Stock assessment of Japanese eels using Japanese abundance indices

Abstract

The paper compiles a catch history of Japanese eels Anguilla japonica in East Asia and some Japanese relative abundance series. Maximum likelihood estimates of stock abundance of eels have been obtained using the abundance series and various biological parameters, such as growth, maturity and natural mortality. Age-and sexstructured models have been used to express the dynamics of stock abundance, and the Beverton and Holt model has been used to express the relationship between stock and recruitment. Data for estimations are standardized catch per unit effort of commercial fishery for exploitable stock (1954-2006 and 1968-2008) and for glass eel (1954-2010, 1972-2004, and 1973-1997). From the results of the base case scenario of estimations, the estimated stock size of individuals aged C1 year was 18.7 thousand tons in 2010, which was 24 % of the carrying capacity. The estimated stock size has recovered since 1990. Maximum sustainable yield was 4,180 tons if only the exploitable stock were utilized, and 266 tons if only the glass eel were utilized. These results and issues relating to estimation and management for reducing the fishery impact on stock are discussed.

Evaluation from otolith Sr stable isotope ratios of possible juvenile growth areas of Japanese eels collected from the West Mariana Ridge spawning area

“…Therefore, it is important to adequately manage the entire river system from the lower estuary to upper reaches, thus allowing eel movement in either direction (Wakiya et al 2016). Furthermore, the demographic heterogeneity among the river systems supporting Japanese eels, pointed to the importance of conserving a variety of habitats in multiple river systems as an inclusive management target, in addition to restoration of habitat diversity of within single river systems (Yokouchi et al 2008;2014).…”

“…However, stock levels of Japanese eels associated with glass eel recruitment have shown serious declines throughout the distribution range in recent decades, as have those of two other Northern Hemisphere temperate eel species, the European eel A. anguilla and American eel A. rostrata. The 2010 catch of exploitable stock of Japanese eels and glass eels in Japan has been estimated as only 8% of maximum post-World War II catch levels (Tanaka 2014), with continued the downward trend thereafter. The European eel is listed as critically endangered on the IUCN Red List (2011 Version), and both Japanese and American eels were considered as "threatened" in 2014 by the IUCN (Japanese eel: Jacoby and Gollock 2014; American eel: .…”

Freshwater eels: A symbol of the effects of global change

“…Concerning the American eel, the recruitment in the upper Saint Lawrence River and Lake Ontario has nearly ceased in one of the most productive areas (Casselman, 2003) and commercial silver eel CPUE dropped by at least 50% in 40 years in the Saint Lawrence River (de Lafontaine, Gagnon, & Côté, 2009). Recruitment of Japanese eel has followed a very similar decline, corresponding to 80% in the last decades (Dekker et al, 2003;Tanaka, 2014). As a result, IUCN classified…”

“…In France, about 25% of the arriving glass eels were harvested by commercial fisheries, and this estimate did not include the catch from illegal fisheries (Figure 8; Drouineau, Beaulaton, Lambert, & Briand, 2016). In Japan, these proportions rose from about 25% in the early 1950s to approximately 40% in the 1980s (Tanaka, 2014 (Nijman, 2015). In Japan, glass eel fisheries are forbidden and a special licence is required to capture seed for aquaculture and research.…”

“…Concerning the American eel, the recruitment in the upper Saint Lawrence River and Lake Ontario has nearly ceased in one of the most productive areas (Casselman, ) and commercial silver eel CPUE dropped by at least 50% in 40 years in the Saint Lawrence River (de Lafontaine, Gagnon, & Côté, ). Recruitment of Japanese eel has followed a very similar decline, corresponding to 80% in the last decades (Dekker et al., ; Tanaka, ). As a result, IUCN classified European eel as critically endangered in 2008 (confirmed in 2010 and 2014) (Jacoby & Gollock, ) while American and Japanese eels have been classified as endangered since 2014 (Jacoby, Casselman, DeLucia, Hammerson, & Gollock, ; Jacoby & Gollock, b).…”