Five centuries of cod catches in Eastern Canada

The fishery for Northern Atlantic cod (Gadus morhua) off Newfoundland and Labrador, Eastern Canada, presents the most spectacular case of an exploited stock crashed in a few decades by an industrial bottom trawl fishery under a seemingly sophisticated management regime after half a millennium of sustainable fishing. The fishery, which had generated annual catches of 100000 to 200000 tonnes from the beginning of the 16th century to the 1950s, peaked in 1968 at 810000 tonnes, followed by a devastating collapse and closure 24 years later. Since then, stock recovery may have been hindered by premature openings, with vessels targeting the remains of the cod population. Previous research paid little attention towards using multicentury time series to inform sustainable catches and recovery plans. Here, we show that a simple stock assessment model can be used to model the cod population trajectory for the entire period from 1508 to 2019 for which catch estimates are available. The model suggests that if fishing effort and mortality had been stabilized in the 1980s, precautionary annual yields of about 200000 tonnes could have been sustained. Our analysis demonstrates the value of incorporating prior knowledge to counteract shifting baseline effects on reference points and contemporary perceptions of historical stock status.publishedVersio

New developments in the analysis of catch time series as the basis for fish stock assessments: The CMSY++ method

Following an introduction to the nature of fisheries catches and their information content, a new development of CMSY, a data-limited stock assessment method for fishes and invertebrates, is presented. This new version, CMSY++, overcomes several of the deficiencies of CMSY, which itself improved upon the “Catch-MSY” method published by S. Martell and R. Froese in 2013. The catch-only application of CMSY++ uses a Bayesian implementation of a modified Schaefer model, which also allows the fitting of abundance indices should such information be available. In the absence of historical catch time series and abundance indices, CMSY++ depends strongly on the provision of appropriate and informative priors for plausible ranges of initial and final stock depletion. An Artificial Neural Network (ANN) now assists in selecting objective priors for relative stock size based on patterns in 400 catch time series used for training. Regarding the cross-validation of the ANN predictions, of the 400 real stocks used in the training of ANN, 94% of final relative biomass (B/k) Bayesian (BSM) estimates were within the approximate 95% confidence limits of the respective CMSY++ estimate. Also, the equilibrium catch-biomass relations of the modified Schaefer model are compared with those of alternative surplus-production and age-structured models, suggesting that the latter two can be strongly biased towards underestimating the biomass required to sustain catches at low abundance. Numerous independent applications demonstrate how CMSY++ can incorporate, in addition to the required catch time series, both abundance data and a wide variety of ancillary information. We stress, however, the caveats and pitfalls of naively using the built-in prior options, which should instead be evaluated case-by-case and ideally be replaced by independent prior knowledge

What has Canada caught, and how much is left? Reconstructing and assessing fisheries in three oceans

Canada’s marine fisheries occur in three oceans, designated by Pacific, Arctic and Atlantic Exclusive Economic Zones (EEZs), where management bodies utilize catch records in order to make decisions regarding the future of their fisheries. However, current catch reporting systems and stock assessment processes are flawed, as catch records are missing key fishery components and assessments may use time series that do not represent the full scale of change. These shortcomings can directly impact the perception of healthy fisheries and influence future management decisions. This research provides a comprehensive catch record for all available marine populations in Canada’s three surrounding EEZs from 1950-2017 in order to estimate their current status and provide reference points that may be useful for managers to secure marine resources for the future. Catch reconstructions initially done by the Sea Around Us group and external collaborators, are refined and updated to 2017. Using reconstructed time series, the most recent ‘CMSY’ stock assessment method allows reference points to be estimated and reveals that the majority of Canadian fisheries need rebuilding. As well, ‘CMSY’ analyses are used to investigate shifting baseline effects on selected official stock assessments that exhibit shortened catch time series. Overall, this research contributes to improving scientific baselines in order to gain a better understanding of Canadian fisheries from a historical and managerial perspective.Science, Faculty ofOceans and Fisheries, Institute for theGraduat

Fisheries Centre research reports, Vol. 29, no. 3

This report presents the key results of a multi-year activity of the Sea Around Us devoted to assessing the status of marine fisheries globally. This was accomplished by estimating, for the Exclusive Economic Zones (EEZ) of all maritime countries and the high seas, the fraction currently left in the sea of the exploited populations of fish and invertebrates that occurred before the onset of large-scale industrial fishing. More precisely, the ‘fraction left’ is the current biomass (B) of a stock relative to its initial biomass (B0), i.e., B/B0. This fraction was estimated for multiple exploited populations (or ‘stocks’) by applying a versatile stock assessment method (CMSY++), whose main features are also described. Altogether, over 2,500 stocks of fish and marine invertebrates (mainly crustaceans such as lobsters and mollusks such as squids) were assessed in the EEZs of countries on five continents and the high seas. These assessments were based mainly on long catch time series (typically 1950 to 2018) but considered, wherever they were available, the results of earlier assessments made by national or international fisheries management bodies. Thus, the evaluations of fisheries status presented herein are not defined by data scarcity; rather, we used all available data pertinent to the status of fisheries in all maritime countries to reduce the uncertainty inherent in all stock assessments. The detailed results of these stock assessments and their supporting data are available on the Sea Around Us website (www.seaaroundus.org). These results will also be used by the Flourishing Ocean Initiative of the Minderoo Foundation, which kindly funded a large part of our catch reconstruction update to 2018 and the stock assessment work described herein.Science, Faculty ofNon UBCOceans and Fisheries, Institute for theUnreviewedFacultyResearche