Despite the extensive use of photographic identification methods to investigate humpback whales in the North Pacific, few quantitative analyses have been conducted. We report on a comprehensive analysis of interchange in the North Pacific among three wintering regions (Mexico, Hawaii, and Japan) each with two to three subareas, and feeding areas that extended from southern California to the Aleutian Islands. Of the 6,413 identification photographs of humpback whales obtained by 16 independent research groups between 1990 and 1993 and examined for this study, 3,650 photographs were determined to be of suitable quality. A total of 1,241 matches was found by two independent matching teams, identifying 2,712 unique whales in the sample (seen one to five times). Site fidelity was greatest at feeding areas where there was a high rate of resightings in the same area in different years and a low rate of interchange among different areas. Migrations between winter regions and feeding areas did not follow a simple pattern, although highest match rates were found for whales that moved between Hawaii and southeastern Alaska, and between mainland and Baja Mexico and California. Interchange among subareas of the three primary wintering regions was extensive for Hawaii, variable (depending on subareas) for Mexico, and low for Japan and reflected the relative distances among subareas. Interchange among these primary wintering regions was rare. This study provides the first quantitative assessment of the migratory structure of humpback whales in the entire North Pacific basin.

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.

We estimated the abundance of humpback whales in the North Pacific by capture‐recapture methods using over 18,000 fluke identification photographs collected in 2004–2006. Our best estimate of abundance was 21,808 (CV = 0.04). We estimated the biases in this value using a simulation model. Births and deaths, which violate the assumption of a closed population, resulted in a bias of +5.2%, exclusion of calves in samples resulted in a bias of −10.5%, failure to achieve random geographic sampling resulted in a bias of −0.4%, and missed matches resulted in a bias of +9.3%. Known sex‐biased sampling favoring males in breeding areas did not add significant bias if both sexes are proportionately sampled in the feeding areas. Our best estimate of abundance was 21,063 after accounting for a net bias of +3.5%. This estimate is likely to be lower than the true abundance due to two additional sources of bias: individual heterogeneity in the probability of being sampled (unquantified) and the likely existence of an unknown and unsampled breeding area (−8.7%). Results confirm that the overall humpback whale population in the North Pacific has continued to increase and is now greater than some prior estimates of prewhaling abundance.

Increased farm salmon production has heightened concerns about the association between disease on farm and wild fish. The controversy is particularly evident in the Broughton Archipelago of Western Canada, where a high prevalence of sea lice (ectoparasitic copepods) was first reported on juvenile wild pink salmon (Oncorhynchus gorbuscha) in 2001. Exposure to sea lice from farmed Atlantic salmon (Salmo salar) was thought to be the cause of the 97% population decline before these fish returned to spawn in 2002, although no diagnostic investigation was done to rule out other causes of mortality. To address the concern that sea lice from fish farms would cause population extinction of wild salmon, we analyzed 10-20 y of fish farm data and 60 y of pink salmon data. We show that the number of pink salmon returning to spawn in the fall predicts the number of female sea lice on farm fish the next spring, which, in turn, accounts for 98% of the annual variability in the prevalence of sea lice on outmigrating wild juvenile salmon. However, productivity of wild salmon is not negatively associated with either farm lice numbers or farm fish production, and all published field and laboratory data support the conclusion that something other than sea lice caused the population decline in 2002. We conclude that separating farm salmon from wild salmon-proposed through coordinated fallowing or closed containment-will not increase wild salmon productivity and that medical analysis can improve our understanding of complex issues related to aquaculture sustainability.B ecause salmon aquaculture production has rapidly increased over the past three decades, the potential for environmental impacts of salmon farms has generated heightened scientific and public interest (1, 2). One concern about salmon farms is that they are the source of ectoparasitic sea lice infestations that might reduce the marine survival of wild salmon (3, 4). In the Broughton Archipelago region of Western Canada (Fig. S1), farming of Atlantic salmon (Salmo salar) began in the late 1980s, and annual farm salmon production increased steadily to 17 Gg by 1999 (Fig. S2). Pink salmon (Oncorhynchus gorbuscha) is the most abundant wild salmon species in the Broughton Archipelago; they enter the marine environment at a very small size (0.2 g), and they return to natal streams to spawn 2 y after their parents (5). Because age at maturity never varies, they have distinct evenand odd-year populations ( Fig. S2 and SI Text). Record high numbers of pink salmon returned to spawn in rivers of the Broughton Archipelago in 2000 and 2001 (Dataset S1), but these returns were followed by population decline of 97% in 2002 and 88% in 2003 (Figs. S2 and S3 and SI Text). When juvenile pink salmon in the Broughton Archipelago were first examined for sea lice in June 2001, more than 90% were infested-leading to the hypothesis that sea lice from fish farms were the cause of population collapse in 2002 (4).Adult pink salmon are a natural host for the sea louse species Lepeophtheirus salmoni...