Li L.,University of British Columbia |
Ainsworth C.,Marine Resources Assessment Group Americas Inc. |
Pitcher T.,University of British Columbia
Progress in Oceanography | Year: 2010
We tested what degree harbour seal (Phoca vitulina) populations compete with fisheries for commercially harvested species, and to what degree seal populations depend on exploited species as prey. In the Strait of Georgia (SoG), harbour seals mainly feed on fisheries target species, Pacific herring (Clupea pallasii) and Pacific hake (Merluccius productus), while herring is also a main prey of hake. Using an Ecopath model constructed based on 2005 conditions, we ran three scenarios: altering herring fishing mortality, removing seal populations and sensitivity analyses of the herring vulnerability parameter. Our results show that with more herring available, the seal population will increase greatly, but with less herring available, the seal populations in the SoG decreases gradually. Our model suggests that the total biomass of commercial fish populations in the SoG may decrease substantially with seals absent. A cull of harbour seals may not increase total fisheries catch in the SoG. Herring benefit from seal predation on herring's largest predator, hake, so that herring may decline when seals are removed. However, this result is highly dependent on model parameterization. When juvenile herring are considered less vulnerable to hake predation (i.e., when we assume there are many refuges in which to hide), the herring population is less negatively impacted by seal removals. This indicates that survival during this crucial life-stage is important to herring abundance. The model also suggests that, with seals removed, the ecosystem would be dominated by hake. © 2010 Elsevier Ltd.
Satterthwaite W.H.,Marine Resources Assessment Group Americas Inc. |
Satterthwaite W.H.,University of California at Santa Cruz |
Kitaysky A.S.,University of Alaska Fairbanks |
Mangel M.,University of California at Santa Cruz |
Mangel M.,University of Bergen
Marine Ecology Progress Series | Year: 2012
We examined the reproductive ecology of black-legged kittiwakes Rissa tridactyla in several breeding colonies in the North Pacific to test if inter-annual changes in the Pacific Decadal Oscillation (PDO), Winter Ice Cover (ICI), or local sea-surface temperature (SST) predict changes in productivity (fledglings per nest) or nutritional stress (corticosterone). We explored the implications of the observed variation in productivity and stress for projected population dynamics based on a previously demonstrated corticosterone-survival relationship. Although productivity was highly variable (0 to 0.9 fledglings nest-1), the relationships between productivity and environmental indices were weak, with local SST providing slightly more explanatory power than PDO or ICI, suggesting that local factors rather than large-scale climate variability may determine variation in productivity. The relationships between stress and environmental indices were stronger than the relationship between productivity and environment. The measured response of stress to environment showed opposite signs between the southern and northern colonies, and typically implied annual mortality rates varying from 11 to 17%. The observed relationships between climate and stress indicate that anticipated warming might bring at least short-term demographic benefits for kittiwakes in the Bering shelf region, while having negative impacts on birds breeding in the Gulf of Alaska and western Aleutians. We predict decline (without immigration) for colonies with the lowest productivity and conclude that climate variability is likely to affect survival of North Pacific kittiwakes on a region-specific basis. Longevity of these birds may not always be sufficient to buffer their populations from low reproductive performance. © Inter-Research 2012.
Ainsworth C.H.,National Oceanic and Atmospheric Administration |
Ainsworth C.H.,Marine Resources Assessment Group Americas Inc.
Marine and Coastal Fisheries | Year: 2011
Ecosystem-based fisheries management requires data on all parts of the ecosystem, and this can be a barrier in data-poor systems. Marine ecologists need a means of drawing together diverse information to reconstruct species abundance trends for a variety of purposes. This article uses a fuzzy logic approach to integrate information from multiple data sources and describe biomass trends for marine species groups in the northern Gulf of California, Mexico. Forty-two species groups were analyzed, comprising fish, invertebrates, birds, mammals, turtles, and algae. The most important new data series comes from recent interviews with fishers in the northern part of the gulf. Respondents were asked to classify the abundance of various targeted and untargeted marine species groups from 1950 to the present. The fuzzy logic method integrates their responses with catch-per-unit-effort series, intrinsic vulnerability to fishing determined from life history parameters, biomass predicted by a Schaefer harvest model, and other simple indices. The output of the fuzzy logic routine is a time series of abundance for each species group that can be compared with known trends. The results suggest a general decline in species abundance across fished and unfished taxa, with a few exceptions. Information gathered from interviews indicated that older fishers tended to recognize a greater relative decrease in species abundance since 1970 than did younger fishers, providing another example of Pauly's (1995) shifting cognitive baselines. © American Fisheries Society 2011.
Samhouri J.F.,Pacific States Marine Fisheries Commission |
Levin P.S.,National Oceanic and Atmospheric Administration |
Ainsworth C.H.,Marine Resources Assessment Group Americas Inc.
PLoS ONE | Year: 2010
Background: One of the greatest obstacles to moving ecosystem-based management (EBM) from concept to practice is the lack of a systematic approach to defining ecosystem-level decision criteria, or reference points that trigger management action. Methodology/Principal Findings: To assist resource managers and policymakers in developing EBM decision criteria, we introduce a quantitative, transferable method for identifying utility thresholds. A utility threshold is the level of humaninduced pressure (e.g., pollution) at which small changes produce substantial improvements toward the EBM goal of protecting an ecosystem's structural (e.g., diversity) and functional (e.g., resilience) attributes. The analytical approach is based on the detection of nonlinearities in relationships between ecosystem attributes and pressures. We illustrate the method with a hypothetical case study of (1) fishing and (2) nearshore habitat pressure using an empirically-validated marine ecosystem model for British Columbia, Canada, and derive numerical threshold values in terms of the density of two empirically-tractable indicator groups, sablefish and jellyfish. We also describe how to incorporate uncertainty into the estimation of utility thresholds and highlight their value in the context of understanding EBM trade-offs. Conclusions/Significance: For any policy scenario, an understanding of utility thresholds provides insight into the amount and type of management intervention required to make significant progress toward improved ecosystem structure and function. The approach outlined in this paper can be applied in the context of single or multiple human-induced pressures, to any marine, freshwater, or terrestrial ecosystem, and should facilitate more effective management.
Morzaria-Luna H.N.,Marine Resources Assessment Group Americas Inc. |
Ainsworth C.H.,Marine Resources Assessment Group Americas Inc. |
Ainsworth C.H.,University of South Florida |
Kaplan I.C.,National Oceanic and Atmospheric Administration |
And 2 more authors.
PLoS ONE | Year: 2013
High bycatch of non-target species and species of conservation concern often drives the implementation of fisheries policies. However, species- or fishery-specific policies may lead to indirect consequences, positive or negative, for other species or fisheries. We use an Atlantis ecosystem model of the Northern Gulf of California to evaluate the effects of fisheries policies directed at reducing bycatch of vaquita (Phocoena sinus) on other species of conservation concern, priority target species, and metrics of ecosystem function and structure. Vaquita, a Critically Endangered porpoise endemic to the Upper Gulf of California, are frequently entangled by finfish gillnets and shrimp driftnets. We tested five fishery management scenarios, projected over 30 years (2008 to 2038), directed at vaquita conservation. The scenarios consider progressively larger spatial restrictions for finfish gillnets and shrimp driftnets. The most restrictive scenario resulted in the highest biomass of species of conservation concern; the scenario without any conservation measures in place resulted in the lowest. Vaquita experienced the largest population increase of any functional group; their biomass increased 2.7 times relative to initial (2008) levels under the most restrictive spatial closure scenario. Bycatch of sea lions, sea turtles, and totoaba decreased > 80% in shrimp driftnets and at least 20% in finfish gillnet fleets under spatial management. We found indirect effects on species and ecosystem function and structure as a result of vaquita management actions. Biomass and catch of forage fish declined, which could affect lower-trophic level fisheries, while other species such as skates, rays, and sharks increased in both biomass and catch. When comparing across performance metrics, we found that scenarios that increased ecosystem function and structure resulted in lower economic performance indicators, underscoring the need for management actions that consider ecological and economic tradeoffs as part of the integrated management of the Upper Gulf of California.