Body size‐dependent responses of a marine fish assemblage to climate change and fishing over a century‐long scale

Abstract

Commercial fishing and climate change have influenced the composition of marine fish assemblages worldwide, but we require a better understanding of their relative influence on long-term changes in species abundance and body-size distributions. In this study, we investigated long-term variability within a demersal fish assemblage in the western English Channel. The region has been subject to commercial fisheries throughout most of the past century, and has undergone interannual changes in sea temperature of over 2.0 1C. We focussed on a core 30 species that comprised 99% of total individuals sampled in the assemblage. Analyses showed that temporal trends in the abundance of smaller multispecies size classes followed thermal regime changes, but that there were persistent declines in abundance of larger size classes. Consistent with these results, larger-growing individual species had the greatest declines in body size, and the most constant declines in abundance, while abundance changes of smaller-growing species were more closely linked to preceding sea temperatures. Together these analyses are suggestive of dichotomous size-dependent responses of species to long-term climate change and commercial fishing over a century scale. Small species had rapid responses to the prevailing thermal environment, suggesting their life history traits predisposed populations to respond quickly to changing climates. Larger species declined in abundance and size, reflecting expectations from sustained size-selective overharvesting. These results demonstrate the importance of considering species traits when developing indicators of human and climatic impacts on marine fauna.

Effects of acute and chronic temperature changes on the functional responses of the dogfish Scyliorhinus canicula (Linnaeus, 1758) towards amphipod prey Echinogammarus marinus (Leach, 1815)

“…Furthermore, Echinogammarus marinus may have an evolutionary advantage, due to body size, at higher temperatures (Genner et al 2010;Di Santo and Lobel 2016), yet this may be mitigated when prey is found in high densities. The rate of warming, and subsequently environmental variation, affects maximum feeding estimates; consequently variation from the mean temperature is likely to have an impact upon predation pressure (Dell et al 2011;Paaijmans et al 2013;Vasseur et al 2014).…”

“…These are ecologically relevant species as E. marinus has large impacts upon community structuring (Duffy and Hay 2000;Dick et al 2005), and is an important prey species (Leite et al 2014) that can additionally be considered a proxy for other small crustacean species and small fish due to strong swimming behaviours. S. canicula is a generalist benthic predator (Kaiser and Spencer 1994;Domi et al 2005) with high abundances (Genner et al 2010;Sguotti et al 2016) that have been found to increase with increasing temperature (Sguotti et al 2016). S. canicula presents as an ideal indicator species that is not affected by fishing mortality, due to lack of fishing pressure and high discard survival rate (Revill et al 2005).…”

Two’s company, three’s a crowd: fine-scale habitat partitioning by depth among sympatric species of marine mesopredator

“…For example, if depth segregation was driven by competitive exclusion then, given recent population declines in most of these species including in the region where they were tracked (Genner et al 2010), it is possible that current population densities are too low for sufficient inter-species competition. Under such conditions interactions between individuals may be too rare to trigger avoidance behaviour and consequently segregation might not be evident (Prenda et al 1997).…”

“…These species have been common and widespread since the last glacial maximum some 20 000 years ago (Chevolot et al 2006b) with distributional ranges that overlap significantly in the WEC (Ellis et al 2005b), although abundance has declined since the 1950s as a result of fishing pressure (Chevolot et al 2006a, Genner et al 2010. In order to reduce direct competition, it might be expected that these four sympatric species would exhibit significant differences in morphology and life history (Hardin 1960).…”

Sustained Observation of Marine Biodiversity and Ecosystems

“…Early ideas about the relative importance of top-down control versus bottom-up forcing stemmed from this work [13]. More recently the time-series has been used to show the response of whole bottom; fish assemblages to climate change [14], enabling the separation of climate change and fishing impacts [15]. There have been major switches in pelagic fish: from herrings in cold periods to pilchards (also called sardines) in warmer periods, which historical analysis showed stretched back to the Middle Ages [16].…”