Change in the dominance structure of two marine‐fish assemblages over three decades

Abstract

Marine fish are an irreplaceable resource, but are currently under threat through overfishing and climate change. To date, most of the emphasis has been on single stocks or populations of economic importance. However, commercially valuable species are embedded in assemblages of many species and there is only limited understanding of the extent to which the structure of whole communities has altered in recent years. Most assemblages are dominated by one or a few species, with these highly abundant species underpinning ecosystem services and harvesting decisions. This paper shows that there have been marked temporal changes in the dominance structure of Scottish marine-fish assemblages over the past three decades, where dominance is measured as the proportional numerical abundance of the most dominant species. We report contrasting patterns in both the identity of the dominant species and shifts in the relative abundance of the dominant in assemblages to the east and west of Scotland, UK. This result highlights the importance of multi-species analyses of harvested stocks and has implications not only for fisheries management but also for consumer choices.

Shifting trophic architecture of marine fisheries in New Zealand: Implications for guiding effective ecosystem‐based management

“…Variability in the abundance of commercial catches of fish has been studied for centuries (Huxley, 1881), especially in highly productive and highly populated regions (Heincke, 1898; Newland, 1999). Globally, abundance of fishing stocks has displayed declines over the past several decades (Worm et al, 2009), with changes in commercial fish assemblages identified for important fishing grounds in north‐western Europe (Moyes & Magurran, 2019), in the north‐eastern Pacific (Levin, Holmes, Piner, & Harvey, 2006) and on the Newfoundland/Labrador Shelf (Gomes, Haedrich, & Villagarcia, 1995). Long‐term impacts of fisheries have included over‐exploitation of target species, by‐catch and habitat destruction, fundamentally altering marine ecosystems worldwide (Hinz et al, 2017; Jackson, 2001; MRAG & IEEP, 2007; Pauly, Christensen, Dalsgaard, Froese, & Torres, 1998; Worm et al, 2009).…”

Temporal change in functional rarity in marine fish assemblages

“…For example, it would be interesting to use a null model approach to examine the interactions between environmental filtering and shifts in assemblage size, particularly when the latter is a response to an increase in carrying capacity linked to climate change. Unravelling the mechanistic links between trends in functional and taxonomic diversity will also be important, in, for instance, discovering the extent to which functional rarity is linked to whether a species is a winner or loser during biodiversity change [ 33 , 57 ].…”

“…For example, we observed higher levels of taxonomic rarity relative to the null expectation (figure 3a,b), as well as reduced evenness, for given levels of richness, in the west coast system (figure 3c) as opposed to the east coast system (figure 3d). Since increased taxonomic rarity can be associated with habitat complexity [45][46][47], this result could reflect the increased structural heterogeneity of the west coast, as well as contrasts in warming trends, and/or recovery from historical fishing pressures [33,48]. Historically, the east coast system (North Sea region) has been more heavily exploited than the west coast system (Celtic Sea area), but, since the beginning of this time series in 1985, fishing pressure has been largely similar in both areas (see electronic supplementary material, figure S7).…”

“…Although matched by latitude, these assemblages belong to different marine ecosystems: the seas to the west of Scotland are part of the Celtic-Biscay Shelf ecosystem [ 31 ] while those to the east of Scotland are placed in the North Sea ecosystem [ 32 ]. These systems share many, but not all, fish species, but have different dominant species, and differ in how species dominance changes over time [ 33 ]. They thus provide an interesting test case in which to ask whether shifts in taxonomic rarity are a proxy for change in functional rarity as well as whether these biodiversity changes are consistent across different geographical regions.…”

Variation in Species Composition, Size and Fitness of Two Multi-Species Sea Turtle Assemblages Using Different Neritic Habitats

“…Multi-species assemblages of marine animals have been studied, however, most research has focused on invertebrates or fish (Barnes, 2019;Moyes and Magurran, 2019;Palumbi et al, 2019). Large marine vertebrates also maintain multispecies groups (Augé et al, 2018;Drymon et al, 2020;Sutton et al, 2020) and because these species typically inhabit a higher trophic level, changes in habitat may have serious consequences.…”