Operational Harvest Control Rules and their Application to a Recovering Forage Fish Stock

Abstract

Since the 1990s, international fisheries management has strived towards implementing precautionary management practices to reduce the risk of overfishing and subsequent stock collapse, and to promote rebuilding stocks from low levels. To achieve this, many fisheries have adopted pre-agreed upon catch setting algorithms known as harvest control rules (HCRs), which compute allowable catch as a function of stock status. Such HCRs can take many functional forms ranging from simple constant catch rules to complex empirical rules based on biomass levels, tagging data, and genetic mark recapture information. Here I examine the application of HCRs to Pacific herring (Clupea pallasii) in Prince William Sound (PWS), Alaska. The population experienced a major population crash in the early 1990s, following the Exxon Valdez oil spill, and has failed to recover in the 30 years since, despite the current HCR recommending no directed fishing take place since 1999. The collapse has therefore cost Alaska communities hundreds of millions of dollars in lost economic activity. Recent increases in biomass have pushed the stock near the lower biomass limit required for reopening the fishery, presenting an opportunity to reassess and evaluate HCRs for the fishery prior to its reopening. I review existing operational examples of HCRs from multiple countries and regions across the world before applying them in a simulation framework to the PWS herring stock. In Chapter 1, I characterize patterns in operational HCR implementation across region, species type, and data availability. There is substantial heterogeneity in HCR design across different regions, and little obvious patterns in HCR type by species. There is, however, a consistent trend of more complex model-based rules being reserved for stocks with the most available data and empirical and catch-based rules being used for data-poor stocks. I present a set of recommendations regarding HCR implementation based on the existing fisheries management literature and patterns in the operational adoption of such rules. In Chapter 2, I develop a Management Strategy Evaluation (MSE) for the Pacific herring stock in PWS, with the specific goal of assessing the ability of using various HCRs to manage the stock over the next thirty years. Ten HCRs were assessed, ranging from simple threshold rules to novel rules that account for population age structure, weight distribution, and recent biomass changes. Simulation results demonstrate that threshold rules, including the existing rule, are able to adequately manage the stock, notably including a rule that allows for fishing at lower biomasses than other rules. Rules that account for age-structure and recent biomass changes also performed well and could be considered reasonable alternatives to the more common threshold rules, despite their lack of adoption in other fisheries. These results, while specific to the unique characteristics of the PWS herring population, demonstrate that careful integration of additional population information (e.g. age structure, trends, etc.) into the functional form of the HCR could be useful for managing stocks for which more typical HCR forms are not adequate, particularly for populations undergoing long periods of population recovery.