Fishing through time: population dynamics of plaice (Pleuronectes platessa) in the Kattegat–Skagerrak over a century

Abstract

Over the past century, advances in technology and historical events such as climate change have resulted in significant changes in the exploitation pattern, population sizes and the potential yield of fish stocks. These variations provide contrast in the data that improves our knowledge on population dynamics and our ability to develop management strategies for long-term sustainable exploitation. In this study, we use a standardized scientific trawl survey to obtain a historical time series of relative abundance, recruitment and size structure for plaice in the Kattegat-Skagerrak. Our work extends the available time series by more than 80 years so that the evaluation of trends is more informative than is possible from the current assessment. We show that the current adult biomass is approximately 40% of the maximum observed at the beginning of the century and during the 1960s. The average maximum individual length has been reduced by 10 cm over the studied time period. An analysis of trends in mean length indicates that fishing mortality was variable during the first half of the century and has increased steadily over the past 20 years. Recruitment has been the highest on record during recent years, suggesting that the alleged link between coastal environmental degradation and juvenile survival is of low importance. The overall findings of our work will provide managers with a historical perspective on the population dynamics of the stock, which will support the long-term management of plaice in the Kattegat-Skagerrak.

Historical spatiotemporal dynamics of eastern North Sea cod

“…Changes in catchability have seldom been estimated for survey data (Marchal et al 2003); however, technological advancement may become relevant when analysing long time series of data collected under the potential effect of increasing catching efficiency (Cardinale et al 2010). Under the reasonable assumption of constant catching efficiency within the 12-year time resolution of our analysis, the estimated spatial structure of cod would not be affected by unaccounted technological creep.…”

“…On average 59 hauls were conducted every year when the sampling occurred during daytime, comprising a total of 4378 observations for the whole time series. Characteristics of the included trawl types and the statistics of validated and approved hauls are summarized in Supplemental Table S1 1 (for more details see Cardinale et al 2009Cardinale et al , 2010. Since 1974, most surveys have been conducted by the Swedish research vessel Argos within IBTS (International Bottom Trawl Survey; ICES 1992), however, national trawl surveys were also carried out.…”

Nutrient reduction and climate change cause a potential shift from pelagic to benthic pathways in a eutrophic marine ecosystem

“…This is illustrated by the long-term decline of flatfish (Cardinale et al, 2009(Cardinale et al, , 2010 and gadoids; in particular the collapse of the Kattegat cod stock (ICES, 2010), one of the most drastic examples of reduction of a once productive cod population. This is illustrated by the long-term decline of flatfish (Cardinale et al, 2009(Cardinale et al, , 2010 and gadoids; in particular the collapse of the Kattegat cod stock (ICES, 2010), one of the most drastic examples of reduction of a once productive cod population.…”

Shifts in nursery habitat utilization by 0-group plaice in the western Dutch Wadden Sea

“…Since densities did not increase in the coastal zone (Tulp et al, 2008), it seems that within the Wadden Sea, despite the relative importance of the various habitats (intertidal, subtidal, tidal channels) has changed, the function of the intertidal area has been compensated for. The same has been observed in western Swedish coastal waters, where despite habitat deterioration, enhanced plaice recruitment has been observed in recent years (Cardinale et al, 2010). This highlights the fact that the presence and quality of alternative habitats is at least as important to consider when evaluating the nursery capacity for fish populations and that nursery grounds are dynamic entities expanding, contracting and shifting in location over time (Stoner et al, 2001).…”