Dovi Kacev grew up in South Africa and San Diego. A longtime La Jolla surfer, Dovi is finishing up a joint SDSU-UC-Davis Ph.D. in Ecology. For the past eleven years, he has carried out research on shark ecology and conservation which has allowed him to study sharks in the wild in San Diego, Baja California, and the Caribbean.
Serge Dedina: As a surfer who grew up in South Africa where there are a lot of sharks, why did you choose to make your life’s work the study of the ocean’s apex predators?
Dovi Kacev: From as early as I can remember I have been interested in sharks, but I did not think of becoming a shark biologist until I was in college. Learning about how important their roles are to maintaining balanced ecosystems, how little we know about their biology, and how much trouble they face due to human pressures, led me to realize that there is a lot that we need to understand better about sharks. This led me to a career in shark biology.
Dedina: On Tuesday, surfers and a photographer spotted what appeared to be a shark in Imperial Beach. What is the typical migratory pattern of these animals and what is their conservation status?
Kacev: We have many different species of shark in Southern Californian waters and each species has different migratory behavior and habitat preferences. The shark in the photograph in question looks like it is either a white shark or a basking shark, both of which are known to use local waters and both are protected species due to conservation concerns. Recent tagging studies have shown that adult white sharks tend to come to California in the fall but migrate offshore to an area in the middle of the Pacific Ocean for much of the year. Juvenile white sharks are known to spend more time in the the Southern California Bight. Much less is known about the behavior of basking sharks, but scientists are trying to learn more about them with a new tagging study. Much like it is difficult to identify the species from the photo, it is not possible to estimate the size without some sort of reference.
The shark in question. Photo courtesy of Dovi Kacev
Dedina: How many white sharks are out there along our coast?
Kacev: This is a difficult question to answer as sightings are so rare and therefore data on white shark abundance is hard to come by. The most recent study of adult white shark abundance in Northern California waters estimated that there are between 200 and 300 adult individuals, which is a pretty small population. Another recent study suggests that the population size may be growing, but growth of shark populations happens at such a slow rate because they take a long time to mature and reproduce at a slow rate. The simplest answer to this question is that the population is likely quite small and that they are more threatened by people than they are a threat to us.
Dedina: Are there any locations in Southern California and especially in San Diego County that you have identified as having larger numbers of sharks?
Kacev: There are areas of seasonal aggregations of leopard sharks and smoothhounds, but none for the larger, more pelagic sharks.
Dedina: What is the role of sharks in maintaining the balance of the ocean? Do we really need sharks?
Kacev: Sharks often act as apex predators and as such they are important for controlling the population sizes and behaviors of the species they feed upon. Research on the East Coast has shown that in certain areas where sharks have been over fished, populations of rays have blossomed leading to the collapse of shell fish fisheries, because the rays feed on the shell fish. Healthy ecosystems need to be in balance and this requires maintenance of all the levels of the food web.
Dedina: You have been traveling down the coast of Baja California to carry out shark research. What have you found there?
Kacev: We have found that in Baja there are a lot of fishing camps that catch a lot of sharks and rays, particularly juveniles. These fisheries are likely to have a large impact in the shark populations in the region. We have also found that in general the fishermen in Baja understand the importance of sustainable fisheries because their livelihoods depend on there being healthy populations of these fish. As a result, most of the fishing camps have been very accommodating to our research.
Dedina: California just passed a ban on the sale of shark fins. Why should we care about the plight of these animals?
Kacev: We should care about the plight of sharks because they are magnificent animals and our ocean ecosystems rely on them. Beyond just the value of sharks for their ecosystem services, it is important to remember that many people’s livelihoods revolve around the oceans and fisheries. Any disturbance that effects the balance of the ecosystem could eventually lead to the collapse of various fisheries.
