How to look deep into the sea

“We rarely see the full event from start,” says Mridula Srinivasan, Marine Biologist from National Oceanic and Atmospheric Administration (NOAA). This inability to view predator-prey interactions is one major difference between the land environment and the ocean, and marine biologists often have to piece together bits of the puzzle to get the larger picture.

One such puzzle Srinivasan is interested in is the way humpback whales interfere when killer whales chase their prey — mostly the prey belongs to some other species, though sometimes the killer whales do prey on the calves of humpback whales — and divert their attention so that the prey escapes. Is this an example of “interspecific altruism” (altruistic behaviour to help an animal belonging to a different species, without any selfish benefit)? It is not yet confirmed. But, the scientists think that the humpback whale is interfering with the hunt, regardless of what species is being preyed upon. We can speculate on motives for such behaviour. From simple altruism to more complex reasons, such as an enhanced form of mobbing or a intrinsic characteristic to be more offensive than defensive when dealing with a powerful and skilled predator depending on the situation. Which is the correct reason? There are no answers right now.

Mridula Srinivasan is chief of Protected Species Science Branch at National Oceanic and Atmospheric Administration, in the United States. She is passionately into the study and conservation of dolphins and advises NOAA Fisheries on issues related to protected species such as dolphins, whales, corals, sea turtles and sea birds. She has a lot to say on the subject of life in the ocean, the importance of marine mammals and how to use science to perfect conservation efforts…

Can you describe the ocean from the point of view of a marine biologist? How does doing marine science compare with studying species on the land?

The ocean is very dynamic, and it’s also a very difficult environment to study. We are not capable of studying all the patterns and processes that are happening in the underwater world. We are getting better at it with the technology that we have. We use several observational platforms to study it, but it is pretty vast, with vast spots of emptiness, it takes a lot of effort to study the ocean, its processes, dynamics and also the relationships. The cool thing is the cross-disciplinary nature of it. When you are a marine scientist you are not just concerned with your species of interest. You have to understand the context, the full ecosystem, how animals are impacted by their immediate environment, by human actions, how does the natural biology and behaviour and life history of the animal contribute to its survival, viability or to its detriment.

There are also similarities with land ecosystems, in that you still have key ecological players. Human effects do impact the viability of the organisms. There is this parallel between ocean and land. You have key megafauna species — sharks, sea turtles, whales, dolphins — which sit at the top of the food chain just like lions and bears. So their protection, understanding their biology, behaviour and impacts helps us understand the broader ecosystem.

Top predators have cascading effects. You see the impact down the food chain. There is also the bottom-up forcing. When there is a lowering of their preferred prey population, the impact can also go up the chain.

So, to summarise, the main difference is that the ocean environment is highly dynamic; very, very large; and very difficult to study. Simply because it’s inaccessible — a foreign, hostile environment compared to land where you get longer observation windows. We mostly study them (ocean dwellers) during the daytime. The similarity is that both have important ecological players that are affected by human activities.

News reports often sound alarms on various species — that this fish is endangered or that coral reef is bleaching, and so on… yet you choose to focus on the animals at the top of the pyramid. For instance, why do you choose to study dolphins?

The top-down forcing is the main reason. I find dolphins incredible. As mammals they have adapted to an alien environment — we can’t survive in the oceans, for instance. Evolutionarily, they have made all these changes that allow them to be fully adapted to this aquatic environment. I find that amazing.

I like predators. I am inspired or impressed by their ability to influence ecosystems, to be behaviourally dynamic. They have evolved complex social systems just like chimps and bonabos and use this to survive and reproduce. They are behaviourally adaptive or plastic: No two species of dolphin behave the same way. They are resilient in comparison to other species, and apart from this, there is their complex problem-solving ability, ability to leverage their social status to address these problems. I found their social decision-making — just like in lions — very fascinating.

Dolphins also occur in all parts of the ocean. They also feed on a variety of prey. So it’s not that I am focussing on the animal but on the system, the question. When you ask these questions about why the dolphins are moving from one area to another; why does the species behave one way or another, etc., you have to go into the details of the prey, the habitat, the environment and the human impact as well. The dolphin is just a model species — what’s really interesting is the question.

In your study of marine mammals, what are the key questions you’ve addressed so far?

I am interested in predation-risk effects and broadly behavioural ecology, which is about the evolutionary consequences of animal behaviour I am interested in predator-prey interaction, particularly how these highly mobile social predators come up with complex strategies to hunt prey. By the same token, the same animals can also be hunted by larger animals. In this case, smaller dolphins get attacked by killer whales — which are larger dolphins. So even though they have the same sensory modalities, they still have to outmanoeuvre each other, outsmart each other. That’s incredibly fascinating for me.

I am really interested in the consequence of predator decision-making. All animals want to survive and reproduce. And I am particularly interested in the survival aspect — how animals evolve various strategies to avoid being eaten by a predator. In the short term, the animal can survive, but in the long term it can have consequences. For example, [it] may decide to eat poor quality food or try to hide in an area that deprives [it] of food or keeps [it] away from the family. When all this happens what is the consequence to that animal? If it decides – Ok I am resting more because there is a predator out there, or I am not being social or mating or feeding, what kind of consequence can there be — if there is a predator out there?

How to look deep into the sea

I am trying to quantify what the cost-benefits are of these anti-predator decision-making. To do this I need to understand how the predator behaves, how the prey behaves and many other factors. Is the predator the sole influencer or is it the environment, or the food? Often what we see is a trade-off between maximising food intake and minimising predation. Animals are always engaged in this decision-making. It’s so complex. Studying it requires you use both modelling and theory.

Another question that interests me is how climate variability affects dolphin distribution and demographics. When there are long-term patterns, do you see a change in their distribution? If so, what is the consequence? We have not come to this stage yet: I am just trying to understand the effect. With oceanographic change with climate change, what kind of effects can we see with dolphins, seabirds, sea turtles etc.

The problem with this research area is that you need a very long time-series. So at the moment most of the work is trying to decide what the best tools are, best approaches and finding that dataset that has the long time-series. It takes years to just look at the effects. Just trying to correlate the different climate variables with the data we have on dolphins is part of my challenge and something I am interested in. That’s the other part. This is very fascinating but a long way to go.

How to look deep into the sea

Another part of my research is the work with my colleague in the U.S. She is leading the effort to develop suction-cup non-invasive tags to track dolphins. We have done a few trials in New Zealand on dusky dolphins. It’s very promising, but again, there is a long way to go. The state of the science is that we are unable to non-invasively track dolphins. That is, use something that doesn’t cause harm or have some side-effects.

We haven’t developed any such technology yet, or anything that is long-duration. So I can know what a dolphin does for a few hours, or maybe a few days, but not for a longer period of time. We need to do it, for they are highly mobile animals and travel hundreds of kilometres. So you need to see the day-to-day changes, seasonal changes, as well as inter-annual changes. Only then you can correlate this behaviour with more dynamic changes like oceanography, prey change and climate, particularly, anthropogenic climate change. This is still at the developmental stage, we have designed a few options but it needs a lot of evaluation. But it’s exciting and we now have a video-camera on it, so we are getting data on social behaviour. The thing with dolphins is you get all this variety of behaviour that you don’t get with others. You never know what you are going to see when you get to the field; everyday is different.

We read about how dolphins show collective behaviour? How does this actually work?

Yeah, they are very synchronised. The river dolphins and porpoises are different from other dolphins, which are social. . They might disperse off when they break into smaller groups but they still have the social affiliative behaviour. They are a unit. And that’s how they survive and are able to feed on scarce resources. They are often found near the coastal regions where food can be sparsely distributed, or there can be hot spots. So depending on the prey distribution, their behaviour can change. It is a trade-off between whether there is a predator in the system and how to meet their foraging or mating needs.

On land, you can run behind a shrub or a tree or a rock — you have a refuge. But for dolphins there’s no real refuge. So most of them go into shallow waters; they literally beach themselves trying to escape a predator. Or they might try to defend themselves. Most of the time they try to out-manoeuvre the predator. It all comes back to early detection of the predator. To be aware of the threats around you, of your partners, family members, to react to signals — they are very good communicators, they vocalise… all this is part of the package of how they survive.

How far can the predator be before they sense it?

This varies. Sometimes they can sense the predator 5-6 km or even 10 km away. Or if the predator is very good — killer whales are good at being stealthy — [it can be much less]. When they are hunting dolphins in particular, they are going to be absolutely quiet. You need the element of surprise, because if the dolphin detects it, it’s going to swim away really fast.

Most of the most interesting events happen deep within the ocean — do you go underwater to detect events?

How to look deep into the sea

No. I don’t think you get much out of that. It really depends on the event and the visibility, because you can’t be there all the time. The best thing is to see the surface behaviours and follow the animals. Chases can go on for 3-4 hours; sometimes you can see nothing but you know something is happening. For example, killer whales may come into an area — there’s nothing there, for the animals have sensed the presence of a predator and fled. Observing a predation event is absolutely rare. Unless it’s happening in an area where you know it’s going to happen repeatedly. You’re never there at the beginning — you are always interrupting the drama that unfolds. Or you see a part of the animal or blubber floating and you know something happened. It’s thrilling to watch.

You have also written and spoken in other places about how it is important to be scientific in your attempts to preserve marine mammals. How do you go about this?

We are still struggling with the question of what is the perfect conservation model. You have to be aware of factors such as livelihood and make sure [people] are part of the decision-making process. Ultimately animal conservation is about managing people; we have to work with people. There are various tradeoffs and you have to compromise. But to get to that point where you start talking about conservation, you still need to do the science. You need to know where your animals are, how many of them are there, and what impacts them; isolate the most critical threats against the smaller ones.

The science is in trying to understand the animal’s environment, behaviour, biology. If you don’t know that, it’s very difficult to propose solutions. For example, you can say, “Reduce vessel speed here.” But if there are no dolphins in that area, or if they are in that area only one month of the year… [it would be a wasted effort]. So you need to know the biology of how these animals behave — the baseline. Once you know the baseline, how they react to impacts, then you can propose mitigative solutions.

But you’re never going to have a perfect solution — don’t let the perfect be the enemy of the good!

One of the things that — again — you have spoken about earlier is stranding response. What does one do when one sees a whale or dolphin on the beach, stranded?

We are seeing if we can help support a national structure for stranding response. It is important having some best practices, because you want everyone following consistent guidelines. It goes back to this point: When you see an animal on the beach — dead or alive — and you collect some data and push it back, you are just taking care of the immediate problem. What you are not addressing is why that animal is on the beach in the first place — maybe it got hit by a boat; maybe it’s diseased; maybe it carries some toxins. All this has an impact; it is an indicator of ocean health. So, when animals are stranded on the beach, if there is some human intervention involved, it is important for us to know. But even if there is a natural reason — if they are weak or starving — it shows there is not enough prey to eat. You need to understand what the problem is.

Oftentimes, you may not know what the cause of death is, but you get some clues, and you want to collect as much data from the animal as possible. You want to know what species it is, what sex it is, its measurements, its age (is it an adult, a calf or a sub-adult?) what is unique about that animal. Does it have a wound, are there marks from a fishing gear, did it get hit by a boat or was there a shark-bite? What did it eat? You can also look into the genetics — is it unique to this area? So you get a lot of data and data is just the first step to asking more questions. It is important to put together a picture about the animal before you can talk about conservation.

If you try to protect something blindly, then you are not helping the animal, the habitat or the ecosystem.

You have to make sure the right people are on the table, getting the data, processing and publishing the data. Obviously, not all of this can be put in peer-reviewed publication, but [you can] make the information public and over time use it to inform conservation planning and further research.

Our code of editorial values

This article is closed for comments.
Please Email the Editor

Printable version | Nov 27, 2021 7:29:53 PM |

Next Story