14. Shifting Baselines, Spying on Whales

14. SHIFTING BASELINES

What an organism eats means everything for its place in the economy of nature. Pull any ecology textbook from before the twenty-first century off the shelf, and you’ll see enshrined the graphic of a trophic pyramid. This pyramid, borrowed from the same visual lexicon that gave American consumers the food pyramid, shows a wide base, followed by smaller, successive steps up the triangle, with a point at the top. These stages are meant to represent the way that energy flows through ecosystems in the natural world, and the corresponding way that biological investment—the collective mass of all the organisms using that energy—winnows at each step. This graphic is a convenient and intuitive way to talk about two important ideas underpinning ecology. First, it shows that energy flows through food webs; second, it compartmentalizes organisms’ roles in a hierarchy, showing the relative number of players at each stage.

In a trophic pyramid, the base layer represents the primary energy fixers of the world, including organisms that can harvest sunlight using photosynthesis, such as plants or, far more abundant in the oceans, phytoplankton. The next layer, above the primary producers, is composed of primary consumers, such as zooplankton, which feed directly on the sun harvesters, followed by successive stages of consumers until crowned by the top consumers—mainly big, charismatic vertebrates but also, arguably, humans. We are the biosphere’s top consumer.

Biomass in marine ecosystem pyramids are actually built differently from those on land. While trophic pyramids on land generally have the stepped structure of a narrow, stacked pyramid with a very large base, marine pyramids are slightly inverted at the base, with far more biomass in zooplankton than with phytoplankton. This difference is largely about the high rate of turnover in phytoplankton—at any one instant, organisms at this lowest level are not as persistent in the environment (that is, long-lived) as those one level up, and thus don’t count as much for instantaneous biomass in an ecosystem.

As zooplankton, krill sit squarely on the second level of a trophic pyramid—one step above phytoplankton, which convert sunlight into biomass. This ecological organization is the reason that scientists describe baleen whales as feeding merely two steps away from sunlight—as long as they have the means to feed efficiently on this part of the trophic pyramid (using baleen), they can capitalize on the greater abundance of prey (by numbers) and minimize energy lost at higher levels. Large baleen whales skip up the pyramid as top predators because there are essentially no creatures that kill them, besides the rare times a pod of killer whales decides to go after an adult. Krill-eating whales thus might not be apex predators in the way that killer whales are—but baleen whales are still fairly characterized as major ocean consumers.

For decades, studies pointed to an overwhelming argument that the boom and bust of primary producers in the ocean (phytoplankton) have a direct correspondence to the occurrence of whales, in timing and geographic space. In other words, whales follow their food in the ocean. Plankton aren’t distributed evenly across the oceans; instead, their presence is dictated by large-scale oceanographic processes, such as upwelling. Ecologists therefore argued that everything about the ecology of whales was controlled from the bottom up—that lower trophic levels had a deterministic effect on top levels.

But there are also top-down trophic interactions that cut against the exclusivity of the bottom-up view. A classic example of top-down trophic mechanisms involves kelp forests off the Pacific coast of the United States. Sea urchins devour kelp fronds, and sea otters are very fond of eating sea urchins. Scientists recognized the impact that sea otters made on the physical structure and expanse of a kelp forest only when sea otters were reintroduced to the Pacific coast after over a century of overhunting, mainly for fur. In places where sea otters were reintroduced, kelp forests rebounded, having been released from the ecological constraint imposed on them by sea urchins.

Now add killer whales into the picture. In 1998 the marine ecologist Jim Estes and his colleagues argued that prey switching by killer whales in southeastern Alaska had unforeseen but clear ecological effects on lower trophic consumers and producers, such as starfish and kelp. In the field, Jim and his colleagues observed killer whales eating sea otters instead of seals and other marine mammals—leading him to wonder about the implications of a dietary equivalent of making lunch out of popcorn instead of an all-you-can-eat buffet. Their argument was pulled from the same logic as the original study on sea urchins and kelp forests: a dietary switch by an organism at the top of the trophic pyramid had effects that echoed down to the bottom levels. Their proposal led to widespread debate among ecologists about the prevalence of top-down versus bottom-up interactions in food webs. Much of the debate, however, didn’t consider recent history—in this case, an outstanding question of what killer whales ate before whaling in Alaska (and other parts of the world) fundamentally reorganized the number of big consumers in the oceans, including many large whale species that likely served as prey.

This question about what happened in marine food webs—what killer whales did before whaling, before the discipline of ecology even existed—underscores perhaps the most important idea in ecology today: we can’t assume that the size of animal populations we see today have always been this way. Shifting baselines is an idea to describe our collective cultural amnesia about how the world once was. This kind of amnesia happens when we try to measure a system undergoing massive degradation and in the meantime forget the location of past goalposts, leading to consistently shifting measures of normalcy, from generation to generation. Fishery scientists first applied the term of shifting baselines for the real phenomenon of diminished expectations of fish size or yields from overfishing. The result over the years was a dramatic shift in the concept of what would be normal for a fishery—smaller and smaller fish, and fewer and fewer of them. The idea has since gained broader traction among conservation biologists because of its utility in describing any ecological system affected by humans. It applies as much to passenger pigeons and bison as it does to whales, because no one alive today remembers the full scope of what the baseline abundance of these animal populations was once like.

There are ways, however, that we can infer what these very recent whale worlds looked like. When there are enough DNA samples available—which is the case for some species of whales, such as humpbacks—scientists can begin to use sophisticated methods to infer what their standing genetic diversity means for the history of their lineage. Humpback whales are among the many baleen whale species where we expect to see signs of genetic bottlenecking because of whaling. At low population sizes, the detrimental effects of insufficient genetic diversity can take hold (inbreeding as one example) and leave a genetic signal that lasts for generations. With some assumptions about mutation rate and knowledge of existing population size, scientists can then estimate population size at different points in the history of a group. One of the startling outcomes of this work in humpbacks was the inference that humpback whales were many times more abundant before whaling than they are today—some six times more, according to the results—a figure that conflicts with the only other source of historical data available, whaling logbooks. These latter records provide tabulations of historic kills, but the results from the genetic diversity studies seem to say that logbooks are not telling us the whole story by underestimating prewhaling populations by several magnitudes. It is hard to discern a likely historical value between these two sources of data, but, if true in any magnitude, the comparison tells us that the depleted world of whales today may be missing much of the ecosystem function and productivity that supported so many more whales only decades or centuries ago. The idea that whale baselines have shifted in the time that we’ve studied their ecology gives us a new way of looking at what we thought we knew about many species and their lives.

Much of the knowledge that we accept as foundational about ecosystem function is born out of fieldwork on a biosphere that has been severely altered by human activity and the resultant removal of huge amounts of biomass. The challenge for any whale ecologist is to understand baselines—and even whether such data matter or exist in the first place—relative to the question at hand. For example, did whales strand in different numbers (or different ways) when there were many more of them? Or what about those whalefall communities in the deep sea—what were they like before (and after) whaling removed hundreds of thousands of potential carcasses that would have otherwise rained down to the seafloor?

The ecological questions about energy use up and down food webs tend to mostly involve questions about organisms eating one another. But organic waste also factors into the equation. Yes: whale poop matters to the ocean ecosystem, on a significant scale. Whale feces aren’t particularly solid; they tend to be fleecy and float at the water’s surface until they fall apart. As they disaggregate into the water column, they bring nutrients to the surface that were previously sequestered much deeper, until a whale ate them at depth and then expelled their remains much farther up in the sunlit zone. Rarely, sperm whales will expel masses of undigested squid beaks that float and hold together like rotten mulch rolled into a ball. These particular feces are called ambergris and were once prized by the perfume industry for the pungent, sweet smell they exude—smoky and almost familiar, like a relative you last saw as a child.

In the oceans, zooplankton like fish keep a cycle of nutrients (mainly compounds with nitrogen) suspended in the photic zone, until their remains—fish bones, plankton exoskeletons, shells—rain down on the seafloor in the form of tiny particles of biological debris called marine snow. (Eventually, millions of years later, these remains may return to the surface via tectonic uplift.) Generally scientists call the processes that keep nutrients moving through the ocean a biological pump, because they move biological productivity across different depths in the water column. But add whales to the picture—especially at the scales of their prewhaling abundance—and suddenly the role of these large consumers becomes important for biological pumps in the ocean. Unlike fish and other zooplankton that migrate up and down in a narrow band of the photic zone (in step with daylight), whales transport tons of nutrients from much deeper depths all the way to the surface, where they need to breath and, as it turns out, poop. The act of defecating at the surface, usually after feeding, essentially fertilizes the entire food web, enhancing further productivity and nutrient cycling by other zooplankton. When biologists calculate the amount of biomass that prewhaling abundances of whales add to this system with their feces, the total amount of nitrogen input into a local food web can exceed that nominal amount brought in by nearby rivers and the atmosphere. Whale poop can supercharge a whole ecosystem.

Consider, for a moment, what happened to these processes during the course of industrial whaling. The systematic removal of living whales—their flesh for meat and oil and their bones, ground to bonemeal or simply dropped overboard—would hinder productivity of these nutrient cycles. We know that we are living in a less abundant world after whaling—are we somehow living in a world with a depressed ecological function too? That remains an open question. The more we discover about the important roles that whales play in ocean ecosystems, the more it’s apparent that the legacy of whaling has far broader consequences than we might have originally imagined.