Equation-free mechanistic ecosystem forecasting using empirical dynamic modeling.

It is well known that current equilibrium-based models fall short as predictive descriptions of natural ecosystems, and particularly of fisheries systems that exhibit nonlinear dynamics. For example, model parameters assumed to be fixed constants may actually vary in time, models may fit well to existing data but lack out-of-sample predictive skill, and key driving variables may be misidentified due to transient (mirage) correlations that are common in nonlinear systems. With these frailties, it is somewhat surprising that static equilibrium models continue to be widely used. Here, we examine empirical dynamic modeling (EDM) as an alternative to imposed model equations and that accommodates both nonequilibrium dynamics and nonlinearity. Using time series from nine stocks of sockeye salmon (Oncorhynchus nerka) from the Fraser River system in British Columbia, Canada, we perform, for the the first time to our knowledge, real-data comparison of contemporary fisheries models with equivalent EDM formulations that explicitly use spawning stock and environmental variables to forecast recruitment. We find that EDM models produce more accurate and precise forecasts, and unlike extensions of the classic Ricker spawner-recruit equation, they show significant improvements when environmental factors are included. Our analysis demonstrates the strategic utility of EDM for incorporating environmental influences into fisheries forecasts and, more generally, for providing insight into how environmental factors can operate in forecast models, thus paving the way for equation-free mechanistic forecasting to be applied in management contexts.

Comment on "Declining wild salmon populations in relation to parasites from farm salmon".

Krkosek et al. (Reports, 14 December 2007, p. 1772) claimed that sea lice spread from salmon farms placed wild pink salmon populations "on a trajectory toward rapid local extinction." Their prediction is inconsistent with observed pink salmon returns and overstates the risks from sea lice and salmon farming.

General effects of climate change on Arctic fishes and fish populations.

Projected shifts in climate forcing variables such as temperature and precipitation are of great relevance to arctic freshwater ecosystems and biota. These will result in many direct and indirect effects upon the ecosystems and fish present therein. Shifts projected for fish populations will range from positive to negative in overall effect, differ among species and also among populations within species depending upon their biology and tolerances, and will be integrated by the fish within their local aquascapes. This results in a wide range of future possibilities for arctic freshwater and diadromous fishes. Owing to a dearth of basic knowledge regarding fish biology and habitat interactions in the north, complicated by scaling issues and uncertainty in future climate projections, only qualitative scenarios can be developed in most cases. This limits preparedness to meet challenges of climate change in the Arctic with respect to fish and fisheries.

An overview of effects of climate change on selected arctic freshwater and anadromous fishes.

Arctic freshwater and diadromous fish species will respond to the various effects of climate change in many ways. For wide-ranging species, many of which are key components of northern aquatic ecosystems and fisheries, there is a large range of possible responses due to inter- and intra-specific variation, differences in the effects of climate drivers within ACIA regions, and differences in drivers among regions. All this diversity, coupled with limited understanding of fish responses to climate parameters generally, permits enumeration only of a range of possible responses which are developed here for selected important fishes. Accordingly, in-depth examination is required of possible effects within species within ACIA regions, as well as comparative studies across regions. Two particularly important species (Arctic char and Atlantic salmon) are examined as case studies to provide background for such studies.

Macroscopic structure of the fin-rays and their annuli in pectoral and pelvic fins of Chinook Salmon, Oncorhynchus tshawytscha.

Light microscopy, enzyme clearing, and staining techniques were used to describe the structure of fin-rays in pectoral and dorsal fins of adult and juvenile chinook salmon,Oncorhynchus tshawytscha. In addition, several decalcification agents, fixatives, and staining methods were employed to demonstrate and determine the nature of the fin-ray annulus (yearly growth ring). Etched, transverse sections of fin-rays were examined by scanning electron microscopy (SEM). A description is provided of specific morphological regions along the length of fin-rays in both fins. Each ray consists of parallel halves, medial and lateral hemisegments, which diverge proximally and embrace underlying radial cartilages and are segmented distally. Fibrocartilage masses are associated with bone and hyaline cartilage in the proximal regions. There is evidence of periosteal, and perhaps endochondral, osteogenesis in the fin-rays. A novel fixation-staining method is described to depict the fin ray annulus in adult chinook salmon. Transverse sections of rays of adults, but not juveniles, demonstrate alternating narrow-dark and wide-light purple bands following prolonged decalcification/fixation in Bouin's fluid only with subsequent hematoxylin-eosin staining. The dark and light bands correspond to translucent (annuli) and opaque zones, respectively, in dried, unstained sections in transmitted light and in backscatter SEM. In conjunction with different light microscopic staining procedures, etched, transverse sections of fin-ray bone in SEM suggest that annuli are a manifestation of an ordered regionalization of the extracellular matrix of the bone in the fin-rays. J. Morphol. 239:297-320, 1999. © 1999 Wiley-Liss, Inc.