Chang Ik Zhang

Climatic regime shifts and their impacts on marine ecosystem and fisheries resources in Korean waters

Abstract There were climatic regime shifts over the North Pacific in 1976 and 1988 which affected the dynamics of the marine ecosystem and fisheries resources in Korean waters. Precipitation in Korean waters showed a decadal scale climatic jump, especially of Ullungdo Island, reflecting the regime shift that occurred in the North Pacific. The variation was also detected in East Asian atmospheric systems. The Aleutian Low and North Pacific High Pressure Systems showed substantial changes in 1976 and around 1987–89. 1976 was an unusually warm year for Korea; mean sea surface temperature (SST) was higher than ‘normal’ and was accompanied by a northward shift in the thermal front. Post 1976, the volume transport of the Kuroshio Current increased and higher seawater and air temperatures persisted until 1988. Other shifts occurred after 1976 such as an increase in mixed layer depth (MLD) and biological changes in the ecosystem of Korean waters including decreases in spring primary production and an increase in autumn primary production. Primary production increased again after 1988, and was followed by a significant increase in zooplankton biomass after 1991. The 1976 regime shift was manifested by a decreased biomass and production of saury, but an increase in biomass and production of sardine and filefish in Korean waters. After 1988, recruitment, biomass, and production of sardine collapsed while those of mackerel substantially increased. Based on these observations, hypotheses on the relationship between the climate-driven oceanic changes and changes in fisheries resources were developed and are discussed.

Stock assessment and management implications of horse mackerel (Trachurus japonicus) in Korean waters, based on the relationships between recruitment and the ocean environment

This study presents an example of horse mackerel (Trachurus japonicus) stock to demonstrate that marine environmental factors are important in stock assessment for the new Korean Total Allowable Catch (TAC)based fisheries management system. The estimated survival rate ( S) of horse mackerel ranged from 0.25 to 0.36. The instantaneous coefficient of natural mortality ( M) was 0.48/year, and the age at first capture was 0.83 year. Annual biomass of horse mackerel in Korean waters was estimated by a biomass-based cohort analysis using annual catch in weight at age during 1965–1995. Yield-per-recruit and spawning biomass-per-recruit were estimated under various harvest strategies at Fmax, F0.1, F30% and F40%. A method for estimating acceptable biological catch (ABC) is proposed for dealing with the large differences in the quality and quantity of information and data available. Using recruitment of horse mackerel estimated from various spawner–recruitment relationship models combined with salinity, volume transport, and zooplankton biomass as environmental factors, the ABC under the best information available was estimated to range from 3100 to 3800 mt.  2001 Elsevier Science Ltd. All rights reserved.

A Revised Alverson and Carney Model for Estimating the Instantaneous Rate of Natural Mortality

Abstract The Alverson and Carney (AC) model for estimating the instantaneous rate of natural mortality (M) was reformulated to include β and t 0 parameters. The revised Zhang and Megrey (ZM) model could be used for the estimation of M instead of the AC model since von Bertalanffy and allometric growth parameters are readily available for most exploited fish stocks. It was determined from the new formulation that the ratios of the age at maximum biomass (t mb) to the maximum age (t max) for pelagic and demersal species were significantly different from 0.38, the value originally proposed by Alverson and Carney. The ratios for these two ecological groups were 0.302 and 0.440, respectively, and were significantly different. We examined the sensitivity and bias in M from the new formulation relative to those from the AC model, which assumed that β = 3.0 and t 0 = 0. Estimates of M from the AC model are most sensitive to the assumption that growth starts at t 0 = 0 when growth rates are high as well as to the ...

Climate variability and its effects on major fisheries in Korea

Understanding in climate effects on marine ecosystem is essential to utilize, predict, and conserve marine living resources in the 21s t century. In this review paper, we summariz ed t h e past history and current status of Korean fisheries as well as the changes in climate and oceanographic phenomena since the 1960s. Ocean ecosystems in Korean waters can be divided into three, based on the marine commercial fish catches; the demersal ecosystem in the Yellow Sea and the East China Sea, the pelagic ecosystem in the Tsushima Warm Current from the East China Sea to the East/Japan Sea, and the demersal ecosystem in the northern part of the East/Japan Sea. Through the interdisciplinary retrospective analysis using available fisheries, oceanographic, and meteorological information in three important fish communities, the trend patterns in major commercial catches and the relationship between climate/ environmental variability and responses of fish populations were identified. Much evidence revealed that marine ecosystems, including the fish community in Korean waters, has been seriously affected by oceanographic changes, and each species has responded differently. In general, species diversity is lessening, and mean trophic level of each ecosystem has decreased during the last 3~4 decades. Future changes in fisheries due to global warming are also considered for major fisheries and aquaculture in Korean waters.

Biomass-Based Cohort Analysis that Incorporates Growth

Abstract A biomass-based model for cohort analysis was examined for its performance in estimating total stock biomass over time. The model is based on the premise that a biomass-based analysis that incorporates growth can account for changes in population biomass resulting from changes in individual weight in addition to changes in number, and thereby give better estimates of population biomass over time. The biomass-based approach also facilitates the direct incorporation of data into the analysis in terms of biomass, bypassing the process of converting from biomass to numbers to do the calculations, and then converting the numbers back to biomass in order to make management decisions based on biomass. To incorporate growth into the analysis, we assumed that growth in weight occurs exponentially over the time increment of the analysis. Sensitivity of the analysis to the assumption of exponential growth was tested by examining its performance on three hypothetical data sets generated by simulations incorp...

Trade-offs associated with different modeling approaches for assessment of fish and shellfish responses to climate change

Considerable progress has been made in integrating carbon, nutrient, phytoplankton and zooplankton dynamics into global-scale physical climate models. Scientists are exploring ways to extend the resolution of the biosphere within these Earth system models (ESMs) to include impacts on global distribution and abundance of commercially exploited fish and shellfish. This paper compares different methods for modeling fish and shellfish responses to climate change on global and regional scales. Several different modeling approaches are considered including: direct applications of ESM’s, use of ESM output for estimation of shifts in bioclimatic windows, using ESM outputs to force single- and multi-species stock projection models, and using ESM and physical climate model outputs to force regional bio-physical models of varying complexity and mechanistic resolution. We evaluate the utility of each of these modeling approaches in addressing nine key questions relevant to climate change impacts on living marine resources. No single modeling approach was capable of fully addressing each question. A blend of highly mechanistic and less computationally intensive methods is recommended to gain mechanistic insights and to identify model uncertainties.

Population ecological parameters and biomass of anchovy kilka Clupeonella engrauliformis in the Caspian Sea

Through most of the last century, three endemic kilka species supported major commercial species in the Caspian Sea. It is clear that catches and abundance of all species have changed, but catch and sampling data are limited and stock assessments are inadequate. Recent changes in the Caspian Sea ecosystem have occurred as a consequence of climatic environmental change (sea level change) and ecologic change caused by the invasive ctenophore Mnemiopsis leidyi. This paper examines the effects of these changes on the population biology and biomass of anchovy kilka Clupeonella engrauliformis in Iranian waters of the Caspian of catch, length-weight relationship, von Bertalanffy growth parameters, condition factors, sex ratios, maturity stages determined from ovarian analysis, natural and fishing mortality, age at first capture, and spawning biomass. The instantaneous coefficient of natural mortality was estimated as 0.473/year and the instantaneous coefficient of fishing mortality varied during the 10-year period between 0.541 and 2.690/year. Biomass of anchovy kilka declined from about 186000 t in 1996 to less than 12000 t in 2004. Recent high fishing rates were not sustainable after the introduction of Mnemiopsis, so overfishing is part of the explanation for the collapse of anchovy kilka in the Caspian Sea.

An introduction to the Beyond El Niño conference: climate variability and marine ecosystem impacts from the tropics to the Arctic

The North Pacific Marine Science Organization (PICES) was established in 1992 during a period of rapid growth of interest in large-scale climate variability and its effects on marine ecosystems. At its inaugural annual meeting in 1992 in Victoria, Canada, PICES convened an international symposium on climate variability and fisheries production (Beamish, 1995). Since then, PICES symposia have continued to foster exchanges of new ideas about how marine ecosystems respond to environmental variation. Perhaps the most significant concept to emerge from the mid-1990s was that of regime shifts (Hare, Minobe, & Wooster, 2000). These are low frequency, high amplitude changes in community composition, species abundance and trophic structure that occur abruptly and concurrently with changes in the North Pacific climate system. An important role for PICES is in providing a forum for ongoing dialogue among scientists of the Pacific Rim. The Beyond El Nino conference held in March 2000 in La Jolla, California gave an opportunity for scientists and representatives of Pacific fisheries organizations (InterAmerican Tropical Tuna Commission, IATTC; International Pacific Halibut Commission, IPHC; Interim Scientific Committee for Tuna and Tuna-like Species, ISC; and the North Pacific Anadromous Fish Commission, NPAFC) and SCOR (Scientific Committee on Ocean Research), to discuss recent advances on topics such as climate regimes and other related developments. The objective of this conference was to consider the current state of knowledge of climate and marine ecosystem variability on all temporal scales. Whereas the intense 1997198 El Nino had temporarily diverted attention to that scale of variability, a major objective of the Beyond El Nino conference was to focus on scales of variability beyond those of El Ninos. The conference was led by a Steering Committee of Drs Warren S. Wooster, Paul H. LeBlond (co-chairs), Robin L. Allen, Bruce M. Learnan, Loh-Lee Low and Michael F. Tillman who organized the conference into 4 daily sessions, each with its own complement of co-convenors. Initially, 144 abstracts were submitted for presentation at the conference. Authors wishing to have their work considered for publication in this volume were invited to submit manuscripts at the conference. Forty manuscripts were submitted, 32 of which were selected with lead authors from 12 countries. An encapsulation of the key findings of each paper by the Guest Editors follows.

Simplified trawl system modeling and design of a depth control system using fuzzy logic

Abstract This paper describes a simplified mathematical model of a mid-water trawl system developed to help and understand the dynamic behavior of trawl, and to design the depth control system of the mid-water trawl operation. The equations of the motion for the vertically moved trawl system were obtained using Lagrange’s equation with respect to the variables of the displacement of the trawler, the length of the trawl warp, the angle of the warp to the horizon, and the angle of the hand rope to the horizon. These equations were modified as simplified types. A fuzzy logic controller was designed to control the depth of a mid-water trawl net. The fuzzy controller calculates the tension of the trawl warp to be changed, based on the depth error between desired depth and actual depth of the trawl net and the ratio of changes in the depth error. The error and error change are calculated every second of sampling time. The control input, i.e., the desirable tension of the trawl warp is determined by inference from the linguistic control rules, which is usually carried out by crew experienced in controlling the depth of the trawl net during manual operation. Computer simulations indicated that the calculated motion of the trawl system using the simplified mathematical model agreed reasonably with those of the original model and actual trawl system obtained from field experiments, and the proposed fuzzy controller rapidly followed the desired depth without steady-state error.

A study on indicators and reference points for the ecosystem-based resource assessment

Ecosystem-based fisheries management requires a holistic assessment of the status of fisheries by integrating fishery ecosystem indicators for management objectives. In this study four objectives were identified such as the maintenance of the sustainability, biodiversity and habitat quality and socio-economic benefits. The ecosystem-based fisheries assessment (EBFA) model to assess fisheries and their resources at the ecosystem level developed for Korean fisheries (Zhang et al., 2009) has a number of indicators for three management objectives. However, it was found that there were some overlapping components among indicators and that there were difficulties in assessing some indicators in the EBFA model. This study identified problems of the approach and suggested more pragmatic and simpler indicators. It also presented alternative reference points to assess indicators and discussed issues associated with the application of the EBFA model to a marine ranching ecosystem. In this study a total of 24 indicators were used for the assessment which included 4 socio-economic indicators. New indicators and reference points were demonstrated by applying it to the Uljin marine ranch.