Paul D. Spencer

Projecting marine mammal distribution in a changing climate

Climate-related shifts in marine mammal range and distribution have been observed in some populations; however, the nature and magnitude of future responses are uncertain in novel environments projected under climate change. This poses a challenge for agencies charged with management and conservation of these species. Specialized diets, restricted ranges, or reliance on specific substrates or sites (e.g., for pupping) make many marine mammal populations particularly vulnerable to climate change. High-latitude, predominantly ice-obligate, species have experienced some of the largest changes in habitat and distribution and these are expected to continue. Efforts to predict and project marine mammal distributions to date have emphasized data-driven statistical habitat models. These have proven successful for short time-scale (e.g., seasonal) management activities, but confidence that such relationships will hold for multi-decade projections and novel environments is limited. Recent advances in mechanistic modeling of marine mammals (i.e., models that rely on robust physiological and ecological principles expected to hold under climate change) may address this limitation. The success of such approaches rests on continued advances in marine mammal ecology, behavior, and physiology together with improved regional climate projections. The broad scope of this challenge suggests initial priorities be placed on vulnerable species or populations (those already experiencing declines or projected to undergo ecological shifts resulting from climate changes that are consistent across climate projections) and species or populations for which ample data already exist (with the hope that these may inform climate change sensitivities in less well observed species or populations elsewhere). The sustained monitoring networks, novel observations, and modeling advances required to more confidently project marine mammal distributions in a changing climate will ultimately benefit management decisions across time-scales, further promoting the resilience of marine mammal populations.

Genetic Analysis Reveals Restricted Dispersal of Northern Rockfish along the Continental Margin of the Bering Sea and Aleutian Islands

Abstract The effective conservation and management of a species require knowledge of its population structure and life history. Fish that are mobile, long-lived, and abundant and that have pelagic larvae are often presumed to disperse over large geographic areas. However, if the individuals of such a species have limited dispersal, spatial scale must be considered when developing management plans. The economically and ecologically important northern rockfish Sebastes polyspinis, which is most abundant along the continental margin of the Aleutian Islands, has the potential to disperse widely during its life. The population genetic structure of a species provides a window into its demographic structure. Consequently, the variation at 11 microsatellite loci was used to characterize the geographic structure and connectivity of northern rockfish collected in 2004 along the continental margin of the Bering Sea slope and the Aleutian Islands. Significant genetic structure (F ST = 0.0017) was detected, and a sign...

The role of flatfishes in the organization and structure of the eastern Bering Sea ecosystem

We evaluated the role of flatfishes in the organization and structure of the eastern Bering Sea ecosystem using the Ecopath/Ecosim approach. As basic input data for the Ecopath/Ecosim model, we used estimates of biomass from bottom trawl surveys and age-structured population models, production/biomass (P/B) ratio, consumption/biomass (Q/B) ratio, diet composition (DC), and fisheries harvests for each component of species or species groups. We estimated the trophic level of each component, niche overlaps among flatfishes, and the impacts of competition and predation on flatfish species in the eastern Bering Sea ecosystem. Based on those estimates, we developed the tropho-dynamic structure of the ecosystem, and the model was used to simulate ecological effects of fishery exploitation patterns. No single flatfish species appeared to have a profound and uniquely important role in the organization and structure of the ecosystem. Instead, the most important component among the guild of flatfish species appeared to be yellowfin sole Pleuronectes asper, which had greater biomass than other flatfish and a relatively diverse diet among the small flatfish species. Pacific halibut Hippoglossus stenolepis, Greenland turbot Reinhardtius hippoglossoides, and arrowtooth flounder Atheresthes stomias were important keystone predators in the eastern Bering Sea ecosystem together with some groups of marine mammals and sea birds. Intra flatfish complex cannibalism was not observed, however, substantial diet overlaps were common in the flatfish guild system.

Erratum to: The role of flatfishes in the organization and structure of the eastern Bering Sea ecosystem

In the 5th paragraph of the ‘‘Model structure’’ subheading of the ‘‘Data and methods’’, lines 6–8 of the text should read: ‘‘...the immigration of i, Yi is the yield of i (i.e., its catch in weight, with Yi = FiBi, where F is the fishing mortality rate), Bj is the biomass of the consumers or predators,...’’. On the 2nd and 4th pages of Table 2, ‘‘35 Myc. & Bathy.’’ in the column headed ‘‘Prey/predator’’ should be ‘‘35 Myc. & bathy.’’ In Fig. 4, ‘‘Myc. & Bathy.’’ on the y axis should also be ‘‘Myc. & bathy.’’ In addition, under the ‘‘Ecosim analyses’’ subheading of the ‘‘Results’’, in the 1st paragraph lines 9–11 should read: ‘‘...Arrowtooth flounder had biomass 3.7 times higher in 2005, and Greenland turbot showed the fastest rate of decrease’’. In the 2nd paragraph lines 17–18 should read: ‘‘...It was only the rate of increase or decrease in the biomass of flatfishes...’’.