Long-Term Changes in the Diet of Gymnogobius isaza from Lake Biwa, Japan: Effects of Body Size and Environmental Prey Availability

Abstract

Body size and environmental prey availability are both key factors determining feeding habits of gape-limited fish predators. However, our understanding of their interactive or relative effects is still limited. In this study, we performed quantitative dietary analysis of different body sizes of goby (Gymnogobius isaza) specimens collected from Lake Biwa between 1962 and 2004. First, we report that the diet was composed mainly of zooplankton (cladocerans and copepods) before the 1980s, and thereafter, shifted to zoobenthos (gammarids). This foraging shift coincided with, and thus can be linked to, known historical events in the lake at that time: decrease in zooplankton abundance with the alleviation of eutrophication, increase in fish body size resulting from fish population collapse, and increase in gammarid abundance due to reduced fish predation pressure. Supporting this view, our data analyses revealed how the long-term changes in the diet composition would be co-mediated by changes in fish body size and environmental prey availability. Specifically, while zoobenthos abundance strongly affected the fish diet composition, larger (smaller) fish preferred zoobenthos (zooplankton). Furthermore, the body size effects were stronger than those of prey availability. These results provide the best long-term evidence that fish feeding habits vary over decades with its body size and prey community due to anthropogenic disturbances.

Predator–prey mass ratio revisited: does preference of relative prey body size depend on individual predator size?

“…According to previous dietary analyses, the fish feeds mainly on zooplankton and zoobenthos (gammarids) (Nakanishi & Nagoshi ; Briones et al . ). A major advantage of using this fish species is that unique long‐term data were available on prey compositions in both predator diet and the environment (Ishikawa, Narita & Urabe ; Nakazawa et al .…”

“…Note that Briones et al . () evaluated prey body masses in dry weight (DW) while Nakazawa et al . () used WW to measure fish body masses.…”

“…Table S1 compiles data on individual body masses of fish predators (Briones et al . ), individual counts of prey in predator guts (Briones et al . ) and relative proportions of zooplankton and benthos in guts (Briones et al .…”

“…), individual counts of prey in predator guts (Briones et al . ) and relative proportions of zooplankton and benthos in guts (Briones et al . ) and environment (Ishikawa, Narita & Urabe ; Hsieh et al .…”

Predicting coexistence in species with continuous ontogenetic niche shifts and competitive asymmetry

“…, Wallace and Leslie , Briones et al. ). Organisms with continuous changes in body size display a wide variety of life histories and changes in competitive abilities through development, many of which are difficult to capture by collapsing the life history into two life stages (Easterling et al.…”