CLIMATE CHANGE AND FISH STOCKS: ONE WAY TO MOVE FORWARD

 

I spend a lot of time writing about fisheries management from a legal perspective—that is, about the Magnuson-Stevens Fishery Conservation and Management Act and its positive impacts on the health of fish stocks, and about how the lack of legally-enforceable mandates at the state and regional level has prevented states, and organizations such as the Atlantic States Marine Fisheries Commission, from emulating federal fisheries managers’ success.

But laws and regulations are only a part of the issue.  The ocean is a dynamic place, where fish populations—and those who seek to manage them—must continually respond to changing oceanographic conditions. 

Some of the changes that fish face are ephemeral, such as the warm-core eddies that break off from the Gulf Stream and bring clear blue water, and the fish that prefer it, into the offshore canyons and up onto the continental shelf, concentrating them until such time as the eddy breaks up or reunites with the Gulf Stream farther down the coast.

Some, while short-lived, can last a little longer.  Cold winters and wet springs appear to boost striped bass spawning success, while warm winters and dry springs can lead to below-average recruitment.  It was hardly surprising that the 2011-2012 winter that wasn’t, which saw high temperatures and little snow throughout the Susquehanna River watershed, led to the lowest Maryland striped bass juvenile abundance index ever recorded, in a time series extending back more than sixty years.

It’s also no surprise that the same winter, which saw unusually warm, salty waters flow across the Northeast’s continental shelf, gave rise to the largest year class of black sea bass ever recorded, because such warm, salty water is directly related to good black sea bass recruitment, which hinges on the number of juvenile fish that survive their first winter at sea.

There are also longer-term, but ultimately transient, oceanographic events such as the North Atlantic Decadal Oscillation, a term which describes periodic and somewhat predictable changes in sea surface temperatures, and can have an impact on fish movements and abundance.

And then there are more permanent changes.  I use the word “permanent” with a little hesitancy, as nothing on Earth is truly permanent—even the Atlantic Ocean itself didn’t exist until somewhere between 170 and 200 million years ago, and geologists are already pointing to signs that, as the continents continue their slow and stately dance across the face of the Earth, it may already be starting to close up and will eventually disappear.  But for purposes of fisheries management, changes that spawn centuries, or even human lifetimes, are permanent enough.

And right now, the biggest such “permanent” change that our fisheries face is climate change.

It already seems to be impacting the health of northeastern fisheries. 

Back in 2013, scientists at the National Oceanic and Atmospheric Administration’s Northeast Fisheries Science Center determined that warming waters—and the Gulf of Maine, off northern New England, is one of the most rapidly warming parts of the entire ocean—have led to a marked reduction in the number of planktonic animals that are available as food for larval cod.

That would have been bad enough if cod stocks were healthy; it is likely that a shortage of the zooplankton that larval cod feed on would have caused a decline in recruitment, and affected the long-term productivity of cod stocks.  Such reduced productivity, in turn, might have forced fisheries managers to reduce annual catch limits and adopt more restrictive measures in order to maintain stock health.

But cod stocks were already badly overfished, which made the situation significantly worse.  NOAA Fisheries issued a press release stating that rising water temperatures “profoundly affected” the zooplankton needed by larval cod and by other fish species, and that the decline in zooplankton thus

“may be influencing the recovery of Atlantic cod and other fish stocks in the region.  [emphasis added]”

It’s important to note that the scientists aren’t blaming warming waters for the cod stocks’ collapse.  Years of unabating overfishing did that.  They’re saying that, with cod stocks already in steep decline, the impacts of climate change on the ocean’s food web, managers are probably going to have a much tougher job ahead of them if they want to rebuild the stock.

Climate change, and its impacts on the food web, is just one more reason why fisheries managers need to take a precautionary approach to managing fish stocks.  If they make a mistake now, the impacts of that mistake will hit the stock harder and be more difficult to correct.

And that’s not only the case in the Northeast.

Recently, a study conducted at East Carolina University, in conjunction with NOAA Fisheries, examined the abundance of larval fish of ten different species in the Beaufort, North Carolina area.  The data used for the study extends back to 1986.  An analysis revealed that larval fish now begin entering the estuaries earlier than they did before, and use the estuary habitat over a longer period of time than they formerly did.  Although water temperatures have only risen a modest amount over the years, larval fish species are entering the estuaries as much as two months earlier.

It’s not completely clear what the implications of that finding may be.  As is the case with cod, the impacts of warming water, and larvae entering the estuaries earlier, may all depend on how the warm water affects the food web.

The early presence of larval predators indicates that predatory fish are spawning earlier; if prey species are also reproducing earlier in the year, there may be no problem.  However, if the predator and prey species have not adapted in the same way, and their spawns are now out of synch, the larval fish in North Carolina may, like the larval cod, have difficulty finding enough food.  In that case, recruitment and, ultimately, adult fish abundance, could decline.

Another problem is that when predatory fish are still in their larval stage, they are prey, too.  They don’t only need food; they also need places to hide, to help prevent them from becoming food for bigger fish.  Much submerged aquatic vegetation where larvae might shelter disappears over the winter, and begins to grow back in the spring.  If such vegetation remains sparse when the larval fish arrive in the estuaries, the larvae might find themselves more vulnerable to predators, and experience significantly higher levels of natural mortality. 

Dr. Rebecca Asch, the professor overseeing the North Carolina study, commented that

“with climate change for most species you’re going to have winners and losers,”

and speculated, in an interview with television station WRAL, that tropical fish that previously only visited North Carolina waters, and were unable to survive there during the winter, might number among the “winners” as winter waters warm, while temperate species might find the same waters becoming too warm for their survival, and number among the “losers.”

Summer flounder, which are becoming less abundant in North Carolina waters, may already be firmly set on a losing track.

The fisheries management approach set out in Magnuson-Stevens is largely focused on managing fishing mortality and rebuilding fish stocks, and not on the impacts of climate change.  However, the discussion draft of a Magnuson-Stevens reauthorization bill, being circulated by Representatives Jared Huffman (D-CA) and Ed Case (D-HI) suggests that such oversight may soon be corrected.

Title I of the discussion draft is named “Climate-Ready Fisheries,” and seeks

“to account for the impacts of environmental changes on stocks of fish.”

It notes that

“Environmental changes associated with climate change, including changes in water temperature, ocean acidification, and deoxygenation, are rapidly altering the abundance, productivity, and distribution of fish and are affecting commercial, recreational, and subsistence fisheries,”

and also that

“The impacts of climate change on fish and their habitats are resulting in management and sustainability challenges that threaten to negatively impact marine ecosystems, fishery resources, and coastal communities.”

If the discussion draft’s language is ever made a part of Magnuson-Stevens, regional fishery management councils, as well as NOAA Fisheries, would be required to give more consideration to the impacts of climate change.  When stock assessments are conducted, they would be required to address the impacts of climate change on the stock’s productivity, and examine the vulnerability of each managed fishery to climate change-related issues.

The discussion draft also includes language intended to promote the development of tools and management approaches that would better allow fisheries to adapt to climate change.  In addition, it would establish a procedural framework that would govern how the regional fishery management councils, as well as NOAA Fisheries, should address the problems created by fish stocks shifting into new waters, and abandoning others, as a result of a changing climate.

Anyone who has spent much time on the water has experienced the impacts of climate change.  Here on Long Island, we’ve enjoyed the recently increased abundance of dolphin (mahi-mahi) and black sea bass in local waters.  But we’ve also lost most of our cod and—especially—winter flounder, cold-water species that were badly overfished, but might have been more readily rebuilt if warming waters didn’t compound their troubles.

Looking at the issue through that local lens, the discussion draft is a most welcome approach, that might, Congress willing, force fisheries managers to fully address, and try to adapt to, the climate change issue.