Economic, ecological and genetic impacts of marine stock enhancement and sea ranching: A systematic review

Abstract

Hatchery release is one of the most popular management tools in fisheries, forestry and wild life management, while its negative impacts on wild populations are a global concern. Research and monitoring of its impacts are generally lacking, and the usefulness of hatchery release for fisheries and conservation objectives is unclear. Here, I evaluated positive and negative impacts of worldwide marine stock enhancement and sea ranching programmes in a systematic review associated with meta‐analyses with the goal of reducing bias of the review. Vast numbers of individuals of more than 180 species are released into the wild each year, but most studies are at experimental stages to assess its potential, and empirical studies are sparse for evaluating the impact on fishery production. Most cases are economically unprofitable except for a few successful cases or unevaluated. The effects of releasing juveniles can be dwarfed by the magnitude of natural recruitment when the spawning stock produces much larger recruitment than released juveniles. Density‐dependent growth caused by competition of food can be substantial, and growth rates of hatchery and wild fish and other competitive species can simultaneously be reduced when stocking exceeded the carrying capacity. Relative reproductive success can vary depending on the species, seed quality and environmental factors. Empirical studies show evidence of substantial gene flow from hatcheries, but fitness reduction in stocked populations has not been reported. The results represent the current state of worldwide marine stock enhancement and sea ranching activity and provide key information for growing fields of artificial propagation and conservation.

Lessons from Japan marine stock enhancement and sea ranching programmes over 100 years

“…I did not analyse net present value (NPV) (Sproul &Tominaga 1992; Moksness & Støle 1997; Moksness et al 1998; Svåsand et al 2000) because various data, such as annual costs for harvest, management, and interest rates, were not available for every case. If the economic efficiency estimates obtained here had relied on NPV, they would have been smaller (Kitada 2018); in that case, the values of the estimates would have depended on interest rates and time duration (although interest rates in Japan are currently low, <0.1%). In addition, the seed cost used in the analysis did not include personnel expenses, facilities, monitoring, or administration costs; furthermore, it did not account for the cost of negative effects on natural populations and ecosystems (Waples 1991; Winton & Hilborn 1994; Hilborn 1998; Waples 1999; Waples & Drake 2004; Amoroso et al 2017).…”

“…Despite the huge number of seeds released every year, most studies have been conducted only at the experimental stage (Taylor et al 2017). In a previous study evaluating the economic performance of 14 cases involving 12 species worldwide, most cases were found to be economically unprofitable because of the high cost of seed production compared with prevailing market prices (Kitada 2018). Empirical studies are still too limited, however, to determine the full effectiveness of hatchery-release efforts (Laikre et al 2010), and basic questions, namely, “Do hatcheries produce extra fish for harvest, or do they simply replace natural fish with hatchery fish?” and “Are hatcheries cost-effective for producing fish?” have seldom been answered (Waples 1999).…”

“…Reviews on salmonids have covered large-scale hatchery releases, mainly focusing on chum salmon and pink salmon; however, their emphasis was mainly on ecology, with stocking effects not fully evaluated (e.g., Kaeriyama 1999; Morita et al 2006; Kaeriyama et al 2012; Nagata et al 2012; Miyakoshi et al 2013; Kitada 2014; Morita 2014). My previous systematic review provided a perspective on economic, ecological, and genetic effects of marine stock enhancement and sea ranching programmes worldwide, including salmon (Kitada 2018), but its focus was global. No integrated review evaluating the results of both marine and salmonid stock enhancement in Japan has yet appeared.…”

“…YPR is defined as the weight of fish caught (g) per individual released (Svåsand et al 2000; Kitada & Kishino 2006; Hamasaki & Kitada 2008b) as follows: where r is the recapture rate of released juveniles, and w (g) is mean body weight per recaptured individual. Economic efficiency ( E ) was calculated as the ratio of net income to release costs: Here, v is fish price per gram, and c is the cost of each seed; therefore, v / c is the cost performance of a seed (Kitada 2018). The true mean for the recapture rate, YPR, and economic efficiency for each study ( y i ) was not observed but instead estimated .…”

“…Assuming for simplicity that does not depend on a particular case, for all i (1,…, n ) and from , the MLE of σ 2 is: By estimating μ by the weighted average given by Eq. (1) and by the mean of the sample variance , the approximate variance estimator is: The MLE of μ used here had a different weight than the weighted mean (also the MLE) used in my previous study (Kitada 2018), while was the same. Eq.…”