Stopping Whale & Vessel Collisions
Commercial whaling drove many whale species to near extinction in the 20th century. At the precipice of their disappearance, these marine giants and their haunting songs caught the attention of the public, and the anti-whaling movement of the 1970s grew to unprecedented international proportions: it was a cause for the global citizen and for the planet at large. It’s a wonderful success story, and whales began repopulating our oceans once again. Unfortunately, we can’t undo the severe damage inflicted in previous centuries simply by banning destructive practices; we need to take active measures to protect whale species if they are to survive. Many whale species today are classified as endangered or vulnerable, and this is still due to human action. One such action is vessel collisions.
Vessel collisions, while accidental, are also preventable. There has been growth in the study of animal movement, which is a more complicated field than it might appear, since it incorporates individual psychological state, locomotive and navigational abilities, and external factors. Advancement in movement ecological theory and better animal tracking technology has allowed this field to become an important one for conservation.
In this study, researchers looked at the movements of the Eastern South Pacific (ESP) blue whale (balaenoptera musculus) in northern Chilean Patagonia in order to figure out where the whales spend their time, and where there is the most overlap with vessel traffic. They combined results from earlier species distribution models (SDM) and tagged 15 blue whales to study their movements for different lengths of time, from just over a week to about three months.
Researchers found that their findings were in line with previous SDMs. Earlier studies found that they could predict the distribution of blue whales by looking at spring chlorophyll-a concentration and the presence of thermal fronts. Krill, the primary prey of blue whales, feed on chlorophyll-containing algae, so where there is a high chlorophyll-a concentration in the spring, krill will soon follow. Adult krill are concentrated by thermal fronts, and this is where the blue whales go to feed. This study found that individual whales modified their behavior in these areas by traveling at a lower velocity with less directional persistence (meaning, more changes in direction). They also found that whales responded to thermal gradients regardless of the presence of spring chlorophyll-a, which could be because thermal fronts increase prey availability.
This study improved upon older movement studies in a few ways. Older studies looked at whale density but not at individual whales, so high whale density could have been caused by multiple individuals entering a space and then leaving. By looking at individual whales, they know that these whales were actually concentrated in certain areas for extended periods of time. In addition, previous models looked only at changes in behavioral states and relied on certain assumptions to fill in the gaps. This new model allowed researchers to estimate velocity and true location of individual whales without having to make assumptions.
With this movement data established, researchers in this study then looked at daily vessel tracking information from the Chilean National Fisheries and Aquaculture Service (SERNAPESCA). It is mandatory for all industrial, artisanal, aquaculture, and transport fleets to provide tracking information to SERNAPESCA. They found that while the artisanal fishing fleet showed the highest degree of spatial overlap with the blue whales, the aquaculture fleet is by far the most densely distributed, so it is likely the major driver of negative interactions. They also found that the highest probability of vessel interaction was in the inner waters.
Researchers emphasized that urgent management actions are needed to keep whales and vessels apart where possible, and other measures (such as speed regulation) are needed where this isn’t possible. Blue whales are unable to avoid vessels unless the vessel is in a relatively slow ascent or descent, and whales cannot move away from vessels horizontally, so it is our responsibility to ensure safe passage for them whenever we can. Research like this can and must be applied to identify safe corridors, and this needs to be done on an international scale. For the blue whale, the loss of even a few individuals per year could mean the difference between extinction and recovery.
It is an unfortunate truth that much of the technology developed over the years has been used to the detriment of animals and the environment. As we face the consequences of our actions, we see that technology can be used to rebuild as well as to destroy. This study is an example of the former, with researchers using the latest technology to call on us to be better stewards of the earth.