Deciding which species “deserve” the most resources and attention in terms of conservation can be a contentious issue at the best of times. Members of the general public tend to favour protecting the cute and cuddly however, are these characteristics really the most effective way to decide how to direct our efforts? Using a publication written by Chapple et al. (2011) and estimating white shark populations in California, USA, as a case-study, this two-blog series aims to highlight:
- The difficulties of estimating population sizes of marine species
- The importance of the production of the most accurate information possible from the scientific community, and
- The impact of these factors on the success of conserving endangered marine species.
Case Study: The White Shark in Californian Waters
The white shark (Carcharodon carcharias) represents one of the world’s most popular apex predators. Due to their cosmopolitan distribution, perceived population declines, concerns for the potential for them to become overfished, as well as the vulnerability inferred from white sharks’:
- Long life span (approximately 30 years)
- Late arrival at sexual maturity (10-15 years)
- Production of between 2 to 10 pups biannually (gestation period of 12-18 months)
White sharks have been protected under legislation and/or fisheries restrictions in the following countries for numerous years:
- South Africa (1991)
- Namibia (1993)
- Australia (1999)
- Malta (2000)
- Mexico (2002)
- New Zealand (2007)
- United States:
- California (1994)
- North-west Atlantic and Gulf of Mexico (1997)
- Remainder of the US Exclusive Economic Zone (EEZ; 2005)
The highly migratory nature of these sharks however, makes it highly probable that these animals will travel outside of protected waters where there is potential for them to fall victim to oceanic and coastal fisheries. As a result of this, white sharks are also currently listed through:
- The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES)
- The Convention on Migratory Species (CMS)
- The International Union for Conservation of Nature
- Lists white sharks as vulnerable
The naturally low numbers of these sharks in an area at any one point in time, alongside their migratory nature, makes accurately estimating their population sizes difficult to achieve and so researchers tend to focus on areas they are known to aggregate. A study by Chapple et al. (2011) did just this, focussing on the areas around the Farallon Islands and Tomales Point to estimate the population size of white sharks off of the central California coast in the USA.
As discussed in my previous blog, Chapple et al. proposed that the central California population of white sharks consists of only 219 mature and sub-adult individuals. This low estimate created serious – and legitimate - concerns about the status of white shark populations in Californian waters, prompting petitions to have the species put on the endangered species lists for the State of California.
What’s the big deal about listing a species as endangered?
The listing of species on endangered lists can be viewed as major achievement by conservation organisations and as a result of this, listing decisions can often be rushed before the published population estimates have a chance to undergo even a minimum level of critical scientific review. Not only do these decisions place substantial demands on governments to devote considerable resources to protecting the animal in question, but they also impact groups within the general public who must forgo social and economic opportunities to ensure that they do not break the protective laws. Most importantly, listing species that are not under true threat of biological extinction will divert resources away from those which are genuinely at risk of meeting this fate; defeating the purpose of implementing these conservation and management policies in the first place.
So, what about the results of Chapple et al.’s study?
If correct, the low estimates of white sharks presented by Chapple et al. justifiably raise concerns for the status of the white shark population in California and the ENP. A recent re-evaluation of the size of the white shark population off the Californian coast conducted by Burgess et al. (2014) however, has since indicated a minimum all-life stages population size of over 2,000; suggesting that the population of white sharks in this area is at least stable.
What does this mean for white sharks in California? Should they still be protected?
In the last two decades, global shark numbers have been in rapid decline due to increased human pressures in the form of long-lines, targeted fisheries, and shark fining practises with populations decreasing by 70% worldwide. The white shark is not immune to these global threats and due to their unfortunate involvement in numerous fatal shark attacks across the past 3-5 years they face the added pressure of being the targeted by multiple drum-line and shark net programs across the globe. Burgess et al.’s newest population estimate and recent observations indicate that the existing conservation and management measures in Californian waters for white sharks are sufficient and their population is likely to be improving. Although this places doubt on whether the white shark should be listed as endangered in this area, it does not mean that the protection of these animals should be stopped. As well as maintaining current protective measures, the status of these animals should be regularly monitored using a variety of techniques to avoid unbiased results.
The results of Burgess et al.’s review also highlight the need for multiple modelling approaches to be used when assessing the population dynamics of such a migratory marine species. Researches should be motivated to undertake a more complete analysis when considering white shark populations to ensure that the most accurate information possible, with full disclosure of uncertainties and potential errors, is available to the public at all times. Aiming to produce the most accurate population estimates possible will ensure that the limited resources available for conservation efforts is not misdirected and that protective measures will be applied to the species which need them most.
Conservation efforts must remain dynamic and flexible to reflect the rapidly changing environment and animal populations around us, especially in a time where the budget for such efforts is minimal. The review of Chapple et al.’s study by Burgess and his colleagues should not be viewed as a corrected mistake, but a step in the right direction and further development of our understanding of these elusive animals. We should always strive to learn more and protect what we have, while we still have it.
Oceans Research P.I. and Field Specialist
Burgess GH, Bruce BD, Cailliet GM, Goldman KJ, Grubbs RD, Lowe CG, Macneil MA, Mollet HF, Weng KC, O’Sullivan JB (2014) A Re-evaluation of the Size of the White Shark (Carcharodon carcharias) Population off California, USA. PLoS ONE 9(6): e98078.
Chapple TK, Jorgensen SJ, Anderson SD, Kanive PE, Klimley AP, et al.. (2011) A first estimate of white shark, Carcharodon carcharias, abundance off central California. Biol Lett 7: 584-583.