Alec D. MacCall

No-take Reserve Networks: Sustaining Fishery Populations and Marine Ecosystems

Abstract Improved management approaches are needed to reduce the rate at which humans are depleting exploited marine populations and degrading marine ecosystems. Networks of no-take marine reserves are promising management tools because of their potential to (1) protect coastal ecosystem structure and functioning, (2) benefit exploited populations and fisheries, (3) improve scientific understanding of marine ecosystems, and (4) provide enriched opportunities for non-extractive human activities. By protecting marine ecosystems and their populations, no-take reserve networks can reduce risk by providing important insurance for fishery managers against overexploitation of individual populations. Replicated reserves also foster strong scientific testing of fishery and conservation management strategies. Reserve networks will require social acceptance, adequate enforcement, and effective scientific evaluation to be successful. Processes for reserve establishment should accommodate adaptive management so bounda...

Predicting climate effects on Pacific sardine.

For many marine species and habitats, climate change and overfishing present a double threat. To manage marine resources effectively, it is necessary to adapt management to changes in the physical environment. Simple relationships between environmental conditions and fish abundance have long been used in both fisheries and fishery management. In many cases, however, physical, biological, and human variables feed back on each other. For these systems, associations between variables can change as the system evolves in time. This can obscure relationships between population dynamics and environmental variability, undermining our ability to forecast changes in populations tied to physical processes. Here we present a methodology for identifying physical forcing variables based on nonlinear forecasting and show how the method provides a predictive understanding of the influence of physical forcing on Pacific sardine.

Climate, fishing, and fluctuations of sardine and anchovy in the California Current

Since the days of Elton, population cycles have challenged ecologists and resource managers. Although the underlying mechanisms remain debated, theory holds that both density-dependent and density-independent processes shape the dynamics. One striking example is the large-scale fluctuations of sardine and anchovy observed across the major upwelling areas of the world. Despite a long history of research, the causes of these fluctuations remain unresolved and heavily debated, with significant implications for fisheries management. We here model the underlying causes of these fluctuations, using the California Current Ecosystem as a case study, and show that the dynamics, accurately reproduced since A.D. 1661 onward, are explained by interacting density-dependent processes (i.e., through species-specific life-history traits) and climate forcing. Furthermore, we demonstrate how fishing modifies the dynamics and show that the sardine collapse of the 1950s was largely unavoidable given poor recruitment conditions. Our approach provides unique insight into the origin of sardine–anchovy fluctuations and a knowledge base for sustainable fisheries management in the California Current Ecosystem and beyond.

How useful is the ratio of fish density outside versus inside no-take marine reserves as a metric for fishery management control rules?

A management strategy evaluation (based on five species in the California, USA, nearshore fishery) of control rules that reduce relative fishing effort as a function of the ratio of fish density outside versus inside no-take marine reserves (as a measure of depletion) showed that although the control rules allowed effort to increase at first, in the long term, they were effective at maintaining spawning stock biomass and yield for all simulated species, including depleted ones. Scenarios with fish movement, illegal fishing in the reserve, or post-dispersal density dependence in recruitment required higher density ratio targets, such as 60% of mature fish or 80% of all fish, to avoid stock depletion. The effort allowed by multispecies density-ratio control rules depended on the relative weight given to more or less depleted species. High variability in recruitment or in monitoring data caused the allowable effort to fluctuate. Density-ratio control rules have the advantages that they require no historical ...

A spatially distinct history of the development of california groundfish fisheries.

During the past century, commercial fisheries have expanded from small vessels fishing in shallow, coastal habitats to a broad suite of vessels and gears that fish virtually every marine habitat on the globe. Understanding how fisheries have developed in space and time is critical for interpreting and managing the response of ecosystems to the effects of fishing, however time series of spatially explicit data are typically rare. Recently, the 1933–1968 portion of the commercial catch dataset from the California Department of Fish and Wildlife was recovered and digitized, completing the full historical series for both commercial and recreational datasets from 1933–2010. These unique datasets include landing estimates at a coarse 10 by 10 minute “grid-block” spatial resolution and extends the entire length of coastal California up to 180 kilometers from shore. In this study, we focus on the catch history of groundfish which were mapped for each grid-block using the year at 50% cumulative catch and total historical catch per habitat area. We then constructed generalized linear models to quantify the relationship between spatiotemporal trends in groundfish catches, distance from ports, depth, percentage of days with wind speed over 15 knots, SST and ocean productivity. Our results indicate that over the history of these fisheries, catches have taken place in increasingly deeper habitat, at a greater distance from ports, and in increasingly inclement weather conditions. Understanding spatial development of groundfish fisheries and catches in California are critical for improving population models and for evaluating whether implicit stock assessment model assumptions of relative homogeneity of fisheries removals over time and space are reasonable. This newly reconstructed catch dataset and analysis provides a comprehensive appreciation for the development of groundfish fisheries with respect to commonly assumed trends of global fisheries patterns that are typically constrained by a lack of long-term spatial datasets.

Use of Known-Biomass Production Models to Determine Productivity of West Coast Groundfish Stocks

Abstract Known-biomass production models use a biomass time series produced by a stock assessment and thereby avoid the imprecision associated with estimating a catchability coefficient. Fluctuations or trends in known biomass are fully as informative as catch (which is used in conventional production models) in estimating stock productivity. Known-biomass production models provide a useful supplement to stock–recruitment models and can serve as a cross-check on the sensibility of stock–recruitment model results. Application of known-biomass production models (ASPIC) to eight stocks of West Coast groundfish shows that current abundances (B) are moderately to seriously below those associated with the maximum sustainable yield (MSY; B is less than B MSY in six of eight cases and less than one-half of B MSY in four of those cases). Recent exploitation rates are lower than those in earlier years and in most cases are now near their appropriate levels, including the rates for stocks that are rebuilding. Harves...

Weak evidence for sardine collapse.

Zwolinski and Demer (1) described indicators suggesting imminent collapse of Pacific sardines (Sardinops sagax) in the California Current. Those indicators are lacking in explanatory or predictive power, and the paper does not recognize fundamental differences between conservative sardine fishery management today and Sardinops fisheries that were virtually unregulated previously in the California Current and in other regions of the world.

Is Logarithmic Transformation Really the Best Procedure for Estimating Stock-Recruitment Relationships?

Abstract The conventional wisdom favoring the use of log-transformation in fitting stock–recruitment relationships is based on the assumed lognormality of the error structure as well as the assumed homogeneity of variance under log-transformation. Although rarely recognized, the latter is an important requirement underlying the conventional bias correction for back-transformation (i.e., exp(s 2/2), where s 2 is the error variance). The homogeneity assumption may be violated much more frequently than is commonly recognized. Stock and recruitment data sets for two of eight West Coast groundfish stocks showed significant heterogeneity of variance under log-transformation, despite the low statistical power of the test (circa 25%). We simulated stock and recruitment data sets of various sample sizes and known amounts of variance heterogeneity and subjected them to three methods of regression analysis: regression under conventional log-transformation, with bias correction for the back-transformation; untransfor...

A heuristic model of socially learned migration behaviour exhibits distinctive spatial and reproductive dynamics

&NA; We explore a “Go With the Older Fish” (GWOF) mechanism of learned migration behaviour for exploited fish populations, where recruits learn a viable migration path by randomly joining a school of older fish. We develop a non‐age‐structured biomass model of spatially independent spawning sites with local density dependence, based on Pacific herring (Clupea pallasii). We compare a diffusion (DIFF) strategy, where recruits adopt spawning sites near their natal site without regard to older fish, with GWOF, where recruits adopt the same spawning sites, but in proportion to the abundance of adults using those sites. In both models, older individuals return to their previous spawning site. The GWOF model leads to higher spatial variance in biomass. As total mortality increases, the DIFF strategy results in an approximately proportional decrease in biomass among spawning sites, whereas the GWOF strategy results in abandonment of less productive sites and maintenance of high biomass at more productive sites. A DIFF strategy leads to dynamics comparable to non‐spatially structured populations. While the aggregate response of the GWOF strategy is distorted, non‐stationary and slow to equilibrate, with a production curve that is distinctly flattened and relatively unproductive. These results indicate that fishing will disproportionately affect populations with GWOF behaviour.