|A new study from the ARC Center of Excellence for Coral Reef Studies revealed that shark pups cannot reach their physical peak if born in a stressful environment. / Photo by: Jukkis via Shutterstock|
Shark babies or pups are born either as eggs or as little sharks already. Depending on the species, sharks can have 1 to 100 pups at a time. Sharks that grow inside their mother before they are born are fewer in number compared to those that hatch from eggs outside the mother’s body. While the mother sharks search for a safe place to give birth or lay their eggs, they do not care for the pups after they are born.
Why marine and human-induced stressors put shark population at risk
A new study from the ARC Center of Excellence for Coral Reef Studies revealed that shark pups cannot reach their physical peak if born in a stressful environment. Larger shark pups born on degraded coral reefs perform worse and grow less compared to smaller shark pups that are born on pristine coral reefs.
There are many marine stressors that lead to ecological changes. One human-induced marine stressor is climate change and this was emphasized by the current research. The team said that the stressors “put shark populations at risk.”
Comparing two populations of baby reef sharks
James Cook University Coral CoE’s shark researcher Dr. Jodie Rummer, who co-authored the study, said that they compared the two populations of pups. The first came from St. Joseph Atoll, an island in Seychelles. The second population was from Moorea, an island in Moorea-Maiao, French Polynesia. They found out that although pups are born heavier, better conditioned, and larger in Moorea, they will, later on, lose their physical advantage over sharks found in St. Joseph.
The team’s study is titled “Same species, different prerequisites: investigating body condition and foraging success in young reef sharks between an atoll and an island system” and published in the scientific journal Nature.
They also detailed that St. Joseph is a small, remote, and uninhabited atoll in Seychelles. At the time of their research, there were no environmental changes that happened in the said outer island. On the other hand, Moorea is a popular tourist attraction but is still recovering from the loss of 95 percent of its coral cover five years prior to the team’s research. Lead author Ornella C. Weideli from the PSL Research University and the Save Our Seas Foundation D'Arros Research Center (SOSF-DRC) stated that newborn sharks have extra fat reserves they get from their mother at the time they were born. The shark pups will use said the energy reserves to sustain them during the first weeks after they were born. That kind of “energy boost” is important for them because they have to be independent immediately.
|Newborn sharks have extra fat reserves they get from their mother at the time they were born. / Photo by: Andrea Izzotti via 123rf|
The international team “captured and measured” 546 shark pups and analyzed what these sharks were eating. The sharks’ energy reserves also vary based on locations they were from. In Moorea, bigger mothers gave birth to bigger pups. However, it doesn't mean that the pups will grow quickly and eat after that. Soon, those bigger pups living in Moorea lost their initial advantage, such as in condition, weight, and size as they were in a stressed environment.
Weideli added that against the team’s expectations, the sharks only started foraging for their food later despite having greater energy reserves at the time they were born. That resulted in a decline in their body. The team believed that those pups lost their advantage because the place experienced a degraded quantity and quality of prey, as well as human-induced environmental stressors. These stressors include coastal development, climate change, and over-fishing in Moorea.
Purpose of the research
The group went on to say that the research is important for spotting “critical” nursery areas for sharks, as well as other marine protected areas and their sanctuaries. The team referred to sharks in Moorea as “slow growers” attributed to the hot temperatures that resulted in coral bleaching. If they are slow growers, it also means that it takes a long time for them to reach their sexual maturity and will mean fewer babies and fewer to survive.
Importance of sharks in the ecosystem
Sharks play an important role in keeping the balance and health of the ocean because they are a part of intricate food webs. An international organization focused on oceans, Oceana, emphasized that as predators, sharks remove the sick and the weak and ensure species diversity in the ocean. They change the spatial habitat of their prey, which alters the diets and feeding strategies of other species.
Because of spatial abundance and control, the apex predators indirectly maintain the coral reef habitats, as well as seagrass. Removing sharks in the coral reef ecosystem means larger predatory fish, including the groupers, will increase and a large number of them will feed on herbivores (animals that get their energy by eating plants). As a result, less marine herbivores means that coral cannot compete and macroalgae expand. Because of algal dominance, the survival of the coral reef system is affected.