Operationalizing ensemble models for scientific advice to fisheries management

This paper explores the possibility of using the ensemble modelling paradigm to fully capture assessment uncertainty and improve the robustness of advice provision. We identify and discuss advantages and challenges of ensemble modelling approaches in the context of scientific advice. There are uncertainties associated with every phase in the stock assessment process: data collection, assessment model choice, model assumptions, interpretation of risk, up to the implementation of management advice. Additionally, the dynamics of fish populations are complex, and our incomplete understanding of those dynamics and limited observations of important mechanisms, necessitate that models are simpler than nature. The aim is for the model to capture enough of the dynamics to accurately estimate trends and abundance, and provide the basis for robust advice about sustainable harvests. The status quo approach to assessment modelling has been to identify the “best” model and generate advice from that model, mostly ignoring advice from other model configurations regardless of how closely they performed relative to the chosen model. We discuss and make suggestions about the utility of ensemble models, including revisions to the formal process of providing advice to management bodies, and recommend further research to evaluate potential gains in modelling and advice performance.publishedVersio

Species-specific effects of four preservative treatments on oocytes and ovarian material of Atlantic cod (Gadus morhua), haddock (Melanogrammus aegleflnus), and American plaice (Hippoglossoides platessoides)

The lack of information concerning the preservation of ovarian material of fish species inhibits standardization of methods for determining fecundity and measuring oocytes. The effects of four preservatives (10% phosphate-buffered formalin, modified Gilson’s solution, 70% ethanol, and freezing) on ovarian material weight and oocyte size were quantified for prespawning Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus), and American plaice (Hippoglossoides platessoides). Effects of preservation were similar between Atlantic cod and haddock but different between Atlantic cod and American plaice for nearly all comparisons. Although all treatments affected the weight of ovarian material, freezing caused the most change and formalin caused the least. Such signif icant species-specific effects should be quantified in the calculation of life history characteristics, such as fecundity, to minimize error. This is one of few studies dedicated to evaluating the effects of preservation on oocytes and ovarian material and is the first to evaluate multiple preservatives on species

Procedures for efficiently producing high-quality fecundity data on a small budget

Though fecundity estimation has typically been very time consuming, efficient methods have recently been developed. Building on these developments, we describe procedures for efficiently producing precise, accurate, fecundity estimates for highly fecund Atlantic cod, using a low-cost laboratory setup. Capturing images with a standard flatbed scanner and analyzing them with free image analysis software (total equipment cost ≈ $100) we were able to process individual samples in as little as 5 min. We show a strong relationship between mean oocyte diameter (range 200–900 μm) and oocyte density (r2 = 0.971, n = 50), and thus are able to estimate fecundity using gravimetric and auto-diametric methods. Testing the precision of the auto-diametric method we find estimates produced by both methods to be highly correlated (r2 = 0.961, n = 26). The success of these methods should assure fisheries scientists that fecundity estimation is no longer the daunting task it once was, and catalyze further production of fecundity data

Egg Production

109 páginas, 53 figuras, 5 tablasThe present chapter deals with the estimation of female fecundity in fishes, mostly teleosts. The chapter is organized in three main blocks. The first block is devoted to technical issues of fish fecundity measurements from fixation, preservation and treatment of ovarian material to automatic oocyte counts. The use of certain staining protocols for the identification of follicular types in ovarian whole mounts and of inexpensive equipments in oocyte counting is also described. Because histology still constitutes the most unbiased method for identifying ovarian structures an array of stereological methods for estimating follicular intensity from assumption/model based methods (e.g. Weibel and oocyte packing density (OPD) method) to assumption/model free methods such as the physical disector or the fractionator principle is also provided. The second block is focused on methods used for the estimation of important variables such as batch fecundity (using hydrated oocytes and or previous developmental stages), daily fecundity and spawning fraction, S. Special emphasis is given to the estimation of S; the postovulatory follicle (POF) method is explicitly described together with its most common bias issues related to POF staging and ageing. In addition, methods that are based on imminent spawners, methods for stocks with high S values, and methods based on the assessment of spawning sites are also descibed. The third block incorporates knowledge acquired in the two other blocks to review what is needed to estimate the annual realized fecundity (the ultimate goal of fecundity studies) in determinate and indeterminate fish species. The autodiametric method for estimating potential annual fecundity, and the impacts of fecundity dowregualtion by atresia and of skipped-spawning in determinate spawners are also included. In short, this chapter will offer the reader an overview of all methodological aspects that need to be considered in fish fecundity investigations.COST Action FRESH (FA0601). NAFO Working Group on Reproductive Potentia

Operationalizing ensemble models for scientific advice to fisheries management

This paper explores the possibility of using the ensemble modelling paradigm to fully capture assessment uncertainty and improve the robustness of advice provision. We identify and discuss advantages and challenges of ensemble modelling approaches in the context of scientific advice. There are uncertainties associated with every phase in the stock assessment process: data collection, assessment model choice, model assumptions, interpretation of risk, up to the implementation of management advice. Additionally, the dynamics of fish populations are complex, and our incomplete understanding of those dynamics and limited observations of important mechanisms, necessitate that models are simpler than nature. The aim is for the model to capture enough of the dynamics to accurately estimate trends and abundance, and provide the basis for robust advice about sustainable harvests. The status quo approach to assessment modelling has been to identify the “best” model and generate advice from that model, mostly ignoring advice from other model configurations regardless of how closely they performed relative to the chosen model. We discuss and make suggestions about the utility of ensemble models, including revisions to the formal process of providing advice to management bodies, and recommend further research to evaluate potential gains in modelling and advice performance