Pacific Salmon Commission

Abstract Mobile acoustic sounding is an effective survey method for fish abundance residing or migrating in large riverine basins and marine areas. A long-standing challenge in acoustic fish surveys with conventional sonar is the uncertainty in identifying fish targets from acquired echo data. Identification errors of fish targets can significantly bias estimates of fish abundances and negatively impact the management of fisheries. In contrast to conventional sonar, adaptive resolution imaging sonar (ARIS), if deployed properly with appropriate settings, can yield high-quality images of fish targets. ARIS images acquired with adequate frame rates can form video recordings to allow for confident identification of fish targets from recorded morphological features, sizes, direction of movements, and speeds. In this paper, we present an approach of using ARIS sonar for mobile surveys of fish passage in a riverine environment. Applications of this approach are demonstrated for its practical values with results from an ARIS-based mobile survey of upstream migrating salmon at an acoustically challenging fish-counting site on the lower Fraser River in British Columbia, Canada.

Abstract Management of data-limited populations is a key challenge to the sustainability of fisheries around the world. For example, sockeye salmon (Oncorhynchus nerka) spawn and rear in many remote coastal watersheds of British Columbia (BC), Canada, making population assessment a challenge. Estimating conservation and management targets for these populations is particularly relevant given their importance to First Nations and commercial fisheries. Most sockeye salmon have obligate lake-rearing as juveniles, and total abundance is typically limited by production in rearing lakes. Although methods have been developed to estimate population capacity based on nursery lake photosynthetic rate (PR) and lake area or volume, they have not yet been widely incorporated into stock-recruit analyses. We tested the value of combining lake-based capacity estimates with traditional stock-recruit based approaches to assess population status using a hierarchical-Bayesian stock-recruit model for 70 populations across coastal BC. This analysis revealed regional variation in sockeye population productivity (Ricker α), with coastal stocks exhibiting lower mean productivity than those in interior watersheds. Using moderately-informative PR estimates of capacity as priors reduced model uncertainty, with a more than five-fold reduction in credible interval width for estimates of conservation benchmarks (e.g. SMAX- spawner abundance at carrying capacity). We estimated that almost half of these remote sockeye stocks are below one commonly applied conservation benchmarks (SMSY), despite substantial reductions in fishing pressure in recent decades. Thus, habitat-based capacity estimates can dramatically reduce scientific uncertainty in model estimates of management targets that underpin sustainable sockeye fisheries. More generally, our analysis reveals opportunities to integrate spatial analyses of habitat characteristics with population models to inform conservation and management of exploited species where population data are limited.

At large spatial scales, aggregating across populations, North American sockeye salmon populations have largely overlapped marine distributions in the North Pacific Ocean (e.g., Bristol Bay and British Columbia stocks, Quinn 2018), but we do not have a good understanding of the marine distribution of sockeye salmon at smaller scales. For example, we do not know how sockeye salmon from different British Columbian rivers are distributed in the North Pacific Ocean. Similarly, we do not know where genetically distinct stocks within a river are distributed in the ocean. Understanding the marine distributions and migratory routes at more granular levels (e.g., stocks within rivers) is beneficial because conservation and fisheries management mostly occur at such scales. Also, it is of considerable scientific interest to understand mechanisms governing long-distance animal movement. Here, we focus on the marine distributions and migratory paths of Fraser River sockeye salmon stocks, whose fisheries management is governed by the Pacific Salmon Treaty between the United States and Canada.

Abstract The impact of freshwater environmental factors on spawning migration mortality was modeled to provide a predictive tool for fisheries management of four run timing groups of Fraser River sockeye salmon Oncorhynchus nerka: early Stuart (Stuart Lake), early summer, summer, and late. We tested the significance of different measures of water temperature, discharge, fish abundance, and entry timing for forecasting discrepancies between lower‐river and upriver escapement estimates using multiple regressions of principal component scores. Descriptive discrepancy models (i.e., “management adjustment” models) identified using Akaike's information criterion were consistent with the known biology of each group. For example, temperature and discharge thresholds were selected for early Stuart run discrepancy models, reflecting the extremes in both variables experienced by these early migrants. Predictive discrepancy models were also generated for each run timing group by using the limited number of environmental variables that are available in‐season to fisheries managers. Even predictive discrepancy models using simple environmental metrics of average river temperature, flow, and river entry timing provide a valuable tool for forecasting relative indices of spawning migration mortality. This study provides an example of how environmentally based predictive tools can be used to inform fisheries management decisions and improve the probability of achieving spawning escapement targets.