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Mortality in the early marine period in a particular habitat is related to the severity of the factors causing mortality and the time that juvenile Pacific salmon Oncorhynchus spp. spend in the habitat. Juvenile sockeye salmon O. nerka produced in the Fraser River rear in the Strait of Georgia immediately upon leaving freshwater. We used catches from trawl and purse seine surveys to develop two estimates of their average residence time in the Strait of Georgia and present a third estimate which pertains to Chilko Lake smolts in particular. The average time between the entry of the last 1% of juvenile sockeye salmon into the Strait of Georgia and the departure of the last juveniles was 54 d. The average time between the point when the maximum number of juvenile sockeye salmon entered the Strait of Georgia and the point when the maximum abundance in the strait occurred was 43 d. Individuals from the Chilko Lake population were shown to spend a minimum of 31–43 d in the Strait of Georgia, indicating...

1. For the overwhelming majority of species, we lack long-term information on the dynamics of populations. As a consequence, we face considerable uncertainty about how to discriminate among competing hypotheses of population decline and design conservation plans. 2. The marbled murrelet Brachyramphus marmoratus is a small seabird that nests in coastal old-growth forest but feeds year-round in near-shore waters of the north-eastern Pacific. Although a decline in nesting habitat is the primary reason why marbled murrelets are listed as threatened in Canada, nest predation and food availability may also influence population abundance. To examine the hypothesis that murrelet populations are influenced by variation in diet quality, we analysed stable-carbon and -nitrogen isotopes in feathers of museum specimens collected in the Georgia Basin, British Columbia. 3. Between 1889 and 1996, we found a decline in stable isotopic signatures that was approximately equal to a 62% drop in trophic feeding level. We also found that the estimated proportion of fish in murrelet diet was related closely to murrelet abundance over the past 40 years, as estimated from volunteer surveys. Using these isotopic data, we modelled population size as a function of variation in reproductive rate due to changes in diet quality and found that our model matched closely the 40-year field estimates. We then applied our 107-year isotopic record to the model to back-cast estimates of population growth rate to 1889. 4. Our results suggest that, up to the 1950s, murrelet populations in the Georgia Basin were capable of growing and were probably limited by factors other than diet quality. After this period, however, our results imply that murrelets were often, but not solely, limited by diet quality. 5. Synthesis and applications. Protecting nesting habitat may not be sufficient to rebuild populations of this highly secretive and threatened seabird and recovery might also require the restoration of marine habitat quality, as well as a better understanding of how ocean climate affects prey abundance and reproductive rate. Combined with contemporary demographic data, stable isotope analysis of historic samples provides a unique opportunity to reconstruct population histories for species where we lack long-term information.

The mean trophic level (TL) of fish landed in fisheries on the east and west coasts of Canada is declining by 0.03–0.10·decade–1, similar to global trends. This finding is based on data from United Nations Food and Agriculture Organization and the Canadian Department of Fisheries and Oceans and other Canadian sources for the period 1873–1997. Significant rates of decline in mean TL were obtained even when key species — Atlantic cod (Gadus morhua) on the east coast and Pacific herring (Clupea pallasi) and Pacific hake (Merluccius productus) on the west coast — were omitted from the analysis. Fish taken in inland water fisheries did not exhibit a decline in mean TL. Two models were developed, based on length and age, respectively, for correcting TL estimates of individual species for the effects of changes in body size due to changes in fishing mortality. Both produced corrections that were small relative to changes in mean TL that resulted from changes in species composition of the catch over time. Overall, these results suggest that the mean TL of fish landed can be used as an index of sustainability in multispecies fisheries and that its reliability will depend on the quality of the data and length of the time series available for analysis.

rapfish is a new multi-disciplinary rapid appraisal technique for evaluating the comparative sustainability of fisheries. For the purpose of this analysis, fisheries may be defined flexibly as entities with a broad scope, such as all the fisheries in a lake, or with narrower scope, such as those in a single jurisdiction, target species, gear type or vessel. A set of fisheries may be compared, or the time trajectories of individual fisheries may be plotted. Attributes are chosen to reflect sustainability within each discipline, and although intended to remain fixed for all analyses, may be refined or substituted as improved information becomes available. Ordinations of sets of attributes are performed using multi-dimensional scaling (MDS) followed by scaling and rotation. Ordinations are anchored by fixed reference points that simulate the best and worst possible fisheries using extremes of the attribute scores, while other anchors secure the ordination in a second axis normal to the first. Randomly scored reference points act as anchors and define significant differences. Separate rapfish ordinations may be performed in ecological, economic, ethical, social and technological disciplines: a further evaluation field expresses compliance with the FAO Code of Conduct for Responsible Fisheries. Monte Carlo simulation can be used to estimate errors, while the leverage of each attribute on scores can be estimated with a stepwise procedure. Status results may be expressed on a scale from 0 to 100%, and scores from several fields may be combined in kite diagrams to facilitate comparison of fisheries or fisheries constructed to represent alternative policies. Some validations of the methodology are presented, using simulated fishery data. Results from published work using rapfish are reviewed briefly, along with prospects for further improvements to the technique.

This chapter describes a new multivariate, multidisciplinary and interdisciplinary rapid appraisal technique that can be used to classify world fisheries and diagnose their problems. For ecological, technological, economic and social categories, we chose 15–25 attributes that (a) are easily and objectively scored on a ranked scale using readily available data, (b) are likely to discriminate among fisheries, and (c) may be easily related to sustainability. A multivariate ordination using multidimensional scaling (MDS) is performed within each disciplinary set of attributes. The ordination scores are then brought together into an overall interdisciplinary analysis, also using MDS. Reference points for evaluating the relative status of fisheries are provided by constructing hypothetical fisheries that are assigned ‘good’, ‘bad’ or ‘random’ scores, defined in terms of sustain-ability for each discipline, or that have a random assignment of attribute values.