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Forecast of the Pacific herring biomass in Prince William Sound, Alaska, 1993. Regional Information Report 5J94-04. Alaska Department of Fish and Game, Juneau, Alaska.

  • Backwater Research

Abstract and Figures

An age-structured assessment (ASA) model is used to forecast the abundance of herring expected to return to spawn in Prince William Sound in 1993. The ASA model develops 1973-92 biomass estimates by smoothing differences in abundance trends suggested by spawn deposition surveys, aerial milt surveys, and the time series of purse seine, gillnet, and spawning age composition samples. The abundance trends in the 1984, and 1988-92 spawn deposition surveys are very different from abundance trends in the other indices. In addition to estimating abundance, the ASA model also estimates natural survival, maturity, and vulnerability to fishing gear. The 1993 spawning biomass is estimated to be 121,684 tonnes. At the 20% exploitation rate under the current harvest policy, the allowable harvest for the 1993 management year is 26,827 tons of herring. Following the allocations specified in the management plan, the fall 1993 food and bait herring fishery is allocated 4,373 tons of herring, the 1993 wild spawn-on-kelp fishery is allocated 2,146 tons of herring (equivalent to 268 tons of spawn-on-kelp product), the 1993 pound spawn-on-kelp fishery is allocated 3,809 tons of herring (equivalent to 305 tons of spawn- on-kelp product), the 1993 purse seine sac roe fishery is allocated 15,586 tons, and the 1993 gillnet sac roe fishery is allocated 912 tons.
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... Herring younger than 3 years of age were collected intermittently in PWS and the sex of fish under 3 years old cannot be determined reliably due to the lack of gonad development. Though herring may live beyond 11 years, we excluded older age classes due to the uncertainty of assigning ages to fish beyond this age and because that is the maximum age used in herring assessment models (Funk, 1994). Herring assigned an age of greater than 11 year represented only 0.46 percent of all fish sampled. ...
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The Pacific herring (Clupea pallasii) population in Prince William Sound, Alaska suffered a sudden collapse in 1993 and has failed to recover. No consensus has been reached for the causes of the collapse, but hypotheses span a range of ecological, environmental, and anthropogenic drivers. During the course of investigations into changes in PWS herring and salmon population dynamics and fisheries we discovered that the observed percentage of male herring in spawning biomass estimates appeared to increase since the mid-1980s. Using available data (1983–2015) we analysed sex ratios of herring caught in close proximity to the spring spawn using various gear types. In recent years, the overall sex ratio of Pacific herring in PWS has been skewed towards males (>60%), but only if samples from cast nets are included, which generally catch spawning fish. In contrast, purse seine samples, generally collected days to weeks prior to the spawn, had relatively equal sex ratios. Age also affected the sex ratio, with a higher proportion of older fish being females. Using an age-structured simulation model, we illustrate that overestimating the number of males in the population can lead to biases in estimated model parameters (such as vulnerability at age) and as a result, biases in the inferred age composition of the population, and other derived quantities. After accounting for differences in sampling gears to improve estimated sex ratios, we recommend that future work focus attention on separating spatial and temporal differences in sex ratios of this otherwise much-studied population.
Heterogeneity in human responses and decision‐making can contribute to the resilience of social–ecological systems in the face of environmental, political and economic pressures. In fishery systems worldwide, the ability of harvesters to maintain a diverse portfolio of fishing strategies is important for building adaptive capacity. We used a case‐study approach to examine the complexity of factors that inhibit or promote diversification in fisheries of Alaska, one of the major fishing regions of the world. Through a combination of harvest records and literature review, we explored shifts in participation and portfolio diversity in Alaskan fisheries over three decades. The four case‐studies examined the responses of fishers, fleets and communities to multiple, intersecting pressures, including biological declines, market and price dynamics, fishery privatization and the 1989 Exxon Valdez oil spill. These cases illustrate how stressors acting at multiple scales can encourage or constrain opportunities for diversification, and that these opportunities may be spread inequitably across participants. Overall, we found evidence for reduced participation and increasing specialization in Alaskan commercial fisheries. While numerous factors explain these trends, policies like individual quota systems and the increasing cost of entry into fisheries are forcing consolidation at local to regional scales. A portfolio approach to managing fisheries that reduces barriers to diversification and includes broad representation of resource users and communities in management may help to maintain opportunity and choice for fishers.
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This paper updates previous reviews of the 1993 stock decline of Pacific herring (Clupea pallasi) in Prince William Sound, Alaska, and focuses on hypotheses about subsequent poor recovery. Recent age structured assessment modeling with covariate analysis indicates that the population dynamics of the sound’s herring are influenced by oceanic factors, nutrition, and, most substantially, hatchery releases of juvenile pink salmon. For the 1993 decline, poor nutrition remains the most probable cause with disease a secondary response. Concerning poor recovery, we examined 16 potential factors and found three to be causal: oceanic factors, poor nutrition, and hatchery releases of juvenile pink salmon. Absences of strong year classes at both Sitka and Prince William Sound after 1993 indicate the action of large-scale ocean processes. Beyond regional-scale environmental factors, two factors specific to the sound influence the population dynamics of herring and are likely impeding recovery. First, pink salmon fry releases have increased to about 600 million annually and may disrupt feeding in young herring, which require adequate nutrition for growth and overwintering survival. Juvenile pink salmon and age-1 herring co-occur in nearshore areas of bays in late spring and summer, and available data on dietary overlap indicates potential competition between the age-1 juvenile herring and juvenile pink salmon. Field studies demonstrate that juvenile herring reduce food intake substantially in the presence of juvenile pink salmon. Second, overwintering humpback whales may consume potentially large amounts of adult herring, but further studies must confirm to what extent whale predation reduces herring biomass.
Conference Paper
Evidence of direct mortality to fishes exposed to oil is very limited. The 1989 Exxon Valdez oil spill had major impacts on marine mammals and seabirds, but was not implicated in the 1993 collapse of the Prince William Sound herring population because of the four year gap. However, we use several independent evidences, including changes in the predation behavior of Steller sea lions, to show that the collapse actually began in 1989. We show the failure to detect the actual timing of the collapse was due to deficiencies in the fishery model used to assess herring population abundance and lack of understanding about the vulnerability of herring. Finally, we show that the oil spill actually had greater impacts than originally believed as a result of catastrophic impacts on the ecosystem from the herring collapse
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The total herring harvest for 1990 is projected to be about 37,449 tons from sac roe and food/bait fisheries, a decrease from the total 1989 harvest of 48,929 tons. Stock levels are projected to be lower in many areas with substantial reductions at Togiak Bay, Kamishak Bay, Sitka Sound, and Kah Shakes. The 1989 harvest had an estimated ex-vessel value of $18,776,473, a substantial decline from prior years because of the much reduced ex-vessel prices offered during the 1989 sac-roe season and the oil spill closures in Prince William Sound. Herring sac roe fisheries are projected to harvest 30,775 tons in 1990, down from the 1989 harvest of 41,387 tons. Herring food and bait fisheries are projected to harvest 6,674 tons in 1990, down from the 1989 harvest of 7,542 tons. The 408 ton projected 1990 herring spawn-on-kelp harvest is up from the 280 ton 1989 harvest, largely because spawn-on-kelp product was not harvested in Prince William Sound as a result of the Exxon Valdez oil spill. The Hoonah Sound pound fishery in Southeast Alaska will be open during 1990 for the first time with an 11 ton guideline harvest level for sac roe product. The strong 1984 year class will return as age 6 in 1989 and is expected to be a major component of the 1990 herring stocks in most areas of the Gulf of Alaska. The 1984 year class is not as strong in Bering Sea areas and is noticeably absent from the Togiak stock of Bristol Bay. No substantial recruitment has been observed in recent years to the important Togiak herring stock. The abundance of the Togiak stock is projected to decline rapidly as the previously strong 1977 and 1978 year classes are approaching senescence. KEY WORDS: Herring, Clupea harengus pallasi, herring harvest projection, herring stock assessment, herring sac roe fishery, herring food and bait fishery, herring spawn-on-kelp.
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We examined the use of catch-at-age data for estimating population abundance, productivity, and year-class abundance. A review section is included where various published models and our new models are shown to form a cohesive theory of catch-at-age analysis linked by level of model complexity. We developed three new models with different error structures: a log-normal measurement error model, a multinomial measurement error model, and a log-normal process error model. By application to data on Pacific halibut (Hippoglossus stenolepis), we show that moderate amounts of auxiliary information, such as fishing effort data or the assumption of a spawner–recruit relationship, are needed to stabilize estimates. The models performed very similarly with moderate amounts of auxiliary information, suggesting a degree of robustness to the underlying error structure. We also developed an extension to classic catch-curve analysis that estimates relative year-class strength reasonably well.
Outlook for the Alaska herring fishery in 1948
  • L N Kolloen
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Age composition, weight, length, and sex of herring, Clupea pallasii, used for reduction in Alaska
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Estimated age-class contribution of Pacific herring to the commercial sac roe harvests of Prince William Sound, 1973-87. Alaska Department of Fish and Game, Division of Commercial Fisheries
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Sandone, G.J. 1988. Estimated age-class contribution of Pacific herring to the commercial sac roe harvests of Prince William Sound, 1973-87. Alaska Department of Fish and Game, Division of Commercial Fisheries, Regional Information Report 2A88-18, Anchorage.
Pacific herring spawn deposition surveys for Prince William Sound, 1988, with hstoric overview. Alaska Department of Fish and Game, Division of Commercial Fisheries
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Biggs, E.F., and F. C. Funk. 1988. Pacific herring spawn deposition surveys for Prince William Sound, 1988, with hstoric overview. Alaska Department of Fish and Game, Division of Commercial Fisheries, Regional Information Report 2C88-07, Anchorage.
Outlook for the Alaska herring fishery in 1943
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