Understanding the life history of organisms helps us learn how they grow and develop traits that help them survive in their environment. It also reveals how vulnerable a population can be if certain behaviors and traits put them at risk of extinction. In our rapidly changing world, studying a species’ life history is important to protect and ensure its future survival. Reproduction is a key part of life history, and knowing how a species reproduces helps answer important questions, like how often they have babies and how many offspring they have. In this post, we’ll discuss the results and implications of a new study on the life history of common dolphins in New Zealand, based on observations of stranded individuals over the years.
Common dolphins in New Zealand
Common dolphins are fascinating creatures that can be found all around the world, including in New Zealand. They inhabit the waters surrounding the North and South Island, as well as smaller offshore islands like the Chatham Islands. Sometimes, you might even see them stranded on land or washed up on the beach. Unfortunately, common dolphins face a significant threat known as bycatch, which happens when they are accidentally caught in fishing nets intended for other species. In fact, they are the most frequently caught dolphin species off the west coast of the North Island.
To better understand the risks these dolphins face, we need to learn more about their life history and other important biological details. Without this knowledge, it’s difficult to determine just how vulnerable they are to factors like bycatch. Additionally, we still have limited information about the overall population numbers of common dolphins in New Zealand.
When dolphins strand, either individually or in groups, we collaborate with Iwi (local groups of Māori, the indigenous people of New Zealand) to obtain permission to collect the carcasses. Then, with help from the Department of Conservation, the carcasses end up in our lab. At Massey University in Auckland, we conduct post-mortem examinations to gather crucial measurements and samples, such as body length, teeth, and reproductive organs. These samples provide us with valuable insights into their age, growth, and reproductive biology. In the laboratory, we process the samples and analyze the results, helping us uncover important information about these awesome creatures.
What does reproduction look like for these dolphins?
Based on our research, we’ve made some fascinating discoveries about female common dolphins off the coast of New Zealand. They typically become sexually mature at around 7.5 years of age. Once they reach maturity, females give birth to a single calf approximately every three years. The pregnancy lasts about 12.5 months. After giving birth, they provide their calf with milk for another 12.5 months, which is essential for the baby’s growth and development. Following this period, females take a break from reproduction for the same duration.
We also found that around one-third of the female common dolphins in this population are pregnant at any given time. It’s interesting to note that these females have the ability to give birth throughout the year, rather than having a specific breeding season. These reproductive patterns align with what has been observed in other common dolphin populations around the world, including those in the North Atlantic, tropical Pacific, and North Pacific.
This study provides valuable insights into the reproductive behaviors of female common dolphins in the waters of New Zealand. It is the first study to establish a baseline understanding of their reproduction in this region. In fact, it is only the second paper published on this species for the entire Southern Hemisphere!
Understanding how species reproduce is crucial for conservation managers and scientists. It enables us to monitor and protect these animals more effectively. Like many other marine mammal species, common dolphins are vulnerable to various human-induced impacts worldwide. By having this knowledge about their reproductive patterns, we can now closely monitor the population and detect any changes that could potentially affect their long-term survival.
This baseline knowledge is a significant step forward in our efforts to preserve common dolphins in New Zealand. It empowers us to take proactive measures and make informed decisions to safeguard their future.
Palmer, E. I., Betty, E. L., Murphy, S., Perrott, M. R., Smith, A. N. H., & Stockin, K. A. (2022) Reproductive biology of female common dolphins (Delphinus delphis) in New Zealand waters. Marine Biology, 169(158). https://doi.org/10.1007/s00227-022-04139-3
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Hi, I'm Emily and I am currently doing my PhD in Zoology at Massey University, Auckland, New Zealand. My thesis is titled "The life history of New Zealand common dolphins (Delphinus delphis)" and focuses on the growth and reproduction of the species. I have been with the Cetacean Ecology Research Group for over 3 years now and am involved with stranding responses and necropsies of cetaceans. My research interests are marine mammalogy, ecology and conservation.