case there is some supply shortage due to an earthquake, volcanic eruption, tsunami or any other sort of natural or human-made disruption of the normal supply chain.
If I was off in my calculations for the week, we sometimes dig into those supplies by the end of the week and then replenish them during the next grocery run.
An ecosystem assessment is a much more complicated task, for a very large family. Just like the family has a budget for groceries, and it may change over time, an ecosystem runs on an energy budget.
In an ocean ecosystem, that comes from the so-called primary producers; these are the “plants” in the ocean, or more specifically the phytoplankton and, to a much lesser extent, the seaweeds along the shores.
They take the energy from the sunlight and the nutrients from the water and multiply. When the water contains a lot of nutrients, the phytoplankton can grow exponentially and make a plankton bloom.
The water temperature plays a role in which species will be the first to bloom and use up the nutrients. Just like in your garden, this could be the tasty vegetables you planted, or it could be the weeds you did not really want.
Some algae are better food for the animal plankton that feed on them than others. In the past decades we have seen an increase in blooms of dinoflagellates, which under some conditions produce a toxin that can accumulate in shellfish and make them a potential risk of paralytic shellfish poisoning when eaten. These dinoflagellates generally thrive in warmer water temperatures, while larger diatoms prefer a colder spring.
Generally, the phytoplankton gets eaten by animals in the zooplankton. These consist of larvae of basically every broadcast spawner out there and those that spend their whole life cycle afloat, most importantly copepods and krill.
Different zooplankton species thrive on different algae, and in the same way fish are selective and, depending on size, prefer certain larger copepods and krill.
Also, sometimes the timing between when the most phytoplankton is there to eat and when the zooplankton larvae are ready to eat it gets out of sync. This can happen if the surface water temperatures increase too soon, and the algae bloom too early for the new recruits of the copepods.
Assume you have a family that eats dinner together; a prerequisite is that everyone knows the exact time when dinner is served. Otherwise, those family members who are early will wait around and get into trouble, those who are on time will eat everything and those who are late will be starving.
In the ocean, these mechanisms determine the composition of the zooplankton. The zooplankton is the food base for a number of different fishes like herring, sandlance, juvenile cod, juvenile salmon and some birds. As we all know, these fish are important for seals, sea lions, more birds, bigger fish, whales and fishermen.
Fisheries managers have the complicated tasks of taking an annual inventory of the different components in these ecosystems and then predicting which of the many players will fare favorably in a given year.
If they predict that a certain species will not do so well, they are supposed to adjust the predator-prey relationships in such a way that things even out.
However, as described above, the budget of the ecosystem is driven by ocean currents and temperatures, which are not in a manager’s power to control.
All management can do is to allow more or less fishing on the stocks that are competing over the resources. You could imagine someone at the dinner table allocating the food to each of the children, except nobody set a time for dinner, nobody knows how much food there is and nobody knows how many children will show up.
If you are a fisheries manager, please accept my apology for this simile; it does not do justice to the complicated work you are asked to do and is merely a feeble attempt to make people see that fisheries management in the decades of climate change effects is a near-impossible task.
Perhaps it is no wonder that on both coasts of the country, many fisheries are failing, while few are flourishing.
One thing scientists and fishermen agree on is that over the last decades the fluctuations between years have been extreme. There have been really strong years, even records for some fisheries, while others have seen unprecedented downs.
One thing both ecosystems have experienced in recent years are periods of ocean heat waves, which have had effects that last more than a single season for some species, especially mammals.
Currently, the Gulf of Maine and Georges Bank, famous for their huge cod fishery in “the old days,” are experiencing low and over-fished cod stocks, low herring and mackerel stocks, warmer-than-usual water, trouble in the scallop fishery, a decent lobster catch, and unusual mortality events in North Atlantic Right Whales, humpback whales, minke whales, and three species of seals (one of them did, however, have a population increase in the years before this mortality event).
All this follows a shift from a time of high to low herring and mackerel biomass. In my studies of this ecosystem, I learned a few fascinating facts that I never knew: There are no sea lions in the North Atlantic, and orca whales are rare with no resident populations. There also are no gray whales.
NOAA’s report on the status of the Gulf of Alaska ecosystem refers back to the effects of the extreme heat wave in 2015-2016 that was accompanied by bird and whale die-offs.
The two years after that were returning conditions back to “normal,” but last year and this year we have seen an unusual mortality event in gray whales, with observations of food-depleted animals.
Humpback whale observations in Prince William Sound report that the whales are in better shape this year than in recent years, when they looked skinny. Zooplankton along the Seward line was showing higher abundance of large copepods, which is generally a good sign, but also warned that the zooplankton bloom was earlier than usual, which can mean trouble if the predators are not ready.
If your head is swimming with too many details that play together in these fishy ecosystems, that is absolutely understandable.
The ocean is an amazing and big place and there are so many influences that are changing its workings. One thing we can take home from all this is that climate change is causing more unpredictability. As always, there will be winners and losers, but the only thing for certain is change.