Laura E. Koehn

Fishing amplifies forage fish population collapses

Significance Forage fish provide substantial benefits to both humans and ocean food webs, but these benefits may be in conflict unless there are effective policies governing human activities, such as fishing. Collapses of forage fish induce widespread ecological effects on dependent predators, but attributing collapses to fishing has been difficult because of natural fluctuations of these stocks. We implicate fishing in forage fish stock collapses by showing that high fishing rates are maintained when stock productivity is in rapid decline. As a consequence, the magnitude and frequency but not duration of stock collapses are far greater than expected from natural fluctuations. Risk-based management policies would provide substantial ecological benefits with little effect on fishery catches. Forage fish support the largest fisheries in the world but also play key roles in marine food webs by transferring energy from plankton to upper trophic-level predators, such as large fish, seabirds, and marine mammals. Fishing can, thereby, have far reaching consequences on marine food webs unless safeguards are in place to avoid depleting forage fish to dangerously low levels, where dependent predators are most vulnerable. However, disentangling the contributions of fishing vs. natural processes on population dynamics has been difficult because of the sensitivity of these stocks to environmental conditions. Here, we overcome this difficulty by collating population time series for forage fish populations that account for nearly two-thirds of global catch of forage fish to identify the fingerprint of fisheries on their population dynamics. Forage fish population collapses shared a set of common and unique characteristics: high fishing pressure for several years before collapse, a sharp drop in natural population productivity, and a lagged response to reduce fishing pressure. Lagged response to natural productivity declines can sharply amplify the magnitude of naturally occurring population fluctuations. Finally, we show that the magnitude and frequency of collapses are greater than expected from natural productivity characteristics and therefore, likely attributed to fishing. The durations of collapses, however, were not different from those expected based on natural productivity shifts. A risk-based management scheme that reduces fishing when populations become scarce would protect forage fish and their predators from collapse with little effect on long-term average catches.

Forage species in predator diets: Synthesis of data from the California Current

Characterization of the diets of upper-trophic pelagic predators that consume forage species is a key ingredient in the development of ecosystem-based fishery management plans, conservation of marine predators, and ecological and economic modeling of trophic interactions. Here we present the California Current Predator Diet Database (CCPDD) for the California Current region of the Pacific Ocean over the past century, assimilating over 190 published records of predator food habits for over 100 predator species and 32 categories of forage taxa (species or groups of similar species). Literature searches targeted all predators that consumed forage species: seabirds, cetaceans, pinnipeds, bony and cartilaginous fishes, and a predatory invertebrate. Diet data were compiled into a relational database. Analysis of the CCPDD highlighted differences in predator diet data availability based on geography, time period and predator taxonomy, as well as prominent prey categories. The top 5 forage taxa with the most predators included juvenile rockfish, northern anchovy, euphausiid krill, Pacific herring and market squid. Predator species with abundant data included Pacific hake, common murre, and California sea lion. Most diet data were collected during the summer; the lack of winter data will restrict future use of the CCPDD to understand seasonal patterns in predator diet unless more such data become available. Increased synthesis of historical information can provide new resources to understand patterns in the role of forage species in predator diet. Increased publication and/or accessibility of long-term datasets and data-sharing will further foster the synthesis of information intended to inform the management, conservation and understanding of marine food webs.

Trade-offs between forage fish fisheries and their predators in the California Current

Trade-offs between forage fish fisheries and their predators in the California Current Laura E. Koehn*, Timothy E. Essington, Kristin N. Marshall, William J. Sydeman, Amber I. Szoboszlai, and Julie A. Thayer School of Aquatic and Fishery Sciences, University of Washington, PO Box 355020, Seattle, WA 98105-5020, USA Cascade Ecology, PO Box 25104, Seattle, WA 98165, USA Farallon Institute, 101 H Street Suite Q, Petaluma, CA 94952, USA

Reply to Szuwalski and Hilborn: Forage fish require an ecosystem approach

In response to our recent paper (1), Szuwalski and Hilborn (2) make several points about the timing of recruitment failures, the effect of fishing on productivity, and our choice of using biomass, not recruitment, as the indicator for collapses. We address these points here to show that not only do they not affect our conclusions, but that we are largely in agreement regarding the biological processes and the implications for fisheries and conservation.

Inclusion of ecosystem information in US fish stock assessments suggests progress toward ecosystem-based fisheries management

&NA; The appetite for ecosystem‐based fisheries management (EBFM) approaches has grown, but the perception persists that implementation is slow. Here, we synthesize progress toward implementing EBFM in the United States through one potential avenue: expanding fish stock assessments to include ecosystem considerations and interactions between species, fleets, and sectors. We reviewed over 200 stock assessments and assessed how the stock assessment reports included information about system influences on the assessed stock. Our goals were to quantify whether and how assessments incorporated broader system‐level considerations, and to explore factors that might contribute to the use of system‐level information. Interactions among fishing fleets (technical interactions) were more commonly included than biophysical interactions (species, habitat, climate). Interactions within the physical environment (habitat, climate) were included twice as often as interactions among species (predation). Many assessment reports included ecological interactions only as background or qualitative considerations, rather than incorporating them in the assessment model. Our analyses suggested that ecosystem characteristics are more likely to be included when the species was overfished (stock status), the assessment is conducted at a science centre with a longstanding stomach contents analysis program, and/or the species life history characteristics suggest it is likely to be influenced by the physical environment, habitat, or predation mortality (short‐lived species, sessile benthic species, or low trophic‐level species). Regional differences in stomach contents analysis programs may limit the inclusion of predation mortality in stock assessments, and more guidance is needed on best practices for the prioritization of when and how biophysical information should be considered. However, our results demonstrate that significant progress has been made to use best available science and data to expand single‐species stock assessments, particularly when a broad definition of EBFM is applied.