Epsilon Archive for Student Projects

Abstract

Fisheries around the world have a substantial impact on marine ecosystems through the removal of biomass and modification of habitats, which alters the conditions within food webs. However, our understanding of this impact and consequences for the ecosystems is limited. Despite this limitation and uncertainty, fisheries have been allowed to develop and expand, causing substantial reductions in many fish stocks due to overfishing. The main reason for stock depletion is overcapacity (leading to non-sustainable fishing effort and catches), which has been largely fueled by government subsidies to fisheries. The Baltic Sea is no exception, high fishing pressure combined with unfavorable conditions for the reproduction of Atlantic cod (Gadus morhua), the historically dominant large predatory fish, resulted in a rapidly decrease of annual landings in the late 1980s, from which cod stocks have not recovered. More recently, landings are dominated by small pelagic species, herring (Clupea harengus), and sprat (Sprattus sprattus), whose high exploitation of the ecosystem can have significant negative consequences for the processes within it. There are several components of fisheries catches that are usually not accounted for and hence not reported, and these are Illegal, Unregulated, and Unreported (IUU) catches. With the hope to contribute to a better understanding of total fisheries impacts and improved management leading to sustainable catch levels, a catch data reconstruction for Swedish fisheries in the Baltic Sea, from 1950-2007, was undertaken. The catch reconstruction estimated IUU catches, including discards, and recreational catches, and added those to a foundation based on the officially reported landings as presented by the International Council for Exploration of the Sea (ICES) on behalf of Swedish government. Data and information on unreported landings were sparse, and much of the estimations had to be based on interpolation between ‘anchor points’, which in turn were formed using an assumption-based approach previously described in the literature that attempts to maximize the use of all available and suitable data and information. The commonly used standard approach of applying ‘zero catch’ to situations where no hard data are available was not acceptable here. If a fisheries component was known to exist it had to be estimated for all of Sweden for the entire time period 1950-2007. In order to avoid the potential for substantial over-estimation, a conservative approach was applied throughout. Information was obtained by data and literature searches (including grey and unpublished literature), and interviews with people involved in Swedish fisheries. The total estimated reconstructed Swedish catch in the Baltic Sea for the 1950-2007 period, was 31 % larger than the officially reported landings, and peaked in1998 at 390,000 t. The total estimated IUU catch consisted of 1.09 million t unreported landings, 0.52 million t discards, and 0.63 million t recreational catches.
In recent years, annual unreported catches, discards, and recreational catches of about 17,900 t, 10,700 t, and 7,100 t, respectively, need to be added to reported annual landings of around 154,000 t, to derive the estimated total catch. Discrepancies between reported landings and the total catch of a species can contribute substantial uncertainties to stock assessments, and addressing this bias is one step towards improved assessments. Therefore, better accounting of all catches is required, which in turn does call for more research. Better accounting of catches would be achieved by a 100 % observer coverage of Swedish fisheries, which is a necessity for accurate studies of discards, and 100 % coverage would also minimize
unreported landings. However, improved data and better understanding and stock assessments alone will be pointless as long as politicians continue to ignore scientific advice. So together with better research and data, public insight and transparency has to increase, due to accountability reasons. This is especially important since fisheries policies, with its subsidies, are the main reason and driving force of overexploitation of fish stocks.