Evidence from the past: exploitation as cause of commercial extinction of autumn-spawning herring in the Gulf of Riga, Baltic Sea

Abstract

Historical marine ecology has shown that many exploited animal populations declined before their abundance was quantified by scientists. This situation applies for autumn-spawning herring (Clupea harengus) in the Baltic Sea. This stock used to be the dominant spawning group of herring in the early decades of the 1900s and supported several commercially important fisheries, including in the Gulf of Riga (GoR). However, the GoR stock declined during the 1960–1970s and has not recovered. Neither the former biomass nor reasons for its decline are known. Here, we recover and analyse historical fishery and biological data and conduct population development simulations to evaluate the hypothesis that exploitation may have been sufficient to lead the stock towards commercial extinction. We found that the estimated exploitation pattern, including exploitation of juveniles, was unsustainable and led to stock decline. The pattern of exploitation of this stock was consistent with that which caused collapses of other herring stocks, which have since recovered. If autumn-spawning herring in the GoR recovers, our findings indicate that this stock could support sustainable annual yields of ∼4000 t and diversify the fishery resource base, which is presently restricted to a relatively small number of species for essentially local coastal inhabitants.

Something old, something new: Historical perspectives provide lessons for blue growth agendas

“…McClenachan, Cooper, McKenzie & Drew, 2015). Despite these very real issues, increasing examples from the literature highlight that best practices can be used in overcoming these challenges (e. g., Fortibuoni, Libralato, Raicevich, Giovanardi & Solidoro, 2010; MacKenzie & Ojaveer, 2018; McClenachan et al, 2015; Sguotti et al, 2016; Thurstan et al, 2016). Thus, we urge managers to work with researchers that are well versed in the historical and social sciences, who can aid in understanding historical resources and their interpretation, as opposed to assuming that novel sources render historical data unreliable.…”

“…Common concerns include the incompleteness of data, the diversity of data types or sources, or uncertainties and biases that are unfamiliar to marine resource managers and practitioners (e.g., McClenachan et al, 2015). Despite these very real issues, increasing examples from the literature highlight that best practices can be used in overcoming these challenges (e. g., Fortibuoni et al, 2010, MacKenzie and Ojaveer, 2018, Sguotti et al, 2016. Thus, we urge managers to work with researchers that are well-versed in the historical and social sciences, who can aid in understanding historical resources and their interpretation, as opposed to assuming that novel sources render historical data unreliable.…”

New historical data for long-term swordfish ecological studies in the Mediterranean Sea

“…For example, many historical datasets have limitations which constrain the kinds of research questions which can be addressed. These limitations typically include gaps and other changes in timespace coverage due to the loss of records, interruptions in the original record keeping practices, or changes in data collection methodologies over time (Engelhard et al, 2016;MacKenzie and Ojaveer, 2018). In addition, the data were often recorded for different purposes (e.g., economic or societal development) than those of interest to 21st-century marine ecologists (Caswell et al, 2020;Lotze and McClenachan, 2013;Schwerdtner Máñez et al, 2014).…”

Serial depletion of Baltic herring since the Viking Age revealed by ancient DNA and population genomics

“…Herring show strong genetic adaptation for spawning season and adaptation to differing salinity conditions 22,[33][34][35][36] , ultimately segregating into two distinct metapopulations: spring spawners and autumn spawners 37,38 . Spring spawners are smaller and mature more quickly than autumn spawners, and prefer to spawn in coastal areas as opposed to the deeper waters used by the slowgrowing, larger autumn spawners 29,39 . Given the larger size of autumn-spawning herring, we expect that earlier fishing efforts prioritized these populations over the smaller spring-spawning aggregations.…”

“…Given the larger size of autumn-spawning herring, we expect that earlier fishing efforts prioritized these populations over the smaller spring-spawning aggregations. Each metapopulation is further separated into management stocks living in the western Baltic (ICES subdivisions [21][22][23][24], central Baltic (ICES subdivisions 25-27, 28.1, 29), and gulfs (ICES subdivisions 28.1, 30-32) (see Fig 1A) 32,29,40 . The western Baltic autumn-spawning stock is the population targeted by the Øresund fishery.…”