An Evaluation Of Bio-economic Models And Management Strategies For Ommastrephes Bartramii In The Northwestern Pacific

The neon flying squid (Ommastrephes bartramii) is a large oceanicspecies which is distributed across the temperate and subtropical waters ofthe Pacific, Indian, and Atlantic Oceans. In the Northwestern Pacific Ocean(NwPO), the neon flying squid is one of the most important commerciallytargeted species for the distant-water fishing fleets of mainland China, theTaiwan Province, and Japan. Given their economic importance, manyaspects of the NwPO stock of this cephalopod have been extensivelyresearched including their basic biology, the formation of their fishinggrounds, the development of their fishery, and the dynamic changes in theirbiomass. However, only limited effort has been given to developing stockassessment models and management strategies, particularly in the area ofbio-economic analysis and the economic evaluation of managementoptions.Fisheries resources exploitation is an integrated system involvingsuch factors as resources biomass, biological characteristics, fishingmethods, economic costs, etc. As an important economic species, differentstates and regions are involved in the exploitation of the neon flying squid resources. Fishing costs and development goals vary greatly from state tostate, which makes it of great practical importance to initiate the research instrategies in resources exploitation based on multi-factors involvingbiological, economic and social issues, and meanwhile, strategies inresources optimum allocation.A systematic study of bio-economic modelsdeveloped for O. bartramii will improve the theoretical framework whichunderpins the development of stock assessment models and the evaluationof management strategies. Thus, this work will ultimately contribute toachieving optimum allocations of squid resources. This study will providetheoretical references for the scientists and policy makers involved inmaking sustainable exploitation and resource utilization decisions for the O.bartramii stock in the NwPO.In this thesis, based on fishery data and economic data (includingdiscount rates, sale prices, and fishing costs) from mainland China, theTaiwan Province, and Japan, we developed bio-economic models for thesquid fishery in the NwPO. Using these models, we investigated theoptimum levels of resource allocation of O. bartramii and discussed thedynamics in biomass, catch, and economic benefits under differentmanagement strategies. We also evaluated the risks of these relevantmanagement strategies. The four key results of this work were: (1) Using the Gordon–Schaefer model withfishery catch and economicdata from the mainland China fleet, we established a dynamicbio-economic model to analyze the effect of the discount rate on theoptimum resource allocation of O. bartramii. The results indicate that themaximum sustainable yield (MSY) for O. bartramii in the NwPOwasapproximately170.2thousand tons. At this level, the correspondingfishing effort (fMSY) was estimated at119thousand fishing days. For themaximum economic yield (MEY;162.9thousand tons), the correspondingfishing effort (fMEY) was estimated at94thousand fishing days and for thebio-economic equilibrium yield (BE;112.8thousand tons)fishing effort (fBE)was188.1thousand fishing days. Fishers report that the NwPOstock ismaintained in good conditionand not overfished. By analyzing the effectsof the discount rate on the optimum biomass level and the optimumsustainable yield, we determined that the optimum biomass level was equalto MSY when the discount rate was equal to0.43. This implies that thediscount rate did not have a significant impact on the optimum biomasslevels of O. bartramii in the NwPO. However, the discount rate did have aremarkable effect on squid prices. The results also showed that when thediscount rate (α) ranged between0.3and0.5, short-term interestsaccounted for20–30%（i.e., D (ratio of the immediate interests to theoverall interests)=0.2–0.3) of the long-term interests. Further, within this range, catch prices were maintained between9,195and12,500RMB perton and stock biomass levels remained relatively stable and achievedoptimum levels. Consequently, under these conditions,the sustainableexploitation and utilization of the neon flying squid stock is likely. Theeconomic data indicates that this price range (9,250–12,500RMB per ton)was achieved between2008and2012. During this time, therefore, catchprices nearly corresponded to the maximum sustainable yield price (PMSY;when α=0.3–0.5).(2) Using theGordon–Schaefer model with fishery catch and economicdata from the mainland China fleet, weestimated the short-term (1–5yearsmedium-term (10years), and long-term (20years) status of the fishery, itseconomic profits, and social effects under different management options.These options reflectedmanagement scenarios wherethe goal of attainingMSY, MEY, and BE were prioritized differently (as indicated by theirweighting).The results showed that the O. bartramiiin stock in the NwPOwas fully exploited, but not overfished. We also simulated future biomassvariations over the next20years under the different management options.Under all the options, biomass levels decreased significantly in the firstfive years and then returned toa stable level. When comparing the differentoptions, this research suggests that Option2(where attaining MEY is themanagement objective) or Option8(where attaining MSY and MEY are given equal priority; e.g., each given a50%weighting) are appropriatemanagement choices. Both options would ensure the sustainableexploitation of O. bartramii with annual catch and biomass estimated to be110thousand tons and220thousand tons, respectively.After comprehensive consideration ofthe ecological, economic, andsocial benefits, four options emerged as the best for securing inclusivebenefits and accumulated profits over the medium-to long-term. Theseoptions were:Option6: securing a MSY is the main management objective (giventwo-thirds of the weighting);Option13: securing a MEY is the main management objective (givena50%weighting);Option12: securing a MSY is the main management objective (givena50%weighting); andOption11: the same weightwas allocated to each managementobjective (MSY and MEY).However, under these options, fishing effort far exceeded fMSY(44.4thousands vessels), causingO. bartramii to be overfished and potentiallyleadingto the collapse of this stock.Consequently, in reality thesemanagement optionsare not suitable. Therefore, the best options wereOptions8and2under which fishing effort is controlled to between39.4 and41.9thousands fishing days. This is achieved by considering the effectsof all the factors, thus maintaining O. bartramii biomassaboveBMSY.(3) Using the Smith’s fleet dynamics model withfishery catch andeconomic data from all three fleets, we established a multi-fleetbio-economic model to simulate the development dynamics of each fleetof the O. bartramii fishery between1997and2047.We also consideredthe dynamics of fishing effort, biomass, yield, and fishery profits and thecorresponding accumulated yields and profits. The results indicate thatcatches of O. bartramii have declined sharply, especially in recent years.Catch per unit effort (CPUE) also appeared to decrease, leading us topreliminarily estimatethat O. bartramii may already be fully exploited,although not overfished. It is essentially, therefore, that fisheriesmanagers and policymakersconsider the spectrum of ecological,economic, and social benefits when developing management measuresfor this species to ensure sustainable exploitation levels aremaintained asthe fisherydevelops in the future.In determining how to optimally allocate the stock resources of theneon flying squid in the NwPO, it is necessary to consider what theactual situation of the Japanese, mainland Chinese, and ChineseTaiwanese fleets is. Optimally, the over exploitation of squid resourcesshould be avoided whilst ensuring that the fleets still remain profitable. Our results show that under all the management options, O. bartramiistock biomass decreased significantly in the first10years with dynamicvariations in fishing efforts. Biomass levels then gradually stabilized andmaintained at a low level after long-term fluctuations. Given a long-termview, a medium accumulated yield and profits were achieved underOption9(i.e., an increasing catchability coefficient for the Taiwanesefleet). This option could balance the economic and social benefits of thethree fleets and could therefore be used as a reference managementobjective for the fishery. From a conservation perspective, the O.bartramii biomass was maintained well under Option4(i.e., fishing costsof the mainland China fleet were increased while the catchabilitycoefficient of the Japanese fleet was appropriately reduced). So, thisoption could also be considered as a reference management objective.(4) Using fishery catch and economic data from all three fishingfleets, a Bayesian-basedbio-economic model was developed.Considering three different model parameter scenarios (i.e., a uniformdistribution, a normal distribution, and a logarithmic normal distributionof prior distributions) we simulated stock statuses and risk analysesforthe NwPO stock under different harvest rates.The results showed thatthe estimated parameters derived from the models, such reference points asMSY, MEY, BE, and fishing mortality were similar under the prior assumptions of the normal and logarithmic normal distributions, but thoseestimates were less than the values under the prior assumption of theuniform distribution. Under above-mentioned three alternative options, thefishing mortalities and total catches from1996to2008were less than thereference points F0.1and MSY, respectively. The annual biomass was abovethe level of BMSY. It indicated that O. bartramii resources were maintainedat the higher level and free from overfishing.When selecting appropriatemanagement strategies, fisheries policy-makers should seek tobalancethe relationships among catch, economic profits, and sustainableexploitation levels. This analysis also indicates that if a stable harvest rateis maintained, future catch rates and biomass levels in2023will behighestwhen an assumption ofuniform distributionis made. Under this scenario,the stock has the highest probability of collapse after2023. If a uniformdistribution is assumed, our conclusion is that to achieve a conservativefishery management approach,the harvest rate should be controlled to0.4and the MSY to200thousand tons. For the other two assumptions, however,the harvest rate should be controlled to0.5and the MSY to180thousandtons.