High stress and large degree of physiology impairment linked to mortality.
Life is unpredictable.
You can schedule an entire day, week or month but plans can change in an instant. Knees crossed, shades upon his head and beard twirling, Enrico Gennari attested to this on the morning of May 22nd after receiving a phone call from the Mossel Bay municipality indicating the beaching of a Great White Shark in the area. He quickly contacted his colleagues around South Africa and made his way to the location of the shark. In the weeks prior, three White Sharks had been found on the shores of Gaansbaai. Having been the targeted victims of Orca attacks, it was expected that the shark in Mossel Bay suffered a similar fate. However, on arrival it was noted that the body was intact, few red markings on the shark and there was a hue in the eyes – the animal had died not long ago. With no indication of harsh physical trauma, how did this shark end up ashore?
Having studied these creatures for more than 15 years, the marine biologist brightens at the opportunity to be at the forefront of this case. Enrico takes the interview to a new dimension as he transports us into his mind and his process of deductive reasoning. Firstly, had the shark died naturally it would have sunk to the bottom of the ocean, likely being consumed by the other scavengers of the sea. Another sign of foul play was the presence of a large J hook on a steel trace in the jaws. It was fishy, fishy indeed.
The loss of an animal is always a tragic event but this beaching provided an opportunity to gain valuable knowledge by exploring from the inside out. Seizing the moment, the biologist contacted the authorities requesting permission to keep the body for a necropsy and invited other scientists to come assist in the dissection. A necropsy is a surgical examination of a deceased animal to identify the cause of death. It is extremely, “difficult to obtain anatomic information on Great White Sharks since they are hardly seen for long periods and do not have to surface for air.” The possible information that may be obtained could benefit not only the scientific community but provide public education into these large ocean dwellers.
The public necropsy performed by Dr Enrico Gennari, Dr Malcolm Smale and Alison Towner took place the following day at the Diaz Museum. But why a public necropsy – would it not be better for the scientific community to privately and more quickly conduct their data collection? Enrico lifts his hand up abruptly and says no. White Sharks are classified as endangered and protected by South African law. With that, anglers are strictly prohibited from targeting White Sharks and fisheries laws state that incidentally captured animals must be released immediately. The procedure offered the opportunity to educate a wide audience and debunk common myths and stereotypes. The most eminent threat to the majestic elasmobranch fish is public perception. Fascination is normally focused on the size of the sharks, their powerful jaws and teeth. Italian charm and comedy work are advantageous tools for Enrico during this open event. In this way, he can discuss fishing and scientific information with a mixture of fun facts.
Many locals have never seen a shark in their life and so it is important to understand and appreciate a Mossel Bay trademark. “The public needs to want the survival of the shark species if there is going to be any progress in the long-term conservation movement.” Moreover, the hope was that fishermen would attend and leave with a greater understanding and a new outlook on their fishing practices.
Sharks play a major role in balancing the oceans because as predators they keep ecosystems in check whose futures are threatened throughout the globe. When sharks are disturbed by intentional fishing or fisheries bycatch – the ecosystem can collapse. In an article published by Australian Institute of Marine Science, it was stated that “where shark numbers are reduced we see a fundamental change in the structure of food chains on reefs. We see increasing numbers of mid-level predators – such as snappers – and a reduction in the numbers of herbivores – such as parrotfishes. The parrotfishes are very important because they eat the algae that would otherwise overwhelm young corals on reefs recovering from natural disturbances." This means that the livelihood of these fishermen is in the hands of this roaming species and is at greater risk due to negligence.
The results of the necropsy highlighted that the shark on Diaz beach showcased no signs of hemorrhaging and was in good health prior to her death. Her pristine teeth and jaws enabled her to kill the prey – a Cape fur seal - in one bite. This is not possible for an animal in poor health as they would lack both the strength and the agility to do so. The dissection also revealed abnormalities in the case of a natural death such as evidence of human interference and chemical imbalances.
The blood sample taken from the shark indicated sky rocketed levels of cortisol, catabolite and lactate. All substances released during extreme stress events. The data levels recorded indicate a fight that would have lasted anywhere possibly up to 8 hours. The stress release process follows along three major steps. It begins with the primary stress response in which compounds are released in the blood flow. The second response involves a release of lactate, calcium, magnesium and other components which can impact processes at cellular and body levels. The hydrogen in the blood level decreases pH causing acidosis whereby the body fluids contain too much acid causing an inability to keep the body’s pH regulated resulting in fatigue. Low oxygen and high carbon dioxide mean less and less oxygen to be transported throughout the body. This causes a large degree of physiological impairment which can be linked to mortality. Finally, even if death does not result from the large stress event, there can be a long-term impact on the behavior of the shark. This change to its fitness can change the gene flows which are passed onto the next generation reducing the fitness of the species. Natural selection causes populations to become the most fit for their environments over time. Therefore, the fishing of the sharks may decrease the heritable phenotypes changing the evolution of the species over time. Although hard to prove, this theory appears logical if we compare it to Darwin’s theory of evolution and natural selection.
Despite not often being targeted, it does not mean that the sharks are not affected by the fishing practices being used. The law is clear, enforcement is the main area that needs to be worked on. Long cut lines can be extremely harmful as regardless of if you cut the line the shark may entrap itself. Fishers should employ every effort to not fish in areas known to have high White Shark populations, they should avoid thick lines and cut lines as close as possible to the animal. If the above cannot be avoided, then the handling and fight time with the creatures should be reduced as much as possible to maximize the physiological and behavioral functioning of the Great White Shark.
By Marissa Callender, Oceans Campus