Estimating the number of whales entering trade using DNA profiling and capture‐recapture analysis of market products

Abstract

Surveys of commercial markets combined with molecular taxonomy (i.e. molecular monitoring) provide a means to detect products from illegal, unregulated and/or unreported (IUU) exploitation, including the sale of fisheries bycatch and wild meat (bushmeat). Capture-recapture analyses of market products using DNA profiling have the potential to estimate the total number of individuals entering the market. However, these analyses are not directly analogous to those of living individuals because a 'market individual' does not die suddenly but, instead, remains available for a time in decreasing quantities, rather like the exponential decay of a radioactive isotope. Here we use mitochondrial DNA (mtDNA) sequences and microsatellite genotypes to individually identify products from North Pacific minke whales (Balaenoptera acutorostrata ssp.) purchased in 12 surveys of markets in the Republic of (South) Korea from 1999 to 2003. By applying a novel capture-recapture model with a decay rate parameter to the 205 unique DNA profiles found among 289 products, we estimated that the total number of whales entering trade across the five-year survey period was 827 (SE, 164; CV, 0.20) and that the average 'half-life' of products from an individual whale on the market was 1.82 months (SE, 0.24; CV, 0.13). Our estimate of whales in trade (reflecting the true numbers killed) was significantly greater than the officially reported bycatch of 458 whales for this period. This unregulated exploitation has serious implications for the survival of this genetically distinct coastal population. Although our capture-recapture model was developed for specific application to the Korean whale-meat markets, the exponential decay function could be modified to improve the estimates of trade in other wildmeat or fisheries markets or abundance of living populations by noninvasive genotyping.

Marine Mammals in Asian Societies; Trends in Consumption, Bait, and Traditional Use

“…Some of these have already been utilized to reveal discrepancies in reported marine mammal bycatch, to determine the magnitude of trade and to develop kits that rapidly identify marine mammal species in situ in Asian markets (Baker et al, 2006(Baker et al, , 2007Lukoschek et al, 2009;Lo et al, 2013). These tools, designed specifically for non-specialists, will allow quantitative data collection both on type and volume of marine mammal parts in Asian markets.…”

Status of J stock minke whales (Balaenoptera acutorostrata)

“…Actually, several studies reported that there was a high number of illegal, unreported or unregulated catches for this stock (Baker et al 2006(Baker et al , 2007Lukoschek et al 2009). Also, the default value of R max was used to estimate PBR for minke whales in this area because the data on R max were insufficient.…”

“…To estimate the status of J stock minke whales, abundance (Kitakado et al 2010) and mortality (Baker et al 2007;Lukoschek et al 2009) data of this stock were used. Also, to investigatethe trend in abundance of minke whales in Korean waters, abundance data of minke whales in the East Sea of Korea from 2000 to 2008 were used .…”

Cetacean By-Catch in the Korean Peninsula—by Chance or by Design?

“…For example, Tinch and Phang (2009) report that prices in 2006 in Japan were around US$16 per kg, compared to prices of up to US$37/kg in South Korea for confiscated fresh whale meat. Illegal hunting is potentially also a major source of meat based on verbal comments by our interviewees and previous studies on whale meat market in South Korea (Dalebout et al 2002;Baker et al 2006Baker et al , 2007. Indeed, one interviewee reported that many restaurant owners would actually only buy token amounts of legal by-catch to cover up their primary illegal source and another confessed in a follow-up chat in 2010 that auction prices of by-catch are highly dependent on 'the illegal supply.'…”