We present a framework for evaluating the cause of fishery declines by integrating covariates into a fisheries stock assessment model. This allows the evaluation of fisheries' effects vs. natural and other human impacts. The analyses presented are based on integrating ecological science and statistics and form the basis for environmental decision-making advice. Hypothesis tests are described to rank hypotheses and determine the size of a multiple covariate model. We extend recent developments in integrated analysis and use novel methods to produce effect size estimates that are relevant to policy makers and include estimates of uncertainty. Results can be directly applied to evaluate trade-offs among alternative management decisions. The methods and results are also broadly applicable outside fisheries stock assessment. We show that multiple factors influence populations and that analysis of factors in isolation can be misleading. We illustrate the framework by applying it to Pacific herring of Prince William Sound, Alaska (USA). The Pacific herring stock that spawns in Prince William Sound is a stock that has collapsed, but there are several competing or alternative hypotheses to account for the initial collapse and subsequent lack of recovery. Factors failing the initial screening tests for statistical significance included indicators of the 1989 Exxon Valdez oil spill, coho salmon predation, sea lion predation, Pacific Decadal Oscillation, Northern Oscillation Index, and effects of containment in the herring egg-on-kelp pound fishery. The overall results indicate that the most statistically significant factors related to the lack of recovery of the herring stock involve competition or predation by juvenile hatchery pink salmon on herring juveniles. Secondary factors identified in the analysis were poor nutrition in the winter, ocean (Gulf of Alaska) temperature in the winter, the viral hemorrhagic septicemia virus, and the pathogen Ichthyophonus hoferi. The implication of this result to fisheries management in Prince William Sound is that it may well be difficult to simultaneously increase the production of pink salmon and maintain a viable Pacific herring fishery. The impact can be extended to other commercially important fisheries, and a whole ecosystem approach may be needed to evaluate the costs and benefits of salmon hatcheries.

Following record harvests of Pacific herring (Clupea pallasi) in Prince William Sound, Alaska, in the 3 years after the Exxon Valdez oil spill, the fishery failed in 1993. The hypotheses advanced to explain this dramatic 1993 decline occur in three categories: (i) effects associated with the 1989 oil spill, (ii) harvesting effects, and (iii) natural phenomena. Based on our review, we are convinced that a combination of increasing Prince William Sound herring biomass and decreasing food supply led to poor condition of Prince William Sound herring, which resulted in the 1993 decline. Other natural causes could have contributed to the decline, including disease, cold water temperatures, increased predation, and other natural stochastic processes. No evidence supports hypotheses that the decline resulted solely from overharvesting or underharvesting. The record high population levels and harvests of Prince William Sound herring in the years after the 1989 oil spill, the lack of change from the expected age-class distribution, and the low level of oil exposure documented for herring in 1989 and the following years all indicate that the 1989 oil spill did not contribute to the 1993 decline. Poor nutritional status, either alone or in combination with disease or other natural factors, was most likely responsible for the 1993 collapse.

No abstract

Behavior of rockfish (Sebastes spp.) exposed to air-gun sounds was examined to establish parameters in a subsequent fishing experiment to determine the effects of a geophysical survey device on fishing success. Rockfish observed in a field enclosure showed startle and alarm responses during 10-min exposures to sounds from a single 1639-cm3 air gun. For olive and black rockfish (S. serranoides and S. melanops), the threshold for the startle responses lay between 200 and 205 dB re 1 μPa. Under sound presentation, blue rockfish (S. mystinus) milled in increasingly tighter mills, and schools of black rockfish collapsed to the bottom. Vermilion (S. miniatus) and olive rockfish formed stationary schools near the bottom and, on sound presentation, either rose in the water column or moved to the bottom and became almost motionless. The general threshold for the alarm responses was about 180 dB re 1 μPa. Regression analyses of changes in depth distribution and shifts to active behaviors suggested that more subtle behavioral responses to sounds might become evident at 161 dB re 1 μPa. These initial responses were sustained only for a few minutes and may differ from those of unconfined fish.

A behavioural bioassay was used to determine the response threshold to squid extract of sablefish, Anoplopoma fimbria, held at three different feeding regimens. Sablefish responded to the odour of bait by changing swimming activity and turning behaviour. The response threshold to bait odour was influenced by both the amount of food eaten and the duration of food deprivation. The total concentration of amino acids in the bait extract was assumed to determine the response threshold as chemical fractionation studies have shown that this class of compounds is essential for the stimulatory capacities of food extracts. When fed to satiation (9.4% wet body weight) and tested after one day of food deprivation, the mean response threshold to total dissolved free amino acids was 4.4 × 10−8m (range=7.6 × 10−8 to 3.6 × 10−8m). When fed at 1.6‐2.3% wet body weight, the threshold sensitivity had increased to a mean value of 1.8 × 10−10m (range=8.4 × 10−10 to 7.0 × 10−11m) after one day of food deprivation; after four days of deprivation, the sensitivity had increased even further to a mean value of 1.4 × 10−11m (range=1.6 × 10−10 to 1.4 × 10−12m). It was also apparent that the intensity of behavioural responses to the bait odour increased with both stimulus concentration and duration of food deprivation. These results suggest that sablefish intensify their search for prey under increased feeding motivation. The active space of a bait source was estimated from the threshold values obtained. Depending on state of food deprivation, rate of chemical release from the bait and the current velocity, maximum lengths of active space within which sablefish would exhibit food searching responses vary from 10 m to several km. Stock assessment based on catch data from baited gear will need techniques that take into account those factors influencing active space for food searching.