Baked Cod: The Path Forward in an Era of Climate Change

In recent weeks, we learned more sobering news for New England’s cod population. A paper published in Science detailed how rapidly increasing ocean temperatures are reducing cod’s productivity and impacting – negatively – the long-term rebuilding potential of New England’s iconic groundfish. The paper confirmed both the theoretical predictions associated with climate change and the recent scientific federal, state, and Canadian trawl surveys that reported a record-low number of cod caught in recent months.

To be clear, the Science authors do not conclude that ocean temperature changes associated with climate change have caused the collapse of cod. We have management-approved overfishing of cod to thank for that.

What rising ocean temperatures do seem to be doing, according to the Science paper, is dramatically changing the productivity of the remaining cod stocks. This makes it more difficult for cod to recover from overfishing today than at any other time in history, and perhaps reduces the ultimate recovery potential even if all fishing were halted. Stock assessments conducted without taking these productivity reductions into full account will dramatically overestimate cod populations and, in turn, fishing quotas.

The Science paper is potentially very important, with major implications for fishing limits on cod for decades to come, But stock assessment scientists have warned for years that their recent models were likely overestimating the amount of cod actually in the water – and the corresponding fishing pressure the stock could withstand. Unfortunately, those warnings have fallen on deaf ears at the New England Fishery Management Council.

In fact, the managers at the Council, dominated by fishermen and state fisheries directors with short-term economic agendas, could hardly have done more than they already have to jeopardize Atlantic cod’s future—climate change or not.

Overfishing, a Weakened Gene Pool, and the Loss of Productive Female Fish

As a result of chronic overfishing, New England’s cod population is likely facing what geneticists call a “population bottleneck,” meaning that the diversity of the remaining cod gene pool is now so greatly reduced that the fish that are left are less resilient to environmental stresses like increasing sea temperatures.

Overfishing has also caused the collapse of the age structure of the cod populations by removing almost all of the larger, more reproductive females (also known as the Big, Old, Fat, Fecund Females, or BOFFFS). Scientists have previously warned that losing these old spawners is a problem for cod productivity, but this new research suggests that the potential damage from their elimination may be significantly greater than imagined as a result of poor, climate change–related ecological conditions.

The Science paper hypothesizes that an underlying factor in the productivity decline of cod this past decade was the correlation between extremely warm spikes in ocean temperatures and the drop in zooplankton species that are critical to the survival of larval cod. With fewer zooplankton, fewer cod larvae make it to their first birthday.

The impacts of this zooplankton decline on cod productivity, however, could be exacerbated by the loss of the BOFFFs. Here’s why:

Cod start to spawn at three to four years old, but young females produce significantly fewer and weaker eggs and cod larvae than their older counterparts. Those elder female fish, on the other hand, produce larger, more viable eggs – sometimes exponentially more healthy eggs – over longer periods of time. If the older female cod population had still been plentiful, they might have produced larvae more capable of surviving variations in zooplankton abundance.

Perhaps the continued presence of larger, older, spawning females to the south of New England (where there is no commercial cod fishery) is one of the reasons that the cod fishery in the nearby warm waters off New Jersey is healthier now than it has been in recent history.

The Cod Aren’t Completely Cooked Yet: Four Potential Solutions

Cod have been in trouble since the 1990s, and now climate change is magnifying these troubles. This new reality, however, is not cause for us to throw in the towel. There are actions that our fishery managers can take now that will make a difference.

First, large cod habitat areas have to be closed to fishingpermanently. This is the only way to protect the large females and increase their number. Designating cod refuges such as the Cashes Ledge Closed Area as a marine national monument will remove the temptation for fishery councils – always under pressure to provide access to fish – to reopen them in the future.

Such monuments would also sustain a critical marine laboratory where more of these complex interactions between cod and our changing ocean environment can be studied and understood.

Second, managers need to gain a better understanding of the cod populations south of Cape Cod. While it is well and good to land “monster” female cod on recreational boat trips, those fish may be the key to re-populating Georges Bank. Caution, rather than a free-for-all, is the best course of action until the patterns of movement of those cod populations, as related to ocean temperature increases, are better understood.

Third, as observed in the Science paper, stock assessment models as well as guidance from the Council’s Science and Statistical Committee must start incorporating more ecosystem variables and reflecting a more appropriate level of scientific precaution in the face of the reality of climate change shifts. Enough talk about scientific uncertainty and ecosystem-based fisheries management; action is needed, and science should have the lead in guiding that action.

Finally, the importance of funding data collection and fishery science is evident from this important Science paper, which was supported by private, philanthropic dollars. NOAA should be undertaking this sort of work – but it is not in a position to even provide adequate and timely stock assessments, because limited funding forces the agency to use the existing outdated models.

NOAA’s funding limitations are constraining both collection of the essential field data needed to understand our changing world as well as the analysis of that data into meaningful and appropriate management advice. If Congress can find $33 million to give fishermen for the most recent “groundfish disaster,” it ought to be able to find money to prevent such avoidable disasters in the future.

Ultimately, the Science paper shines some much needed light on our climate change–related fishery issues in New England, but we can’t let it overshadow decades of mismanagement or justify a fatalistic attitude toward cod rebuilding. Steps can and must be taken, and fishery managers are still on the hook for the success or failure of our current and future cod stocks.

Zooplankton: A tiny creature with a big role in the cod crisis

One of the North Atlantic’s smallest ocean critters is making big waves in New England.

Centropages. Photo courtesy NOAA
Centropages. Photo courtesy NOAA

Over the last decade, we’ve seen the collapse of our iconic Atlantic cod fishery due to extreme overfishing. Now, a new study is showing a potentially disastrous link between the effects of climate change and the ailing species’ chance of recovery.

Warming waters are bound to be bad news for a cold water fish, but the problem goes much deeper than that, affecting the entire life cycle of the species. Some of this is due to tiny, microscopic creatures called zooplankton. So what are these little guys, and why are they so important?

Zooplankton is a categorization of a type of ocean organism that includes various species, including Pseudocalanus spp, and Centropages typicus. These two species happen to be the major food source of larval cod in the Gulf of Maine.

Zooplankton, which are usually smaller than 1/10 of an inch, play a major role in the Atlantic’s food web. When there are lots of them, things are pretty good. Young fish prey on them and grow to be healthy, adult fish.

But when there aren’t enough plankton to go around, species like Atlantic cod can suffer. When cod larvae aren’t easily able to find the food they need to grow, fewer of them make it to their first birthday.

And without lots of cod that survive to be at least 4 years old (the age at which females begin spawning), the recovery of the entire stock can stall. The stock needs larger, older, more productive females to thrive in order to have any hope for recovery.

Warming and shifting

But why would the plankton be in such short supply? This is where climate change comes in. According to NOAA, temperature changes can cause the redistribution of plankton communities. In the Gulf of Maine, scientists have found fewer plankton in the same areas where cod populations have been found to be struggling. The shifts in temperature lead to the displacement of a critical food source, making it difficult for young cod to survive.

Larval cod. Photo courtesy NOAA
Larval cod. Photo courtesy NOAA

With the Gulf of Maine is warming faster than 99% of ocean areas, this is an enormously alarming problem. More temperature changes and the shifting of plankton populations could make it even harder for New England cod populations to return to healthy, sustainable levels.

While the cod crisis is the result of many factors – but the loss of tiny zooplankton is a big problem. When considering how to best help cod stocks recover, fishery managers must take into account the effects of climate change, or else risk the total collapse of the species.

Not Your Average Drifter – Plankton Part II

Last week we met some of our most important New England residents – the phytoplankton. Now, we are happy to introduce their animal counterparts – the zooplankton. These animals drift around in the sea in truly astonishing number and form . If you missed our post on their plant partners – the phytoplankton – you can find it here. Go ahead and read it, I’ll wait.

Okay? Well, those phytoplankton are extremely productive, and they’re eaten by many animals, most of which fall into the category of “zooplankton.”

Microscopic or massive, if you’re an animal that can’t swim against the current you’re part of the zooplankton. Some of these animals drift in the water their entire lives. These are what we scientists (who enjoy inventing and using large words) call the holoplankton (holo = entire, plankton = wanderer). The copepods are a perfect example of this.

Copepods may be the most abundant animal group on the planet, and although they contain considerable diversity, most of them are holoplanktonic. They are also usually gonorchoristic (I know, again with the huge words), which means they come in both the male and female variety. When two of them get together, so to speak, the fertilized egg will develop through many larval stages, until they finally metamorphose into the adult form. But all the way through this life cycle – egg to adult – the copepod will remain drifting along in the water.

The same is true for countless other animals, from the familiar jelly to the bizarre Phronima. All of them spending a life adrift, in a world that seems more like science fiction than reality.

Contrast this to members of the meroplankton (meros = partial), who spend only a portion of their lives in the water column. These animals may not be so foreign to you, as most of the meroplankton are the larval forms of animals that we know and love (and love to eat!). These animals drift around as larvae until they metamorphose and become large enough to swim against the current (at which point they are said to be “nektonic” – like a fast-swimming fish), or until they settle to a life on the sea floor (these animals are “benthic” – like a snail or mussel).

Most fish have larvae, as do barnacles, urchins, lobsters, mollusks, and many others. Some have giant spikes coming out of their heads, others look like flying saucers. But the fact that free-living larval stages exist in most marine animals means that they are (or were) evolutionarily important. Perhaps they evolved for dispersal – to avoid competition or inbreeding. Or maybe larvae evolved as a means to temporarily avoid predation on the sea floor… in truth, we don’t know for sure why the larval form evolved.

What we do know is that they are extremely abundant, and together with the holoplankton they make up an undeniably important and enormous group of animals. If the phytoplankton are at the base of the food chain, then the zooplankton are at the first rung. They are so massive in number that they can sustain huge populations of larger animals, some as large as our own North Atlantic right whales, which filter copepods, krill, and other zooplankton out of the water. But some zooplankton are eaten by their tiny buddies (other carnivorous plankton, like some fish larvae), which can make the marine food web a bit complicated.

And though they can’t swim against the current, they’re on the move. Their ecological importance makes the news of a study showing that climate change has caused dramatic shifts in the distribution of many planktonic species troubling. In the study, the investigators found that phytoplankton and zooplankton were two of the groups whose distribution was changing the quickest. As the authors’ of the study state, “species’ interactions and marine ecosystem functions may be substantially reorganized at the regional scale, potentially triggering a range of cascading effects.”

Translation: As the great drifter Bob Dylan said, “The times they are a changin’.” But that doesn’t mean you have to sit idly by… “If your time to you is worth savin’” then find out how you can help.

Up next in our plankton series – we’ll talk about a really cool citizen science plankton project you can get involved in using little more than your smart phone. Stay tuned!

Casey Diederich is a 5th year PhD candidate in Tuft’s University’s Biology Department, and is conducting his research on slipper-shell snails. We are thrilled to have Casey guest blogging for us about some of the more fascinating plants and animals in our ocean. – Ed.

Images copyright of Dr Richard Kirby, Plymouth University. These and other images can be found in the book on plankton, “Ocean Drifters, a secret world beneath the waves.”

A Movable Feast

When you think about grazing, you picture a big mammal with hooves eating a helpless plant – placidly chewing and digesting, right? Well, there’s another kind of grazing that is much more dynamic. Researchers at the University of Rhode Island have, for the first time known to science, discovered a plant that “runs away” to avoid being munched. The tiny Heterosigma akashiwo you see above on the right, not only makes tracks when predators like the Favella favella are after it (the big, mouthy guy on the left), but it will even avoid areas where there used to be predators, but no longer are. They are, in effect, fleeing the scent of danger.

Before you stand up and cheer for the little guy, you should know that this particular plant is one of the “red tide” phytoplankton that can cause major fish kills when it blooms. Dr. Susanne Menden-Deuer, an oceanography professor who studies the plankton at the University of Rhode Island, speculates that its ability to flee may be one of the mechanisms that allow Heterosigma to grow prolifically enough to kill fish. The plant, a type of algae, will take refuge in areas with lowered salinity – places where its predators cannot survive. As the algae move into these areas of refuge, they are free to reproduce with little to check their population explosion.

These harmful algal blooms can cause major devastation and millions of dollars in economic damage to fisheries – killing not only finfish like salmon and herring, but also harming oysters, copepods, and sea urchins.

Usually, though, Heterosigma are not harmful at all, blooming only occasionally in spring and fall. In fact, they provide many benefits to us – they are an important food source at the bottom of our productive ocean food chain. Not only that, but phytoplankton are responsible for giving us the oxygen in half the air we breathe.

Menden-Deuer plans to conduct further research to find out what the connections are between the fleeing behavior and harmful algal blooms, and if other plants might be up to this evasive behavior.

Photo credit: Elizabeth Harvey (URI-GSO). Digital enhancement by Cynthia
Beth Rubin (RISD).