Douglas P. DeMaster’s research while affiliated with Northwest Fisheries Science Center and other places

The first dedicated aerial surveys for beluga whales in the Norton Sound/Yukon Delta region of Alaska were flown during May, June and September 1992. During May 1992 surveys, all of the survey area was covered with pack ice and only a few belugas were seen. In June 1992, many whales were seen in the region of Pastol Bay and the Yukon River Delta, with a few animals seen in eastern Norton Sound. In September 1992, whales were more dispersed and occurred both off the Yukon Delta and in coastal waters of northern Norton Sound. Based on those results, subsequent surveys were flown in June 1993-95 and 1999-2000. In all years except 1999 when there was extensive sea ice in the area, belugas were common off the Yukon Delta and in southern Norton Sound. In most years they were also seen in central Norton Sound. Density and abundance were estimated from the 2000 survey as it represented the most recent data and had the most complete and systematic coverage of the area. In June 2000, belugas were rare in the northern portion of Norton Sound, so the study area was reduced to central and southern Norton Sound and the Yukon Delta, which was divided into four strata by latitude. The density that was estimated with the model that received most Akaike Information Criterion support was 0.121 belugas km-2 and the number of belugas at the surface in the study area was estimated to be 3,497 (CV = 0.37). A generally accepted correction factor for availability of 2.0 was applied, resulting in an abundance estimate for the eastern Bering Sea beluga stock in June 2000 of 6,994 (95% confidence interval 3,162-15,472). This estimate is likely to be conservative. There are no previous abundance estimates for this region, so a population trend cannot be determined. The available evidence suggests that the current Alaska Native subsistence harvest from this stock is sustainable. Beluga consumption of prey populations is likely significant in the regional ecosystem and may have a particular impact on some stocks of Pacific salmon.

Southern Hemisphere humpback whales (Megaptera novaeangliae) migrate from wintering grounds in tropical latitudes to feeding areas in the Antarctic Ocean. In 2003 and 2005, satellite transmitters were deployed on humpback whales on their wintering grounds off the eastern coast of South America (Breeding Stock A). Seven whales were tracked for a period of 16 to 205 days travelling between 902 and 7,258km. The tracks of these whales provided partial or full information on the migratory schedule, migration routes and location of the feeding ground in the Southern Oceans. Whales departed from the coast of Brazil from late October to late December between 20˚ and 25˚S and gradually moved away from the South American coast as they moved towards high latitudes. They followed a somewhat direct, linear path, with an approximate geographic heading of 170˚. Satellite telemetry data indicated that the migratory corridors are restricted to a relatively narrow (~500–800km) strip in the South Atlantic Ocean. Migration speed to the feeding grounds averaged 80.2km/day and lasted from 40–58 days. Four individuals arrived at the feeding ground located to the north of the South Sandwich Islands, where they were tracked up to 102 days. Movements in this area were erratic at a mean travelling speed of 22.3km/day. Satellite telemetry data indicate that the main feeding grounds for the population wintering off eastern South America lie between 22˚W and 33˚W and in the southern South Atlantic Ocean south of the Antarctic Convergence but north of 60˚S. This is only partially consistent with the currently proposed stock boundaries for this population on the feeding grounds.

One can define an endangered species based solely on demographic characteristics; i.e., the abundance of the species is so low or abundance is declining so precipitously or the species range has retracted so greatly that the species is in danger of becoming extinct. Note that while an endangered species may be synonymous with a taxonomic species, it can also be defined as a distinct population segmentof the species. An alternate approach is to consider a species endangered because of threats that could lead to its extinction. Ultimately, what makes a species endangered is some marked change to the species itself or to its ecosystem (e.g., increased exploitation, loss of habitats, etc.). Many, if not most, marine mammal species considered being at risk of extinction reached this situation because of human activity (i.e., harvesting). Only in recent decades have humans affected marine mammal habitat sufficiently to place species at risk. These more recent habitat impacts now place more marine mammal species at risk of extinction, even those not formerly at risk due to harvesting. Various aspects of marine mammal demography also contribute to their extinction vulnerability. By the beginning of the twentieth century, many marine mammal populations had reached perilously low levels.

Editor's Note: The Letter of response above by Wade et al. was limited by me to addressing only the new analysis presented in the Letter by Springer et al. (2008). The Letter by Estes et al. on pages 748–754 is the opportunity to rebut this response. These two Letters, which stem from responses to the original paper by Springer et al. 2003 and rebuttals to the responses will be the last Letters published in Marine Mammal Science in this string of responses. The Journal will look forward to papers that provide new data that address the hypotheses and questions raised by these various publications.

Thirty-eight aerial surveys of beluga or white whales (Delphinapterus leucas) were conducted in Bristol Bay, Alaska, during six different years between 1993 and 2005. Belugas were sighted mainly close to shore in the upper parts of Nushagak and Kvichak bays, as well as along the coast between these bays and in the lower parts of major rivers. Data from 28 complete counts made in good or excellent survey conditions were analysed for trend. Counts ranged from 264 to 1,067. The estimated rate of increase over the 12-year period was 4.8%/year (95% CI = 2.1%-7.5%). Such a rate of increase suggests that either the population was below the environmental carrying capacity in the early 1990s or, alternatively, that factors that had been limiting population increase were alleviated after that time. A review of possible changes in human-caused mortality, predation and prey availability did not reveal a single likely cause of the increase. Among the factors that could have played a role are recovery from research kills in the 1960s, a modest decline in subsistence removals and a delayed response to increases in Pacific salmon (Oncorhynchus spp.) abundance in the 1980s. The positive growth rate for this population shows that in recent years there has been no substantial negative impact of human or natural factors, acting either alone or in combination, and there is no need for changes to the current management regime.

The U.S. Endangered Species Act (ESA) mandates that recovery plans include specific criteria to determine when a species should be removed from the List of Endangered and Threatened Wildlife. To meet this mandate, we developed a new approach to determining classification criteria for long-lived vertebrates. The key idea is that endangerment depends on two critical aspects of a population: population size and trends in population size due to intrinsic variability in population growth rates. The way to combine these features is to identify a population size and range of population growth rates (where λ denotes the annual multiplicative rate of change of a population) above which there is a negligible probability of extinction. To do so, (1) information on the current population size and its variance is specified; (2) available information on vital rates or changes in abundance over time is used to generate a probability distribution for the population's λ; (3) the lower fifth percentile value for λ (denoted as λ(0.05) ) is obtained from the frequency distribution of λs; and (4) if λ(0.05) is <1.0, a backwards population trajectory starting at 500 individuals for a period of 10 years is performed and the resulting population size is designated as the threshold for listing a species as endangered, or if λ(0.05) is ≥1.0, the threshold for endangerment is set at 500 animals. A similar approach can be used to determine the threshold for listing a species as threatened under the ESA. We applied this approach to North Pacific humpback whales ( Megaptera novaeangliae) and used Monte Carlo simulations to produce a frequency distribution of λs for the whales under three different scenarios. Using λ(0.05), it was determined that the best estimates of current abundance for the central population of North Pacific humpback whales were larger than the estimated threshold for endangered status but less than the estimated threshold for threatened status. If accepted by the responsible management agency, this analysis would be consistent with a recommendation to downlist the central stock of humpback whales to a status of threatened, whereas the status of eastern and western stocks would remain endangered. Resumen: El acta de Especies Amenazadas de los Estados Unidos (ESA) demanda que los planes de recuperación incluyan criterios específicos para determinar cuando una especie debe ser removida de la Lista de Especies de Vida Silvestre en Peligro. Para alcanzar este mandato, desarrollamos una nueva aproximación para determinar los criterios de clasificación para vertebrados de vida larga. La idea clave es que las amenazas dependen de dos aspecto críticos de una población: tamaño poblacional y tendencias en tamaño poblacional debido a la variabilidad intrínseca de las tasas de crecimiento poblacional. La forma de combinar estas características es la identificación de un tamaño poblacional y el rango de tasas de crecimiento poblacional (donde λ denota la tasa anual multiplicativa de cambio de una población) por arriba de la cual existe una probabilidad de extinción neglibible. Para hacer esto 1) Se especifica la información sobre el tamaño poblacional actual y su varianza; 2) Se utiliza información viable sobre tasas vitales o cambios en abundancia sobre el tiempo para generar una distribución de probabilidades para la población; 3) se obtiene el valor del percentil mas bajo para λ (denotado como λ(0.05)) de la distribución de frecuencias de λs; y 4) si λ(0.05) es <1.0, se efectúa una trayectoria hacia atrás iniciando con 500 individuos por un período de 10 años y el tamaño poblacional resultante se designa como el límite para enlistar una especie bajo el estatus de en peligro ó si el λ(0.05) es ≥1.0, el límite para considerar amenaza se establece en 500 animales. Una aproximación similar puede ser usada para determinar los límites para enlistar especies como en peligro bajo la ESA. Aplicamos esta aproximación para la ballena jorobada del Pacífico Norte ( Megaptera novaeangliae) y utilizamos simulaciones Monte Carlo para producir distribuciones de frecuencia de λs para ballenas bajo diferentes escenarios. Utilizando el λ(0.05), se determinó que los mejores estimadores de la abundancia actual para la población central de la ballena jorobada del Pacífico Norte fueron mayores que los límites estimados para ser considerada en el estatus de en peligro, pero menor a los límites de estatus de amenazada. Si este análisis es aceptado por las agencias de manejo responsables, podría ser consistente con una recomendación de desenlistar el grupo central de ballenas jorobadas y pasarlo al estatus de amenazadas, mientras que el estatus de los grupos del Este y Oeste deberán permanecer en el estatus de en peligro.

Assessing animal population growth curves is an essential feature of field studies in ecology and wildlife management. We used five models to assess population growth rates with a number of sets of population growth rate data. A ‘generalized’ logistic curve provides a better model than do four other popular models. Use of difference equations for fitting was checked by a comparison of that method and direct fitting of the analytical (integrated) solution for three of the models. Fits to field data indicate that estimates of the asymptote, K, from the ‘generalized logistic’ and the ordinary logistic agree well enough to support use of estimates of K from the ordinary logistic on data that cannot be satisfactorily fitted with the generalized logistic. Akaike's information criterion is widely used, often with a small sample version AICc. Our study of five models indicated a bias in the AICc criterion, so we recommend checking results with estimates of variance about regression for fitted models. Fitting growth curves provides a valuable supplement to, and check on computer models of populations.

The western Steller sea lion Eumetopias jubatus population has experienced a chronic decline since the 1960s. The causes are likely multifactorial and a combination of anthropogenic and natural factors. A draft revised recovery plan for the Steller sea lion has been published by the US National Marine Fisheries Service, listing both anthropogenic and natural factors that may have contributed to the observed decline or which may be a threat to the recovery of the western Steller sea lion population. The purpose of this review is to consider the anthropogenic threats to this stock. Anthropogenic sources of mortality include fisheries competition resulting in nutritional stress, mortality incidental to commercial fisheries (i.e. fisheries by‐catch), subsistence hunts, legal and illegal shooting, commercial hunts, anthropogenic‐related contamination, and research‐induced mortalities. We present evidence that the following anthropogenic factors likely contributed to the decline of the western Steller sea lion population over the last 40 years: (i) mortality incidental to commercial fisheries (i.e. by‐catch); (ii) commercial hunting of western Steller sea lions; and (iii) legal and illegal shooting; whereas the subsistence hunts for western Steller sea lions and mortality incidental to research were not likely to be contributors to the observed decline. Further, we present evidence that the following can be excluded as significant anthropogenic threats to the recovery of the western Steller sea lion population: (i) mortality incidental to commercial fishing; (ii) legal and illegal shooting; (iii) commercial hunts of Steller sea lions; (iv) subsistence hunting; and (v) mortality incidental to research. Competition with fisheries resulting in nutritional stress, and the potential impacts of contaminants, are two anthropogenic factors that should continue to be a priority for the various organizations currently doing research on this population.

Ecosystem-based management (EBM) in the ocean is a relatively new approach, and existing applications are evolving from more traditional management of portions of ecosystems. Because comprehensive examples of EBM in the marine environment do not yet exist, we first summarize EBM principles that emerge from the fisheries and marine social and ecological literature. We then apply those principles to four cases in which large parts of marine ecosystems are being managed, and ask how including additional components of an EBM approach might improve the prospects for those ecosystems. The case studies provide examples of how additional elements of EBM approaches, if applied, could improve ecosystem function. In particular, two promising next steps for applying EBM are to identify management objectives for the ecosystem, including natural and human goals, and to ensure that the governance structure matches with the scale over which ecosystem elements are measured and managed.