Proceedings of the International Symposium on King and Tanner Crabs, by Alaska Sea Grant College Program

Lyman Thorsteinson
1991 Arctic  
In November 1989 an international symposium on the biology and management of king and Tanner crabs was held in Anchorage, Alaska. Agency, university, and industry representatives from five nations (U.S., Canada, U.S.S.R., Japan, and Argentina) met for three days to discuss the status of fishable populations, biological research, and management practices relative to these crabs. The conference was the eighth of the Lowell Wakefield series, designed to promote technology transfer among various
more » ... er among various segments of the fishing industry. This was articulated in the opening remarks by Dr. John Costlow (Duke University), who described the societal benefits conferred by such information exchanges, extolling their role in the management and conservation of our coastal resources. More than 50 technical papers described various aspects of the natural histories, ecologies, and fisheries for king and Tanner crabs. The concluding session at the symposium was an open workshop discussion where participants expressed their concerns for research needs and, quite candidly, their philosophies regarding the management of these lucrative fisheries. The symposium proceedings is a collection of most of the technical papers presented at the symposium, including a transcript of the closing workshop. Collectively, the papers provide a valuable singlesource reference for all professionals participating in research and management of these or similar crustacean resources. The document organizes the manuscripts into five categories: life history, feeding and growth, mortality, population structure and dynamics, and stock assessment and management. The contents are not meant to be comprehensive reviews; and individual contributions vary widely in content. Individually, the manuscripts are of an autonomous nature, having been prepared in standard scientific formats. As such, they provide excellent sources regarding a multitude of field and analytical techniques currently in use in the study of crab populations. Editorially, the papers vary in writing quality and style. Some would benefit from additional peer review. However, considering the number of papers involved, the international nature of the meeting, the relatively fast publication schedule, and the price of the book, the overall quality is very good. The meeting was heavily attended by U.S. scientists studying Alaskan crabs. As a result, a majority of the papers address king crab resources and issues pertaining to the Gulf of Alaska and Bering Sea. Considering the past and potential value of this fishery, these papers are particularly timely. Several species of commercially harvested crabs are included by the king and Tanner crab taxonomic designations. Commercial quantities of Lithodidae (king) and Majidae (snow and Tanner) crabs are widely distributed in temperate and higher latitude seas of the northern and, to a lesser extent, southern hemispheres. Major fisheries are located in inland waters of southeast Alaska, on shelf areas of the Gulf of Alaska, Bering Sea and the Sea of Japan, and, in Canada, off British Columbia and in the Gulf of St. Lawrence. A southern form of king crab (and two congeners) are harvested in sub-Antarctic waters of Chile and Argentina. Apparently, few species occur in sufficient numbers or densities to support viable commercial fisheries. The existing fisheries exploit populations of four species of king crab and two species of Tanner crabs. Within the king crab group, red king crabs are without question the most famous and biologically well known. However, at least six other, lesser known, congeners are currently harvested or are probable targets of expanding fisheries. During the early 1980s red king crab populations declined throughout Alaska; they remain depressed today. This decline quickly led the fishing industry to shift to more abundant but less valuable Tanner crab resources. This is evidenced by the rapid economic growth in the snow crab fisheries that has occurred during the past decade. Although several species are cap tured, C. bairdi and C. opilio crabs constitute the bulk of all landings. The unifying theme of the symposium was the socioeconomic and biological information needed to bring stability to the seafood industry. High interannual variation in resource abundance typifies the king and Tanner crab fisheries of the world. They have historically followed economic cycles of "boom or bust," and it is during periods of diminished resource abundance that fishery effects become most profound. The stock fluctuations are pervasive in the seafood industries, affecting individual and corporate incomes, capitalization, and the marketplace. In a sense these fluctuations are reflective of the dynamic nature of marine ecosystems, where shifts in abundance follow the complex interplay of abiotic and biotic factors responsible for exceptional year class successes or failures. At the species level, the growth and decline of populations underlie the biological and economical instability that pervades both the management and harvest sectors of the fishing industry. Achievement of increased economic and regulatory stability may be possible with improved knowledge of the causes, magnitudes, and periodicities in recruitment and with foresight of the economic effects of resource management. The management of crab stocks requires, among other things, reliable information about the magnitude and condition of the resource at any given time. This has traditionally been accomplished by means of broad-scale resource surveys designed to provide data on the size, sex, and relative abundance of fishable stocks. Landing statistics as a surrogate for stock abundance should also be monitored to examine trends within exploited populations. Since variability is pervasive in the marine environment, longterm records of biological and oceanographic data are necessary to document change and assess the significance of fishery activities. A shared goal of management and industry alike is for biological stability within the king and Tanner crab populations. If realized, exploited populations would be able to maintain and perpetuate themselves while annual harvests remain relatively constant in the face of variable recruitment. Various strategies are employed to protect stocks; and most commonly, a quota system limiting catches of certain sizes is employed. The size restriction generally applies to male crabs old enough to have mated at least once prior to recruitment into the fishery. However, the determination of age in crabs is imprecise. Further, field and laboratory observations provide conflicting results as to the effective size male crabs must be in the wild for successful first mating. The determination of morphometric maturity in male C. opilio crabs is also uncertain and may be better indicated by claw size than by conventional measures of carapace width. In each instance, these problems have direct bearing on the determination of the reproductive potential of these populations. Since there is a tendency to overfish, questions persist about possible fishery effects on declining or depressed stocks. A number of numerical models are used to describe relationships between age and growth and stock abundance in crabs. The effects of temperature-dependent growth, varying size, and sex restrictions on the management strategies for red king crab as explored in modeling efforts are described in a number of papers. A comparison of the predictive capabilities of traditional spawner-recruit and cohort analysis models used to forecast year class strengths in red king crab suggests biological and statistical advantages to the latter approach. Evidently, cohort analysis more accurately describes the parent-recruitment relationship over the lifetime of the crab. Crabs have interannual variations in abundance that range over an order of magnitude at the exploited stage. These variations have led biologists to seek explanations for cycles within the dynamics of local crab populations and in their relationships to habitat attributes. The book contains numerous examples of recent studies investigating various determinants of year class success. They include field studies concerning the 1) migration and movement behaviors of crabs, 2) the role of ocean temperatures and currents on ontogenic development and larval drift, and 3) food habits and growth in crabs. In the laboratory, experiments concerning the effects of 1) temperature and salinity on the growth of larval and juvenile crabs and 2) diet on growth in crabs have been recently conducted to explore environmental influ-
doi:10.14430/arctic1897 fatcat:tbn7kruyxnaxzb27u235typtpy