Wobbegongs: behavior to light can help determine ocean health

One of the more unusual sharks found throughout the temperate and tropical waters of the western Pacific Ocean is the wobbegong. A bottom-feeder, the wobbegong has camouflaging motley coloration and frilly appendages around its mouth that some believe act as a lure for unsuspecting prey.

While the populations of various shark species that cruise the reefs can be used as a barometer as to the overall health of the ecosystem, according to researchers in Australia, the behavior of the wobbegong can also be used as an indicator of a healthy environment. By studying the behavior and understanding what geographical or habitat factors determine that behavior, then any recorded change in behavior may point to changes in the marine environment.

Dr. Susan Theiss of the University of Queensland has studied the light sensitivity of several wobbegong species and how different sensitivity establishes different levels of activity. She reported, "It appears that the wobbegong species we studied have different visual adaptations that could be linked to times of increased activity. For example, the spotted and dwarf spotted wobbegongs are probably more active in low-light conditions such as night time, or in the early morning or late afternoon, whereas the western and ornate wobbegongs are visually suited to a range of light conditions."

Professor Shaun Collin of the University of Western Australia, who also worked with Dr. Theiss in the study, said, "Almost nothing is known about the behaviour of wobbegongs, but what our research on the visual systems can do is predict their behaviour, so we look at the shark's visual system at the level of the photoreceptors, which are the cells that detect light. If you see these common species interacting and behaving normally in a particular environment, this can be a good indicator of the health of that part of the ocean."

Marine biologists study the role that sharks play as predators and scavengers in maintaining a healthy marine ecosystem. Declining shark populations, due to commercial overfishing, can have pronounced effects on the ocean environment - from changes in the health of other fish species to degraded water quality and even reduced oxygen levels. By monitoring the behaviors of animals like the wobbegong shark, researchers gain insight into how animals respond to changes in their environment.

"This research is important in establishing general trends and predictions in biogeography and ecology that we don't yet have data for," Dr Theiss said.

Oh, and yes, we are related. I am her proud uncle. Dr. Theiss is a U.S. national working for the University of Queensland and I someday hope to get across the Pacific and have her show me some of her frilly-mouthed friends first hand.

Read about the wobbegong research in Science Alert.

Shifting Baselines: what is the appropriate measurement of a healthy ocean?

When we examine a marine ecosystem or the population of a particular species and observe that "it's not what it once was," we are, in simple terms, observing a shifting baseline. The use of shifting baselines, or what has sometimes been called Shifting Baseline Syndrome (SBS), has become a common but controversial tool in evaluating fishery management, species population, and general ocean vitality. In fact, it has been used as the basis of study for a variety of scientific and societal conditions - from ocean conservation to Hollywood entertainment.

One of the challenges in using SBS is in determining what the fundamental baseline is - what is the baseline that represents a fully healthy, functioning marine ecosystem or species population? Is it what it was 10 years ago? A century? Or before the arrival of mankind? To determine such an ultimate starting point, scientists often have to take a variety of empirical and anecdotal data and work backwards. Sometimes this works, sometimes not.

As an example, one study in the late 1990's determined that the appropriate baseline population for green sea turtles in the Caribbean was 660 million, based on an extrapolation of the extent of a particular sea grass that figured prominently in the turtle's diet. Several years later, based on a reevaluation of the sea grass growth, that number was scaled back to 16 to 33 million - quite a reduction but still, given today's population of less than 200,000, what can we realistically expect as a conservation goal?

In other situations, SBS gets oversimplified in its application regarding policy. When research determined that over-fishing was the primary cause of a drop in Canadian cod fisheries, a moratorium was put in place in the early 90's. However, the cod population has failed to recover and the moratorium remains in place. What may have been missed is some unforeseen cascade effect, some other component to a healthy cod population that is missing or altered, perhaps triggered by the over-fishing, perhaps not.

Many scientists see value in using SBS but there are some who feel that it must be utilized in a more comprehensive fashion that also incorporates other theoretical approaches including resilience and social-ecological systems (SES) which introduce variables of human involvement or impact while trying to determine an appropriate future baseline.

In the end, it can be a vexing question: as we consider the health of marine species or ecosystems, what is the ideal goal that we can truly expect to strive for, regardless of how things were in the past? Can science accurately and reliably make that determination? Hopefully, it can but it will require a broad spectrum of scientific approaches to do so.

Click here for a proponent web site that explains shifting baselines.
Click here to read a scientific paper on SBS weaknesses and solutions.