Magnificent Animals: Why Sharks are Good for the Ocean and For Us

Dovi Kacev at work. Courtesy: Dovi Kacev.

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 11 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 appears to be 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.

Dedina: Is it likely the shark is still hanging out in Imperial Beach? Is there enough food locally to sustain them? And what are they typically feeding on?

Kacev: This all depends on the size and species. Last year basking sharks were sighted spending time off of Imperial Beach. They primarily filter feed on small copepods in the water column. Juvenile white sharks seem to take up residency in Southern Californian waters. As juveniles, they are fish feeders, and pose little risk to people. Adult white sharks are known to be seasonal residents in certain locations in central California and Mexico, but to the best of our knowledge tend to be just transient in our waters. If that was an adult white shark, there is no reason to expect that it is still in the area.

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 Californian 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.

Photo courtesy Dovi Kacev.

Dedina: You have been carrying out research outside of Black’s Beach. What are you and your colleagues observing there?

Kacev: The area off of Black’s Beach is interesting because of a large submarine canyon. We see a lot of leopard sharks, guitarfish, and bat rays. We occasionally catch juvenile thresher sharks in the area, which we tag and track.  In all of my time surfing, diving and fishing in that area, I have yet to see any large, potentially dangerous sharks.  This is not to say they do not exist there, but not in particularly high densities.

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.

Shark carcasses in Mexico. Courtesy Dovi Kacev

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: There seems to be a lot of documentation and reporting now about shark sightings along the California coast. Is the population of sharks increasing?

Photo courtesy of Dovi Kacev.

Kacev: It is difficult to say whether shark populations are increasing, the population of ocean users is increasing, or the likelihood of people reporting sightings is increasing. It may also be a combination of all three factors. It is important to note that most shark populations are low relative to historical abundances, so even if their populations are increasing they are still of conservation concern. Even if shark populations are increasing, they do so at a very slow rate. Also, since sharks play such an important role in our coastal ecosystems and many species are of conservation concern, we should be celebrating if their population are indeed increasing. I hope that with continued increase in public curiosity and education, people will realize that sharks are a welcome part of our ocean system.  Instead of fearing them, we should respect them.

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.

Photo courtesy of Dovi Kacev.

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